Deformation Enhanced Recrystallization of Titanite: Insight from the Western Gneiss Region Ultrahigh-Pressure Terrane

NASA Astrophysics Data System (ADS)

Gordon, S. M.; Reddy, S. M.; Blatchford, H.; Whitney, D. L.; Kirkland, C. L.; Teyssier, C.; Evans, N. J.; McDonald, B.

2016-12-01

Titanite readily recrystallizes due to metamorphism, deformation, and/or fluids making it an ideal chronometer for tracking the exhumation of high-grade rocks. The Western Gneiss Region (WGR), Norway, is a giant UHP terrane exhumed as a fairly coherent slab. Parts of the WGR underwent little deformation during exhumation; however, meters-scale shear zones, located across the WGR, deformed over a range of pressures, from (U)HP to amphibolite facies. Titanite from quartzofeldpathic gneiss within, directly adjacent to, and 300 m away from a mylonitic shear zone within the southern WGR have been analyzed to track exhumation and investigate effects of deformation on recrystallization and trace-element mobility. EBSD was used to characterize the microstructural evolution of the gneisses, and trace-element concentrations and timing of recrystallization were estimated by split-stream LA-ICPMS. Titanite grain size decreases from outside (>200) to inside (<75 µm) the shear zone. Gneiss in and directly adjacent to the shear zone contain partially to completely recrystallized grains, with 207-corrected 206Pb/238U ages of <405 Ma. Gneiss within the shear zone shows a greater percentage of recrystallized grains. EBSD data indicate that some titanite comprises multiple subgrains within an optically coherent single grain. Subgrains in titanite cores show evidence of inherited radiogenic Pb, whereas subgrains in rims and tails of deformed sigma grains were recrystallized. In a gneiss directly adjacent to the shear zone, optically coherent grains are zoned, with increasing Sr and decreasing Zr from core to rim; titanite subgrains within the shear-zone gneiss are too small to analyze. In comparison, titanite from the gneiss outside the shear zone does not show any internal microstructures or evidence for Scandian recrystallization and has low U and high 204Pb. These results show that most trace elements are unaffected by deformation of titanite; however, Pb is mobile. Deformation thus plays an important role in resetting U-Pb systematics and allows the timing of shear zone development to be linked to the early stages of eclogite exhumation at ca. 405 Ma. Atom-probe analyses of adjacent subgrains, one that has recrystallized and one with an inherited age, will provide insight into trace-element mobility on the nm-scale.

Deformation ages within the Klong Marui continental wrench fault, southern Thailand

NASA Astrophysics Data System (ADS)

Kanjanapayont, P.; Grasemann, B.; Edwards, M. A.

2009-04-01

The Klong Marui Fault is a ductile to brittle dextral strike-slip shear zone characterized by strong NNE-SSW geomorphic ridges trending up to 150 km. from Thai Gulf to Andaman Sea. At it southern part in the Phung Nga region, the ductile core forms a 40km long ridge. The geology within this wrench zone consisted of steep strongly deformed layers of migmatitic gneisses, mylonitic granites/pegmatites and phyllonitic metapelites. Brittle cataclasitc zones were localized in the eastern and western margin of this ductile core zone. The first deformation stage was dextral ductile strike-slip movement at mid to upper crustal levels and formed the main mylonitic foliation (c), secondary synthetic foliations (c'), and lineation in the migmatitic gneisses, mylonitic granites and metapelites. Locally sillimanite-clasts in high-temperature recrystallization quartz fabric fabric suggest deformation at amphibolite facies condition. More typically, quartz dynamically recrystallize by subgrain rotation and grain boundary migration under greenschist facies conditions. Microstructure of myrmekite and "V"-pull-apart clearly indicates dextral sense of shear. Pegmatites cross-cut the main mylonitic foliation but were sheared at the rims indicating syn-kinematic emplacement. Dynamically recrystallizing quartz mainly by basal gliding, bulging and low-temperature subgrain rotation record the latest stage of ductile dextral strike-slip deformation during decreasing temperature conditions. The NNE-SSW trending dextral strike-slip deformation accommodated the E-W transpression as a result of the differential movement of the northward drifting Indian craton and Asia. The brittle/ductile deformation produced cataclasites and minor faults which overprint the higher temperature fabric causing exhumation and juxtaposition of fault rocks developed under different metamorphic conditions in a positive flower structure.

Optically induced melting of colloidal crystals and their recrystallization.

PubMed

Harada, Masashi; Ishii, Masahiko; Nakamura, Hiroshi

2007-04-15

Colloidal crystals melt by applying focused light of optical tweezers and recrystallize after removing it. The disturbed zone by the light grows radially from the focus point and the ordering starts from the interface with the crystal. Although the larger disturbed zone is observed for the higher power optical tweezers, a master curve is extracted by normalization of the disturbed zone. The temporal changes of the normalized disturbed zone are well described with exponential functions, indicating that the melting and recrystallization process is governed by a simple relaxation mechanism.

Microstructural and rheological evolution of calcite mylonites during shear zone thinning: Constraints from the Mount Irene shear zone, Fiordland, New Zealand

NASA Astrophysics Data System (ADS)

Negrini, Marianne; Smith, Steven A. F.; Scott, James M.; Tarling, Matthew S.

2018-01-01

Layers of calc-mylonite in the Mount Irene shear zone, Fiordland, New Zealand, show substantial variations in thickness due to deflection of the shear zone boundaries around wall rock asperities. In relatively thick parts (c. 2.6 m) of the shear zone, calcite porphyroclasts are internally strained, contain abundant subgrain boundaries and have a strong shape preferred orientation (SPO) and crystallographic preferred orientation (CPO), suggesting that deformation occurred mainly by dislocation creep involving subgrain-rotation recrystallization. In relatively thin parts (c. 1.5 m) of the shear zone, aggregates of fine-grained recrystallized calcite surrounding flattened porphyroclasts have a weak SPO and CPO, and contain polygonal calcite grains with low degrees of internal misorientation. The recrystallized aggregates also contain microstructures (e.g. grain quadruple junctions, randomized misorientation axes) similar to those reported for neighbor-switching processes during grain-boundary sliding. Comparison of subgrain sizes in the porphyroclasts to published grain-size differential-stress relationships indicates that stresses and strain rates were substantially higher in relatively thin parts of the shear zone. The primary microstructural response to higher stresses and strain rates was an increase in the amount of recrystallization to produce aggregates that deformed by grain-boundary sliding. However, even after the development of interconnected networks of recrystallized grains, dislocation creep by subgrain-rotation recrystallization continued to occur within porphyroclasts. This behavior suggests that the bulk rheology of shear zones undergoing thinning and thickening can be controlled by concomitant grain-size insensitive and grain-size sensitive mechanisms. Overall, our observations show that shear zone thickness variations at constant P-T can result in highly variable stresses and strain rates, which in turn modifies microstructure, deformation mechanism and shear zone rheology.

Characterization of friction stir welded joint of low nickel austenitic stainless steel and modified ferritic stainless steel

NASA Astrophysics Data System (ADS)

Mondal, Mounarik; Das, Hrishikesh; Ahn, Eun Yeong; Hong, Sung Tae; Kim, Moon-Jo; Han, Heung Nam; Pal, Tapan Kumar

2017-09-01

Friction stir welding (FSW) of dissimilar stainless steels, low nickel austenitic stainless steel and 409M ferritic stainless steel, is experimentally investigated. Process responses during FSW and the microstructures of the resultant dissimilar joints are evaluated. Material flow in the stir zone is investigated in detail by elemental mapping. Elemental mapping of the dissimilar joints clearly indicates that the material flow pattern during FSW depends on the process parameter combination. Dynamic recrystallization and recovery are also observed in the dissimilar joints. Among the two different stainless steels selected in the present study, the ferritic stainless steels shows more severe dynamic recrystallization, resulting in a very fine microstructure, probably due to the higher stacking fault energy.

Microstructural Evolution of HSLA ISO 3183 X80M (API 5L X80) Friction Stir Welded Joints

NASA Astrophysics Data System (ADS)

Hermenegildo, Tahiana F. C.; Santos, Tiago F. A.; Torres, Edwar A.; Afonso, Conrado R. M.; Ramirez, Antonio J.

2018-03-01

Evaluation was made of friction stir welded joints, identifying conditions that resulted in satisfactory welded joints free from defects and with microstructural characteristics that provided good mechanical properties. Microstructural characterization and cooling curve analysis of the joints with lower and higher heat inputs evidenced deformation below and above the non-recrystallization temperature (Tnr) and dynamic recrystallization during microstructural evolution. Microscopy analyses showed acicular ferrite, bainitic ferrite, and coalesced bainite microstructures in the stir zone of the cold weld (lower heat input), while the stir zone of the hot weld (higher heat input) contained bainitic ferrite, acicular ferrite, coalesced bainite, martensite, and dispersed carbides. Granular bainite and dispersed carbides were observed in all the heat affected zones. Analysis of the microstructural transformations, together with the thermal history of the joints, showed that the variable that had the greatest influence on the morphology of the bainite (granular bainite/bainitic ferrite) was the deformation temperature.

Feedbacks Between Deformation and Fluid Flow in Mantle Shear Zones from Zabargad, Red Sea

NASA Astrophysics Data System (ADS)

Tommasi, A.; Boudier, F. I.; Vauchez, A. R.; Zaderatzky, M.

2016-12-01

Peridotites in the Zabargad island, Red Sea, record different stages of lithospheric thinning and asthenospheric upwelling during rifting. Field mapping highlights a pervasive high-temperature NW-SE, subvertical foliation with lineations pluning 50°NW. This foliation is overprinted by a series of lower-temperature mylonitic zones with slightly oblique foliations and subhorizontal lineations, which record progressive strain localization under retrogressive conditions during the final exhumation of the peridotites (Nicolas and Boudier, JGR 1987). We performed a petrostructural study of ca. 50 samples collected by A. Nicolas and F. Boudier in the 80s from the different deformation facies. This study highlights: (1) a rather pervasive, but highly heterogeneous distribution of the LT deformation and (2) a feedback between deformation and fluid flow. The HT deformation is recorded in medium grained plagioclase- and spinel-peridotites by a homogeneous foliation and lineation marked by a shape-preferred orientation of plagioclase and olivine and a consistent CPO of all major-rock forming phases. The LT temperature deformation results in dynamic recrystallization of olivine leading to a marked grain size reduction by dynamic recrystallization of olivine, remobilization of orthopyroxene by dissolution-precipitation, and crystallization of amphibole. Increasing finite strain is recorded by the increase in the volume of the fine-grained material and of the amphibole proportion. The latter may attain in totally recrystallized cm-wide ultramylonite bands up to 30%. This together with the strong amphibole SPO and CPO corroborate fluid focusing and enhanced reaction rates into active shear zones. In the LT shear zones we also document: (1) changes in the olivine CPO, indicating changes in the dominant slip system and (2) unusual orthopyroxene CPO, which we interpret as due to oriented crystallization. Static replacement of pyroxenes by amphibole with no associated LT deformation is also observed indicating that the presence of fluids does not suffice to trigger strain localization.

Imaging Water in Deformed Quartzites: Examples from Caledonian and Himalayan Shear Zones

NASA Astrophysics Data System (ADS)

Kronenberg, Andreas; Ashley, Kyle; Hasnan, Hasnor; Holyoke, Caleb; Jezek, Lynna; Law, Richard; Thomas, Jay

2016-04-01

Infrared IR measurements of OH absorption bands due to water in deformed quartz grains have been collected from major shear zones of the Caledonian and Himalayan orogens. Mean intragranular water contents were determined from the magnitude of the broad OH absorption at 3400 cm-1 as a function of structural position, averaging over multiple grains, using an IR microscope coupled to a conventional FTIR spectrometer with apertures of 50-100 μm. Images of water content were generated by scanning areas of up to 4 mm2 of individual specimens with a 10 μm synchrotron-generated IR beam and contouring OH absorptions. Water contents vary with structural level relative to the central cores of shear zones and they vary at the grain scale corresponding to deformation and recrystallization microstructures. Gradients in quartz water content expressed over structural distances of 10 to 400 m from the centers of the Moine Thrust (Stack of Glencoul, NW Scotland), the Main Central Thrust (Sutlej valley of NW India), and the South Tibetan Detachment System (Rongbuk valley north of Mount Everest) indicate that these shear zones functioned as fluid conduits. However, the gradients differ substantially: in some cases, enhanced fluid fluxes appear to have increased quartz water contents, while in others, they served to decrease water contents. Water contents of Moine thrust quartzites appear to have been reduced during shear at greenschist facies by processes of regime II BLG/SGR dislocation creep. Intragranular water contents of the protolith 70 m below the central fault core are large (4078 ± 247 ppm, H/106 Si) while mylonites within 5 mm of the Moine hanging wall rocks have water contents of only 1570 (± 229) ppm. Water contents between these extremes vary systematically with structural level and correlate inversely with the extent of dynamic recrystallization (20 to 100%). Quartz intragranular water contents of Himalayan thrust and low-angle detachment zones sheared at upper amphibolite conditions by regime III GBM creep show varying trends with structural level. Water contents increase toward the Lhotse detachment of the Rongbuk valley, reaching 11,350 (± 1095) ppm, whereas they decrease toward the Main Central Thrust exposed in the western part of the Sutlej valley to values as low as 170 (± 25) ppm. Maps of intragranular water content correspond to populations of fluid inclusions, which depend on the history of deformation and dynamic recrystallization. Increases in water content require the introduction of secondary fluid inclusions, generally by brittle microcracking followed by crack healing and processes of inclusion redistribution documented in milky quartz experiments. Decreases in water content result from dynamic recrystallization, as mobile grain boundaries sweep through wet porphyroclasts, leaving behind dry recrystallized grains. Intragranular water contents throughout greenschist mylonites of the Moine thrust are comparable to those of quartz weakened by water in laboratory experiments. However, water contents of upper amphibolite mylonites of the Main Central Thrust are far below those required for water weakening at experimental strain rates and offer challenges to our understanding of quartz rheology.

High-quality Silicon Films Prepared by Zone-melting Recrystallization

NASA Technical Reports Server (NTRS)

Chen, C. K.; Geis, M. W.; Tsaur, B. Y.; Fan, J. C. C.

1984-01-01

The graphite strip heater zone melting recrystallization (ZMR) technique is described. The material properties of the ZMR films, and SOI device results are reviewed. Although our ZMR work is primarily motivated by integrated circuit applications, this work evolved in part from earlier research on laser crystallization of thick amorphous GaAs and Si films, which was undertaken with the goal of producing low cost photovoltaic materials. The ZMR growth process and its effect on the properties of the recrystallized films may contribute some insight to a general understanding of the rapid recrystallization of Si for solar cells. Adaptation of ZMR for solar cell fabrication is considered.

Microstructure Characterization and Stress Corrosion Evaluation of Autogenous and Hybrid Friction Stir Welded Al-Cu-Li 2195 Alloy

NASA Technical Reports Server (NTRS)

Li, Zhixian; Arbegast, William J.; Meletis, Efstathios I.

1997-01-01

Friction stir welding process is being evaluated for application on the Al-Cu-Li 2195 Super-Light Weight External Tank of the Space Transportation System. In the present investigation Al-Cu-Li 2195 plates were joined by autogenous friction stir welding (FSW) and hybrid FSW (friction stir welding over existing variable polarity plasma arc weld). Optical microscopy and transmission electron microscopy (TEM) were utilized to characterize microstructures of the weldments processed by both welding methods. TEM observations of autogenous FSW coupons in the center section of the dynamically-recrystallized zone showed an equiaxed recrystallized microstructure with an average grain size of approx. 3.8 microns. No T(sub 1), precipitates were present in the above-mentioned zone. Instead, T(sub B) and alpha precipitates were found in this zone with a lower population. Alternate immersion, anodic polarization, constant load, and slow strain tests were carried out to evaluate the general corrosion and stress-corrosion properties of autogenous and hybrid FSW prepared coupons. The experimental results will be discussed.

Hot Deformation and Dynamic Recrystallization Behavior of the Cu-Cr-Zr-Y Alloy

NASA Astrophysics Data System (ADS)

Zhang, Yi; Huili, Sun; Volinsky, Alex A.; Tian, Baohong; Chai, Zhe; Liu, Ping; Liu, Yong

2016-03-01

To study the workability and to optimize the hot deformation processing parameters of the Cu-Cr-Zr-Y alloy, the strain hardening effect and dynamic softening behavior of the Cu-Cr-Zr-Y alloy were investigated. The flow stress increases with the strain rate and stress decreases with deformation temperature. The critical conditions, including the critical strain and stress for the occurrence of dynamic recrystallization, were determined based on the alloy strain hardening rate. The critical stress related to the onset of dynamic recrystallization decreases with temperature. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Dynamic recrystallization appears at high temperatures and low strain rates. The addition of Y can refine the grain and effectively accelerate dynamic recrystallization. Dislocation generation and multiplication are the main hot deformation mechanisms for the alloy. The deformation temperature increase and the strain rate decrease can promote dynamic recrystallization of the alloy.

Synthesis and deformation of a Ti doped quartz aggregate

NASA Astrophysics Data System (ADS)

Nachlas, William O.; Hirth, Greg; Teyssier, Christian; Whitney, Donna L.; Zimmerman, Mark

2013-04-01

A primary advantage of studying mylonites for thermobarometric reconstructions of tectonic events is that it enables direct comparison of P-T estimates with the mechanics of quartz deformation. Quartz is a common phase in crustal mylonites and is a particularly sensitive recorder of metamorphic and rheologic conditions in shear zones, owing to its responsiveness to dynamic recrystallization, involvement in metamorphic reaction, and propensity for dissolution and precipitation. The signature of its trace element chemistry, particularly Ti, can reflect involvement from each of these processes. The concentration of Ti in mylonites is typically heterogeneous at the thin section scale, providing a rich record of the different factors that influence the incorporation of Ti in quartz. Observations of quartz in deformed mylonite and undeformed protolith from an extensional shear zone in the North American Cordillera (Shuswap Complex, Canada) show that an originally uniform Ti distribution was modified during deformation to form zoned crystals in which the core preserves a higher Ti concentration than the rim. The zoned Ti concentration likely records a continuum of deformation conditions during extension-related exhumation, and this presents a challenge in resolving the effect of deformation on the equilibrium solubility of Ti in quartz in natural settings. By conducting deformation experiments on synthetic quartz aggregates with known Ti concentration at a constant, elevated temperature and pressure under high strain conditions, we investigate the influence of progressive dynamic recrystallization on Ti solubility in quartz. This study applies a novel doping technique that enables the synthesis of a large population of quartz crystals with a precisely controlled Ti concentration and distribution. This produces a sample that most closely replicates the protolith of extensional shear zones that typically develop under retrograde conditions. This strategy can be used to generate the equilibrium concentration predicted by previous solubility calibrations for selected P-T conditions. Experiments were performed using a shear assembly to deform quartz samples to high shear strain in dislocation creep at constant temperature, pressure, and strain rate for 24, 48, and 72 h with and without the addition of 0.1 wt% H2O. Experiments were also run under hydrostatic conditions for equivalent lengths of time for comparison with deformed samples. Experimental specimens were prepared as a two layer sample with a doped half and an undoped half to study Ti mobility during deformation. Experimental samples are analyzed with EMPA and SIMS to determine the Ti concentration of quartz in the sample, SEM-CL to observe the distribution of Ti in quartz grains, and SEM-EBSD to evaluate crystallographic fabrics and grain size. Results suggest that the duration of dynamic recrystallization influences the final Ti concentration, implying the importance of kinetics and diffusion even at the elevated temperatures of the experiments. Water content affects Ti concentration, potentially owing to the importance of point defect concentration on the solubility of Ti in quartz. Furthermore, recrystallized grain size shows a dependence on Ti concentration, as samples doped at supersaturated levels recrystallize with finer grain sizes relative to undoped samples. This suggests that exceeding the equilibrium solubility of Ti in quartz may pin grain boundary migration. The ultimate expression of Ti supersaturation in quartz is strain-induced rutilation and the progressive rotation and boudinage of exsolved rutile needles.

Microstructure and critical strain of dynamic recrystallization of 6082 aluminum alloy in thermal deformation

NASA Astrophysics Data System (ADS)

Ren, W. W.; Xu, C. G.; Chen, X. L.; Qin, S. X.

2018-05-01

Using high temperature compression experiments, true stress true strain curve of 6082 aluminium alloy were obtained at the temperature 460°C-560°C and the strain rate 0.01 s-1-10 s-1. The effects of deformation temperature and strain rate on the microstructure are investigated; (‑∂lnθ/∂ε) ‑ ε curves are plotted based on σ-ε curve. Critical strains of dynamic recrystallization of 6082 aluminium alloy model were obtained. The results showed lower strain rates were beneficial to increase the volume fraction of recrystallization, the average recrystallized grain size was coarse; High strain rates are beneficial to refine average grain size, the volume fraction of dynamic recrystallized grain is less than that by using low strain rates. High temperature reduced the dislocation density and provided less driving force for recrystallization so that coarse grains remained. Dynamic recrystallization critical strain model and thermal experiment results can effectively predict recrystallization critical point of 6082 aluminium alloy during thermal deformation.

Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puli, Ramesh, E-mail: rameshpuli2000@gmail.com; Janaki Ram, G.D.

2012-12-15

Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener-Hollomon parameter during friction surfacing. - Highlights: Black-Right-Pointing-Pointer Dynamic recrystallization in alloy 316L friction surfaced coatings is examined. Black-Right-Pointing-Pointer Friction surfacing leads to discontinuous dynamic recrystallization in alloy 316L. Black-Right-Pointing-Pointer Strain rates in friction surfacing exceed 400 s{sup -1}. Black-Right-Pointing-Pointer Estimated grain size matches well with experimental observations in 316L coatings.

Friction Stir Back Extrusion of Aluminium Alloys for Automotive Applications

NASA Astrophysics Data System (ADS)

Xu, Zeren

Since the invention of Friction Stir Welding in 1991 as a solid state joining technique, extensive scientific investigations have been carried out to understand fundamental aspects of material behaviors when processed by this technique, in order to optimize processing conditions as well as mechanical properties of the welds. Based on the basic principles of Friction Stir Welding, several derivatives have also been developed such as Friction Stir Processing, Friction Extrusion and Friction Stir Back Extrusion. Friction Stir Back Extrusion is a novel technique that is proposed recently and designed for fabricating tubes from lightweight alloys. Some preliminary results have been reported regarding microstructure and mechanical properties of Friction Stir Back Extrusion processed AZ31 magnesium alloy, however, systematic study and in-depth investigations are still needed to understand the materials behaviors and underlying mechanisms when subjected to Friction Stir Back Extrusion, especially for age-hardenable Al alloys. In the present study, Friction Stir Back Extrusion processed AA6063-T5 and AA7075-T6 alloys are analyzed with respect to grain structure evolution, micro-texture change, recrystallization mechanisms, precipitation sequence as well as mechanical properties. Optical Microscopy, Electron Backscatter Diffraction, Transmission Electron Microscopy, Vickers Hardness measurements and uniaxial tensile tests are carried out to characterize the microstructural change as well as micro and macro mechanical properties of the processed tubes. Special attention is paid to the micro-texture evolution across the entire tube and dynamic recrystallization mechanisms that are responsible for grain refinement. Significant grain refinement has been observed near the processing zone while the tube wall is characterized by inhomogeneous grain structure across the thickness for both alloys. Dissolution of existing precipitates is noticed under the thermal hysterias imposed by Friction Stir Back Extrusion process, resulting in decreased strength but improved elongation of the processed tubes; a post-process aging step can effectively restore the mechanical properties of the processed tubes by allowing for the reprecipitation of solute elements in the form of fine, dispersed precipitates. Texture analysis performed for AA6063 alloy suggests the dominance of simple shear type textures with clear transition from initial texture to stable B/ ?B components via intermediate types that are stable under moderate strain levels. In order to identify the texture components properly, rigid body rotations are applied to the existing coordinate system to align it to local shear reference frame. Surprisingly, for AA7075 tubes, and fibers are observed to be the dominant texture components in the transition region as well as thermomechanically affected zone while the processing zone is characterized by random texture. The underlying mechanisms responsible for the formation of random texture are discussed in Chapter 5 based on Electron Backscatter Diffraction analysis. Comparative discussions are also carried out for the recrystallization mechanisms that are responsible for grain structure evolution of both alloys. Continuous grain subdivision and reorientation is cited as the dominant mechanism for the recrystallization of AA6063 alloys, while dynamic recrystallization occurs mainly in the form of Geometric Dynamic Recrystallization and progressive subgrain rotations near grain boundaries in AA7075 alloys.

Petrologic and chemical changes in ductile shear zones as a function of depth in the continental crust

NASA Astrophysics Data System (ADS)

Yang, Xin-Yue

Petrologic and geochemical changes in ductile shear zones are important for understanding deformational and geochemical processes of the continental crust. This study examines three shear zones that formed under conditions varying from lower greenschist facies to upper amphibolite facies in order to document the petrologic and geochemical changes of deformed rocks at various metamorphic grades. The studied shear zones include two greenschist facies shear zones in the southern Appalachians and an upper amphibolite facies shear zone in southern Ontario. The mylonitic gneisses and mylonites in the Roses Mill shear zone of central Virginia are derived from a ferrodiorite protolith and characterized by a lower greenschist facies mineral assemblage. Both pressure solution and recrystallization were operative deformation mechanisms during mylonitization in this shear zone. Strain-driven dissolution and solution transfer played an important role in the mobilization of felsic components (Si, Al, K, Na, and Ca). During mylonitization, 17% to 32% bulk rock volume losses of mylonites are mainly attributed to removal of these mobile felsic components by a fluid phase. Mafic components (Fe, Mg, Ti, Mn and P) and trace elements, REE, Y, V and Sc, were immobile. At Rosman, North Carolina, the Brevard shear zone (BSZ) shows a deformational transition from the coarse-grained Henderson augen gneiss (HAG) to proto-mylonite, mylonite and ultra-mylonite. The mylonites contain a retrograde mineral assemblage as a product of fluid-assisted chemical breakdown of K-feldspar and biotite at higher greenschist facies conditions. Recrystallization and intra-crystalline plastic deformation are major deformation mechanisms in the BSZ. Fluid-assisted mylonitization in the BSZ led to 6% to 23% bulk volume losses in mylonites. During mylonitization, both major felsic and mafic elements and trace elements, Rb, Sr, Zr, V, Sc, and LREE were mobile; however, the HREEs were likely immobile. A shear zone in the Parry Sound domain, Ontario, formed at upper amphibolite facies conditions. The deformation process of the shear zone involves fully plastic deformation and high-temperature dynamic recrystallization and annealing recovery of both quartz and plagioclase. Geochemical evidence indicates that the chemical changes in the deformed rocks resulted from mixing of mafic and felsic layers together with fluid-assisted mass transfer within the shear zone. A geochemical model that incorporates closed-system two-component mixing with open-system mass transfer can well explain the observed major and trace element data.

Physical Simulation of a Duplex Stainless Steel Friction Stir Welding by the Numerical and Experimental Analysis of Hot Torsion Tests

NASA Astrophysics Data System (ADS)

da Fonseca, Eduardo Bertoni; Santos, Tiago Felipe Abreu; Button, Sergio Tonini; Ramirez, Antonio Jose

2016-09-01

Physical simulation of friction stir welding (FSW) by means of hot torsion tests was performed on UNS S32205 duplex stainless steel. A thermomechanical simulator Gleeble 3800® with a custom-built liquid nitrogen cooling system was employed to reproduce the thermal cycle measured during FSW and carry out the torsion tests. Microstructures were compared by means of light optical microscopy and electron backscatter diffraction. True strain and strain rate were calculated by numerical simulation of the torsion tests. Thermomechanically affected zone (TMAZ) was reproduced at peak temperature of 1303 K (1030 °C), rotational speeds of 52.4 rad s-1 (500 rpm) and 74.5 rad s-1 (750 rpm), and 0.5 to 0.75 revolutions, which represent strain rate between 10 and 16 s-1 and true strain between 0.5 and 0.8. Strong grain refinement, similar to the one observed in the stir zone (SZ), was attained at peak temperature of 1403 K (1130 °C), rotational speed of 74.5 rad s-1 (750 rpm), and 1.2 revolution, which represent strain rate of 19 s-1 and true strain of 1.3. Continuous dynamic recrystallization in ferrite and dynamic recrystallization in austenite were observed in the TMAZ simulation. At higher temperature, dynamic recovery of austenite was also observed.

The Rheological Evolution of Brittle-Ductile Transition Rocks During the Earthquake Cycle: Evidence for a Ductile Precursor to Pseudotachylyte in an Extensional Fault System, South Mountains, Arizona

NASA Astrophysics Data System (ADS)

Stewart, Craig A.; Miranda, Elena A.

2017-12-01

We investigate how the rheological evolution of shear zone rocks from beneath the brittle-ductile transition (BDT) is affected by coeval ductile shear and pseudotachylyte development associated with seismicity during the earthquake cycle. We focus our study on footwall rocks of the South Mountains core complex, and we use electron backscatter diffraction (EBSD) analyses to examine how strain is localized in granodiorite mylonites both prior to and during pseudotachylyte development beneath the BDT. In mylonites that are host to pseudotachylytes, deformation is partitioned into quartz, where quartz exhibits crystallographic-preferred orientation patterns and microstructures indicative of dynamic recrystallization during dislocation creep. Grain size reduction during dynamic recrystallization led to the onset of grain boundary sliding (GBS) accommodated by fluid-assisted grain size-sensitive (GSS) creep, localizing strain in quartz-rich layers prior to pseudotachylyte development. The foliation-parallel zones of GBS in the host mylonites, and the presence of GBS traits in polycrystalline quartz survivor clasts indicate that GBS zones were the ductile precursors to in situ pseudotachylyte generation. During pseudotachylyte development, strain was partitioned into the melt phase, and GSS deformation in the survivor clasts continued until crystallization of melt impeded flow, inducing pseudotachylyte development in other GBS zones. We interpret the coeval pseudotachylytes with ductile precursors as evidence of seismic events near the BDT. Grain size piezometry yields high differential stresses in both host mylonites ( 160 MPa) and pseudotachylyte survivor clasts (> 200 MPa), consistent with high stresses during interseismic and coseismic phases of the earthquake cycle, respectively.

Microstructure Evolution and Mechanical Properties of High-Speed Friction Stir Welded Aluminum Alloy Thin Plate Joints

NASA Astrophysics Data System (ADS)

Liu, Fenjun; Fu, Li; Chen, Haiyan

2018-06-01

Sound friction stir welded (FSW) joints of 6061-T6 aluminum alloy sheets with an 0.8 mm thickness were obtained at conventional speed (2000 rpm, 300 mm/min) and high speed (11,000 rpm, 1500 mm/min). The recrystallization mechanism, precipitate evolution, mechanical properties and fracture behavior were investigated in detail. Microstructure analyses revealed that the grain structure evolution in the nugget zone (NZ) was dominated by continuous dynamic recrystallization. In the process of FSW, high speed facilitates the formation of finer equiaxed recrystallized grains, higher density of dislocations and substructures, and a larger number of precipitates in the NZ compared to the conventional speed, which further significantly improves the hardness and tensile strength of the joints. The maximum tensile strength was obtained with 292.6 MPa, 83.2% for the 6061-T6 aluminum alloy and 122.6% for the conventional-speed FSW joints. This work provides an effective method for preparing FSW aluminum alloy thin plate joints with excellent mechanical properties.

Rheology linked with phase changes as recorded by development of shear bands in the South Armorican Shear Zone

NASA Astrophysics Data System (ADS)

Jeřábek, Petr; Bukovská, Zita

2015-04-01

The South Armorican Shear Zone in France represents a major right-lateral strike slip shear zone formed in the late stages of Variscan orogeny. The active deformation in this shear zone is associated with the development of S-C fabrics in granitoids where thin shear bands (C) overprint an earlier higher grade metamorphic foliation (S). In the studied samples covering low to high intensity of shear band overprint, we identified three stages of shear band evolution associated with distinct microstructures and deformation mechanisms. The initiation of shear bands stage I is associated with the formation of microcracks crosscutting the S fabric and detected namely in the recrystallized quartz aggregates. The microcracks of suitable orientation are filled by microcline, albite, muscovite and chlorite which is a typical assemblage also for the well developed shear bands. Phase equilibrium modeling in PERPLEX indicates that this assemblage formed at pressure-temperature range of 0.1-0.4 GPa and 300-340 °C. Stage II of shear band evolution is characterized by dynamic recrystallization and grain size reduction of quartz aggregates along the microcracks and replacement of quartz by microcline along grain boundaries. This process leads to disintegration of quartz aggregate fabric and phase mixing in the shear bands. The inferred deformation mechanism for this stage is solution-precipitation creep although recrystallization of quartz is still active at the contact between quartz aggregates and shear bands. The coarse grained microstructure of quartz aggregates with ca ~250 microns average grain size reduces to ~10 microns grain size when recrystallized along extremely thin shear bands/microcracks and to ~20 microns grain size when recrystallized along the thicker shear bands. By using the flow law of Patterson and Luan (1990) for dislocation creep in quartz and the quartz piezometer of Stipp and Tullis (2003) corrected after Holyoke and Kronenberg (2010), the quartz recrystallization along thin shear bands records strain rates of ~10^-14 whereas the recrystallization along thick shear bands records strain rates of ~10^-15. The contemporaneous operation of solution-precipitation creep in shear bands and dislocation creep in quartz along the shear band boundary suggests low viscosity contrast between the mixed phase shear band matrix and pure quartz aggregate implying that the solution-precipitation creep reflect similar stress and strain rate conditions as the dislocation creep in quartz. Stage III of shear band evolution is characterized by interconnection of dispersed muscovite grains and the deformation becomes accommodated by dislocation creep in thin muscovite bands separating the inactive domains of stage II microstructure. References: Holyoke III, C. W., & Kronenberg, A. K. (2010). Accurate differential stress measurement using the molten salt cell and solid salt assemblies in the Griggs apparatus with applications to strength, piezometers and rheology. Tectonophysics, 494(1-2), 17-31. Paterson, M. S., & Luan, F. C. (1990). Quartzite rheology under geological conditions. In R. J. Knipe & E. H. Rutter (Eds.), Deformation Mechanisms, Rheology and Tectonics (pp. 299-307). London: Geological Society Special Publications. Stipp, M., & Tullis, J. (2003). The recrystallized grain size piezometer for quartz. Geophysical Research Letters, 30(21), 1-5.

Textural and Rb-Sr isotopic evidence for late Paleozoic mylonitization within the Honey Hill fault zone southeastern Connecticut

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Hara, K.D.; Gromet, L.P.

A petrographic and Rb-Sr isotopic study of rocks within and near the Honey Hill fault zone places important constraints on its history of movement. Rb-Sr apparent ages for micas and plagioclase from these rocks have been reset and range from Permian to Triassic, considerably younger than the minimum stratigraphic age (Ordovician) of the rocks studied or of Acadian (Devonian) regional metamorphism. Permian Rb-Sr ages of dynamically recrystallized muscovite date the development of mylonite fabric. An older age is precluded by the excellent preservation of unrecovered quartz, which indicates that these rocks did not experience temperatures high enough to anneal quartzmore » or thermally reset Rb-Sr isotopic systems in muscovite since the time of mylonitization. Metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist-lower amphibolite grade conditions during Permian to Triassic time. Collectively these results indicate that the Honey Hill fault zone was active during the Late Paleozoic and that ductile deformation and metamorphism associated with the Alleghanian orogeny extend well into southern Connecticut. An Alleghanian age for mylonitization within the Honey Hill fault zone suggests it should be considered as a possible site for the major Late Paleozoic strike-slip displacements inferred from paleomagnetic studies for parts of coastal New England and maritime Canada.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shenyang; Joshi, Vineet; Lavender, Curt A.

Experiments showed that recrystallization dramatically speeds up the gas bubble swelling kinetics in metallic UMo fuels. In this work a recrystallization model is developed to study the effect of microstructures and radiation conditions on recrystallization kinetics. The model integrates the rate theory of intra-granular gas bubble and interstitial loop evolution and a phase field model of recrystallization zone evolution. A fast passage method is employed to describe one dimensional diffusion of interstitials which have diffusivity several order magnitude larger than that of the fission gas Xe. With the model, the effect of grain sizes on recrystallization kinetics is simulated.

A Rate-Theory-Phase-Field Model of Irradiation-Induced Recrystallization in UMo Nuclear Fuels

NASA Astrophysics Data System (ADS)

Hu, Shenyang; Joshi, Vineet; Lavender, Curt A.

2017-12-01

In this work, we developed a recrystallization model to study the effect of microstructures and radiation conditions on recrystallization kinetics in UMo fuels. The model integrates the rate theory of intragranular gas bubble and interstitial loop evolutions and a phase-field model of recrystallization zone evolution. A first passage method is employed to describe one-dimensional diffusion of interstitials with a diffusivity value several orders of magnitude larger than that of fission gas xenons. With the model, the effect of grain sizes on recrystallization kinetics is simulated. The results show that (1) recrystallization in large grains starts earlier than that in small grains, (2) the recrystallization kinetics (recrystallization volume fraction) decrease as the grain size increases, (3) the predicted recrystallization kinetics are consistent with the experimental results, and (4) the recrystallization kinetics can be described by the modified Avrami equation, but the parameters of the Avrami equation strongly depend on the grain size.

Effect of the Rate of Hot Compressive Deformation on the Kinetics of Dynamic and Static Recrystallization of Novel Medium-Carbon Medium-Alloy Steel

NASA Astrophysics Data System (ADS)

Khlusova, E. I.; Zisman, A. A.; Knyazyuk, T. V.; Novoskol'tsev, N. N.

2018-03-01

Dynamic and static recrystallization occurring under hot deformation at a rate of 1 and 100 sec - 1 in high-strength medium-carbon wear-resistant steels developed at CRISM "Prometey" for die forming of parts of driven elements of tillage machines is studied. The critical strain of dynamic recrystallization and the threshold temperatures and times of finish of static recrystallization are determined for the studied deformation rates at various temperatures.

Experimental constraints and theoretical bases for microstructural damage in plate boundary shear zones

NASA Astrophysics Data System (ADS)

Skemer, P. A.; Cross, A. J.; Bercovici, D.

2016-12-01

(Ultra)mylonites from plate boundary shear zones are characterized by severe grain-size reduction and well-mixed mineral phases. The evolution from relatively undeformed tectonite protoliths to highly deformed (ultra)mylonites via the formation of new grain and phase boundaries is described as microstructural `damage.' Microstructural damage is important for two reasons: grain-size reduction is thought to result in significant rheological weakening, while phase mixing inhibits mechanical recovery and preserves the zone of weakness to be reactivated repeatedly throughout the tectonic cycle. Grain-size reduction by dynamic recrystallization has been studied extensively in both geologic and engineered materials, yet the progressive mixing of mineral phases during high pressure/temperature shear - the other essential element of damage or mylonitization - is not well understood. In this contribution we present new experimental results and theory related to two distinct phase mixing processes. First, we describe high strain torsion experiments on calcite and anhydrite mixtures and a simple geometric mixing model related to the stretching and thinning of monophase domains. Second, we describe a grain-switching mechanism that is driven by the surface-tension driven migration of newly formed interphase triple junctions. Unlike dynamic recrystallization, which occurs at relatively small strains, both phase mixing mechanisms described here appear to require extremely large strains, a prediction that is consistent with geologic observations. These data suggest that ductile shear zones experience long, transient intervals of microstructural evolution during which rheology is not at steady state. Microstructural damage may be interpreted as the product of several interconnected physical processes, which are collectively essential to the preservation of long-lived, Earth-like plate tectonics.

Solid State Research.

DTIC Science & Technology

1982-11-22

48 Fabricated in Zone-Melting-Recrystallized Si Films on Si0 2-Coated Si Substrates V 4. MICROELECTRONICS 55 4.1 Charge-Coupled Devices: Time...OMCVD to the CLEFT (cleavage of lateral epitaxial films for transfer) process, a continuous epitaxial GaAs layer 3 Ym thick has been grown over a...complete-island-etch or local-oxidation-of-Si isolation, that were fabricated in zone-melting-recrystallized Si films on Si02-coated Si substrates. As

Oman Drilling Project GT3 site survey: dynamics at the roof of an oceanic magma chamber

NASA Astrophysics Data System (ADS)

France, L.; Nicollet, C.; Debret, B.; Lombard, M.; Berthod, C.; Ildefonse, B.; Koepke, J.

2017-12-01

Oman Drilling Project (OmanDP) aims at bringing new constraints on oceanic crust accretion and evolution by drilling Holes in the whole ophiolite section (mantle and crust). Among those, operations at GT3 in the Sumail massif drilled 400 m to sample the dike - gabbro transition that corresponds to the top (gabbros) and roof (dikes) of the axial magma chamber, an interface where hydrothermal and magmatic system interacts. Previous studies based on oceanic crust formed at present day fast-spreading ridges and preserved in ophiolites have highlighted that this interface is a dynamic horizon where the axial melt lens that top the main magma chamber can intrude, reheat, and partially assimilate previously hydrothermally altered roof rocks. Here we present the preliminary results obtained in GT3 area that have allowed the community to choose the drilling site. We provide a geological and structural map of the area, together with new petrographic and chemical constraints on the dynamics of the dike - gabbro transition. Our new results allow us to quantify the dynamic processes, and to propose that 1/ the intrusive contact of the varitextured gabbro within the dikes highlights the intrusion of the melt lens top in the dike rooting zone, 2/ both dikes and previously crystallized gabbros are reheated, and recrystallized by underlying melt lens dynamics (up to 1050°C, largely above the hydrous solidus temperature of altered dikes and gabbros), 3/ the reheating range can be > 200°C, 4/ the melt lens depth variations for a given ridge position is > 200m, 5/ the reheating stage and associated recrystallization within the dikes occurred under hydrous conditions, 6/ the reheating stage is recorded at the root zone of the sheeted dike complex by one of the highest stable conductive thermal gradient ever recorded on Earth ( 3°C/m), 7/ local chemical variations in recrystallized dikes and gabbros are highlighted and used to quantify crystallization and anatectic processes, and the presence of trapped melt, 8/ melt lens cannibalism is attested by numerous assimilation figures close its roof. Besides providing a general context for future studies at OmanDP GT3 site, those new results allow us to quantify the dynamic processes that govern the layer 2 - layer 3 transition in ocean lithosphere.

Deformation-Induced Dynamic Precipitation and Resulting Microstructure in a Mg-Zn-Ca Alloy

NASA Astrophysics Data System (ADS)

Du, Yuzhou; Zheng, Mingyi; Jiang, Bailing; Zhou, Kesong

2018-05-01

The microstructure of an Mg-Zn-Ca extrusion was investigated by transmission electron microscopy, and the interaction between dynamic precipitation and dynamic recrystallization was analyzed. The results showed that dynamic precipitation significantly affected the microstructure of the as-extruded Mg-Zn-Ca alloy. The pinning effects of precipitates on dislocations effectively prohibited dynamic recrystallization processes, while the grain boundary precipitate Ca2Mg6Zn3, inhibited the growth of dynamically recrystallized grains. Consequently, a bimodal microstructure with fine dynamically recrystallized (DRXed) grains and elongated deformed regions was obtained for the Mg-Zn-Ca extrusion. High-resolution transmission electron microscopy indicated that the intragranular precipitate MgZn2 had a crystal orientation relationship with α-Mg in the form of (0002)Mg//(10-13)MgZn2 and [1-100]Mg//[1-210]MgZn2, which was beneficial for strength improvement.

Effect of strain on evolution of dynamic recrystallization in Nb-1 wt%Zr-0.1 wt%C alloy at 1500 and 1600 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behera, A.N.

Uniaxial compression tests were carried out on Nb-1 wt%Zr-0.1 wt%C alloy at temperature of 1500 and 1600 °C and strain rate of 0.1 s{sup −1} to study the evolution of dynamic recrystallization with strain. Electron back scatter diffraction was used to quantify the microstructural evolution. Nb-1Zr-0.1C alloy showed a necklace structure at a strain of 0.9 when deformed at 1500 °C and at strain of 0.6 when deformed at 1600 °C, both at strain rate of 0.1 s{sup −1}. This suggested the occurrence of dynamic recrystallization. At 1500 °C and strain of 0.9 the local average misorientation and the grainmore » orientation spread was low confirming the presence of dynamic recrystallization at this deformation condition. At both 1500 and 1600 °C and all measured strains the recrystallized grains had a strong fiber component of <001>. - Highlights: • Necklace formation of dynamically recrystallized grains occurred at strain of 0.6 and 0.9 for 1500 and 1600 °C, respectively. • Equiaxed microstructures were seen with increase in strain for both 1500 and 1600 °C. • At large strains the predominant recrystallized texture evolved to <001> pole.« less

Dynamic Recrystallization Behavior of Zr-1Sn-0.3Nb Alloy During Hot Rolling Process

NASA Astrophysics Data System (ADS)

Zhao, Siyu; Liu, Huiqun; Lin, Gaoyong; Jiang, Yilan; Xun, Jian

2017-11-01

Zirconium alloys are advanced materials with properties that are greatly affected by their crystalline structure. To investigate this, sheets of Zr-1Sn-0.3Nb alloy were hot rolled with different reductions (10%, 30%, 50%, and 60%) at 1023 K and 1073 K to investigate the alloy's dynamic recrystallization behavior. Recrystallization kinetics was observed via electron backscattering diffraction and transmission electron microscopy, and the results were compared with estimates based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The values of the JMAK exponent n and k increased with the rolling temperature. The estimates and microstructural observations of dynamic recrystallization (DRX) kinetics were in good agreement.

Texture Development and Material Flow Behavior During Refill Friction Stir Spot Welding of AlMgSc

NASA Astrophysics Data System (ADS)

Shen, Junjun; Lage, Sara B. M.; Suhuddin, Uceu F. H.; Bolfarini, Claudemiro; dos Santos, Jorge F.

2018-01-01

The microstructural evolution during refill friction stir spot welding of an AlMgSc alloy was studied. The primary texture that developed in all regions, with the exception of the weld center, was determined to be 〈110〉 fibers and interpreted as a simple shear texture with the 〈110〉 direction aligned with the shear direction. The material flow is mainly driven by two components: the simple shear acting on the horizontal plane causing an inward-directed spiral flow and the extrusion acting on the vertical plane causing an upward-directed or downward-directed flow. Under such a complex material flow, the weld center, which is subjected to minimal local strain, is the least recrystallized. In addition to the geometric effects of strain and grain subdivision, thermally activated high-angle grain boundary migration, particularly continuous dynamic recrystallization, drives the formation of refined grains in the stirred zone.

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

NASA Astrophysics Data System (ADS)

Molli, Giancarlo; Menegon, Luca; Malasoma, Alessandro

2017-04-01

The switching in deformation mode (from distributed to localized) and mechanism (viscous versus frictional) represent a relevant issue in the frame of processes of crustal deformation in turn connected with the concept of the brittle-"ductile" transition and seismogenesis. On the other hand the role of brittle precursors in nucleating crystal-plastic shear zones has received more and more consideration being now recognized as having a fundamental role in the localization of deformation and shear zone development, thus representing a case in which switching deformation mode and mechanisms interact and relate to each other. This contribution analyses an example of a crystal plastic shear zone localized by brittle precursor formed within a host granitic-mylonite during deformation in subduction-related environment. The studied sample come from the external Corsican continental crust units involved in alpine age subduction and characterized by a low grade blueschist facies peak assemblages. The blueschist facies host rock is cut by a thin (< 1 cm thick) brittle-viscous shear zone that preserves domains with a cataclastic microstructure overprinted by mylonitic deformation. Blue amphibole is stable in the shear zone foliation, which therefore formed under HP/LT metamorphic conditions in a subduction environment. Quartz microstructure in the damage zone flanking the brittle-viscous shear zone shows evidence of both microcracking and dislocation glide, with limited recrystallization localized in intracrystalline bands. In the mylonite portion of the shear zone, quartz forms polycrystalline ribbons of dynamically recrystallized grains with a crossed-girdle c-axis CPO. Extrapolation of laboratory-derived flow laws indicates strain rate of ca. 3.5 * 10-12 s-1 during viscous flow in the shear zone. The studied structures, possibly formed by transient instability related to episodic stress/strain rate variations, may be considered as a small scale example of fault behaviour associated with a cycle of interseismic creep with coseismic rupture and then a fossil example of stick-slip strain accommodation in subduction environment of continental crust.

Surface recrystallization theory of the wear of copper in liquid methane

NASA Technical Reports Server (NTRS)

Bill, R. C.; Wisander, D. W.

1974-01-01

Copper was subjected to sliding against 440C in liquid methane. The normal load range was from 1/4 to 2 kilograms, and the sliding velocity range was from 3.1 to 25 meters per second. Over this range of experimental parameters, the wear rate of the copper rider was found to be proportional to the sliding velocity squared and to the normal load. Transmission electron microscopy was used to study the dislocation structure in the copper very near the wear scar surface. It was found that near the wear scar surface, the microstructure was characterized by a fine-cell recrystallized zone in which individual dislocations could be distinguished in the cell walls. The interiors of the cells, about 0.5 micrometer in diameter, were nearly dislocation free. Below the recrystallized layer was a zone that was intensely cold worked by the friction process. With increasing depth, this intensely cold worked zone gradually became indistinguishable from the partially cold worked bulk of the copper, representative of the initial condition of the material.

Detailed Microstructural Characterization and Restoration Mechanisms of Duplex and Superduplex Stainless Steel Friction-Stir-Welded Joints

NASA Astrophysics Data System (ADS)

Santos, T. F. A.; Torres, E. A.; Lippold, J. C.; Ramirez, A. J.

2016-12-01

Duplex stainless steels are successfully used in a wide variety of applications in areas such as the food industry, petrochemical installations, and sea water desalination plants, where high corrosion resistance and high mechanical strength are required. However, during fusion welding operations, there can be changes to the favorable microstructure of these materials that compromise their performance. Friction stir welding with a non-consumable pin enables welded joints to be obtained in the solid state, which avoids typical problems associated with solidification of the molten pool, such as segregation of alloying elements and the formation of solidification and liquefaction cracks. In the case of superduplex stainless steels, use of the technique can avoid unbalanced proportions of ferrite and austenite, formation of deleterious second phases, or growth of ferritic grains in the heat-affected zone. Consolidated joints with full penetration were obtained for 6-mm-thick plates of UNS S32101 and S32205 duplex stainless steels, and S32750 and S32760 superduplex steels. The welding heat cycles employed avoided the conditions required for formation of deleterious phases, except in the case of the welded joint of the S32760 steel, where SEM images indicated the formation of secondary phases, as corroborated by decreased mechanical performance. Analysis using EBSD and transmission electron microscopy revealed continuous dynamic recrystallization by the formation of cellular arrays of dislocations in the ferrite and discontinuous dynamic recrystallization in the austenite. Microtexture evaluation indicated the presence of fibers typical of shear in the thermomechanically affected zone. These fibers were not obviously present in the stir zone, probably due to the intensity of microstructural reformulation to which this region was subjected.

Petrofabrics of high-pressure rocks exhumed at the slab-mantle interface from the "point of no return" in a subduction zone (Sivrihisar, Turkey)

NASA Astrophysics Data System (ADS)

Whitney, Donna L.; Teyssier, Christian; Seaton, Nicholas C. A.; Fornash, Katherine F.

2014-12-01

The highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is 2.5 GPa, corresponding to the maximum decoupling depth (MDD) (80 ± 10 km) identified in active subduction zones; beyond the MDD (the "point of no return") exhumation is unlikely. The Sivrihisar massif (Turkey) is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from 80 to 45 km. Crystallographic fabrics and other features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, microstructures and crystallographic fabrics record deformation in the dislocation creep regime, including dynamic recrystallization during decompression, and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression ( 2.5 to 1.5 GPa). Phengite, lawsonite, and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation, and omphacite developed an L-type crystallographic fabric. In marble, aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite (P > 1.2 GPa). Results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface. This large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return.

Dynamic recrystallization behavior of an as-cast TiAl alloy during hot compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jianbo, E-mail: lijianbo1205@163.com; Liu, Yong, E-mail: yonliu@csu.edu.cn; Wang, Yan, E-mail: wangyan@csu.edu.cn

2014-11-15

High temperature compressive deformation behaviors of as-cast Ti–43Al–4Nb–1.4W–0.6B alloy were investigated at temperatures ranging from 1050 °C to 1200 °C, and strain rates from 0.001 s{sup −1} to 1 s{sup −1}. Electron back scattered diffraction technique, scanning electron microscopy and transmission electron microscopy were employed to investigate the microstructural evolutions and nucleation mechanisms of the dynamic recrystallization. The results indicated that the true stress–true strain curves show a dynamic flow softening behavior. The dependence of the peak stress on the deformation temperature and the strain rate can well be expressed by a hyperbolic-sine type equation. The activation energy decreases withmore » increasing the strain. The size of the dynamically recrystallized β grains decreases with increasing the value of the Zener–Hollomon parameter (Z). When the flow stress reaches a steady state, the size of β grains almost remains constant with increasing the deformation strain. The continuous dynamic recrystallization plays a dominant role in the deformation. In order to characterize the evolution of dynamic recrystallization volume fraction, the dynamic recrystallization kinetics was studied by Avrami-type equation. Besides, the role of β phase and the softening mechanism during the hot deformation was also discussed in details. - Highlights: • The size of DRXed β grains decreases with increasing the value of the Z. • The CDRX plays a dominant role in the deformation. • The broken TiB{sub 2} particles can promote the nucleation of DRX.« less

Unified Static and Dynamic Recrystallization Model for the Minerals of Earth's Mantle Using Internal State Variable Model

NASA Astrophysics Data System (ADS)

Cho, H. E.; Horstemeyer, M. F.; Baumgardner, J. R.

2017-12-01

In this study, we present an internal state variable (ISV) constitutive model developed to model static and dynamic recrystallization and grain size progression in a unified manner. This method accurately captures temperature, pressure and strain rate effect on the recrystallization and grain size. Because this ISV approach treats dislocation density, volume fraction of recrystallization and grain size as internal variables, this model can simultaneously track their history during the deformation with unprecedented realism. Based on this deformation history, this method can capture realistic mechanical properties such as stress-strain behavior in the relationship of microstructure-mechanical property. Also, both the transient grain size during the deformation and the steady-state grain size of dynamic recrystallization can be predicted from the history variable of recrystallization volume fraction. Furthermore, because this model has a capability to simultaneously handle plasticity and creep behaviors (unified creep-plasticity), the mechanisms (static recovery (or diffusion creep), dynamic recovery (or dislocation creep) and hardening) related to dislocation dynamics can also be captured. To model these comprehensive mechanical behaviors, the mathematical formulation of this model includes elasticity to evaluate yield stress, work hardening in treating plasticity, creep, as well as the unified recrystallization and grain size progression. Because pressure sensitivity is especially important for the mantle minerals, we developed a yield function combining Drucker-Prager shear failure and von Mises yield surfaces to model the pressure dependent yield stress, while using pressure dependent work hardening and creep terms. Using these formulations, we calibrated against experimental data of the minerals acquired from the literature. Additionally, we also calibrated experimental data for metals to show the general applicability of our model. Understanding of realistic mantle dynamics can only be acquired once the various deformation regimes and mechanisms are comprehensively modeled. The results of this study demonstrate that this ISV model is a good modeling candidate to help reveal the realistic dynamics of the Earth's mantle.

The Microstructure and Gamma Prime Distributions in Inertia Friction Welded Joint of P/M Superalloy FGH96

NASA Astrophysics Data System (ADS)

Zhang, Chi; Shen, Wenfei; Zhang, Liwen; Xia, Yingnan; Li, Ruiqin

2017-04-01

A gamma prime ( γ') precipitation ( 35% in volume)-hardened powder metallurgy (P/M) superalloy FGH96 was welded using inertia friction welding (IFW). The microstructure and γ' distributions in the joints in two conditions, hot isostatic pressed state and solution-treated and aged state, were characterized. The recrystallization of grains, the dissolution and re-precipitation of γ' in the joints were discussed in terms of the temperature evolutions which were calculated by finite element model analysis. Regardless of the initial states, fully recrystallized fine grain structure formed at welded zone. Meanwhile, very fine γ' precipitations were re-precipitated at the welded zone. These recrystallized grain structure and fine re-precipitated γ' resulted in increasing hardness of IFW joint while making the hardness dependent on the microstructure and γ' precipitation.

Modeling Deformation Flow Curves and Dynamic Recrystallization of BA-160 Steel During Hot Compression

NASA Astrophysics Data System (ADS)

Shahriari, Babak; Vafaei, Reza; Mohammad Sharifi, Ehsan; Farmanesh, Khosro

2018-03-01

The hot deformation behavior of a high strength low carbon steel was investigated using hot compression test at the temperature range of 850-1100 °C and under strain rates varying from 0.001 to 1 s-1. It was found that the flow curves of the steel were typical of dynamic recrystallization at the temperature of 950 °C and above; at tested strain rates lower than 1 s-1. A very good correlation between the flow stress and Zener-Hollomon parameter was obtained using a hyperbolic sine function. The activation energy of deformation was found to be around 390 kJ mol-1. The kinetics of dynamic recrystallization of the steel was studied by comparing it with a hypothetical dynamic recovery curve, and the dynamically fraction recrystallized was modeled by the Kolmogorov-Johnson-Mehl-Avrami relation. The Avrami exponent was approximately constant around 1.8, which suggested that the type of nucleation was one of site saturation on grain boundaries and edges.

Microstructure and Mechanical Properties of Welds of Al - Mg - Si Alloys After Different Modes of Impulse Friction Stir Welding

NASA Astrophysics Data System (ADS)

Kondrat'ev, S. Yu.; Morozova, Yu. N.; Golubev, Yu. A.; Hantelmann, C.; Naumov, A. A.; Mikhailov, V. G.

2018-03-01

Welded joints of aluminum alloy 6082-T6 formed by the method of impulse friction stir welding are studied. The effect of the power and frequency of the pulses on the microstructure and mechanical properties of the welded joints is determined. Application of an additional pulse during the welding affects the surface quality and the shape of the weld, the distribution of the oxide layer and of particles of the hardening phase, and the grain size in the zone of dynamic recrystallization.

Failure Mechanisms of Thermomechanically Loaded SnAgCu/Plastic Core Solder Ball Composite Joints in Low-Temperature Co-Fired Ceramic/Printed Wiring Board Assemblies

NASA Astrophysics Data System (ADS)

Nousiainen, O.; Putaala, J.; Kangasvieri, T.; Rautioaho, R.; Vähäkangas, J.

2007-03-01

The thermal fatigue endurance of completely lead-free 95.5Sn4Ag0.7Cu/plastic core solder ball (PCSB) composite joint structures in low-temperature Co-fired ceramic/printed wiring board (LTCC/PWB) assemblies was investigated using thermal cycling tests over the temperature ranges of -40°C 125°C and 0°C 100°C. Two separate creep/fatigue failures initiated and propagated in the joints during the tests: (1) a crack along the intermetallic compound (IMC)/solder interface on the LTCC side of the joint, which formed at the high-temperature extremes; and (2) a crack in the solder near the LTCC solder land, which formed at the low-temperature extremes. Moreover, localized recrystallization was detected at the outer edge of the joints that were tested in the harsh (-40°C 125°C) test conditions. The failure mechanism was creep/fatigue-induced mixed intergranular and transgranular cracking in the recrystallized zone, but it was dominated by transgranular thermal fatigue failure beyond the recrystallized zone. The change in the failure mechanism increased the rate of crack growth. When the lower temperature extreme was raised from -40°C to 0°C, no recrystallized zone was detected and the failure was due to intergranular cracks.

Study on the dynamic recrystallization model and mechanism of nuclear grade 316LN austenitic stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shenglong; Zhang, Mingxian; Wu, Huanchun

In this study, the dynamic recrystallization behaviors of a nuclear grade 316LN austenitic stainless steel were researched through hot compression experiment performed on a Gleeble-1500 simulator at temperatures of 900–1250 °C and strain rates of 0.01–1 s{sup −1}. By multiple linear regressions of the flow stress-strain data, the dynamic recrystallization mathematical models of this steel as functions of strain rate, strain and temperature were developed. Then these models were verified in a real experiment. Furthermore, the dynamic recrystallization mechanism of the steel was determined. The results indicated that the subgrains in this steel are formed through dislocations polygonization and thenmore » grow up through subgrain boundaries migration towards high density dislocation areas and subgrain coalescence mechanism. Dynamic recrystallization nucleation performs in grain boundary bulging mechanism and subgrain growth mechanism. The nuclei grow up through high angle grain boundaries migration. - Highlights: •Establish the DRX mathematical models of nuclear grade 316LN stainless steel •Determine the DRX mechanism of this steel •Subgrains are formed through dislocations polygonization. •Subgrains grow up through subgrain boundaries migration and coalescence mechanism. •DRX nucleation performs in grain boundary bulging mechanism and subgrain growth mechanism.« less

Strain Evolution in Cold-Warm Forged Steel Components Studied by Means of EBSD Technique

PubMed Central

Bonollo, Franco; Bassan, Fabio; Berto, Filippo

2017-01-01

Electron BackScatter Diffraction (EBSD) in conjunction with Field-Emission Environmental Scanning Electron Microscopy (FEG-ESEM) has been used to evaluate the microstructural and local plastic strain evolution in different alloys (AISI 1005, AISI 304L and Duplex 2205) deformed by a single-stage cold and warm forging process. The present work is aimed to describe the different behavior of the austenite and ferrite during plastic deformation as a function of different forging temperatures. Several topological EBSD maps have been measured on the deformed and undeformed states. Then, image quality factor, distributions of the grain size and misorientation have been analyzed in detail. In the austenitic stainless steel, the γ-phase has been found to harden more easily, then α-phase and γ-phase in AISI 1005 and in duplex stainless steel, sequentially. Compared to the high fraction of continuous dynamic recrystallized austenitic zones observed in stainless steels samples forged at low temperatures, the austenitic microstructure of samples forged at higher temperatures, 600–700 °C, has been found to be mainly characterized by large and elongated grains with some colonies of fine nearly-equiaxed grains attributed to discontinuous dynamic recrystallization. PMID:29258249

Dynamic Recrystallization of the Constituent γ Phase and Mechanical Properties of Ti-43Al-9V-0.2Y Alloy Sheet.

PubMed

Zhang, Yu; Wang, Xiaopeng; Kong, Fantao; Chen, Yuyong

2017-09-15

A crack-free Ti-43Al-9V-0.2Y alloy sheet was successfully fabricated via hot-pack rolling at 1200 °C. After hot-rolling, the β/γ lamellar microstructure of the as-forged TiAl alloy was completely converted into a homogeneous duplex microstructure with an average γ grain size of 10.5 μm. The dynamic recrystallization (DRX) of the γ phase was systematically investigated. A recrystallization fraction of 62.5% was obtained for the γ phase in the TiAl alloy sheet, when a threshold value of 0.8° was applied to the distribution of grain orientation spread (GOS) values. The high strain rate and high stress associated with hot-rolling are conducive for discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), respectively. A certain high-angle boundary (HAGB: θ = 89° ± 3°<100>), which is associated with DDRX, occurs in both the recrystallized and deformed γ grains. The twin boundaries play an important role in the DDRX of the γ phase. Additionally, the sub-structures and sub-boundaries originating from low-angle boundaries in the deformed grains also indicate that CDRX occurs. The mechanical properties of the alloy sheet were determined at both room and elevated temperatures. At 750 °C, the alloy sheet exhibited excellent elongation (53%), corresponding to a failure strength of 467 MPa.

Cyclic Ductile-Brittle Deformation during Temperature Decrease in Quartz-Rich Mylonites: Insights from the Calamita Schists (Elba Island, Italy)

NASA Astrophysics Data System (ADS)

Papeschi, S.; Menegon, L. M.; Musumeci, G.

2017-12-01

The Calamita Schists are a metamorphic complex that experienced transient (< 1 Ma) upper Miocene HT/LP metamorphism related to the emplacement of the Porto Azzurro pluton at P<0.2 GPa. HT/LP metamorphism was coeval with regional scale contractional tectonics leading to the development of meter to decameter ductile east-verging high-strain domains marked by mylonitic fabric overprinted by non-Andersonian brittle faults. In order to investigate the switch in deformation mechanism during temperature decrease at constant pressure (P<0.2 GPa), a sample of mylonitic quartzite with S-C' fabric was examined by Electron Backscatter Diffraction (EBSD), optical microscopy and Scanning Electron Microscope (SEM). Mylonitic fabric is marked by synkinematic biotite + cordierite + andalusite + K-feldspar assemblage, which is progressively replaced by retrograde white mica + chlorite. Quartz microfabric is defined by coarse-grained (100-900 µm) quartz porphyroclasts wrapped by ribbons of dynamically recrystallized finer grains ( 50 µm) showing a strong CPO. This fabric is cross cut by conjugate and synthetic C'-shear bands localized in porphyroclasts and marked by recrystallized fine grains (5-50 µm). EBSD data indicate that prism was the dominant slip system during crystal plastic deformation and dynamic recrystallization in the polycrystalline ribbons. Subsequently, brittle deformation localized along intracrystalline bands (both in conjugate sets and parallel to C' shear bands) within quartz porphyroclasts. The bands evolved in localized cataclastic micro-shear zones and in shear fractures, which localized fluid infiltration and healing by solution precipitation. The quartz new grains filling the bands are preferentially oriented with their c-axis parallel to the shear band boundary. This work highlights that deformation in the Calamita Schists switched over time from high-temperature dynamic recrystallization, accommodated by prism slip to low grade brittle-ductile processes. At the brittle-ductile transition strain partitioning was controlled by grain size and fluid penetration and was characterized by cyclical ductile-brittle mechanisms. In particular brittle failure localized in coarse-grains acted as the precursor for ductile C' shear bands.

Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)

NASA Astrophysics Data System (ADS)

Trincal, Vincent; Buatier, Martine; Charpentier, Delphine; Lacroix, Brice; Lanari, Pierre; Labaume, Pierre; Lahfid, Abdeltif; Vennemann, Torsten

2017-09-01

In orogens, shortening is mainly accommodated by thrusts, which constitute preferential zones for fluid-rock interactions. Fluid flow, mass transfer, and mineralogical reactions taking place along thrusts have been intensely investigated, especially in sedimentary basins for petroleum and uranium research. This study combines petrological investigations, mineralogical quantifications, and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties (nature, origin, temperature, and redox) and fluid-host rock interactions (mass transfers, recrystallization mechanisms, and newly formed synkinematic mineralization) in the Pic-de-Port-Vieux thrust fault zone (Pyrenees, Spain). We demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low-grade metamorphism conditions during thrusting. The hanging-wall Triassic red pelite was locally bleached, while the footwall Cretaceous dolomitic limestone was mylonitized. The results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite. Geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior (tectonic and hydraulic), and improve our knowledge of fluid-rock interactions in open fluid systems in the crust.

Deformation Characteristics and Recrystallization Response of a 9310 Steel Alloy

NASA Astrophysics Data System (ADS)

Snyder, David; Chen, Edward Y.; Chen, Charlie C.; Tin, Sammy

2013-01-01

The flow behavior and recrystallization response of a 9310 steel alloy deformed in the ferrite temperature range were studied in this work. Samples were compressed under various conditions of strain (0.6, 0.8 and multi-axial), strain rate (10-4 seconds-1 to 10-1 seconds-1) and temperature [811 K to 1033 K (538 °C to 760 °C)] using a Gleeble thermo-mechanical simulator. Deformation was characterized by both qualitative and quantitative means, using standard microscopy, electron backscatter diffraction (EBSD) analysis and flow stress modeling. The results indicate that deformation is primarily accommodated through dynamic recovery in sub-grain formation. EBSD analysis shows a continuous increase in sub-grain boundary misorientation with increasing strain, ultimately producing recrystallized grains from the sub-grains at high strains. This suggests that a sub-grain rotation recrystallization mechanism predominates in this temperature range. Analyses of the results reveal a decreasing mean dynamically recrystallized grain size with increasing Zener-Hollomon parameter, and an increasing recrystallized fraction with increasing strain.

Microstructural Evolution and Dynamic Softening Mechanisms of Al-Zn-Mg-Cu Alloy during Hot Compressive Deformation

PubMed Central

Shi, Cangji; Lai, Jing; Chen, X.-Grant

2014-01-01

The hot deformation behavior and microstructural evolution of an Al-Zn-Mg-Cu (7150) alloy was studied during hot compression at various temperatures (300 to 450 °C) and strain rates (0.001 to 10 s−1). A decline ratio map of flow stresses was proposed and divided into five deformation domains, in which the flow stress behavior was correlated with different microstructures and dynamic softening mechanisms. The results reveal that the dynamic recovery is the sole softening mechanism at temperatures of 300 to 400 °C with various strain rates and at temperatures of 400 to 450 °C with strain rates between 1 and 10 s−1. The level of dynamic recovery increases with increasing temperature and with decreasing strain rate. At the high deformation temperature of 450 °C with strain rates of 0.001 to 0.1 s−1, a partially recrystallized microstructure was observed, and the dynamic recrystallization (DRX) provided an alternative softening mechanism. Two kinds of DRX might operate at the high temperature, in which discontinuous dynamic recrystallization was involved at higher strain rates and continuous dynamic recrystallization was implied at lower strain rates. PMID:28788454

The Effect of Dynamic Recrystallization on Monotonic and Cyclic Behaviour of Al-Cu-Mg Alloy.

PubMed

Tomczyk, Adam; Seweryn, Andrzej; Grądzka-Dahlke, Małgorzata

2018-05-23

The paper presents an investigation that was conducted to determine the possibility of the occurrence of the process of dynamic recrystallization in 2024 alloy during monotonic tensile and creep tests at the elevated temperatures of 100 °C, 200 °C, and 300 °C. As-extruded material was subjected to creep process with constant force at elevated temperatures, until two varying degrees of deformation were reached. After cooling at ambient temperature, the pre-deformed material was subjected to monotonic and fatigue tests as well as metallographic analysis. The process of dynamic recrystallization was determined in monotonic tests to occur at low strain rate (0.0015/s) only at the temperature of 300 °C. However, in the creep tests, this process occurred with varying efficiency, both during creep at 200 °C and 300 °C. Dynamic recrystallization was indicated to have a significant influence on the monotonic and cyclic properties of the material.

The effect of water on recrystallization behavior and grain boundary morphology in calcite observations of natural marble mylonites

NASA Astrophysics Data System (ADS)

Schenk, Oliver; Urai, Janos L.; Evans, Brian

2005-10-01

Fluids are inferred to play a major role in the deformation and recrystallization of many minerals (e.g. quartz, olivine, halite, feldspar). In this study, we sought to identify the effect of fluids on grain boundary morphology and recrystallization processes in marble mylonites during shear zone evolution. We compared the chemistry, microstructure and mesostructure of calcite marble mylonites from the Schneeberg Complex, Southern Tyrole, Italy, to that from the Naxos Metamorphic Core Complex, Greece. These two areas were selected for comparison because they have similar lithology and resemble each other in chemical composition. In addition, calcite-dolomite geothermometry indicates similar temperatures for shear zone formation: 279±25 °C (Schneeberg Complex) and 271±15 °C (Naxos high-grade core). However, the two settings are different in the nature of the fluids present during the shear zone evolution. In the Schneeberg mylonites, both the alteration of minerals during retrograde metamorphism in the neighboring micaschists and the existence of veins suggest that aqueous fluids were present during mylonitization. The absence of these features in the Naxos samples indicates that aqueous fluids were not as prevalent during deformation. This conclusion is also supported by the stable isotope signature. Observations of broken and planar surfaces using optical and scanning electron microscopes did not indicate major differences between the two mylonites: grain boundaries in both settings display pores with shapes controlled by crystallography, and have pore morphologies that are similar to observations from crack and grain-boundary healing experiments. Grain size reduction was predominantly the result of subgrain rotation recrystallization. However, the coarse grains inside the wet protomylonites (Schneeberg) are characterized by intracrystalline shear zones.

Dynamic Recrystallization of the Constituent γ Phase and Mechanical Properties of Ti-43Al-9V-0.2Y Alloy Sheet

PubMed Central

Zhang, Yu; Wang, Xiaopeng; Kong, Fantao

2017-01-01

A crack-free Ti-43Al-9V-0.2Y alloy sheet was successfully fabricated via hot-pack rolling at 1200 °C. After hot-rolling, the β/γ lamellar microstructure of the as-forged TiAl alloy was completely converted into a homogeneous duplex microstructure with an average γ grain size of 10.5 μm. The dynamic recrystallization (DRX) of the γ phase was systematically investigated. A recrystallization fraction of 62.5% was obtained for the γ phase in the TiAl alloy sheet, when a threshold value of 0.8° was applied to the distribution of grain orientation spread (GOS) values. The high strain rate and high stress associated with hot-rolling are conducive for discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), respectively. A certain high-angle boundary (HAGB: θ = 89° ± 3°<100>), which is associated with DDRX, occurs in both the recrystallized and deformed γ grains. The twin boundaries play an important role in the DDRX of the γ phase. Additionally, the sub-structures and sub-boundaries originating from low-angle boundaries in the deformed grains also indicate that CDRX occurs. The mechanical properties of the alloy sheet were determined at both room and elevated temperatures. At 750 °C, the alloy sheet exhibited excellent elongation (53%), corresponding to a failure strength of 467 MPa. PMID:28914797

Diffusion-Controlled Recrystallization of Water Sorbed into Poly(meth)acrylates Revealed by Variable-Temperature Mid-Infrared Spectroscopy and Molecular Dynamics Simulation.

PubMed

Yasoshima, Nobuhiro; Fukuoka, Mizuki; Kitano, Hiromi; Kagaya, Shigehiro; Ishiyama, Tatsuya; Gemmei-Ide, Makoto

2017-05-18

Recrystallization behaviors of water sorbed into four poly(meth)acrylates, poly(2-methoxyethyl acrylate), poly(tetrahydrofurfuryl acrylate), poly(methyl acrylate), and poly(methyl methacrylate), are investigated by variable-temperature mid-infrared (VT-MIR) spectroscopy and molecular dynamics (MD) simulation. VT-MIR spectra demonstrate that recrystallization temperatures of water sorbed into the polymers are positively correlated with their glass-transition temperatures reported previously. The present MD simulation shows that a lower-limit temperature of the diffusion for the sorbed water and the glass-transition temperatures of the polymers also have a positive correlation, indicating that the recrystallization is controlled by diffusion mechanism rather than reorientation mechanism. Detailed molecular processes of not only recrystallization during rewarming but also crystallization during cooling and hydrogen-bonding states of water in the polymers are systematically analyzed and discussed.

Stress in recrystallized quartz by electron backscatter diffraction mapping

NASA Astrophysics Data System (ADS)

Llana-Fúnez, S.

2017-07-01

The long-term state of stress at middle and lower crustal depths can be estimated through the study of the microstructure of exhumed rocks from active and/or ancient shear zones. Constitutive equations for deformation mechanisms in experimentally deformed rocks relate differential stress to the size of recrystallized grains. Cross et al. (2017) take advantage of electron backscatter diffraction mapping to systematically separate new recrystallized grains from host grains on the basis of the measurable lattice distorsion within the grains. They produce the first calibrated piezometer for quartz with this technique, reproducing within error a previous calibration based on optical microscopy.

Direct observation of growth front movement in electron beam recrystallization of silicon layer on insulator

NASA Astrophysics Data System (ADS)

Inoue, Tomoyasu; Hamasaki, Toshihiko

1987-04-01

A high-speed movie technique was used to investigate the growth front movement during electron beam recrystallization of thin silicon layers on insulating material. In a laterally epitaxial growth process, it was clearly observed that the molten zone shape dramatically changes across a seed opening, which is due to nonuniformity in heat dissipation toward the substrate in the vicinity of the seed opening. The molten zone width and velocities of the melt front and growth front were quantitatively analyzed using digital film motion analysis. The growth front velocity was found to drastically change by ˜30% across the seed opening.

Strain rate dependent activation of slip systems in calcite marbles from Syros (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Grasemann, Bernhard; Morales, Luiz F. G.; Huet, Benjamin; White, Joseph C.

2017-04-01

The activation of certain slip systems in calcite has been experimentally proven to be highly temperature dependent, but also the strain rate plays an important role on the activation of the dominant slip system. In this study, observations from a flanking structure (i.e. shear zone) that developed under lower greenschist-facies conditions, in an almost pure calcite marble (Syros Island, Greece) are presented. The shear zone is characterized by a strain gradient from the slightly deformed tips (γ ˜ 50) to the highly strained centre (γ up to 1000) while the host rock is moderately deformed (γ ˜ 3). During the shear zone development, the strain gradient coincided with a strain rate gradient with strain rate varying from 10-13 to 10-9 s-1. The studied outcrop thus represents the final state of a natural experiment and gives us a great opportunity to get natural constraints on strain rate dependent mechanical behaviour in a calcite marble. Detailed microstructural analyses have been performed via optical microscopy, electron microscopy, electron backscatter diffraction mapping and transmission electron microscopy, on samples from the highly strained shear zone and the host rock. The analyses show that the calcite microfabric varies depending on position within the shear zone, indicating activation of different deformation, recrystallization mechanisms and slip systems at different strain rates. Up to strain rates of ˜10-10 s-1 the marble deformed exclusively within the dislocation creep field, showing a change in recrystallization mechanism and dominant active slip system. While the marble preferentially recrystallized by grain boundary migration at relatively low strain rates (˜10-13 s-1), subgrain rotation recrystallization seems to be the dominant mechanism at higher strain rates (˜10-12 to 10-10 s-1). At higher strain rates (˜10-9 s-1), the recrystallization mechanism is bulging, resulting in the development of an extremely fine grained ultramylonite (average grain size ˜3 μm) accompanied by a switch in deformation mechanism from dislocation creep to a combined deformation by grain boundary sliding and dislocation activity. Constraints on dominant active slip system depending on deformation strain rate have been made by a combination of misorientation analyses and viscoplastic self-consistent modelling.

Characterization of the Micro Textures in a Friction Stir Weld

NASA Technical Reports Server (NTRS)

Schneider, Judy; Nunes, Arthur C.

2004-01-01

In friction stir welding (FSW), a rotating threaded pin tool is inserted into a weld seam and literally stirs the edges of the seam together. The Dynamically-Recrystallized-Zone (DXZ) of a polished and etched FSW cross-section exhibits contrasting bands (the "onion-ring" structure), the origins of which are unclear. An orientation image mapping (OIM) study suggests that the corresponding bands may correspond respectively to a "straight-through" current of metal bypassing the pin tool in a single rotation or less and a "maelstrom" current rotating a number of times around the pin tool.

Dynamic recrystallization and grain boundary migration in B2 FeAl

NASA Technical Reports Server (NTRS)

Baker, I.; Gaydosh, D. J.

1987-01-01

Transmission electron microscopy and optical microscopy were used to examine polycrystalline specimens of the B2-structured alloy FeAl strained under tension to fracture at elevated temperature. Strain-induced grain boundary migration was observed above 900 K and dynamic recrystallization was found at 1000 K and 1100 K. Little evidence of dynamic recovery was evident but some networks were formed at 1100 K.

A Continuum Model for the Effect of Dynamic Recrystallization on the Stress⁻Strain Response.

PubMed

Kooiker, H; Perdahcıoğlu, E S; van den Boogaard, A H

2018-05-22

Austenitic Stainless Steels and High-Strength Low-Alloy (HSLA) steels show significant dynamic recovery and dynamic recrystallization (DRX) during hot forming. In order to design optimal and safe hot-formed products, a good understanding and constitutive description of the material behavior is vital. A new continuum model is presented and validated on a wide range of deformation conditions including high strain rate deformation. The model is presented in rate form to allow for the prediction of material behavior in transient process conditions. The proposed model is capable of accurately describing the stress⁻strain behavior of AISI 316LN in hot forming conditions, also the high strain rate DRX-induced softening observed during hot torsion of HSLA is accurately predicted. It is shown that the increase in recrystallization rate at high strain rates observed in experiments can be captured by including the elastic energy due to the dynamic stress in the driving pressure for recrystallization. Furthermore, the predicted resulting grain sizes follow the power-law dependence with steady state stress that is often reported in literature and the evolution during hot deformation shows the expected trend.

Relating rheology to geometry in large-scale natural shear zones

NASA Astrophysics Data System (ADS)

Platt, John

2016-04-01

The geometry and width of the ductile roots of plate boundary scale faults are very poorly understood. Some field and geophysical data suggests widths of tens of km in the lower crust, possibly more in the upper mantle. Other observations suggest they are much narrower. Dip slip shear zones may flatten out and merge into zones of subhorizontal lower crustal or asthenospheric flow. The width of a ductile shear zone is simply related to relative velocity and strain rate. Strain rate is related to stress through the constitutive relationship. Can we constrain the stress, and do we understand the rheology of materials in ductile shear zones? A lot depends on how shear zones are initiated. If they are localized by pre-existing structures, width and/or rheology may be inherited, and we have too many variables. If shear zones are localized primarily by shear heating, initial shear stress has to be very high (> 1 GPa) to overcome conductive heat loss, and very large feedbacks (both positive and negative) make the system highly unstable. Microstructural weakening requires a minimum level of stress to cause deformation and damage in surrounding rock, thereby buffering the stress. Microstructural weakening leads to grain-size sensitive creep, for which we have constitutive laws, but these are complicated by phase mixing in polyphase materials, by viscous anisotropy, by hydration, and by changes in mineral assemblage. Here are some questions that need to be addressed. (1) If grain-size reduction by dynamic recrystallization results in a switch to grain-size sensitive creep (GSSC) in a stress-buffered shear zone, does dynamic recrystallization stop? Does grain growth set in? If grain-size is still controlled by dislocation processes, then the effective stress exponent for GSSC is 4-5, even though the dominant mechanism may be diffusion and/or grain-boundary sliding (GBS). (2) Is phase mixing in ultramylonites primarily a result of GBS + neighbour switching, creep cavitation and diffusion, or metamorphic reactions? (3) In two-phase / polyphase mixtures, does the strong phase generally form a load-bearing framework, favoring constant strain-rate (Voigt) bound behavior, or does the weak phase form through-going strain pathways, favoring constant stress (Reuss) bound behavior, or do the phases remain well mixed, favoring an intermediate behavior (e.g., Tullis et al model)? (4) How do we deal with the rheological effect of water? Is it simply an unconstrained variable in nature? Is the water fugacity model in flow laws adequate? (5) How can we better relate experimental results (often carried out at constant strain-rate, and not reaching microstructural steady state) to deformation in natural shear zones? Rheological observations on well-constrained natural shear zones are helping us answer some of these questions.

Oxygen isotope geospeedometry by SIMS

NASA Astrophysics Data System (ADS)

Bonamici, C. E.; Valley, J. W.

2013-12-01

Geospeedometry, a discipline closely related and complimentary to thermochronology, exploits the phenomenon of diffusion in order to extract rate and duration information for segments of a rock's thermal history. Geospeedometry data, when anchored in absolute time by geochronologic data, allow for the construction of detailed temperature-time paths for specific terranes and geologic processes. We highlight the developing field of SIMS-based oxygen isotope geospeedometry with an application from granulites of the Adirondack Mountains (New York) and discuss potential future applications based on a recently updated and expanded modeling tool, the Fast Grain Boundary diffusion program (FGB; Eiler et al. 1994). Equilibrium oxygen isotope ratios in minerals are a function of temperature and bulk rock composition. In dynamic systems, intragrain oxygen isotope zoning can develop in response to geologic events that affect the thermal state of a rock and/or induce recrystallization, especially tectonic deformation and fluid infiltration. As an example, titanite grains from late-Grenville shear zones in the northwestern Adirondack Mountains exhibit a range of δ18O zoning patterns that record post-peak metamorphic cooling, episodic fluid infiltration, and deformation-facilitated recrystallization. Many titanite grains preserve smooth, core-to-rim decreasing, diffusional δ18O profiles, which are amenable to diffusion modeling. FGB models that best fit the measured δ18O profiles indicate cooling from ~700-500°C in just 2-5 m.y., a rapid thermal change signaling the final gravitational collapse of the late-Grenville orogen. Titanite can also be utilized as a U-Pb chronometer, and comparison of δ18O and U-Pb age zoning patterns within the Adirondack titanites pins the episode of rapid cooling inferred from the δ18O record to some time between 1054 and 1047 Ma. The expanded capabilities of FGB also allow for evaluation of a range of heating-cooling histories for the Adirondack granulites. Diffusional δ18O zoning profiles in titanite are best fit by complete re-equilibration at temperatures above 675 °C followed by rapid, monotonic cooling; FGB models that include only partial re-equilibration and/or episodes of reheating along the retrograde path do not fit the observed δ18O profiles. Beyond the Adirondack titanite example, FGB can be used as a predictive tool to target either specific minerals within a rock or specific rock types within a terrane for oxygen isotope geospeedometry and zoning studies. FGB generates predictions of δ18O zoning for all minerals in a rock of a given mineralogy and heating-cooling history. Different minerals within the same rock will record different segments of the thermal and fluid history based on their individual diffusivities, phase stabilities, and propensities for deformation-induced/facilitated recrystallization. It should therefore be possible to extract long thermal histories from a single sample by measuring oxygen isotope zoning profiles across several minerals with different partial retention zones for oxygen.

Modelling and simulation of dynamic recrystallization (DRX) in OFHC copper at very high strain rates

NASA Astrophysics Data System (ADS)

Testa, G.; Bonora, N.; Ruggiero, A.; Iannitti, G.; Persechino, I.; Hörnqvist, M.; Mortazavi, N.

2017-01-01

At high strain rates, deformation processes are essentially adiabatic and if the plastic work is large enough dynamic recrystallization can occur. In this work, an examination on microstructure evolution of OFHC copper in Dynamic Tensile Extrusion (DTE) test, performed at 400 m/s, was carried out. EBSD investigations, along the center line of the fragment remaining in the extrusion die, showed a progressive elongation of the grains, and an accompanying development of a strong <001> + <111> dual fiber texture. Discontinuous dynamic recrystallization (DRX) occurred at larger strains, and it was showed that nucleation occurred during straining. A criterion for DRX to occur, based on the evolution of Zener-Hollomon parameter during the dynamic deformation process, is proposed. Finally, DTE test was simulated using the modified Rusinek-Klepaczko constitutive model incorporating a model for the prediction of DRX initiation.

Dynamic moisture sorption characteristics of enzyme-resistant recrystallized cassava starch.

PubMed

Mutungi, Christopher; Schuldt, Stefan; Onyango, Calvin; Schneider, Yvonne; Jaros, Doris; Rohm, Harald

2011-03-14

The interaction of moisture with enzyme-resistant recrystallized starch, prepared by heat-moisture treatment of debranched acid-modified or debranched non-acid-modified cassava starch, was investigated in comparison with the native granules. Crystallinities of the powdered products were estimated by X-ray diffraction. Moisture sorption was determined using dynamic vapor sorption analyzer and data fitted to various models. Percent crystallinities of native starch (NS), non-acid-modified recrystallized starch (NAMRS), and acid-modified recrystallized starch (AMRS) were 39.7, 51.9, and 56.1%, respectively. In a(w) below 0.8, sorption decreased in the order NS > NAMRS > AMRS in line with increasing sample crystallinities but did not follow this crystallinity dependence at higher a(w) because of condensation and polymer dissolution effects. Adsorbed moisture became internally absorbed in NS but not in NAMRS and AMRS, which might explain the high resistance of the recrystallized starches to digestion because enzyme and starch cannot approach each other over fairly sufficient surface at the molecular level.

Recrystallization texture in nickel heavily deformed by accumulative roll bonding

NASA Astrophysics Data System (ADS)

Mishin, O. V.; Zhang, Y. B.; Godfrey, A.

2017-07-01

The recrystallization behavior of Ni processed by accumulative roll bonding to a total accumulated von Mises strain of 4.8 has been examined, and analyzed with respect to heterogeneity in the deformation microstructure. The regions near the bonding interface are found to be more refined and contain particle deformation zones around fragments of the steel wire brush used to prepare the surface for bonding. Sample-scale gradients are also observed, manifested as differences between the subsurface, intermediate and central layers, where the distributions of texture components are different. These heterogeneities affect the progress of recrystallization. While the subsurface and near-interface regions typically contain lower frequencies of cube-oriented grains than anywhere else in the sample, a strong cube texture forms in the sample during recrystallization, attributed to both a high nucleation rate and fast growth rate of cube-oriented grains. The observations highlight the sensitivity of recrystallization to heterogeneity in the deformation microstructure and demonstrate the importance of characterizing this heterogeneity over several length scales.

Structures, microfabrics, fractal analysis and temperature-pressure estimation of the Mesozoic Xingcheng-Taili ductile shear zone in the North China craton

NASA Astrophysics Data System (ADS)

Liang, Chenyue; Neubauer, Franz; Liu, Yongjiang; Jin, Wei; Zeng, Zuoxun; Bernroider, Manfred; Li, Weimin; Wen, Quanbo; Han, Guoqing; Zhao, Yingli

2014-05-01

The ductile shear zone in Xingcheng-Taili area (western Liaoning Province in China) is tectonically located in the eastern section of the northern margin of the North China craton, and dominantly comprises deformed granitic rocks of Neoarchean and Triassic to Late Jurassic age, which were affected by shearing within middle- to low-grade metamorphic conditions. Because a high-temperature metamorphic overprint is lacking, microstructures attesting to low-temperature ductile deformation are well preserved. However, the rocks and its structures have not been previously analyzed in detail except by U-Pb zircon dating and some geochemistry. Here, we describe the deformation characteristics and tectonic evolution of the Xingcheng-Taili ductile shear zone, in order to understand the mode of lithosphericscale reactivation, extension and thinning of the North China craton. The ductile deformation history comprises four successive deformation phases: (1) In the Neoarchean granitic rocks, a steep gneissosity and banded structures trend nearly E-W (D1). (2) A NE-striking sinistral structure of Upper Triassic rocks may indicate a deformation event (D2) in Late Triassic times, which ductile deformation structures superimposed on Neoarchean granitic rocks. (3) A gneissose structure with S-C fabrics as well as an ENE-trending sinistral strike-slip characteristic (D3) developed in Upper Jurassic biotite adamellite and show the deformation characteristics of a shallow crustal level and generated mylonitic fabrics superimposed on previous structures. (4) Late granitic dykes show different deformational behavior, and shortening with D4 folds. The attitude of the foliation S and mineral stretching lineation of three main types of rocks shows remarkable differences in orientation. The shapes of recrystallized quartz grains from three main types of granitic rocks with their jagged and indented boundaries were natural records of deformation conditions (D1to D3). Crystal preferred orientation of quartz determined by electron back scatter diffraction (EBSD) suggest sinistral strike-slip displacement within a temperature at about 400 to 500° C. Quartz mainly shows low-temperature fabrics with dominant {0001}-slip system. As the deformed rocks show obvious deformation overprint, we have estimated flow stresses from dynamically recrystallized grain sizes of quartz separately. But coincident fractal analysis showed that the boundaries of recrystallized grains had statistically self similarities with the numbers of fractal dimension from 1.153 to 1.196 with the range of deformation temperatures from 500 to 600° C, which is corresponding to upper greenschist to lower amphibolite facies conditions. Together with published flow laws to estimated deformation rates between the region of 10-11 - 10-13 S-1depending on the temperature 500 ° C, and the paleo-stress was calculated with grain size of recrystallized quartz to be at 5.0 to 32.3 MPa. Even though the deformation history and kinematics are different, progressive microstructures and texture analysis indicate an overprint by the low-temperature deformation (D3). Typical regional-dynamic metamorphic conditions ere deduced by mineral pair hornblende-plagioclase and phengite barometry identified within the ductile shear zone. The hornblende-plagioclase pair of porphyritic granitic gneiss gives metamorphic conditions of T =450-500 ° C and p=0.39 GPa, which indicate a metamorphic grade of lower-amphibolite facies conditions and a depth of around 13 km estimated following a normal lithostatic pressure. All of the structural characteristics indicate that the Xingcheng-Taili ductile shear zone represents a mainly ENE-striking sinistral ductile strike-slip zone, which formed after intrusion of the Upper Jurassic biotite adamellite and transformed and superimposed previous deformation structures. This deformation event might have occurred in Early Cretaceous times and was related to the lithospheric thinning and extension, due to roll-back of the Pacific plate beneath the eastern North China craton.

Heat-Affected Zone Liquation Cracking Resistance of Friction Stir Processed Aluminum-Copper Alloy AA 2219

NASA Astrophysics Data System (ADS)

Karthik, G. M.; Janaki Ram, G. D.; Kottada, Ravi Sankar

2017-04-01

In the current work, the effect of friction stir processing on heat-affected zone (HAZ) liquation cracking resistance of aluminum-copper alloy AA 2219 was evaluated. In Gleeble hot-ductility tests and longitudinal Varestraint tests, the FSPed material, despite its very fine dynamically recrystallized equiaxed grain structure, showed considerably higher susceptibility to HAZ liquation cracking when compared to the base material. Detailed microstructural studies showed that the increased cracking susceptibility of the FSPed material is due to (i) increase in the amount of liquating θ phase (equilibrium Al2Cu) and (ii) increase in the population of grain boundary θ particles. An important learning from the current work is that, in certain materials like alloy 2219, the use of FSP as a pretreatment to fusion welding can be counterproductive.

Friction stir welding process and material microstructure evolution modeling in 2000 and 5000 series of aluminum alloy

NASA Astrophysics Data System (ADS)

Yalavarthy, Harshavardhan

Interactions between the rotating and advancing pin-shaped tool (terminated at one end with a circular-cylindrical shoulder) with the clamped welding-plates and the associated material and heat transport during a Friction Stir Welding (FSW) process are studied computationally using a fully-coupled thermo-mechanical finite-element analysis. To surmount potential numerical problems associated with extensive mesh distortions/entanglement, an Arbitrary Lagrangian Eulerian (ALE) formulation was used which enabled adaptive re-meshing (to ensure the continuing presence of a high-quality mesh) while allowing full tracking of the material free surfaces. To demonstrate the utility of the present computational approach, the analysis is applied to the cases of same-alloy FSW of two Aluminum-alloy grades: (a) AA5083 (a solid-solution strengthened and strain-hardened/stabilized Al-Mg-Mn alloy); and (b) AA2139 (a precipitation hardened quaternary Al-Cu-Mg-Ag alloy). Both of these alloys are currently being used in military-vehicle hull structural and armor systems. In the case of non-age-hardenable AA5083, the dominant microstructure evolution processes taking place during FSW are extensive plastic deformation and dynamic recrystallization of highly-deformed material subjected to elevated temperatures approaching the melting temperature. To account for the competition between plastic-deformation controlled strengthening and dynamic-recrystallization induced softening phenomena during the FSW process, the original Johnson-Cook strain- and strain-rate hardening and temperature-softening material strength model is modified in the present work using the available recrystallization-kinetics experimental data. In the case of AA2139, in addition to plastic deformation and dynamic recrystallization, precipitates coarsening, over-aging, dissolution and re-precipitation had to be also considered. Limited data available in the open literature pertaining to the kinetics of the aforementioned microstructure-evolution processes are used to predict variation in the material hardness and the residual stresses throughout the various FSW zones of the two alloys. The results showed that with proper modeling of the material behavior under high-temperature/severe-plastic-deformation conditions, significantly improved agreement can be attained between the computed and measured post-FSW residual-stress and material-strength distribution results. Keywords: Friction Stir Welding; AA5083; AA2139; Johnson-Cook Strength Model; Finite Element Analysis; Hardness Prediction.

Hot Deformation Behavior and Dynamic Recrystallization of Medium Carbon LZ50 Steel

NASA Astrophysics Data System (ADS)

Du, Shiwen; Chen, Shuangmei; Song, Jianjun; Li, Yongtang

2017-03-01

Hot deformation and dynamic recrystallization behaviors of a medium carbon steel LZ50 were systematically investigated in the temperature range from 1143 K to 1443 K (870 °C to 1170 °C) at strain rates from 0.05 to 3s-1 using a Gleeble-3500 thermo-simulation machine. The flow stress constitutive equation for hot deformation of this steel was developed with the two-stage Laasraoui equation. The activation energy of the tested steel was 304.27 KJ/mol, which was in reasonable agreement with those reported previously. The flow stress of this steel in hot deformation was mainly controlled by dislocation climb during their intragranular motion. The effect of Zener-Hollomon parameter on the characteristic points of the flow curves was studied, and the dependence of critical strain on peak strain obeyed a linear equation. Dynamic recrystallization was the most important softening mechanism for the tested steel during hot deformation. Kinetic equation of this steel was also established based on the flow stress. The austenite grain size of complete dynamic recrystallization was a power law function of Zener-Hollomon parameter with an exponent of -0.2956. Moreover, the microstructures induced under different deformation conditions were analyzed.

A Continuum Model for the Effect of Dynamic Recrystallization on the Stress–Strain Response

PubMed Central

Perdahcıoğlu, E. S.; van den Boogaard, A. H.

2018-01-01

Austenitic Stainless Steels and High-Strength Low-Alloy (HSLA) steels show significant dynamic recovery and dynamic recrystallization (DRX) during hot forming. In order to design optimal and safe hot-formed products, a good understanding and constitutive description of the material behavior is vital. A new continuum model is presented and validated on a wide range of deformation conditions including high strain rate deformation. The model is presented in rate form to allow for the prediction of material behavior in transient process conditions. The proposed model is capable of accurately describing the stress–strain behavior of AISI 316LN in hot forming conditions, also the high strain rate DRX-induced softening observed during hot torsion of HSLA is accurately predicted. It is shown that the increase in recrystallization rate at high strain rates observed in experiments can be captured by including the elastic energy due to the dynamic stress in the driving pressure for recrystallization. Furthermore, the predicted resulting grain sizes follow the power-law dependence with steady state stress that is often reported in literature and the evolution during hot deformation shows the expected trend. PMID:29789492

Genesis of Microstructures in Friction Stir Welding of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Tchein, Gnofam Jacques; Jacquin, Dimitri; Coupard, Dominique; Lacoste, Eric; Girot Mata, Franck

2018-06-01

This paper is focused on the genesis of microstructures in friction stir welding (FSW) of the Ti-6Al-4V alloy. Several titanium joints, initially prepared with four different preheat treatments, were processed by FSW. Detailed microstructural analyses were performed in order to investigate change in the microstructure during the process. In this work, the FSW processing allows a controlled and stable microstructure to be produced in the stirring zone, regardless of the initial heat treatment or the welding conditions. The welded material undergoes a severe thermomechanical treatment which can be divided into two steps. First, the friction in the shoulder and the plastic strain give rise to the necessary conditions to allow a continuous dynamic recrystallization of the β phase. This operation produces a fine and equiaxed β grain structure. Second, once the pin has moved away, the temperature decreases, and the material undergoes a heat treatment equivalent to air quenching. The material thus exhibits a β → β + α transformation with germination of a fine intergranular Widmanstätten phase within the ex-fully-recrystallized- β grains.

Plasticity-mediated collapse and recrystallization in hollow copper nanowires: a molecular dynamics simulation.

PubMed

Dutta, Amlan; Raychaudhuri, Arup Kumar; Saha-Dasgupta, Tanusri

2016-01-01

We study the thermal stability of hollow copper nanowires using molecular dynamics simulation. We find that the plasticity-mediated structural evolution leads to transformation of the initial hollow structure to a solid wire. The process involves three distinct stages, namely, collapse, recrystallization and slow recovery. We calculate the time scales associated with different stages of the evolution process. Our findings suggest a plasticity-mediated mechanism of collapse and recrystallization. This contradicts the prevailing notion of diffusion driven transport of vacancies from the interior to outer surface being responsible for collapse, which would involve much longer time scales as compared to the plasticity-based mechanism.

Development of high-temperature Kolsky compression bar techniques for recrystallization investigation

NASA Astrophysics Data System (ADS)

Song, B.; Antoun, B. R.; Boston, M.

2012-05-01

We modified the design originally developed by Kuokkala's group to develop an automated high-temperature Kolsky compression bar for characterizing high-rate properties of 304L stainless steel at elevated temperatures. Additional features have been implemented to this high-temperature Kolsky compression bar for recrystallization investigation. The new features ensure a single loading on the specimen and precise time and temperature control for quenching to the specimen after dynamic loading. Dynamic compressive stress-strain curves of 304L stainless steel were obtained at 21, 204, 427, 649, and 871 °C (or 70, 400, 800, 1200, and 1600 °F) at the same constant strain rate of 332 s-1. The specimen subjected to specific time and temperature control for quenching after a single dynamic loading was preserved for investigating microstructure recrystallization.

Characterization of Multilayered Multipass Friction Stir Weld on ASTM A572 G50 Steel

DOE PAGES

Lim, Yong Chae; Sanderson, Samuel; Mahoney, Murray; ...

2014-01-01

A multilayered multipass friction stir weld (MM-FSW) on ASTM A572 Grade 50 steel was characterized to understand its potential application for thick-section structures. The 15-mm-thick section was fabricated by stacking up three steel plates and then friction stir welding the plates together in a total of 5 passes. The unique butt/lap joint configuration encountered in the multilayer weld was examined to understand the effect of tool rotation direction on the joint quality especially the formation of hooking defect. Charpy V-notch impact toughness tests showed generally higher impact toughness energy for the stir zone than the base metal with a ductilemore » fracture mode. The microhardness value was measured from 195 to 220 HV in the stir zone, while the base metal showed an average value of 170 HV. The microstructure in the stir zone and the adjacent heat affected zone was quantified using Optical and Scanning Electron Microscopy (SEM) including Electron Backscatter Diffraction (EBSD). The increased toughness and hardness were correlated with the refined microstructure in stir zone, resulting from severe plastic deformation and subsequent dynamic recrystallization during friction stir welding.« less

Disclination mediated dynamic recrystallization in metals at low temperature.

PubMed

Aramfard, Mohammad; Deng, Chuang

2015-09-16

Recrystallization is one of the most important physical phenomena in condensed matter that has been utilized for materials processing for thousands of years in human history. It is generally believed that recrystallization is thermally activated and a minimum temperature must be achieved for the necessary atomic mechanisms to occur. Here, using atomistic simulations, we report a new mechanism of dynamic recrystallization that can operate at temperature as low as T = 10 K in metals during deformation. In contrast to previously proposed dislocation-based models, this mechanism relies on the generation of disclination quadrupoles, which are special defects that form during deformation when the grain boundary migration is restricted by structural defects such as triple junctions, cracks or obstacles. This mechanism offers an alternative explanation for the grain refinement in metals during severe plastic deformation at cryogenic temperature and may suggest a new method to tailor the microstructure in general crystalline materials.

Disclination mediated dynamic recrystallization in metals at low temperature

PubMed Central

Aramfard, Mohammad; Deng, Chuang

2015-01-01

Recrystallization is one of the most important physical phenomena in condensed matter that has been utilized for materials processing for thousands of years in human history. It is generally believed that recrystallization is thermally activated and a minimum temperature must be achieved for the necessary atomic mechanisms to occur. Here, using atomistic simulations, we report a new mechanism of dynamic recrystallization that can operate at temperature as low as T = 10 K in metals during deformation. In contrast to previously proposed dislocation-based models, this mechanism relies on the generation of disclination quadrupoles, which are special defects that form during deformation when the grain boundary migration is restricted by structural defects such as triple junctions, cracks or obstacles. This mechanism offers an alternative explanation for the grain refinement in metals during severe plastic deformation at cryogenic temperature and may suggest a new method to tailor the microstructure in general crystalline materials. PMID:26374603

Magma-assisted strain localization in an orogen-parallel transcurrent shear zone of southern Brazil

NASA Astrophysics Data System (ADS)

Tommasi, AndréA.; Vauchez, Alain; Femandes, Luis A. D.; Porcher, Carla C.

1994-04-01

In a lithospheric-scale, orogen-parallel transcurrent shear zone of the Pan-African Dom Feliciano belt of southern Brazil, two successive generations of magmas, an early calc-alkaline and a late peraluminous, have been emplaced during deformation. Microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions. Magmatic deformation is indicated by the coexistence of aligned K-feldspar, plagioclase, micas, and/or tourmaline with undeformed quartz. Submagmatic deformation is characterized by strain features, such as fractures, lattice bending, or replacement reactions affecting only the early crystallized phases. High-temperature solid-state deformation is characterized by extensive grain boundary migration in quartz, myrmekitic K-feldspar replacement, and dynamic recrystallization of both K-feldspar and plagioclase. Decreasing temperature during solid-state deformation is inferred from changes in quartz crystallographic fabrics, decrease in grain size of recrystallized feldspars, and lower Ti amount in recrystallized biotites. Final low-temperature deformation is characterized by feldspar replacement by micas. The geochemical evolution of the synkinematic magmatism, from calc-alkaline metaluminous granodiorites with intermediate 87Sr/86Sr initial ratio to peraluminous granites with very high 87Sr/86Sr initial ratio, suggests an early lower crustal source or a mixed mantle/crustal source, followed by a middle to upper crustal source for the melts. Shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle, but, whatever the process initiating partial melting, lithospheric transcurrent shear zones may collect melt at different depths. Because they enhance the vertical permeability of the crust, these zones may then act as heat conductors (by advection), promoting an upward propagation of partial melting in the crust. Synkinematic granitoids localize most, if not all, deformation in the studied shear zone. The regional continuity and the pervasive character of the magmatic fabric in the various synkinematic granitic bodies, consistently displaying similar plane and direction of flow, argue for accommodation of large amounts of orogen-parallel movement by viscous deformation of these magmas. Moreover, activation of high-temperature deformation mechanisms probably allowed a much easier deformation of the hot synkinematic granites than of the colder country rock and, consequently, contributed significantly to the localization of deformation. Finally, the small extent of the low-temperature deformation suggests that the strike-slip deformation ended approximately synchronously with the final cooling of the peraluminous granites. The evolution of the deformation reflects the strong influence of synkinematic magma emplacement and subsequent cooling on the thermomechanical evolution of the shear zone. Magma intrusion in an orogen-scale transcurrent shear zone deeply modifies the rheological behavior of the continental crust. It triggers an efficient thermomechanical softening localized within the fault that may subsist long enough for large displacements to be accommodated. Therefore the close association of deformation and synkinematic magmatism probably represents an important factor controlling the mechanical response of continental plates in collisional environments.

Plasticity-mediated collapse and recrystallization in hollow copper nanowires: a molecular dynamics simulation

PubMed Central

Raychaudhuri, Arup Kumar; Saha-Dasgupta, Tanusri

2016-01-01

Summary We study the thermal stability of hollow copper nanowires using molecular dynamics simulation. We find that the plasticity-mediated structural evolution leads to transformation of the initial hollow structure to a solid wire. The process involves three distinct stages, namely, collapse, recrystallization and slow recovery. We calculate the time scales associated with different stages of the evolution process. Our findings suggest a plasticity-mediated mechanism of collapse and recrystallization. This contradicts the prevailing notion of diffusion driven transport of vacancies from the interior to outer surface being responsible for collapse, which would involve much longer time scales as compared to the plasticity-based mechanism. PMID:26977380

Molecular Dynamics at the Interface between Ice and Poly(vinyl alcohol) and Ice Recrystallization Inhibition.

PubMed

Weng, Lindong; Stott, Shannon L; Toner, Mehmet

2018-05-01

Ice formation is a ubiquitous process that poses serious challenges for many areas. Nature has evolved a variety of different mechanisms to regulate ice formation. For example, many cold-adapted species produce antifreeze proteins (AFPs) and/or antifreeze glycoproteins (AFGPs) to inhibit ice recrystallization. Although several synthetic substitutes for AF(G)Ps have been developed, the fundamental principles of designing AF(G)P mimics are still missing. In this study, we explored the molecular dynamics of ice recrystallization inhibition (IRI) by poly(vinyl alcohol) (PVA), a well-recognized ice recrystallization inhibitor, to shed light on the otherwise hidden ice-binding mechanisms of chain polymers. Our molecular dynamics simulations revealed a stereoscopic, geometrical match between the hydroxyl groups of PVA and the water molecules of ice, and provided microscopic evidence of the adsorption of PVA to both the basal and prism faces of ice and the incorporation of short-chain PVA into the ice lattice. The length of PVA, i.e., the number of hydroxyl groups, seems to be a key factor dictating the performance of IRI, as the PVA molecule must be large enough to prevent the joining together of adjacent curvatures in the ice front. The findings in this study will help pave the path for addressing a pressing challenge in designing synthetic ice recrystallization inhibitors rationally, by enriching our mechanistic understanding of IRI process by macromolecules.

Constitutive modeling and dynamic softening mechanism during hot deformation of an ultra-pure 17%Cr ferritic stainless steel stabilized with Nb

NASA Astrophysics Data System (ADS)

Gao, Fei; Liu, Zhenyu; Misra, R. D. K.; Liu, Haitao; Yu, Fuxiao

2014-09-01

The hot deformation behavior of an ultra-pure 17%Cr ferritic stainless steel was studied in the temperature range of 750-1000 °C and strain rates of 0.5 to 10 s-1 using isothermal hot compression tests in a thermomechanical simulator. The microstructural evolution was investigated using electron backscattered diffraction and transmission electron microscopy. A modified constitutive equation considering the effect of strain on material constant was developed, which predicted the flow stress for the deformation conditions studied, except at 950 °C in 1 s-1 and 900 °C in 10 s-1. Decreasing deformation temperature and increasing strain was beneficial in refining the microstructure. Decreasing deformation temperature, the in-grain shear bands appeared in the microstructure. It is suggested that the dynamic softening mechanism is closely related to deformation temperature. At low deformation temperature, dynamic recovery was major softening mechanism and no dynamic recrystallization occurred. At high deformation temperature, dynamic softening was explained in terms of efficient dynamic recovery and limited continuous dynamic recrystallization. A drop in the flow stress was not found due to very small fraction of new grains nucleated during dynamic recrystallization.

Ion-specific ice recrystallization provides a facile approach for the fabrication of porous materials

NASA Astrophysics Data System (ADS)

Wu, Shuwang; Zhu, Chongqin; He, Zhiyuan; Xue, Han; Fan, Qingrui; Song, Yanlin; Francisco, Joseph S.; Zeng, Xiao Cheng; Wang, Jianjun

2017-05-01

Ice recrystallization is of great importance to both fundamental research and practical applications, however understanding and controlling ice recrystallization processes remains challenging. Here, we report the discovery of an ion-specific effect on ice recrystallization. By simply changing the initial type and concentration of ions in an aqueous solution, the size of ice grains after recrystallization can be tuned from 27.4+/-4.1 to 277.5+/-30.9 μm. Molecular dynamics simulations show that the ability of the ion to be incorporated into the ice phase plays a key role in the ultimate size of the ice grains after recrystallization. Moreover, by using recrystallized ice crystals as templates, 2D and 3D porous networks with tuneable pore sizes could be prepared from various materials, for example, NaBr, collagen, quantum dots, silver and polystyrene colloids. These porous materials are suitable for a wide range of applications, for example, in organic electronics, catalysis and bioengineering.

Ion-specific ice recrystallization provides a facile approach for the fabrication of porous materials

PubMed Central

Wu, Shuwang; Zhu, Chongqin; He, Zhiyuan; Xue, Han; Fan, Qingrui; Song, Yanlin; Francisco, Joseph S.; Zeng, Xiao Cheng; Wang, Jianjun

2017-01-01

Ice recrystallization is of great importance to both fundamental research and practical applications, however understanding and controlling ice recrystallization processes remains challenging. Here, we report the discovery of an ion-specific effect on ice recrystallization. By simply changing the initial type and concentration of ions in an aqueous solution, the size of ice grains after recrystallization can be tuned from 27.4±4.1 to 277.5±30.9 μm. Molecular dynamics simulations show that the ability of the ion to be incorporated into the ice phase plays a key role in the ultimate size of the ice grains after recrystallization. Moreover, by using recrystallized ice crystals as templates, 2D and 3D porous networks with tuneable pore sizes could be prepared from various materials, for example, NaBr, collagen, quantum dots, silver and polystyrene colloids. These porous materials are suitable for a wide range of applications, for example, in organic electronics, catalysis and bioengineering. PMID:28462937

Ion-specific ice recrystallization provides a facile approach for the fabrication of porous materials.

PubMed

Wu, Shuwang; Zhu, Chongqin; He, Zhiyuan; Xue, Han; Fan, Qingrui; Song, Yanlin; Francisco, Joseph S; Zeng, Xiao Cheng; Wang, Jianjun

2017-05-02

Ice recrystallization is of great importance to both fundamental research and practical applications, however understanding and controlling ice recrystallization processes remains challenging. Here, we report the discovery of an ion-specific effect on ice recrystallization. By simply changing the initial type and concentration of ions in an aqueous solution, the size of ice grains after recrystallization can be tuned from 27.4±4.1 to 277.5±30.9 μm. Molecular dynamics simulations show that the ability of the ion to be incorporated into the ice phase plays a key role in the ultimate size of the ice grains after recrystallization. Moreover, by using recrystallized ice crystals as templates, 2D and 3D porous networks with tuneable pore sizes could be prepared from various materials, for example, NaBr, collagen, quantum dots, silver and polystyrene colloids. These porous materials are suitable for a wide range of applications, for example, in organic electronics, catalysis and bioengineering.

Refining the structural framework of the Khimti Khola region, east-central Nepal Himalaya, using quartz textures and c-axis fabrics

NASA Astrophysics Data System (ADS)

Larson, Kyle P.

2018-02-01

New quartz texture and c-axis fabric data from across the Paleoproterozoic Ulleri-Phaplu-Melung orthogneiss in the Khimti Khola region of east central Nepal provide new constraints on the internal structural framework of the Himalaya that help shed light on the convergence accommodation processes active in the upper portion of the crust during orogenesis. These data outline a strain history that varies across the unit. Deformation near the base of the unit occurred at ∼605 (±50) °C with evidence of significant static recrystallization and recovery preserved in quartz, whereas deformation near the top of the unit occurred at ∼540 (±50) ˚C with quartz characterized by dynamic recrystallization mechanisms. The strength of the quartz c-axis fabrics follows a similar spatial pattern, with those from near the top of the unit recording stronger fabrics than those measured from lower in the unit. Together, these data are interpreted to indicate strain localization, possibly at progressively lower temperature, near the top of the Ulleri-Phaplu-Melung orthogneiss. This interpretation is consistent with cooling ages that indicate the upper boundary of the unit coincides with an out-of-sequence shear zone. This study not only provides a structural characterization of the shear zone, helping to refine the kinematic framework of this portion of the Himalaya, but also confirms the utility of fabric strength analysis in deciphering strain localization within pervasively deformed rocks.

The Effect of Welding Energy on the Microstructural and Mechanical Properties of Ultrasonic-Welded Copper Joints

PubMed Central

Yang, Jingwei; Cao, Biao; Lu, Qinghua

2017-01-01

The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld interfaces was observed and had an ultra-fine grain structure. With an increase in welding energy, the weld interface progressively changed from flat to sinusoidal, and eventually turned into a convoluted wavy pattern, bearing similarities to shear instabilities, as observed in fluid dynamics. The lap shear load of the joints initially increased and then remained stable as the welding energy increased. The tensile characteristics of the joints significantly depended on the development of plastic deformation at the interface. The influence of the microstructure on the hardness was also discussed. PMID:28772553

The Effect of Welding Energy on the Microstructural and Mechanical Properties of Ultrasonic-Welded Copper Joints.

PubMed

Yang, Jingwei; Cao, Biao; Lu, Qinghua

2017-02-16

The effects of welding energy on the mechanical and microstructural characteristics of ultrasonic-welded pure copper plates were investigated. Complex dynamic recrystallization and grain growth occurred inside the weld zone during ultrasonic welding. At a low welding energy, a thin band of straight weld interfaces was observed and had an ultra-fine grain structure. With an increase in welding energy, the weld interface progressively changed from flat to sinusoidal, and eventually turned into a convoluted wavy pattern, bearing similarities to shear instabilities, as observed in fluid dynamics. The lap shear load of the joints initially increased and then remained stable as the welding energy increased. The tensile characteristics of the joints significantly depended on the development of plastic deformation at the interface. The influence of the microstructure on the hardness was also discussed.

Crystal defects in solar cells produced by the method of thermomigration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lozovskii, V. N.; Lomov, A. A.; Lunin, L. S.

2017-03-15

The results of studying the crystal structure of regions in silicon, recrystallized during the course of thermomigration of the liquid Si–Al zone in the volume of the silicon substrate, are reported (similar regions doped with an acceptor impurity are used to obtain high-voltage solar cells). X-ray methods (including measurements of both diffraction-reflection curves and topograms) and also high-resolution electron microscopy indicate that single-crystal regions in the form of a series of thin strips or rectangular grids are formed as a result of the thermomigration of liquid zones. Dislocation half-loops are detected in the surface layers of the front and backmore » surfaces of the substrate. (311)-type defects are observed in the recrystallized regions.« less

Ferrite grain refinement in low carbon Cu–P–Cr–Ni–Mo weathering steel at various temperatures in the (α + γ) region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Chunling, E-mail: zhangchl@ysu.edu.cn; School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300401; Zhang, Mengmeng

2016-03-15

Self-designed Cu–P–Cr–Ni–Mo weathering steel was subjected to compression test to determine the mechanism of ferrite grain refinement from 750 °C to 925 °C. Optical microscopic images showed that ferrite grain size declined, whereas the ferrite volume fraction increased with increasing compression temperature. Electron backscatter diffraction patterns revealed that several low-angle boundaries shifted to high-angle boundaries, thereby generating fine ferrite grains surrounded by high-angle boundaries. Numerous low-angle boundaries were observed within ferrite grains at 750 °C, which indicated the existence of pre-eutectoid ferrite. Results showed that ferrite grain refinement could be due to continuous dynamic recrystallization at 750 °C and 775more » °C, and deformation-induced ferrite transformation could be the main mechanism at 800 °C and 850 °C. Fine equiaxed ferrite grains with size ranging from 1.77 μm to 2.69 μm were produced in the (α + γ) dual-phase region. - Graphical abstract: There is a close relationship between the microstructure evolution and flow curves during deformation. Fine equiaxed ferrite grains with size ranging from 1.77 μm to 2.69 μm were achieved in the (α + γ) dual-phase region. Ferrite grain refinement could be due to continuous dynamic recrystallization at 750 °C and 775 °C, and deformation-induced ferrite transformation at 800 °C and 850 °C. The occurrence of deformation-induced ferrite transformation and continuous dynamic recrystallization can be monitored by analysis of flow curves and microstructures. Deformation-induced ferrite transformation leads to the dynamic softening in flow curve when temperature just below A{sub r3}, while the dynamic softening in flow curve is ferrite continuous dynamic recrystallization (Special Fig. 5b). - Highlights: • Compression deformation was operated at temperatures from 750 °C to 925 °C at a strain rate of 0.1 s–1, and a strain of 1.2. • Fine equiaxed ferrite grains of ~1.77–2.19 μm were obtained at 750 °C and 775 °C via continuous dynamic recrystallization. • Ferrite grain size of ~2.31–2.69 μm at 800 °C and 850 °C can be obtained by deformation-induced ferrite transformation. • With decreasing deformation temperature the average grain size of ferrite decreased while volume fraction increased. • Ferrite refinement was from deformation-induced ferrite to continuous dynamic recrystallization as temperature reduced.« less

Evaluation of Microstructure, Mechanical Properties and Corrosion Resistance of Friction Stir-Welded Aluminum and Magnesium Dissimilar Alloys

NASA Astrophysics Data System (ADS)

Verma, Jagesvar; Taiwade, Ravindra V.; Sapate, Sanjay G.; Patil, Awanikumar P.; Dhoble, Ashwinkumar S.

2017-10-01

Microstructure, mechanical properties and corrosion resistance of dissimilar friction stir-welded aluminum and magnesium alloys were investigated by applying three different rotational speeds at two different travel speeds. Sound joints were obtained in all the conditions. The microstructure was examined by an optical and scanning electron microscope, whereas localized chemical information was studied by energy-dispersive spectroscopy. Stir zone microstructure showed mixed bands of Al and Mg with coarse and fine equiaxed grains. Grain size of stir zone reduced compared to base metals, indicated by dynamic recrystallization. More Al patches were observed in the stir zone as rotational speed increased. X-ray diffraction showed the presence of intermetallics in the stir zone. Higher tensile strength and hardness were obtained at a high rotational speed corresponding to low travel speed. Tensile fractured surface indicated brittle nature of joints. Dissimilar friction stir weld joints showed different behaviors in different corrosive environments, and better corrosion resistance was observed at a high rotational speed corresponding to low travel speed (FW3) in a sulfuric and chloride environments. Increasing travel speed did not significantly affect on microstructure, mechanical properties and corrosion resistance as much as the rotational speed.

Prediction of the Grain-Microstructure Evolution Within a Friction Stir Welding (FSW) Joint via the Use of the Monte Carlo Simulation Method

NASA Astrophysics Data System (ADS)

Grujicic, M.; Ramaswami, S.; Snipes, J. S.; Avuthu, V.; Galgalikar, R.; Zhang, Z.

2015-09-01

A thermo-mechanical finite element analysis of the friction stir welding (FSW) process is carried out and the evolution of the material state (e.g., temperature, the extent of plastic deformation, etc.) monitored. Subsequently, the finite-element results are used as input to a Monte-Carlo simulation algorithm in order to predict the evolution of the grain microstructure within different weld zones, during the FSW process and the subsequent cooling of the material within the weld to room temperature. To help delineate different weld zones, (a) temperature and deformation fields during the welding process, and during the subsequent cooling, are monitored; and (b) competition between the grain growth (driven by the reduction in the total grain-boundary surface area) and dynamic-recrystallization grain refinement (driven by the replacement of highly deformed material with an effectively "dislocation-free" material) is simulated. The results obtained clearly revealed that different weld zones form as a result of different outcomes of the competition between the grain growth and grain refinement processes.

Crystallographic control and texture inheritance during mylonitization of coarse grained quartz veins

NASA Astrophysics Data System (ADS)

Ceccato, Alberto; Pennacchioni, Giorgio; Menegon, Luca; Bestmann, Michel

2017-10-01

Quartz veins within Rieserferner pluton underwent deformation during post-magmatic cooling at temperature around 450 °C. Different crystallographic orientations of cm-sized quartz vein crystals conditioned the evolution of microstructures and crystallographic preferred orientations (CPO) during vein-parallel simple shear up to high shear strains (γ ≈ 10). For γ < 2, crystals stretched to ribbons of variable aspect ratios. The highest aspect ratios resulted from {m} glide in ribbons with c-axis sub-parallel to the shear zone vorticity Y-axis. Ribbons with c-axis orthogonal to Y (XZ-type ribbons) were stronger and hardened more quickly: they show lower aspect ratios and fine (grain size 10-20 μm) recrystallization along sets of microshear zones (μSZs) exploiting crystallographic planes. Distortion of XZ-type ribbons and recrystallization preferentially exploited the slip systems with misorientation axis close to Y. New grains of μSZs initiated by subgrain rotation recrystallization (SGR) and thereupon achieved high angle misorientations by a concurrent process of heterogeneous rigid grain rotation around Y associated with the confined shear within the μSZ. Dauphiné twinning occurred pervasively, but did not play a dominant role on μSZ nucleation. Recrystallization became widespread at γ > 2 and pervasive at γ ≈ 10. Ultramylonitic quartz veins are fine grained ( 10 μm, similar to new grains of μSZ) and show a CPO banding resulting in a bulk c-axis CPO with a Y-maximum, as part of a single girdle about orthogonal to the foliation, and orientations at the pole figure periphery at moderate to high angle to the foliation. This bulk CPO derives from steady-state SGR associated with preferential activity, in the different CPO bands, of slip systems generating subgrain boundaries with misorientation axes close to Y. The CPO of individual recrystallized bands is largely inherited from the original crystallographic orientation of the ribbons (and therefore vein crystals) from which they derived. High strain and pervasive recrystallization were not enough to reset the initial crystallographic heterogeneity and this CPO memory is explained by the dominance of SGR. This contrast with experimental observation of a rapid erasure of a pristine CPO by cannibalism from grains with the most favourably oriented slip system under dominant grain boundary migration recrystallization.

Effects of V addition on recrystallization resistance of 7150 aluminum alloy after simulative hot deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lai, Jing; Shi, Cangji; Chen, X.-Grant, E-mail: xgrant_chen@uqac.ca

2014-10-15

The effects of different V contents (0.01 to 0.19 wt.%) on the recrystallization resistance of 7150 aluminum alloys during post-deformation heat treatment were investigated. The microstructural evolutions at as-cast, as-homogenized conditions and after post-deformation annealing were studied using optical, scanning electron and transmission electron microscopes and using the electron backscattered diffraction technique. The precipitation of Al{sub 21}V{sub 2} dispersoids was observed in alloys containing 0.11 to 0.19 wt.% V after homogenization. The dispersoids were mainly distributed in the dendrite cells, and the precipitate-free zones occurred in the interdendritic regions and near grain boundaries. V addition could significantly enhance the recrystallizationmore » resistance during post-deformation annealing, particularly in the presence of a great number of Al{sub 21}V{sub 2} dispersoids. Recrystallized grain growth was effectively restricted because of the dispersoid pinning effect. The alloy containing 0.15 wt.% V exhibited the highest recrystallization resistance amongst all V-containing alloys studied. - Highlights: • Investigated the effect of V level on microstructure and flow stress of 7150 alloys • Characterized microstructures using optical microscopy, SEM, TEM and EBSD • Described the precipitation behavior of V-dispersoids in the dendritic structure • Studied the V effect on recrystallization resistance during post heat treatment • V addition greatly enhanced the recrystallization resistance during annealing.« less

Greenschist-Facies Pseudotachylytes and Gouge: a Microstructural Study of the Deformation Propagation at the Boundary Between Hp-Metabasite and Calcite Bearing Metasediments

NASA Astrophysics Data System (ADS)

Crispini, L.; Scambelluri, M.; Capponi, G.

2013-12-01

Recent friction experiments on calcite-bearing systems reproduce pseudotachylyte structures, that are diagnostic of dinamic calcite recrystallization related to seismic slip in the shallow crust. Here we provide the study of a pseudotachylyte (PT) bearing low angle oblique-slip fault. The fault is linked to the exhumation of Alpine HP-ophiolites and it is syn- to post-metamorphic with respect to retrograde greenschist facies metamorphism. The observed microstructures developed at the brittle-ductile transition and suggest that seismic and interseismic slip was enhanced by interaction with fluids. The fault zone is in-between high-pressure eclogite-facies metabasites (hangingwall) and calcite bearing metasediments (footwall). The mafic rocks largely consist of upper greenschist facies hornblende, albite, chlorite, epidote with relict eclogitic garnet, Na-pyroxene and rutile; metasediments correspond to calcschist and micaschist with quartz, phengite, zoisite, chlorite, calcite and relics of garnet. Key features of the oucrop are: the thickness and geometry of the PT and gouge; the multiple production of PT characterized by overprinting plastic and brittle deformation; the occurrence in footwall metasediments of mm-thick bands of finely recrystallized calcite coeval with PT development in the hangingwall. The damage zone is ca. 2 m-thick and is characterized by two black, ultra-finegrained straight and sharp Principal Slip Zones (PSZ) marked by PT. The damage zone shows a variety of fault rocks (cataclasite and ultracataclasite, gouge and PT) with multiple crosscutting relationships. Within the two main PSZ, PT occurs in 10-20 cm thick layer, in small scale injection veins and in microfractures. In the mafic hanging wall, the PT is recrystallized and does not preserve glass: it shows flow structures with subrounded, embayed and rebsorbed quartz in a fine grained matrix composed of isotropic albite + chlorite + quartz + epidote + titanite, suggesting recrystallization at ca. 270-300°C, 8-10 km of the original glass. PT show plastic deformations overprinted by shear bands and fracturing. The matrix of cataclastic layers has the same mineral assemblage as PT and clasts of recrystallised PT, to indicate polyphase PSZ formation. In the metasedimentary footwall, the original foliation is deflected parallel to the PSZ and is cut by cm-spaced shear bands parallel to PSZ. Deformation propagates in the footwall through mm-thick injections veins, shear bans, P-shears and veins. Pockets of recrystallized PT occur along the pre-existing mylonitic foliation of metasediments. Worthnote is the presence of mm-thick deformation bands (CDB) that are post-mylonitic foliation and mainly composed of fine grained calcite bounded by dissolution seams or ribbon grains of deformed calcite. CDB are characterised by subrounded embayed and rebsorbed quartz grains rimmed by new Ca-Mg amphibole, K-feldspar (90-93%K), in a dinamic recrystallized calcite 2-10 micron in size and slightly elongated. The features of the CDB suggest that these structures can be considered as diagnostic of localised deformation during coesismic slip in metasedimentary rocks.

Rapid Grain Size Reduction in the Upper Mantle at a Plate Boundary

NASA Astrophysics Data System (ADS)

Kidder, S. B.; Scott, J.; Prior, D. J.; Lubicich, E. J.

2017-12-01

A few spinel peridotite xenoliths found near the Alpine Fault, New Zealand, exhibit a mylonitic texture and, locally, an extremely fine 30 micron grain size. The harzburgite xenoliths were emplaced in a 200 km-long elongate dike zone interpreted as a gigantic tension fracture or Reidel shear associated with Alpine Fault initiation 25 Ma. The presence of thin ( 1 mm) ultramylonite zones with px-ol phase mixing and fine grain sizes, minimal crustal-scale strain associated with the dike swarm, and the absence of mylonites at four of the five xenolith localities associated with the dike swarm indicate that upper mantle deformation was highly localized. Strings of small, recrystallized grains (planes in 3D) are found in the interiors of olivine porphyroclasts. In some cases, bands 1-2 grains thick are traced from the edges of olivine grains and terminate in their interiors. Thicker zones of recrystallized grains are also observed crossing olivine porphyroclasts without apparent offset of the unrecrystallized remnants of the porphyroclasts. We suggest a brittle-plastic origin for these features since the traditional recrystallization mechanisms associated with dislocation creep require much more strain than occurred within these porphyroclasts. Analogous microstructures in quartz and feldspar in mid-crust deformation zones are attributed to brittle-plastic processes. We hypothesize that such fine-grained zones were the precursors of the observed, higher-strain ultramylonite zones. Given the size of the new grains preserved in the porphyroclasts ( 100 micron) and a moho temperature > 650°C, grain growth calculations indicate that the observed brittle-plastic deformation occurred <10,000 yrs. prior to eruption. It is likely then that either brittle-plastic deformation was coeval with the ductile shearing occurring in the ultramylonite bands, or possibly, if deformation can be separated into brittle-plastic (early) and ductile (later) phases, that the entire localization process was very rapid (<10,000 yrs). In either case we interpret that semi-brittle deformation was a key process responsible for rapid localization in this initiating plate-scale mantle shear zone.

Glass-Transition Temperature of the β-Relaxation as the Major Predictive Parameter for Recrystallization of Neat Amorphous Drugs.

PubMed

Kissi, Eric Ofosu; Grohganz, Holger; Löbmann, Korbinian; Ruggiero, Michael T; Zeitler, J Axel; Rades, Thomas

2018-03-15

Recrystallization of amorphous drugs is currently limiting the simple approach to improve solubility and bioavailability of poorly water-soluble drugs by amorphization of a crystalline form of the drug. In view of this, molecular mobility, α-relaxation and β-relaxation processes with the associated transition temperatures T gα and T gβ , was investigated using dynamic mechanical analysis (DMA). The correlation between the transition temperatures and the onset of recrystallization for nine amorphous drugs, stored under dry conditions at a temperature of 296 K, was determined. From the results obtained, T gα does not correlate with the onset of recrystallization under the experimental storage conditions. However, a clear correlation between T gβ and the onset of recrystallization was observed. It is shown that at storage temperature below T gβ , amorphous nifedipine retains its amorphous form. On the basis of the correlation, an empirical correlation is proposed for predicting the onset of recrystallization for drugs stored at 0% RH and 296 K.

TEM observations of radiation damage in tungsten irradiated by 20 MeV W ions

NASA Astrophysics Data System (ADS)

Ciupiński, Ł.; Ogorodnikova, O. V.; Płociński, T.; Andrzejczuk, M.; Rasiński, M.; Mayer, M.; Kurzydłowski, K. J.

2013-12-01

Polycrystalline, recrystallized W targets were subjected to implantation with 20 MeV W6+ ions in order to simulate radiation damage caused by fusion neutrons. Three samples with cumulative damage of 0.01, 0.1 and 0.89 dpa were produced. The near-surface zone of each sample has been analyzed by transmission electron microscopy (TEM). To this end, lamellae oriented perpendicularly to the targets implanted surface were milled out using focused ion beam (FIB). A reference lamella from non-irradiated, recrystallized W target was also prepared to estimate the damage introduced during FIB processing. TEM studies revealed a complex microstructure of the damaged zones as well as its evolution with cumulative damage level. The experimentally observed damage depth agrees very well with the one calculated using the Stopping and Range of Ions in Matter (SRIM) software.

Analysing the strength of friction stir welded dissimilar aluminium alloys using Sugeno Fuzzy model

NASA Astrophysics Data System (ADS)

Barath, V. R.; Vaira Vignesh, R.; Padmanaban, R.

2018-02-01

Friction stir welding (FSW) is a promising solid state joining technique for aluminium alloys. In this study, FSW trials were conducted on two dissimilar plates of aluminium alloy AA2024 and AA7075 by varying the tool rotation speed (TRS) and welding speed (WS). Tensile strength (TS) of the joints were measured and a Sugeno - Fuzzy model was developed to interconnect the FSW process parameters with the tensile strength. From the developed model, it was observed that the optimum heat generation at WS of 15 mm.min-1 and TRS of 1050 rpm resulted in dynamic recovery and dynamic recrystallization of the material. This refined the grains in the FSW zone and resulted in peak tensile strength among the tested specimens. Crest parabolic trend was observed in tensile strength with variation of TRS from 900 rpm to 1200 rpm and TTS from 10 mm.min-1 to 20 mm.min-1.

Hydride reorientation and its impact on ambient temperature mechanical properties of high burn-up irradiated and unirradiated recrystallized Zircaloy-2 nuclear fuel cladding with an inner liner

NASA Astrophysics Data System (ADS)

Auzoux, Q.; Bouffioux, P.; Machiels, A.; Yagnik, S.; Bourdiliau, B.; Mallet, C.; Mozzani, N.; Colas, K.

2017-10-01

Precipitation of radial hydrides in zirconium-based alloy cladding concomitant with the cooling of spent nuclear fuel during dry storage can potentially compromise cladding integrity during its subsequent handling and transportation. This paper investigates hydride reorientation and its impact on ductility in unirradiated and irradiated recrystallized Zircaloy-2 cladding with an inner liner (cladding for boiling water reactors) subjected to hydride reorientation treatments. Cooling from 400 °C, hydride reorientation occurs in recrystallized Zircaloy-2 with liner at a lower effective stress in irradiated samples (below 40 MPa) than in unirradiated specimens (between 40 and 80 MPa). Despite significant hydride reorientation, unirradiated recrystallized Zircaloy-2 with liner cladding containing ∼200 wppm hydrogen shows a high diametral strain at fracture (>15%) during burst tests at ambient temperature. This ductile behavior is due to (1) the lower yield stress of the recrystallized cladding materials in comparison to hydride fracture strength (corrected by the compression stress arising from the precipitation) and (2) the hydride or hydrogen-depleted zone as a result of segregation of hydrogen into the liner layer. In irradiated Zircaloy-2 with liner cladding containing ∼340 wppm hydrogen, the conservation of some ductility during ring tensile tests at ambient temperature after reorientation treatment at 400 °C with cooling rates of ∼60 °C/h is also attributed to the existence of a hydride-depleted zone. Treatments at lower cooling rates (∼6 °C/h and 0.6 °C/h) promote greater levels of hydrogen segregation into the liner and allow for increased irradiation defect annealing, both of which result in a significant increase in ductility. Based on this investigation, given the very low cooling rates typical of dry storage systems, it can be concluded that the thermal transients associated with dry storage should not degrade, and more likely should actually improve, ductility of recrystallized Zircaloy-2 cladding with inner liner with such hydrogen content.

Heterogeneous brittle-ductile deformation at shallow crustal levels under high thermal conditions: The case of a synkinematic contact aureole in the inner northern Apennines, southeastern Elba Island, Italy

NASA Astrophysics Data System (ADS)

Papeschi, Samuele; Musumeci, Giovanni; Mazzarini, Francesco

2017-10-01

We present an example of interaction between magmatism and tectonics at shallow crustal levels. In the Late Miocene the metamorphic units of the eastern Elba Island (northern Apennines) were intruded at very shallow crustal levels by a large pluton (> 60 km2) with the development of an hectometre-sized contact aureole defined by growth of low-pressure/high-temperature mineral assemblages (Pmax < 0.2 GPa, Tmax 650 °C). Structural data show that the contact aureole is associated with a km-sized antiform of the foliation and by several metre- to decametre-thick high-strain domains consisting of strongly foliated rocks containing synkinematic HT/LP mineral assemblages and ductile shear zones of variable thickness. These shear zones are characterized by a mylonitic foliation variably overprinted by cataclasis. Quartz microfabrics indicate that the dynamic crystallization processes progressively changed from grain boundary migration, associated with the thermal peak of contact metamorphism, to subgrain rotation and bulging recrystallization, the latter mostly associated with the cataclastic overprint. These transitions of recrystallization mechanisms in quartz are related to a progressive decrease of temperature during deformation. Deformation accompanied the development and cooling of the contact aureole, which recorded the switch from high temperature ductile to low temperature brittle conditions. The geometry of the studied deformation structures is consistent with the constraints of the regional tectonic evolution and its local interaction with the localized and transient thermal anomaly related to the coeval emplacement of igneous rocks.

Evolution of a calcite marble shear zone complex on Thassos Island, Greece: microstructural and textural fabrics and their kinematic significance

NASA Astrophysics Data System (ADS)

Bestmann, Michel; Kunze, Karsten; Matthews, Alan

2000-11-01

The deformation history of a monophase calcite marble shear zone complex on Thassos Island, Northern Greece, is reconstructed by detailed geometric studies of the textural and microstructural patterns relative to a fixed reference system (shear zone boundary, SZB). Strain localization within the massive marble complex is linked to decreasing P- T conditions during the exhumation process of the metamorphic core complex. Solvus thermometry indicates that temperatures of 300-350°C prevailed during part of the shear zone deformation history. The coarse-grained marble protolith outside the shear zone is characterized by symmetrically oriented twin sets due to early coaxial deformation. A component of heterogeneous non-coaxial deformation is first recorded within the adjacent protomylonite. Enhanced strain weakening by dynamic recrystallization promoted strong localization of plastic deformation in the ultramylonite of the calcite shear zone, where high strain was accommodated by non-coaxial flow. This study demonstrates that both a pure shear and a simple shear strain path can result in similar crystallographic preferred orientations (single c-axis maximum perpendicular to the SZB) by different dominant deformation mechanisms. Separated a-axis pole figures (+ a- and - a-axis) show different density distributions with orthorhombic texture symmetry in the protolith marble and monoclinic symmetry in the ultramylonite marble consistently with the observed grain fabric symmetry.

A New Cellular Automaton Method Coupled with a Rate-dependent (CARD) Model for Predicting Dynamic Recrystallization Behavior

NASA Astrophysics Data System (ADS)

Azarbarmas, M.; Aghaie-Khafri, M.

2018-03-01

A comprehensive cellular automaton (CA) model should be coupled with a rate-dependent (RD) model for analyzing the RD deformation of alloys at high temperatures. In the present study, a new CA technique coupled with an RD model—namely, CARD—was developed. The proposed CARD model was used to simulate the dynamic recrystallization phenomenon during the hot deformation of the Inconel 718 superalloy. This model is capable of calculating the mean grain size and volume fraction of dynamic recrystallized grains, and estimating the phenomenological flow behavior of the material. In the presented model, an actual orientation definition comprising three Euler angles was used by implementing the electron backscatter diffraction data. For calculating the lattice rotation of grains, it was assumed that all slip systems of grains are active during the high-temperature deformation because of the intrinsic rate dependency of the procedure. Moreover, the morphological changes in grains were obtained using a topological module.

Effect of Mo on dynamic recrystallization and microstructure development of microalloyed steels

NASA Astrophysics Data System (ADS)

Schambron, Thomas; Dehghan-Manshadi, Ali; Chen, Liang; Gooch, Taliah; Killmore, Chris; Pereloma, Elena

2017-07-01

The dynamic recrystallization (DRX) behaviour, mechanical properties and microstructure development of four low carbon, Nb-Ti-containing micro-alloyed steels with Mo contents from 0 to 0.27 wt% were studied. Plane strain compression tests were performed in a Gleeble 3500 thermomechanical simulator. The effects of composition, deformation temperature and strain rate on the DRX parameters and resultant microstructures were examined. The volume fraction of recrystallised grains was estimated from micrographs and a DRX model. The stress-strain curves showed the typical signs of DRX over a wide range of deformation conditions. Dynamic recovery was only observed for higher strain rates (5 s-1) and/or lower deformation temperatures (below 1000 °C). It was shown that Mo increases the hot strength by around 100 MPa per weight percent. In addition, it has an effect on retarding recrystallization in microalloyed steels by increasing the activation energy for DRX by 320 kJ/molK per weight percent. This was attributed to solute drag and the interaction with other microalloying elements.

Constitutive relations for determining the critical conditions for dynamic recrystallization behavior

NASA Astrophysics Data System (ADS)

Choe, J. I.

2016-04-01

A series mathematical model has been developed for the prediction of flow stress and microstructure evolution during the hot deformation of metals such as copper or austenitic steels with low stacking fault energies, involving features of both diffusional flow and dislocation motion. As the strain rate increases, multiple peaks on the stress-strain curve decrease. At a high strain rate, the stress rises to a single peak, while dynamic recrystallization causes an oscillatory behavior. At a low strain rate (when there is sufficient time for the recrystallizing grains to grow before they become saturated with high dislocation density with an increase in strain rate), the difference in stored stress between recrystallizing and old grains diminishes, resulting in reduced driving force for grain growth and rendering smaller grains in the alloy. The final average grain size at the steady stage (large strain) increases with a decrease in the strain rate. During large strain deformation, grain size reduction accompanying dislocation creep might be balanced by the grain growth at the border delimiting the ranges of realization (field boundary) of the dislocation-creep and diffusion-creep mechanisms.

Varying rock responses as an indicator of changes in CO2-H2O fluid composition

NASA Technical Reports Server (NTRS)

Friend, C. R. L.

1986-01-01

The formation of the late Archean charnockite zone of southern India was ascribed to dehydration recrystallization due to an influx of CO2. Pressure temperature conditions for the metamorphism were calculated at about 750 C and 7.5 Kbar. The composition of the volatile species presently contained in fluid inclusions in the rocks changes across the transition zone. The transition zone was studied at Kabbaldurga and the paths taken by the fluids were identified.

Deformation Mechanisms of Darreh Sary Metapelites, Sanandaj‒Sirjan Zone, Iran

NASA Astrophysics Data System (ADS)

Hemmati, O.; Tabatabaei Manesh, S. M.; Nadimi, A. R.

2018-03-01

The Darreh Sary metapelitic rocks are located in the northeast of Zagros orogenic belt and Sanandaj-Sirjan structural zone. The lithological composition of these rocks includes slate, phyllite, muscovitebiotite schist, garnet schist, staurolite-garnet schist and staurolite schist. The shale is the protolith of these metamorphic rocks, which was originated from the continental island arc tectonic setting and has been subjected to processes of Zagros orogeny. The deformation mechanisms in these rocks include bulging recrystallization (BLG), subgrain rotation recrystallization (SGR) and grain boundary migration recrystallization (GBM), which are considered as the key to estimate the deformation temperature of the rocks. The estimated ranges of deformation temperature and depth in these rocks show the temperatures of 275-375, 375-500, and >500°C and the depths of 10 to 17 km. The observed structures in these rocks such as faults, fractures and folds, often with the NW-SE direction coordinate with the structural trends of Zagros orogenic belt structures. The S-C mylonite fabrics is observed in these rocks with other microstructures such as mica fish, σ fabric and garnet deformation indicate the dextral shear deformation movements of study area. Based on the obtained results of this research, the stages of tectonic evolution of Darreh Sary area were developed.

The Influence of Grain Boundary Fluids on the Recrystallization Behavior in Calcite: A Comparison of "dry" and "wet" Marble Mylonites

NASA Astrophysics Data System (ADS)

Schenk, O.; Urai, J.; Evans, B.

2003-12-01

Carbonate rocks are able to accumulate large amounts of strain and deform crystal-plastically even at low p-T conditions and thus, marble sequences are often the site of strain localization in the upper crust during late-stage deformation in mountain building processes. In this study we sought to identify the effect of fluids on grain boundary morphology and recrystallization processes in marble mylonites during shear zone evolution, as fluids play a major role in the flow behavior of many rock materials during deformation (e.g. quartz, olivine, halite, feldspar). We compared calcite marble mylonites from two geological settings: (a) Schneeberg Complex, Southern Tyrole, Italy and (b) Naxos Metamorphic Core Complex, Greece. The shear zones of the selected areas are suitable for comparison, because they consist of similar lithology and the marble mylonites resemble each other in chemical composition. In addition, calcite-dolomite solvus geothermometry and TEM observations indicate similar p-T conditions for the shear zones formation. However, the two settings are different in the availability of fluids during the shear zone evolution: In the Schneeberg mylonites, both the alteration of minerals during retrograde metamorphism of neighboring micaschists and the existence of veins suggest that fluids were present during mylonitization. The absence of these features in the Naxos samples indicates that fluids were not present during deformation of these mylonites. This difference is also supported by the signature of stable isotopes. Microstructural investigations using optical and scanning electron microscopes on broken and planar surfaces did not indicate major differences between wet and dry mylonites: Grain boundaries of both types of samples display pores with shapes controlled by crystallography, and pore morphologies that are similar to observations from crack and grain-boundary healing experiments. Grain size reduction was predominantly the result of subgrain rotation recrystallization. However, the coarse grains inside the wet protomylonites (Schneeberg) are characterized by intracrystalline shear zones. With the exception of the intracrystalline shear zones, there were no obvious microstructural signatures that were obvious indicators of the presence of fluids, at least for these two field examples.

Metamorphic reactions, grain size reduction and deformation of mafic lower crustal rocks

NASA Astrophysics Data System (ADS)

Degli Alessandrini, Giulia; Menegon, Luca; Beltrando, Marco; Dijkstra, Arjan; Anderson, Mark

2016-04-01

This study investigates grain-scale deformation mechanisms associated with strain localization in the mafic continental lower crust, with particular focus on the role of syn-kinematic metamorphic reactions and their product - symplectites - in promoting grain size reduction and phase mixing. The investigated shear zone is hosted in the Finero mafic-ultramafic complex in the Italian Southern Alps. Shearing occurred at T ≥ 650° C and P ≥ 0.4-0.6 GPa. The shear zone reworks both mafic and ultramafic lithologies and displays anastomosing patterns of (ultra)mylonitic high strain zones wrapping less foliated, weakly deformed low strain domains. Field and microstructural observations indicate that different compositional layers of the shear zone responded differently to deformation, resulting in strain partitioning. Four distinct microstructural domains have been identified: (1) an ultramylonitic domain characterized by an amph + pl matrix (grain size < 30μm) with large amphibole porphyroclasts (grain size between 200μm and 5000μm) and rare garnets; (2) a domain rich in garnet porphyroclasts embedded in a matrix of monomineralic plagioclase displaying a core and mantle structure (average grain size 45μm) (3) a metagabbroic domain with porphyroclasts of clinopyroxene, orthopyroxene and garnets (200μm average grain size) wrapped by monomineralic ribbons of recrystallized plagioclase and (4) a garnet-free ultramylonitic domain composed of an intermixed amph + cpx + opx + pl matrix (6μm average grain size). In these domains, each porphyroclastic mineral responds differently to deformation: amphibole readily breaks down to symplectitic intergrowths of amph + pl or opx + pl. Garnet undergoes fracturing (in domain 2) or reacts to give symplectites of pl + opx (in domain 3). Plagioclase dynamically recrystallizes in mono-phase aggregates, whereas clinopyroxene undergoes fracturing and orthopyroxene undergoes plastic deformation. The behaviour of the different phases and their relative abundance in the layers are believed to influence the deformation of the layers themselves. In symplectite-rich layers (domains 1, 4) deformation is localised, grain-size is below 30μm and phases are well mixed. On the other hand, in pyroxene or plagioclase-rich layers, deformation is less localised, the phases are less mixed and the grain size is larger (domain 2, 3). These preliminary results suggest that syn-kinematic metamorphic reactions forming symplectites played an essential role in grain size reduction, phase mixing and strain localization. We speculate that the compositional domains with symplectites localized deformation more efficiently, by activation of grain size sensitive creep, most likely because those domains were originally more hydrated than the others. On the contrary, domains without symplectites accommodated deformation less efficiently, either through fracturing (clinopyroxene, garnet) or dislocation creep + recrystallization (orthopyroxene, plagioclase).

Progressive softening of brittle-ductile transition due to interplay between chemical and deformation processes

NASA Astrophysics Data System (ADS)

Jeřábek, Petr; Bukovská, Zita; Morales, Luiz F. G.

2017-04-01

The micro-scale shear zones (shear bands) in granitoids from the South Armorican Shear Zone reflect localization of deformation and progressive weakening in the conditions of brittle-ductile transition. We studied microstructures in the shear bands with the aim to establish their P-T conditions and to derive stress and strain rates for specific deformation mechanisms. The evolving microstructure within shear bands documents switches in deformation mechanisms related to positive feedbacks between deformation and chemical processes and imposes mechanical constraints on the evolution of the brittle-ductile transition in the continental transform fault domains. The metamorphic mineral assemblage present in the shear bands indicate their formation at 300-350 ˚ C and 100-400 MPa. Focusing on the early development of shear bands, we identified three stages of shear band evolution. The early stage I associated with initiation of shear bands occurs via formation of microcracks with possible yielding differential stress of up to 250 MPa (Diamond and Tarantola, 2015). Stage II is associated with subgrain rotation recrystallization and dislocation creep in quartz and coeval dissolution-precipitation creep of microcline. Recrystallized quartz grains in shear bands show continual increase in size, and decrease in stress and strain rates from 94 MPa to 17-26 MPa (Stipp and Tullis, 2003) and 3.8*10-12 s-1- 1.8*10-14 s-1 (Patterson and Luan, 1990) associated with deformation partitioning into weaker microcline layer and shear band widening. The quartz mechanical data allowed us to set some constrains for coeval dissolution-precipitation of microcline which at our estimated P-T conditions suggests creep at 17-26 MPa differential stress and 3.8*10-13 s-1 strain rate. Stage III is characterized by localized slip along interconnected white mica bands accommodated by dislocation creep at strain rate 3.8*10-12 s-1 and stress 9.36 MPa (Mares and Kronenberg, 1993). The studied example documents a competition between shear zone widening and narrowing mechanisms, i.e. distributed and localized deformation, depending on the specific mineral phase and deformation mechanism active in each moment of the shear zone evolution. In addition, our mechanical data point to dynamic evolution of the studied brittle-ductile transition characterized by major weakening to strengths ˜10 MPa. Such non-steady-state evolution may be common in crustal shear zones especially when phase transformations are involved. References: Diamond, L. W., and A. Tarantola (2015), Interpretation of fluid inclusions in quartz deformed by weak ductile shearing: Reconstruction of differential stress magnitudes and pre-deformation fluid properties, Earth Planet. Sci. Lett., 417, 107-119. Mares, V. M., and A. K. Kronenberg (1993), Experimental deformation of muscovite, J. Struct. Geol., 15(9), 1061-1075. Paterson, M. S., and F. C. Luan (1990), Quartzite rheology under geological conditions, Geol. Soc. London, Spec. Publ., 54(1), 299-307. Stipp, M., and J. Tullis (2003), The recrystallized grain size piezometer for quartz, Geophys. Res. Lett., 30(21), 1-5.

Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD.

PubMed

Chauve, T; Montagnat, M; Barou, F; Hidas, K; Tommasi, A; Mainprice, D

2017-02-13

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms.This article is part of the themed issue 'Microdynamics of ice'. © 2016 The Author(s).

Dynamic Recrystallization Behavior and Corrosion Resistance of a Dual-Phase Mg-Li Alloy

PubMed Central

Liu, Gang; Xie, Wen; Wei, Guobing; Yang, Yan; Liu, Junwei; Xu, Tiancai; Xie, Weidong; Peng, Xiaodong

2018-01-01

The hot deformation and dynamic recrystallization behavior of the dual-phase Mg-9Li-3Al-2Sr-2Y alloy had been investigated using a compression test. The typical dual-phase structure was observed, and average of grain size of as-homogenized alloy is about 110 µm. It mainly contains β-Li, α-Mg, Al4Sr and Al2Y phases. The dynamic recrystallization (DRX) kinetic was established based on an Avrami type equation. The onset of the DRX process occurred before the peak of the stress–strain flow curves. It shows that the DRX volume fraction increases with increasing deformation temperature or decreasing strain rate. The microstructure evolution during the hot compression at various temperatures and strain rates had been investigated. The DRX grain size became larger with the increasing testing temperature or decreasing strain rate because the higher temperature or lower strain rate can improve the migration of DRX grain boundaries. The fully recrystallized microstructure can be achieved in a small strain due to the dispersed island-shape α-Mg phases, continuous the Al4Sr phases and spheroidal Al2Y particles, which can accelerate the nucleation. The continuous Al4Sr phases along the grain boundaries are very helpful for enhancing the corrosion resistance of the duplex structured Mg-Li alloy, which can prevent the pitting corrosion and filiform corrosion. PMID:29522473

Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD

PubMed Central

Barou, F.; Hidas, K.; Tommasi, A.; Mainprice, D.

2017-01-01

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=−5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the ‘parent’ ones suggests the possibility of ‘spontaneous’ nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms. This article is part of the themed issue ‘Microdynamics of ice’. PMID:28025294

Dynamic Recrystallization Behavior and Corrosion Resistance of a Dual-Phase Mg-Li Alloy.

PubMed

Liu, Gang; Xie, Wen; Wei, Guobing; Yang, Yan; Liu, Junwei; Xu, Tiancai; Xie, Weidong; Peng, Xiaodong

2018-03-09

The hot deformation and dynamic recrystallization behavior of the dual-phase Mg-9Li-3Al-2Sr-2Y alloy had been investigated using a compression test. The typical dual-phase structure was observed, and average of grain size of as-homogenized alloy is about 110 µm. It mainly contains β-Li, α-Mg, Al₄Sr and Al₂Y phases. The dynamic recrystallization (DRX) kinetic was established based on an Avrami type equation. The onset of the DRX process occurred before the peak of the stress-strain flow curves. It shows that the DRX volume fraction increases with increasing deformation temperature or decreasing strain rate. The microstructure evolution during the hot compression at various temperatures and strain rates had been investigated. The DRX grain size became larger with the increasing testing temperature or decreasing strain rate because the higher temperature or lower strain rate can improve the migration of DRX grain boundaries. The fully recrystallized microstructure can be achieved in a small strain due to the dispersed island-shape α-Mg phases, continuous the Al₄Sr phases and spheroidal Al₂Y particles, which can accelerate the nucleation. The continuous Al₄Sr phases along the grain boundaries are very helpful for enhancing the corrosion resistance of the duplex structured Mg-Li alloy, which can prevent the pitting corrosion and filiform corrosion.

EBSD characterization of low temperature deformation mechanisms in modern alloys

NASA Astrophysics Data System (ADS)

Kozmel, Thomas S., II

For structural applications, grain refinement has been shown to enhance mechanical properties such as strength, fatigue resistance, and fracture toughness. Through control of the thermos-mechanical processing parameters, dynamic recrystallization mechanisms were used to produce microstructures consisting of sub-micron grains in 9310 steel, 4140 steel, and Ti-6Al-4V. In both 9310 and 4140 steel, the distribution of carbides throughout the microstructure affected the ability of the material to dynamically recrystallize and determined the size of the dynamically recrystallized grains. Processing the materials at lower temperatures and higher strain rates resulted in finer dynamically recrystallized grains. Microstructural process models that can be used to estimate the resulting microstructure based on the processing parameters were developed for both 9310 and 4140 steel. Heat treatment studies performed on 9310 steel showed that the sub-micron grain size obtained during deformation could not be retained due to the low equilibrium volume fraction of carbides. Commercially available aluminum alloys were investigated to explain their high strain rate deformation behavior. Alloys such as 2139, 2519, 5083, and 7039 exhibit strain softening after an ultimate strength is reached, followed by a rapid degradation of mechanical properties after a critical strain level has been reached. Microstructural analysis showed that the formation of shear bands typically preceded this rapid degradation in properties. Shear band boundary misorientations increased as a function of equivalent strain in all cases. Precipitation behavior was found to greatly influence the microstructural response of the alloys. Additionally, precipitation strengthened alloys were found to exhibit similar flow stress behavior, whereas solid solution strengthened alloys exhibited lower flow stresses but higher ductility during dynamic loading. Schmid factor maps demonstrated that shear band formation behavior was influenced by texturing in these alloys.

Microstructure and Crystallographic Texture Evolution During the Friction-Stir Processing of a Precipitation-Hardenable Aluminum Alloy

NASA Astrophysics Data System (ADS)

Nadammal, Naresh; Kailas, Satish V.; Szpunar, Jerzy; Suwas, Satyam

2015-05-01

Friction-stir processing (FSP) has been proven as a successful method for the grain refinement of high-strength aluminum alloys. The most important attributes of this process are the fine-grain microstructure and characteristic texture, which impart suitable properties in the as-processed material. In the current work, FSP of the precipitation-hardenable aluminum alloy 2219 has been carried out and the consequent evolution of microstructure and texture has been studied. The as-processed materials were characterized using electron back-scattered diffraction, x-ray diffraction, and electron probe microanalysis. Onion-ring formation was observed in the nugget zone, which has been found to be related to the precipitation response and crystallographic texture of the alloy. Texture development in the alloy has been attributed to the combined effect of shear deformation and dynamic recrystallization. The texture was found heterogeneous even within the nugget zone. A microtexture analysis revealed the dominance of shear texture components, with C component at the top of nugget zone and the B and A2* components in the middle and bottom. The bulk texture measurement in the nugget zone revealed a dominant C component. The development of a weaker texture along with the presence of some large particles in the nugget zone indicates particle-stimulated nucleation as the dominant nucleation mechanism during FSP. Grain growth follows the Burke and Turnbull mechanism and geometrical coalescence.

Microstructural Evolution during Mid-Crustal Shear Zone Thickening and Thinning, Mount Irene Detachment Zone, Fiordland, New Zealand

NASA Astrophysics Data System (ADS)

Negrini, M.; Smith, S. A. F.; Scott, J.; Rooney, J. S.; Demurtas, M.

2016-12-01

Recent work has shown that ductile shear zones experience cyclic variations in stress and strain rate due to, for example, elastic loading from earthquake slip on brittle faults or the presence of rigid particles and asperities within the shear zone. Such non-steady state flow conditions can promote microstructural changes including a decrease in grain sizes followed by a switch in the main deformation mechanisms. Understanding the microstructural changes that occur during non steady-state deformation is therefore critical in evaluating shear zone rheology. The Mount Irene shear zone formed during Cretaceous extension in the middle crust and was active at temperatures of 600°C and pressures of 6 kbar. The shear zone localized in a basal calcite marble layer typically 3-5 m thick containing hundreds of thin (mm-cm) calc-silicate bands that are now parallel to the shear zone boundaries. The lower boundary of the shear zone preserves meter-scale undulations that cause the shear zone to be squeezed in to regions that are <1.5 m thick. The calc-silicate bands act as "flow markers" and allow individual shear zone layers to be traced continuously through thick and thin regions, implying that the mylonites experienced cyclic variations in stress and strain rate. Calc-mylonite samples collected from the same layer close to the base of the shear zone reveal that layer thinning was accompanied by progressive microstructural changes including intense twinning, stretching and flattening of large calcite porphyroclasts as well as the development of interconnected networks of recrystallized calcite aggregates. EBSD analysis shows that the recrystallized aggregates contain polygonal calcite grains with microstructures (e.g. grain quadruple junctions) similar to those reported for neighbor-switching processes associated with grain boundary sliding and superplasticity. Ongoing and future work will utilize samples from across the full thickness of the shear zone to determine key microstructural changes and deformation mechanisms that accommodated shear zone thinning and thickening during non-steady state deformation.

Strain softening during tension in cold drawn Cu–Ag alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, L.L., E-mail: lilichang@sdu.edu.cn; Wen, S.; Li, S.L.

2015-10-15

Experiments were conducted on Cu–0.1wt.%Ag alloys to evaluate the influence of producing procedures and annealing conditions on microstructure evolution and mechanical properties of Cu–Ag alloys. Optical microscopy (OM), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for microstructural evaluation and mechanical properties were characterized by tensile tests. The results indicated that hot-extruded Cu–Ag alloys had a typical dynamic recrystallized microstructure with equiaxed grains. Cold drawing at room temperature leaded to partial recrystallized microstructure with a mixture of coarse and fine grains. The dominate {001}<100 > cubic texture formed during hot extrusion was changed tomore » be {112}<111 > copper texture by cold drawing. Strain softening occurred during room temperature tension of cold drawn Cu–Ag alloys with an average grain size of 13–19.7 μm. - Highlights: • Strain softening occurred during tension of Cu–Ag alloys with coarse grain size. • Work hardening was observed in hot-extruded and annealed Cu–0.1wt.%Ag alloys. • Strain softening was ascribed to dynamic recovery and dynamic recrystallization.« less

Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by austenitic filler metal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eghlimi, Abbas, E-mail: a.eghlimi@ma.iut.ac.ir; Shamanian, Morteza; Eskandarian, Masoomeh

The evolution of microstructure and texture across an as-welded dissimilar UNS S32750 super duplex/UNS S30403 austenitic stainless steel joint welded by UNS S30986 (AWS A5.9 ER309LMo) austenitic stainless steel filler metal using gas tungsten arc welding process was evaluated by optical micrography and EBSD techniques. Due to their fabrication through rolling process, both parent metals had texture components resulted from deformation and recrystallization. The weld metal showed the highest amount of residual strain and had large austenite grain colonies of similar orientations with little amounts of skeletal ferrite, both oriented preferentially in the < 001 > direction with cub-on-cube orientationmore » relationship. While the super duplex stainless steel's heat affected zone contained higher ferrite than its parent metal, an excessive grain growth was observed at the austenitic stainless steel's counterpart. At both heat affected zones, austenite underwent some recrystallization and formed twin boundaries which led to an increase in the fraction of high angle boundaries as compared with the respective base metals. These regions showed the least amount of residual strain and highest amount of recrystallized austenite grains. Due to the static recrystallization, the fraction of low degree of fit (Σ) coincident site lattice boundaries, especially Σ3 boundaries, was increased in the austenitic stainless steel heat affected zone, while the formation of subgrains in the ferrite phase increased the content of < 5° low angle boundaries at that of the super duplex stainless steel. - Graphical abstract: Display Omitted - Highlights: • Extensive grain growth in the HAZ of austenitic stainless steel was observed. • Intensification of < 100 > orientated grains was observed adjacent to both fusion lines. • Annealing twins with Σ3 CSL boundaries were formed in the austenite of both HAZ. • Cub-on-cube OR was observed between austenite and ferrite in the weld metal. • Weld metal had the lowest texture intensity and ratio of low angle and CSL boundaries.« less

Recrystallization as a controlling process in the wear of some f.c.c. metals

NASA Technical Reports Server (NTRS)

Bill, R. C.; Wisander, D.

1977-01-01

Detailed examination of copper specimens after sliding against 440 C steel in liquid methane at speeds up to 25 m/s and loads of up to 2 kg showed the metal comprising the wear surface to possess a fine cell recrystallized structure. Wear proceeded by the plastic shearing of metal in this near surface region without the occurrence of visible metal transfer. A dynamic balance between the intense shear process at the surface and the nucleation of recrystallized grains was proposed to account for the behavior of the metal at the wear surface. Sliding wear experiments were also conducted on Ag, Cu-10% Al, Cu-10% Sn, Ni and Al. It was found that low wear and the absence of heavy metal transfer were associated with those metals observed to undergo recrystallization nucleation without prior recovery.

Progressive deformation of ultramafic rocks accompanied with deflection of layered structure and mylonitization culminating into a pseudotachylyte-bearing seismogenic fault - a field evidence of plastic instability

NASA Astrophysics Data System (ADS)

Ueda, T.; Obata, M.

2011-12-01

Plastic instability leading to rupture nucleation and propagetion (e.g. Hobbs et al.1986, Kelemen and Hirth, 2007) is an attractive hypothesis for deep earthquakes but lacked clear field evidences. 1D across-fault shear localization observed in some places (e.g. Jin et al.1998) is not clear if the deformation is directly related with seismicity. We present a clear field evidence of plastic instability as guided by pyroxenite/peridotite layering deflection structure (hereafter called LD structure, see figure) accompanied with mylonitization in spinel(Sp)-peridotite facies (P>~1GPa) in Balmuccia peridotite, Ivrea-Verbano Zone, Italy. The studied area contains abundant PST-bearing faults and N-S trending primary pyroxenite layers. Many faults in the area cut pyroxenite layers, but LD structure is found only in one place presented here. Many PSTs in the area have been (re)crystallized in Sp-peridotite facies, and have typically ultramylonitic texture (Ueda et al., 2008) with some injection veins. The fault with LD structure is situated in a fault system, which has two dominant attitudes with regional N-S extension. The shear strain of LD structure measured on outcrop surface is ~2.0. Near the fault, elongated Opx porphyroclasts (ellipses in figure) oblique to local layering are visible in peridotite. The dominant deformation textures are dynamic recrystallization in peridotite and kinking or undulatory extinction in pyroxenite. The mineral assemblages of the mylonite neoblast in the peridotite and the pyroxenite are Ol+Opx+Cpx+Sp+hornblende(Hbl), Cpx+Opx+Sp, respectively. Hbl typically occur only in neoblast. In the vicinity (several hundreds of micron) of the fault, dolomite(Dol) also occur in equilibrium with the assemblage above. The recrystallized grain sizes are 20-50 microns in peridotite and 10-30 microns in pyroxenite. The rarity of LD structure is consistent with general conception that deformation processes which lead to dynamic rupture initiation ought to be recorded in limited area on a resultant fault surface. The N-S extensional arrangement of the fault system including the fault of LD structure, the depth of PST (re)crystallization and mylonitization, all indicate that the rupture nucleation occurred in extensional tectonics (Souquiere and Fabbri , 2010). The occurrence of Dol in the vicinity of the PST fault suggests that this is the very place where plastic instability accompanied with fluid chemistry evolution (from H2O-rich to CO2-rich, caused by mylonitization and hydration) of Ueda et al. (2008.) had taken place.

Pressure Solution Creep and Textural Softening in Greenschist Facies Phyllonites

NASA Astrophysics Data System (ADS)

Wintsch, R. P.; Attenoukon, M.; Kunk, M. J.; McAleer, R. J.; Wathen, B.; Yi, D.

2016-12-01

We have found evidence for dissolution-precipitation creep (DPC) in phyllites and phyllonites naturally deformed at greenschist facies conditions. Since the experiments of Kronenberg et al. (1990) and Mares and Kronenberg (1993) micas are known to be among the weakest of rock-forming minerals. They deform by dislocation glide in their basal plane and when these micas are aligned and contiguous in an orientation favorable for glide they tend to localize strain into shear zones. Therefore, these closed-system experiments suggest that dislocation glide should be the dominant deformation mechanism in mica-rich shear zones from near surface through greenschist facies conditions. In contrast, in naturally deformed rocks we have found strong textural and chemical evidence that micas deform by dissolution-precipitation creep in phyllites at upper and lower greenschist facies conditions. In the Littleton Formation (N.H.) we find retrograde muscovite (pg5)-rich folia (Sn) truncating amphibolite facies Na-rich muscovite and biotite grains that define earlier foliations. Na-rich muscovite grains are also selectively replaced along crenulation axes and boudin necks where plastic and elastic strain are highest. In biotite grade regional metamorphic rocks in the Tananao schist of Taiwan muscovite-rich folia (Sn) truncate crenulated muscovite-biotite schists at high angles. In still lower (chlorite) grade phyllonitic fault zones marking terrane boundaries in southern New England (East Derby shear zone) and in Taiwan (Daugan shear zone) crenulated older fabrics are cut by new undeformed muscovite grains in chlorite-free planar folia. Further evidence for recrystallization rather than dislocation glide comes from the 40Ar/39Ar ages of muscovite in the new Sn folia younger than the age of the truncated folia. The younger ages in each case demonstrate that recrystallization was activated at lower shear stresses than dislocation glide, and that the recrystallization occurred at lower greenschist facies conditions below the closure temperature for diffusion of argon in muscovite. The increase in muscovite/chlorite ratios and change in microchemistry of Sn muscovite, the truncating microstructures, and isotopic results are all incompatible with deformation by dislocation creep.

Microstructure in Worn Surface of Hadfield Steel Crossing

NASA Astrophysics Data System (ADS)

Zhang, F. C.; Lv, B.; Wang, T. S.; Zheng, C. L.; Li, M.; Zhang, M.

In this paper a failed Hadfield (high manganese austenite) steel crossing used in railway system was studied. The microstructure in the worn surfaces of the crossing was investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy and Mössbauer spectroscopy. The results indicated that a nanocrystallization layer formed on the surface of the crossing served. The formation mechanism of the nanocrystalline is the discontinuous dynamic recrystallization. The energy for the recrystallization nucleus formation originates from the interactions between the twins, the dislocations, as well as twin and dislocation. High-density vacancies promoted the recrystallization process including the dislocation climb and the atom diffusion.

High-pressure metamorphism in the southern New England Orogen: Implications for long-lived accretionary orogenesis in eastern Australia

NASA Astrophysics Data System (ADS)

Phillips, G.; Offler, R.; Rubatto, D.; Phillips, D.

2015-09-01

New geochemical, metamorphic, and isotopic data are presented from high-pressure metamorphic rocks in the southern New England Orogen (eastern Australia). Conventional and optimal thermobarometry are augmented by U-Pb zircon and 40Ar/39Ar phengite dating to define pressure-temperature-time (P-T-t) histories for the rocks. The P-T-t histories are compared with competing geodynamic models for the Tasmanides, which can be summarized as (i) a retreating orogen model, the Tasmanides formed above a continuous, west dipping, and eastward retreating subduction zone, and (ii) a punctuated orogen model, the Tasmanides formed by several arc accretion, subduction flip, and/or transference events. Whereas both scenarios are potentially supported by the new data, an overlap between the timing of metamorphic recrystallization and key stages of Tasmanides evolution favors a relationship between a single, long-lived subduction zone and the formation, exhumation, and exposure of the high-pressure rocks. By comparison with the retreating orogen model, the following links with the P-T-t histories emerge: (i) exhumation and underplating of oceanic eclogite during the Delamerian Orogeny, (ii) recrystallization of underplated and exhuming high-pressure rocks at amphibolite facies conditions coeval with a period of rollback, and (iii) selective recrystallization of high-pressure rocks at blueschist facies conditions, reflecting metamorphism in a cooled subduction zone. The retreating orogen model can also account for the anomalous location of the Cambrian-Ordovician high-pressure rocks in the Devonian-Carboniferous New England Orogen, where sequential rollback cycles detached and translated parts of the leading edge of the overriding plate to the next, younger orogenic cycle.

Microstructure evolution and dynamic recrystallization behavior of a powder metallurgy Ti-22Al-25Nb alloy during hot compression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Jianbo

The flow behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy during hot compression tests has been investigated at a strain rate of 0.01 s{sup −1} and a temperature range of 980–1100 °C up to various true strains from 0.1 to 0.9. The effects of deformation temperature and strain on microstructure characterization and nucleation mechanisms of dynamic recrystallization (DRX) were assessed by means of Optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques, respectively. The results indicated that the process of DRX was promoted by increasing deformation temperature and strain. By regression analysis, a power exponent relationshipmore » between peak stresses and sizes of stable DRX grains was developed. In addition, it is suggested that the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) controlled nucleation mechanisms for DRX grains operated simultaneously during the whole hot process, and which played the leading role varied with hot process parameters of temperature and strain. It was further demonstrated that the CDRX featured by progressive subgrain rotation was weakened by elevating deformation temperatures. - Highlights: •Flow behavior of a P/M Ti-22Al-25Nb is studied by hot compression tests. •Microstructure evolution of alloy is affected by deformation temperature and strain. •The relationship between peak stress and stable DRX grain size was developed. •The process of DRX was promoted by increasing deformation temperature and strain. •Nucleation mechanisms of DRX were identified by EBSD analysis and TEM observation.« less

Yttrium geothermometry: an approach to determine the oldest garnet growth recrystallization conditions from micaschists (Yunquera Unit, Betic Cordilleras, southern Spain

NASA Astrophysics Data System (ADS)

Esteban, J. J.; Cuevas, J.; Tubía, J. M.; Gil Ibarguchi, J. I.

2012-04-01

The garnet-xenotime geothermometry is nowadays been using as a tool to identify low-grade relic garnets and even to calculate garnet growth temperatures in metapelites that have undergone a polymetamorphic evolution (Pyle and Spear, 2000; Borghi et al., 2006). A prograde metamorphic evolution, under continuously increasing temperature, can induce garnet and accompanying phase's composition homogenization by intra-crystalline diffusion, leading to flat zoning profiles. Consequently, the application of conventional geothermobarometers on those mineral assemblages does establish minimum P-T conditions. Therefore, the less susceptible elements to diffusion processes, like trace elements, should be taken into account in order to reconstruct their metamorphic evolution. We studied a polymetamorphic micaschist recovered from the Yunquera Unit, one of the tectonic slices of the Internal Zone of the Betic Cordilleras (southern Spain) (Dürr, 1963). The Yunquera unit evidences three stages of recrystallization at different P-T conditions. According to conventional geothermobarometry (Esteban et al., 2005) the metamorphic peak, M2, is estimated at 1200-1300 MPa and 560-695 °C and the decompression path, M3, at 600 MPa and 700 °C. The lack of mineral paragenesis in apparent chemical equilibrium during M1, does not allow determining accurately its recrystallization conditions. Xenotime, identified by scanning electron microprobe, appears as matrix mineral and therefore the entire garnets are assumed to be in chemical equilibrium with it. Yttrium profiles of two garnets show a mean bell-shape compositional variation that differs significatively from the discontinuous profiles shown by Ca, Mg and Fe. This difference accounts for different diffusion rates for those elements and agree with the original Y-zoning preservation. A third Y-profile shows an oscillatory compositional variation. The internal part of garnets, bounded by sharp inclusion trails, are characterized by sawed bell-shape zoning in the range of ca. 500-2000 ppm of Y, that abruptly decreases to less than 500 ppm to the borders. Temperature distribution calculated from the garnet-xenotime geothermometer of Pyle and Spear (2000) is outlined by flat patterns, matching up with the cores of the garnets, and by a slightly increase to the rim. The metamorphic temperature calculated using the Y-concentration of the central portions of garnet cores is ca. 520 °C, whereas towards the rim the temperature does increase up to ca. 575-625 °C. The estimation of garnet recrystallization pressure is still a matter of discussion, furthermore when the hypothetical equilibrium paragenesis is absent. According to the presented data, we suggest that the oldest garnet growth generation did occur at ca. 520 °C and therefore, the preservation of original Y-zonings can be used for thermal history reconstructions, as Y-content in garnet is T-dependent.

Recrystallization of freezable bound water in aqueous solutions of medium concentration

NASA Astrophysics Data System (ADS)

Lishan, Zhao; Liqing, Pan; Ailing, Ji; Zexian, Cao; Qiang, Wang

2016-07-01

For aqueous solutions with freezable bound water, vitrification and recrystallization are mingled, which brings difficulty to application and misleads the interpretation of relevant experiments. Here, we report a quantification scheme for the freezable bound water based on the water-content dependence of glass transition temperature, by which also the concentration range for the solutions that may undergo recrystallization finds a clear definition. Furthermore, we find that depending on the amount of the freezable bound water, different temperature protocols should be devised to achieve a complete recrystallization. Our results may be helpful for understanding the dynamics of supercooled aqueous solutions and for improving their manipulation in various industries. Project supported by the Knowledge Innovation Project of Chinese Academy of Sciences on Water Science Research (Grant No. KJZD-EW-M03) and the National Natural Science Foundation of China (Grant Nos. 11474325 and 11290161).

Surface premelting/recrystallization governing the collapse of open-cell nanoporous Cu via thermal annealing.

PubMed

Wang, L; Zhang, X M; Deng, L; Tang, J F; Xiao, S F; Deng, H Q; Hu, W Y

2018-06-04

We systematically investigate the collapse of a set of open-cell nanoporous Cu (np-Cu) materials with the same porosity and shape but different specific surface areas, during thermal annealing, by performing large-scale molecular dynamics simulations. Two mechanisms govern the collapse of np-Cu. One is direct surface premelting, facilitating the collapse of np-Cu, when the specific surface area is less than a critical value (∼2.38 nm-1). The other is recrystallization followed by surface premelting, accelerating the sloughing of ligaments and the annihilation of voids, when the critical specific surface area is exceeded. Surface premelting results from surface reconstruction by prompting localized "disordering" and "chaos" on the surface, and the melting temperature reduces linearly with the increase of the specific surface area. Recrystallization is followed by surface premelting as the melting temperature is below the supercooling point, where a liquid is unstable and instantaneously recrystallizes.

A Naturally-Calibrated Flow Law for Quartz

NASA Astrophysics Data System (ADS)

Lusk, A. D.; Platt, J. P.

2017-12-01

Flow laws for power-law behavior of quartz deforming by crystal-plastic processes with grain size sensitive creep included take the general form: ė = A σn f(H2O) exp(-Q/RT) dmWhere A - prefactor; σ - differential stress; n - stress exponent; f(H2O) - water fugacity; Q - activation energy; R - gas constant; T - temperature (K); d - grain size sensitivity raised to power m. Assuming the dynamically recrystallized grain size for quartz follows the peizometric relationship, substitute dm = (K σ-p)m, where K - piezometric constant; σ - differential stress; p - piezometric exponent. Rearranging the above flow law: ė = A K σ(n-pm) f(H2O) exp(-Q/RT)We use deformation temperatures, paleo-stresses, and strain rates calculated from rocks deformed in the Caledonian Orogeny, NW Scotland, along with existing experimental data, to compare naturally-calibrated values of stress exponent (n-pm) and activation energy (Q) to those determined experimentally. Microstructures preserved in the naturally-strained rocks closely resemble those produced by experimental work, indicating that quartz was deformed by the same mechanism(s). These observations validate the use of predetermined values for A as well as the addition of experimental data to calculate Q. Values for f(H2O) are based on calculated pressure and temperature conditions. Using the abovementioned constraints, we compare results, discuss challenges, and explore implications of naturally- vs. experimentally-derived flow laws for dislocation creep in quartz. Rocks used for this study include quartzite and quartz-rich psammite of the Cambrian-Ordovician shelf sequence and tectonically overlying Moine Supergroup. In both cases, quartz is likely the primary phase that controlled rheological behavior. We use the empirically derived piezometer for the dynamically recrystallized grain size of quartz to calculate the magnitude of differential stress, along with the Ti-in-quartz thermobarometer and the c-axis opening angle thermometer to determine temperatures of deformation. Tensor strain rates are calculated from plate convergence rate, based on total displacement and duration of thrusting within the Moine thrust zone, and shear zone thickness calculated from four detailed structural and microstructural transects taken parallel to the direction of displacement.

High-Temperature Flow Stress and Recrystallization Characteristics of Al-Bearing Microalloyed TWIP Steels

NASA Astrophysics Data System (ADS)

Somani, Mahesh Chandra; Porter, David A.; Hamada, Atef S.; Karjalainen, L. Pentti

2015-11-01

In this study, the effects of microalloying (Nb,V) and aluminum on the constitutive flow behavior and static recrystallization (SRX) characteristics of microalloyed TWIP steels (Fe-20Mn-0.6C-Al-(Nb,V)) have been investigated under hot deformation conditions. Compression tests in a Gleeble simulator, including the double-hit technique, enabled the acquisition of flow stress and recrystallization data. These were analyzed to determine the powers of strain and strain rate as well as the activation energies of deformation and recrystallization ( Q def and Q rex). Aluminum increased the flow stress and activation energy of deformation and delayed the onset of dynamic recrystallization of microalloyed TWIP steels. While microalloying with V up to 0.3 pct seems to have little or no effect on the SRX kinetics, microalloying with 0.026 pct Nb significantly slowed down the SRX rate, similarly as in the case of low C-Mn steels. Addition of high aluminum (4.9 pct) marginally retarded the SRX kinetics in comparison with the steels with low aluminum (1.5 pct), with or without microalloying with V.

Effects of two-step homogenization on precipitation behavior of Al{sub 3}Zr dispersoids and recrystallization resistance in 7150 aluminum alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Zhanying; Key Laboratory for Anisotropy and Texture of Materials, Northeastern University, Shenyang 110819, China,; Zhao, Gang

2015-04-15

The effect of two-step homogenization treatments on the precipitation behavior of Al{sub 3}Zr dispersoids was investigated by transmission electron microscopy (TEM) in 7150 alloys. Two-step treatments with the first step in the temperature range of 300–400 °C followed by the second step at 470 °C were applied during homogenization. Compared with the conventional one-step homogenization, both a finer particle size and a higher number density of Al{sub 3}Zr dispersoids were obtained with two-step homogenization treatments. The most effective dispersoid distribution was attained using the first step held at 300 °C. In addition, the two-step homogenization minimized the precipitate free zonesmore » and greatly increased the number density of dispersoids near dendrite grain boundaries. The effect of two-step homogenization on recrystallization resistance of 7150 alloys with different Zr contents was quantitatively analyzed using the electron backscattered diffraction (EBSD) technique. It was found that the improved dispersoid distribution through the two-step treatment can effectively inhibit the recrystallization process during the post-deformation annealing for 7150 alloys containing 0.04–0.09 wt.% Zr, resulting in a remarkable reduction of the volume fraction and grain size of recrystallization grains. - Highlights: • Effect of two-step homogenization on Al{sub 3}Zr dispersoids was investigated by TEM. • Finer and higher number of dispersoids obtained with two-step homogenization • Minimized the precipitate free zones and improved the dispersoid distribution • Recrystallization resistance with varying Zr content was quantified by EBSD. • Effectively inhibit the recrystallization through two-step treatments in 7150 alloy.« less

Pulverized granite at the brittle-ductile transition: An example from the Kellyland fault zone, eastern Maine, U.S.A.

NASA Astrophysics Data System (ADS)

Sullivan, Walter A.; Peterman, Emily M.

2017-08-01

Granite from a 50-200-m-wide damage zone adjacent to the brittle-ductile Kellyland Fault Zone contains healed fracture networks that exhibit almost all of the characteristics of dynamically pulverized rocks. Fracture networks exhibit only weak preferred orientations, are mutually cross-cutting, separate jigsaw-like interlocking fragments, and are associated with recrystallized areas likely derived from pervasively comminuted material. Fracture networks in samples with primary igneous grain shapes further indicate pulverization. Minimum fracture densities in microcline are ∼100 mm/mm2. Larger fractures in microcline and quartz are sometimes marked by neoblasts, but most fractures are optically continuous with host grains and only visible in cathodoluminescence images. Fractures in plagioclase are crystallographically controlled and typically biotite filled. Petrologic observations and cross-cutting relationships between brittle structures and mylonitic rocks show that fracturing occurred at temperatures of 400 °C or more and pressures of 200 MPa. These constraints extend the known range of pulverization to much higher temperature and pressure conditions than previously thought possible. The mutually cross-cutting healed fractures also provide the first record of repeated damage in pulverized rocks. Furthermore, pulverization must have had a significant but transient effect on wall-rock porosity, and biotite-filled fracture networks in plagioclase form weak zones that could accommodate future strain localization.

Field-based Constraints on Lower Crustal Flow From the World's Largest Exposure of Lower Continental Crust, Northern Saskatchewan, Canada

NASA Astrophysics Data System (ADS)

Dumond, G.; Gonclaves, P.; Williams, M. L.; Bowring, S. A.

2005-12-01

Predictions about the behavior and geometry of lower continental crust during orogenesis have included: it is rheologically weak; it flows under the influence of a tectonic or topographic load; and it is characterized by pervasive shallow fabrics produced by high-temperature deformation mechanisms. Arguably the world's largest exposure of lower continental crust that still preserves much of its deep crustal deformation history is the central portion of the Snowbird tectonic zone in the western Canadian Shield. Recent fieldwork along a ca. 100 km-long transect of this exposure is characterized by an early, penetrative shallow fabric. A 40 km-long segment of this transect, dominated by charnockite and granodiorite orthogneisses, is characterized by km-scale domains of shallow, granulite-grade gneissic foliation (S1) with a spectacular rodding lineation (L1) defined by: 1) discontinuous ribbons of recrystallized Pl + Qtz + Hb + Cpx + Opx, in addition to mm- to cm-scale core-and-mantle structure in Pl and Kfs, and 2) near-continuous, 10s of cm-long rods of compositional banding. Isoclinally-folded layering is locally preserved perpendicular to (L1). We interpret (L1) as a composite lineation with both intersection and extension components. Thermobarometric data, microstructural, and kinematic observations are compatible with high-grade (700-800°C) ductile, top-to-the-ESE flow during production of S1 at 1.0-1.1 GPa (30-40 km paleodepths in the Neoarchean. S1 is variably transposed into upright, open, shallowly-plunging F2 folds with sub-horizontal, NW-striking enveloping surfaces. The weakly folded S1 is locally overprinted by <10 m-wide penetrative high-strain zones in which S1 has been transposed into steeply-dipping, NE-striking foliation (S2). D2 high-strain zones contain shallow SW-plunging stretching lineations (locally L-tectonites) and dextral, oblique-slip kinematics. D2 low-strain zones preserve Type 2 (mushroom-crescent) fold interference patterns resulting from superposition of upright F2 folds with sub-vertical NE-striking axial planes onto isoclinal, recumbent F1 folds. Metamorphic reactions that led to Grt-production during development of S1 were intrinsically syn-kinematic, with garnet growing in the Na-rich recrystallized mantles of Pl-porphyroclasts. Relatively H2O-poor and/or CO2-rich conditions are required by the preservation of fine-grained microstructures and absence of grain-coarsening or recrystallization in the S1 tectonite. We speculate that the shallow S1 tectonite exposed in the central Snowbird tectonic zone transect represents an important and unique field-based analog for the nature of deep crustal reflectivity and lower crustal flow in collisional orogens. Furthermore, our results suggest that the strength of the lower continental crust is dynamic and evolving. In this particular case, flow of relatively weak lower crust during production of S1 was followed by a period of near-isobaric cooling and strengthening. Subsequent deformation events produced steep fabrics (e.g. S2), 10s of m- to 100s of km-scale moderately- to steeply-dipping shear zones, and local reactivation of S1, reflecting the dramatic effects of strain partitioning in a heterogeneous and anisotropic medium.

Deformation Behavior of a Coarse-Grained Mg-8Al-1.5Ca-0.2Sr Magnesium Alloy at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Lou, Yan; Liu, Xiao

2018-02-01

The compression tests were carried out on a coarse-grained Mg-8Al-1.5Ca-0.2Sr magnesium alloy samples at temperatures from 300 to 450 °C and strain rates from 0.001 to 10 s-1. The flow stress curves were analyzed using the double-differentiation method, and double minima were detected on the flow curves. The first set of minima is shown to identify the critical strain for twinning, while the second set indicates the critical strain for the initiation of dynamic recrystallization (DRX). Twin variant selection was numerically identified by comprehensive analysis of the Schmid factors for different deformation modes and the accommodation strains imposed on neighboring grains. It was found that twinning is initiated before DRX. Dynamic recrystallization volume increases with strain rate at a given deformation temperature. At high strain rate, various twin variants are activated to accommodate deformation, leading to the formation of twin intersections and high DRX volume. Fully dynamic recrystallized structure can be obtained at both high and low strain rates due to the high mobility of the grain and twin boundaries at the temperature of 400 °C.

Dynamic recrystallization behavior of a biomedical Ti-13Nb-13Zr alloy.

PubMed

Bobbili, Ravindranadh; Madhu, V

2016-06-01

The dynamic recrystallization (DRX) behavior of a biomedical titanium Ti-13Nb-13Zr alloy has been investigated using the high temperature compression tests under wide range of strain rates (0.001-1/s) and temperatures 900-1050°C. A constitutive equation represented as a function of temperature, strain rate and true strain is developed and the hot deformation apparent activation energy is calculated about 534kJ/mol. By considering the exponential relationship between work-hardening rate (θ) and stress, a new mathematical model was proposed for predicting flow stress up to the critical strain during hot deformation. The mathematical model for predicting flow stress up to the critical strain exhibits better consistency and accuracy. The DRX kinetic equation of Ti-13Nb-13Zr alloy is described as XDRX=1-exp[-0.32(Ɛ-ƐcƐ(*))(2.3)] . The DRX kinetic model was validated by microstructure observation. It was also found that the process of DRX was promoted by decreasing strain rate and increasing deformation temperature. Eventually, the continuous dynamic recrystallization (CDRX) was identified to be the DRX mechanism using transmission electron microscope (TEM). Copyright © 2015 Elsevier Ltd. All rights reserved.

Evolution of Continental Lower Crust Recorded By an Exhumed Deep Crustal Intracontinental Shear Zone

NASA Astrophysics Data System (ADS)

Dumond, G.; Mahan, K. H.; Regan, S. P.; Williams, M. L.; Goncalves, P.; Wood, V. R.

2014-12-01

Exposures of deep crustal shear zones are fundamental records of strain localization and the temporal evolution of ductile to brittle behavior as these tectonites were exhumed to the surface. We present results from a decade of field-based research on a deeply exhumed (~35 km-paleodepths) strike-slip shear zone in the western Churchill province of the Canadian Shield. The Grease River shear zone is a >400 km-long and 7 km-thick structure that cuts the Athabasca granulite terrane, North America's largest exposure of continental lower crust (>20,000 km2). The shear zone is dominated by granulite- to amphibolite-grade L-S and L>S tectonites characterized by penetrative NE-striking steeply-dipping foliations with gently-plunging to sub-horizontal stretching and intersection lineations. These fabrics are locally overprinted by pseudotachylyte and narrow (<500 m-thick) greenschist-grade zones of cataclasite. Dextral kinematics are defined by deflected foliation trajectories, C' shear bands, and well-developed σ- and δ-type porphyroclasts of Kfs + Pl + Opx + Grt + Hb in felsic to intermediate granulite paragneisses and orthogneisses. Data collected along a well-exposed, nearly 150 km-long segment of the shear zone documents a >100 m.y. episodic record of transpressive to strike-slip intracontinental strain accumulation that coincided with two oppositely convergent orogenies: the east-vergent arc-continent collision of the 1.94-1.90 Ga Taltson orogen and the west-vergent continent-continent collision of the 1.9-1.8 Ga Trans-Hudson orogen. Deformation mechanisms evolved from distributed ductile dynamic recrystallization and grain-size reduction to localized pseudotachylyte development, cataclastic flow, and brittle faulting. Lower crustal behavior during strain localization was dynamic. Melt-weakened mono-cyclic crust was juxtaposed against strong isobarically-cooled poly-cyclic crust along the shear zone at 1.92-1.90 Ga. Brittle-ductile reactivation of the structure during exhumation to middle crustal levels was coincident with fluid-mediated retrograde reactions that facilitated crustal-scale segmentation and transpressive uplift of lower crustal granulites at 1.85 Ga. This study illustrates that lower crustal rheology is spatially and temporally heterogeneous.

Fabrics and geochronology of the Wushan ductile shear zone: Tectonic implications for the Shangdan suture zone in the Qinling orogen, Central China

NASA Astrophysics Data System (ADS)

Liang, Xiao; Sun, Shengshi; Dong, Yunpeng; Yang, Zhao; Liu, Xiaoming; He, Dengfeng

2017-04-01

The ductile shearing along the Shangdan suture zone during the Paleozoic time is a key to understand the collisional deformation and tectonic regime of amalgamation between the North China Block and the South China Blocks. The Wushan ductile shear zone, a branch of the Shangdan suture, records mylonitic deformation that affected granitic and felsic rocks outcropping in an over 1 km wide belt in the western Qinling Orogenic belt. Shear sense indicators and kinematic vorticity number (0.79-0.99) of the mylonites reveal a dextral shear deformation. The quartz c-axis fabrics indicate activation of combined basal and rhomb slip, prism slip and prism slip. The dynamic recrystallization of quartz is accommodated by combined subgrain rotation and grain boundary migration. These characteristics suggest that the mylonites experienced ductile shear deformation under amphibolite facies conditions at temperatures of 500-650 C. Zircons from granitic mylonite yield a U-Pb age of 910 ± 4.8 Ma, which represents the formation age of the protolith of the mylonite. The ductile shear zone was intruded by a granitic dyke, which yields a zircon U-Pb age of 403 ± 3.5 Ma constraining the minimum age of the ductile shear deformation. Together with regional geology and available geochronological data, these structural characteristics and ages indicate that the Wushan ductile shear zone was formed by dextral shearing following the N-S shortening as a result of collision between the North China and South China blocks along the Shangdan suture.

Fabrics and geochronology of the Wushan ductile shear zone: Tectonic implications for the Shangdan suture zone in the Qinling orogen, Central China

NASA Astrophysics Data System (ADS)

Liang, Xiao; Sun, Shengsi; Dong, Yunpeng; Yang, Zhao; Liu, Xiaoming; He, Dengfeng

2017-05-01

The ductile shearing along the Shangdan suture zone during the Paleozoic time is a key to understand the collisional deformation and tectonic regime of amalgamation between the North China Block and the South China Blocks. The Wushan ductile shear zone, a branch of the Shangdan suture, records mylonitic deformation that affected granitic and felsic rocks outcropping in an over 1 km wide belt in the western Qinling Orogenic belt. Shear sense indicators and kinematic vorticity number (0.79-0.99) of the mylonites reveal a dextral shear deformation. The quartz c-axis fabrics indicate activation of combined basal and rhomb slip, prism slip and prism slip. The dynamic recrystallization of quartz is accommodated by combined subgrain rotation and grain boundary migration. These characteristics suggest that the mylonites experienced ductile shear deformation under amphibolite facies conditions at temperatures of ∼500-650 °C. Zircons from granitic mylonite yield a U-Pb age of 910 ± 4.8 Ma, which represents the formation age of the protolith of the mylonite. The ductile shear zone was intruded by a granitic dyke, which yields a zircon U-Pb age of 403 ± 3.5 Ma constraining the minimum age of the ductile shear deformation. Together with regional geology and available geochronological data, these structural characteristics and ages indicate that the Wushan ductile shear zone was formed by dextral shearing following the N-S shortening as a result of collision between the North China and South China blocks along the Shangdan suture.

Modeling of AA5083 Material-Microstructure Evolution During Butt Friction-Stir Welding

NASA Astrophysics Data System (ADS)

Grujicic, M.; Arakere, G.; Yalavarthy, H. V.; He, T.; Yen, C.-F.; Cheeseman, B. A.

2010-07-01

A concise yet a fairly comprehensive overview of the friction stir welding (FSW) process is provided. This is followed by a computational investigation in which FSW behavior of a prototypical solution-strengthened and strain-hardened aluminum alloy, AA5083-H131, is modeled using a fully coupled thermo-mechanical finite-element procedure developed in our prior study. Particular attention is given to proper modeling of the welding work-piece material behavior during the FSW process. Specifically, competition and interactions between plastic-deformation and dynamic-recrystallization processes are considered to properly account for the material-microstructure evolution in the weld nugget zone. The results showed that with proper modeling of the material behavior under high-temperature/severe-plastic-deformation conditions, significantly improved agreement can be attained between the computed and measured post-FSW residual-stress and material-strength distribution results.

Validation of the Dynamic Recrystallization (DRX) Mechanism for Whisker and Hillock Growth on Sn Thin Films

NASA Astrophysics Data System (ADS)

Vianco, P. T.; Neilsen, M. K.; Rejent, J. A.; Grant, R. P.

2015-10-01

A study was performed to validate a first-principles model for whisker and hillock formation based on the cyclic dynamic recrystallization (DRX) mechanism in conjunction with long-range diffusion. The test specimens were evaporated Sn films on Si having thicknesses of 0.25 μm, 0.50 μm, 1.0 μm, 2.0 μm, and 4.9 μm. Air annealing was performed at 35°C, 60°C, 100°C, 120°C, or 150°C over a time duration of 9 days. The stresses, anelastic strains, and strain rates in the Sn films were predicted by a computational model based upon the constitutive properties of 95.5Sn-3.9Ag-0.6Cu (wt.%) as a surrogate for pure Sn. The cyclic DRX mechanism and, in particular, whether long whiskers or hillocks were formed, was validated by comparing the empirical data against the three hierarchal requirements: (1) DRX to occur at all: ɛc = A D o m Z n , (2) DRX to be cyclic: D o < 2 D r, and (3) Grain boundary pinning (thin films): h versus d. Continuous DRX took place in the 2.0- μm and 4.9- μm films that resulted in short stubby whiskers. Depleted zones, which resulted solely from a tensile stress-driven diffusion mechanism, confirmed the pervasiveness of long-range diffusion so that it did not control whisker or hillock formation other than a small loss of activity by reduced thermal activation at lower temperatures. A first-principles DRX model paves the way to develop like mitigation strategies against long whisker growth.

Validation of the dynamic recrystallization (DRX) mechanism for whisker and hillock growth on thin films

DOE PAGES

Vianco, Paul T.; Neilsen, Michael K.; Rejent, Jerome A.; ...

2015-05-01

Our study was performed to validate a first-principles model for whisker and hillock formation based on the cyclic dynamic recrystallization (DRX) mechanism in conjunction with long-range diffusion. The test specimens were evaporated Sn films on Si having thicknesses of 0.25 μm, 0.50 μm, 1.0 μm, 2.0 μm, and 4.9 μm. Air annealing was performed at 35°C, 60°C, 100°C, 120°C, or 150°C over a time duration of 9 days. The stresses, anelastic strains, and strain rates in the Sn films were predicted by a computational model based upon the constitutive properties of 95.5Sn-3.9Ag-0.6Cu (wt.%) as a surrogate for pure Sn. Themore » cyclic DRX mechanism and, in particular, whether long whiskers or hillocks were formed, was validated by comparing the empirical data against the three hierarchal requirements: (1) DRX to occur at all: εc = A D o m Z n , (2) DRX to be cyclic: D o < 2D r, and (3) Grain boundary pinning (thin films): h versus d. Continuous DRX took place in the 2.0-μm and 4.9-μm films that resulted in short stubby whiskers. Depleted zones, which resulted solely from a tensile stress-driven diffusion mechanism, confirmed the pervasiveness of long-range diffusion so that it did not control whisker or hillock formation other than a small loss of activity by reduced thermal activation at lower temperatures. Furthermore, a first-principles DRX model paves the way to develop like mitigation strategies against long whisker growth.« less

CNEA/ANL collaboration program to develop an optimized version of DART validation and assessment by means of U{sub 3}Si{sub x} and U{sub 3}O{sub 8-}Al dispersed CNEA miniplate irradiation behavior.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solis, D.

1998-10-16

The DART code is based upon a thermomechanical model that can predict swelling, recrystallization, fuel-meat interdiffusion and other issues related with MTR dispersed FE behavior under irradiation. As a part of a common effort to develop an optimized version of DART, a comparison between DART predictions and CNEA miniplates irradiation experimental data was made. The irradiation took place during 1981-82 for U3O8 miniplates and 1985-86 for U{sub 3}Si{sub x} at Oak Ridge Research Reactor (ORR). The microphotographs were studied by means of IMAWIN 3.0 Image Analysis Code and different fission gas bubbles distributions were obtained. Also it was possible tomore » find and identify different morphologic zones. In both kinds of fuels, different phases were recognized, like particle peripheral zones with evidence of Al-U reaction, internal recrystallized zones and bubbles. A very good agreement between code prediction and irradiation results was found. The few discrepancies are due to local, fabrication and irradiation uncertainties, as the presence of U{sub 3}Si phase in U{sub 3}Si{sub 2} particles and effective burnup.« less

Characterizing 3D grain size distributions from 2D sections in mylonites using a modified version of the Saltykov method

NASA Astrophysics Data System (ADS)

Lopez-Sanchez, Marco; Llana-Fúnez, Sergio

2016-04-01

The understanding of creep behaviour in rocks requires knowledge of 3D grain size distributions (GSD) that result from dynamic recrystallization processes during deformation. The methods to estimate directly the 3D grain size distribution -serial sectioning, synchrotron or X-ray-based tomography- are expensive, time-consuming and, in most cases and at best, challenging. This means that in practice grain size distributions are mostly derived from 2D sections. Although there are a number of methods in the literature to derive the actual 3D grain size distributions from 2D sections, the most popular in highly deformed rocks is the so-called Saltykov method. It has though two major drawbacks: the method assumes no interaction between grains, which is not true in the case of recrystallised mylonites; and uses histograms to describe distributions, which limits the quantification of the GSD. The first aim of this contribution is to test whether the interaction between grains in mylonites, i.e. random grain packing, affects significantly the GSDs estimated by the Saltykov method. We test this using the random resampling technique in a large data set (n = 12298). The full data set is built from several parallel thin sections that cut a completely dynamically recrystallized quartz aggregate in a rock sample from a Variscan shear zone in NW Spain. The results proved that the Saltykov method is reliable as long as the number of grains is large (n > 1000). Assuming that a lognormal distribution is an optimal approximation for the GSD in a completely dynamically recrystallized rock, we introduce an additional step to the Saltykov method, which allows estimating a continuous probability distribution function of the 3D grain size population. The additional step takes the midpoints of the classes obtained by the Saltykov method and fits a lognormal distribution with a trust region using a non-linear least squares algorithm. The new protocol is named the two-step method. The conclusion of this work is that both the Saltykov and the two-step methods are accurate and simple enough to be useful in practice in rocks, alloys or ceramics with near-equant grains and expected lognormal distributions. The Saltykov method is particularly suitable to estimate the volumes of particular grain fractions, while the two-step method to quantify the full GSD (mean and standard deviation in log grain size). The two-step method is implemented in a free, open-source and easy-to-handle script (see http://marcoalopez.github.io/GrainSizeTools/).

Surface damage and structure evolution of recrystallized tungsten exposed to ELM-like transient loads

NASA Astrophysics Data System (ADS)

Yuan, Y.; Du, J.; Wirtz, M.; Luo, G.-N.; Lu, G.-H.; Liu, W.

2016-03-01

Surface damage and structure evolution of the full tungsten ITER divertor under transient heat loads is a key concern for component lifetime and plasma operations. Recrystallization caused by transients and steady-state heat loads can lead to degradation of the material properties and is therefore one of the most serious issues for tungsten armor. In order to investigate the thermal response of the recrystallized tungsten under edge localized mode-like transient thermal loads, fully recrystallized tungsten samples with different average grain sizes are exposed to cyclic thermal shocks in the electron beam facility JUDITH 1. The results indicate that not only does the microstructure change due to recrystallization, but that the surface residual stress induced by mechanical polishing strongly influences the surface cracking behavior. The stress-free surface prepared by electro-polishing is shown to be more resistant to cracking than the mechanically polished one. The resulting surface roughness depends largely on the loading conditions instead of the recrystallized-grain size. As the base temperature increases from room temperature to 400 °C, surface roughening mainly due to the shear bands in each grain becomes more pronounced, and sub-grains (up to 3 μm) are simultaneously formed in the sub-surface. The directions of the shear bands exhibit strong grain-orientation dependence, and they are generally aligned with the traces of {1 1 2} twin habit planes. The results suggest that twinning deformation and dynamic recrystallization represent the predominant mechanism for surface roughening and related microstructure evolution.

The Prediction of Microstructure Evolution of 6005A Aluminum Alloy in a P-ECAP Extrusion Study

NASA Astrophysics Data System (ADS)

Lei, Shi; Jiu-Ba, Wen; Chang, Ren

2018-05-01

Finite element modeling (FEM) was applied for predicting the recrystallized structure in extruded 6005 aluminum alloy, and simulated results were experimentally validated. First, microstructure evolution of 6005 aluminum alloy during deformation was studied by means of isothermal compression test, where the processing parameters were chosen to reproduce the typical industrial conditions. Second, microstructure evolution was analyzed, and the obtained information was used to fit a dynamic recrystallization model implementing inside the DEFORM-3D FEM code environment. FEM of deformation of 6005 aluminum has been established and validated by microstructure comparison. Finally, the obtained dynamic recrystallization model was applied to tube extrusion by using a portholes-equal channel angular pressing die. The finite element analysis results showed that coarse DRX grains occur in the extruded tube at higher temperature and in the extruded tube at the faster speed of the stem. The test results showed material from the front end of the extruded tube has coarse grains (60 μm) and other extruded tube has finer grains (20 μm).

The Prediction of Microstructure Evolution of 6005A Aluminum Alloy in a P-ECAP Extrusion Study

NASA Astrophysics Data System (ADS)

Lei, Shi; Jiu-Ba, Wen; Chang, Ren

2018-04-01

Finite element modeling (FEM) was applied for predicting the recrystallized structure in extruded 6005 aluminum alloy, and simulated results were experimentally validated. First, microstructure evolution of 6005 aluminum alloy during deformation was studied by means of isothermal compression test, where the processing parameters were chosen to reproduce the typical industrial conditions. Second, microstructure evolution was analyzed, and the obtained information was used to fit a dynamic recrystallization model implementing inside the DEFORM-3D FEM code environment. FEM of deformation of 6005 aluminum has been established and validated by microstructure comparison. Finally, the obtained dynamic recrystallization model was applied to tube extrusion by using a portholes-equal channel angular pressing die. The finite element analysis results showed that coarse DRX grains occur in the extruded tube at higher temperature and in the extruded tube at the faster speed of the stem. The test results showed material from the front end of the extruded tube has coarse grains (60 μm) and other extruded tube has finer grains (20 μm).

Understanding the Effect of Grain Boundary Character on Dynamic Recrystallization in Stainless Steel 316L

NASA Astrophysics Data System (ADS)

Beck, Megan; Morse, Michael; Corolewski, Caleb; Fritchman, Koyuki; Stifter, Chris; Poole, Callum; Hurley, Michael; Frary, Megan

2017-08-01

Dynamic recrystallization (DRX) occurs during high-temperature deformation in metals and alloys with low to medium stacking fault energies. Previous simulations and experimental research have shown the effect of temperature and grain size on DRX behavior, but not the effect of the grain boundary character distribution. To investigate the effects of the distribution of grain boundary types, experimental testing was performed on stainless steel 316L specimens with different initial special boundary fractions (SBF). This work was completed in conjunction with computer simulations that used a modified Monte Carlo method which allowed for the addition of anisotropic grain boundary energies using orientation data from electron backscatter diffraction (EBSD). The correlation of the experimental and simulation work allows for a better understanding of how the input parameters in the simulations correspond to what occurs experimentally. Results from both simulations and experiments showed that a higher fraction of so-called "special" boundaries ( e.g., Σ3 twin boundaries) delayed the onset of recrystallization to larger strains and that it is energetically favorable for nuclei to form on triple junctions without these so-called "special" boundaries.

Orogen-scale along-strike continuity in quartz recrystallization microstructures adjacent to the Main Central Thrust: implications for deformation temperatures, strain rates and flow stresses

NASA Astrophysics Data System (ADS)

Law, Richard

2015-04-01

Traced for ~ 1500 km along the foreland edge of the Himalaya from NW India to Bhutan published reports indicate a remarkable along-strike continuity of quartz recrystallization microstructures in the footwall and hanging wall to the Main Central Thrust (MCT). Recrystallization in Lesser Himalayan Series (LHS) rocks in the footwall to the MCT is dominated by grain boundary bulging (BLG) microstructures, while recrystallization in Greater Himalayan Series (GHS) rocks in the hanging wall is dominated by grain boundary migration microstructures that traced structurally upwards transition in to the anatectic core of the GHS. In foreland-positioned high-strain rocks adjacent to the MCT recrystallization is dominated by subgrain rotation (SGR) with transitional BLG-SGR and SGR-GBM microstructures being recorded at structural distances of up to a few hundred meters below and above the MCT, respectively. Correlation with available information on temperatures of metamorphism indicated by mineral phase equilibria and RSCM data suggests that recrystallization in the structural zones dominated by BLG, SGR and GBM occurred at temperatures of ~ 350-450, 450-550 and 550- > 650 °C, respectively. It should be kept in mind, however, that these temperatures are likely to be 'close-to-peak' temperatures of metamorphism, whereas penetrative shearing and recrystallization may have continued during cooling. The dominance of SGR along the more foreland-positioned exposures of the MCT intuitively suggests that shearing occurred under a relatively restricted range of deformation temperatures and strain rates. Plotting the 'close-to-peak' 450-500 °C temperatures of metamorphism indicated for SGR-dominated rocks located at up to a few hundred meters below/above the MCT on the quartz recrystallization map developed by Stipp et al. (2002) indicates 'ball-park' strain rates of ~ 10-13 to 10-10 sec-1. However, only strain rates slower than 10-12 sec-1 on the MCT are likely to be compatible with know convergence rates between the Indian and Asian plates. If shearing continued during retrograde cooling while remaining in the SGR field, then the recrystallization map suggests that a significant drop in deformation temperature (> ~75-100 °C) would result in a decrease in strain rate. In general, however, the presence of a single recrystallization microstructure traced over a large (regional scale) distance does not necessarily mean that deformation temperature (or strain rate) remains constant but could, for example, indicate that spatial variations in deformation temperature are compensated for by changes in strain rate, with grain-scale deformation remaining within a particular recrystallization regime. Constant stress conditions plot along a straight line in the 1/T versus log strain rate space used in the quartz recrystallization mechanism map. This suggests that the observed along-strike consistency of SGR-dominated recrystallization microstructures may indicate near to constant stress boundary conditions (albeit with varying temperatures and strain rates) prevailing along what are now the more foreland-positioned exposures of the MCT. Extrapolation of the Hirth et al. (2001) flow law suggests a flow stress of ~ 30-50 MPa based on the deformation temperatures and strain rates inferred for foreland-positioned exposures of the MCT, in agreement with flow stresses estimated from recrystallized quartz grain size data.

Texture Development in a Friction Stir Lap-Welded AZ31B Magnesium Alloy

NASA Astrophysics Data System (ADS)

Naik, B. S.; Chen, D. L.; Cao, X.; Wanjara, P.

2014-09-01

The present study was aimed at characterizing the microstructure, texture, hardness, and tensile properties of an AZ31B-H24 Mg alloy that was friction stir lap welded (FSLWed) at varying tool rotational rates and welding speeds. Friction stir lap welding (FSLW) resulted in the presence of recrystallized grains and an associated hardness drop in the stir zone (SZ). Microstructural investigation showed that both the AZ31B-H24 Mg base metal (BM) and SZ contained β-Mg17Al12 and Al8Mn5 second phase particles. The AZ31B-H24 BM contained a type of basal texture (0001)<110> with the (0001) plane nearly parallel to the rolled sheet surface and <110> directions aligned in the rolling direction. FSLW resulted in the formation of another type of basal texture (0001)<100> in the SZ, where the basal planes (0001) became slightly tilted toward the transverse direction, and the prismatic planes (100) and pyramidal planes (101) exhibited a 30 deg + ( n - 1) × 60 deg rotation ( n = 1, 2, 3, …) with respect to the rolled sheet normal direction, due to the shear plastic flow near the pin surface that occurred from the intense local stirring. With increasing tool rotational rate and decreasing welding speed, the maximum intensity of the basal poles (0001) in the SZ decreased due to a higher degree of dynamic recrystallization that led to a weaker or more random texture. The tool rotational rate and welding speed had a strong effect on the failure load of FSLWed joints. A combination of relatively high welding speed (20 mm/s) and low tool rotational rate (1000 rpm) was observed to be capable of achieving a high failure load. This was attributed to the relatively small recrystallized grains and high intensity of the basal poles in the SZ arising from the low heat input as well as the presence of a small hooking defect.

A Geothermochronologic Investigation of the Coyote Mountains Metamorphic Core Complex (AZ)

NASA Astrophysics Data System (ADS)

Borel, M.; Gottardi, R.; Casale, G.

2017-12-01

The Coyote Mountains metamorphic core complex (CM-MCC) makes up the northern end of the Baboquivari Mountain complex, which is composed of Mesozoic rocks, Tertiary granites, pegmatites, and metasediments. The CM-MCC expose the Pan Tak granite, a 58 Ma intrusive muscovite-biotite-garnet peraluminous granite. The Pan Tak and other intrusions within the Baboquivari Mountains have been interpreted as anatectic melts representing the culmination of a Laramide crustal shortening orogenic event started in the Late Cretaceous ( 70 Ma). Evidence of this magmatic episode includes polysynthetic twinning in plagioclase, myrmekitic texture in alkali feldspars, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary tectonic fabric, associated with the exhumation of the CM-MCC along the Ajo road décollement and associated shear zone. In the shear zone, the Pan Tak mylonite display N-dipping foliation defined by gneissic layering and aligned muscovite, and N-trending mineral stretching lineation. Various shear sense indicators are all consistent with a top-to the-N shear sense. Preliminary argon geochronology results suggest that the shear zone was exhumed 29 Ma ago, an age similar to the onset of detachment faulting in other nearby MCCs (Catalina, Rincon, Pinaleño). In the Pan Tak mylonite, quartz grains display regime 2 to 3 microstructures and shows extensive recrystallization by subgrain rotation and grain boundary migration. The recrystallized grain size ranges between 20 and 50 µm in all samples. Quartz crystallographic preferred orientation measured using electron backscatter diffraction (EBSD) shows that recrystallization was accommodated by dominant prism and minor rhomb slip, suggesting deformation temperature ranging from 450°C to 550°C. These preliminary results constrain the timing of uplift and exhumation, and thermomechanical evolution of the CM-MCC, and improve our understanding of recycling of the continental crust in southern Arizona.

Investigation of primary static recrystallization in a NiTiFe shape memory alloy subjected to cold canning compression using the coupling crystal plasticity finite element method with cellular automaton

NASA Astrophysics Data System (ADS)

Zhang, Yanqiu; Jiang, Shuyong; Hu, Li; Zhao, Yanan; Sun, Dong

2017-10-01

The behavior of primary static recrystallization (SRX) in a NiTiFe shape memory alloy (SMA) subjected to cold canning compression was investigated using the coupling crystal plasticity finite element method (CPFEM) with the cellular automaton (CA) method, where the distribution of the dislocation density and the deformed grain topology quantified by CPFEM were used as the input for the subsequent SRX simulation performed using the CA method. The simulation results were confirmed by the experimental ones in terms of microstructures, average grain size and recrystallization fraction, which indicates that the proposed coupling method is well able to describe the SRX behavior of the NiTiFe SMA. The results show that the dislocation density exhibits an inhomogeneous distribution in the deformed sample and the recrystallization nuclei mainly concentrate on zones where the dislocation density is relatively higher. An increase in the compressive deformation degree leads to an increase in nucleation rate and a decrease in grain boundary spaces in the compression direction, which reduces the growth spaces for the SRX nuclei and impedes their further growth. In addition, both the mechanisms of local grain refinement in the incomplete SRX and the influence of compressive deformation degree on the grain size of SRX were vividly illustrated by the corresponding physical models.

Research on flow stress model and dynamic recrystallization model of X12CrMoWVNbN10-1-1 steel

NASA Astrophysics Data System (ADS)

Sui, Da-shan; Wang, Wei; Fu, Bo; Cui, Zhen-shan

2013-05-01

Plastic deformation behavior of X12CrMoWVNbN10-1-1 ferrite heat-resistant steel was studied systematically at high temperature. The stress-strain curves were measured at the temperature of 950°C-1250°C and strain rate of 0.0005s-1-0.1s-1 by Gleeble thermo-mechanical simulator. The flow stress model and dynamic recrystallization model were established based on Laasraoui two-stage model. The activation energy was calculated and the parameters were determined accordingly based on the experimental results and Sellars creep equation. The verification was performed to prove the models and it indicated the calculated results were identical to the experimental data.

Resistance spot welding of ultra-fine grained steel sheets produced by constrained groove pressing: Optimization and characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khodabakhshi, F.; Kazeminezhad, M., E-mail: mkazemi@sharif.edu; Kokabi, A.H.

2012-07-15

Constrained groove pressing as a severe plastic deformation method is utilized to produce ultra-fine grained low carbon steel sheets. The ultra-fine grained sheets are joined via resistance spot welding process and the characteristics of spot welds are investigated. Resistance spot welding process is optimized for welding of the sheets with different severe deformations and their results are compared with those of as-received samples. The effects of failure mode and expulsion on the performance of ultra-fine grained sheet spot welds have been investigated in the present paper and the welding current and time of resistance spot welding process according to thesemore » subjects are optimized. Failure mode and failure load obtained in tensile-shear test, microhardness, X-ray diffraction, transmission electron microscope and scanning electron microscope images have been used to describe the performance of spot welds. The region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. The results show that optimum welding parameters (welding current and welding time) for ultra-fine grained sheets are shifted to lower values with respect to those for as-received specimens. In ultra-fine grained sheets, one new region is formed named recrystallized zone in addition to fusion zone, heat affected zone and base metal. It is shown that microstructures of different zones in ultra-fine grained sheets are finer than those of as-received sheets. - Highlights: Black-Right-Pointing-Pointer Resistance spot welding process is optimized for joining of UFG steel sheets. Black-Right-Pointing-Pointer Optimum welding current and time are decreased with increasing the CGP pass number. Black-Right-Pointing-Pointer Microhardness at BM, HAZ, FZ and recrystallized zone is enhanced due to CGP.« less

Influence of warm rolling temperature on ferrite recrystallization in low C and IF steels

NASA Astrophysics Data System (ADS)

Barnett, Matthew Robert

Experiments involving single pass laboratory rolling and isothermal salt bath annealing were carried out; three steels were studied: a titanium stabilized interstitial free grade and two low carbon grades, one of which contained a particularly low level of manganese (˜0.009wt.%). The two low carbon grades were produced such that any complication from AlN precipitation was avoided. X-ray, neutron diffraction, optical metallography and mechanical testing measurements were carried out on the samples before and after annealing. The main aim of this work was to further the understanding of the metallurgy of recrystallization after ferrite rolling at temperatures between room temperature and 700sp°C. Deformation textures, recrystallization kinetics, final grain sizes and recrystallization textures were quantified for all the samples and experimental conditions. A major conclusion based on these data is that the influence of rolling temperature is far greater in the low carbon samples than in the IF grade. Indeed, the IF results alter only marginally with increasing temperature. In the low carbon grades, however, the rolling texture sharpens, recrystallization slows, the final grain size coarsens, and the recrystallization texture changes when the rolling temperature is increased. This distinct difference between the two steel types is explained in terms of their contrasting deformation behaviors. Solute carbon and nitrogen in the low carbon grades interact with dislocations causing high stored energy levels after low temperature rolling (due to dynamic strain aging) and high strain rate sensitivities during high temperature rolling (due to the solute drag of dislocations in the transition region between DSA and DRC). Nucleation during subsequent recrystallization is strongly influenced by both the stored energy and the strain rate sensitivity. The latter affects the occurrence of the flow localisations that enhance nucleation.

Microstructure Evolution during Dissimilar Friction Stir Welding of AA7003-T4 and AA6060-T4.

PubMed

Dong, Jialiang; Zhang, Datong; Zhang, Weiwen; Zhang, Wen; Qiu, Cheng

2018-02-27

In this work, the dissimilar joint of AA7003-T4 and 6060-T4 alloy has been produced by friction stir welding (FSW). The microstructure was examined by optical microscope (OM), electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and the mechanical properties of the joint were investigated. It is demonstrated that sound dissimilar joint can be produced through FSW. In the nugget; precipitations dissolve into the matrix and η' reprecipitate subsequently; and the elongated aluminum grains are replaced by fine and equiaxed grains due to dynamic recrystallization (DRX). In the heat affected zone (HAZ), coarse β' and η precipitates are formed and the aluminum grains are coarser as compared to the base materials. In the thermo-mechanical affected zone (TMAZ), equiaxed and elongated grains coexist due to incomplete DRX. The ultimate tensile strength of the dissimilar joint is 159.2 MPa and its elongation is 10.4%. The weak area exists in the HAZ of 6060 alloy, which is placed in the retreating side during FSW. The correlations between the microstucture and mechanical properties of the dissimilar joint are discussed.

Microstructure Evolution during Dissimilar Friction Stir Welding of AA7003-T4 and AA6060-T4

PubMed Central

Dong, Jialiang; Zhang, Datong; Zhang, Weiwen; Zhang, Wen; Qiu, Cheng

2018-01-01

In this work, the dissimilar joint of AA7003-T4 and 6060-T4 alloy has been produced by friction stir welding (FSW). The microstructure was examined by optical microscope (OM), electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and the mechanical properties of the joint were investigated. It is demonstrated that sound dissimilar joint can be produced through FSW. In the nugget; precipitations dissolve into the matrix and η′ reprecipitate subsequently; and the elongated aluminum grains are replaced by fine and equiaxed grains due to dynamic recrystallization (DRX). In the heat affected zone (HAZ), coarse β′ and η precipitates are formed and the aluminum grains are coarser as compared to the base materials. In the thermo-mechanical affected zone (TMAZ), equiaxed and elongated grains coexist due to incomplete DRX. The ultimate tensile strength of the dissimilar joint is 159.2 MPa and its elongation is 10.4%. The weak area exists in the HAZ of 6060 alloy, which is placed in the retreating side during FSW. The correlations between the microstucture and mechanical properties of the dissimilar joint are discussed. PMID:29495463

Combination of dynamic transformation and dynamic recrystallization for realizing ultrafine-grained steels with superior mechanical properties

PubMed Central

Zhao, Lijia; Park, Nokeun; Tian, Yanzhong; Shibata, Akinobu; Tsuji, Nobuhiro

2016-01-01

Dynamic recrystallization (DRX) is an important grain refinement mechanism to fabricate steels with high strength and high ductility (toughness). The conventional DRX mechanism has reached the limitation of refining grains to several microns even though employing high-strain deformation. Here we show a DRX phenomenon occurring in the dynamically transformed (DT) ferrite, by which the required strain for the operation of DRX and the formation of ultrafine grains is significantly reduced. The DRX of DT ferrite shows an unconventional temperature dependence, which suggests an optimal condition for grain refinement. We further show that new strategies for ultra grain refinement can be evoked by combining DT and DRX mechanisms, based on which fully ultrafine microstructures having a mean grain size down to 0.35 microns can be obtained without high-strain deformation and exhibit superior mechanical properties. This study will open the door to achieving optimal grain refinement to nanoscale in a variety of steels requiring no high-strain deformation in practical industrial application. PMID:27966603

Pioneering In Situ Recrystallization during Bead Milling: A Top-down Approach to Prepare Zeolite A Nanocrystals.

PubMed

Anand, Chokkalingam; Yamaguchi, Yudai; Liu, Zhendong; Ibe, Sayoko; Elangovan, Shanmugam P; Ishii, Toshihiro; Ishikawa, Tsuyoshi; Endo, Akira; Okubo, Tatsuya; Wakihara, Toru

2016-07-05

Top-down approach has been viewed as an efficient and straightforward method to prepare nanosized zeolites. Yet, the mechanical breaking of zeolite causes amorphization, which usually requires a post-milling recrystallization to obtain fully crystalline nanoparticles. Herein we present a facile methodology to prepare zeolite nanocrystals, where milling and recrystallization can be performed in situ. A milling apparatus specially designed to work under conditions of high alkalinity and temperature enables the in situ recrystallization during milling. Taking zeolite A as an example, we demonstrate its size reduction from ~3 μm to 66 nm in 30 min, which is quite faster than previous methods reported. Three functions, viz., miniaturization, amorphization and recrystallization were found to take effect concurrently during this one-pot process. The dynamic balance between these three functions was achieved by adjusting the milling period and temperature, which lead to the tuning of zeolite A particle size. Particle size and crystallinity of the zeolite A nanocrystals were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and water adsorption-desorption. This work presents a pioneering advancement in this field of nanosized zeolites, and will facilitate the mass production as well as boost the wide applications of nanosized zeolites.

Pioneering In Situ Recrystallization during Bead Milling: A Top-down Approach to Prepare Zeolite A Nanocrystals

PubMed Central

Anand, Chokkalingam; Yamaguchi, Yudai; Liu, Zhendong; Ibe, Sayoko; Elangovan, Shanmugam P.; Ishii, Toshihiro; Ishikawa, Tsuyoshi; Endo, Akira; Okubo, Tatsuya; Wakihara, Toru

2016-01-01

Top-down approach has been viewed as an efficient and straightforward method to prepare nanosized zeolites. Yet, the mechanical breaking of zeolite causes amorphization, which usually requires a post-milling recrystallization to obtain fully crystalline nanoparticles. Herein we present a facile methodology to prepare zeolite nanocrystals, where milling and recrystallization can be performed in situ. A milling apparatus specially designed to work under conditions of high alkalinity and temperature enables the in situ recrystallization during milling. Taking zeolite A as an example, we demonstrate its size reduction from ~3 μm to 66 nm in 30 min, which is quite faster than previous methods reported. Three functions, viz., miniaturization, amorphization and recrystallization were found to take effect concurrently during this one-pot process. The dynamic balance between these three functions was achieved by adjusting the milling period and temperature, which lead to the tuning of zeolite A particle size. Particle size and crystallinity of the zeolite A nanocrystals were confirmed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and water adsorption-desorption. This work presents a pioneering advancement in this field of nanosized zeolites, and will facilitate the mass production as well as boost the wide applications of nanosized zeolites. PMID:27378145

Gas tungsten arc welding and friction stir welding of ultrafine grained AISI 304L stainless steel: Microstructural and mechanical behavior characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabooni, S., E-mail: s.sabooni@ma.iut.ac.ir; Karimzadeh, F.; Enayati, M.H.

In the present study, an ultrafine grained (UFG) AISI 304L stainless steel with the average grain size of 650 nm was successfully welded by both gas tungsten arc welding (GTAW) and friction stir welding (FSW). GTAW was applied without any filler metal. FSW was also performed at a constant rotational speed of 630 rpm and different welding speeds from 20 to 80 mm/min. Microstructural characterization was carried out by High Resolution Scanning Electron Microscopy (HRSEM) with Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). Nanoindentation, microhardness measurements and tensile tests were also performed to study the mechanical properties ofmore » the base metal and weldments. The results showed that the solidification mode in the GTAW welded sample is FA (ferrite–austenite) type with the microstructure consisting of an austenite matrix embedded with lath type and skeletal type ferrite. The nugget zone microstructure in the FSW welded samples consisted of equiaxed dynamically recrystallized austenite grains with some amount of elongated delta ferrite. Sigma phase precipitates were formed in the region ahead the rotating tool during the heating cycle of FSW, which were finally fragmented into nanometric particles and distributed in the weld nugget. Also there is a high possibility that the existing delta ferrite in the microstructure rapidly transforms into sigma phase particles during the short thermal cycle of FSW. These suggest that high strain and deformation during FSW can promote sigma phase formation. The final austenite grain size in the nugget zone was found to decrease with increasing Zener–Hollomon parameter, which was obtained quantitatively by measuring the peak temperature, calculating the strain rate during FSW and exact examination of hot deformation activation energy by considering the actual grain size before the occurrence of dynamic recrystallization. Mechanical properties observations showed that the welding efficiency of the FSW welded sample is around 70%, which is more than 20% higher than the GTAW welded sample. - Highlights: • Microstructure and mechanical properties of UFG 304L stainless steel were studied during GTAW and FSW. • Sigma phase formation mechanism was studied during FSW of 304L stainless steel. • THERMOCALC analysis was performed to obtain possible formation temperatures for sigma phase. • Nano-mechanical twins were found in the TMAZ region.« less

Dynamic recrystallization during deformation of polycrystalline ice: insights from numerical simulations

PubMed Central

Griera, Albert; Steinbach, Florian; Bons, Paul D.; Jansen, Daniela; Roessiger, Jens; Lebensohn, Ricardo A.

2017-01-01

The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice crystals that have hexagonal symmetry (ice lh). To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallization (DRX) controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with DRX of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless of the amount of DRX and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localization occurs in all simulations, especially in simple shear cases. Recrystallization suppresses localization, which necessitates the activation of hard, non-basal slip systems. This article is part of the themed issue ‘Microdynamics of ice’. PMID:28025295

The effect of deformation temperature on the microstructure evolution of Inconel 625 superalloy

NASA Astrophysics Data System (ADS)

Guo, Qingmiao; Li, Defu; Guo, Shengli; Peng, Haijian; Hu, Jie

2011-07-01

Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 °C and 1200 °C with different true strains and a strain rate of 0.1 s -1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of deformation temperature on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of deformation temperatures on the nucleation mechanisms of DRX are observed at different deformation stages. At lower deformation temperatures, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early deformation stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later deformation stage. At higher deformation temperatures, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early deformation stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the deformation temperature, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.

Dynamic recrystallization during deformation of polycrystalline ice: insights from numerical simulations.

PubMed

Llorens, Maria-Gema; Griera, Albert; Steinbach, Florian; Bons, Paul D; Gomez-Rivas, Enrique; Jansen, Daniela; Roessiger, Jens; Lebensohn, Ricardo A; Weikusat, Ilka

2017-02-13

The flow of glaciers and polar ice sheets is controlled by the highly anisotropic rheology of ice crystals that have hexagonal symmetry (ice lh). To improve our knowledge of ice sheet dynamics, it is necessary to understand how dynamic recrystallization (DRX) controls ice microstructures and rheology at different boundary conditions that range from pure shear flattening at the top to simple shear near the base of the sheets. We present a series of two-dimensional numerical simulations that couple ice deformation with DRX of various intensities, paying special attention to the effect of boundary conditions. The simulations show how similar orientations of c-axis maxima with respect to the finite deformation direction develop regardless of the amount of DRX and applied boundary conditions. In pure shear this direction is parallel to the maximum compressional stress, while it rotates towards the shear direction in simple shear. This leads to strain hardening and increased activity of non-basal slip systems in pure shear and to strain softening in simple shear. Therefore, it is expected that ice is effectively weaker in the lower parts of the ice sheets than in the upper parts. Strain-rate localization occurs in all simulations, especially in simple shear cases. Recrystallization suppresses localization, which necessitates the activation of hard, non-basal slip systems.This article is part of the themed issue 'Microdynamics of ice'. © 2016 The Author(s).

New Insights on the Recrystallization and New Growth of Extensively Radiation-damaged Zircon

NASA Astrophysics Data System (ADS)

Hanchar, J. M.; Schmitz, M. D.; Wirth, R.

2012-12-01

Approximately 10 grams of cm-sized nearly metamict zircon crystals from the Saranac Prospect in the Bancroft District of Ontario were combined by breaking into small pieces and then ground under ethanol to a fine powder with an agate mortar and pestle in order to make enough homogeneously mixed material for multiple powder X-Ray and diffraction scans, high-resolution transmission electron microscopy (HR-TEM) measurements, and chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-TIMS). While these large zircon crystals ground to a powder have a larger surface area and not in the same physical state (i.e., brown and metamict) as what is typically analyzed in single zircon CA-ID-TIMS U-Pb analysis (clear euhedral grains), the physical and chemical changes that occur during the heat treatment used in CA-TIMS are thought to be similar processes. Aliquots of the ground zircon powder were annealed in situ using a Pt furnace in a powder diffractometer during which time simultaneous powder diffraction patterns were acquired starting at 25°C, at elevated temperature (from 500°C to 1400°C) at selected time intervals, and then again at 25°C. The powder X-ray diffraction results indicate that below ~900°C the recrystallization of the zircon powder commences but is incomplete, even after 36 hours, with diffuse low intensity diffraction peaks. At 1150°C the zircon powder shows significant recrystallization. At 1150°C, the recrystallization is essentially complete in less than one hour. Before heating the zircon powder samples consisted of clear, transparent to brown, translucent, complexly zoned fragments. After heating at 900°C the zircon powder retained a smaller percentage of clear or brown complexly zoned fragments, while the majority of material had transformed to oscillatory or irregularly zoned, dominantly white opaque microcrystalline fragments. The clear fragments were hypothesized to be preexisting original crystalline zircon, the brown complexly zoned fragments preexisting metamict zircon, and the white opaque fragment new recrystallized zircon and other oxides. At 1150°C all that remained after heating were dominantly white opaque fragments and extremely rare clear fragments. A variety of fragment types from unannealed, 900°C and 1150°C anneals were chemically abraded in concentrated hydrofluoric acid at 190°C for 12 hours. Upon treatment with chemical abrasion, all unannealed material, nearly all material from the 900°C anneal, and all white opaque microcrystalline material from the 1150°C anneal dissolved; only the rare residual clear, transparent fragments from the 1150°C anneal were robust to chemical abrasion at these conditions. Residual clear fragments yielded concordant U-Pb ID-TIMS dates of 1064 Ma (considering updated U decay constant ratio), confirming the hypothesis that low-U closed system domains are preserved through annealing up to 1150°C and can be extracted via chemical abrasion from even dominantly metamict zircon crystals. By contrast, newly formed crystallites resulting from metamict zircon breakdown during annealing appear to be quite soluble during chemical abrasion. Further experiments are underway to refine minimum threshold chemical abrasion conditions necessary to eliminate open-system domains in the Saranac zircon.

Multi-scale strain localization within orthogneiss during subduction and exhumation (Tenda unit, Alpine Corsica)

NASA Astrophysics Data System (ADS)

Beaudoin, Alexandre; Augier, Romain; Jolivet, Laurent; Raimbourg, Hugues; Jourdon, Anthony; Scaillet, Stéphane; Cardello, Giovanni Luca

2016-04-01

Strain localization depends upon scale-related factors resulting in a gap between small-scale studies of deformation mechanisms and large-scale numerical and tectonic models. The former often ignore the variations in composition and water content across tectonic units, while the latter oversimplify the role of the deformation mechanisms. This study aims to heal this gap, by considering microstructures and strain localization not only at a single shear zone-scale but across a 40km-wide tectonic unit and throughout its complex polyphased evolution. The Tenda unit (Alpine Corsica) is an external continental unit mainly composed of granites, bounded by the East Tenda Shear Zone (ETSZ) that separates it from the overlying oceanic-derived HP tectonic units. Previous studies substantially agreed on (1) the burial of the Tenda unit down to blueschist-facies conditions associated with top-to-the-west shearing (D1) and (2) subsequent exhumation accommodated by a localized top-to-the-east shear zone (D2). Reaction-softening is the main localizing mechanism proposed in the literature, being associated with the transformation of K-feldspar into white-mica. In this work, the Tenda unit is reviewed through (1) the construction of a new field-based strain map accompanied by cross-sections representing volumes of rock deformed at different grades related to large-scale factors of strain localization and (2) the structural study of hand-specimens and thin-sections coupled with EBSD analysis in order to target the deformation processes. We aim to find how softening and localization are in relation to the map-scale distribution of strain. The large-scale study shows that the whole Tenda unit is affected by the two successive stages of deformation. However, a more intense deformation is observed along the eastern margin, which originally led to the definition of the ETSZ, with a present-day anastomosed geometry of deformation. Strain localization is clearly linked to rheological/lithological contrasts as it concentrates either along preexisting intrusive and tectonic contacts. As K-feldspar-poor granites remain relatively undeformed, reaction-softening seems to be a major mechanism during D1. However, evidences suggest that this mechanism is in competition with dynamic recrystallization: at outcrop and hand-specimen scale, the correlation between localized structures such as C-planes and phengite-rich zones is not always observed. This same competition remains active during D2 where top-to-the-east C-planes are common in phengite-rich layers, but an overall grain-size reduction is also observed across the different strain grades, suggesting that dynamic recrystallization remains active during the whole story. Final localization is sometimes observed in phengite-poor aplitic ultramylonites characterized by a very fine quartz-albite matrix suggesting that grain-size sensitive flow would be the major mechanism involved in the final rheology of the ETSZ.

Determination of Dynamic Recrystallization Process by Equivalent Strain

NASA Astrophysics Data System (ADS)

Qin, Xiaomei; Deng, Wei

Based on Tpнoвckiй's displacement field, equivalent strain expression was derived. And according to the dynamic recrystallization (DRX) critical strain, DRX process was determined by equivalent strain. It was found that equivalent strain distribution in deformed specimen is inhomogeneous, and it increases with increasing true strain. Under a certain true strain, equivalent strains at the center, demisemi radius or on tangential plane just below the surface of the specimen are higher than the true strain. Thus, micrographs at those positions can not exactly reflect the true microstructures under the certain true strain. With increasing strain rate, the initial and finish time of DRX decrease. The frozen microstructures of 20Mn23AlV steel with the experimental condition validate the feasibility of predicting DRX process by equivalent strain.

Geology of the Biwabik Iron Formation and Duluth Complex.

PubMed

Jirsa, Mark A; Miller, James D; Morey, G B

2008-10-01

The Biwabik Iron Formation is a approximately 1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by approximately 1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact.

Effects of Preprocessing on Multi-Direction Properties of Aluminum Alloy Cold-Spray Deposits

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nardi, A. T.; Champagne, V. K.; Nutt, S. R.

2018-05-01

The effects of powder preprocessing (degassing at 400 °C for 6 h) on microstructure and mechanical properties of 5056 aluminum deposits produced by high-pressure cold spray were investigated. To investigate directionality of the mechanical properties, microtensile coupons were excised from different directions of the deposit, i.e., longitudinal, short transverse, long transverse, and diagonal and then tested. The results were compared to properties of wrought 5056 and the coating deposited with as-received 5056 Al powder and correlated with the observed microstructures. Preprocessing softened the particles and eliminated the pores within them, resulting in more extensive and uniform deformation upon impact with the substrate and with underlying deposited material. Microstructural characterization and finite element simulation indicated that upon particle impact, the peripheral regions experienced more extensive deformation and higher temperatures than the central contact zone. This led to more recrystallization and stronger bonding at peripheral regions relative to the contact zone area and yielded superior properties in the longitudinal direction compared with the short transverse direction. Fractography revealed that crack propagation takes place along the particle-particle interfaces in the transverse directions (caused by insufficient bonding and recrystallization), whereas through the deposited particles, fracture is dominant in the longitudinal direction.

Geology of the Biwabik Iron Formation and Duluth Complex

USGS Publications Warehouse

Jirsa, M.A.; Miller, J.D.; Morey, G.B.

2008-01-01

The Biwabik Iron Formation is a ???1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by ???1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. ?? 2007 Elsevier Inc. All rights reserved.

Paleozoic-Mesozoic boundary in the Berry Creek Quadrangle, northwestern Sierra Nevada, California

USGS Publications Warehouse

Hietanen, Anna Martta

1977-01-01

Structural and petrologic studies in the Berry Creek quadrangle at the north end of the western metamorphic belt of the Sierra Nevada have yielded new information that helps in distinguishing between the chemically similar Paleozoic and Mesozoic rocks. The distinguishing features are structural and textural and result from different degrees of deformation. Most Paleozoic rocks are strongly deformed and thoroughly recrystallized. Phenocrysts in meta volcanic rocks are granulated and drawn out into lenses that have sutured outlines. In contrast, the phenocrysts in the Mesozoic metavolcanic rocks show well-preserved straight crystal faces, are only slightly or not at all granulated, and contain fewer mineral inclusions than do those in the Paleozoic rocks. The groundmass in the Paleozoic rocks is recrystallized to a fairly coarse grained albite-epidote-amphibole-chlorite rock, whereas in the Mesozoic rocks the groundmass is a very fine grained feltlike mesh with only spotty occurrence of well-recrystallized finegrained albite-epidote-chlorite-actinolite rock. Primary minerals, such as augite, are locally preserved in the Mesozoic rocks but are altered to a mixture of amphibole, chlorite, and epidote in the Paleozoic rocks. In the contact aureoles of the plutons, and within the Big Bend fault zone, which crosses the area parallel to the structural trends, all rocks are thoroughly recrystallized and strongly deformed. Identification of the Paleozoic and Mesozoic rocks in these parts of the area was based on the continuity of the rock units in the field and on gradual changes in microscopic textures toward the plutons.

Geochemistry of speleothems affected by aragonite to calcite recrystallization - Potential inheritance from the precursor mineral

NASA Astrophysics Data System (ADS)

Domínguez-Villar, David; Krklec, Kristina; Pelicon, Primož; Fairchild, Ian J.; Cheng, Hai; Edwards, Lawrence R.

2017-03-01

Formerly aragonite speleothems recrystallized to calcite result from solutions subsaturated in aragonite and supersaturated in calcite that infiltrate into the speleothem through the interconnected porosity. In most cases, the crystal replacement takes place through a thin solution film. This diagenetic process can occur under open or semi-closed geochemical conditions. Thus, secondary calcite crystals record the composition of the fluid at the time of diagenesis affected by calcite partition coefficients and fractionation factors (open system) or partly inherit the composition of the primary aragonite (semi-closed system). So, whether or not recrystallized aragonite speleothems can record reliable geochemical signals from the time of speleothem primary deposition still is an open debate. We studied a stalagmite from Eagle Cave (Spain) predominantly composed of secondary calcite that replaced aragonite, although a core of primary aragonite extending 45 mm along the growth direction was preserved at the base of the sample. We obtained Mg and Sr compositional maps, paired U-Th dating and δ18O and δ13C profiles across the diagenetic front. Additionally, two parallel isotope records were obtained along the speleothem growth direction in the aragonite and calcite sectors. Our results support that recrystallization of this speleothem took place in open system conditions for δ18O, δ13C, Mg and Sr, but in semi-closed system conditions for U and Th. The recrystallization of this sample took place during one or several events, likely after the Younger Dryas as a result of climate change influencing drip water composition. Based on compositional zoned patterns, we suggest that the advance of diagenetic fronts in this speleothem had an average rate of 50 ± 45 μm/yr. Such recrystallization rate can transform any aragonite speleothem into calcite within a few centuries. We suggest that the volume of water interacting with the speleothem at the time of recrystallization is of critical importance for inheritance of different elements. The volume of solution is controlled by (1) the discharge of water passing through the sample and (2) the lapse time between aragonite dissolution and calcite precipitation. Hydrology and hydrochemistry of the interacting solution, together with the mineralogy and texture of the speleothem are the essential controls for the diagenesis of the speleothem. Recrystallization of aragonite speleothems does not follow stratigraphical levels of the sample but occurs along sites with preferential flow paths in any sector of the speleothem. In these cases the relationship between age and distance from base is not preserved. However, alternation of periods of recrystallization with periods of aragonite precipitation causing speleothem accretion can result in recrystallized speleothems with coherent distance from the base-age relationship. Thus, early diagenesis of speleothems affected by seasonal or inter-annual oscillation of drip waters supersaturated and subsaturated in aragonite may provide best-scenario conditions for dating and preservation of paleoenvironmental records along recrystallized speleothems. However, even in this scenario, the variable discharge and the diagenetic rate control the geochemical inheritance from the primary aragonite crystals.

Migmatites to mylonites - Crustal deformation mechanisms in the Western Gneiss Region, Norway

NASA Astrophysics Data System (ADS)

Lee, A. L.; Torvela, T.; Lloyd, G. E.; Walker, A.

2016-12-01

Strain and fluids localise into shear zones while crustal blocks remain comparatively dry, rigid and deform less. However when H2O is present in the crustal blocks they start to melt, deformation becomes more distributed and is no longer strongly localised into the weak shear zones. Using examples from the Western Gneiss Region (WGR), Norway, we show the deformation characteristics when mylonitic shear zones and migmatites coexist. The WGR is the lowest structural level of the Caledonian Orogeny, exposing Silurian to Devonian metamorphism and deformation of the Precambrian crust. WGR is predominantly composed of amphibolite-facies quartzofeldspathic gneiss that has undergone partial melting. This study focuses on the southwestern peninsula of the island of Gurskøy. Over a 1.2 kilometre section there is a diverse deformation sequence of migmatized gneiss, mylonitic shear zones, sillimanite bearing garnet-mica schists, augen gneiss and boudinaged amphibolite dykes resulting in a large competence differences between the lithologies over the area. The strongly deformed mylonitic shear zones extend from 5 to over 100 meters in width, but deformation is also high in the migmatitic layers as shown from S-C fabrics and isoclinal folding of leucratic and restitic layers. Microstructural evidence of dynamic recrystallization, symplectite textures and magmatic flow show deformation is widespread over the peninsula. Strain localisation, melting, and their interactions are shown by a combination of outcrop and quantitative modelling that uses field data, microstructural analysis, crystallographic preferred orientations and numerical Eshelby modelling. Detailed field mapping and microstructural analysis of samples from across the peninsula allows melt quantification and thus an understanding of strain mechanisms when melt is present. This area is important as it shows the heterogeneity of deformation within the partially melted lower crust on the sub-seismic scale.

Shape Fixing via Salt Recrystallization: A Morphology-Controlled Approach To Convert Nanostructured Polymer to Carbon Nanomaterial as a Highly Active Catalyst for Oxygen Reduction Reaction.

PubMed

Ding, Wei; Li, Li; Xiong, Kun; Wang, Yao; Li, Wei; Nie, Yao; Chen, Siguo; Qi, Xueqiang; Wei, Zidong

2015-04-29

Herein, we report a "shape fixing via salt recrystallization" method to efficiently synthesize nitrogen-doped carbon material with a large number of active sites exposed to the three-phase zones, for use as an ORR catalyst. Self-assembled polyaniline with a 3D network structure was fixed and fully sealed inside NaCl via recrystallization of NaCl solution. During pyrolysis, the NaCl crystal functions as a fully sealed nanoreactor, which facilitates nitrogen incorporation and graphitization. The gasification in such a closed nanoreactor creates a large number of pores in the resultant samples. The 3D network structure, which is conducive to mass transport and high utilization of active sites, was found to have been accurately transferred to the final N-doped carbon materials, after dissolution of the NaCl. Use of the invented cathode catalyst in a proton exchange membrane fuel cell produces a peak power of 600 mW cm(-2), making this among the best nonprecious metal catalysts for the ORR reported so far. Furthermore, N-doped carbon materials with a nanotube or nanoshell morphology can be realized by the invented method.

Large-scale recrystallization of the S-layer of Bacillus coagulans E38-66 at the air/water interface and on lipid films.

PubMed Central

Pum, D; Weinhandl, M; Hödl, C; Sleytr, U B

1993-01-01

S-layer protein isolated from Bacillus coagulans E38-66 could be recrystallized into large-scale coherent monolayers at an air/water interface and on phospholipid films spread on a Langmuir-Blodgett trough. Because of the asymmetry in the physiochemical surface properties of the S-layer protein, the subunits were associated with their more hydrophobic outer face with the air/water interface and oriented with their negatively charged inner face to the zwitterionic head groups of the dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine (DPPE) monolayer films. The dynamic crystal growth at both types of interfaces was first initiated at several distant nucleation points. The individual monocrystalline areas grew isotropically in all directions until the front edge of neighboring crystals was met. The recrystallized S-layer protein and the S-layer-DPPE layer could be chemically cross-linked from the subphase with glutaraldehyde. Images PMID:8478338

Structure and mechanical properties of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation by high-pressure torsion

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-04-01

The structural and phase transformations have been studied in aging commercial aluminum-lithium alloy Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg in the as-delivered state and after severe plastic deformation by torsion for 1, 5 and 10 revolutions under a high pressure of 4 GPa. Deformation-induced nanofragmentation and dynamic recrystallization have been found to occur in the alloy. The degree of recrystallization increases with deformation. Nanofragmentation and recrystallization processes are accompanied by the deformation-induced decomposition of solid solution and changes in both the nucleation mechanism of precipitation and the phase composition of the alloy. The influence of a nanostructured nanophase state of the alloy on its mechanical properties (microhardness, plasticity, elastic modulus, and stiffness) is discussed.

Early Cretaceous Ductile Deformation of Marbles from the Western Hills of Beijing, North China Craton

NASA Astrophysics Data System (ADS)

Feng, H.; Liu, J.

2017-12-01

During the Early Cretaceous tectonic lithosphere extension, the pre-mesozoic rocks from the Western Hills in the central part of the North China Craton suffered from weak metamorphism but intense shear deformation. The prominent features of the deformation structures are the coexisting layer-parallel shear zones and intrafolia folds, and the along-strike thickness variations of the marble layers from the highly sheared Mesoproterozoic Jing'eryu Formation. Platy marbles are well-developed in the thinner layers, while intrafolia folds are often observed in the thicker layers. Most folds are tight recumbent folds and their axial planes are parallel to the foliations and layerings of the marbles. The folds are A-type folds with hinges being always paralleling to the stretching lineations consistently oriented at 130°-310° directions throughout the entire area. SPO and microstructural analyses of the sheared marbles suggest that the thicker layers suffered from deformations homogeneously, while strain localization can be distinguished in the thinner layers. Calcite twin morphology and CPO analysis indicate that the deformation of marbles from both thinner and thicker layers happened at temperatures of 300 to 500°C. The above analysis suggests that marbles in the thicker layers experienced a progressive sequence of thermodynamic events: 1) regional metamorphism, 2) early ductile deformation dominated by relatively higher temperature conditions, during which all the mineral particles elongated and oriented limitedly and the calcite grains are deformed mainly by mechanical twinning, and 3) late superimposition of relatively lower temperature deformation and recrystallization, which superposed the early deformation, and made the calcites finely granulated, elongated and oriented by dynamical recrystallization along with other grains. Marbles from the thinner layers, however, experienced a similar, but different sequence of thermo-dynamic events, i.e. regional metamorphism, early ductile deformation and weak superimposition by subsequent deformation, which caused the development of the strain localization. It is also shown that the intensity of progressive superimposition deformation contributed to the thinning and thickening of the marble layers.

Constraints on strain rate and fabric partitioning in ductilely deformed black quartzites (Badajoz-Córdoba Shear Zone, Iberian Massif)

NASA Astrophysics Data System (ADS)

Puelles, Pablo; Ábalos, Benito; Fernández-Armas, Sergio

2013-04-01

The Badajoz-Córdoba Shear Zone is a is 30-40 km wide and 400 km long, NW-SE trending structure located at the boundary between the Ossa-Morena and Central-Iberian Zones of the Iberian Massif. Two elongated domains can be differentiated inside: the Obejo-Valsequillo domain to the NE and the Ductile Shear Belt (DSB) to the SW. The former exhibits Precambrian to Cambrian volcano-sedimentary rocks unconformably overlaying a Neoproterozoic basement formed by the "Serie Negra". The latter, 5-15 km wide, is composed mainly of metamorphic tectonites including the "Serie Negra" and other units located structurally under it. The petrofabric of "Serie Negra" black quartzites from the DSB is analyzed in this study with the Electron Back-Scattered Diffraction technique (EBSD). Black quartzites represent originally siliceous, chemical-biochemical shallow-water marine deposits, currently composed almost exclusively of quartz and graphite. Macroscopically they exhibit an outstanding planolinear tectonic fabric. Petrographically, coarse- and fine-grained dynamically recrystallized quartz bands alternate. The former contain quartz grains with irregular shapes, mica inclusions and "pinning" grain boundaries. Oriented mica grains and graphite particles constrain irregular quartz grain shapes. Quartz ribbons with chessboard microstructures also occur, indicating recrystallization under elevated temperatures coeval with extreme stretching. Fine-grained recrystallized quartz bands are dominated by quartz grains with straight boundaries, triple junctions, a scarcer evidence of bulging, and a higher concentration of dispersed, minute graphite grains. Quartz lattice-preferred orientation (LPO) patterns permit to identify two well-developed maxima for [c] axes: one close to the Y structural direction and the other one around Z, and -axes girdles normal to Y and Z. Although both [c] axis maxima appear in the coarse- and fine-grained bands, subsets can be isolated with grain cluster orientations around Y and Z. Quartz [c]-axis orientations close to Y predominate in coarser-grained bands, whereas [c]-axes scatter around Z in fine-grained zones. A relationship between microstructure and crystal orientation can thus be unraveled. In both fabric types the asymmetry of the LPOs with respect to the external XYZ reference unravel non-coaxial deformation components. Microstructural and LPO evidences indicate that two intracrystalline quartz deformation modes have operated in the "Serie Negra" black quartzites in parallel domains interleaved at the mm- to cm scale. Unless one of them took place under higher-temperature conditions ({m} slip in the high-T amphibolite-facies) and is a relic feature, both modes should have operated simultaneously. Thus, high-temperature boundary migration and the dispersed inclusion pattern of small mica and graphite grains constrained the pinning grain boundary microstructures, the {m} intracrystalline slip, and the larger size of some quartz crystals. Simultaneously, a larger concentration of disseminated graphite led to formation of finer-grained quartz aggregates (due to grain growth) deformed by the (0001) intracrystalline slip systems, that dominate lower-T quartz plasticity (under greenschist- to amphibolite-facies conditions). Arguably, this intracrystalline slip system partitioning was initially constrained by primary variations in inclusion concentration. Likely, these induced a domainal variation in the rate of plastic strain accommodation that led to the current banded microstructural and fabric organization.

Influence of the Starting Microstructure on the Hot Deformation Behavior of a Low Stacking Fault Energy Ni-based Superalloy

NASA Astrophysics Data System (ADS)

McCarley, Joshua; Alabbad, B.; Tin, S.

2018-03-01

The influence of varying fractions of primary gamma prime precipitates on the hot deformation and annealing behavior of an experimental Nickel-based superalloy containing 24 wt pct. Co was investigated. Billets heat treated at 1110 °C or 1135 °C were subjected to hot compression tests at temperatures ranging from 1020 °C to 1060 °C and strain rates ranging from 0.001 to 0.1/s. The microstructures were characterized using electron back scatter diffraction in the as-deformed condition as well as following a super-solvus anneal heat treatment at 1140 °C for 1 hour. This investigation sought to quantify and understand what effect the volume fraction of primary gamma prime precipitates has on the dynamic recrystallization behavior and resulting length fraction ∑3 twin boundaries in the low stacking fault superalloy following annealing. Although deformation at the lower temperatures and higher strain rates led to dynamic recrystallization for both starting microstructures, comparatively lower recrystallized fractions were observed in the 1135 °C billet microstructures deformed at strain rates of 0.1/s and 0.05/s. Subsequent annealing of the 1135 °C billet microstructures led to a higher proportion of annealing twins when compared to the annealed 1110 °C billet microstructures.

Dynamic Recrystallization Kinetics of 690 Alloy During Hot Compression of Double-Cone Samples

NASA Astrophysics Data System (ADS)

Wang, Jue; Zhai, Shun-Chao

2017-03-01

Hot compression tests of double-cone samples were conducted for 690 alloy to study the kinetic behavior of the complete dynamic recrystallization (DRX) process under low deformation temperatures from 960 to 1080 °C. The microstructure of 82 points in the vertical section of every deformed sample was quantitatively analyzed to determine the DRX fraction. Corresponding strain of these points was calculated by finite element simulations. Kinetic curves of the specimens with different preheating temperatures were then constructed. The features of various boundaries with different misorientation angles were investigated by electron backscatter diffraction technology and transmission electron microscope. The results showed that the strain is continuously and symmetrically distributed along the centerline of the vertical section. Large strain of 1.84 was obtained when the compression amount is 12 mm for double-cone samples. All the fitted kinetic curves display an "S" type, which possess a low growth rate of DRX at the beginning and the end of compression. The critical strain of recrystallization decreases with the increase in preheating temperature, while the completion strain remains around 1.5 for all the samples. The initial and maximum growth rates of DRX fraction have the opposite trend with the change in temperature, which is considered to be attributed to the behaviors of different misorientation boundaries.

Microstructural Evolution and Local Mechanical Properties of Friction Stir Processed Mg-3Gd-1Zn Cast Alloy

NASA Astrophysics Data System (ADS)

Sabbaghian, M.; Mahmudi, R.

2016-05-01

Microstructural evolution, hardness, and shear strength of the cast plates of GZ31 magnesium alloy were investigated after friction stir processing (FSP). Due to severe plastic deformation and dynamic recrystallization, FSP breaks the dendrites and results in a fine homogenous structure in the stirred zone (SZ) having average grain sizes of about 4.0 and 2.5 μm in the one and two-pass FSPed plates, respectively. As a novel approach, strength of the processed plates was examined by shear punch testing in three regions of the SZ on the surface layer, namely, center line (CL), retreating side (RS), and advancing side (AS). FSP showed great potential in the enhancement of SZ ultimate shear strength from 114 to about 152 and 155 MPa in the one and two-pass FSPed materials, respectively. The same trend was observed in hardness values of the SZ, where the average hardness of the base material increased from 41 to 60 and 68 Vickers after one and two passes of FSP, respectively. The variations in the shear strength of the CL, RS, and AS zones of the SZ were about 5% for the first pass of FSP, the effect which was decreased to less than 2% after two passes of FSP.

Comparison between different techniques applied to quartz CPO determination in granitoid mylonites

NASA Astrophysics Data System (ADS)

Fazio, Eugenio; Punturo, Rosalda; Cirrincione, Rosolino; Kern, Hartmut; Wenk, Hans-Rudolph; Pezzino, Antonino; Goswami, Shalini; Mamtani, Manish

2016-04-01

Since the second half of the last century, several techniques have been adopted to resolve the crystallographic preferred orientation (CPO) of major minerals constituting crustal and mantle rocks. To this aim, many efforts have been made to increase the accuracy of such analytical devices as well as to progressively reduce the time needed to perform microstructural analysis. It is worth noting that many of these microstructural studies deal with quartz CPO because of the wide occurrence of this mineral phase in crustal rocks as well as its quite simple chemical composition. In the present work, four different techniques were applied to define CPOs of dynamically recrystallized quartz domains from naturally deformed rocks collected from a ductile crustal scale shear zone in order to compare their advantages and limitation. The selected Alpine shear zone is located in the Aspromonte Massif (Calabrian Peloritani Orogen, southern Italy) representing granitoid lithotypes. The adopted methods span from "classical" universal stage (US), to image analysis technique (CIP), electron back-scattered diffraction (EBSD), and time of flight neutron diffraction (TOF). When compared, bulk texture pole figures obtained by means of these different techniques show a good correlation. Advances in analytical techniques used for microstructural investigations are outlined by discussing results of quartz CPO that are presented in this study.

Rapid solidification and dynamic compaction of Ni-base superalloy powders

NASA Technical Reports Server (NTRS)

Field, R. D.; Hales, S. J.; Powers, W. O.; Fraser, H. L.

1984-01-01

A Ni-base superalloy containing 13Al-9Mo-2Ta (in at. percent) has been characterized in both the rapidly solidified condition and after dynamic compaction. Dynamically compacted specimens were examined in the as-compacted condition and observations related to current theories of interparticle bonding. In addition, the recrystallization behavior of the compacted material at relatively low temperature (about 0.5-0.75 Tm) was investigated.

Characterization on White Etching Layer Formed During Ceramic Milling of Inconel 718

NASA Astrophysics Data System (ADS)

Kruk, A.; Wusatowska-Sarnek, A. M.; Ziętara, M.; Jemielniak, K.; Siemiątkowski, Z.; Czyrska-Filemonowicz, A.

2018-03-01

A comprehensive characterization of the near surface formed during the interrupted high-speed dry ceramic milling of IN718 was performed using light imaging, SEM/EDX, TEM and nano-hardness methods. It was found out that even an initial cut by a fresh tool creates a sub-surface alteration roughly 20 µm deep. The depth of altered sub-surface progressively changed to a roughly 40 µm when the tool reached an approximately half of its life, and almost 60 µm at the tool's end of the life. In the last two cases, the visible WEL (utilizing a light microscope) of the thickness roughly 6 and 15 µm was created, respectively. The outermost layer of the deformed subsurface was found to be for all three cases approximately 1.5 µm thick and composed of dynamically recrystallized γ phase grains with the average diameter of approximately 150 nm. This layer was free of δ phase and γ' or γ″ precipitates. It was followed by a plastically deformed zone.

Microstructure and Fatigue Properties of Ultrasonic Spot Welded Joints of Aluminum 5754 Alloy

NASA Astrophysics Data System (ADS)

Mirza, F. A.; Macwan, A.; Bhole, S. D.; Chen, D. L.

2016-05-01

The purpose of this investigation was to evaluate the microstructural change, lap shear tensile load, and fatigue resistance of ultrasonic spot welded joints of aluminum 5754 alloy for automotive applications. A unique "necklace"-type structure with very fine equiaxed grains was observed to form along the weld line due to the mechanical interlocking coupled with the occurrence of dynamic recrystallization. The maximum lap shear tensile strength of 85 MPa and the fatigue limit of about 0.5 kN (at 1 × 107 cycles) were achieved. The tensile fracture occurred at the Al/Al interface in the case of lower energy inputs, and at the edge of nugget zone in the case of higher energy inputs. The maximum cyclic stress for the transition of fatigue fracture mode from the transverse through-thickness crack growth to the interfacial failure increased with increasing energy input. Fatigue crack propagation was mainly characterized by the formation of fatigue striations, which usually appeared perpendicular to the fatigue crack propagation.

The clumped-isotope geochemistry of exhumed marbles from Naxos, Greece

NASA Astrophysics Data System (ADS)

Ryb, U.; Lloyd, M. K.; Stolper, D. A.; Eiler, J. M.

2017-07-01

Exhumation and accompanying retrograde metamorphism alter the compositions and textures of metamorphic rocks through deformation, mineral-mineral reactions, water-rock reactions, and diffusion-controlled intra- and inter-mineral atomic mobility. Here, we demonstrate that these processes are recorded in the clumped- and single-isotope (δ13 C and δ18 O) compositions of marbles, which can be used to constrain retrograde metamorphic histories. We collected 27 calcite and dolomite marbles along a transect from the rim to the center of the metamorphic core-complex of Naxos (Greece), and analyzed their carbonate single- and clumped-isotope compositions. The majority of Δ47 values of whole-rock samples are consistent with exhumation- controlled cooling of the metamorphic complex. However, the data also reveal that water-rock interaction, deformation driven recrystallization and thermal shock associated with hydrothermal alteration may considerably impact the overall distribution of Δ47 values. We analyzed specific carbonate fabrics influenced by deformation and fluid-rock reaction to study how these processes register in the carbonate clumped-isotope system. Δ47 values of domains drilled from a calcite marble show a bimodal distribution. Low Δ47 values correspond to an apparent temperature of 260 °C and are common in static fabrics; high Δ47 values correspond to an apparent temperature of 200 °C and are common in dynamically recrystallized fabrics. We suggest that the low Δ47 values reflect diffusion-controlled isotopic reordering during cooling, whereas high Δ47 values reflect isotopic reordering driven by dynamic recrystallization. We further studied the mechanism by which dynamic recrystallization may alter Δ47 values by controlled heating experiments. Results show no significant difference between laboratory reactions rates in the static and dynamic fabrics, consistent with a mineral-extrinsic mechanism, in which slip along crystal planes was associated with atomic-scale isotopic reordering in the calcite lattice. An intrinsic mechanism (enhanced isotopic reordering rate in deformed minerals) is contraindicated by these experiments. We suggest that Δ47 values of dynamically recrystallized fabrics that form below the diffusion-controlled blocking-temperature for calcite constrain the temperature of deformation. We find that Δ47-based temperatures of static fabrics from Naxos marbles are ∼60-80 °C higher than commonly observed in slowly cooled metamorphic rocks, and would suggest cooling rates of ∼105 °CMyr-1. A similar thermal history is inferred for dolomite marbles from the core vicinity, which preserve apparent temperatures up to 200 °C higher than a typical blocking temperature (∼300 °C). This finding could be explained by a hydrothermal event driving a brief thermal pulse and locally resetting Δ47 values. Rapid cooling of the core-complex region is consistent with a compilation of published cooling ages and a new apatite U-Th/He age, associating the thermal event with the emplacement of a granodiorite pluton at ∼12 Ma.

Thick crystalline films on foreign substrates

DOEpatents

Smith, Henry I.; Atwater, Harry A.; Geis, Michael W.

1986-01-01

To achieve a uniform texture, large crystalline grains or, in some cases, a single crystalline orientation in a thick (>1 .mu.m) film on a foreign substrate, the film is formed so as to be thin (<1 .mu.m) in a certain section. Zone-melting recrystallization is initiated in the thin section and then extended into the thick section. The method may employ planar constriction patterns of orientation filter patterns.

Thick crystalline films on foreign substrates

DOEpatents

Smith, H.I.; Atwater, H.A.; Geis, M.W.

1986-03-18

To achieve a uniform texture, large crystalline grains or, in some cases, a single crystalline orientation in a thick (>1 [mu]m) film on a foreign substrate, the film is formed so as to be thin (<1 [mu]m) in a certain section. Zone-melting recrystallization is initiated in the thin section and then extended into the thick section. The method may employ planar constriction patterns of orientation filter patterns. 2 figs.

Dolomitization of Quaternary reef limestones, Aitutaki, Cook Islands

USGS Publications Warehouse

Hein, J.R.; Gray, S.C.; Richmond, B.M.; White, L.D.

1992-01-01

The primary reef framework is considered to have been deposited during several highstands of sea level. Following partial to local recrystallization of the limestone, a signle episode of dolomitization occurred. Both tidal and thermal pumping drove large quantities of seawater through the porous rocks and perhaps maintained a wide mixing zone. However, the isotopic, geochemical and petrographic data do not clearly indicate the extent of seawater mixing. -from Authors

Evolution of twinning in extruded AZ31 alloy with bimodal grain structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcés, G., E-mail: ggarces@cenim.csic.es

2017-04-15

Twinning in extruded AZ31 alloy with a bimodal grain structure is studied under compression along the extrusion direction. This study has combined in-situ measurements during the compression tests by Synchrotron Radiation Diffraction and Acoustic Emission techniques and the evaluation of the microstructure and texture in post-mortem compression samples deformed at different strains. The microstructure of the alloy is characterized by the coexistence of large areas of fine dynamic recrystallized grains and coarse non-recrystallized grains elongated along extrusion direction. Twinning occurs initially in large elongated grains before the macroscopic yield stress which is controlled by the twinning in equiaxed dynamically recrystallizedmore » grains. - Highlights: • The AZ31 extruded at low temperature exhibits a bimodal grains structure. • Twinning takes place before macroscopic yielding in coarse non-DRXed grains. • DRXed grains controls the beginning of plasticity in magnesium alloys with bimodal grain structure.« less

Rheology and stress in subduction zones around the aseismic/seismic transition

NASA Astrophysics Data System (ADS)

Platt, John P.; Xia, Haoran; Schmidt, William Lamborn

2018-12-01

Subduction channels are commonly occupied by deformed and metamorphosed basaltic rocks, together with clastic and pelagic sediments, which form a zone up to several kilometers thick to depths of at least 40 km. At temperatures above 350 °C (corresponding to depths of > 25-35 km), the subduction zone undergoes a transition to aseismic behavior, and much of the relative motion is accommodated by ductile deformation in the subduction channel. Microstructures in metagreywacke suggest deformation occurs mainly by solution-redeposition creep in quartz. Interlayered metachert shows evidence for dislocation creep at relatively low stresses (8-13 MPa shear stress). Metachert is likely to be somewhat stronger than metagreywacke, so this value may be an upper limit for the shear stress in the channel as a whole. Metabasaltic rocks deform mainly by transformation-assisted diffusional creep during low-temperature metamorphism and, when dry, are somewhat stronger than metachert. Quartz flow laws for dislocation and solution-redeposition creep suggest strain rates of 10-12 s-1 at 500 °C and 10 MPa shear stress: this is sufficient to accommodate a 100 mm/yr. convergence rate within a 1 km wide ductile shear zone. The up-dip transition into the seismic zone occurs through a region where deformation is still distributed over a thickness of several kilometers, but occurs by a combination of microfolding, dilational microcracking, and solution-redeposition creep. This process requires a high fluid flux, released by dehydration reactions down-dip, and produces a highly differentiated deformational fabric with alternating millimeter-scale quartz and phyllosilicate-rich bands, and very abundant quartz veins. Bursts of dilational microcracking in zones 100-200 m thick may cause cyclic fluctuations in fluid pressure and may be associated with episodic tremor and slow slip events. Shear stress estimates from dislocation creep microstructures in dynamically recrystallized metachert are 10 MPa. [Figure not available: see fulltext.

High temperature pseudotachylytes and ductile shear zones in dry rocks from the continental lower crust (Lofoten, Norway)

NASA Astrophysics Data System (ADS)

Menegon, Luca; Pennacchioni, Giorgio; Harris, Katherine; Wood, Elliot

2014-05-01

Understanding the mechanisms of initiation and growth of shear zones under lower crustal conditions is of fundamental importance when assessing lithosphere rheology and strength. In this study we investigate brittle-ductile shear zones developed under lower crustal conditions in anorthosites from Nusfjord, Lofoten (northern Norway). Steep ductile shear zones trend E-W to ESE-WSW and have a stretching lineation plunging steeply to the SSW or SSE. The shear sense is normal (south block down to the south) as indicated by SC and SC' fabrics and sigmoidal foliations. The shear zone show a mylonitic to ultramylonitic fabric, sharp boundaries to the host anorthosites, and abundant anastomosing dark fine-grained layers along the main foliation. The fine-grained layers localized much of the strain. Relatively lower strain domains within or adjacent to shear zones indicate that the fine dark bands of mylonites represent transposed pseudotachylyte which still locally preserve the pristine structures such as chilled margins, breccia textures with angular clasts of the host rock and injection veins; intersecting veins of pseudotachylyte record multiple stages of seismic slip. The orientation of injection veins and marker offset along the most preserved pseudotachylyte fault veins indicate approximately a sinistral strike slip kinematic during faulting event responsible for the friction-induced melting. These observations indicate that ductile shear zones exploited pre-existing brittle fault zones including a network of pseudotachylytes, and that the fine-grained "ultramylonites" derive from former fine-grained pseudotachylytes. The pseudotachylyte microstructure is dominated by plagioclase microlites dispersed in a groundmass of fine-grained clinopyroxene. Clinopyroxene recrystallizes in the damage zone flanking the pseudotachylytes, indicating high metamorphic grade during pseudotachylyte formation. Small idioblastic or cauliflower garnet are scattered through the matrix and overgrow the plagioclase porphyroclasts; in some cases small garnets nucleated along thin microfractures discordant to the pseudotachylyte vein or along the pseudotachylyte boundary. In the host rock garnet form thin continuous coronitic rims surrounding biotite and opaque and discontinuous one around pyroxene. The mineral assemblage of ultramlylonites is also consistent with high grade metamorphic conditions (recrystallized plagioclase and clinopyroxene, biotite and amphibole). Nucleation of ductile shear zones is dictated by the availability of pseudotachylyte veins; remarkably, lithological boundaries have not been exploited by ductile shear zones. Brittle deformation and extreme grain size reduction are likely to be necessary conditions in order to promote ductile strain localization in dry rocks in the lower crust.

The deformation behavior and microstructure evolution of duplex Mg-9Li-1Al alloy during superplasticity tensile testing

NASA Astrophysics Data System (ADS)

Liu, Meiduo; Zheng, Haipeng; Zhang, Tianlong; Wu, Ruizhi

2017-12-01

The superplastic mechanical properties and microstructure evolution of the duplex Mg-9Li-1Al alloy were investigated. The tensile testing results show that, the elongation of the as-extruded Mg-9Li-1Al alloy reaches 510% at 573 K with a strain rate of 2×10-4 s-1. During the deformation process, the strips of α phase break into equiaxed structure. This phenomenon can be attributed to a particular dynamic recrystallization, which suggests that the β phase can recrystallize in the α phase due to the small misfit degree between α phase and β phase.

Friction Stir Weld Inspection Through Conductivity Imaging Using Shaped Field MWM(Registered Trademark) - Arrays

NASA Technical Reports Server (NTRS)

Goldfine, Neil; Grundy, David; Zilberstein, Vladimir; Kinchen, David G.; McCool, Alex (Technical Monitor)

2002-01-01

Friction Stir Welds (FSW) of Al 2195-T8 and Al 2219-T8, provided by Lockheed Martin Michoud Operations, were inspected for lack-of-penetration (LOP) defects using a custom designed MWM-Array, a multi-element eddy-current sensor. MWM (registered trademark) electrical conductivity mapping demonstrated high sensitivity to LOP as small as 0.75 mm (0.03 in.), as confirmed by metallographic data that characterized the extent of LOP defects. High sensitivity and high spatial resolution was achieved via a 37-element custom designed MWM-Array allowing LOP detection using the normalized longitudinal component of the MWM measured conductivity. This permitted both LOP detection and correlation of MWM conductivity features with the LOP defect size, as changes in conductivity were apparently associated with metallurgical features within the near-surface layer of the LOP defect zone. MWM conductivity mapping reveals information similar to macro-etching as the MWM-Array is sensitive to small changes in conductivity due to changes in microstructure associated with material thermal processing, in this case welding. The electrical conductivity measured on the root side of FSWs varies across the weld due to microstructural differences introduced by the FSW process, as well as those caused by planar flaws. Weld metal, i.e., dynamically recrystallized zone (DXZ), thermomechanically affected zone (TMZ), heat-affected zone (HAZ), and parent metal (PM) are all evident in the conductivity maps. While prior efforts had met with limited success for NDE (Nondestructive Evaluation) of dissimilar alloy, Al2219 to Al2195 FSW, the new custom designed multi-element MWM-Array achieved detection of all LOP defects even in dissimilar metal welds.

Development of SiC Nanoparticles and Second Phases Synergistically Reinforced Mg-Based Composites Processed by Multi-Pass Forging with Varying Temperatures

PubMed Central

Nie, Kaibo; Guo, Yachao; Deng, Kunkun; Wang, Xiaojun; Wu, Kun

2018-01-01

In this study, SiC nanoparticles were added into matrix alloy through a combination of semisolid stirring and ultrasonic vibration while dynamic precipitation of second phases was obtained through multi-pass forging with varying temperatures. During single-pass forging of the present composite, as the deformation temperature increased, the extent of recrystallization increased, and grains were refined due to the inhibition effect of the increasing amount of dispersed SiC nanoparticles. A small amount of twins within the SiC nanoparticle dense zone could be found while the precipitated phases of Mg17Al12 in long strips and deformation bands with high density dislocations were formed in the particle sparse zone after single-pass forging at 350 °C. This indicated that the particle sparse zone was mainly deformed by dislocation slip while the nanoparticle dense zone may have been deformed by twinning. The yield strength and ultimate tensile strength of the composites were gradually enhanced through increasing the single-pass forging temperature from 300 °C to 400 °C, which demonstrated that initial high forging temperature contributed to the improvement of the mechanical properties. During multi-pass forging with varying temperatures, the grain size of the composite was gradually decreased while the grain size distribution tended to be uniform with reducing the deformation temperature and extending the forging passes. In addition, the amount of precipitated second phases was significantly increased compared with that after multi-pass forging under a constant temperature. The improvement in the yield strength of the developed composite was related to grain refinement strengthening and Orowan strengthening resulting from synergistical effect of the externally applied SiC nanoparticles and internally precipitated second phases. PMID:29342883

Development of SiC Nanoparticles and Second Phases Synergistically Reinforced Mg-Based Composites Processed by Multi-Pass Forging with Varying Temperatures.

PubMed

Nie, Kaibo; Guo, Yachao; Deng, Kunkun; Wang, Xiaojun; Wu, Kun

2018-01-13

In this study, SiC nanoparticles were added into matrix alloy through a combination of semisolid stirring and ultrasonic vibration while dynamic precipitation of second phases was obtained through multi-pass forging with varying temperatures. During single-pass forging of the present composite, as the deformation temperature increased, the extent of recrystallization increased, and grains were refined due to the inhibition effect of the increasing amount of dispersed SiC nanoparticles. A small amount of twins within the SiC nanoparticle dense zone could be found while the precipitated phases of Mg 17 Al 12 in long strips and deformation bands with high density dislocations were formed in the particle sparse zone after single-pass forging at 350 °C. This indicated that the particle sparse zone was mainly deformed by dislocation slip while the nanoparticle dense zone may have been deformed by twinning. The yield strength and ultimate tensile strength of the composites were gradually enhanced through increasing the single-pass forging temperature from 300 °C to 400 °C, which demonstrated that initial high forging temperature contributed to the improvement of the mechanical properties. During multi-pass forging with varying temperatures, the grain size of the composite was gradually decreased while the grain size distribution tended to be uniform with reducing the deformation temperature and extending the forging passes. In addition, the amount of precipitated second phases was significantly increased compared with that after multi-pass forging under a constant temperature. The improvement in the yield strength of the developed composite was related to grain refinement strengthening and Orowan strengthening resulting from synergistical effect of the externally applied SiC nanoparticles and internally precipitated second phases.

Development of Microstructure and Crystallographic Texture in a Double-Sided Friction Stir Welded Microalloyed Steel

NASA Astrophysics Data System (ADS)

Rahimi, S.; Wynne, B. P.; Baker, T. N.

2017-01-01

The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the center of stirred zone reached a temperature between Ac1 and Ac3 during FSW, resulting in a dual-phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool shows the dominance of simple shear components across the whole weld. The austenite texture at Ac1 - Ac3 is dominated by the B { {1bar{1}2} }< 110rangle and bar{B} { {bar{1}1bar{2}} }< bar{1}bar{1}0rangle simple shear texture components, where the bainite phase textures formed on cooling were inherited from the shear textures of the austenite phase with relatively strong variant selection. The ferrite portion of the stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1 { {bar{1}bar{1}2} }< 111rangle and D2 { {11bar{2}} }< 111rangle simple shear texture components. The formation of ultrafine equiaxed ferrite with submicron grain size has been observed in the overlapped area between the first and second weld pass. This is due to continuous dynamic strain-induced recrystallization as a result of simultaneous severe shear deformation and drastic undercooling.

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

PubMed Central

Coucheron, David A.; Fokine, Michael; Patil, Nilesh; Breiby, Dag Werner; Buset, Ole Tore; Healy, Noel; Peacock, Anna C.; Hawkins, Thomas; Jones, Max; Ballato, John; Gibson, Ursula J.

2016-01-01

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core. PMID:27775066

Microstructures and mechanical properties of Cu-Sn alloy subjected to elevated-temperature heat deformation

NASA Astrophysics Data System (ADS)

Hui, Jun; Feng, Zaixin; Fan, Wenxin; Wang, Pengfei

2018-04-01

Cu-Sn alloy was subjected to elevated-temperature isothermal compression with 0.01 s‑1 strain rate and 500 ∼ 700 °C temperature range. The thermal compression curve reflected a competing process of work hardening versus dynamic recovery (DRV) and recrystallization, which exhibited an obvious softening trend. Meanwhile, high-temperature deformation and microstructural features in different regions of the alloy was analyzed through EBSD. The results show that grains grow as the temperature rises, competition among recrystallization, substructural, and deformation regions tends to increase with the increase of temperature, and distribution frequency of recrystallization regions gradually increases and then drops suddenly at 650 °C. At 500 ∼ 550 °C, preferentially oriented texturing phenomenon occurs, low angle boundaries(LABs) are gradually transformed into high angle boundaries (HABs) and the Σ (CSL) boundaries turn gradually into Σ3 boundaries. In tensile test of tin bronze, elongation at break increases slowly, whereas yield strength (YS) and ultimate tensile strength (TS) decrease gradually.

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

NASA Astrophysics Data System (ADS)

Coucheron, David A.; Fokine, Michael; Patil, Nilesh; Breiby, Dag Werner; Buset, Ole Tore; Healy, Noel; Peacock, Anna C.; Hawkins, Thomas; Jones, Max; Ballato, John; Gibson, Ursula J.

2016-10-01

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

Shock induced crystallization of amorphous Nickel powders

NASA Astrophysics Data System (ADS)

Cherukara, Mathew; Strachan, Alejandro

2015-06-01

Recent experimental work has shown the efficacy of amorphous Ni/crystalline Al composites as energetic materials, with flame velocities twice that of a comparable crystalline Ni/crystalline Al system. Of further interest is the recrystallization mechanisms in the pure amorphous Ni powders, both thermally induced and mechanically induced. We present large-scale molecular dynamics simulations of shock-induced recrystallization in loosely packed amorphous Nickel powders. We study the time dependent nucleation and growth processes by holding the shocked samples at the induced pressures and temperatures for extended periods following the passage of the shock (up to 6 ns). We find that the nanostructure of the recrystallized Ni and time scales of recrystallization are dependent on the piston velocity. At low piston velocities, nucleation events are rare, leading to long incubation times and a relatively coarse nanostructure. At higher piston velocities, local variations in temperature due to jetting phenomena and void collapse, give rise to multiple nucleation events on time scales comparable to the passage of the shock wave, leading to the formation of a fine-grained nanostructure. Interestingly, we observe that the nucleation and growth process occurs in two steps, with the first nuclei crystallizing into the BCC structure, before evolving over time into the expected FCC structure. U.S. Defense Threat Reduction Agency, HDTRA1-10-1-0119 (Program Manager Suhithi Peiris).

An extension of the Saltykov method to quantify 3D grain size distributions in mylonites

NASA Astrophysics Data System (ADS)

Lopez-Sanchez, Marco A.; Llana-Fúnez, Sergio

2016-12-01

The estimation of 3D grain size distributions (GSDs) in mylonites is key to understanding the rheological properties of crystalline aggregates and to constraining dynamic recrystallization models. This paper investigates whether a common stereological method, the Saltykov method, is appropriate for the study of GSDs in mylonites. In addition, we present a new stereological method, named the two-step method, which estimates a lognormal probability density function describing the 3D GSD. Both methods are tested for reproducibility and accuracy using natural and synthetic data sets. The main conclusion is that both methods are accurate and simple enough to be systematically used in recrystallized aggregates with near-equant grains. The Saltykov method is particularly suitable for estimating the volume percentage of particular grain-size fractions with an absolute uncertainty of ±5 in the estimates. The two-step method is suitable for quantifying the shape of the actual 3D GSD in recrystallized rocks using a single value, the multiplicative standard deviation (MSD) parameter, and providing a precision in the estimate typically better than 5%. The novel method provides a MSD value in recrystallized quartz that differs from previous estimates based on apparent 2D GSDs, highlighting the inconvenience of using apparent GSDs for such tasks.

Microstructural evolution of a superaustenitic stainless steel during a two-step deformation process

NASA Astrophysics Data System (ADS)

Bayat, N.; Ebrahimi, G. R.; Momeni, A.; Ezatpour, H. R.

2018-02-01

Single- and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s-1. In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.

Physical stability of the amorphous anticholesterol agent (ezetimibe): the role of molecular mobility.

PubMed

Knapik, J; Wojnarowska, Z; Grzybowska, K; Hawelek, L; Sawicki, W; Wlodarski, K; Markowski, J; Paluch, M

2014-11-03

The purpose of this paper is to examine the role of molecular mobility in the recrystallization process from the amorphous state of the anticholesterol drug ezetimibe. Both the molecular dynamics and crystallization kinetics have been studied using various experimental techniques, such as broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Our investigations have shown that ezetimibe easily recrystallizes from the disordered state, both below and above its glass transition temperature (Tg = 336 K). Moreover, we found that an only slightly elevated pressure (5 MPa) significantly accelerates the recrystallization process at T > Tg. We predict that the structural relaxation time of amorphous ezetimibe at 293 K (storage temperature) and ambient pressure is only 22 days. This result corresponds to the characteristic time, determined from XRD measurements, for amorphous ezetimibe to recrystallize during storage at Troom = 298 K. It leads to the conclusion that the molecular mobility reflected in structural relaxation of ezetimibe is mainly responsible for devitrification of this drug. Finally, we determined a relatively easy way to improve the physical stability of the drug by preparing a binary amorphous ezetimibe-Soluplus mixture. Ezetimibe in an amorphous mixture with 20 wt % Soluplus has a much better (over six times) solubility than the pure crystalline material.

Morphology Controls on Calcite Recrystallization.

PubMed

Heberling, Frank; Paulig, Leonie; Nie, Zhe; Schild, Dieter; Finck, Nicolas

2016-11-01

Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10 -13 mol/(m 2 ·s).

The microstructure of polar ice. Part II: State of the art

NASA Astrophysics Data System (ADS)

Faria, Sérgio H.; Weikusat, Ilka; Azuma, Nobuhiko

2014-04-01

An important feature of natural ice, in addition to the obvious relevance of glaciers and ice sheets for climate-related issues, is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point, without losing its polycrystalline character. This fact, together with its strong mechanical anisotropy and other notable properties, makes natural ice an interesting model material for studying the high-temperature creep and recrystallization of rocks in Earth's interior. After having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in Part I of this work (Faria et al., 2014), here in Part II we present an up-to-date view of the modern understanding of natural ice microstructures and the deformation processes that may produce them. In particular, we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure (also known as the "three-stage model," cf. Part I). These results prove that grain growth in ice sheets is dynamic, in the sense that it occurs during deformation and is markedly affected by the stored strain energy, as well as by air inclusions and other impurities. The strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal, which demand large amounts of strain accommodation. From the microstructural analyses of ice cores, we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice. Additionally, in fine-grained, high-impurity ice layers (e.g. cloudy bands), strain may sometimes be accommodated by diffusional flow (at low temperatures and stresses) or microscopic grain boundary sliding via microshear (in anisotropic ice sheared at high temperatures). Grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets. Evidence of nucleation of new grains is also observed at various depths, provided that the local concentration of strain energy is high enough (which is not seldom the case). As a substitute for the tripartite paradigm, we propose a novel dynamic recrystallization diagram in the three-dimensional state space of strain rate, temperature, and mean grain size, which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure.

The Rock Record of Seismic Nucleation: examples from pseudotachylites beneath the Whipple Detachment Fault, eastern California

NASA Astrophysics Data System (ADS)

Ortega-Arroyo, D.; Behr, W. M.; Gentry, E.

2017-12-01

The mechanisms that lead to nucleation and dynamic weakening in the middle crust are not well understood. Proposed mechanisms include flash heating of asperities, thermal pressurization of pore fluids, dynamic instabilities, and fracture interactions. We investigate this issue in the rock record using exhumed mid-crustal rocks exposed beneath the Whipple Detachment fault (WDF) in eastern CA. Analysis of pseudotachylites (PS) beneath the WDF, representing paleo-earthquakes, reveal two types: Type 1 PS exhibit little to no precursory cataclasis and are concentrated along shear bands at the margins of feldspar-rich lenses embedded in more quartz-rich domains. These appear synkinematic with S-C fabrics in the surrounding mylonites and they exhibit finely dynamically recrystallized grains in quartz at their margins, suggesting coeval ductile deformation. By contrast, Type 2 PS occur along the principal slip surface of a brittle shear zone and show evidence for precursory cataclasis, brecciation, and fracturing. Some cataclasites inject into the host rock, forming eddies along the boundary with the PS. Slip appears to localize progressively into a 2 cm thick fault core, with PS concentrated primarily in the interior- the presence of solidified melt and fluidized cataclasite as clasts within the fault core suggests multiple slip events are preserved. We interpret the two types of pseudotachylites to represent different conditions and mechanisms of earthquake nucleation near the brittle-ductile transition (BDT). Type 1 PS are interpreted to represent nucleation in deeper sections of the BDT by failure along mineralogically-controlled stress concentrations hosted within an otherwise viscously deforming mylonite. Our data suggest that these do not develop into large-magnitude EQ's because seismic slip is dampened into the surrounding quartz-rich viscous matrix; instead they may represent deep microseismicity and/or seismic tremor. By contrast, Type 2 PS are interpreted to nucleate when thermally pressurized pore fluids are able to escape into the permeable damage zone, causing a recovery in the fault's effective friction, and promoting melting. Type 2 PS appear to experience greater weakening, accumulate larger slip, and may represent larger-magnitude seismicity at the base of the seismogenic zone.

Grain size evolution and convection regimes of the terrestrial planets

NASA Astrophysics Data System (ADS)

Rozel, A.; Golabek, G. J.; Boutonnet, E.

2011-12-01

A new model of grain size evolution has recently been proposed in Rozel et al. 2010. This new approach stipulates that the grain size dynamics is governed by two additive and simultaneous processes: grain growth and dynamic recrystallization. We use the usual normal grain growth laws for the growth part. For dynamic recrystallization, reducing the mean grain size increases the total area of grain boundaries. Grain boundaries carry some surface tension, so some energy is required to decrease the mean grain size. We consider that this energy is available during mechanical work. It is usually considered to produce some heat via viscous dissipation. A partitioning parameter f is then required to know what amount of energy is dissipated and what part is converted in surface tension. This study gives a new calibration of the partitioning parameter on major Earth materials involved in the dynamic of the terrestrial planets. Our calibration is in adequation with the published piezometric relations available in the literature (equilibrium grain size versus shear stress). We test this new model of grain size evolution in a set of numerical computations of the dynamics of the Earth using stagYY. We show that the grain size evolution has a major effect on the convection regimes of terrestrial planets.

Deformation induced dynamic recrystallization and precipitation strengthening in an Mg−Zn−Mn alloy processed by high strain rate rolling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Jimiao; Song, Min

2016-11-15

The microstructure of a high strain-rate rolled Mg−Zn−Mn alloy was investigated by transmission electron microscopy to understand the relationship between the microstructure and mechanical properties. The results indicate that: (1) a bimodal microstructure consisting of the fine dynamic recrystallized grains and the largely deformed grains was formed; (2) a large number of dynamic precipitates including plate-like MgZn{sub 2} phase, spherical MgZn{sub 2} phase and spherical Mn particles distribute uniformly in the grains; (3) the major facets of many plate-like MgZn{sub 2} precipitates deviated several to tens of degrees (3°–30°) from the matrix basal plane. It has been shown that themore » high strength of the alloy is attributed to the formation of the bimodal microstructure, dynamic precipitation, and the interaction between the dislocations and the dynamic precipitates. - Highlights: •A bimodal microstructure was formed in a high strain-rate rolled Mg−Zn−Mn alloy. •Plate-like MgZn{sub 2}, spherical MgZn{sub 2} and spherical Mn phases were observed. •The major facet of the plate-like MgZn{sub 2} deviated from the matrix basal plane.« less

Hot Deformation Behavior and Intrinsic Workability of Carbon Nanotube-Aluminum Reinforced ZA27 Composites

NASA Astrophysics Data System (ADS)

Liu, Yang; Geng, Cong; Zhu, Yunke; Peng, Jinfeng; Xu, Junrui

2017-04-01

Using a controlled thermal simulator system, hybrid carbon nanotube-aluminum reinforced ZA27 composites were subjected to hot compression testing in the temperature range of 473-523 K with strain rates of 0.01-10 s-1. Based on experimental results, a developed-flow stress model was established using a constitutive equation coupled with strain to describe strain softening arising from dynamic recrystallization. The intrinsic workability was further investigated by constructing three-dimensional (3D) processing maps aided by optical observations of microstructures. The 3D processing maps were constructed based on a dynamic model of materials to delineate variations in the efficiency of power dissipation and flow instability domains. The instability domains exhibited adiabatic shear band and flow localization, which need to be prevented during hot processing. The recommended domain is predicated to be within the temperature range 550-590 K and strain rate range 0.01-0.35 s-1. In this state, the main softening mechanism is dynamic recrystallization. The results from processing maps agree well with the microstructure observations.

Effect of Hot Rolling on the Microstructure and Mechanical Properties of Nitrogen Alloyed Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Chenna Krishna, S.; Karthick, N. K.; Jha, Abhay K.; Pant, Bhanu; Cherian, Roy M.

2018-05-01

In the present investigation, the effect of multi-pass hot rolling in the temperature range of 700-1000 °C on the microstructure and mechanical properties of nitrogen alloyed austenitic stainless steel was studied with the aid of optical microscopy, tensile testing and x-ray diffraction measurements. The microstructural changes that occurred in the hot rolled specimens were elongation of grains in rolling direction, nucleation of new grains at the grain boundaries of elongated grains and growth of nucleated grains to form fully recrystallized grains. Elongated grains formed at lower rolling temperature (700-800 °C) due to inadequate strain/temperature for the initiation of dynamic recrystallization. At higher rolling temperature (900-1000 °C), fine grains formed due to dynamic recrystallization. Tensile properties showed strong dependency on the rolling temperature. Tensile strength increased with the decrease in the rolling temperature at the cost of ductility. Maximum strength was observed in samples hot rolled at 700 °C with yield strength of 917 MPa and ductility of 25%. This variation in the tensile properties with the rolling temperature is attributed to changes in the dislocation density and grain structure. The estimated yield strength from the dislocation density, solid solution and grain boundary strengthening closely matched with experimentally determined yield strength confirming the role of dislocation density and grain size in the strengthening.

Effect of Hot Rolling on the Microstructure and Mechanical Properties of Nitrogen Alloyed Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Chenna Krishna, S.; Karthick, N. K.; Jha, Abhay K.; Pant, Bhanu; Cherian, Roy M.

2018-04-01

In the present investigation, the effect of multi-pass hot rolling in the temperature range of 700-1000 °C on the microstructure and mechanical properties of nitrogen alloyed austenitic stainless steel was studied with the aid of optical microscopy, tensile testing and x-ray diffraction measurements. The microstructural changes that occurred in the hot rolled specimens were elongation of grains in rolling direction, nucleation of new grains at the grain boundaries of elongated grains and growth of nucleated grains to form fully recrystallized grains. Elongated grains formed at lower rolling temperature (700-800 °C) due to inadequate strain/temperature for the initiation of dynamic recrystallization. At higher rolling temperature (900-1000 °C), fine grains formed due to dynamic recrystallization. Tensile properties showed strong dependency on the rolling temperature. Tensile strength increased with the decrease in the rolling temperature at the cost of ductility. Maximum strength was observed in samples hot rolled at 700 °C with yield strength of 917 MPa and ductility of 25%. This variation in the tensile properties with the rolling temperature is attributed to changes in the dislocation density and grain structure. The estimated yield strength from the dislocation density, solid solution and grain boundary strengthening closely matched with experimentally determined yield strength confirming the role of dislocation density and grain size in the strengthening.

Fiber Laser Welded AZ31 Magnesium Alloy: The Effect of Welding Speed on Microstructure and Mechanical Properties

NASA Astrophysics Data System (ADS)

Chowdhury, S. H.; Chen, D. L.; Bhole, S. D.; Powidajko, E.; Weckman, D. C.; Zhou, Y.

2012-06-01

This study was aimed at characterizing microstructural change and evaluating tensile and fatigue properties of fiber laser welded AZ31B-H24 Mg alloy with special attention to the effect of welding speed. Laser welding led to the formation of equiaxed dendrites in the fusion zone and columnar dendrites near the fusion zone boundary along with divorced eutectic Mg17Al12 particles and recrystallized grains in the heat-affected zone. The lowest hardness across the weld appeared in the fusion zone. Although the yield strength, ductility, and fatigue life decreased, the hardening capacity increased after laser welding, with a joint efficiency reaching about 90 pct. A higher welding speed resulted in a narrower fusion zone, smaller grain size, higher yield strength, and longer fatigue life, as well as a slightly lower strain-hardening capacity mainly because of the smaller grain sizes. Tensile fracture occurred in the fusion zone, whereas fatigue failure appeared essentially in between the heat-affected zone and the fusion zone. Fatigue cracks initiated from the near-surface welding defects and propagated by the formation of fatigue striations together with secondary cracks.

Hydration index--a better parameter for explaining small molecule hydration in inhibition of ice recrystallization.

PubMed

Tam, Roger Y; Ferreira, Sandra S; Czechura, Pawel; Chaytor, Jennifer L; Ben, Robert N

2008-12-24

Several simple mono- and disaccharides have been assessed for their ability to inhibit ice recrystallization. Two carbohydrates were found to be effective recrystallization inhibitors. D-galactose (1) was the best monosaccharide and D-melibiose (5) was the most active disaccharide. The ability of each carbohydrate to inhibit ice growth was correlated to its respective hydration number reported in the literature. A hydration number reflects the number of tightly bound water molecules to the carbohydrate and is a function of carbohydrate stereochemistry. It was discovered that using the absolute hydration number of a carbohydrate does not allow one to accurately predict its ability to inhibit ice recrystallization. Consequently, we have defined a hydration index in which the hydration number is divided by the molar volume of the carbohydrate. This new parameter not only takes into account the number of water molecules tightly bound to a carbohydrate but also the size or volume of a particular solute and ultimately the concentration of hydrated water molecules. The hydration index of both mono- and disaccharides correlates well with experimentally measured RI activity. C-Linked derivatives of the monosaccharides appear to have RI activity comparable to that of their O-linked saccharides but a more thorough investigation is required. The relationship between carbohydrate concentration and RI activity was shown to be noncolligative and a 0.022 M solution of D-galactose (1) and C-linked galactose derivative (10) inhibited recrystallization as well as a 3% DMSO solution. The carbohydrates examined in this study did not possess any thermal hysteresis activity (selective depression of freezing point relative to melting point) or dynamic ice shaping. As such, we propose that they are inhibiting recrystallization at the interface between bulk water and the quasi liquid layer (a semiordered interface between ice and bulk water) by disrupting the preordering of water.

Numerical Study on Stress Heterogeneity Development in Two-Phase Rocks with Large Rheological Contrast and Implications in the Lower Crust

NASA Astrophysics Data System (ADS)

Xu, Junshan; Zhang, Baohua

2018-03-01

Development of stress heterogeneity in two-phase rocks was investigated via a finite element method at 1000-1200 K and 100 MPa. Two groups of rock models were considered: anorthite-diopside and anorthite-clinopyroxene, with a phase volume ratio of 1:1 in each group and different dislocation creep rates between phases ( 4-8 orders of magnitude). Our numerical results indicate that the stress inside the model can be several times higher than the differential stress applied to the model and stress will tend to concentrate in hard phase, especially near the sharp boundaries with soft phase. Moreover, large stress gradient in hard phase and nearly homogeneous stress in soft phase will lead to the initialization of localized dynamic recrystallization or fracture. These numerical observations suggest that the rheological contrast between two phases plays a crucial role in stress heterogeneity rather than other factors (such as grain size, the boundary conditions or mesh density), which may eventually accelerate development of stress heterogeneity in the lower crust. Our study provides new insights into the dynamic processes of grain size reduction in the lower crust, which may cause the transformation from dislocation creep to diffusion creep and enable the weakened shear zones.

Cyclical shear fracture and viscous flow during transitional ductile-brittle deformation in the Saddlebag Lake Shear Zone, California

NASA Astrophysics Data System (ADS)

Compton, Katharine E.; Kirkpatrick, James D.; Holk, Gregory J.

2017-06-01

Exhumed shear zones often contain folded and/or dynamically recrystallized structures, such as veins and pseudotachylytes, which record broadly contemporaneous brittle and ductile deformation. Here, we investigate veins within the Saddlebag Lake Shear Zone, central Sierra Nevada, California, to constrain the conditions and processes that caused fractures to form during ductile deformation. The shear zone mylonites contain compositional banding at centimeter- to meter- scales, and a ubiquitous, grain-scale, continuous- to spaced-foliation defined by aligned muscovite and chlorite grains. Veins of multiple compositions formed in two predominant sets: sub-parallel to the foliation and at high angle to the foliation. Some foliation sub-parallel veins show apparent shear offset consistent with the overall kinematics of the shear zone. These veins are folded with the foliation and are commonly boudinaged, showing they were rigid inclusions after formation. Quartz microstructures and fluid inclusion thermobarometry measurements indicate the veins formed by fracture at temperatures between 400-600 °C. Quartz, feldspar and tourmaline δ18O values (+ 2.5 to + 16.5) suggest extended fluid-rock interaction that involved magmatic, metamorphic, and meteoric-hydrothermal fluids. The orientation and spatial distribution of the veins shows that shear fractures formed along mechanically weak foliation planes. We infer fracture was promoted by perturbations to the strain rate and/or pore pressure during frictional-viscous deformation in a low effective stress environment. Evidence for repeated fracture and subsequent flow suggest both the stress and pore pressure varied, and that the tendency to fracture was controlled by the rates of pore pressure recovery, facilitated by fracture cementation. The tectonic setting and inferred phenomenological behavior were similar to intra-continental transform faults that host triggered tectonic tremor, suggesting the mechanisms that caused brittle fracture during viscous deformation may be important for comparable active systems.

Compositional changes of minerals associated with dynamic recrystallizatin

NASA Astrophysics Data System (ADS)

Yund, Richard A.; Tullis, Jan

1991-09-01

The rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously. The enhanced exchange rate may result from a reduction in grain size (shorter distance for volume diffusion), dissolution and growth of grains by diffusion creep (pressure solution), or the movement of high-angle grain boundaries through strained grains during recrystallization in the dislocation creep regime. The migration of high-angle grain boundaries provides high diffusivity paths for the rapid exchange of components during recrystallization. The operation of the latter process has been demonstrated by deforming aggregates consisting of two plagioclases (An1 and An79) at 900°C, 1 GPa confining pressure, and a strain rate of ˜2x10-6s-1. The polygonal, recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable but often intermediate composition. At the conditions of these experiments, the volume interdiffusion rate of NaSi/CaAl is too slow to produce any observable chemical change, and microstructural-chemical relations indicate that the contribution from diffusion creep was insignificant except for initially fine-grained (2 10 μm) aggregates. These results indicate that strain-induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for resetting the isotope systematics of minerals such as feldspars, pyroxenes, and amphiboles.

Molecular Factors Governing the Liquid and Glassy States Recrystallization of Celecoxib in Binary Mixtures with Excipients of Different Molecular Weights.

PubMed

Grzybowska, K; Chmiel, K; Knapik-Kowalczuk, J; Grzybowski, A; Jurkiewicz, K; Paluch, M

2017-04-03

Transformation of poorly water-soluble crystalline pharmaceuticals to the amorphous form is one of the most promising strategies to improve their oral bioavailability. Unfortunately, the amorphous drugs are usually thermodynamically unstable and may quickly return to their crystalline form. A very promising way to enhance the physical stability of amorphous drugs is to prepare amorphous compositions of APIs with certain excipients which can be characterized by significantly different molecular weights, such as polymers, acetate saccharides, and other APIs. By using different experimental techniques (broadband dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction) we compare the effect of adding the large molecular weight polymer-polyvinylpyrrolidone (PVP K30)-and the small molecular weight excipient-octaacetylmaltose (acMAL)-on molecular dynamics as well as the tendency to recrystallization of the amorphous celecoxib (CEL) in the amorphous solid dispersions: CEL-PVP and CEL-acMAL. The physical stability investigations of the binary systems were performed in both the supercooled liquid and glassy states. We found that acMAL is a better inhibitor of recrystallization of amorphous CEL than PVP K30 deep in the glassy state (T < T g ). In contrast, PVP K30 is a better crystallization inhibitor of CEL than acMAL in the supercooled liquid state (at T > T g ). We discuss molecular factors governing the recrystallization of amorphous CEL in examined solid dispersions.

Hot Deformation Behavior of As-Cast 2101 Grade Lean Duplex Stainless Steel and the Associated Changes in Microstructure and Crystallographic Texture

NASA Astrophysics Data System (ADS)

Patra, Sudipta; Ghosh, Abhijit; Singhal, Lokesh Kumar; Podder, Arijit Saha; Sood, Jagmohan; Kumar, Vinod; Chakrabarti, Debalay

2017-01-01

The hot deformation behavior of 2101 grade lean duplex stainless steel (DSS, containing 5 wt pct Mn, 0.2 wt pct N, and 1.4 wt pct Ni) and associated microstructural changes within δ-ferrite and austenite ( γ) phases were investigated by hot-compression testing in a GLEEBLE 3500 simulator over a range of deformation temperatures, T def [1073 K to 1373 K (800 °C to 1100 °C)], and applied strains, ɛ (0.25 to 0.80), at a constant true strain rate of 1/s. The microstructural softening inside γ was dictated by discontinuous dynamic recrystallization (DDRX) at a higher T def [1273 K to 1373 K (1000 °C to 1100 °C)], while the same was dictated by continuous dynamic recrystallization (CDRX) at a lower T def (1173 K (900 °C)]. Dynamic recovery (DRV) and CDRX dominated the softening inside δ-ferrite at T def ≥ 1173 K (900 °C). The dynamic recrystallization (DRX) inside δ and γ could not take place upon deformation at 1073 K (800 °C). The average flow stress level increased 2 to 3 times as the T def dropped from 1273 to 1173 K (1000 °C to 900 °C) and finally to 1073 K (800 °C). The average microhardness values taken from δ-ferrite and γ regions of the deformed samples showed a different trend. At T def of 1373 K (1100 °C), microhardness decreased with the increase in strain, while at T def of 1173 K (900 °C), microhardness increased with the increase in strain. The microstructural changes and hardness variation within individual phases of hot-deformed samples are explained in view of the chemical composition of the steel and deformation parameters ( T def and ɛ).

Influence of Copper on the Hot Ductility of 20CrMnTi Steel

NASA Astrophysics Data System (ADS)

Peng, Hong-bing; Chen, Wei-qing; Chen, Lie; Guo, Dong

2015-02-01

The hot ductility of 20CrMnTi steel with x% copper (x = 0, 0.34) was investigated. Results show that copper can reduce its hot ductility, but there is no significant copper-segregation at the boundary tested by EPMA. The average copper content at grain boundaries and substrate is 0.352% and 0.318% respectively in steel containing 0.34% copper tensile-tested at 950 °C. The fracture morphology was examined with SEM and many small and shallow dimples were found on the fracture of steel with copper, and fine copper sulfide was found from carbon extraction replicas using TEM. Additionally, adding 0.34% copper caused an increase in the dynamic recrystallization temperature from 950 °C to 1000 °C, which indicates that copper can retard the dynamic recrystallization (DRX) of austenite. The detrimental influence of copper on hot ductility of 20CrMnTi steel is due mainly to the fine copper sulfide in the steel and its retarding the DRX.

Grain Refinement Kinetics in a Low Alloyed Cu–Cr–Zr Alloy Subjected to Large Strain Deformation

PubMed Central

Morozova, Anna; Borodin, Elijah; Bratov, Vladimir; Zherebtsov, Sergey; Kaibyshev, Rustam

2017-01-01

This paper investigates the microstructural evolution and grain refinement kinetics of a solution-treated Cu–0.1Cr–0.06Zr alloy during equal channel angular pressing (ECAP) at a temperature of 673 K via route BC. The microstructural change during plastic deformation was accompanied by the formation of the microband and an increase in the misorientations of strain-induced subboundaries. We argue that continuous dynamic recrystallization refined the initially coarse grains, and discuss the dynamic recrystallization kinetics in terms of grain/subgrain boundary triple junction evolution. A modified Johnson–Mehl–Avrami–Kolmogorov relationship with a strain exponent of about 1.49 is used to express the strain dependence of the triple junctions of high-angle boundaries. Severe plastic deformation by ECAP led to substantial strengthening of the Cu–0.1Cr–0.06Zr alloy. The yield strength increased from 60 MPa in the initial state to 445 MPa after a total strain level of 12. PMID:29210990

Microstructural Characteristic of the Al-Fe-Cu Alloy During High-Speed Repetitive Continuous Extrusion Forming

NASA Astrophysics Data System (ADS)

Hu, Jiamin; Teng, Jie; Ji, Xiankun; Kong, Xiangxin; Jiang, Fulin; Zhang, Hui

2016-11-01

High-speed repetitive continuous extrusion forming process (R-Conform process) was performed on the Al-Fe-Cu alloy. The microstructural evolution and mechanical properties were studied by x-ray diffraction, electron backscatter diffraction, transmission electron microscopy and tensile testing. The results show that a significant improvement of tensile ductility concurs with a considerable loss of tensile strength before four passes, after that the process on mechanical properties variation tends to be steady, indicating an accelerated mechanical softening occurs when comparing to low-speed R-Conform process. Microstructure characterization indicates that the accumulated strain promotes the transformation of low angle boundaries to high angle boundaries, thus leading to the acceleration of continuous dynamic recrystallization process, and the precipitates are broken, spheroidized and homogeneously distribute in Al matrix as increasing R-Conform passes. Massive microshear bands are observed after initial passes of R-Conform process, which may promote continuous dynamic recrystallization and further grain refinement during high-speed R-Conform process.

Dynamic Recrystallization Behavior of AISI 422 Stainless Steel During Hot Deformation Processes

NASA Astrophysics Data System (ADS)

Ahmadabadi, R. Mohammadi; Naderi, M.; Mohandesi, J. Aghazadeh; Cabrera, Jose Maria

2018-02-01

In this work, hot compression tests were performed to investigate the dynamic recrystallization (DRX) process of a martensitic stainless steel (AISI 422) at temperatures of 950, 1000, 1050, 1100 and 1150 °C and strain rates of 0.01, 0.1 and 1 s-1. The dependency of strain-hardening rate on flow stress was used to estimate the critical stress for the onset of DRX. Accordingly, the critical stress to peak stress ratio was calculated as 0.84. Moreover, the effect of true strain was examined by fitting stress values to an Arrhenius type constitutive equation, and then considering material constants as a function of strain by using a third-order polynomial equation. Finally, two constitutive models were used to investigate the competency of the strain-dependent constitutive equations to predict the flow stress curves of the studied steel. It was concluded that one model offers better precision on the flow stress values after the peak stress, while the other model gives more accurate results before the peak stress.

An Electron Microscopy Study of Graphite Growth in Nodular Cast Irons

NASA Astrophysics Data System (ADS)

Laffont, L.; Jday, R.; Lacaze, J.

2018-04-01

Growth of graphite during solidification and high-temperature solid-state transformation has been investigated in samples cut out from a thin-wall casting which solidified partly in the stable (iron-graphite) and partly in the metastable (iron-cementite) systems. Transmission electron microscopy has been used to characterize graphite nodules in as-cast state and in samples having been fully graphitized at various temperatures in the austenite field. Nodules in the as-cast material show a twofold structure characterized by an inner zone where graphite is disoriented and an outer zone where it is well crystallized. In heat-treated samples, graphite nodules consist of well-crystallized sectors radiating from the nucleus. These observations suggest that the disoriented zone appears because of mechanical deformation when the liquid contracts during its solidification in the metastable system. During heat-treatment, the graphite in this zone recrystallizes. In turn, it can be concluded that nodular graphite growth mechanism is the same during solidification and solid-state transformation.

Metamorphism, metasomatism, retrogression: the common control on isotope transport

NASA Astrophysics Data System (ADS)

Villa, I. M.; Williams, M. L.

2011-12-01

Compositional or isotopic modification of a mineral can be viewed as a single process with many names. Depending on the large-scale context, different names are used: aqueous alteration, retrogression, metasomatism, metamorphism, but it should be clear that the underlying atomic-scale mechanism is the same. Changes in stoichiometry and in crystallographic structure require recrystallization. Following [1], all recrystallization processes can be viewed as nano-scale dissolution/reprecipitation, mediated by an aqueous fluid. In fact, aqueous fluids are the main control on the formation of all metamorphic parageneses [2], and also isotope exchange in minerals [3]. The reason is that the rate constants for fluid-mediated isotope transport are orders of magnitude larger, and activation energies much smaller, than those for diffusion. Recrystallisation is energetically less costly at almost any temperature than diffusive reequilibration [3]. However, recrystallization is not the only cause of isotope loss/exchange. Temperature can also play a role in reducing the retentivity of a geochronometer by increasing diffusivity. In cases where diffusion was the factor limiting isotopic closure (or chemical closure), a bell-shaped isotope (or element) concentration profile is observed. The criterion to decide whether in a particular sample diffusion or recrystallization was the principal control on chemical/isotope transport lies in the spatial variation of elemental or isotopic composition. Patchy spatial patterns are certain evidence of fluid-mediated local recrystallization. Bell-shaped gradients are compatible with (but not unambiguous proof of) volume diffusion. In-situ dating over three decades has never described bell-shaped isotope gradients in patchily zoned minerals. On the contrary, age mapping usually coincides with microchemical mapping [4]. This is best explained by a common cause for the recrystallization and the isotope transport. The cause, fluid-mediated dissolution/reprecipitation, depends mainly on water activity and only very loosely on temperature, i.e. provides a geohygrometric but not a geothermometric datum. We conclude that only in rare cases diffusion is the sole promoter of isotope resetting. The observations require a major shift in perspective on the significance of mineral ages. Just as the "diffusionist" view that zircon discordance is due to thermal disturbances (e.g. [5]) was superseded by the petrological understanding that it is due to recrystallization (e.g. [6]), a blanket interpretation of intra-mineral age variations in terms of a purely thermal history neglecting the petrogenetic context is no longer tenable. [1] Putnis A (2009) Rev Mineral Geochem 70, 87-124 [2] Lasaga A (1986) Mineral Mag 50, 359-373 [3] Cole DR et al (1983) Geochim Cosmochim Acta 47, 1681-1693 [4] Williams ML et al (2007) Ann Rev Earth Planet Sci 35, 137-175 [5] Steiger RH, Wasserburg GJ (1969) Geochim Cosmochim Acta 33, 1213-1232 [6] Mezger K, Krogstadt EJ (1997) J Metam Geol 15, 127-140

Effect of Strain Rate on Hot Ductility Behavior of a High Nitrogen Cr-Mn Austenitic Steel

NASA Astrophysics Data System (ADS)

Wang, Zhenhua; Meng, Qing; Qu, Minggui; Zhou, Zean; Wang, Bo; Fu, Wantang

2016-03-01

18Mn18Cr0.6N steel specimens were tensile tested between 1173 K and 1473 K (900 °C and 1200 °C) at 9 strain rates ranging from 0.001 to 10 s-1. The tensile strained microstructures were analyzed through electron backscatter diffraction analysis. The strain rate was found to affect hot ductility by influencing the strain distribution, the extent of dynamic recrystallization and the resulting grain size, and dynamic recovery. The crack nucleation sites were primarily located at grain boundaries and were not influenced by the strain rate. At 1473 K (1200 °C), a higher strain rate was beneficial for grain refinement and preventing hot cracking; however, dynamic recovery appreciably occurred at 0.001 s-1 and induced transgranular crack propagation. At 1373 K (1100 °C), a high extent of dynamic recrystallization and fine new grains at medium strain rates led to good hot ductility. The strain gradient from the interior of the grain to the grain boundary increased with decreasing strain rate at 1173 K and 1273 K (900 °C and 1000 °C), which promoted hot cracking. Grain boundary sliding accompanied grain rotation and did not contribute to hot cracking.

Microstructure and Mechanical Properties of Laser Solid Formed Ti-6Al-4V Alloy Under Dynamic Shear Loading

NASA Astrophysics Data System (ADS)

Zhou, Ping; Guo, Wei-Guo; Su, Yu; Wang, Jianjun; Lin, Xin; Huang, Weidong

2017-07-01

To investigate the mechanical properties of the Ti-6Al-4V alloy fabricated by laser solid forming technology, both static and dynamic shear tests were conducted on hat-shaped specimens by a servohydraulic testing machine and an enhanced split Hopkinson pressure bar system, over a temperature range of 173-573 K. The microstructure of both the original and deformed specimens was characterized by optical microscopy and scanning electron microscopy. The results show that: (1) the anisotropy of shear properties is not significant regardless of the visible stratification and the prior- β grains that grow epitaxially along the depositing direction; (2) the ultimate shear strength of this material is lower than that of those Ti-6Al-4V alloys fabricated by forging and extrusion; (3) the adiabatic shear bands of approximately 25.6-36.4 μm in width can develop at all selected temperatures during the dynamic shear deformation; and (4) the observed microstructure and measured microhardness indicate that the grains become refined in adiabatic shear band. Estimation of the temperature rise shows that the temperature in shear band exceeds the recrystallization temperature. The process of rotational dynamic recrystallization is considered to be the cause of the grain refinement in shear band.

Evaluating flow laws for dynamically recrystallized quartz based on field data

NASA Astrophysics Data System (ADS)

Peters, Max; Herwegh, Marco

2013-04-01

The extrapolation of experimentally controlled deformation conditions, and the resulting relations between physical parameters acting during ductile deformation, to nature is considered controversial (see Herwegh et al., 2005 and references therein). Whereas the relationship between flow stress and recrystallized grain size can be empirically derived from lab experiments using paleopiezometers (e.g. Stipp & Tullis, 2003), the relation between recrystallized grain size, strain rate, differential stress, temperature and activation energy for dislocation creep requires further constraints. For these relations, various power law flow laws for dynamically recrystallized quartz were proposed over the past years (Paterson & Luan, 1990; Luan & Paterson, 1992; Gleason & Tullis, 1995; Hirth et al., 2001, Rutter & Brodie, 2004). The variations in the flow laws are mainly characterized by different starting materials, experimental conditions, the activation energy for dislocation creep and the stress exponent n. In this study we compare and evaluate experimentally derived flow laws regarding their reliability for the prediction of rheology of background deformation of naturally deformed crystalline samples from mylonites of the Aar massif (Swiss Central Alps). The majority of samples comprises highly deformed rocks (e.g. Central Aare granite), which exhibit severe grain size reduction. This reduction dominantly occurred by subgrain rotation (SGR), in the case of low temperature overprint by bulging recrystallization (BLG). Towards elevated temperatures, grain boundary migration (GBM) and SGR recrystallization were active. Along the metamorphic gradient (300 - 475°C) quartz microstructures and associated recrystallized grain size distributions indicate steady state mean grain sizes. The quantification of the metamorphic gradient (temperature, pressure, water fugacity) over the sampling area allowed the application of flow laws, yielding variations of 6 orders of magnitude in deformation rates between different calibrations for one corresponding grain size. The calibrations of Paterson & Luan (1990) and Hirth et al. (2001) yield most reliable results for peak metamorphic conditions, which are in line with the geological framework. Strain rates range between 10E-13 and 10E-10 s-1 (Paterson & Luan, 1990) with corresponding flow stresses between ca. 200 MPa (BLG) to ca. 20 MPa (SGR and transition SGR-GBM). Nevertheless, the applicability of single flow laws shall be discussed in greater detail. REFERENCES Herwegh, M., de Bresser, J.H.P. and ter Heege, J.H. 2005: Combining natural microstructures with composite flow laws: an improved approach for the extrapolation of lab data to nature. Journal of Structural Geology, 27. Hirth, G., Teyssier, C. and Dunlap, W.J. 2011: An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks. International Journal of Earth Sciences, 90. Luan, F.C. and Paterson, S.R. 1992: Perparation and deformation of synthetic aggregates of quartz. Journal of Geophysical Research, 97. Paterson, S.R. and Luan, F.C. 1990: Quartzite rheology under geological conditions. In: de Meer, S., Drury, M.R., de Bresser, J.H.P., Pennock, G.M Deformation mechanisms, rheology and tectonics: from minerals to the lithosphere. Geological Society of Lonodn Special Publications, 54. Rutter, E.H. and Brodie, K.H. 2004: Experimental grain size-sensitive flow of hot-pressed Brazilian quartz aggregates. Journal of Structural Geology, 26. Stipp, M. and Tullis, J. 2003: The recrystallized grain size piezometer for quartz. Geophysical Research Letters, 30.

Microstructure effects on the recrystallization of low-symmetry alpha-uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCabe, Rodney James; Richards, Andrew Walter; Coughlin, Daniel Robert

2015-10-01

We employ electron backscatter diffraction (EBSD) to investigate microstructural evolution of uranium during recrystallization. To understand the relationship between microstructure and recrystallization, we use measures of intra-granular misorientation within grains and near grain boundaries in both deformed (non-recrystallized) uranium and recrystallizing uranium. The data show that the level of intra-granular misorientation depends on crystallographic orientation. However, contrary to expectation, this relationship does not significantly affect the recrystallization texture. Rather, the analysis suggests that recrystallization nucleation occurs along high angle grain boundaries in the deformed microstructure. Specifically, we show that the nucleation of recrystallized grains correlates well with the spatially heterogeneousmore » distribution of high angle boundaries. Due to the inhomogeneous distribution of high angle boundaries, the recrystallized microstructure after long times exhibits clustered distributions of small and large grains. Twin boundaries do not appear to act as recrystallization nucleation sites.« less

Development of a Model for Dynamic Recrystallization Consistent with the Second Derivative Criterion.

PubMed

Imran, Muhammad; Kühbach, Markus; Roters, Franz; Bambach, Markus

2017-11-02

Dynamic recrystallization (DRX) processes are widely used in industrial hot working operations, not only to keep the forming forces low but also to control the microstructure and final properties of the workpiece. According to the second derivative criterion (SDC) by Poliak and Jonas, the onset of DRX can be detected from an inflection point in the strain-hardening rate as a function of flow stress. Various models are available that can predict the evolution of flow stress from incipient plastic flow up to steady-state deformation in the presence of DRX. Some of these models have been implemented into finite element codes and are widely used for the design of metal forming processes, but their consistency with the SDC has not been investigated. This work identifies three sources of inconsistencies that models for DRX may exhibit. For a consistent modeling of the DRX kinetics, a new strain-hardening model for the hardening stages III to IV is proposed and combined with consistent recrystallization kinetics. The model is devised in the Kocks-Mecking space based on characteristic transition in the strain-hardening rate. A linear variation of the transition and inflection points is observed for alloy 800H at all tested temperatures and strain rates. The comparison of experimental and model results shows that the model is able to follow the course of the strain-hardening rate very precisely, such that highly accurate flow stress predictions are obtained.

Development of a Model for Dynamic Recrystallization Consistent with the Second Derivative Criterion

PubMed Central

Imran, Muhammad; Kühbach, Markus; Roters, Franz; Bambach, Markus

2017-01-01

Dynamic recrystallization (DRX) processes are widely used in industrial hot working operations, not only to keep the forming forces low but also to control the microstructure and final properties of the workpiece. According to the second derivative criterion (SDC) by Poliak and Jonas, the onset of DRX can be detected from an inflection point in the strain-hardening rate as a function of flow stress. Various models are available that can predict the evolution of flow stress from incipient plastic flow up to steady-state deformation in the presence of DRX. Some of these models have been implemented into finite element codes and are widely used for the design of metal forming processes, but their consistency with the SDC has not been investigated. This work identifies three sources of inconsistencies that models for DRX may exhibit. For a consistent modeling of the DRX kinetics, a new strain-hardening model for the hardening stages III to IV is proposed and combined with consistent recrystallization kinetics. The model is devised in the Kocks-Mecking space based on characteristic transition in the strain-hardening rate. A linear variation of the transition and inflection points is observed for alloy 800H at all tested temperatures and strain rates. The comparison of experimental and model results shows that the model is able to follow the course of the strain-hardening rate very precisely, such that highly accurate flow stress predictions are obtained. PMID:29099068

Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

NASA Astrophysics Data System (ADS)

Ding, Zong-ye; Hu, Qiao-dan; Zeng, Long; Li, Jian-guo

2016-11-01

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical (USC) rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250°C at strain rates ranging from 0.001 to 1 s-1. The softening mechanism was dynamic recovery (DRV) at 950°C and the strain rate of 1 s-1, whereas it was dynamic recrystallization (DRX) under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJ•mol-1. The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate ( θ)-flow stress ( σ) and -∂ θ/∂ σ-σ curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200°C and a strain-rate range from 0.001 to 0.08 s-1, with a power dissipation efficiency η greater than 31%.

Influence of shoulder diameter on Temperature and Z-parameter during friction stir welding of Al 6082 alloy

NASA Astrophysics Data System (ADS)

Kishore Mugada, Krishna; Adepu, Kumar

2018-03-01

In this research article, the effect of increasing shoulder diameter on temperature and Zener Holloman (Z)-parameter for friction stir butt welded AA6082-T6 was studied. The temperature at the Advancing side (AS) of weld was measured using the K-Type thermocouple at four different equidistant locations. The developed analytical model is utilized to predict the maximum temperature (Tpeak) during the welding. The strain, strain rate, Z- Parameter for all the shoulders at four distinct locations were evaluated. The temperature increases with increase in shoulder diameter and the maximum temperature was recorded for 24mm shoulder diameter. The computed log Z values are compared with the available process map and results shows that the values are in stable flow region and near to stir zone the values are in Dynamic recrystallization region (DRX). The axial load (Fz) and total tool torque (N-m) are found to be higher for shoulder diameter of 21 mm i.e., 6.3 kN and 56.5 N-m respectively.

Solid State Research.

DTIC Science & Technology

1984-02-15

Diode Lasers 10 - 3. MATERIALS RESEARCH 15 3.1 Role of Oxygen in Zone-Melting Recrystallization of Si Films on Si0 2 -Coated Si Substrates 15 3.2 Triple... Film that Has Been Etch-Delineated to Show Sub- ndaries. Upper Graphite Heater Was Scanned in Direction from top to Bottom of Micrograph. 15 3-2...Operation at 1060 nm with a 5-percent differential power efficiency has been obtained from a flashlamp-pumped laser rod of the sensitized garnet Nd:Cr:Gd 3Sc

Microstructural study of the Mertz shear zone, East Antarctica. Implications for deformation processes and seismic anisotropy.

NASA Astrophysics Data System (ADS)

Lamarque, Gaëlle; Bascou, Jérôme; Maurice, Claire; Cottin, Jean-Yves; Ménot, René-Pierre

2015-04-01

The Mertz Shear Zone (MSZ; 146°E 67°S; East Antarctica) is one major lithospheric-scale structure which outcrops on the eastern edge of the Terre Adélie Craton (Ménot et al., 2007) and that could connected with shear zones of South Australia (e.g., Kalinjala or Coorong shear zone (Kleinschmidt and Talarico, 2000; Gibson et al., 2013)) before the Cretaceous opening of the Southern Ocean. Geochronological and metamorphic studies indicated an MSZ activity at 1.7 and 1.5 Ga respectively in amphibolite and greenschists facies conditions. The deformation affects both the intermediate and lower crust levels, without associated voluminous magma injection. Granulite crop out in the area of the MSZ. They were dated at 2.4 Ga (Ménot et al., 2005) and could represent some preserved Neoarchean tectonites. These rocks show various degrees of deformation including penetrative structures that may display comparable features with that observed in amphibolite and greenschists facies rocks, i.e. NS-striking and steeply dipping foliation with weekly plunging lineation. In the field, cinematic indicators for the MSZ argue for a dominant dextral shear sense. We proceed to optical analysis and crystallographic preferred orientation (CPO) measurements using EBSD technique in order to better constrain the deformation processes. Our results highlight (1) a microstructural gradient from highly deformed rocks (mylonites), forming plurimetric large shear bands and showing evidences of plastic deformation, to slightly deformed rocks in preserved cores with no evidences of plastic deformation or with a clear strong static recrystallization; (2) CPO of minerals related with variations on deformation conditions. Feldspar and quartz CPO argue for plastic deformation at high temperature in the most deformed domains and for the absence of deformation or an important stage of static recrystallization in preserved cores; (3) uncommon CPO in orthopyroxene which are characterized by [010]-axes perpendicular to the foliation and [001]-axes parallel to the lineation. These CPO seem to be related to static recrystallization processes. Seismic properties of amphibolite and granulite rocks from the MSZ were calculated in order to evaluate the impact of deformation observed in amphibolite and granulite tectonites to seismic anisotropy. Computations were performed from measured CPO, single crystal elastic stiffness matrix, modal composition and density of characteristic samples. P- and S-waves anisotropies of the cratonic crust affected by the MSZ are small and even tend to be isotropic in the case of S-waves propagating vertically in the crust. These results permit us to better discuss seismic studies and in particular SKS analysis which were recently carried out in this area (Lamarque et al., 2015).

Potential of pressure solution for strain localization in the Baccu Locci Shear Zone (Sardinia, Italy)

NASA Astrophysics Data System (ADS)

Casini, Leonardo; Funedda, Antonio

2014-09-01

The mylonites of the Baccu Locci Shear Zone (BLSZ), Sardinia (Italy), were deformed during thrusting along a bottom-to-top strain gradient in lower greenschist facies. The microstructure of metavolcanic protoliths shows evidence for composite deformation accommodated by dislocation creep within strong quartz porphyroclasts, and pressure solution in the finer grained matrix. The evolution of mylonite is simulated in two sets of numerical experiments, assuming either a constant width of the deforming zone (model 1) or a narrowing shear zone (model 2). A 2-5 mm y-1 constant-external-velocity boundary condition is applied on the basis of geologic constraints. Inputs to the models are provided by inverting paleostress values obtained from quartz recrystallized grain-size paleopiezometry. Both models predict a significant stress drop across the shear zone. However, model 1 involves a dramatic decrease in strain rate towards the zone of apparent strain localization. In contrast, model 2 predicts an increase in strain rate with time (from 10-14 to 10-12 s-1), which is consistent with stabilization of the shear zone profile and localization of deformation near the hanging wall. Extrapolating these results to the general context of crust strength suggests that pressure-solution creep may be a critical process for strain softening and for the stabilization of deformation within shear zones.

The effect of hydrocarbons on the microstructural evolution in rock salt: a case study on hydrocarbon bearing Ara salt from the South Oman Salt Basin

NASA Astrophysics Data System (ADS)

Schmatz, Joyce; Urai, Janos L.; Wübbeler, Franziska M. M.; Sadler, Marc

2014-05-01

It has been shown that dilatant deformation promotes the incorporation of hydrocarbons into typically low permeable rock salt (Schoenherr et al., 2007). However, there is not much knowledge on subsequent mechanisms related to recrystallization processes, which cause morphological and chemical changes of the carbonic inclusions. This work aims to contribute to an increased understanding of fluid inclusion dynamics related to grain boundary migration recrystallization and hence to facilitate the interpretation of complex microstructures in recrystallized, multiphase salt rocks. In this case study we investigate hydrocarbon-impregnated salt from the Cambrian Ara Group in the South Oman Salt Basin. The samples were cored from cm-m thick anhydrite-salt sequences overlying hydrocarbon bearing carbonate stringers in 3300 m depth. The anhydrite layers consist mainly of fine-grained anhydrite, which contains calcite, dolomite, and olivine inclusions. Solid bitumen and lighter hydrocarbon phases are observed in between the anhydrite grains and along cracks. Anhydrite layers host salt veins, which contain fragments of anhydrite. These fragments do not differ in composition or structure from the host material and the related vein microstructures indicate crack-seal mechanisms. Halite in the salt layers is almost entirely recrystallized with solid inclusions consisting of anhydrite, calcite, dolomite and olivine with hydrocarbon-coatings present inside grains and along grain boundaries. Solid inclusions cause pinning indicated by a decreased recrystallized grain size and by the presence of grains with preserved substructures representing earlier deformation phases. We observe two types of carbonic inclusions: I) solid bitumen coatings along grain boundaries and microcracks, interpreted to be incorporated into the salt in an overpressure state that allowed dilatancy of the salt, and II) less degraded, liquid hydrocarbons along grain boundaries in the vicinity of the anhydrite, interpreted to be incorporated into the salt in a subsequent deformation phase. Type II inclusions usually form arrays of isolated inclusions (liquid hydrocarbons, vapor, and aqueous phases in minor proportions) along grain boundaries of the recrystallized grains, presumably formed in a surface-energy controlled shrinking process from thin fluid films. Here, the contact with mobile grain boundaries promoted necking down and decomposition of multiphase inclusions. We present a model, which describes the dynamic behavior of liquid hydrocarbons in mobile grain boundaries after their enclosure into the salt layers. The model is based on numerous microanalytical methods, such as optical microscopy, fluorescence microscopy, cryo-SEM, and EDX. Schoenherr, J., et al. (2007), Limits to the sealing capacity of rock salt: A case study of the infra-Cambrian Ara Salt from the South Oman salt basin, AAPG Bulletin, 91(11), 1541-1557

High-Temperature Deformation Behavior of HCP Alloys -- An Internal Variable Approach

DTIC Science & Technology

2006-05-31

successfully to characterize the high temperature deformation behavior of various metallic materials such as Al alloys, Pb-Sn hyper- eutectic alloy, and...implying dynamic recrystallization (DRX) and GBS as the major deformation mechanisms at 523 K and 10-4 /s. Large cavities are observed at the

Fundamental Investigation of the Microstructural Parameters to Improve Dynamic Response in Al-Cu Model System

DTIC Science & Technology

2014-05-01

grain size. Recrystallization was then induced via annealing just above the solvus temperature. After quenching , the bars were immediately placed into...that the values were statistically significant. Precipitate sizes ranged from approximately 100 nanometers in diameter up to 2-5 microns in diameter

Hurst exponent used as a tool to differentiate between magmatic and fluid-induced processes as reflected in crystal geochemistry

NASA Astrophysics Data System (ADS)

Domonik, A.; Słaby, E.; Śmigielski, M.

2012-04-01

A self-similarity parameter, the Hurst exponent (H) (called also roughness exponent) has been used to show the long-range dependence of element behaviour during the processes. The H value ranges between 0 and 1; a value of 0.5 indicates a random distribution indistinguishable from noise. For values greater or less than 0.5, the system shows non-linear dynamics. H < 0.5 represents anti-persistent (more chaotic) behaviour, whereas H > 0.5 corresponds to increasing persistence (less chaotic). Such persistence is characterized as an effect of a long-term memory, and thus by a large degree of positive correlation. In theory, the preceding data constantly affect the next in the whole temporal series. Applied to chaotic dynamics, the system shows a subtle sensitivity to initial conditions. The process can show some degree of chaos, due to local variations, but generally, the trend preserves its persistent character through time. If the exponent value is low, the process shows frequent and sudden reversals e.g. the trends of such a process show mutual negative correlation of the succeding values in the data series. Thus, the system can be described as having a high degree of deterministic chaos. Alkali feldspar megacrysts grown from mixed magmas and recrystallized due to interaction with fluids have been selected for the study (Słaby et al., 2011). Hurst exponent variability has been calculated within some primary-magmatic and secondary-recrystallized crystal domains for some elements redistributed by crystal fluid interaction. Based on the Hurst exponent value two different processes can easily be recognized. In the core of the megacrysts the element distribution can be ascribed to magmatic growth. By contrast, the marginal zones can relate to inferred late crystal-fluid interactions. Both processes are deterministic, not random. The spatial distribution of elements in the crystal margins is irregular, with high-H values identifying the process as persistent. The trace element distributions in feldspar cores are almost homogeneous and only relatively small and irregular variations in trace element contents makes their growth morphology slightly patchy. Despite homogenization the fractal statistics reveal that trace elements were incorporated chaotically into the growing crystal. The anti-persistent chaotic behaviour of elements during magmatic growth of the feldspars progressively changes into persistent behaviour within domains, where re-crystallization reaction took place. Elements demonstrate variable dynamics of this exchange corresponding to increasing persistency. This dynamics is different for individual elements compared to analogical, observed for crystallization process proceeding from mixed magmas. Consequently, it appears that fractal statistics clearly discriminate between two different processes, with contrasted element behaviour during these processes. One process is magma crystallization and it is recorded in the core of the megacrysts; the second is recorded in the crystal rims and along cleavages and cracks, such that it can be related to a post-crystallization process linked to fluid percolation. Słaby, E., Martin, H., Hamada, M., Śmigielski, M., Domonik, A., Götze, J., Hoefs, J., Hałas, S., Simon, K., Devidal, J-L., Moyen, J-F., Jayananda, M. (2011) Evidence in Archaean alkali-feldspar megacrysts for high-temperature interaction with mantle fluids. Journal of Petrology (on line). doi:10.1093/petrology/egr056

Susceptibility of Goethite to Fe2+-Catalyzed Recrystallization over Time.

PubMed

Joshi, Prachi; Fantle, Matthew S; Larese-Casanova, Philip; Gorski, Christopher A

2017-10-17

Recent work has shown that iron oxides, such as goethite and hematite, may recrystallize in the presence of aqueous Fe 2+ under anoxic conditions. This process, referred to as Fe 2+ -catalyzed recrystallization, can influence water quality by causing the incorporation/release of environmental contaminants and biological nutrients. Accounting for the effects of Fe 2+ -catalyzed recrystallization on water quality requires knowing the time scale over which recrystallization occurs. Here, we tested the hypothesis that nanoparticulate goethite becomes less susceptible to Fe 2+ -catalyzed recrystallization over time. We set up two batches of reactors in which 55 Fe 2+ tracer was added at two different time points and tracked the 55 Fe partitioning in the aqueous and goethite phases over 60 days. Less 55 Fe uptake occurred between 30 and 60 days than between 0 and 30 days, suggesting goethite recrystallization slowed with time. Fitting the data with a box model indicated that 17% of the goethite recrystallized after 30 days of reaction, and an additional 2% recrystallized between 30 and 60 days. The decreasing susceptibility of goethite to recrystallize as it reacted with aqueous Fe 2+ suggested that recrystallization is likely only an important process over short time scales.

Eurekan deformation on Prins Karls Forland, Svalbard - new insights from Ar40/Ar39 muscovite dating

NASA Astrophysics Data System (ADS)

Faehnrich, Karol; Schneider, David; Manecki, Maciej; Czerny, Jerzy; Myhre, Per Inge; Majka, Jarosław; Kośmińska, Karolina; Barnes, Christopher; Maraszewska, Maria

2017-04-01

Eurekan deformation has been proven to be a complex sequence of tectonic episodes, dominated by compression in the Circum Arctic region. It was associated with early Cenozoic collision of Eurasia, North America and Greenland plates producing fold-thrust belt style of deformation. Timing of this enigmatic event has not yet been extensively resolved by radiometric dating (Piepjohn et al. 2016, Journal of the Geological Society, 173(6), 1007-1024). Reinhardt et al. (2013, Z. Dt. Ges. Geowiss., 164 (1), 131-147) dated syn-tectonic volcanic ashes at c. 60 Ma and 54 Ma on Ellesmere Island, Canada. Tagner et al. (2011, Earth and Planetary Science Letters, 303(3), 203-214) interpreted c. 49-47 Ma 40Ar/39Ar ages on trachyte flows in northern Greenland as peak compression during the Eurekan event. On Svalbard, Tessensohn et al. (2001, Geologisches Jahrbuch, B 91, 83-104) reported K/Ar whole rock ages ranging from c. 67 to 49 Ma for the slates from Svartfjella-Eidembukta-Daudmannsodden Lineament. Bentonite layers in the Central Tertiary Basin are as young as c. 56 Ma (Charles et al. 2011, Geochem. Geophys. Geosyst., 12, 1-19), predating latest deformation. Moreover, Barnes et al (2017, in prep.) applied (U-Th)/He thermochronology along the western margin of Svalbard and resolved Early to Middle Eocene heating, likely documenting burial related to thrusting. Here we present new results from 40Ar/39Ar muscovite dating of ductile to brittle shear zone on Prins Karls Forland, Svalbard, indicating Eurekan age of thrusting. Prins Karls Forland is dominated by Neoproterozoic siliciclastic metasediments (comprising Caledonian basement) regionally metamorphosed to greenschist facies conditions. A ˜1 km wide ductile to brittle shear zone (the Bouréefjellet shear zone) separates the amphibolite facies Pinkie Unit from the lower grade upper structural unit, the Grampianfjella Formation (Faehnrich et al. 2016, EGU 2016). The age of the amphibolite facies metamorphism (c. 370-355 Ma) indicates Ellesmerian tectonism, unlike other higher grade rocks on Svalbard (Kośmińska et al. 2016, EGU 2016). Ten metasedimentary rocks from within the shear zone were collected for dating, with eight muscovite crystals dated per sample via 40Ar/39Ar total fusion. High strain is evinced by mylonitic fabric, mica fish or C' shear zones. Moreover, quartz was dynamically recrystallized with significant grain boundary migration. There is notable age dispersion between the samples with weighted mean ages varying from 45 up to 103 Ma and single grain ages are more than 300 Ma, reflecting partial recrystallization and resetting during Eurekan deformation. Younger ages were obtained from lower structural levels, yielding dates of 44 to 54 Ma for the Eurekan deformation on Prins Karls Forland. We suggest that an Ellesmerian ductile shear zone was reactivated during Eocene (commencing as early as 54 Ma) progressing to brittle conditions which continued after 44 Ma. These are the first documented Eurekan 40Ar/39Ar muscovite deformation ages from Svalbard, and enable to better distinguish individual stages of the Eurekan deformation in the Eocene improving our understanding of relative plate tectonic movements. This work is partially funded by AGH research grant no 11.11.140.319 and the NCN research projects 2013/11/N/ST10/00357 and 2015/17/B/ST10/03114.

Geological constraints on the mechanism of tectonic tremor

NASA Astrophysics Data System (ADS)

Kirkpatrick, J. D.

2016-12-01

Observations of tectonic tremor in a wide variety of tectonic settings suggest that transitional behavior involving contemporaneous shear fracture and aseismic creep transients occurs in many major faults. Seismological and geophysical data indicate shear failure on critically stressed faults, likely under low effective stress conditions, are consistent characteristics, even though rock types and grain scale deformation mechanisms vary at these different locations. Geological observations could add additional insight into the specific failure mechanisms if the structures that form during tremor episodes can be identified. Exhumed shear zones often contain folded, boudinaged and/or dynamically recrystallized veins that record cyclical fracture and viscous deformation representing mixed bulk rheology. Examples from a Cretaceous transpressional continental shear zone in the Sierra Nevada, CA, include quartz-filled veins meters to tens of meters long with millimeters to centimeters of shear offset that preferentially developed along foliation planes in a high strain zone. Ambient temperatures during deformation were 400-600°C, and opening mode vein orientations and abundance suggest fluid pressure was near lithostatic at times. The orientation and spatial distribution of the veins indicate they formed under differential stress large enough for shear failure with pore pressures sufficiently high for the rocks to be critically stressed along mechanically weak foliation planes. Bulk deformation of the surrounding rock was accommodated viscously by crystal plastic deformation mechanisms. The mode of fracturing and overall behavior of the system was controlled by the local competition between the rates of stress recovery following fracture and stress drop, and pore pressure build up. The inferred mixed rheology recorded by the veins is phenomenologically similar to tremor. These shear fractures, and the conditions of failure they record, could be comparable to the mechanism that produces tectonic tremor.

The Recrystallization Behavior of Unalloyed Mg and a Mg-Al Alloy

NASA Astrophysics Data System (ADS)

Murphy, Aeriel D.; Allison, John E.

2018-02-01

The static recrystallization behavior of pure Mg and Mg-4Al was characterized over a range of annealing temperatures. The electron backscatter diffraction grain orientation spread technique was used to quantify the level of recrystallization at various annealing times. Recrystallization kinetics were characterized using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) relationship and it was found that two sequential annealing stages exist. Stage 1 involves heterogeneous nucleation of recrystallization in regions with a high stored energy, including twins and grain boundaries, and can be represented by an Avrami exponent of n 1 ranging from 0.35 to 0.6. During Stage 2, recrystallization occurred predominately in the interior of deformed grains with incomplete recrystallization generally observed even at annealing times in excess of two weeks. The second recrystallization stage exhibited a much lower Avrami exponent, n 2, ranging from 0.02 to 0.2. Increasing the starting grain size in the pure Mg condition led to a significant delay in recrystallization. The addition of Al had a minimal effect on the recrystallization kinetics of Mg.

New insights on the rheological properties of a rocksalt

NASA Astrophysics Data System (ADS)

Speranza, G.; Vinciguerra, S.; Di Genova, D.; Romano, C.; Vona, A.; Mollo, S.; Iarocci, A.

2013-12-01

The importance and economic interest on rocksalt deposits and salt bodies are well known and extensively studied. The physical and mechanical properties of salt have a profound influence on the tectonics as well as they are considered to be vital for applicative purposes such as mining, petroleum and nuclear waste storage. However, previous scientific works have mainly focused on synthetic rocksalt or commercial salt, whereas natural salt facies have been scarcely investigated. In this view, we present new data on the role of natural heterogeneities (i.e., relative abundance of primary salt crystals and impurities) on the rheological parameters of a rocksalt. This rock belongs to the Saline di Volterra formation (Volterra basin, Tuscany, central Italy) that was deposited during the Messinian Salinity Crisis. The 49-metre-thick salt sequence (intersected by the S1113 borehole of the Solvay company) is characterized by a high salt facies variability. In particular, three end-members have been recognized: the first contains abundant primary salt crystals, with minor or no recrystallizazion; the second member is extensively recrystallized, with scarce primary crystal remnants; the third shows a great abundance of clay impurities. Rheological parameters, such as static and dynamic Young's Modulus and coefficient of linear expansion, were measured for the three rocksalt end-members throughout P and S seismic velocities, uniaxial compressive strength and thermal expansion measurements. Seismic velocity has been measured on cubic samples with a side ranging from 4 to 7 cm. A clear effect of the salt facies was found: the average velocity is faster in mostly recrystallized salt samples (4500 m/s), slower in primary salt-rich samples (4300 m/s), and intermediate (4350 m/s) in presence of clay impurities. Dynamic Young's Modulus calculated on velocities (average value ≈ 38 GPa) mirrors this behavior, with lowest values related to primary salt. The anisotropic effect induced by the deformation is evident considering the wave velocities measured for each axis of the cubes, with lower velocities along the Z (vertical) axis. Uniaxial compressive tests (carried out at ambient temperature) revealed the effect of the salt facies in the mechanical properties and, particularly, in the elastic properties and in the absolute peak stress value. Static Young's Moduli (average value ≈ 5,3 GPa) result much lower than the dynamic ones. In this case lowest values are related to recrystallized salt. Notably, the peak stress is inversely proportional to the static Young's Moduli. Moreover, data from thermal expansion curves (from 20 to 700 °C) show a greater amount of volume expansion of primary salt and allowed to identify an 'instability zone', between 300 and 500 °C, where fluid emission, samples cracking and a sudden increase in volume expansivity occur. Results from our experiments indicate that the different characteristics of salt facies determine the bulk rheological parameters and, consequently, the rocksalt deformation behavior. Although further analyses are necessary, we suggest that studies on salt bodies cannot be approached without detailed petrophysical and rheological analyses of rocksalt facies.

Recrystallization of polycrystalline silicon

NASA Technical Reports Server (NTRS)

Lall, C.; Kulkarni, S. B.; Graham, C. D., Jr.; Pope, D. P.

1981-01-01

Optical metallography is used to investigate the recrystallization properties of polycrystalline semiconductor-grade silicon. It is found that polycrystalline silicon recrystallizes at 1380 C in relatively short times, provided that the prior deformation is greater than 30%. For a prior deformation of about 40%, the recrystallization process is essentially complete in about 30 minutes. Silicon recrystallizes at a substantially slower rate than metals at equivalent homologous temperatures. The recrystallized grain size is insensitive to the amount of prestrain for strains in the range of 10-50%.

Forging property, processing map, and mesoscale microstructural evolution modeling of a Ti-17 alloy with a lamellar (α+β) starting microstructure

NASA Astrophysics Data System (ADS)

Matsumoto, Hiroaki; Naito, Daiki; Miyoshi, Kento; Yamanaka, Kenta; Chiba, Akihiko; Yamabe-Mitarai, Yoko

2017-12-01

This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10-3 s-1 to 1 s-1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In the β phase, continuous dynamic recrystallization is the dominant mode below the transition temperature, Tβ (880 890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures above Tβ, continuous dynamic recrystallization of the β phase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+β) region.

Forging property, processing map, and mesoscale microstructural evolution modeling of a Ti-17 alloy with a lamellar (α+β) starting microstructure

PubMed Central

Matsumoto, Hiroaki; Naito, Daiki; Miyoshi, Kento; Yamanaka, Kenta; Chiba, Akihiko; Yamabe-Mitarai, Yoko

2017-01-01

Abstract This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10−3 s−1 to 1 s−1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In the β phase, continuous dynamic recrystallization is the dominant mode below the transition temperature, T β (880~890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures above T β, continuous dynamic recrystallization of the β phase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+β) region. PMID:29152021

Forging property, processing map, and mesoscale microstructural evolution modeling of a Ti-17 alloy with a lamellar (α+β) starting microstructure.

PubMed

Matsumoto, Hiroaki; Naito, Daiki; Miyoshi, Kento; Yamanaka, Kenta; Chiba, Akihiko; Yamabe-Mitarai, Yoko

2017-01-01

This work identifies microstructural conversion mechanisms during hot deformation (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10 -3  s -1 to 1 s -1 ) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure and establishes constitutive formulae for predicting the microstructural evolution using finite-element analysis. In the α phase, lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. In the β phase, continuous dynamic recrystallization is the dominant mode below the transition temperature, T β (880~890 °C). Dynamic recovery tends to be more active at conditions of lower strain rates and higher temperatures. At temperatures above T β , continuous dynamic recrystallization of the β phase frequently occurs, especially in the lower strain rate region. A set of constitutive equations modeling the microstructural evolution and processing map characteristic are established by optimizing the experimental data and were later implemented in the DEFORM-3D software package. There is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging in the (α+ β ) region.

Characterization of transpressive deformation in shear zones of the Archean North Caribou greenstone belt (NW Superior Province) and the relationship with regional metamorphism

NASA Astrophysics Data System (ADS)

Gagnon, Émilie; Schneider, David A.; Kalbfleisch, Tash; Habler, Gerlinde; Biczok, John

2016-12-01

The 2.7-3.0 Ga North Caribou greenstone belt (NCGB), host to the Musselwhite BIF-hosted gold deposit, possesses abundant shear zones on its northern margins, which appear to have formed under amphibolite facies conditions. Protracted deformation and regional metamorphism are coeval with widespread magmatism and accretion events during crustal amalgamation of the Western Superior Province, and are responsible for folding the ore-hosting BIF and channeling fluids. The importance of shear zones in behaving as conduits for fluids during the tectonic evolution of the NCGB is not well known and their relationship with metamorphism is equivocal, yet higher-grade, syn- to post-tectonic metamorphic minerals seem to correlate with loci of higher strain. Structural analyses support oblique transpressive collision that produced steeply-dipping planar and shallowly-plunging linear fabrics with dominant dextral kinematics, that trend broadly parallel to the doubly arcuate shape of the belt. Electron backscatter diffraction analyses were conducted on strategic samples across one shear zone in order to characterize crustal conditions during transpressive deformation. The Dinnick Lake shear zone cuts through mafic metavolcanics and at its core is an L-tectonite granite composed of recrystallized quartz. Whole rock geochemistry shows little variation in Ca, Na, Mg and K (often used as indicators of hydrothermal alteration) from surrounding less deformed units, suggesting deformation in a dry environment. Microstructural analysis indicates subgrain rotation recrystallization and deformation by prism a- and c-slip in quartz, as well as aligned hornblende that suggest deformation temperatures above 500 °C. Quartz in mafic rocks along the margins of the shear zone also exhibits a basal a-slip component, indicating a slight decrease in strain or temperature. Although the NCGB exhibits some first-order evidence of vertical tectonism (dome and keel geometries), the dominant strain record within shear zones is that of horizontal (oblique transpressive) displacement. This is in agreement with other greenstone belts in the Western Superior Province where vertical tectonism and horizontal tectonism were coeval. Table A1. Whole rock geochemistry of basalts. Table A2. Whole rock geochemistry of granites. Table B.1. Parameters and conditions of machine during EBSD data collection. Table D1. Table of corresponding probability and critical d values of the K-S test. Fig. E1. Feldspar pole figures. Fig. E2. Hornblende pole figures. Fig. F1. Grain boundary misorientation histograms of feldspars. Fig. F2. Grain boundary misorientation histograms of hornblende.

Rheology and Deformation Mechanisms in a High Temperature Shear Zone from a Microstructural and Crystalographic Preferred Orientation Approach: AN Example from se Brazil

NASA Astrophysics Data System (ADS)

Cavalcante, G. C.; Egydio-Silva, M.; Vauchez, A. R.; Lagoeiro, L. E.

2014-12-01

The Ribeira belt, located in southeastern Brazil, was formed during the Brasiliano (Pan- African) orogeny by the collision between the proto South American and African continents resulting in the amalgamation of Western Gondwana at around 670-480 Ma. Its northern termination displays a transcurrent shear zone network, the 250 km long Além Paraíba-Pádua shear zone, which involves granulites, migmatites and granites facies mylonites deformed in transpression. A detailed microstructural and crystallographic preferred orientation (CPO) study of the rock-forming minerals is being undertaken to infer constraints on the rheology of continental crust during the nucleation and development of this shear zone. A variety of mylonites (from protomylonites to ultramylonites) have been analyzed by Electron Backscattering Diffraction (EBSD) in order to determine the CPO of minerals, especially quartz, feldspars, amphibole, pyroxene and biotite. High-grade mylonites often exhibit ribbon-shaped quartz, probably due to high temperature grain boundary migration. They frequently wrap around K-feldspar porphyroclast exhibiting undulose extinction and core-mantle structures that may be related to bulging and/or subgrain rotation recrystallisation. In these HT mylonites, plagioclase is dynamically recrystallized and form fine-grained layers alternating with quartz-ribbons. Hornblende porphyroclasts present strain shadows of opaque mineral. Medium to high-grade mylonites derived from each felsic and mafic granulite and migmatitic gneisses show plagioclase with undulose extinction and deformation twins, quartz grains with both ribbon and porphyroclast shapes (> 3mm in size), orthopyroxene and garnet as porhyroclast and porphyroblast, respectively, and strongly oriented biotite. CPO of quartz indicates that it was deformed through plastic deformation with the activation of prism {a}. Feldspar CPOs show concentrations of [001] close to the lineation, of [010] close to the pole of the foliation and of [100] close to the Y strain axis, suggesting activation of the [001] (010) slip system.

Modeling of the flow behavior of SAE 8620H combing microstructure evolution in hot forming

NASA Astrophysics Data System (ADS)

Fu, Xiaobin; Wang, Baoyu; Tang, Xuefeng

2017-10-01

With the development of net-shape forming technology, hot forming process is widely applied to manufacturing gear parts, during which, materials suffer severe plastic distortion and microstructure changes continually. In this paper, to understand and model the flow behavior and microstructure evolution, SAE 8620H, a widely used gear steel, is selected as the object and the flow behavior and microstructure evolution are observed by an isothermal hot compression tests at 1273-1373 K with a strain rate of 0.1-10 s-1. Depending on the results of the compression test, a set of internal-state-variable based unified constitutive equations is put forward to describe the flow behavior and microstructure evaluation of SAE 8620H. Moreover, the evaluation of the dislocation density and the fraction of dynamic recrystallization based on the theory of thermal activation is modeled and reincorporated into the constitutive law. The material parameters in the constitutive model are calculated based on the measured flow stress and dynamic recrystallization fraction. The predicted flow stress under different deformation conditions has a good agreement with the measured results.

The Microstructural Evolution and Special Flow Behavior of Ti-5Al-2Sn-2Zr-4Mo-4Cr During Isothermal Compression at a Low Strain Rate

NASA Astrophysics Data System (ADS)

Sun, J. Z.; Li, M. Q.; Li, H.

2017-09-01

The microstructural evolution and special flow behavior of Ti-5Al-2Sn-2Zr-4Mo-4Cr during isothermal compression at a strain rate of 0.0001 s-1 were investigated. The dislocation climbs in elongated α grains resulted in the formation of low-angle boundaries that transform into high-angle boundaries with greater deformation, and the elongated α grains subsequently separated into homogenous globular α grains with the penetration of the β phase. The simultaneous occurrence of discontinuous dynamic recrystallization and continuous dynamic recrystallization in the primary β grains resulted in a trimode grain distribution. The β grains surrounded by dislocations presented an equilateral-hexagonal morphology, which suggests that grain boundary sliding through dislocation climbs was the main deformation mechanism. The true stress-strain curves for 1073 and 1113 K abnormally intersect at a strain of 0.35, related to the α → β phase transformation and distinct growth of the β grain size.

Molecular Dynamics, Recrystallization Behavior, and Water Solubility of the Amorphous Anticancer Agent Bicalutamide and Its Polyvinylpyrrolidone Mixtures.

PubMed

Szczurek, Justyna; Rams-Baron, Marzena; Knapik-Kowalczuk, Justyna; Antosik, Agata; Szafraniec, Joanna; Jamróz, Witold; Dulski, Mateusz; Jachowicz, Renata; Paluch, Marian

2017-04-03

In this paper, we investigated the molecular mobility and physical stability of amorphous bicalutamide, a poorly water-soluble drug widely used in prostate cancer treatment. Our broadband dielectric spectroscopy measurements and differential scanning calorimetry studies revealed that amorphous BIC is a moderately fragile material with a strong tendency to recrystallize from the amorphous state. However, mixing the drug with polymer polyvinylpyrrolidone results in a substantial improvement of physical stability attributed to the antiplasticizing effect governed by the polymer additive. Furthermore, IR study demonstrated the existence of specific interactions between the drug and excipient. We found out that preparation of bicalutamide-polyvinylpyrrolidone mixture in a 2-1 weight ratio completely hinder material recrystallization. Moreover, we determined the time-scale of structural relaxation in the glassy state for investigated materials. Because molecular mobility is considered an important factor governing crystallization behavior, such information was used to approximate the long-term physical stability of an amorphous drug and drug-polymer systems upon their storage at room temperature. Moreover, we found that such systems have distinctly higher water solubility and dissolution rate in comparison to the pure amorphous form, indicating the genuine formulation potential of the proposed approach.

Effects of various tool pin profiles on mechanical and metallurgical properties of friction stir welded joints of cryorolled AA2219 aluminium alloy

NASA Astrophysics Data System (ADS)

Kamal Babu, Karupannan; Panneerselvam, Kavan; Sathiya, Paulraj; Noorul Haq, Abdul Haq; Sundarrajan, Srinivasan; Mastanaiah, Potta; Srinivasa Murthy, Chunduri Venkata

2018-02-01

Friction stir welding (FSW) process was conducted on cryorolled (CR) AA2219 plate using different tool pin profiles such as cylindrical pin, threaded cylindrical pin, square pin and hexagonal pin profiles. The FSW was carried out with pairs of 6 mm thick CR aluminium plates with different tool pin profiles. The different tool pin profile weld portions' behaviors like mechanical (tensile strength, impact and hardness) and metallurgical characteristics were analyzed. The results of the mechanical analysis revealed that the joint made by the hexagonal pin tool had good strength compared to other pin profiles. This was due to the pulsating action and material flow of the tool resulting in dynamic recrystallization in the weld zone. This was confirmed by the ultra fine grain structure formation in Weld Nugget (WN) of hexagonal pin tool joint with a higher percentage of precipitate dissolution. The fractograph of the hexagonal tool pin weld portion confirmed the finer dimple structure morphology without having any interior defect compared to other tool pin profiles. The lowest weld joint strength was obtained from cylindrical pin profile weld joint due to insufficient material flow during welding. The Transmission Electron Microscope and EDX analysis showed the dissolution of the metastable θ″, θ' (Al2Cu) partial precipitates in the WN and proved the influence of metastable precipitates on enhancement of mechanical behavior of weld. The XRD results also confirmed the Al2Cu precipitation dissolution in the weld zone.

Evolution of microstructure of Haynes 230 and Inconel 617 under mechanical testing at high temperatures

NASA Astrophysics Data System (ADS)

Hrutkay, Kyle

Haynes 230 and Inconel 617 are austenitic nickel based superalloys, which are candidate structural materials for next generation high temperature nuclear reactors. High temperature deformation behavior of Haynes 230 and Inconel 617 have been investigated at the microstructural level in order to gain a better understanding of mechanical properties. Tensile tests were performed at strain rates ranging from 10-3-10-5 s -1 at room temperature, 600 °C, 800 °C and 950 °C. Subsequent microstructural analysis, including Scanning Electron Microscopy, Transmission Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, and X-Ray Diffraction were used to relate the microstructural evolution at high temperatures to that of room temperature samples. Grain sizes and precipitate morphologies were used to determine high temperature behavior and fracture mechanics. Serrated flow was observed at intermediate and high temperatures as a result of discontinuous slip and dynamic recrystallization. The amplitude of serration increased with a decrease in the strain rate and increase in the temperature. Dynamic strain ageing was responsible for serrations at intermediate temperatures by means of a locking and unlocking phenomenon between dislocations and solute atoms. Dynamic recrystallization nucleated by grain and twin bulging resulting in a refinement of grain size. Existing models found in the literature were discussed to explain both of these phenomena.

Monazite behaviours during high-temperature metamorphism: a case study from Dinggye region, Tibetan Himalaya

NASA Astrophysics Data System (ADS)

Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Shi-Ran; Zhang, Jin-Jiang

2017-04-01

Monazite is a key accessory mineral for metamorphic geochronology, but its growth mechanisms during melt-bearing high-temperature metamorphism is not well understood. Therefore, the petrology, pressure-temperature and timing of metamorphism have been investigated in pelitic and psammitic granulites from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent an isothermal decompression process from pressure conditions of >10 kbar to <5 kbar with constant temperatures of 750-830°C, and recorded three metamorphic stages of kyanite-grade (M1), sillimanite-grade (M2) and cordierite-spinel grade (M3). Monazite and zircon crystals were analyzed for ages by microbeam techniques either in mounts or thin sections. Ages were linked to specific conditions of mineral growth by comprehensive studies on zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural correlations with coexisting minerals. The results show that inherited domains (500-400 Ma) are common in monazite even at granulite-facies conditions. Few monazites formed at the M1-stage ( 30-29 Ma) and recorded heterogeneous Th, Y, and HREE compositions, which formed by recrystallization related to muscovite dehydration melting reaction. These monazite grains were protected from dissolution or lateral overprinting mainly by the armour effect of matrix crystals (biotite and quartz). Most monazite grains formed at the M3-stage (21-19 Ma) through either dissolution-reprecipitation or recrystallization that was related to biotite dehydration melting reaction. These monazite grains record HREE and Y signatures in local equilibrium with different reactions involving either garnet breakdown or peritectic garnet growth. Another peak of monazite growth occurs during melt crystallization ( 15 Ma), and these monazites are unzoned and have homogeneous compositions. Our results documented the widespread recrystallization to account for monazite growth during high-temperature metamorphism and related melting reactions that trigger monazite recrystallization. In a regional sense, our P-T-t data along with published data indicate that the pre-M1 eclogite-facies metamorphism occurred at 39-30 Ma in the Dinggye Himalaya. Our results are in favour of a steady exhumation of the GHC rocks since Oligocene that was contributed by partial melting. Key words: U-Th-Pb geochronology, Monazite, Recrystallization, Pelitic granulite, Himalaya

The silicon on dust substrate path to make solar cells directly from a gaseous feedstock

NASA Astrophysics Data System (ADS)

Serra, J M; Pinto, C R; Silva, J A; Brito, M C; Maia Alves, J; Vallêra, A M

2009-04-01

In this paper, we present a silicon on dust substrate (SDS) process, a new method for the growth of silicon ribbons. As a demonstration of the concept, we also present results on solar cells made of these new silicon ribbons. SDS ribbons were obtained directly from a gaseous feedstock by a fast CVD step using silane. The resulting self-supported intrinsic ribbons were microcrystalline and porous. To make these ribbon films suitable for photovoltaic applications, a novel recrystallization with an in situ doping step was developed. To this purpose, the ribbons were sprayed with boric acid and then recrystallized by float zone melting. Simple solar cells were prepared by employing: aluminium back contacts, Ti/Pd/Ag front grid contacts, with no anti-reflective coating, doping optimization, passivation or gettering. The 1-sun I-V characteristics of the cells were: Voc ~ 530 mV and Jsc ~ 24 mA cm-2. The minority carrier diffusion length obtained from a spectral response at long wavelengths gave values of Ln ~ 70 µm.

High-pressure crystallization vs. recrystallization origin of garnet pyroxenite-eclogite within subduction related lithologies

NASA Astrophysics Data System (ADS)

Faryad, S. W.; Jedlicka, R.; Hauzenberger, C.; Racek, M.

2018-03-01

Mafic layers displaying transition between clinopyroxenite and eclogite within peridotite from felsic granulite in the Bohemian Massif (Lower Austria) have been investigated. The mafic-ultramafic bodies shared a common granulite facies metamorphism with its hosting felsic rocks, but they still preserve evidence of eclogite facies metamorphism. The selected mafic layer for this study is represented by garnet with omphacite in the core of coarse-grained clinopyroxene, while fine-grained clinopyroxene in the matrix is diopside. In addition, garnet contains inclusions of omphacite, alkali feldspars, hydrous and other phases with halogens and/or CO2. Textural relations along with compositional zoning in garnet from the clinopyroxenite-eclogite layers favour solid-state recrystallization of the precursor minerals in the inclusions and formation of garnet and omphacite during subduction. Textures and major and trace element distribution in garnet indicate two stages of garnet growth that record eclogite facies and subsequent granulite facies overprint. The possible model explaining the textural and compositional changes of minerals is that the granulite facies overprint occurred after formation and exhumation of the eclogite facies rocks.

Geologic history and hydrogeologic setting of the Edwards-Trinity aquifer system, west-central Texas

USGS Publications Warehouse

Barker, R.A.; Bush, P.W.; Baker, E.T.

1994-01-01

Because the diagenetic effects of cementation, recrystallization, and mineral replacement diminish the hydraulic conductivity of most rocks composing the Trinity and Edwards-Trinity aquifers, transmissivity values average less than 10,000 feet squared per day over more than 90 percent of the study area. However, the effects of tectonic fractures and dissolution in the Balcones fault zone cause transmissivity values to average about 750,000 feet squared per day in the Edwards aquifer, which occupies less than 10 percent of the study area.

Purification of organic nonlinear optical materials for bulk crystal growth from melt

NASA Astrophysics Data System (ADS)

Gebre, Tesfaye; Bhat, Kamala N.; Batra, Ashok K.; Lal, Ravindra B.; Aggarwal, Mohan D.; Penn, Benjamin G.; Frazier, Donald O.

2002-10-01

The techniques developed for purification of nonlinear optical organic materials, such as benzil, 2-methyl-4-nitroaniline (MNA), Dicyanovinyl anisole (DIVA) and its derivatives, nitrophenyl prolinol (NPP) and other Schiff's base compounds, include Kugelrohy method, physical vapor transport, zone refining and recrystallization from the solvent are described. Purity of the materials is tested using differential thermal analysis, gas chromatograph/Mass detector, Fourier Transform Infrared spectroscopy and melting point measurements. The purified materials were later used in the growth of single crystal by Bridgman-Stockbarger and Czochralski techniques.

Modeling and simulation framework for dynamic strain localization in elasto-viscoplastic metallic materials subject to large deformations

DOE PAGES

Mourad, Hashem Mourad; Bronkhorst, Curt Allan; Livescu, Veronica; ...

2016-09-23

This study describes a theoretical and computational framework for the treatment of adiabatic shear band formation in rate-sensitive polycrystalline metallic materials. From a computational perspective, accurate representation of strain localization behavior has been a long-standing challenge. In addition, the underlying physical mechanisms leading to the localization of plastic deformation are still not fully understood. The proposed framework is built around an enhanced-strain finite element formulation, designed to alleviate numerical pathologies known to arise in localization problems, by allowing a localization band of given finite width (weak discontinuity) to be embedded within individual elements. The mechanical threshold strength (MTS) model ismore » used to represent the temperature and strain rate-dependent viscoplastic response of the material. This classical flow stress model employs an internal state variable to quantify the effect of dislocation structure evolution (work hardening and recovery). In light of growing evidence suggesting that the softening effect of dynamic recrystallization may play a significant role, alongside thermal softening, in the process of shear band formation and growth, a simple dynamic recrystallization model is proposed and cast within the context of the MTS model with the aid of the aforementioned internal state variable. An initiation criterion for shear localization in rate and temperature-sensitive materials is introduced and used in the present context of high-rate loading, where material rate-dependence is pronounced and substantial temperature increases are achieved due to the dissipative nature of viscoplastic processes. In addition, explicit time integration is adopted to facilitate treatment of the dynamic problems under consideration, where strain rates in excess of 10 4 s –1 are typically attained. Two series of experiments are conducted on AISI 316L stainless steel, employing the commonly used top-hat sample geometry and the Split-Hopkinson Pressure Bar dynamic test system. Axi-symmetric finite element simulation results are compared to cross-sectional micrographs of recovered samples and experimental load–displacement results, in order to examine the performance of the proposed framework and demonstrate its effectiveness in treating the initiation and growth of adiabatic shear banding in dynamically loaded metallic materials. These comparisons demonstrate that thermal softening alone is insufficient to induce shear localization behaviors observed in some materials, such as stainless steel, and support the hypothesis that dynamic recrystallization and/or other softening mechanisms play an essential role in this process.« less

Hot Deformation Behavior of Hot-Extruded AA7175 Through Hot Torsion Tests.

PubMed

Lee, Se-Yeon; Jung, Taek-Kyun; Son, Hyeon-Woo; Kim, Sang-Wook; Son, Kwang-Tae; Choi, Ho-Joon; Oh, Sang-Ho; Lee, Ji-Woon; Hyun, Soong-Keun

2018-03-01

The hot deformation behavior of hot-extruded AA7175 was investigated with flow curves and processing maps through hot torsion tests. The flow curves and the deformed microstructures revealed that dynamic recrystallization (DRX) occurred in the hot-extruded AA7175 during hot working. The failure strain was highest at medium temperature. This was mainly influenced by the dynamic precipitation of fine rod-shaped MgZn2. The processing map determined the optimal deformation condition for the alloy during hot working.

A STATE-VARIABLE APPROACH FOR PREDICTING THE TIME REQUIRED FOR 50% RECRYSTALLIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

M. STOUT; ET AL

2000-08-01

It is important to be able to model the recrystallization kinetics in aluminum alloys during hot deformation. The industrial relevant process of hot rolling is an example of where the knowledge of whether or not a material recrystallizes is critical to making a product with the correct properties. Classically, the equations that describe the kinetics of recrystallization predict the time to 50% recrystallization. These equations are largely empirical; they are based on the free energy for recrystallization, a Zener-Holloman parameter, and have several adjustable exponents to fit the equation to engineering data. We have modified this form of classical theorymore » replacing the Zener-Hollomon parameter with a deformation energy increment, a free energy available to drive recrystallization. The advantage of this formulation is that the deformation energy increment is calculated based on the previously determined temperature and strain-rate sensitivity of the constitutive response. We modeled the constitutive response of the AA5182 aluminum using a state variable approach, the value of the state variable is a function of the temperature and strain-rate history of deformation. Thus, the recrystallization kinetics is a function of only the state variable and free energy for recrystallization. There are no adjustable exponents as in classical theory. Using this approach combined with engineering recrystallization data we have been able to predict the kinetics of recrystallization in AA5182 as a function of deformation strain rate and temperature.« less

Grain Boundary Sliding (GBS) as a Plastic Instability Leading to Coeval Pseudotachylyte Development in Mylonites: an EBSD Study of the Seismic Cycle in Brittle-Ductile Transition Rocks of the South Mountains Core Complex, Arizona, USA

NASA Astrophysics Data System (ADS)

Miranda, E.; Stewart, C.

2017-12-01

Exposures of coeval pseudotachylytes and mylonites are relatively rare, but are crucial for understanding the seismic cycle in the vicinity of the brittle-ductile transition (BDT). We use both field observations and electron backscatter diffraction (EBSD) analysis to investigate the coeval pseudotachylytes and granodiorite mylonites exposed in the footwall of the South Mountains core complex, Arizona, to evaluate how strain is localized both prior to and during pseudotachylyte development at the BDT. In the field, we observe numerous pseudotachylyte veins oriented parallel to mylonitic foliation; the veins have synthetic shear sense with adjacent mylonites, and are < 2 cm thick, laterally discontinuous, and confined to a few m in structural thickness. EBSD analysis reveals that deformation is strongly partitioned into quartz in mylonites, where quartz shows subgrain rotation overprinted by bulging recrystallization microstructures and lattice preferred orientation (LPO) patterns indicative of dislocation creep. Foliation-parallel zones of finely recrystallized, (< 5 μm diameter) bulge-nucleated grains in the mylonites show four-grain junctions and randomized LPO patterns consistent with grain boundary sliding (GBS). Pseudotachylyte veins have elongate polycrystalline quartz survivor clasts that also exhibit GBS traits, suggesting that pseudotachylytes form within GBS zones in mylonites. We interpret the onset of GBS as a triggering mechanism for coeval pseudotachylyte development, where the accompanying decrease in effective viscosity and increase in strain rate initiated seismic slip and pseudotachylyte formation within GBS zones. Strain became localized within the pseudotachylyte until crystallization of melt impeded flow, inducing pseudotachylyte development in other GBS zones. We associate the pseudotachylyte veins and host mylonites with the coseismic and interseismic parts of the seismic cycle, respectively, where the abundance and lateral discontinuity of pseudotachylyte veins suggests repeated events. We speculate that periodic, GBS-initiated pseudotachylyte generation may correlate with intermediate slip rate seismic events in the vicinity of the BDT, suggesting that coeval pseudotachylytes and mylonites are evidence of a unique class of seismic event.

Complicated secondary textures in zircon record evolution of the host granitic rocks: Studies from Western Tauern Window and Ötztal-Stubai Crystalline Complex (Eastern Alps, Western Austria)

NASA Astrophysics Data System (ADS)

Kovaleva, Elizaveta; Harlov, Daniel; Klötzli, Urs

2017-07-01

Samples of metamorphosed and deformed granitic rocks were collected from two Alpine complexes with well-constrained metamorphic history: Western Tauern Window and Ötztal-Stubai Crystalline Complex. Zircon grains from these samples were investigated in situ by a combination of scanning electron microscope techniques, cathodoluminescence (CL) imaging and Raman spectroscopy. The aims were: to describe and interpret complicated secondary textures and microstructures in zircon; based on cross-cutting relationships between secondary microstructures, reconstruct the sequence of processes, affecting zircon crystals; link the evolution of zircon with the history of the host rocks. The results indicate that zircon in the sampled granitic rocks forms growth twins and multi-grain aggregates, which are unusual for this mineral. Moreover, various secondary textures have been found in the sampled zircon, often cross-cutting each other in a single crystal. These include: distorted oscillatory CL zoning with inner zones forming inward-penetrating, CL-bright embayments, which are the evidence of dry recrystallization via annealing/lattice recovery; CL mosaicism with no preservation of growth zoning, but abundant nano- and micro-scale pores and mineral inclusions, which are the evidence of recrystallization by coupled dissolution-reprecipitation and/or leaching; embayed zircon boundaries filled with apatite, monazite, epidote and mylonitic matrix, indicating mineral-fluid reactions resulting in zircon dissolution and fragmentation; overgrowth CL-dark rims, which contain nano-pores and point to transport and precipitation of dissolved zircon matter. We conclude that zircon in our meta-granites is sensitive to metamorphism/deformation events, and was reactive with metamorphic fluids. Additionally, we have found evidence of crystal-plastic deformation in the form of low angle boundaries and bent grain tips, which is a result of shearing and ductile deformation of the host rock. We suggest that the observed complicated secondary textures in zircon can be linked to the evolutionary stages of the host rocks such as magmatic crystallization, prograde metamorphism, peak of amphibolite-facies metamorphism, post-peak cooling and exhumation, formation of ductile shear zones and final cooling to 250 °C.

Microstructural Characterization of Friction Stir Welded Aluminum-Steel Joints

NASA Astrophysics Data System (ADS)

Patterson, Erin E.; Hovanski, Yuri; Field, David P.

2016-06-01

This work focuses on the microstructural characterization of aluminum to steel friction stir welded joints. Lap weld configuration coupled with scribe technology used for the weld tool have produced joints of adequate quality, despite the significant differences in hardness and melting temperatures of the alloys. Common to friction stir processes, especially those of dissimilar alloys, are microstructural gradients including grain size, crystallographic texture, and precipitation of intermetallic compounds. Because of the significant influence that intermetallic compound formation has on mechanical and ballistic behavior, the characterization of the specific intermetallic phases and the degree to which they are formed in the weld microstructure is critical to predicting weld performance. This study used electron backscatter diffraction, energy dispersive spectroscopy, scanning electron microscopy, and Vickers micro-hardness indentation to explore and characterize the microstructures of lap friction stir welds between an applique 6061-T6 aluminum armor plate alloy and a RHA homogeneous armor plate steel alloy. Macroscopic defects such as micro-cracks were observed in the cross-sectional samples, and binary intermetallic compound layers were found to exist at the aluminum-steel interfaces of the steel particles stirred into the aluminum weld matrix and across the interfaces of the weld joints. Energy dispersive spectroscopy chemical analysis identified the intermetallic layer as monoclinic Al3Fe. Dramatic decreases in grain size in the thermo-mechanically affected zones and weld zones that evidenced grain refinement through plastic deformation and recrystallization. Crystallographic grain orientation and texture were examined using electron backscatter diffraction. Striated regions in the orientations of the aluminum alloy were determined to be the result of the severe deformation induced by the complex weld tool geometry. Many of the textures observed in the weld zone and thermo-mechanically affected zones exhibited shear texture components; however, there were many textures that deviated from ideal simple shear. Factors affecting the microstructure which are characteristic of the friction stir welding process, such as post-recrystallization deformation and complex deformation induced by tool geometry were discussed as causes for deviation from simple shear textures.

Ice patterns and hydrothermal plumes, Lake Baikal, Russia - Insights from Space Shuttle hand-held photography

NASA Technical Reports Server (NTRS)

Evans, Cynthia A.; Helfert, Michael R.; Helms, David R.

1992-01-01

Earth photography from the Space Shuttle is used to examine the ice cover on Lake Baikal and correlate the patterns of weakened and melting ice with known hydrothermal areas in the Siberian lake. Particular zones of melted and broken ice may be surface expressions of elevated heat flow in Lake Baikal. The possibility is explored that hydrothermal vents can introduce local convective upwelling and disrupt a stable water column to the extent that the melt zones which are observed in the lake's ice cover are produced. A heat flow map and photographs of the lake are overlaid to compare specific areas of thinned or broken ice with the hot spots. The regions of known hydrothermal activity and high heat flow correlate extremely well with circular regions of thinned ice, and zones of broken and recrystallized ice. Local and regional climate data and other sources of warm water, such as river inlets, are considered.

Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia)

NASA Astrophysics Data System (ADS)

Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo

2016-04-01

The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the same shear zone. The observation that pst is preferentially sheared indicates that it is weaker than the host rock, although their bulk compositions are about the same, suggesting that the governing factors for localization are the finer grain size and the elongate, nearly planar geometry of the original pst generation zone. The same may be true of the sheared dolerite dykes, which are long, narrow and generally finer grained than the surrounding gneiss or granite. Although quartz-rich pegmatites are not preferred sites of localization, quartzo-feldspathic mylonites are fully recrystallized with a relatively coarse grain size (typically > 50 microns) typical of rather low long-term flow stress. We therefore propose that localization in the lower crust only occurs on long planar layers with a finer grain size that can promote weakening by grain-size sensitive creep. Coarser-grained lithological layers and boundaries are not exploited during the initiation of a shear zone and, in particular, quartz-rich layers are not preferentially sheared.

40Ar/39Ar mica ages from marble mylonites: a cautionary tale

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Huet, Benjamin; Schneider, David; Grasemann, Bernhard

2014-05-01

40Ar/39Ar geochronology on white mica is a popular method to date deformation under moderate (brittle-ductile) temperatures. In particular, deformation events preserved in greenschist facies shear zones have been successfully dated with this method. A consequence of strain localization in many tectonic settings that bear calcitic marbles is the formation of marble mylonites and ultramylonites. Little is known, however, about the behaviour of the K/Ar systems and the influence of deformation on the ages in such rocks. We studied an extremely localized shear zone (2 cm thick) in marble from Syros (Cyclades, Greece) and performed microstructural, chemical and isotopic analysis on samples from the host rock and the shear zone. The host rock is composed of coarse-grained (300 µm) calcite with only minor undulatory extinction and slightly curved grain boundaries. This initial large grain size is likely to have formed during the Eocene high-pressure - low-temperature event that is well documented in the Cyclades. In contrast, the marble within the shear zone shows evidence of strong intracrystalline deformation and recrystallization resulting in grain size reduction and the formation of an ultramylonite. Both microstructures and kinematics are consistent with the low grade evolution described on Syros. White mica (100's microns in size) are preferentially orientated parallel to the foliation. In both samples there is no clear evidence for crystal plastic deformation of the mica grains. Bigger grains behave brittle resulting in grain size reduction. A deformation mechanism map for calcite at 300 °C indicates that the host rock deformed at strain rates of around 10-12.5 s-1 whereas within the shear zone strain rates of up to 10-9.5 s-1 are attained. We performed laser-heating 40Ar/39Ar analysis on white mica located in the host rock and the shear zone. The low-strain host rock yielded a ca. 40 Ma age, and the shear zone recorded a ca. 37 Ma age; both ages are statistically indistinguishable when errors are considered. These dates correspond to the regional Eocene high-pressure - low-temperature event and not the later low grade deformation event that is responsible for the formation of the studied shear zone. Although the marble within the shear zone was deformed at extremely fast strain rates, we observe no resetting in the isotopic system. Moreover, mineral chemistry demonstrates that (1) white mica is homogeneous and (2) there is no compositional difference between the host rock and the shear zone. This is in agreement with thermodynamical modelling, which indicates that the observed assemblage (calcite + dolomite + quartz + white mica) is stable without any composition change along the pressure-temperature path followed by the metamorphic rocks of Syros. Our case study emphasizes it is not the amount of strain the rock suffered but the degree of mica recrystallization that is important for resetting of the K/Ar system at low temperatures.

Mesoscale model for fission-induced recrystallization in U-7Mo alloy

DOE PAGES

Liang, Linyun; Mei, Zhi -Gang; Kim, Yeon Soo; ...

2016-08-09

A mesoscale model is developed by integrating the rate theory and phase-field models and is used to study the fission-induced recrystallization in U-7Mo alloy. The rate theory model is used to predict the dislocation density and the recrystallization nuclei density due to irradiation. The predicted fission rate and temperature dependences of the dislocation density are in good agreement with experimental measurements. This information is used as input for the multiphase phase-field model to investigate the fission-induced recrystallization kinetics. The simulated recrystallization volume fraction and bubble induced swelling agree well with experimental data. The effects of the fission rate, initial grainmore » size, and grain morphology on the recrystallization kinetics are discussed based on an analysis of recrystallization growth rate using the modified Avrami equation. Here, we conclude that the initial microstructure of the U-Mo fuels, especially the grain size, can be used to effectively control the rate of fission-induced recrystallization and therefore swelling.« less

Effect of Carbon Nanotube on High-Temperature Formability of AZ31 Magnesium Alloy

NASA Astrophysics Data System (ADS)

Hassan, S. Fida; Paramsothy, M.; Gasem, Z. M.; Patel, F.; Gupta, M.

2014-08-01

Room-temperature tensile properties of AZ31 alloy have significantly been improved when reinforced with carbon nanotube via ingot metallurgy process. However, high-temperature (up to 250 °C) elongation-to-failure tensile test of the developed nanocomposite revealed a considerable softening in the AZ31 alloy matrix accompanied by an incredible ductility increment (up to 132%). Microstructural characterization of the fractured samples revealed that the dynamic recrystallization process has induced a complete recrystallization in the AZ31 alloy at a lower temperature (150 °C) followed by substantial grain growth at a higher temperature used in this study. Fractography on the fractured surfaces revealed that the room-temperature mixed brittle-ductile modes of fracture behavior of AZ31 alloy have transformed into a complete ductile mode of fracture at high temperature.

Effects of homogenization treatment on recrystallization behavior of 7150 aluminum sheet during post-rolling annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Zhanying; Department of Applied Science, University of Québec at Chicoutimi, Saguenay, QC G7H 2B1; Zhao, Gang

2016-04-15

The effects of two homogenization treatments applied to the direct chill (DC) cast billet on the recrystallization behavior in 7150 aluminum alloy during post-rolling annealing have been investigated using the electron backscatter diffraction (EBSD) technique. Following hot and cold rolling to the sheet, measured orientation maps, the recrystallization fraction and grain size, the misorientation angle and the subgrain size were used to characterize the recovery and recrystallization processes at different annealing temperatures. The results were compared between the conventional one-step homogenization and the new two-step homogenization, with the first step being pretreated at 250 °C. Al{sub 3}Zr dispersoids with highermore » densities and smaller sizes were obtained after the two-step homogenization, which strongly retarded subgrain/grain boundary mobility and inhibited recrystallization. Compared with the conventional one-step homogenized samples, a significantly lower recrystallized fraction and a smaller recrystallized grain size were obtained under all annealing conditions after cold rolling in the two-step homogenized samples. - Highlights: • Effects of two homogenization treatments on recrystallization in 7150 Al sheets • Quantitative study on the recrystallization evolution during post-rolling annealing • Al{sub 3}Zr dispersoids with higher densities and smaller sizes after two-step treatment • Higher recrystallization resistance of 7150 sheets with two-step homogenization.« less

On the Coupling between Recrystallization and Precipitation Following Hot Deformation in a γ-γ' Nickel-Based Superalloy

NASA Astrophysics Data System (ADS)

Seret, Anthony; Moussa, Charbel; Bernacki, Marc; Bozzolo, Nathalie

2018-06-01

Postdynamic recrystallization and γ' precipitation during cooling from γ' supersolvus temperature after hot compression were studied in the AD730 (AD730 is a trademark of Aubert et Duval Company in Paris, France) γ-γ' nickel-based superalloy. Emphasis was on not only both phenomena as distinct mechanisms but also on their mutual influence in terms of physical mechanisms. The growth of γ' precipitates is hastened in the unrecrystallized grains compared to the recrystallized ones. This could possibly be attributed to the higher dislocation content acting as high-diffusivity paths. Postdynamic recrystallization is not prevented by Smith-Zener pinning of the recrystallization front by the γ' precipitates. Instead, the recrystallization front dissolves γ' precipitates, which then reprecipitate discontinuously or continuously and coherently with the surrounding γ matrix in the recrystallized grains.

Pressure Dependence of Magnesite Flow Strength

NASA Astrophysics Data System (ADS)

Millard, J. W.; Holyoke, C. W., III; McDaniel, C.; Raterron, P.; Kronenberg, A. K.; Tokle, L.

2017-12-01

Recent experiments by Holyoke et al. (2014) indicate that magnesite is weak compared with olivine, leading to strain localization into magnesite-bearing horizons of downgoing subducting slabs, potentially leading to intermediate (200-400 km) deep focus earthquakes DFEs. Flow strengths (σ) of magnesite were determined as functions of strain rate and temperature (T), but not of pressure (P). In order to determine the pressure dependence of magnesite deforming by dislocation creep and low temperature plasticity (LTP), we performed triaxial deformation experiments on natural, coarse-grained (80 μm) magnesite aggregates at T = 900oC, strain rate of 2*10-5/s and P from 3.2 to 7.9 GPa in the D-DIA at Beamline 6-BMB at the Advanced Photon Source at Argonne National Lab. Strengths of magnesite aggregates increase as a function of pressure, from σ=0.85 GPa (at P = 3.2 GPa) to 1.69 GPa (at P = 7.9 GPa). Microstructures developed at P ≤ 6.2 GPa include grain flattening and sweeping undulatory extinction, and dynamic recrystallization at grain boundaries (by bulge nucleation), consistent with dislocation creep. Microstructures generated at P ≥ 6.7 GPa include some twins and kink bands, grain flattening and patchy undulatory extinction, and bulging recrystallization at grain boundaries. These microstructures indicate contributions to strain of both LTP and dislocation creep mechanisms. The pressure dependence can be described by a thermally activated enthalpy, where s increases with P by way of an activation volume V*. Based on both D-DIA and Griggs apparatus results (of Holyoke et al., 2014), V* = 8.5 (± 0.5) × 10-6 m3 mol-1. This value is comparable to V* determined for creep of olivine (9.5 (± 7) × 10-6 m3 mol-1 Durham et al., 2009), indicating that the strength difference between magnesite and olivine will continue to be significant at high pressures, and lead to strain localization at all subduction zone depths.

Igneous activity, metamorphism, and deformation in the Mount Rogers area of SW Virginia and NW North Carolina: A geologic record of Precambrian tectonic evolution of the southern Blue Ridge Province

USGS Publications Warehouse

Tollo, Richard P.; Aleinikoff, John N.; Mundil, Roland; Southworth, C. Scott; Cosca, Michael A.; Rankin, Douglas W.; Rubin, Allison E.; Kentner, Adrienne; Parendo, Christopher A.; Ray, Molly S.

2012-01-01

Mesoproterozoic basement in the vicinity of Mount Rogers is characterized by considerable lithologic variability, including major map units composed of gneiss, amphibolite, migmatite, meta-quartz monzodiorite and various types of granitoid. SHRIMP U-Pb geochronology and field mapping indicate that basement units define four types of occurrences, including (1) xenoliths of ca. 1.33 to ≥1.18 Ga age, (2) an early magmatic suite including meta-granitoids of ca. 1185–1140 Ma age that enclose or locally intrude the xenoliths, (3) metasedimentary rocks represented by layered granofels and biotite schist whose protoliths were likely deposited on the older meta-granitoids, and (4) a late magmatic suite composed of younger, ca. 1075–1030 Ma intrusive rocks of variable chemical composition that intruded the older rocks. The magmatic protolith of granofels constituting part of a layered, map-scale xenolith crystallized at ca. 1327 Ma, indicating that the lithology represents the oldest, intact crust presently recognized in the southern Appalachians. SHRIMP U-Pb data indicate that periods of regional Mesoproterozoic metamorphism occurred at 1170–1140 and 1070–1020 Ma. The near synchroneity in timing of regional metamorphism and magmatism suggests that magmas were emplaced into crust that was likely at near-solidus temperatures and that melts might have contributed to the regional heat budget. Much of the area is cut by numerous, generally east- to northeast-striking Paleozoic fault zones characterized by variable degrees of ductile deformation and recrystallization. These high-strain fault zones dismember the terrane, resulting in juxtaposition of units and transformation of basement lithologies to quartz- and mica-rich tectonites with protomylonitic and mylonitic textures. Mineral assemblages developed within such zones indicate that deformation and recrystallization likely occurred at greenschist-facies conditions at ca. 340 Ma.

The importance of grain size to mantle dynamics and seismological observations

NASA Astrophysics Data System (ADS)

Gassmoeller, R.; Dannberg, J.; Eilon, Z.; Faul, U.; Moulik, P.; Myhill, R.

2017-12-01

Grain size plays a key role in controlling the mechanical properties of the Earth's mantle, affecting both long-timescale flow patterns and anelasticity on the timescales of seismic wave propagation. However, dynamic models of Earth's convecting mantle usually implement flow laws with constant grain size, stress-independent viscosity, and a limited treatment of changes in mineral assemblage. We study grain size evolution, its interplay with stress and strain rate in the convecting mantle, and its influence on seismic velocities and attenuation. Our geodynamic models include the simultaneous and competing effects of dynamic recrystallization resulting from dislocation creep, grain growth in multiphase assemblages, and recrystallization at phase transitions. They show that grain size evolution drastically affects the dynamics of mantle convection and the rheology of the mantle, leading to lateral viscosity variations of six orders of magnitude due to grain size alone, and controlling the shape of upwellings and downwellings. Using laboratory-derived scaling relationships, we convert model output to seismologically-observable parameters (velocity, attenuation) facilitating comparison to Earth structure. Reproducing the fundamental features of the Earth's attenuation profile requires reduced activation volume and relaxed shear moduli in the lower mantle compared to the upper mantle, in agreement with geodynamic constraints. Faster lower mantle grain growth yields best fit to seismic observations, consistent with our re-examination of high pressure grain growth parameters. We also show that ignoring grain size in interpretations of seismic anomalies may underestimate the Earth's true temperature variations.

Hot Ductility Characterization of Sanicro-28 Super-Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Mirzaei, A.; Zarei-Hanzaki, A.; Abedi, H. R.

2016-05-01

The hot ductility behavior of a super-austenitic stainless steel has been studied using tensile testing method in the temperature range from 1073 K to 1373 K (800 °C to 1100 °C) under the strain rates of 0.1, 0.01, and 0.001 s-1. The hot compression tests were also performed at the same deformation condition to identify the activated restoration mechanisms. At lower temperatures [ i.e., 1073 K and 1173 K (800 °C and 900 °C)], the serration of initial grain boundaries confirms the occurrence of dynamic recovery as the predominant restoration process. However, in the course of applied deformation, the initial microstructure is recrystallized at higher temperatures [ i.e., 1273 K and 1373 K (1000 °C and 1100 °C)]. In this respect, annealing the twin boundaries could well stimulate the recrystallization kinetic through initiation new annealing twins on prior annealing twin boundaries. The hot tensile results show that there is a general trend of increasing ductility by temperature. However, two regions of ductility drop are recognized at 1273 K and 1373 K (1000°C)/0.1s-1 and (1100°C)/0.01s-1. The ductility variations at different conditions of temperature and strain rate are discussed in terms of simultaneous activation of grain boundary sliding and restoration processes. The observed ductility troughs are attributed to the occurrence of grain boundary sliding and the resulting R-type and W-type cracks. The occurrence of dynamic recrystallization is also considered as the main factor increasing the ductility at higher temperatures. The enhanced ductility is primarily originated from the post-uniform elongation behavior, which is directly associated with the strain rate sensitivity of the experimental material.

Microstructure and Mechanical Performance of Friction Stir Spot-Welded Aluminum-5754 Sheets

NASA Astrophysics Data System (ADS)

Pathak, N.; Bandyopadhyay, K.; Sarangi, M.; Panda, Sushanta Kumar

2013-01-01

Friction stir spot welding (FSSW) is a recent trend of joining light-weight sheet metals while fabricating automotive and aerospace body components. For the successful application of this solid-state welding process, it is imperative to have a thorough understanding of the weld microstructure, mechanical performance, and failure mechanism. In the present study, FSSW of aluminum-5754 sheet metal was tried using tools with circular and tapered pin considering different tool rotational speeds, plunge depths, and dwell times. The effects of tool design and process parameters on temperature distribution near the sheet-tool interface, weld microstructure, weld strength, and failure modes were studied. It was found that the peak temperature was higher while welding with a tool having circular pin compared to tapered pin, leading to a bigger dynamic recrystallized stir zone (SZ) with a hook tip bending towards the upper sheet and away from the keyhole. Hence, higher lap shear separation load was observed in the welds made from circular pin compared to those made from tapered pin. Due to influence of size and hardness of SZ on crack propagation, three different failure modes of weld nugget were observed through optical cross-sectional micrograph and SEM fractographs.

Role of orthopyroxene in rheological weakening of the lithosphere via dynamic recrystallization

PubMed Central

Farla, Robert J. M.; Karato, Shun-ichiro; Cai, Zhengyu

2013-01-01

For plate tectonics to operate on a terrestrial planet, the surface layer (the lithosphere) must have a modest strength (Earth, ≤200 MPa), but a standard strength profile based on olivine far exceeds this threshold value. Consequently, it is essential to identify mechanisms that reduce the strength of the lithosphere on Earth. Here we report results of high-strain laboratory deformation experiments on a representative olivine–orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window. The reduction in strength is associated with the formation of small orthopyroxene and olivine grains. Our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones: fine-grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated. A model is developed to apply these results to geological conditions. Such a model, combined with our experimental observations, suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range, leading to long-term weakening associated with strain localization in the lithosphere. PMID:24067645

Influence of Fe(2+)-catalysed iron oxide recrystallization on metal cycling.

PubMed

Latta, Drew E; Gorski, Christopher A; Scherer, Michelle M

2012-12-01

Recent work has indicated that iron (oxyhydr-)oxides are capable of structurally incorporating and releasing metals and nutrients as a result of Fe2+-induced iron oxide recrystallization. In the present paper, we briefly review the current literature examining the mechanisms by which iron oxides recrystallize and summarize how recrystallization affects metal incorporation and release. We also provide new experimental evidence for the Fe2+-induced release of structural manganese from manganese-doped goethite. Currently, the exact mechanism(s) for Fe2+-induced recrystallization remain elusive, although they are likely to be both oxide-and metal-dependent. We conclude by discussing some future research directions for Fe2+-catalysed iron oxide recrystallization.

Negative Temperature Dependence of Recrystallized Grain Size: Formulation and Experimental Confirmation on Copper

PubMed Central

Elmasry, Mohamed; Liu, Fan; Jiang, Yao; Mao, Ze Ning; Liu, Ying; Wang, Jing Tao

2017-01-01

The catalyzing effect on nucleation of recrystallization from existing grains resulting from previous lower temperature deformation is analyzed, analogous to the size effect of foreign nucleus in heterogeneous nucleation. Analytical formulation of the effective nucleation site for recrystallization leads to a negative temperature dependence of recrystallized grain size of metals. Non-isochronal annealing—where annealing time is set just enough for the completion of recrystallization at different temperatures—is conducted on pure copper after severe plastic deformation. More homogeneous and smaller grains are obtained at higher annealing temperature. The good fit between analytical and experimental results unveils the intrinsic feature of this negative temperature dependence of recrystallized grain size. PMID:28772676

Deformation in the hanging wall of Cretaceous HP rocks (Austroalpine Ötztal-Stubai Complex, European Eastern Alps): constraints on timing, conditions and kinematics

NASA Astrophysics Data System (ADS)

Habler, Gerlinde; Thöni, Martin; Grasemann, Bernhard; Sölva, Helmuth; Cotza, Gianluca

2010-05-01

The position and nature of the tectonic boundary between the Cretaceous eclogite facies metamorphic Texel Complex (Sölva et al. 2005, TC) and the Ötztal-Stubai Complex sensu stricto (OSC) with predominantly pre-Cretaceous tectonometamorphic imprint remained a matter of discussion (Fügenschuh et al. 2009). Sölva et al (2005) described the Cretaceous Schneeberg Normal Fault Zone (SNFZ) as the major tectonic boundary between the exhuming TC and the OSC, where the major portion of ductile deformation was partitioned into the rheologically weak Schneeberg/Monteneve Unit (SMU). In contrast, other authors proposed a model of a coherent vertical crustal section in the southern OSC (Schmid and Haas 1989), which was rotated and exhumed by erosion due to Oligocene large scale refolding (Fügenschuh et al. 2009). Here, new Rb-Sr data of muscovite and biotite from para- and orthogneisses from the Ferwalltal and Timmelsjoch areas (Austria/Italy) were correlated with mineral chemical and structural data in order to constrain the age and kinematics of the predominant deformational imprint in the OSC representing the hanging wall of the SNFZ. In the Ferwalltal the undisturbed OSC/SMU boundary is exposed. Above that boundary an amphibolite facies mylonitic foliation (Sc1) represented by the compositional layering of coarse grained Qtz, Bt and dynamically recrystallized Pl interferes with an overprinting mylonitic foliation (Sc2) with spatially heterogeneous intensity. Sc1-planes were syn-tectonically overgrown by euhedral Grt with single phase continuous prograde chemical zoning and Bt-porphyroblasts. Dc2 postdated garnet growth and caused the formation of SCC' fabrics in Bt-Pl gneisses. Still Qtz recrystallized dynamically, whereas Ms and Bt newly crystallized during Dc2. In the study area, the lithological boundaries in the OSC mainly are subparallel to the predominant foliation Sc1. These planes dip with 45-50° to the NW-NNW and show a WNW-plunging stretching lineation (LSc1) of dynamically recrystallized plagioclase and quartz. Shear kinematics of Dc1 alternate between Top to WNW or ESE. Sc2 foliation planes and the lithological-tectonic OSC/SMU boundary dip with intermediate angles towards N - NNW but also bear a W-plunging stretching lineation (LSc2). Dc2 structures consistently indicate W-directed shear kinematics. Due to the angular relationship of Sc1 and Sc2 the lithological boundaries of the OSC are truncated at the boundary with the SMU. Cretaceous Rb-Sr isochrons were obtained from Bt-granite-gneiss about 400m structurally above the OSC/SMU boundary. Fine-grained muscovite forming part of the major foliation Sc1 yielded a Rb-Sr Ms-WR age of 86.1 ± 0.9 Ma interpreted as a crystallization age constraining the timing of Dc1. The evidence of isotopic equilibration was supported by the homogeneous major element Ms composition. Rb-Sr Bt-WR data from the same material yielded 80.8±0.8 Ma interpreted to reflect cooling below c. 300°C. Several Rb-Sr Bt-WR data obtained from the Ferwalltal area gave age-results between 80.0 and 84.7 Ma and thus range among numerous Bt-WR Rb-Sr ages available from the wider study area (Thöni and Hoinkes 1987). Both deformation stages Dc1 and Dc2 predate this cooling period, as the Qtz-mica-fabrics demand significantly higher T-conditions. Subsequent deformation covers strongly partitioned brittle-ductile shear zones dipping with 50 - 60° to NW, as well as ultra-cataclasites bearing pseudotachylites, which reactivated Sc1- or Sc2 planes about 50 - 70 meters above the OSC/SMU boundary. Both brittle-ductile and brittle structures showed W-directed kinematics of normal faulting. The continuation of consistent shear kinematics to the brittle regime, as well as the extensive database of mica ages indicating cooling to below c. 300°C in the OSC adjacent to the SMU between 85 - 80 Ma (Thöni and Hoinkes 1987, with references) contradict a model of Oligocene ductile refolding. References: Fügenschuh B, Flöss D, Speckbacher R (2009) In Alpine Workshop Cogne. Schmid SM, Haas R (1989) Tectonics 8: 697-718. Sölva H, Grasemann B, Thöni M, Thiede RC, Habler G (2005) Tectonophysics 401: 143-166. Thöni M, Hoinkes G (1987) In Geodynamics of the Eastern Alps, pp. 200-213. Edited by Flügel HW and Faupl P. Vienna: Deuticke.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Linyun; Mei, Zhi -Gang; Kim, Yeon Soo

A mesoscale model is developed by integrating the rate theory and phase-field models and is used to study the fission-induced recrystallization in U-7Mo alloy. The rate theory model is used to predict the dislocation density and the recrystallization nuclei density due to irradiation. The predicted fission rate and temperature dependences of the dislocation density are in good agreement with experimental measurements. This information is used as input for the multiphase phase-field model to investigate the fission-induced recrystallization kinetics. The simulated recrystallization volume fraction and bubble induced swelling agree well with experimental data. The effects of the fission rate, initial grainmore » size, and grain morphology on the recrystallization kinetics are discussed based on an analysis of recrystallization growth rate using the modified Avrami equation. Here, we conclude that the initial microstructure of the U-Mo fuels, especially the grain size, can be used to effectively control the rate of fission-induced recrystallization and therefore swelling.« less

Adaptive characterization of recrystallization kinetics in IF steel by electron backscatter diffraction.

PubMed

Kim, Dong-Kyu; Park, Won-Woong; Lee, Ho Won; Kang, Seong-Hoon; Im, Yong-Taek

2013-12-01

In this study, a rigorous methodology for quantifying recrystallization kinetics by electron backscatter diffraction is proposed in order to reduce errors associated with the operator's skill. An adaptive criterion to determine adjustable grain orientation spread depending on the recrystallization stage is proposed to better identify the recrystallized grains in the partially recrystallized microstructure. The proposed method was applied in characterizing the microstructure evolution during annealing of interstitial-free steel cold rolled to low and high true strain levels of 0.7 and 1.6, respectively. The recrystallization kinetics determined by the proposed method was found to be consistent with the standard method of Vickers microhardness. The application of the proposed method to the overall recrystallization stages showed that it can be used for the rigorous characterization of progressive microstructure evolution, especially for the severely deformed material. © 2013 The Authors Journal of Microscopy © 2013 Royal Microscopical Society.

Modeling the Controlled Recrystallization of Particle-Containing Aluminum Alloys

NASA Astrophysics Data System (ADS)

Adam, Khaled; Root, Jameson M.; Long, Zhengdong; Field, David P.

2017-01-01

The recrystallized fraction for AA7050 during the solution heat treatment is highly dependent upon the history of deformation during thermomechanical processing. In this work, a state variable model was developed to predict the recrystallization volume fraction as a function of processing parameters. Particle stimulated nucleation (PSN) was observed as a dominant mechanism of recrystallization in AA7050. The mesoscale Monte Carlo Potts model was used to simulate the evolved microstructure during static recrystallization with the given recrystallization fraction determined already by the state variable model for AA7050 alloy. The spatial inhomogeneity of nucleation is obtained from the measurement of the actual second-phase particle distribution in the matrix identified using backscattered electron (BSE) imaging. The state variable model showed good fit with the experimental results, and the simulated microstructures were quantitatively comparable to the experimental results for the PSN recrystallized microstructure of 7050 aluminum alloy. It was also found that the volume fraction of recrystallization did not proceed as dictated by the Avrami equation in this alloy because of the presence of the growth inhibitors.

Through-thickness recrystallization characteristics of a laminated AA3xxx–AA6xxx aluminum alloy system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao, L.H., E-mail: l2liao@uwaterloo.ca; Jin, H.; Gallerneault, M.

2015-03-15

The through-thickness annealing behavior of a laminated AA3xxx–AA6xxx alloy system at 300 °C has been studied by scanning electron microscopy, electron backscatter diffraction analysis, electron probe micro-analysis, differential scanning calorimetry, and hardness measurement. Results show that the recrystallization process starts at the interface region between the AA3xxx (clad) and AA6xxx (core) layers. Subsequently, the recrystallization process front progresses into the core layer, while the clad layer is the last region to recrystallize. It is also found that precipitation precedes recrystallization in the entire laminate at the investigated temperature. The preferential onset of recrystallization at the interface region is attributed tomore » the net driving pressure being the highest in this region. The factors that lead to such enhanced net driving pressure are (a) deformation incompatibility between the two alloy layers, (b) lower solute content of the interface, which also leads to lower volume fraction of precipitates, and (c) an accelerated rate of precipitate coarsening due to the presence of a higher density of dislocations. The gradual progress of recrystallization from the interface towards the core layer is dictated by precipitate coarsening and the dependence of its rate on the density of deformation-induced dislocations. The lower driving pressure due to lower work hardening capacity, high solute drag pressure due to Mn, and additional Zener drag from precipitates that form due to solute redistribution during annealing explain the late initiation of recrystallization in the clad layer. - Highlights: • The through-thickness recrystallization of a laminated system is investigated. • The early onset of recrystallization at the interface is discussed. • The effects of precipitation and coarsening on recrystallization are analyzed.« less

Effect of milling on particle shape and surface energy heterogeneity of needle-shaped crystals.

PubMed

Ho, Raimundo; Naderi, Majid; Heng, Jerry Y Y; Williams, Daryl R; Thielmann, Frank; Bouza, Peter; Keith, Adam R; Thiele, Greg; Burnett, Daniel J

2012-10-01

Milling and micronization of particles are routinely employed in the pharmaceutical industry to obtain small particles with desired particle size characteristics. The aim of this study is to demonstrate that particle shape is an important factor affecting the fracture mechanism in milling. Needle-shaped crystals of the β polymorph of D-mannitol were prepared from recrystallization in water. A portion of the recrystallized materials was ball-milled. Unmilled and milled sieved fractions of recrystallized D-mannitol were analyzed by dynamic image analysis (DIA) and inverse gas chromatography (IGC) at finite concentration to explain the breakage/fracture behavior. In the process of ball-milling, D-mannitol preferentially fractured along their shortest axis, exposing (011) plane with increased hydrophilicity and increased bounding rectangular aspect ratio. This is in contrary to attachment energy modeling which predicts a fracture mechanism across the (010) plane with increased hydrophobicity, and small change in particle shape. Crystal size, and more importantly, crystal shape and facet-specific mechanical properties, can dictate the fracture/cleavage behavior of organic crystalline materials. Thorough understanding of the crystal slip systems, combining attachment energy prediction with particle shape and surface characterization using DIA and IGC, are important in understanding fracture behavior of organic crystalline solids in milling and micronization.

Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somani, M.C.; Muraleedharan, K.; Birla, N.C.

1994-08-01

The characteristics of hot deformation of INCONEL alloy MA 754 have been studies using processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700 C to 1,150 C and strain rate range 0.001 to 100 s[sup [minus]1]. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range 800 C to 1,075 C and strain rate range 0.02 to 2 s[sup [minus]1], with a peak efficiency of 18 pct occurring at 950 C and 0.1 s [sup [minus]1]. Transmission electron microscope (TEM) micrographs revealed stable subgrain structuremore » in this domain with the subgrain size increasing exponentially with an increase in temperature. (2) A domain exhibiting grain boundary cracking occurs at temperatures lower than 800 C and strain rates lower than 0.01 s[sup [minus]1]. (3) A domain exhibiting intense grain boundary cavitation occurs at temperatures higher than 1075 C. The material did not exhibit a dynamic recrystallization (DRX) domain, unlike other superalloys. At strain rates higher than about 1 s[sup [minus]1], the material exhibits flow instabilities manifesting as kinking of the elongated grains and adiabatic shear bands. The materials may be safely worked in the domain of dynamic recovery but can only be statically recrystallized.« less

Bioinspired Materials for Controlling Ice Nucleation, Growth, and Recrystallization.

PubMed

He, Zhiyuan; Liu, Kai; Wang, Jianjun

2018-05-15

Ice formation, mainly consisting of ice nucleation, ice growth, and ice recrystallization, is ubiquitous and crucial in wide-ranging fields from cryobiology to atmospheric physics. Despite active research for more than a century, the mechanism of ice formation is still far from satisfactory. Meanwhile, nature has unique ways of controlling ice formation and can provide resourceful avenues to unravel the mechanism of ice formation. For instance, antifreeze proteins (AFPs) protect living organisms from freezing damage via controlling ice formation, for example, tuning ice nucleation, shaping ice crystals, and inhibiting ice growth and recrystallization. In addition, AFP mimics can have applications in cryopreservation of cells, tissues, and organs, food storage, and anti-icing materials. Therefore, continuous efforts have been made to understand the mechanism of AFPs and design AFP inspired materials. In this Account, we first review our recent research progress in understanding the mechanism of AFPs in controlling ice formation. A Janus effect of AFPs on ice nucleation was discovered, which was achieved via selectively tethering the ice-binding face (IBF) or the non-ice-binding face (NIBF) of AFPs to solid surfaces and investigating specifically the effect of the other face on ice nucleation. Through molecular dynamics (MD) simulation analysis, we observed ordered hexagonal ice-like water structure atop the IBF and disordered water structure atop the NIBF. Therefore, we conclude that the interfacial water plays a critical role in controlling ice formation. Next, we discuss the design and fabrication of AFP mimics with capabilities in tuning ice nucleation and controlling ice shape and growth, as well as inhibiting ice recrystallization. For example, we tuned ice nucleation via modifying solid surfaces with supercharged unfolded polypeptides (SUPs) and polyelectrolyte brushes (PBs) with different counterions. We found graphene oxide (GO) and oxidized quasi-carbon nitride quantum dots (OQCNs) had profound effects in controlling ice shape and inhibiting ice growth. We also studied the ion-specific effect on ice recrystallization inhibition (IRI) with a large variety of anions and cations. All functionalities are achieved by tuning the properties of interfacial water on these materials, which reinforces the importance of the interfacial water in controlling ice formation. Finally, we review the development of novel application-oriented materials emerging from our enhanced understanding of ice formation, for example, ultralow ice adhesion coatings with aqueous lubricating layer, cryopreservation of cells by inhibiting ice recrystallization, and two-dimensional (2D) and three-dimensional (3D) porous materials with tunable pore sizes through recrystallized ice crystal templates. This Account sheds new light on the molecular mechanism of ice formation and will inspire the design of unprecedented functional materials based on controlled ice formation.

Spatial variations in deformation mechanisms along the Main Central thrust zone: Implications for the evolution of the MCT in the Darjeeling -Sikkim Himalaya

NASA Astrophysics Data System (ADS)

Bhattacharyya, Kathakali; Mitra, Gautam

2014-12-01

In the Darjeeling-Sikkim Himalaya, we recognize two distinct MCT sheets: the structurally higher MCT1 and the lower MCT2. Microstructural studies from three different segments along the transport direction of the MCT2 fault zone suggest that the fault has undergone strain softening by different mechanisms. The geometry of the tapered crystalline orogenic wedge resulted in variation of overburden along the MCT2. Strain softening by different deformation mechanisms accommodated translation of ⩾100 km along a thin MCT2 fault zone. As the mylonitic trailing part of the MCT2 in Pelling had the greatest overburden, deformation took place by dislocation creep in quartz and by microfracturing in feldspar. Reaction softening of feldspar produced an intrinsically weak matrix that primarily controlled the deformation, resulting in a strain softening fault zone. At Soreng MCT2 zone, under intermediate crustal conditions, finer-grained recrystallized quartz and micaceous matrix deformed by grain-size sensitive diffusion creep mechanisms resulting in strain softening. The fault rocks at Sivitar had the least overburden and record a prominent mineralogical change from the protolith; strain softening occurred by pressure solution slip, possibly by a combination of grain-size reduction by cataclasis and an increase in fluid activity.

Strain rate dependent calcite microfabric evolution - An experiment carried out by nature

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

2014-12-01

A flanking structure developed along a secondary shear zone in calcite marbles, on Syros (Cyclades, Greece), provides a natural laboratory for directly studying the effects of strain rate variations on calcite deformation at identical pressure and temperature conditions. The presence and rotation of a fracture during progressive deformation caused extreme variations in finite strain and strain rate, forming a localized ductile shear zone that shows different microstructures and textures. Textures and the degree of intracrystalline deformation were measured by electron backscattered diffraction. Marbles from the host rocks and the shear zone, which deformed at various strain rates, display crystal-preferred orientation, suggesting that the calcite preferentially deformed by intracrystalline-plastic deformation. Increasing strain rate results in a switch from subgrain rotation to bulging recrystallization in the dislocation-creep regime. With increasing strain rate, we observe in fine-grained (3 μm) ultramylonitic zones a change in deformation regime from grain-size insensitive to grain-size sensitive. Paleowattmeter and the paleopiezometer suggest strain rates for the localized shear zone around 10-10 s-1 and for the marble host rock around 10-12 s-1. We conclude that varying natural strain rates can have a first-order effect on the microstructures and textures that developed under the same metamorphic conditions.

Stable mineral recrystallization in low temperature aqueous systems: A critical review

NASA Astrophysics Data System (ADS)

Gorski, Christopher A.; Fantle, Matthew S.

2017-02-01

Minerals may undergo recrystallization reactions in low temperature (<100 °C) aqueous systems, during which they exchange isotopes and trace elements with the dissolved reservoir without undergoing overt structural, bulk compositional, or morphological changes. These interfacial reactions, which are often referred to in the literature as "atom exchange" and herein as "stable mineral recrystallization", have important implications for the use of isotopic and elemental proxies to interpret past temperatures, oxidation states, and aqueous chemistries on Earth. The reactions are also significant for modern environments, including engineered systems, as they imply that mineral lattices may be substantially more open to exchanging toxic elements and radionuclides with coexisting solutions than previously thought. To date, observations of stable mineral recrystallization are distributed among several disciplines, and no work has attempted to review their findings comprehensively. Accordingly, this review article presents laboratory evidence for stable mineral recrystallization, describes data collection and interpretation strategies, summarizes similar recrystallization systematics observed in multiple studies, explores the potential occurrence of stable mineral recrystallization in natural systems, and discusses possible mechanisms by which stable mineral recrystallization occurs. The review focuses primarily on carbonates, sulfates, and iron oxides because these minerals have been studied most extensively to date. The review concludes by presenting key questions that should be addressed in this field to further understand and account for stable mineral recrystallization in natural and engineered aqueous systems at low temperatures.

Nanostructure of vortex during explosion welding.

PubMed

Rybin, V V; Greenberg, B A; Ivanov, M A; Patselov, A M; Antonova, O V; Elkina, O A; Inozemtsev, A V; Salishchev, G A

2011-10-01

The microstructure of a bimetallic joint made by explosion welding of orthorhombic titanium aluminide (Ti-30Al-16Nb-1Zr-1Mo) with commercially pure titanium is studied. It is found that the welded joint has a multilayered structure including a severely deformed zone observed in both materials, a recrystallized zone of titanium, and a transition zone near the interface. Typical elements of the transition zone-a wavy interface, macrorotations of the lattice, vortices and tracks of fragments of the initial materials-are determined. It is shown that the observed vortices are formed most probably due to local melting of the material near the contact surface. Evidence for this assumption is deduced from the presence of dipoles, which consist of two vortices of different helicity and an ultrafine duplex structure of the vortex. Also, high mixing of the material near the vortex is only possible by the turbulent transport whose coefficient is several orders of magnitude larger than the coefficient of atomic diffusion in liquids. The role played by fragmentation in both the formation of lattice macrorotations and the passage of coarse particles of one material through the bulk of the other is determined.

The lateral boundary of a metamorphic core complex: The Moutsounas shear zone on Naxos, Cyclades, Greece☆

PubMed Central

Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai

2013-01-01

We describe the structure, microstructures, texture and paleopiezometry of quartz-rich phyllites and marbles along N-trending Moutsounas shear zone at the eastern margin of the Naxos metamorphic core complex (MCC). Fabrics consistently indicate a top-to-the-NNE non-coaxial shear and formed during the main stage of updoming and exhumation between ca. 14 and 11 Ma of the Naxos MCC. The main stage of exhumation postdates the deposition of overlying Miocene sedimentary successions and predates the overlying Upper Miocene/Pliocene conglomerates. Detailed microstructural and textural analysis reveals that the movement along the Moutsounas shear zone is associated with a retrograde greenschist to subgreenschist facies overprint of the early higher-temperature rocks. Paleopiezometry on recrystallized quartz and calcite yields differential stresses of 20–77 MPa and a strain rate of 10−15–10−13 s−1 at 350 °C for quartz and ca. 300 °C for calcite. Chlorite geothermometry of the shear zone yields two temperature regimes, 300–360 °C, and 200–250 °C. The lower temperature group is interpreted to result from late-stage hydrothermal overprint. PMID:26523079

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, H.; Tse, J. S., E-mail: john.tse@usask.ca; Hu, M. Y.

2015-10-28

The pressure-induced amorphization and subsequent recrystallization of SnI{sub 4} have been investigated using first principles molecular dynamics calculations together with high-pressure {sup 119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI{sub 4} under ambient conditions. Although high pressure structures of SnI{sub 4} were thought to be determined by randommore » packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.« less

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of Snl 4

DOE PAGES

Liu, Hanyu; Tse, John S.; Hu, Michael Y.; ...

2015-10-27

The pressure-induced amorphization and subsequent recrystallization of SnI 4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI 4 under ambient conditions. Although high pressure structures of SnI 4 were thought to be determined by random packingmore » of equal-sized spheres, we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.« less

Investigation on the effect of friction stir processing on tribological and mechanical properties of Al 7075-T651 alloy

NASA Astrophysics Data System (ADS)

Murthy, Veeresh; Rajaprakash, B. M.

2018-04-01

Friction Stir Processing (FSP) is generally used as a novel method for surface properties enhancement. The surface developed through FSP alters the tribological and mechanical properties of the material in a single step. This commendable enhancement in the properties by recrystallized equiaxed microstructure attained by dynamic recrystallization can be achieved in just one step there by increasing the performance. In this study, the effect of the FSP passes on the tribological & mechanical properties such as hardness, wear resistance and tensile strength for commercially available AA7075-T651 of 6mm thick sheet was studied. Properties in terms of hardness, wear rate and tensile strength were compared with the base alloy and Friction Stir Processed (FSPed) alloy. It was observed that the hardness, wear rate of the FSPed FSP3 was enhanced by 44% and 60% as compared to that of the unprocessed sample.

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI4.

PubMed

Liu, H; Tse, J S; Hu, M Y; Bi, W; Zhao, J; Alp, E E; Pasternak, M; Taylor, R D; Lashley, J C

2015-10-28

The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure (119)Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.

Effect of aging and ice structuring proteins on the morphology of frozen hydrated gluten networks.

PubMed

Kontogiorgos, Vassilis; Goff, H Douglas; Kasapis, Stefan

2007-04-01

The present investigation constitutes an attempt to rationalize the effect of aging and ice structuring proteins (ISPs) on the network morphology of frozen hydrated gluten. In doing so, it employs differential scanning calorimetry, time-domain NMR, dynamic oscillation on shear, creep testing, and electron microscopy. Experimentation and first principles modeling allows identification and description of the processes of ice formation and recrystallization in molecular terms. It is demonstrated that in the absence of a readily discernible glass transition temperature in gluten-ice composites, the approach of considering the melting point and aging at constant or fluctuating temperature conditions in the vicinity of this point can provide a valid index of functional quality. A theoretical framework supporting the concept of capillary confined frozen water in the gluten matrix was advanced, and it was found that ISPs were effective in controlling recrystallization both within these confines and within ice in the bulk.

Using a Simulated Industrial Setting for the Development of an Improved Solvent System for the Recrystallization of Benzoic Acid: A Student-Centered Project

ERIC Educational Resources Information Center

Hightower, Timothy R.; Heeren, Jay D.

2006-01-01

Recrystallization of benzoic acid is an excellent way to remove insoluble impurities. In a traditional organic laboratory experiment, insoluble impurities are removed through the recrystallization of benzoic acid utilizing water as the recrystallization solvent. It was our goal to develop a peer-led, problem-solving organic laboratory exercise…

Static Recrystallization Behavior of Z12CN13 Martensite Stainless Steel

NASA Astrophysics Data System (ADS)

Luo, Min; Zhou, Bing; Li, Rong-bin; Xu, Chun; Guo, Yan-hui

2017-09-01

In order to increase the hot workability and provide proper hot forming parameters of forging Z12CN13 martensite stainless steel for the simulation and production, the static recrystallization behavior has been studied by double-pass hot compression tests. The effects of deformation temperature, strain rate and inter-pass time on the static recrystallization fraction by the 2% offset method are extensively studied. The results indicate that increasing the inter-pass time and the deformation temperature as well as strain rate appropriately can increase the fraction of static recrystallization. At the temperature of 1050-1150 °C, inter-pass time of 30-100 s and strain rate of 0.1-5 s-1, the static recrystallization behavior is obvious. In addition, the kinetics of static recrystallization behavior of Z12CN13 steel has been established and the activation energy of static recrystallization is 173.030 kJ/mol. The substructure and precipitates have been studied by TEM. The results reveal that the nucleation mode is bulging at grain boundary. Undissolved precipitates such as MoNi3 and Fe3C have a retarding effect on the recrystallization kinetics. The effect is weaker than the accelerating effect of deformation temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Linyun; Mei, Zhi-Gang; Yacout, Abdellatif M.

We have developed a mesoscale phase-field model for studying the effect of recrystallization on the gas-bubble-driven swelling in irradiated U-Mo alloy fuel. The model can simulate the microstructural evolution of the intergranular gas bubbles on the grain boundaries as well as the recrystallization process. Our simulation results show that the intergranular gas-bubble-induced fuel swelling exhibits two stages: slow swelling kinetics before recrystallization and rapid swelling kinetics with recrystallization. We observe that the recrystallization can significantly expedite the formation and growth of gas bubbles at high fission densities. The reason is that the recrystallization process increases the nucleation probability of gasmore » bubbles and reduces the diffusion time of fission gases from grain interior to grain boundaries by increasing the grain boundary area and decreasing the diffusion distance. The simulated gas bubble shape, size distribution, and density on the grain boundaries are consistent with experimental measurements. We investigate the effect of the recrystallization on the gas-bubble-driven fuel swelling in UMo through varying the initial grain size and grain aspect ratio. We conclude that the initial microstructure of fuel, such as grain size and grain aspect ratio, can be used to effectively control the recrystallization and therefore reduce the swelling in U-Mo fuel.« less

Insights into the Timing, Origin, and Deformation of the Highland Mountains Gneiss Dome in Southwestern Montana, USA

NASA Astrophysics Data System (ADS)

Boyer, Lane Markes

The Highland Mountains of southwestern Montana offer a unique view of the Archean igneous and metamorphic rocks within the Great Falls tectonic zone (GFTZ). A Paleoproterozoic structural gneiss dome has been interpreted in the southern extent of the Highland Mountains. The ˜ 130km2 of exhumed metamorphic rocks and gneiss dome exposed in the Highland Mountains are the primary focus of this research. The formation of the Highland Mountains gneiss dome is proposed to be directly related to a northwest-side down detachment (the Steels Pass shear zone) that formed during terrane collision along the GFTZ. The field investigation determined foliation and lineation orientation measurements taken at 65 stations. Twenty-two field oriented samples were obtained from a variety of rock types distributed across the ˜ 24 km2 field area. Three field-based domains were established from the lithology, foliation, and lineation observations. Full-section X-ray maps of three sample thin-sections were collected via EPMA to identify all monazite grains. Twenty-eight grains were mapped at high-spatial resolution (0.3--6.0 mum). Thin section micro-structures observed show effects of a multistage deformation history with both dynamic and static recrystallization processes. Monazite geochronology of one thin section revealed two distinct populations of monazite grains; Archean (˜ 2.5 Ga) and Mesoproterozoic (˜ 1.5 Ga). The older population represents the crystallization age of either, or both the Medicine Hat block and the Wyoming province terranes. The younger population is hypothesized to have grown during deformation/alteration associated with the formation of the Belt-Purcell Rift Basin.

Influence of brazing conditions on the strength of brazed joints of alumina dispersion-strengthened copper to 316 stainless steel

NASA Astrophysics Data System (ADS)

Nishi, H.; Kikuchi, K.

1998-10-01

Brazing of alumina dispersion-strengthened copper (DS Cu) to 316 stainless steel were conducted in order to investigate the influence of filler metals and brazing conditions on the joint strength. The brazing were performed with a silver-base (BAg-8) and three kinds of gold-base (BAu-2,4,11) filler metals with varying brazing joint clearance and brazing time. The filler metal had a greater effect on the joint strength than the brazing joint clearance and brazing time. The joint with BAu-2 was superior to the joint with other filler metals. The tensile strength of the joint with BAu-2 was as large as that of DS Cu, however, the Charpy and low cycle fatigue strength were lower than those of DS Cu. The DS Cu melted near the brazed zone, consequently recrystallization and agglomeration of alumina occurred in the diffusion layer for all filler metals. The grain size after the recrystallization was small in order of BAu-2, BAu-4 and BAu-11, that was in accordance with the order of the brazing temperature. The excellent fracture strength for the joint with BAu-2 was attributed to the smallest grain size.

In situ rutile petrochronology: texture-related T, Paleoproterozoic inheritance and a Pan-African overprint in the oldest subduction-related eclogites, Usagaran Orogen, Tanzania

NASA Astrophysics Data System (ADS)

Moeller, A.; Kraus, K.; Herms, P.; Appel, P.; Raase, P.

2014-12-01

Rutile U-Pb thermochronology is applied successfully by both TIMS and beam methods to date cooling events in mafic and metapelitic rocks, as well as in detrital studies. The Zr-in-rutile thermometer is very robust to thermal diffusion, and generally requires complete recrystallization to change recorded crystallization temperatures. Evidence for diffusion of HFSE elements in rutile is sparse; whereas U-Pb chronology generally records diffusion controlled cooling from the last event. This study follows conventional thermobarometry and U-Pb TIMS results on monazite, sphene and rutile of Möller et al. (1995) establishing a 2 Ga eclogite facies event from MORB-like metabasic, and metapelitic rocks in the Usagaran Orogen of Tanzania, interpreted to be the oldest outcrops of subduction-related eclogites. Rutile from both rock types were discordant near a ca. 500 Ma lower intercept, confirming a thermal overprint postulated on the basis of K-Ar and Rb-Sr mica ages by e.g. Wendt et al. (1972). The age of the eclogite-facies event was confirmed by U-Pb zircon dating of a 1991±2 Ma crosscutting pegmatite (Collins et al., 1999). We present in situ LA-ICP-MS rutile petrochronology on five metabasic and metapelitic eclogite facies samples with variable retrograde amphibolite-facies recrystallization. Thermometry confirms conventional Fe-Mg results, including higher peak temperatures in metabasites. Traverses on rutile inclusions in large garnet prophyroblasts in metapelites show increasing temperatures from cores outwards and a slight decrease towards outermost rims, with peak T coinciding with highest Mg# and highest grossular content, hence consistent with preservation of prograde zoning in the garnets and a brief eclogite facies event. Large rutiles (800μm) in recrystallized samples record temperature zoning profiles. U-Pb results show inheritance of near concordant 2 Ga domains, but dominantly confirm the ca. 490 Ma amphibolite facies overprint. The study is an excellent example of the potential of in-situ rutile petrochronology in complex, polymetamorphic rocks when meticulous attention is given to textural context. Möller et al., 1995, Geology, v. 23, p. 1067-1070. Collins et al., 2004, Earth Planet. Sci. Lett., v. 224, p. 175-192. Wendt et al., 1972, 24th Internat. Geol. Congr., Proc., p. 295-314.

Dolomitization in Late Jurassic-Early Cretaceous Platform Carbonates (Berdiga Formation), Ayralaksa Yayla (Trabzon), NE Turkey

NASA Astrophysics Data System (ADS)

Yıldız, Merve; Ziya Kırmacı, Mehmet; Kandemir, Raif

2017-04-01

ABSTRACT Pontides constitute an E-W trending orogenic mountain belt that extends about 1100 km along the northern side of Turkey from the immediate east of Istanbul to the Georgian border at the east. Tectono-stratigraphically, the Pontides are divided into three different parts: Eastern, Central, and Western Pontides. The Eastern Pontides, including the studied area, comprise an area of 500 km in length and 100 km in width, extending along the southeast coast of the Black Sea from the Kizilirmak and Yesilirmak Rivers in the vicinity of Samsun to the Little Caucasus. This area is bordered by the Eastern Black Sea basin to the north and the Ankara-Erzincan Neotethyan suture zone to the south. The Late Jurassic-Early Cretaceous platform carbonates are widely exposed in E-W direction in the Eastern Pontides (NE Turkey). The Platform carbonates shows varying lithofacies changing from supratidal to platform margin reef laterally and vertically, and was buried until the end of Late Cretaceous. The studied Ayralaksa Yayla (Trabzon, NE Turkey) area comprises one of the best typical exposures of formation in northern zone of Eastern Pontides. In this area, the lower parts of the formation are pervasively dolomitized by fabric-destructive and fabric-preserving replacement dolomite which are Ca-rich and nonstoichiometric (Ca56-66Mg34-44). Replacement dolomites (Rd) are represented by D18O values of -19.0 to -4.2 (VPDB), D13C values of 4.4 to 2.1 \\permil (VPDB) and 87Sr/86Sr ratios of 0.70889 to 0.70636. Petrographic and geochemical data indicate that Rd dolomites are formed prior to compaction at shallow-moderate burial depths from Late Jurassic-Early Cretaceous seawater and/or partly modified seawater as a result of water/rock interaction and they were recrystallized at elevated temperatures during subsequent burial. In the subsequent diagenetic process during the Late Cretaceous when the region became a magmatic arc, as a result of interaction with Early Jurassic volcanic rocks of basic composition, Rd dolomites were recrystallized by hydrothermal fluids of marine origin. Key words: Dolomitization; Geochemistry; Seawater origin; Recrystallization; Late Jurassic-Early Cretaceous, Platform carbonates; Berdiga Formation; Eastern Pontides, NE Turkey.

Mineral parageneses, regional architecture, and tectonic evolution of Franciscan metagraywackes, Cape Mendocino-Garberville-Covelo 30' x 60' quadrangles, northwest California

USGS Publications Warehouse

Ernst, W.G.; McLaughlin, Robert J.

2012-01-01

The Franciscan Complex is a classic subduction-zone assemblage. In northwest California, it comprises a stack of west vergent thrust sheets: westernmost Eastern Belt outliers; Central Belt mélange; Coastal Belt Yager terrane; Coastal Belt Coastal terrane; Coastal Belt King Range/False Cape terranes. We collected samples and determined P-T conditions of recrystallization for 88 medium-fine-grained metasandstones to assess their subduction-exhumation histories and assembly of the host allochthons. Feebly recrystallized Yager, Coastal, and King Range strata retain clear detrital features. Scattered neoblastic prehnite occurs in several Coastal terrane metasandstones; traces of possible pumpellyite are present in three Yager metaclastic rocks. Pumpellyite ± lawsonite ± aragonite-bearing Central Belt metasandstones are moderately deformed and reconstituted. Intensely contorted, thoroughly recrystallized Eastern Belt affinity quartzose metagraywackes contain lawsonite + jadeitic pyroxene ± aragonite ± glaucophane. We microprobed neoblastic phases in 23 rocks, documenting mineral parageneses that constrain the tectonic accretion and metamorphic P-T evolution of these sheets. Quasi-stable mineral assemblages typify Eastern Belt metasandstones, but mm-sized domains in the Central and Coastal belt rocks failed to achieve chemical equilibrium. Eastern Belt slabs rose from subduction depths approaching 25–30 km, whereas structurally lower Central Belt mélanges returned from ∼15–18 km. Coastal Belt assemblages suggest burial depths less than 5–8 km. Eastern and Central belt allochthons sequentially decoupled from the downgoing oceanic lithosphere and ascended into the accretionary margin; K-feldspar-rich Coastal Belt rocks were stranded along the continental edge without undergoing appreciable subduction, probably during Paleogene unroofing of the older, deeply subducted units of the Franciscan Complex in east-vergent crustal wedges.

Unraveling Recrystallization Mechanisms Governing Texture Development from Rare Earth Element Additions to Magnesium

NASA Astrophysics Data System (ADS)

Imandoust, Aidin

The origin of texture components associated with rare-earth (RE) element additions in wrought magnesium (Mg) alloys is a long-standing problem in magnesium technology. The objective of this research is to identify the mechanisms accountable for rare-earth texture during dynamic recrystallization (DRX). Towards this end, we designed binary Mg-Cerium and Mg-Gadolinium alloys along with complex alloy compositions containing zinc, yttrium and Mischmetal. Binary alloys along with pure Mg were designed to individually investigate their effects on texture evolutions, while complex compositions are designed to develop randomized texture, and be used in automotive and aerospace applications. We selected indirect extrusion to thermo-mechanically process our materials. Different extrusion ratios and speeds were designed to produce partially and fully recrystallized microstructures, allowing us to analyze DRX from its early stages to completion. X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to conduct microstructure and texture analyses. Our analyses revealed that rare-earth elements in zinc-containing magnesium alloys promote discontinuous dynamic recrystallization at the grain boundaries. During nucleation, the effect of rare earth elements on orientation selection was explained by the concomitant actions of multiple Taylor axes in the same grain. Isotropic grain growth was observed due to rare earth elements segregating to grain boundaries, which lead to texture randomization. The nucleation in binary Mg-RE alloys took place by continuous formation of necklace structures. Stochastic relaxation of basal and non-basal dislocations into low-angle grain boundaries produced chains of embryos with nearly random orientations. Schmid factor analysis showed a lower net activation of dislocations in RE textured grains compared to ones on the other side of the stereographic triangle. Lower dislocation densities within RE grains favored their growth by setting the boundary migration direction toward grains with higher dislocation density, thereby decreasing the system energy. We investigated the influence of RE elements on extension twinning induced hardening. RE addition enhanced tensile twinning induced hardening significantly. EBSD analysis illustrated that tensile twins cross low angle grain boundaries in Mg-RE alloys, which produced large twins and facilitated transmutation of basal to prismatic dislocations. Higher activity of pyramidal II dislocations in Mg-RE alloys resulted in higher twinning induced hardening.

Solvent Selection for Recrystallization: An Undergraduate Organic Experiment.

ERIC Educational Resources Information Center

Baumann, Jacob B.

1979-01-01

This experiment develops the students' ability to carry out a simple recrystallization effectively, and demonstrates how a solvent may be selected or rejected for the recrystallization of a specific organic compound. (Author/BB)

Nano-Sized Grain Refinement Using Friction Stir Processing

DTIC Science & Technology

2013-03-01

friction stir weld is a very fine grain microstructure produced as a result of dynamic recrystallization. The friction stir ... Friction Stir Processing, Magnesium, Nano-size grains Abstract A key characteristic of a friction stir weld is a very fine grain microstructure...state process developed on the basis of the friction stir welding (FSW) technique invented by The Welding Institute (TWI) in 1991 [2]. During

On the use of copper-based substrates for YBCO coated conductors

NASA Astrophysics Data System (ADS)

Vannozzi, A.; Fabbri, F.; Augieri, A.; Angrisani Armenio, A.; Galluzzi, V.; Mancini, A.; Rizzo, F.; Rufoloni, A.; Padilla, J. A.; Xuriguera, E.; De Felicis, D.; Bemporad, E.; Celentano, G.

2014-05-01

It is well known that the recrystallization texture of heavily cold-rolled pure copper is almost completely cubic. However, one of the main drawbacks concerning the use of pure copper cube-textured substrates for YBCO coated conductor is the reduced secondary recrystallization temperature. The onset of secondary recrystallization (i.e., the occurrence of abnormal grains with unpredictable orientation) in pure copper substrate was observed within the typical temperature range required for buffer layer and YBCO processing (600-850 °C). To avoid the formation of abnormal grains the effect of both grain size adjustment (GSA) and recrystallization annealing was analyzed. The combined use of a small initial grain size and a recrystallization two-step annealing (TSA) drastically reduced the presence of abnormal grains in pure copper tapes. Another way to overcome the limitation imposed by the formation of abnormal grains is to deposit a buffer layer at temperatures where secondary recrystallization does not occur. For example, La2Zr2O7 (LZO) film with a high degree of epitaxy was grown by metal-organic decomposition (MOD) at 1000 °C on pure copper substrate. In several samples the substrate underwent secondary recrystallization. Our experiments indicate that the motion of grain boundaries occurring during secondary recrystallization process does not affect the quality of LZO film.

Effect of Sn Micro-alloying on Recrystallization Nucleation and Growth Processes of Ferritic Stainless Steels

NASA Astrophysics Data System (ADS)

He, Tong; Bai, Yang; Liu, Xiuting; Guo, Dan; Liu, Yandong

2018-04-01

We investigated the effect of Sn micro-alloying on recrystallization nucleation and growth processes of ferritic stainless steels. The as-received hot rolled sheets were cold rolled up to 80% reduction and then annealed at 740-880 °C for 5 min. The cold rolling and recrystallization microstructures and micro-textures of Sn-containing and Sn-free ferritic stainless steels were all determined by electron backscatter diffraction. Our Results show that Sn micro-alloying has important effects on recrystallization nucleation and growth processes of ferritic stainless steels. Sn micro-alloying conduces to grain fragmentation in the deformation band, more fragmented grains are existed in Sn-containing cold rolled sheets, which provides more sites for recrystallization nucleation. Sn micro-alloying also promotes recrystallization process and inhibits the growth of recrystallized grains. The recrystallization nucleation and growth mechanism of Sn-containing and Sn-free ferritic stainless steels are both characterized by orientation nucleation and selective growth, but Sn micro-alloying promotes the formation of γ-oriented grains. Furthermore, Sn micro-alloying contributes to the formation of Σ13b CSL boundaries and homogeneous γ-fiber texture. Combining the results of microstructure and micro-texture, the formability of Sn-containing ferritic stainless steels will be improved to some extent.

Studying heat-affected zone deformations of electric arc welding

NASA Astrophysics Data System (ADS)

Suleimanov, R. I.; Zainagalina, L. Z.; Khabibullin, M. Ya; Zaripova, L. M.; Kovalev, N. O.

2018-03-01

The paper studies the influence of the most common defects in permanent electric arc welds made during the welding butt joints in infield oil pipelines, onto the strength characteristics of the welded pipe material around the heat-affected zone. A specimen of a butt weld with an obvious defect was used as a subject of the study. The changes in the geometric parameters of the weld were measured with the standard means; Rockwell hardness in the heat-affected zone was determined in certain areas with justification for the weld process modes. The cause of softening was found to be an increased width of the hot spot on the one side of the weld, where an enlarged crystalline structure appears as a result of the pipe material recrystallization under the influence of heat. Changes in the geometry of the thermal action area are determined by accumulation of molten filler on the one side of the weld when the welding rate is decreased. Some recommendations are given to prevent destruction of the welded structures and appearance of emergencies in infield oil pipelines.

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel

NASA Astrophysics Data System (ADS)

Hayakawa, Yasuyuki

2017-12-01

Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 106 primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model.

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel

PubMed Central

Hayakawa, Yasuyuki

2017-01-01

Abstract Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 106 primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model. PMID:28804524

Evaluation of the recrystallization kinetics of hot-melt extruded polymeric solid dispersions using an improved Avrami equation

PubMed Central

Feng, Xin; Ye, Xingyou; Park, Jun-Bom; Lu, Wenli; Morott, Joe; Beissner, Brad; Lian, Zhuoyang John; Pinto, Elanor; Bi, Vivian; Porter, Stu; Durig, Tom; Majumdar, Soumyajit; Repka, Michael A.

2017-01-01

The recrystallization of an amorphous drug in a solid dispersion system could lead to a loss in the drug solubility and bioavailability. The primary objective of the current research was to use an improved kinetic model to evaluate the recrystallization kinetics of amorphous structures and to further understand the factors influencing the physical stability of amorphous solid dispersions. Amorphous solid dispersions of fenofibrate with different molecular weights of hydroxypropylcellulose, HPC (Klucel™ LF, EF, ELF) were prepared utilizing hot-melt extrusion technology. Differential scanning calorimetry was utilized to quantitatively analyze the extent of recrystallization in the samples stored at different temperatures and relative humidity (RH) conditions. The experimental data were fitted into the improved kinetics model of a modified Avrami equation to calculate the recrystallization rate constants. Klucel LF, the largest molecular weight among the HPCs used, demonstrated the greatest inhibition of fenofibrate recrystallization. Additionally, the recrystallization rate (k) decreased with increasing polymer content, however exponentially increased with higher temperature. Also k increased linearly rather than exponentially over the range of RH studied. PMID:25224341

Investigating the principles of recrystallization from glyceride melts.

PubMed

Windbergs, Maike; Strachan, Clare J; Kleinebudde, Peter

2009-01-01

Different lipids were melted and resolidified as model systems to gain deeper insight into the principles of recrystallization processes in lipid-based dosage forms. Solid-state characterization was performed on the samples with differential scanning calorimetry and X-ray powder diffraction. Several recrystallization processes could be identified during storage of the lipid layers. Pure triglycerides that generally crystallize to the metastable alpha-form from the melt followed by a recrystallization process to the stable beta-form with time showed a chain-length-dependent behavior during storage. With increasing chain length, the recrystallization to the stable beta-form was decelerated. Partial glycerides exhibited a more complex recrystallization behavior due to the fact that these substances are less homogenous. Mixtures of a long-chain triglyceride and a partial glyceride showed evidence of some interaction between the two components as the partial glyceride hindered the recrystallization of the triglyceride to the stable beta-form. In addition, the extent of this phenomenon depended on the amount of partial glyceride in the mixture. Based on these results, changes in solid dosage forms based on glycerides during processing and storage can be better understood.

Evaluation of the recrystallization kinetics of hot-melt extruded polymeric solid dispersions using an improved Avrami equation.

PubMed

Feng, Xin; Ye, Xingyou; Park, Jun-Bom; Lu, Wenli; Morott, Joe; Beissner, Brad; Lian, Zhuoyang John; Pinto, Elanor; Bi, Vivian; Porter, Stu; Durig, Tom; Majumdar, Soumyajit; Repka, Michael A

2015-01-01

The recrystallization of an amorphous drug in a solid dispersion system could lead to a loss in the drug solubility and bioavailability. The primary objective of the current research was to use an improved kinetic model to evaluate the recrystallization kinetics of amorphous structures and to further understand the factors influencing the physical stability of amorphous solid dispersions. Amorphous solid dispersions of fenofibrate with different molecular weights of hydroxypropylcellulose, HPC (Klucel™ LF, EF, ELF) were prepared utilizing hot-melt extrusion technology. Differential scanning calorimetry was utilized to quantitatively analyze the extent of recrystallization in the samples stored at different temperatures and relative humidity (RH) conditions. The experimental data were fitted into the improved kinetics model of a modified Avrami equation to calculate the recrystallization rate constants. Klucel LF, the largest molecular weight among the HPCs used, demonstrated the greatest inhibition of fenofibrate recrystallization. Additionally, the recrystallization rate (k) decreased with increasing polymer content, however exponentially increased with higher temperature. Also k increased linearly rather than exponentially over the range of RH studied.

Mechanism of secondary recrystallization of Goss grains in grain-oriented electrical steel.

PubMed

Hayakawa, Yasuyuki

2017-01-01

Since its invention by Goss in 1934, grain-oriented (GO) electrical steel has been widely used as a core material in transformers. GO exhibits a grain size of over several millimeters attained by secondary recrystallization during high-temperature final batch annealing. In addition to the unusually large grain size, the crystal direction in the rolling direction is aligned with <001>, which is the easy magnetization axis of α-iron. Secondary recrystallization is the phenomenon in which a certain very small number of {110}<001> (Goss) grains grow selectively (about one in 10 6 primary grains) at the expense of many other primary recrystallized grains. The question of why the Goss orientation is exclusively selected during secondary recrystallization has long been a main research subject in this field. The general criterion for secondary recrystallization is a small and uniform primary grain size, which is achieved through the inhibition of normal grain growth by fine precipitates called inhibitors. This paper describes several conceivable mechanisms of secondary recrystallization of Goss grains mainly based on the selective growth model.

Microfabric and Structures in Glacial Ice

NASA Astrophysics Data System (ADS)

Monz, M.; Hudleston, P. J.

2017-12-01

Similar to rocks in active orogens, glacial ice develops both structures and fabrics that reflect deformation. Crystallographic preferred orientation (CPO), associated with mechanical anisotropy, develops as ice deforms, and as in rock, directly reflects the conditions and mechanisms of deformation and influences the overall strength. This project aims to better constrain the rheologic properties of natural ice through microstructural analysis and to establish the relationship of microfabric to macroscale structures. The focus is on enigmatic fabric patterns found in coarse grained, "warm" (T > -10oC) ice deep in ice sheets and in valley glaciers. Deformation mechanisms that produce such patterns are poorly understood. Detailed mapping of surface structures, including bedding, foliation, and blue bands (bubble-free veins of ice), was done in the ablation zone of Storglaciären, a polythermal valley glacier in northern Sweden. Microstructural studies on samples from a transect across the ablation zone were carried out in a cold room. Crystal size was too large for use of electron backscattered diffraction to determine CPO, therefore a Rigsby universal stage, designed specifically for ice, was used. In thick and thin sections, recrystallized grains are locally variable in both size (1mm-7cm in one thin section) and shape and clearly reflect recrystallization involving highly mobile grain boundaries. Larger crystals are often branching, and appear multiple times throughout one thin section. There is a clear shape preferred orientation that is generally parallel with foliation defined by bubble alignment and concentration. Locally, there appears to be an inverse correlation between bubble concentration and smoothness of grain boundaries. Fabric in samples that have undergone prolonged shear display roughly symmetrical multimaxima patterns centered around the pole to foliation. The angular distances between maxima suggest a possible twin relationship that may have developed from a preexisting single-maximum fabric.

Eocene and Miocene extension, meteoric fluid infiltration, and core complex formation in the Great Basin (Raft River Mountains, Utah)

USGS Publications Warehouse

Methner, Katharina; Mulch, Andreas; Teyssier, Christian; Wells, Michael L.; Cosca, Michael A.; Gottardi, Raphael; Gebelin, Aude; Chamberlain, C. Page

2015-01-01

Metamorphic core complexes (MCCs) in the North American Cordillera reflect the effects of lithospheric extension and contribute to crustal adjustments both during and after a protracted subduction history along the Pacific plate margin. While the Miocene-to-recent history of most MCCs in the Great Basin, including the Raft River-Albion-Grouse Creek MCC, is well documented, early Cenozoic tectonic fabrics are commonly severely overprinted. We present stable isotope, geochronological (40Ar/39Ar), and microstructural data from the Raft River detachment shear zone. Hydrogen isotope ratios of syntectonic white mica (δ2Hms) from mylonitic quartzite within the shear zone are very low (−90‰ to −154‰, Vienna SMOW) and result from multiphase synkinematic interaction with surface-derived fluids. 40Ar/39Ar geochronology reveals Eocene (re)crystallization of white mica with δ2Hms ≥ −154‰ in quartzite mylonite of the western segment of the detachment system. These δ2Hms values are distinctively lower than in localities farther east (δ2Hms ≥ −125‰), where 40Ar/39Ar geochronological data indicate Miocene (18–15 Ma) extensional shearing and mylonitic fabric formation. These data indicate that very low δ2H surface-derived fluids penetrated the brittle-ductile transition as early as the mid-Eocene during a first phase of exhumation along a detachment rooted to the east. In the eastern part of the core complex, prominent top-to-the-east ductile shearing, mid-Miocene 40Ar/39Ar ages, and higher δ2H values of recrystallized white mica, indicate Miocene structural and isotopic overprinting of Eocene fabrics.

Texture transition in experimentally deformed quartzite

NASA Astrophysics Data System (ADS)

Kilian, Rüdiger; Heilbronner, Renée

2017-04-01

Quartz crystallographic preferred orientations (textures), most commonly presented in the form of pole figures, are often used to infer deformation processes or conditions - despite the fact that we still do not understand fully how the different types of texture are generated. Here, we re-analyse experimentally deformed Black Hills Quartzite using EBSD maps. Samples were deformed in general shear in the dislocation creep regimes 1 to 3 at temperatures ranging from 875 to 915°C, constant shear strain rates of 1e-5/s (Heilbronner & Tullis, 2006), and resulting flow stresses of (600 MPa ≥ Tau ≥ 100 MPa). Already at low strain, a strong alignment of <11-20> in the shear plane and of {10-11} with the maximum principal stress direction is observed. [0001] pole figures of recrystallized grains in regime 1 exhibit a peripheral maximum, roughly perpendicular to the shear plane while in regime 3 two elongated maxima are formed very close to the kinematic y-direction. Regime 2 shows a mixture of these two texture types. In regime 1, dynamic recrystallization is dominated by bulging recrystallization (nucleation of new grains), and in regime 3 by subgrain rotation recrystallization. In regime 2, again a mixture of regime 1 and 3 can be observed. Texture strength increases with the amount of crystal plastic deformation and is generally the lowest for the texture type with peripheral [0001]. During crystal plastic deformation [0001] rotate towards the kinematic y-direction. The coexistence and transition from one to the other texture type is suggested to result from two different texture-forming processes. The first process is thought to be crystal plasticity by glide on various <11-20> slip systems and associated rotation of the crystal lattice, with the attractor of [0001] close to - but not exactly parallel to - the kinematic y-direction. The second process is suggested to be the growth of oriented grains during bulging recrystallization and associated (fracturing and) grain boundary sliding. The contribution of both processes results in the final texture type. The most distinctive difference of the three suites of experiments is the flow stress, decreasing from regime 1 to regime 3. Since the temperature and strain rate differences in these experiments are very small indeed, it is argued that the two end-member texture types do not indicate a temperature dependence of a slip system. Rather, they seem to depend on the flow stress and hence on the recrystallization mechanism. It remains to be tested whether this relation also holds in natural quartz mylonites where those texture types are frequently observed.

Effect of controlling recrystallization from the melt on the residual stress and structural properties of the Silica-clad Ge core fiber

NASA Astrophysics Data System (ADS)

Zhao, Ziwen; Cheng, Xueli; He, Ting; Xue, Fei; Zhang, Wei; Chen, Na; Wen, Jianxiang; Zeng, Xianglong; Wang, Tingyun

2017-09-01

Effect of controlling recrystallization from the melt (1000 °C) on the residual stress and structural properties of a Ge core fiber via molten core drawing (MCD) method is investigated. Ge core fibers is investigated using Raman spectroscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). Compared with the as-drawn Ge fiber, the Raman peak of the recrystallized Ge fiber shift from 300 cm-1 to 300.6 cm-1 and full width at half maximum (FWHM) decreased from 5.36 cm-1 to 4.48 cm-1. The Ge crystal grains which sizes are of 200-600 nm were formed during the process of recrystallization; the XRD peak of (1 1 1) plane is observed after recrystallization. These results show that controlling recrystallization allows the release of the thermal stress, and improvement of the crystal quality of Ge core.

Microstructure heterogeneity after the ECAP process and its influence on recrystallization in aluminium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wronski, S., E-mail: wronski@fis.agh.edu.pl; Tarasiuk, J., E-mail: tarasiuk@ftj.agh.edu.pl; Bacroix, B., E-mail: brigitte.bacroix@univ-paris13.fr

The main purpose of the present work is to describe the qualitative and quantitative behaviours of aluminium during high strain plastic deformation and the effect of deformation on the subsequent recrystallization process. An Electron Backscatter Diffraction analysis of aluminium after the Equal channel angular pressing (ECAP) and recrystallization process is presented. In order to do this, several topological maps are measured for samples processed by 4 and 8 passes and recrystallized. The processing was conducted with route C. For all samples, distributions of grain size, misorientation, image quality factor (IQ) and texture were preceded and then analysed in some detail.more » - Highlights: ► Describe the microstructure fragmentation in aluminum. ► High strain plastic deformation and effect of deformation on recrystallization. ► The microstructure fragmentation and its influence on recrystallization. ► Image quality factor and misorientation characteristics are examined using EBSD.« less

The Freyenstein Shear Zone - Implications for exhumation of the South Bohemian Batholith (Moldanubian Superunit, Strudengau, Austria)

NASA Astrophysics Data System (ADS)

Griesmeier, Gerit; Iglseder, Christoph; Konstantin, Petrakakis

2016-04-01

The Moldanubian superunit is part of the internal zone of the Variscan Orogen in Europe and borders on the Saxothuringian and Sudetes zones in the north. In the south, it is blanketed by the Alpine foreland molasse. Tectonically it is subdivided into the Moldanubian Nappes (MN), the South Bohemian Batholith (SBB) and the Bavarian Nappes. This work describes the ~ 500 m thick Freyenstein shear zone, which is located at the southern border of the Bohemian Massif north and south of the Danube near Freyenstein (Strudengau, Lower Austria). The area is built up by granites of Weinsberg-type, which are interlayered by numerous dikes and paragneisses of the Ostrong nappe system. These dikes include medium grained granites and finegrained granites (Mauthausen-type granites), which form huge intrusions. In addition, smaller intrusions of dark, finegrained diorites und aplitic dikes are observed. These rocks are affected by the Freyenstein shear zone und ductily deformed. Highly deformed pegmatoides containing white mica crystals up to one cm cut through the deformed rocks and form the last dike generation. The Freyenstein shear zone is a NE-SW striking shear zone at the eastern edge of the SBB. The mylonitic foliation is dipping to the SE with angles around 60°. Shear-sense criteria like clast geometries, SĆ structures as well as microstructures show normal faulting top to S/SW with steep (ca. 50°) angles. The Freyenstein shear zone records a polyphase history of deformation and crystallization: In a first phase, mylonitized mineral assemblages in deformed granitoides can be observed, which consist of pre- to syntectonic muscovite-porphyroclasts and biotite as well as dynamically recrystallized potassium feldspar, plagioclase and quartz. The muscovite porphyroclasts often form mica fishes and show top to S/SW directed shear-sense. The lack of syntectonic chlorite crystals points to metamorphic conditions of lower amphibolite-facies > than 450° C. In a later stage fluid infiltration under lower greenschist-facies conditions locally lead to sericitization of feldspar and development of pseudomorphs after it. In addition, syn-mylonitic biotite has been chloritized mimetically. Chlorite growth across the mylonitic foliation occurs rarely. Brittle faulting, overprinting the shear zone features, is documented by the occurrence of numerous harnish planes. They show normal faulting to the N with angles around 30° and locally sinistral shear-sense. The Freyenstein shear zone belongs to a system of NE-SW striking shear zones and faults in the Moldanubian superunit and is located at the border between the SBB and MN ductily deforming both. Therefore, it plays an important role in exhumation processes of last stage SBB (synkinematic) intrusions during Late Variscan orogenic extension. According to cooling ages in other shear zones and (synkinematic) intrusions an age of ca. 320-290 Ma for the ductile deformation can be assumed.

Rapid hydrothermal cooling above the axial melt lens at fast-spreading mid-ocean ridge: Quantification through intra-plagioclase diffusion revealed by IODP Hole 1256D

NASA Astrophysics Data System (ADS)

Zhang, C.; Koepke, J.; Kirchner, C.; Götze, N.; Behrens, H.

2014-12-01

At fast-spreading mid-ocean ridges the axial melt lenses sandwiched between the lower oceanic crust and the sheeted dike sequences are assumed to be the major magma source of oceanic crust accretion. According to the widely discussed "gabbro glacier" model, the formation of the lower oceanic crust requires efficient cooling of the axial melt lens, resulting in partly crystallization and leading to crystal-melt mush which may subside down to form the lower crust. These processes are believed to be controlled dominantly by periodical magma supply and hydrothermal circulation above melt lens. Here we quantify the cooling rate above melt lens using chemical zoning of plagioclase from hornfelsic recrystallized sheeted dikes overlying the uppermost gabbros, which are part of the dike-gabbro transition zone drilled in Hole 1256D in the Eastern equatorial Pacific by the Integrated Ocean Drilling Program, where for the first time the dike-gabbro transition zone of an intact oceanic crust was penetrated and sampled. The measured zoning patterns are supposed to be a combined result of diffusion during both on-ridge and off-ridge cooling. We estimate the on-ridge cooling rate using a forward modelling approach based on CaAl-NaSi interdiffusion in plagioclase. The results show that the recrystallized sheeted dikes have been cooled from the peak thermal overprint at 1000-1050 °C to 600 °C within about 5-30 years as a result of hydrothermal circulation above a melt lens during a period of magma starvation, corresponding to a cooling rate of 30±15 °C/yr. Heat balance calculation also approves that in order to balance the heat output of a melt lens at a fast-spreading mid-ocean ridge similar to the case of IODP Hole 1256D, the cooling rate above the melt lens is required to be around 30 °C/yr. The estimated rapid hydrothermal cooling rate coincides with the observed annual to decal episodes of melt lens fluctuation and lava eruption, which favors the "gabbro glacier" model and explains how the effective heat extraction from melt lens is achieved at fast-spreading mid-ocean ridges.

Modifications in the AA5083 Johnson-Cook Material Model for Use in Friction Stir Welding Computational Analyses

NASA Astrophysics Data System (ADS)

Grujicic, M.; Pandurangan, B.; Yen, C.-F.; Cheeseman, B. A.

2012-11-01

Johnson-Cook strength material model is frequently used in finite-element analyses of various manufacturing processes involving plastic deformation of metallic materials. The main attraction to this model arises from its mathematical simplicity and its ability to capture the first-order metal-working effects (e.g., those associated with the influence of plastic deformation, rate of deformation, and the attendant temperature). However, this model displays serious shortcomings when used in the engineering analyses of various hot-working processes (i.e., those utilizing temperatures higher than the material recrystallization temperature). These shortcomings are related to the fact that microstructural changes involving: (i) irreversible decrease in the dislocation density due to the operation of annealing/recrystallization processes; (ii) increase in grain-size due to high-temperature exposure; and (iii) dynamic-recrystallization-induced grain refinement are not accounted for by the model. In this study, an attempt is made to combine the basic physical-metallurgy principles with the associated kinetics relations to properly modify the Johnson-Cook material model, so that the model can be used in the analyses of metal hot-working and joining processes. The model is next used to help establish relationships between process parameters, material microstructure and properties in friction stir welding welds of AA5083 (a non-age-hardenable, solid-solution strengthened, strain-hardened/stabilized Al-Mg-Mn alloy).

Unraveling Recrystallization Mechanisms Governing Texture Development from Rare-Earth Element Additions to Magnesium

NASA Astrophysics Data System (ADS)

Imandoust, Aidin; Barrett, Christopher D.; Al-Samman, Talal; Tschopp, Mark A.; Essadiqi, Elhachmi; Hort, Norbert; El Kadiri, Haitham

2018-03-01

The origin of texture components often associated with rare-earth element (REE) additions in wrought magnesium alloys is a long-standing problem in magnesium technology. While their influence on the texture is unquestionable, it is not yet clear why certain texture components, such as < 11\\bar{2}1 > ||{extrusion}{direction}, are favored over other components typically observed in traditional magnesium alloys. The objective of this research is to identify the mechanisms accountable for these RE textures during early stages of recrystallization. Electron backscattered diffraction and transmission electron microscopy analyses reveal that REEs in zinc-containing magnesium alloys corroborate discontinuous dynamic recrystallization. REEs promote isotropic growth for all nuclei generated through the bulging mechanism. During nucleation, the effect of REEs on orientation selection was explained by the diversified activity of both < 10\\bar{1}0 > and [0001] Taylor axes in the same grain with a marked preference for [0001] rotations to occur first. During nuclei growth, no growth preference was observed when sufficient REEs are added in the zinc-containing magnesium alloys, instead isotropic nuclei growth across all grain orientations occurs. This phenomenon is attributed to REEs segregating to grain boundaries (GBs), in agreement with prior computational and theoretical results (Barrett et al., Scripta Mater 146:46-50, 2018) that show a more isotropic GB energy and mobility after segregation.

Stress Dependence of Microstructures in Experimentally Deformed Calcite

NASA Astrophysics Data System (ADS)

Platt, J. P.; De Bresser, J. H. P.

2017-12-01

Measurements of dynamically recrystallized grain size (Dr), subgrain size (Sg), minimum bulge size (Blg), and the maximum scale length for surface-energy driven grain-boundary migration (γGBM) in experimentally deformed Cararra marble help define the dependence of these microstructural features on stress and temperature. Measurements were made optically on ultra-thin sections in order to allow these features to be defined during measurement on the basis of microstructural setting and geometry. Taken together with previously published data Dr defines a paleopiezometer with a stress exponent of -1.09. There is no discernible temperature dependence over the 500°C temperature range of the experiments. Recrystallization occured mainly by bulging and subgrain rotation, and the two processes operated together, so that it is not possible to separate grains nucleated by the two mechanisms. Sg and Dr measured in the same samples are closely similar in size, suggesting that new grains do not grow significantly after nucleation, and that subgrain size is likely to be the primary control on recrystallized grain size. Blg and γGBM measured on each sample define a relationship to stress with an exponent of approximately -1.6, which helps define the boundary in stress - grain-size space between a region of dominant strain-energy-driven grain-boundary migration at high stress, from a region of dominant surface-energy-driven grain-boundary migration at low stress.

Diverse dissolution-recrystallization structural transformations and sequential Förster resonance energy transfer behavior of a luminescent porous Cd-MOF.

PubMed

Cao, Li-Hui; Li, Hai-Yang; Xu, Hong; Wei, Yong-Li; Zang, Shuang-Quan

2017-09-12

Metal-organic frameworks (MOFs) with light-harvesting building blocks provide an excellent platform to study energy transfer in networks with well-defined structures. Here, we report the synthesis, dissolution-recrystallization structural transformation (DRST) and the Förster resonance energy transfer (FRET) properties of a 2D microporous MOF {[Cd 2 (L 1 ) 3 (Hdabco) 2 ]·5DMAc·6H 2 O} n (Cd-MOF, 1). Complex 1 can be dissolved in water and three other products with different dimensions recrystallized from the aqueous solution under diverse reaction conditions were obtained. Due to the porosity and excellent blue luminescence properties of complex 1, we also studied the FRET process between 1 and guest dyes. Two distinct organic dye molecules viz., acridine orange (AO) and rhodamine B (RhB), are encapsulated in 1 which has honeycomb-type nanochannels, and their influence on fluorescence emission has also been studied. The microporous complex 1 in (AO + RhB)@1 serves as an energy funnel that harvests high energy excitation and channels it onto AO and then onto RhB. The steady-state fluorescence and fluorescence dynamics of emission reveal successfully the process of stepwise vectorial energy transfer. Therefore, MOFs could be a class of promising host materials to be further explored in the field of energy transfer between MOF-host and organic guests.

Microstructural variation in the transport direction of a large-scale mid-crustal thrust (Woodroffe Thrust, Central Australia)

NASA Astrophysics Data System (ADS)

Wex, Sebastian; Mancktelow, Neil S.; Hawemann, Friedrich; Pennacchioni, Giorgio; Camacho, Alfredo

2016-04-01

The over ˜600 km long E-W trending mid-crustal Woodroffe Thrust is one the most prominent structures of a range of large-scale shear zones that developed in the Musgrave Ranges region in Central Australia. During the Petermann Orogeny around 550 Ma the Woodroffe Thrust placed 1.2 Ga granulites onto similarly-aged amphibolite and granulite facies gneisses along a south-dipping plane with a top-to-north shear sense. Due to late-stage open folding of the thrust plane, a nearly continuous N-S profile of 60 km length in the direction of thrusting could be studied for variation in microstructure. The regional P/T variations in the mylonitized footwall (600 to 500 °C at ~ 0.8 GPa from S to N) indicate that the original angle of dip was shallow (~ 10°) towards the south. Along the profile, evidence for fluid-present conditions are effectively absent in the more southerly areas and only present on a local scale in the north, characterizing the regional conditions to be "dry". This is indicated by: 1) only rare syntectonic quartz veins in the footwall; 2) very little sericitization of plagioclase; 3) breakdown of plagioclase to kyanite + garnet, rather than kyanite + clinozoisite; and 4) variable presence of hydrothermally introduced calcite. These changes in P/T conditions and fluid availability are associated with corresponding changes in mineral assemblage and microstructure. Mylonitized dolerites consists of a syn-kinematic assemblage (decreasing modal amounts from left to right) of Pl + Cpx + Grt + Ky + Rt + Ilm ± Opx ± Amp ± Qz in the central/southern areas and Pl + Bt + Amp + Chl + Ilm ± Kfs ± Mag ± Ap in the north. The amount of newly grown garnet decreases towards the north and garnet is generally absent in the northernmost exposures of the Woodroffe Thrust. Mylonitized felsic granulites and granitoids consist of syn-kinematic assemblages of Qz + Pl + Kfs + Grt + Cpx + Ky + Ilm + Rt ± Bt ± Amp ± Opx ± Ap in the south and Qz + Pl + Kfs + Bt + Czo + Grt + Ilm ± Mag + Ttn ± Ms ± Amp ± Ap in the north. Plagioclase and K-feldspar dynamically recrystallized (grainsize < 10 μm) along the entire 60 km N-S transect, but with an increasing degree in the more southern exposures. Over the entire area dynamically recrystallized quartz aggregates in mylonites show polygonal, strain-free, equigranular grains, with a morphology indicating SGR recrystallization, under temperatures usually considered typical for GBM, which could potentially be due to the relatively "dry" conditions. Quartz grainsizes are on average 24 μm and 44 μm in the southern and northern areas, respectively. The increase in grain size towards the north correlates well with the increasing influx of fluids, but is in contrast to the trend of higher metamorphic grade towards the south. This suggests that fluid, rather than temperature, may be the main factor controlling the rheology of such "dry" middle crust.

Universal scaling of grain size distributions during dislocation creep

NASA Astrophysics Data System (ADS)

Aupart, Claire; Dunkel, Kristina G.; Angheluta, Luiza; Austrheim, Håkon; Ildefonse, Benoît; Malthe-Sørenssen, Anders; Jamtveit, Bjørn

2017-04-01

Grain size distributions are major sources of information about the mechanisms involved in ductile deformation processes and are often used as paleopiezometers (stress gauges). Several factors have been claimed to influence the stress vs grain size relation, including the water content (Jung & Karato 2001), the temperature (De Bresser et al., 2001), the crystal orientation (Linckens et al., 2016), the presence of second phase particles (Doherty et al. 1997; Cross et al., 2015), and heterogeneous stress distributions (Platt & Behr 2011). However, most of the studies of paleopiezometers have been done in the laboratory under conditions different from those in natural systems. It is therefore essential to complement these studies with observations of naturally deformed rocks. We have measured olivine grain sizes in ultramafic rocks from the Leka ophiolite in Norway and from Alpine Corsica using electron backscatter diffraction (EBSD) data, and calculated the corresponding probability density functions. We compared our results with samples from other studies and localities that have formed under a wide range of stress and strain rate conditions. All distributions collapse onto one universal curve in a log-log diagram where grain sizes are normalized by the mean grain size of each sample. The curve is composed of two straight segments with distinct slopes for grains above and below the mean grain size. These observations indicate that a surprisingly simple and universal power-law scaling describes the grain size distribution in ultramafic rocks during dislocation creep irrespective of stress levels and strain rates. Cross, Andrew J., Susan Ellis, and David J. Prior. 2015. « A Phenomenological Numerical Approach for Investigating Grain Size Evolution in Ductiley Deforming Rocks ». Journal of Structural Geology 76 (juillet): 22-34. doi:10.1016/j.jsg.2015.04.001. De Bresser, J. H. P., J. H. Ter Heege, and C. J. Spiers. 2001. « Grain Size Reduction by Dynamic Recrystallization: Can It Result in Major Theological Weakening? » International Journal of Earth Sciences 90 (1): 28-45. Doherty, R. D., D. A. Hughes, F. J. Humphreys, J. J. Jonas, D. J. Jensen, M. E. Kassner, W. E. King, T. R. McNelley, H. J. McQueen, and A. D. Rollett. 1997. « Current Issues in Recrystallization: A Review ». Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing 238 (2): 219-74. doi:10.1016/S0921-5093(97)00424-3. Jung, H., and S. I. Karato. 2001. « Effects of Water on Dynamically Recrystallized Grain-Size of Olivine ». Journal of Structural Geology 23 (9): 1337-44. doi:10.1016/S0191-8141(01)00005-0. Linckens, J., G. Zulauf, and J. Hammer. 2016. « Experimental Deformation of Coarse-Grained Rock Salt to High Strain ». Journal of Geophysical Research-Solid Earth 121 (8): 6150-71. doi:10.1002/2016JB012890. Platt, J.P., and W.M. Behr. 2011. « Grainsize Evolution in Ductile Shear Zones: Implications for Strain Localization and the Strength of the Lithosphere ». Journal of Structural Geology 33 (4): 537-50. doi:10.1016/j.jsg.2011.01.018.

Strain induced grain boundary migration effects on grain growth of an austenitic stainless steel during static and metadynamic recrystallization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paggi, A., E-mail: alpaggi@tenaris.com; Angella, G.; Donnini, R.

Static and metadynamic recrystallization of an AISI 304L austenitic stainless steel was investigated at 1100 °C and 10{sup −} {sup 2} s{sup −} {sup 1} strain rate. The kinetics of recrystallization was determined through double hit compression tests. Two strain levels were selected for the first compression hit: ε{sub f} = 0.15 for static recrystallization (SRX) and 0.25 for metadynamic recrystallization (MDRX). Both the as-deformed and the recrystallized microstructures were investigated through optical microscopy and electron back-scattered diffraction (EBSD) technique. During deformation, strain induced grain boundary migration appeared to be significant, producing a square-like grain boundary structure aligned along themore » directions of the maximum shear stresses in compression. EBSD analysis revealed to be as a fundamental technique that the dislocation density was distributed heterogeneously in the deformed grains. Grain growth driven by surface energy reduction was also investigated, finding that it was too slow to explain the experimental data. Based on microstructural results, it was concluded that saturation of the nucleation sites occurred in the first stages of recrystallization, while grain growth driven by strain induced grain boundary migration (SIGBM) dominated the subsequent stages. - Highlights: • Recrystallization behavior of a stainless steel was investigated at 1100 °C. • EBSD revealed that the dislocation density distribution was heterogeneous during deformation. • Saturation of nucleation sites occurred in the first stages of recrystallization. • Strain induced grain boundary migration (SIGBM) effects were significant. • Grain growth driven by SIGBM dominated the subsequent stages.« less

Quantifying the Variation in Shear Zone Character with Depth: a Case Study from the Simplon Shear Zone, Central Alps

NASA Astrophysics Data System (ADS)

Cawood, T. K.; Platt, J. P.

2017-12-01

A widely-accepted model for the rheology of crustal-scale shear zones states that they comprise distributed strain at depth, in wide, high-temperature shear zones, which narrow to more localized, high-strain zones at lower temperature and shallower crustal levels. We test and quantify this model by investigating how the width, stress, temperature and deformation mechanisms change with depth in the Simplon Shear Zone (SSZ). The SSZ marks a major tectonic boundary in the central Alps, where normal-sense motion and rapid exhumation of the footwall have preserved evidence of older, deeper deformation in rocks progressively further into the currently-exposed footwall. As such, microstructures further from the brittle fault (which represents the most localized, most recently-active part of the SSZ) represent earlier, higher- temperature deformation from deeper crustal levels, while rocks closer to the fault have been overprinted by successively later, cooler deformation at shallower depths. This study uses field mapping and microstructural studies to identify zones representing deformation at various crustal levels, and characterize each in terms of zone width (representing width of the shear zone at that time and depth) and dominant deformation mechanism. In addition, quartz- (by Electron Backscatter Diffraction, EBSD) and feldspar grain size (measured optically) piezometry are used to calculate the flow stress for each zone, while the Ti-in-quartz thermometer (TitaniQ) is used to calculate the corresponding temperature of deformation. We document the presence of a broad zone in which quartz is recrystallized by the Grain Boundary Migration (GBM) mechanism and feldspar by Subgrain Rotation (SGR), which represents the broad, deep zone of deformation occurring at relatively high temperatures and low stresses. In map view, this transitions to successively narrower zones, respectively characterized by quartz SGR and feldspar Bulge Nucleation (BLG); quartz BLG and brittle deformation of feldspar; and finally, a zone of generally brittle deformation. These zones represent deformation in progressively narrower regions at shallower depths, under lower temperatures and higher stresses.

The Silurian Hoedongri Formation in the Taebaeksan Basin of Korea Revisited: its Significance in the Tectonic Reconstruction of East Asia

NASA Astrophysics Data System (ADS)

Chae, S.; Hong, J.; Jung, S.; Ree, J.

2011-12-01

The Silurian Hoedongri Formation of the Taebaeksan Basin of South Korea has been used as a key unit to the correlation of tectonic provinces of East Asia since the South China craton (or Yangtz block) contains Silurian-Devonian sequences as well as Cambrian-Ordovician ones in the Paleozoic basins while the North China craton (or Sino-Korea block) is devoid of Silurian-Devonian sequences. In the Biryongdong area near the type locality of the Hoedongri Formation, it has been reported that the gray limestone of the Hoedongri Formation unconformably overlies brownish gray limestone of the Ordovician Haengmae Formation. However, our detailed examination on the Biryongdong section reveals that both of the brownish gray and gray limestones are mylonitic marbles with the boundary between the two units being a healed fault breccia zone (~ 12 m thick). The main difference of the two units is that repeated cycles of plastic deformation and fracturing occurred in the underlying brownish gray marble ('Haengmae') while the gray marble ('Hoedongri') deformed mainly by intracrystalline plasticity. The mylonitic foliation strikes NW with a low to moderate dip angle (20-60°) to NE. The ridge-in-groove type lineation on foliation surface trends NNW. The shape-preferred foliation of elongated calcite grains are oblique to the mylonitic foliation defined by layers with a grain-size variation, indicating a top-to-the-SSE shear sense. The mylonitic marble consists of elongated remnant grains (80-120 μm) with deformation twins and dynamically recrystallized matrix grains (10-40 μm). Grain boundaries and twin boundaries are lobate or wavy, indicating dynamic boundary migration. Some layers of the gray mylonitic marble are composed entirely of larger (80-120 μm) elongated calcite grains. In the brownish gray mylonitic marble unit, layers of brittle fracturing overprinting mylonitic foliation occur. In some of these layers, fragments (several cm - tens of cm) of the mylonitic marble are angular to subangular with coarse calcite fillings between the fragments. In other layers, mylonitic marble fragments are elongated with matrix foliation wrapping around them. These features suggest repeated cycles of plastic deformation and fracturing. Tectonic significance of this shear zone (at least 90 m thick) is not clear at present, and the regional extent and absolute age constraint of the shear zone should be clarified.

Gelatinization and freeze-concentration effects on recrystallization in corn and potato starch gels.

PubMed

Ronda, Felicidad; Roos, Yrjö H

2008-04-07

Freeze-concentration of starch gels was controlled by temperature and gelatinization with glucose and lactose. The aim of the study was to evaluate the effects of freezing temperature and gel composition on starch recrystallization behaviour of corn and potato starch gels (water content 70%, w/w) in water or glucose or lactose (10%, w/w) solutions. Starch gels were obtained by heating in differential scanning calorimetry (DSC). Samples of starch gels were frozen at -10 degrees C, -20 degrees C and -30 degrees C for 24h and, after thawing, stored at +2 degrees C for 0, 1, 2, 4 and 8 days. The extent of starch recrystallization was taken from the enthalpy of melting of the recrystallized starch by DSC. Freezing temperatures, glucose, lactose and the origin of the starch affected the recrystallization behaviour greatly. The recrystallization of amorphous starch during storage was enhanced by freeze-concentration of gels at temperatures above T'(m). Molecular mobility was enhanced by unfrozen water and consequently molecular rearrangements for nucleation could take place. Further storage at a higher temperature enhanced the growth and the maturation of crystals. In particular, glucose decreased the T'(m) of the gels and consequently lower freezing temperatures were needed to reduce enhanced recrystallization during storage. Freeze-concentration temperatures also showed a significant effect on the size and the perfection of crystals formed in starch recrystallization.

Ultrasonic Determination Of Recrystallization

NASA Technical Reports Server (NTRS)

Generazio, Edward R.

1988-01-01

State of recrystallization identified. Measurement of ultrasonic attenuation shows promise as means of detecting recrystallization in metal. Technique applicable to real-time acoustic monitoring of thermomechanical treatments. Starting with work-hardened material, one ultrasonically determines effect of annealing, using correlation between ultrasonic attenuation and temperature.

A texture-component Avrami model for predicting recrystallization textures, kinetics and grain size

NASA Astrophysics Data System (ADS)

Raabe, Dierk

2007-03-01

The study presents an analytical model for predicting crystallographic textures and the final grain size during primary static recrystallization of metals using texture components. The kinetics is formulated as a matrix variant of the Johnson-Mehl-Avrami-Kolmogorov equation. The matrix form is required since the kinetic and crystallographic evolution of the microstructure is described in terms of a limited set of growing (recrystallizing) and swept (deformed) texture components. The number of components required (5-10) defines the order of the matrix since the kinetic coupling occurs between all recrystallizing and all deformed components. Each such couple is characterized by corresponding values for the nucleation energy and grain boundary mobility. The values of these parameters can be obtained by analytical or numerical coarse graining according to a renormalization scheme which replaces many individual grains which grow via recrystallization in a deformed texture component by a single equivalent recrystallization texture component or by fitting to experimental data. Each deformed component is further characterized by an average stored deformation energy. Each element of the kinetic matrix, reflecting one of the possible couplings between a deformed and a recrystallizing texture component, is then derived in each time step by a set of two differential equations. The first equation describes the thermally activated nucleation and growth processes for the expanded (free) volume for a particular couple of a deformed and a recrystallizing texture component and the second equation is used for calculating the constrained (real) volume for that couple which corrects the free volume for those portions of the deformation component which were already swept. The new method is particularly developed for the fast and physically based process simulation of recrystallization textures with respect to processing. The present paper introduces the method and applies it to the primary recrystallization of low carbon steels.

Mesoscale Modeling of Dynamic Compression of Boron Carbide Polycrystals

DTIC Science & Technology

2013-05-01

reported later. Recrystallization has not been reported in the literature and is precluded by the model, meaning : 0 →1 is irreversible. Following...average HEL, above which a measurable strength loss is evident (Vogler et al., 2004), though amorphization has not been definitively proven to cause... definition (A.7) is exact when ı2 E→ 0 (Clayton, 2012). This criterion agrees exactly with that for classical stability under hydrostatic loading

Slip Zone versus Damage Zone Micromechanics, Arima-Takasuki Tectonic Line, Japan

NASA Astrophysics Data System (ADS)

White, J. C.; Lin, A.

2017-12-01

The Arima-Takasuki Tectonic Line (ATTL) of southern Honshu, Japan is defined by historically active faults and multiple splays producing M7 earthquakes. The damage zone of the ATTL comprises a broad zone of crushed, comminuted and pulverized granite/rhyolite1,2containing cm-scale slip zones and highly comminuted injection veins. In this presentation, prior work on the ATTL fault rocks is extending to include microstructural characterization by transmission electron microscopy (TEM) from recent trenching of the primary slip zone, as well as secondary slip zones. This is necessary to adequately characterize the extremely fine-grained material (typically less than 1mm) in both damage and core zones. Damage zone material exhibits generally random textures3 whereas slip zones are macroscopically foliated, and compositionally layered, notwithstanding a fairly homogeneous protolith. The latter reflects fluid-rock interaction during both coseismic and interseismic periods. The slip zones are microstructurally heterogeneous at all scales, comprising not only cataclasites and phyllosilicate (clay)-rich gouge zones, but Fe/Mn pellets or clasts that are contained within gouge. These structures appear to have rolled and would suggest rapid recrystallization and/or growth. A central question related to earthquake recurrence along existing faults is the nature of the gouge. In both near-surface exposures and ongoing drilling at depth, "plastic" or "viscous" gouge zones comprise ultra-fine-grained clay-siliciclastic particles that would not necessarily respond in a simple frictional manner. Depending on whether the plastic nature of these slip zones develops during or after slip, subsequent focusing of slip within them could be complicated. 1 Mitchell, T.A., Ben-Zion, Y., Shimamoto, T., 2011. Ear. Planet. Sci. Lett. 308, 284-297. 2 Lin, A., Yamashita, K, Tanaka, M. J., 2013. Struc. Geol. 48, 3-13. 3 White, J.C., Lin, A. 2016. Proc. AGU Fall Mtg., T42-02 San Francisco.

Comparisons of Different Models on Dynamic Recrystallization of Plate during Asymmetrical Shear Rolling

PubMed Central

Zhang, Tao; Li, Lei; Lu, Shi-Hong; Gong, Hai; Wu, Yun-Xin

2018-01-01

Asymmetrical shear rolling with velocity asymmetry and geometry asymmetry is beneficial to enlarge deformation and refine grain size at the center of the thick plate compared to conventional symmetrical rolling. Dynamic recrystallization (DRX) plays a vital role in grain refinement during hot deformation. Finite element models (FEM) coupled with microstructure evolution models and cellular automata models (CA) are established to study the microstructure evolution of plate during asymmetrical shear rolling. The results show that a larger DRX fraction and a smaller average grain size can be obtained at the lower layer of the plate. The DRX fraction at the lower part increases with the ascending speed ratio, while that at upper part decreases. With the increase of the offset distance, the DRX fraction slightly decreases for the whole thickness of the plate. The differences in the DRX fraction and average grain size between the upper and lower surfaces increase with the ascending speed ratio; however, it varies little with the change of the speed ratio. Experiments are conducted and the CA models have a higher accuracy than FEM models as the grain morphology, DRX nuclei, and grain growth are taken into consideration in CA models, which are more similar to the actual DRX process during hot deformation. PMID:29342080

Structure/property (constitutive and dynamic strength/damage) characterization of additively manufactured 316L SS

NASA Astrophysics Data System (ADS)

Gray, G. T., III; Livescu, V.; Rigg, P. A.; Trujillo, C. P.; Cady, C. M.; Chen, S. R.; Carpenter, J. S.; Lienert, T. J.; Fensin, S.

2015-09-01

For additive manufacturing (AM), the certification and qualification paradigm needs to evolve as there exists no "ASTM-type" additive manufacturing certified process or AM-material produced specifications. Accordingly, utilization of AM materials to meet engineering applications requires quantification of the constitutive properties of these evolving materials in comparison to conventionally-manufactured metals and alloys. Cylinders of 316L SS were produced using a LENS MR-7 laser additive manufacturing system from Optomec (Albuquerque, NM) equipped with a 1kW Yb-fiber laser. The microstructure of the AM-316L SS is detailed in both the as-built condition and following heat-treatments designed to obtain full recrystallization. The constitutive behavior as a function of strain rate and temperature is presented and compared to that of nominal annealed wrought 316L SS plate. The dynamic damage evolution and failure response of all three materials was probed using flyer-plate impact driven spallation experiments at a peak stress of 4.5 GPa to examine incipient spallation response. The spall strength of AM-produced 316L SS was found to be very similar for the peak shock stress studied to that of annealed wrought or AM-316L SS following recrystallization. The damage evolution as a function of microstructure was characterized using optical metallography.

Comparisons of Different Models on Dynamic Recrystallization of Plate during Asymmetrical Shear Rolling.

PubMed

Zhang, Tao; Li, Lei; Lu, Shi-Hong; Gong, Hai; Wu, Yun-Xin

2018-01-17

Asymmetrical shear rolling with velocity asymmetry and geometry asymmetry is beneficial to enlarge deformation and refine grain size at the center of the thick plate compared to conventional symmetrical rolling. Dynamic recrystallization (DRX) plays a vital role in grain refinement during hot deformation. Finite element models (FEM) coupled with microstructure evolution models and cellular automata models (CA) are established to study the microstructure evolution of plate during asymmetrical shear rolling. The results show that a larger DRX fraction and a smaller average grain size can be obtained at the lower layer of the plate. The DRX fraction at the lower part increases with the ascending speed ratio, while that at upper part decreases. With the increase of the offset distance, the DRX fraction slightly decreases for the whole thickness of the plate. The differences in the DRX fraction and average grain size between the upper and lower surfaces increase with the ascending speed ratio; however, it varies little with the change of the speed ratio. Experiments are conducted and the CA models have a higher accuracy than FEM models as the grain morphology, DRX nuclei, and grain growth are taken into consideration in CA models, which are more similar to the actual DRX process during hot deformation.

An improved kinetics approach to describe the physical stability of amorphous solid dispersions.

PubMed

Yang, Jiao; Grey, Kristin; Doney, John

2010-01-15

The recrystallization of amorphous solid dispersions may lead to a loss in the dissolution rate, and consequently reduce bioavailability. The purpose of this work is to understand factors governing the recrystallization of amorphous drug-polymer solid dispersions, and develop a kinetics model capable of accurately predicting their physical stability. Recrystallization kinetics was measured using differential scanning calorimetry for initially amorphous efavirenz-polyvinylpyrrolidone solid dispersions stored at controlled temperature and relative humidity. The experimental measurements were fitted by a new kinetic model to estimate the recrystallization rate constant and microscopic geometry of crystal growth. The new kinetics model was used to illustrate the governing factors of amorphous solid dispersions stability. Temperature was found to affect efavirenz recrystallization in an Arrhenius manner, while recrystallization rate constant was shown to increase linearly with relative humidity. Polymer content tremendously inhibited the recrystallization process by increasing the crystallization activation energy and decreasing the equilibrium crystallinity. The new kinetic model was validated by the good agreement between model fits and experiment measurements. A small increase in polyvinylpyrrolidone resulted in substantial stability enhancements of efavirenz amorphous solid dispersion. The new established kinetics model provided more accurate predictions than the Avrami equation.

Pairing Heterocyclic Cations with closo-Icosahedral Borane and Carborane Anions, II: Benchtop Alternative Synthetic Methodologies for Binary Triazolium and Tetrazolium Salts with Significant Water Solubility (POSTPRINT)

DTIC Science & Technology

2012-01-01

interesting property, eutectic melting-point depression. Recrystallization of ternary salts 12–14 was not attempted because of a concern that a cation... recrystallization solvent mixture for these powders, and while some individual successes resulted, a general efficient solvent system for all salt...product recrystallizations could not be found. So, rather than recrystallizing each individual adduct, spectroscopic examination of the amorphous solids was

Ultrasonic determination of recrystallization

NASA Technical Reports Server (NTRS)

Generazio, E. R.

1986-01-01

Ultrasonic attenuation was measured for cold worked Nickel 200 samples annealed at increasing temperatures. Localized dislocation density variations, crystalline order and colume percent of recrystallized phase were determined over the anneal temperature range using transmission electron microscopy, X-ray diffraction, and metallurgy. The exponent of the frequency dependence of the attenuation was found to be a key variable relating ultrasonic attenuation to the thermal kinetics of the recrystallization process. Identification of this key variable allows for the ultrasonic determination of onset, degree, and completion of recrystallization.

Chitinoidellids from the Early Tithonian-Early Valanginian Vaca Muerta Formation in the Northern Neuquén Basin, Argentina

NASA Astrophysics Data System (ADS)

Kietzmann, Diego A.

2017-07-01

As part of microfacies studies carried out on the Tithonian - Valanginian carbonate ramp of the Neuquén Basin, two stratigraphic sections of the Vaca Muerta Formation (Arroyo Loncoche and Río Seco de la Cara Cura) were chosen in order to analyze the chitinoidellid content and distribution. Calpionellids in the studied sections are relatively poorly preserved; hyaline calcite walls are often recrystallized making the systematic determination difficult. However, microgranular calcite walls seem to have resisted better the incipient neomorphism presented by the limestones of the Vaca Muerta Formation. Seven known species of Chitinoidellidae and four known species of Calpionellidae are recognized. The distribution of calpionellid species allows recognizing the Chitinoidella and Crassicollaria Zones in the Neuquén Basin. The Chitinoidella Zone correlates with the Virgatosphinctes mendozanus-Windhauseniceras internispinosum Andean ammonite Zones, and can be divided into two subzones. The lower one is poorly defined, while the upper one can be assigned to the Boneti Subzone. The Crassicollaria Zone in the Neuquén basin needs a detailed revision, but data provided in this work enable its correlation at least with the Corongoceras alternans ammonite Zone. Similar associations were reported in Mexico and Cuba, showing good consistency between these regions. However, in the Neuquén Basin unlike the Tethys, chitinoidellids persist until the lower Berriasian.

Comparison Between Different Processing Schedules for the Development of Ultrafine-Grained Dual-Phase Steel

NASA Astrophysics Data System (ADS)

Karmakar, Anish; Sivaprasad, S.; Nath, S. K.; Misra, R. D. K.; Chakrabarti, Debalay

2014-05-01

A comparative study was carried out on the development of ultrafine-grained dual-phase (DP) (ferrite-martensite) structures in a low-carbon microalloyed steel processed using two thermomechanical processing routes, (i) intercritical deformation and (ii) warm-deformation and intercritical annealing. The samples were deformed using Gleeble3500® simulator, maintaining a constant total strain ( ɛ = 1) and strain rate ( = 1/s). Evolution of microstructure and micro-texture was investigated by SEM, TEM, and EBSD. Ultrafine-grained DP structures could be formed by careful selection of deformation temperature, T def (for intercritical deformation) or annealing temperature, T anneal (for warm-deformation and annealing). Overall, the ferrite grain sizes ranged from 1.5 to 4.0 μm, and the sizes and fractions of the uniformly distributed fine-martensitic islands ranged from 1.5 to 3.0 μm and 15 to 45 pct, respectively. Dynamic strain-induced austenite-to-ferrite transformation followed by continuous (dynamic) recrystallization of the ferrite dictated the grain refinement during intercritical deformation, while, continuous (static) recrystallization by pronounced recovery dictated the grain refinement during the warm-deformation and the annealing. Regarding intercritical deformation, the samples cooled to T def indicated finer grain size compared with the samples heated to T def, which are explained in terms of the effects of strain partitioning on the ferrite and the heating during deformation. Alpha-fiber components dominated the texture in all the samples, and the fraction of high-angle boundaries (with >15 deg misorientation) increased with the increasing T def or T anneal, depending on the processing schedule. Fine carbide particles, microalloyed precipitates and austenitic islands played important roles in defining the mechanism of grain refinement that involved retarding conventional ferrite recrystallization and ferrite grain growth. With regard to the intercritical deformation, warm-deformation followed by annealing is a simpler process to control in the rolling mill; however, the need for high-power rolling mill and controlled annealing facility imposes industrial challenges.

Structural analysis of the Valence basin (SE France) based on kriging and borehole data: implications for hercynian fault zone behaviour in geothermic reservoirs.

NASA Astrophysics Data System (ADS)

Chabani, Arezki; Mehl, Caroline; Bruel, Dominique; Cojan, Isabelle

2017-04-01

The Valence basin is a 130 km-long and 60 km-wide Tertiary sub-basin situated north to the SE basin of France, in the central part of the European Cenozoic RIft System (ECRIS). That structural key position in a naturally fractured hostrock associated with a favorable thermal regime make that basin a good target for geothermal exploitation in France. The structure and kinematics of the Valence basin is controlled by a several kilometer-scale hercynian fault system that may have a strong influence on fluid flows and thermal anomalies within the basin. This study aimed to constrain the geometry of deposits and the way they fracture regards to the major faults, to determine their diagenetic evolution and to characterize the hydraulic behavior of the major faults. We thus performed a structural model of the basin and analyzed the Montoison borehole. Kriging on data pointed on 348 boreholes from BSS, synthetic boreholes calculated from two seismic lines and isohypses from existing models allowed modeling the geometry of basement and the ceno-mesozoic unconformity. Basement is structured by two pluri-kilometer long fault corridors striking N/S to NE/SW. The central extends laterally on around 1 kilometer and has been identified as a segment of the Cevennes fault. The maximum depth of the basement is around 6000 m and is situated between the two corridors. Interpretations on seismic lines highlight a westward migration of Cenozoic depocenters within time. A structural analysis of the Montoison borehole confirms it is affected by a major fault interpreted as the Cevennes fault. Fault zone cuts across the Keuper and is characterized by an heterometric breccia within marly layers. The entire sedimentary pile recorded 2 sets of fractures: perpendicular and parallel to the borehole axis. Both sets are recrystallized. Nature of recrystallization (quartz, calcite and dolomite) strongly depends on the hostrock. An important thread of barite is located under the fault zone, putting forward the potential role of drain of that fault in the fluid flows across the basin.

Characterization of molybdenum particles reinforced Al6082 aluminum matrix composites with improved ductility produced using friction stir processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Selvakumar, S., E-mail: lathaselvam1963@gmail.com

Aluminum matrix composites (AMCs) reinforced with various ceramic particles suffer a loss in ductility. Hard metallic particles can be used as reinforcement to improve ductility. The present investigation focuses on using molybdenum (Mo) as potential reinforcement for Mo(0,6,12 and 18 vol.%)/6082Al AMCs produced using friction stir processing (FSP). Mo particles were successfully retained in the aluminum matrix in its elemental form without any interfacial reaction. A homogenous distribution of Mo particles in the composite was achieved. The distribution was independent upon the region within the stir zone. The grains in the composites were refined considerably due to dynamic recrystallization andmore » pinning effect. The tensile test results showed that Mo particles improved the strength of the composite without compromising on ductility. The fracture surfaces of the composites were characterized with deeply developed dimples confirming appreciable ductility. - Highlights: •Molybdenum particles used as reinforcement for aluminum composites to improve ductility. •Molybdenum particles were retained in elemental form without interfacial reaction. •Homogeneous dispersion of molybdenum particles were observed in the composite. •Molybdenum particles improved tensile strength without major loss in ductility. •Deeply developed dimples on the fracture surfaces confirmed improved ductility.« less

Microstructure and Tensile Properties of Friction Stir Processed Mg–Sn–Zn Alloy

PubMed Central

Chen, Xiaoyang; Dai, Qiao; Li, Xingcheng; Lu, Yalin; Zhang, Yang

2018-01-01

In this study, as-cast Mg–6Sn–2Zn (wt.%) alloy was subjected to friction stir processing (FSP) and the microstructure and tensile properties of FSP Mg–6Sn–2Zn samples were investigated. It was found that, in the stir zone (SZ) of FSP Mg–6Sn–2Zn samples, α-Mg grains were significantly refined via dynamic recrystallization (DRX) and the Mg2Sn phase was broken and partially dissolved. The microstructure in SZ was nonuniform and DRXed grains in the SZ-up regions were coarser than those in the SZ-down regions. Coarse broken Mg2Sn particles were observed in the SZ-up regions, while only fine Mg2Sn particles were observed in the SZ-down regions. Strong {0001} basal texture developed in the SZ regions of Mg–6Sn–2Zn samples after FSP. The increase of travel speed had little effect on the texture of different SZ regions. The ductility of FSP Mg–6Sn–2Zn samples was obviously improved, while the improvement in strength was negligible when compared to the as-cast sample. The tensile properties of FSP Mg–6Sn–2Zn samples were influenced by grain refinement, texture modification, and the breaking up and dissolution of the Mg2Sn phase. PMID:29690590

Microstructure and Tensile Properties of Friction Stir Processed Mg⁻Sn⁻Zn Alloy.

PubMed

Chen, Xiaoyang; Dai, Qiao; Li, Xingcheng; Lu, Yalin; Zhang, Yang

2018-04-23

In this study, as-cast Mg⁻6Sn⁻2Zn (wt.%) alloy was subjected to friction stir processing (FSP) and the microstructure and tensile properties of FSP Mg⁻6Sn⁻2Zn samples were investigated. It was found that, in the stir zone (SZ) of FSP Mg⁻6Sn⁻2Zn samples, α-Mg grains were significantly refined via dynamic recrystallization (DRX) and the Mg₂Sn phase was broken and partially dissolved. The microstructure in SZ was nonuniform and DRXed grains in the SZ-up regions were coarser than those in the SZ-down regions. Coarse broken Mg₂Sn particles were observed in the SZ-up regions, while only fine Mg₂Sn particles were observed in the SZ-down regions. Strong {0001} basal texture developed in the SZ regions of Mg⁻6Sn⁻2Zn samples after FSP. The increase of travel speed had little effect on the texture of different SZ regions. The ductility of FSP Mg⁻6Sn⁻2Zn samples was obviously improved, while the improvement in strength was negligible when compared to the as-cast sample. The tensile properties of FSP Mg⁻6Sn⁻2Zn samples were influenced by grain refinement, texture modification, and the breaking up and dissolution of the Mg₂Sn phase.

Dextral strike-slip along the Kapıdağ shear zone (NW Turkey): evidence for Eocene westward translation of the Anatolian plate

NASA Astrophysics Data System (ADS)

Türkoğlu, Ercan; Zulauf, Gernold; Linckens, Jolien; Ustaömer, Timur

2016-10-01

The northern part of the Kapıdağ Peninsula (Marmara Sea, NW Turkey) is affected by the E-W trending Kapıdağ shear zone, which cuts through calc-alkaline granitoids of the Ocaklar pluton resulting in mylonitic orthogneiss. Macroscopic and microscopic shear-sense indicators, such as SC fabrics, shear bands, σ-clasts and mica fish, unequivocally suggest dextral strike-slip for the Kapıdağ shear zone. Based on petrographic data, deformation microfabrics of quartz and feldspar, and the slip systems in quartz, the dextral shearing should have been active at T = 500-300 °C and P < 5 kbar. Published K-Ar and 39Ar-40Ar cooling ages of hornblende and biotite suggest that cooling below 500-300 °C occurred during the Eocene (ca. 45-ca. 35 Ma), meaning that the Kapıdağ shear zone should have been active during Middle to Late Eocene times. The differential stress related to the shearing was <50 MPa as is indicated by the size of recrystallized quartz grains. Based on the new and published data, it is concluded that the westward movement of the Anatolian plate might have been active almost continuously from the Middle Eocene until recent times.

The effect of fluids on the frictional behavior of calcite gouge

NASA Astrophysics Data System (ADS)

Rempe, M.; Di Toro, G.; Mitchell, T. M.; Hirose, T.; Smith, S. A. F.; Renner, J.

2016-12-01

The presence of fluids in fault zones affects the faults' strength and the nucleation and propagation of earthquakes due to mechanical or physico-chemical weakening effects. To better understand the effect of pore fluids on the frictional behavior of gouge-bearing faults, a series of intermediate- to high-velocity experiments was conducted using the Phv rotary-shear apparatus (Kochi Core Center, Japan) equipped with a servo-controlled pore-fluid pressure system. Calcite gouge was sheared up to several meters displacement at room-humidity (dry) and water-saturated conditions. The pore-fluid factor, λ=pf/σn, ranged from 0.15 to 0.7 and the effective normal stress, σn,eff=σn-pf, from 1 to 12 MPa. Sheared samples were analyzed using scanning electron microscopy and Raman spectroscopy. The steady-state shear stress is lower for saturated than for dry gouges sliding at V=1 mm/s, possibly due to higher intergranular lubrication and/or accelerated subcritical crack growth, as evidenced also by the observed higher degree of compaction. At V=1 m/s, dry gouges show a pronounced strengthening phase preceding the onset of dynamic weakening; saturated gouges weaken abruptly. The higher λ, the lower the peak and steady-state shear stress, but -counterintuitively- the less localized deformation. Degree of weakening and localization might be influenced by insufficient drainage at high λ. In undrained experiments, the shear stress is slightly decreased likely due to thermal pressurization of the pore fluid, but the onset of dynamic weakening is not accelerated, indicating that dynamic weakening is due to more efficient mechanisms. For example, amorphous carbon may lubricate the slip surfaces of dry and saturated calcite gouges and cause dynamic weakening, yet Raman spectra only show the presence of disordered carbon on the principal slip surface. Furthermore, the presence of small recrystallized grains suggests that strain accommodation during steady-state slip might occur by non-frictional processes, such as grain-boundary sliding aided by diffusion creep.

Deformation-Induced Recrystallization of Magnesium Single Crystals at Ambient Temperature

NASA Astrophysics Data System (ADS)

Molodov, K. D.; Al-Samman, T.; Molodov, D. A.

2015-04-01

Specially oriented magnesium single crystals were subjected to plane strain compression along the <112¯0> direction in c-axis extension at ambient temperature. The samples exhibited outstanding formability deforming up to a logarithmic final strain of -1. Investigations by optical and orientation imaging microscopy revealed that massive {101¯2} extension twinning at low strains consumed the whole sample and resulted in new soft orientations for slip. Observations also indicated that additional twinning took place in the completely twinned matrix by secondary and tertiary twinning events. At advanced stages of deformation newly formed, equiaxed small grains were observed within numerous bands related to former deformation twins. These “recrystallized” grains characterized by a low grain orientation spread of less than 1° generated new orientations, which led to a substantial weakening and randomization of the texture during deformation up to very large strains. The reported results in this paper are discussed with regard to the microstructure evolution arising from multiple twinning and continuous dynamic recrystallization at room temperature.

Microstructure Characterization of Weakly Textured and Fine Grained AZ61 Sheet

NASA Astrophysics Data System (ADS)

Berman, T. D.; Donlon, W.; Hung, C. K.; Milligan, P.; Decker, R.; Pollock, T. M.; Jones, J. W.

Formability in magnesium alloy sheet is strongly limited by a strong basal texture in the as-rolled material, which is difficulty to remove by thermal processing. We introduce a new process to the control of texture by combining Thixomolding and Thermomechanical Processing (TTMP). Plates of AZ61L with a divorced β-Mg17Al12 eutectic are produced by Thixomolding, resulting in a non-textured, fine grained (2.8 µm) precursor. Sheet produced from the plate by single pass warm-rolling exhibits a weaker texture, and more isotropic tensile deformation than generally observed in AZ-series alloy sheet. Recrystallization annealing produces a further reduction in texture and average grain size (2.3 µm) and results in nearly isotropic room temperature deformation, a yield strength of 220 MPa, and an elongation of 23%. Particle stimulated nucleation of new grains by the β-phase during both dynamic and static recrystallization, is critical for achieving the low levels of texture. The influence of β-phase distribution in microstructure development is discussed.

Pn anisotropy beneath the South Island of New Zealand and implications for distributed deformation in continental lithosphere

NASA Astrophysics Data System (ADS)

Collins, John A.; Molnar, Peter

2014-10-01

Pn travel times from regional earthquakes recorded both by stations on New Zealand and by ocean bottom seismographs deployed offshore indicate anisotropy in the uppermost mantle beneath the region. The largest anisotropy of ~8% (±2%, 1σ) lies beneath the deforming part of the South Island to just off its West Coast, a zone roughly 100-200 km wide. The fastest propagation is aligned N60°E (±3°), essentially parallel to the largely strike-slip relative plate motion since 20 Ma, also ~ N60°E. The magnitude of anisotropy decreases abruptly northwest and southeast of this zone, and on the southeast side of the island, the orientation of fastest propagation is between N32°W and N-S. The ~ N60°E orientation of fast propagation is consistent with finite strain within the uppermost part of the mantle lithosphere if the measured 850 km of displacement of the Pacific plate past the Australia plate is spread over a region with a width of 100-200 km. The agreement of this orientation of fast propagation with the orientation or relative plate motion suggests the possibility of but does not require some dynamic recrystallization in rock as cold as 500-800°C, where Peierls creep seems to be the likely deformation mechanism. Such a strain distribution matches deformation of a thin viscous sheet that obeys a constitutive relationship of the form ɛ>˙ ~ τn, where ɛ>˙ is the average strain rate and τ is the operative deviatoric stress, with an average value of n ≈ 3-10. Presumably, the NW-SE fast propagation in the region southeast of the island results from strain that precedes the Cenozoic deformation that has shaped the island.

Matrix recrystallization for MALDI-MS imaging of maize lipids at high-spatial resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duenas, Maria Emilia; Carlucci, Laura; Lee, Young Jin

Matrix recrystallization is optimized and applied to improve lipid ion signals in maize embryos and leaves. A systematic study was performed varying solvent and incubation time. During this study, unexpected side reactions were found when methanol was used as a recrystallization solvent, resulting in the formation of a methyl ester of phosphatidic acid. Furthermore, using an optimum recrystallization condition with isopropanol, there is no apparent delocalization demonstrated with a transmission electron microscopy (TEM) pattern and maize leaf images obtained at 10 μm spatial resolution.

Matrix recrystallization for MALDI-MS imaging of maize lipids at high-spatial resolution

DOE PAGES

Duenas, Maria Emilia; Carlucci, Laura; Lee, Young Jin

2016-06-27

Matrix recrystallization is optimized and applied to improve lipid ion signals in maize embryos and leaves. A systematic study was performed varying solvent and incubation time. During this study, unexpected side reactions were found when methanol was used as a recrystallization solvent, resulting in the formation of a methyl ester of phosphatidic acid. Furthermore, using an optimum recrystallization condition with isopropanol, there is no apparent delocalization demonstrated with a transmission electron microscopy (TEM) pattern and maize leaf images obtained at 10 μm spatial resolution.

Matrix Recrystallization for MALDI-MS Imaging of Maize Lipids at High-Spatial Resolution

NASA Astrophysics Data System (ADS)

Dueñas, Maria Emilia; Carlucci, Laura; Lee, Young Jin

2016-09-01

Matrix recrystallization is optimized and applied to improve lipid ion signals in maize embryos and leaves. A systematic study was performed varying solvent and incubation time. During this study, unexpected side reactions were found when methanol was used as a recrystallization solvent, resulting in the formation of a methyl ester of phosphatidic acid. Using an optimum recrystallization condition with isopropanol, there is no apparent delocalization demonstrated with a transmission electron microscopy (TEM) pattern and maize leaf images obtained at 10 μm spatial resolution.

Correlation buildup during recrystallization in three-dimensional dusty plasma clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schella, André; Mulsow, Matthias; Melzer, André

2014-05-15

The recrystallization process of finite three-dimensional dust clouds after laser heating is studied experimentally. The time-dependent Coulomb coupling parameter is presented, showing that the recrystallization starts with an exponential cooling phase where cooling is slower than damping by the neutral gas friction. At later times, the coupling parameter oscillates into equilibrium. It is found that a large fraction of cluster states after recrystallization experiments is in metastable states. The temporal evolution of the correlation buildup shows that correlation occurs on even slower time scale than cooling.

Matrix Recrystallization for MALDI-MS Imaging of Maize Lipids at High-Spatial Resolution.

PubMed

Dueñas, Maria Emilia; Carlucci, Laura; Lee, Young Jin

2016-09-01

Matrix recrystallization is optimized and applied to improve lipid ion signals in maize embryos and leaves. A systematic study was performed varying solvent and incubation time. During this study, unexpected side reactions were found when methanol was used as a recrystallization solvent, resulting in the formation of a methyl ester of phosphatidic acid. Using an optimum recrystallization condition with isopropanol, there is no apparent delocalization demonstrated with a transmission electron microscopy (TEM) pattern and maize leaf images obtained at 10 μm spatial resolution. Graphical Abstract ᅟ.

Ultrasonic attenuation measurements determine onset, degree, and completion of recrystallization

NASA Technical Reports Server (NTRS)

Generazio, E. R.

1988-01-01

Ultrasonic attenuation was measured for cold worked Nickel 200 samples annealed at increasing temperatures. Localized dislocation density variations, crystalline order and volume percent of recrystallized phase were determined over the anneal temperature range using transmission electron microscopy, X-ray diffraction, and metallurgy. The exponent of the frequency dependence of the attenuation was found to be a key variable relating ultrasonic attenuation to the thermal kinetics of the recrystallization process. Identification of this key variable allows for the ultrasonic determination of onset, degree, and completion of recrystallization.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y. B.; Budai, J. D.; Tischler, J. Z.

How boundaries surrounding recrystallization grains migrate through the 3D network of dislocation boundaries in deformed crystalline materials is unknown and critical for the resulting recrystallized crystalline materials. Furthermore, by using X-ray Laue diffraction microscopy, we show for the first time the migration pattern of a typical recrystallization boundary through a well-characterized deformation matrix. The data provide a unique possibility to investigate effects of both boundary misorientation and plane normal on the migration, information which cannot be accessed with any other techniques. Our results show that neither of these two parameters can explain the observed migration behavior. Instead we suggest thatmore » the subdivision of the deformed microstructure ahead of the boundary plays the dominant role. Our experimental observations challenge the assumptions of existing recrystallization theories, and set the stage for determination of mobilities of recrystallization boundaries.« less

Grain Boundary Evolution of Cold-Rolled FePd Alloy during Recrystallization at Disordering Temperature

PubMed Central

Lin, Hung-Pin; Chen, Delphic; Kuo, Jui-Chao

2015-01-01

In this study, the grain boundary character and texture of 50% and 90% cold-rolled FePd alloy was investigated during recrystallization at 700 °C. Electron backscatter diffraction (EBSD) measurements were performed on the rolling direction to normal direction section. Kernel average misorientation (KAM) calculated from EBSD measurements was employed to determine the recrystallization fraction. The Avrami exponent n of recrystallization is 1.9 and 4.9 for 50% and 90% cold rolling, respectively. The new formation of texture reveals random texture during the recrystallization process. As annealing time increased, the number of high angle boundary (HAGB) and coincidence site lattice (CSL) increased with consumption of low angle boundary (LAGB). In addition, possible transformations between different grain boundaries are observed here.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Kun; Bannister, Mark E.; Meyer, Fred W.

Here, in a magnetic fusion energy (MFE) device, the plasma-facing materials (PFMs) will be subjected to tremendous fluxes of ions, heat, and neutrons. The response of PFMs to the fusion environment is still not well defined. Tungsten metal is the present candidate of choice for PFM applications such as the divertor in ITER. However, tungsten's microstructure will evolve in service, possibly to include recrystallization. How tungsten's response to plasma exposure evolves with changes in microstructure is presently unknown. In this work, we have exposed hot-worked and recrystallized tungsten to an 80 eV helium ion beam at a temperature of 900more » °C to fluences of 2 × 10 23 or 20 × 10 23 He/m 2. This resulted in a faceted surface structure at the lower fluence or short but well-developed nanofuzz structure at the higher fluence. There was little difference in the hot-rolled or recrystallized material's near-surface (≤50 nm) bubbles at either fluence. At higher fluence and deeper depth, the bubble populations of the hot-rolled and recrystallized were different, the recrystallized being larger and deeper. This may explain previous high-fluence results showing pronounced differences in recrystallized material. The deeper penetration in recrystallized material also implies that grain boundaries are traps, rather than high-diffusivity paths.« less

High temperature microstructural stability and recrystallization mechanisms in 14YWT alloys

DOE PAGES

Aydogan, E.; El-Atwani, O.; Takajo, S.; ...

2018-02-09

In-situ neutron diffraction experiments were performed on room temperature compressed 14YWT nanostructured ferritic alloys at 1100°C and 1150°C to understand their thermally activated static recrystallization mechanisms. The existence of high density of Y-Ti-O rich nano-oxides (<5 nm) shift the recrystallization temperature up due to Zener pinning of the grain boundaries, making these materials attractive for high temperature applications. This study serves to quantify the texture evolution in-situ and understand the effect of particles on the recrystallization mechanisms in 14YWT alloys. We have shown, both experimentally and theoretically, that there is considerable recovery in the 20% compressed sample after 6.5 hmore » annealing at 1100°C while recrystallization occurs within an hour of annealing at 1100°C and 1150°C in the 60% compressed samples. Moreover, the 60% compressed samples show {112}<110> and {112}<111> texture components during annealing, in contrast to the conventional recrystallization textures in body centered cubic alloys. Furthermore, nano-oxide size, shape, density and distribution are considerably different in unrecrystallized and abnormally grown grains. Transmission electron microscopy analysis shows that oxide particles having a size between 5 and 30 nm play a critical role for recrystallization mechanisms in 14YWT nanostructured ferritic alloys.« less

High temperature microstructural stability and recrystallization mechanisms in 14YWT alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aydogan, E.; El-Atwani, O.; Takajo, S.

In-situ neutron diffraction experiments were performed on room temperature compressed 14YWT nanostructured ferritic alloys at 1100°C and 1150°C to understand their thermally activated static recrystallization mechanisms. The existence of high density of Y-Ti-O rich nano-oxides (<5 nm) shift the recrystallization temperature up due to Zener pinning of the grain boundaries, making these materials attractive for high temperature applications. This study serves to quantify the texture evolution in-situ and understand the effect of particles on the recrystallization mechanisms in 14YWT alloys. We have shown, both experimentally and theoretically, that there is considerable recovery in the 20% compressed sample after 6.5 hmore » annealing at 1100°C while recrystallization occurs within an hour of annealing at 1100°C and 1150°C in the 60% compressed samples. Moreover, the 60% compressed samples show {112}<110> and {112}<111> texture components during annealing, in contrast to the conventional recrystallization textures in body centered cubic alloys. Furthermore, nano-oxide size, shape, density and distribution are considerably different in unrecrystallized and abnormally grown grains. Transmission electron microscopy analysis shows that oxide particles having a size between 5 and 30 nm play a critical role for recrystallization mechanisms in 14YWT nanostructured ferritic alloys.« less

Recrystallization and grain growth behavior of rolled tungsten under VDE-like short pulse high heat flux loads

NASA Astrophysics Data System (ADS)

Yuan, Y.; Greuner, H.; Böswirth, B.; Krieger, K.; Luo, G.-N.; Xu, H. Y.; Fu, B. Q.; Li, M.; Liu, W.

2013-02-01

Short pulse heat loads expected for vertical displacement events (VDEs) in ITER were applied in the high heat flux (HHF) test facility GLADIS at IPP-Garching onto samples of rolled W. Pulsed neutral beams with the central heat flux of 23 MW/m2 were applied for 0.5, 1.0 and 1.5 s, respectively. Rapid recrystallization of the adiabatically loaded 3 mm thick samples was observed when the pulse duration was up to 1.0 s. Grains grew markedly following recrystallization with increasing pulse length. The recrystallization temperature and temperature dependence of the recrystallized grain size were also investigated. The results showed that the recrystallization temperature of the W grade was around 2480 °C under the applied heat loading condition, which was nearly 1150 °C higher than the conventional recrystallization temperature, and the grains were much finer. A linear relationship between the logarithm of average grain size (ln d) and the inverse of maximum surface temperature (1/Tmax) was found and accordingly the activation energy for grain growth in temperature evolution up to Tmax in 1.5 s of the short pulse HHF load was deduced to be 4.1 eV. This provided an effective clue to predict the structure evolution under short pulse HHF loads.

Low grade metamorphism fluid circulation in a sedimentary environment thrust fault zone: properties and modeling

NASA Astrophysics Data System (ADS)

Trincal, Vincent; Lacroix, Brice; Buatier, Martine D.; Charpentier, Delphine; Labaume, Pierre; Lahfid, Abdeltif

2014-05-01

In fold-and-thrust belts, shortening is mainly accommodated by thrust faults that can constitute preferential pathways for fluid circulation. The present study focuses on the Pic de Port Vieux thrust, a second-order thrust related to major Gavarnie thrust in the Axial Zone of the Pyrenees. The fault juxtaposes lower Triassic red siltstones and sandstones in the hanging-wall and Upper Cretaceous limestone in the footwall. A dense network of synkinematic quartz-chlorite veins is present in outcrop and allows to unravel the nature of the fluid that circulated in the fault zone. The hanging wall part of fault zone comprises a core which consists of intensely foliated phyllonite; the green color of this shear zone is related to the presence of abundant newly-formed chlorite. Above, the damage zone consists of red pelites and sandstones. Both domains feature kinematic markers like S-C type shear structures associated with shear and extension quartz-chlorite veins and indicate a top to the south displacement. In the footwall, the limestone display increasing mylonitization and marmorization when getting close to the contact. In order to investigate the mineralogical and geochemical changes induced by deformation and subsequent fluid flow, sampling was conducted along a complete transect of the fault zone, from the footwall limestone to the red pelites of the hanging wall. In the footwall limestone, stable isotope and Raman spectroscopy analyzes were performed. The strain gradient is strongly correlated with a high decrease in δ18OV PDB values (from -5.5 to -14) when approaching the thrust (i.e. passing from limestone to marble) while the deformation temperatures estimated with Raman spectroscopy on carbon remain constant around 300° C. These results suggest that deformation is associated to a dynamic calcite recrystallization of carbonate in a fluid-open system. In the hanging wall, SEM observations, bulk chemical XRF analyses and mineral quantification from XRD analyses were conducted in order to compare the green phyllonites from the fault core zone with the red pelites from the damage zone. Quartz, muscovite 2M1, chlorite (clinochlore), calcite and rutile are present in all samples. Hematite occurs in the damage zone but is absent in the core zone. Synkinematic chlorites are abundant in the core and damage zones and are mainly located in veins, sometimes in association with quartz. The temperature of formation of these newly-formed chlorites is 300-350° C according to Inoue (2009) geothermometer. Mössbauer spectroscopic analyses were performed on bulk rock samples. In the damage zone, Fe3+/Fetotal vary between 0.7 and 0.8, whereas in the core zone Fe3+/Fetotal is about 0.35. This decrease in Fe3+ from the damage zone to the core zone can be related to the dissolution of hematite. In contrast, Fe3+/Fetotal in phyllosilicates is clearly related to the chlorite content relative to mica, as Fe2+ increases with chlorite content. All these data allow us to propose a model of fluid circulation in relation with the Pic de Port Vieux thrust activity. The origin of the fluid, its interactions with host-rock and the consequences on fault zone mineralizations will be discussed. Inoue, A., Meunier, A., Patrier-Mas, P., Rigault, C., Beaufort, D., Vieillard, P., 2009. Application of chemical geothermometry to low-temperature trioctahedral chlorites. Clay Clay Min. 57, 371-382.

Automatic twin vessel recrystallizer. Effective purification of acetaminophen by successive automatic recrystallization and absolute determination of purity by DSC.

PubMed

Nara, Osamu

2011-01-24

I describe an interchangeable twin vessel (J, N) automatic glass recrystallizer that eliminates the time-consuming recovery and recycling of crystals for repeated recrystallization. The sample goes in the dissolution vessel J containing a magnetic stir-bar K; J is clamped to the upper joint H of recrystallizer body D. Empty crystallization vessel N is clamped to the lower joint M. Pure solvent is delivered to the dissolution vessel and the crystallization vessel via the head of the condenser A. Crystallization vessel is heated (P). The dissolution reservoir is stirred and heated by the solvent vapor (F). Continuous outflow of filtrate E out of J keeps N at a stable boiling temperature. This results in efficient dissolution, evaporation and separation of pure crystals Q. Pure solvent in the dissolution reservoir is recovered by suction. Empty dissolution and crystallization vessels are detached. Stirrer magnet is transferred to the crystallization vessel and the role of the vessels are then reversed. Evacuating mother liquor out of the upper twin vessel, the apparatus unit is ready for the next automatic recrystallization by refilling twin vessels with pure solvent. We show successive automatic recrystallization of acetaminophen from diethyl ether obtaining acetaminophen of higher melting temperatures than USP and JP reference standards by 8× automatic recrystallization, 96% yield at each stage. Also, I demonstrate a novel approach to the determination of absolute purity by combining the successive automatic recrystallization with differential scanning calorimetry (DSC) measurement requiring no reference standards. This involves the measurement of the criterial melting temperature T(0) corresponding to the 100% pure material and quantitative ΔT in DSC based on the van't Hoff law of melting point depression. The purity of six commercial acetaminophen samples and reference standards and an eight times recrystallized product evaluated were 98.8 mol%, 97.9 mol%, 99.1 mol%, 98.3 mol%, 98.4 mol%, 98.5 mol% and 99.3 mol% respectively. Copyright © 2010 Elsevier B.V. All rights reserved.

Evolution of Navajo eclogites and hydration of the mantle wedge below the Colorado Plateau, southwestern United States

NASA Astrophysics Data System (ADS)

Smith, Douglas; Connelly, James N.; Manser, Kathryn; Moser, Desmond E.; Housh, Todd B.; McDowell, Fred W.; Mack, Lawrence E.

2004-04-01

Eclogite and pyroxenite xenoliths from ultramafic diatremes of the Navajo province on the Colorado Plateau have been analyzed to investigate hydration of continental mantle and effects of low-angle subduction on the mantle wedge. Xenoliths have been characterized by petrographic and electron probe analysis and by Sm-Nd, Rb-Sr, K-Ar, and O isotopic analysis of mineral separates from one eclogite and by U-Pb isotopic analysis of zircons from three samples. K-Ar analysis of phengite establishes eruption of a Garnet Ridge, Arizona, diatreme at 30 Ma. Sm-Nd and Rb-Sr analyses of clinopyroxene and garnet from that eclogite document recrystallization shortly preceding eruption. Three zircon fractions have been analyzed from that eclogite and from two others representing the nearby Moses Rock and Mule Ear diatremes. Seven of nine small multigrain fractions scatter about a poorly fit discordia between ca. 35 Ma and 1515 Ma (fractions range from overlapping concordia at the lower intercept to a 207Pb/206Pb age of ca. 1220 Ma). The discordant fractions establish a mid-Proterozoic zircon component in each eclogite, inconsistent with an origin from basalt of the Farallon plate. The pressure recorded by one of these eclogites (3.3 GPa) exceeds that of an eclogite previously attributed to the Farallon plate. Nonetheless, each of the eclogites contains a fraction of nearly concordant zircons with ages in the range 35 to 41 Ma, and one rock also contains a fraction that is nearly concordant at 70 Ma. These concordant ages are interpreted to record episodic zircon growth during recrystallization of Proterozoic mantle. The concordant zircon ages are consistent with published data that establish recrystallization of Navajo eclogites from 81 to 33 Ma, a time interval similar to that of the Laramide orogeny. The eclogite-facies recrystallization and growth of new zircon are attributed to the catalytic effects of water introduced into the mantle from the Farallon slab. Water penetrated fracture zones extending for at least tens of kilometers into the mantle wedge above the Farallon slab during low-angle subduction. Magmatism in the San Juan volcanic field to the northeast of the diatremes may be related to similar hydration.

Reconstructing Volatile Evolution at Lastarria Volcano (CVZ, Northern Chile) Using Melt Inclusions Analysis

NASA Astrophysics Data System (ADS)

Pizarro, M.; Cannatelli, C.; Morata, D.

2017-12-01

Melt inclusions Assemblages (MIAs) are considered the best tool available to provide insights into the pre-eruptive volatile contents in the magma and define the pattern of degassing at depth. Lastarria volcano is located in northern Chile, in the Central Volcanic Zone (CVZ). Lastarria's fumarolic activity is currently the most important source of gases of the CVZ and the volcano also exhibits constant deformation. The study of volatile contents in MIAs, allows us to determine the magmatic processes beneath Lastarria volcano, and there for, understand the current status of the volcanic system (deformation and fumarolic activity). We determined the pre-eruptive volatile content (H2O, CO2, F, S, Cl) in the magma by analyzing MIs hosted in feldspars and pyroxenes from 7 samples of lava and pyroclastic rocks, belonging to different eruptive periods of the volcano. All the samples are andesitic in composition. Lava samples contain phenocrysts of plagioclase and pyroxene (up to 45%) and a vitreous groundmass with microlites of plagioclase, pyroxenes, opaque minerals, and limited biotites. Pyroclastic samples contain phenocrysts of plagioclase and pyroxene (up to 30%), and a vitreous matrix with microlites of plagioclase and pyroxene. At least 3 MIAs have been described in feldspars from the lava samples: MIA1, completely homogenized, MIA2 composed of homogeneous glass and one bubble, and MIA3 composed of homogeneous glass and multiple bubbles. All MIAs display sizes between 3 and 200 um. In the pyroxenes, we have observed a wide range of MIAs, showing different sizes and various degrees of recrystallization, from completely homogenized to totally recrystallized. The petrographic study in the feldespars from the pyroclastic rocks shows two types of MIAs: MIA1, containing homogeneous glass associated with a single bubble, and MIA2, showing homogeneous glass with multiple bubbles. Few MIs appear to be slightly recrystallized. The size of this MIAs varies between 3 and 150 um. Pyroxene-hosted MIs are almost all recrystallized, with sizes varying between 3 and 60 um. Preliminary observations show that MIAs hosted in pyroclastic rocks contain a greater amount of bubbles than MIAs hosted in the lava, possibly indicating that a greater degree of volatile saturation can be linked with the explosive phase of Lastarria volcano.

The risk of recrystallization: changes to the toxicity and morphology of pyrimethamine.

PubMed

Perold, Zak; Caira, Mino R; Brits, Marius

2014-01-01

Pyrimethamine, an anti-malarial agent known to exhibit solid state polymorphism, may be purified by means of recrystallization. Recrystallization may alter the solid state chemistry of pharmaceuticals, which may impact the toxicity and/or manufacturability thereof. We evaluated the risks associated with the recrystallization of pyrimethamine. Pyrimethamine was recrystallized using several organic solvents. X-ray diffraction, thermal analysis, infra-red spectroscopy, microscopy, flowability -, solubility and dissolution testing as well as computational work were employed to evaluate the recrystallized products. A toxic solvatomorph of pyrimethamine (Pyr-MeOH) was found to be the product from methanol recrystallization. The elucidation of - and the elaboration on the unique characteristics of Pyr-MeOH provides the pharmaceutical industry with several means to identify Pyr-MeOH and to distinguish it from the pharmaceutically preferred anhydrous form (Pyr). Thermal methods of analysis found that the toxicity of Pyr-MeOH may be reversed by overcoming a desolvation activation energy of 148 kJ/mol. In addition it was found that recrystallization altered the morphology of Pyr. Angle of repose and tapped density determinations identified that the different morphologies of Pyr displayed differences in powder flow and compressibility behaviour and In Silico calculations were successful in rendering morphologies resembling that found experimentally. We present a solvatomorph of pyrimethamine and provide several characteristic means to identify this unwanted toxic form and quantified the energy required to overcome its toxicity. In addition we describe that Pyr may present in different morphologies and show how it may impact the manufacturability thereof.

Analysis of Particle-Stimulated Nucleation (PSN)-Dominated Recrystallization for Hot-Rolled 7050 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Adam, Khaled F.; Long, Zhengdong; Field, David P.

2017-04-01

In 7xxx series aluminum alloys, the constituent large and small second-phase particles present during deformation process. The fraction and spatial distribution of these second-phase particles significantly influence the recrystallized structure, kinetics, and texture in the subsequent treatment. In the present work, the Monte Carlo Potts model was used to model particle-stimulated nucleation (PSN)-dominated recrystallization and grain growth in high-strength aluminum alloy 7050. The driving force for recrystallization is deformation-induced stored energy, which is also strongly affected by the coarse particle distribution. The actual microstructure and particle distribution of hot-rolled plate were used as an initial point for modeling of recrystallization during the subsequent solution heat treatment. Measurements from bright-field TEM images were performed to enhance qualitative interpretations of the developed microstructure. The influence of texture inhomogeneity has been demonstrated from a theoretical point of view using pole figures. Additionally, in situ annealing measurements in SEM were performed to track the orientational and microstructural changes and to provide experimental support for the recrystallization mechanism of PSN in AA7050.

Facile synthesis of hollow zeolite microspheres through dissolution–recrystallization procedure in the presence of organosilanes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Haixiang; Ren, Jiawen; Liu, Xiaohui

2013-04-15

Hollow zeolite microspheres have been hydrothermally synthesized in the presence of organosilanes via a dissolution–recrystallization procedure. In the presence of organosilanes, zeolite particles with a core/shell structure formed at the first stage of hydrothermal treatment, then the core was consumed and recrystallized into zeolite framework to form the hollow structure during the second hydrothermal process. The influence of organosilanes was discussed, and a related dissolution–recrystallization mechanism was proposed. In addition, the hollow zeolite microspheres exhibited an obvious advantage in catalytic reactions compared to conventional ZSM-5 catalysts, such as in the alkylation of toluene with benzyl chloride. - Graphical abstract: Hollowmore » zeolite spheres with aggregated zeolite nanocrystals were synthesized via a dissolution–recrystallization procedure in the presence of organosiline. Highlights: ► Hollow zeolite spheres with aggregated zeolite nanocrystals were synthesized via a dissolution–recrystallization procedure. ► Organosilane influences both the morphology and hollow structure of zeolite spheres. ► Hollow zeolite spheres showed an excellent catalytic performance in alkylation of toluene with benzyl chloride.« less

Effect of Prestraining of Recrystallization Temperature and Mechanical Properties of Commercial, Sintered, Wrought Molybdenum

NASA Technical Reports Server (NTRS)

Dike, Kenneth C; Long, Roger A

1953-01-01

Given three presumably identical lots of commercial, sintered, wrought molybdenum, the 1-hour recrystallization temperature of one lot remained above 2900 F by limiting the amount of effective restraining to 35 percent or less. Different recrystallization temperatures were obtained in various atmospheres, the highest in argon and the lowest in hydrogen. Metal thus fabricated and then stress-relieved possessed an ultimate tensile strength at room temperature within 10 percent of metal swaged 99 percent and also possessed equivalent ductility. At 1800 F, equivalent strength and ductility was obtained irrespective of the amount of swaging over the range of 10 to 99 percent. The amount of swaging greatly influenced the recrystallized grain size but the difference in grain size is not the major controlling factor which determines whether recrystallized molybdenum is ductile or brittle at room temperature.

Optimum rolling ratio for obtaining {001}<110> recrystallization texture in Ti-Nb-Al biomedical shape memory alloy.

PubMed

Inamura, T; Shimizu, R; Kim, H Y; Miyazaki, S; Hosoda, H

2016-04-01

The rolling rate (r) dependence of textures was investigated in the Ti-26Nb-3Al (mol%) alloy to reveal the conditions required to form the {001}<110> recrystallization texture, which is a desirable orientation for the β-titanium shape memory alloy. {001}<110> was the dominant cold-rolling texture when r=90% and it was transferred to the recrystallization texture without forming {112}<110>, which is detrimental for the isotropic mechanical properties of the rolled sheet. A further increase in r resulted in the formation of {112}<110> in both rolling and recrystallization textures. Therefore, r should be controlled to form only the {001}<110> rolling texture, because the {112}<110> texture can overwhelm the {001}<110> texture during recrystallization. Copyright © 2016 Elsevier B.V. All rights reserved.

Low-Temperature Thermochronology for Unraveling Thermal Processes and Dating of Fault Zones

NASA Astrophysics Data System (ADS)

Tagami, T.

2016-12-01

Thermal signatures as well as timing of fault motions can be constrained by thermochronological analyses of fault-zone rocks (e.g., Tagami, 2012). Fault-zone materials suitable for such analyses are produced by tectocic and geochemical processes, such as (1) mechanical fragmentation of host rocks, grain-size reduction of fragments and recrystallization of grains to form mica and clay minerals, (2) secondary heating/melting of host rocks by frictional fault motions, and (3) mineral vein formation as a consequence of fluid advection associated with fault motions. The geothermal structure of fault zones are primarily controlled by the following three factors: (a) regional geothermal structure around the fault zone that reflect background thermo-tectonic history of studied province, (b) frictional heating of wall rocks by fault motions and resultant heat transfer into surrounding rocks, and (c) thermal influences by hot fluid advection in and around the fault zone. Thermochronological methods widely applied in fault zones are K-Ar (40Ar/39Ar), fission-track (FT), and U-Th methods. In addition, OSL, TL, ESR and (U-Th)/He methods are applied in some fault zones, in order to extract temporal imformation related to low temperature and/or very recent fault activities. Here I briefly review the thermal sensitivity of individual thermochronological systems, which basically controls the response of each method against faulting processes. Then, the thermal sensitivity of FTs is highlighted, with a particular focus on the thermal processes characteristic to fault zones, i.e., flash and hydrothermal heating. On these basis, representative examples as well as key issues, including sampling strategy, are presented to make thermochronologic analysis of fault-zone materials, such as fault gouges, pseudotachylytes and mylonites, along with geological, geomorphological and seismological implications. Finally, the thermochronologic analyses of the Nojima fault are overviewed, as an example of multidisciplinary investigations of an active seismogenic fault system. References: T. Tagami, 2012. Thermochronological investigation of fault zones. Tectonophys., 538-540, 67-85, doi:10.1016/j.tecto.2012.01.032.

Willy: A prize noble Ur-Fremdling - Its history and implications for the formation of Fremdlinge and CAI

NASA Technical Reports Server (NTRS)

Armstrong, J. T.; El Goresy, A.; Wasserburg, G. J.

1985-01-01

The structure and composition of Willy, a 150-micron-diameter Fremdling in CAI 5241 from the Allende meteorite, are investigated using optical, secondary-electron, and electron-backscatter microscopy and electron-microprobe analysis. The results are presented in diagrams, maps, tables, graphs, and micrographs and compared with those for other Allende Fremdlinge. Willy is found to have a concentric-zone structure comprising a complex porous core of magnetite, metal, sulfide, scheelite, and other minor phases; a compact magnetite-apatite mantle; a thin (20 microns or less) reaction-assemblage zone; and a dense outer rim of fassaite with minor spinel. A multistage formation sequence involving changes in T and fO2 and preceding the introduction of Willy into the CAI (which itself preceded CAI spinel and silicate formation) is postulated, and it is inferred from the apparent lack of post-capture recrystallization that Willy has not been subjected to temperatures in excess of 600 C and may represent the precursor material for many other Fremdlinge.

Characteristics of AZ31 Mg alloy joint using automatic TIG welding

NASA Astrophysics Data System (ADS)

Liu, Hong-tao; Zhou, Ji-xue; Zhao, Dong-qing; Liu, Yun-teng; Wu, Jian-hua; Yang, Yuan-sheng; Ma, Bai-chang; Zhuang, Hai-hua

2017-01-01

The automatic tungsten-inert gas welding (ATIGW) of AZ31 Mg alloys was performed using a six-axis robot. The evolution of the microstructure and texture of the AZ31 auto-welded joints was studied by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. The ATIGW process resulted in coarse recrystallized grains in the heat affected zone (HAZ) and epitaxial growth of columnar grains in the fusion zone (FZ). Substantial changes of texture between the base material (BM) and the FZ were detected. The {0002} basal plane in the BM was largely parallel to the sheet rolling plane, whereas the c-axis of the crystal lattice in the FZ inclined approximately 25° with respect to the welding direction. The maximum pole density increased from 9.45 in the BM to 12.9 in the FZ. The microhardness distribution, tensile properties, and fracture features of the AZ31 auto-welded joints were also investigated.

Analysis of ablation debris from natural and artificial iron meteorites

NASA Technical Reports Server (NTRS)

Blanchard, M. B.; Davis, A. S.

1977-01-01

Artificial ablation studies were performed on iron and nickel-iron samples using an arc-heated plasma of ionized air. Experiment conditions simulated a meteoroid traveling about 12 km/sec at an altitude of 70 km. The artificially produced fusion crusts and ablation debris show features very similar to natural fusion crusts of the iron meteorites Boguslavka, Norfork, and N'Kandhla and to magnetic spherules recovered from Mn nodules. X-ray diffraction, electron microprobe, optical, and scanning electron microscope analyses reveal that important mineralogical, elemental, and textural changes occur during ablation. Some metal is melted and ablated. The outer margin of the melted rind is oxidized and recrystallizes as a discontinuous crust of magnetite and wustite. Adjacent to the oxidized metallic ablation zone is an unoxidized metallic ablation zone in which structures such as Widmannstatten bands are obliterated as the metal is transformed to unequilibrated alpha 2 nickel-iron. Volatile elements are vaporized and less volatile elements undergo fractionation.

Effect of starting microstructure on helium plasma-materials interaction in tungsten

DOE PAGES

Wang, Kun; Bannister, Mark E.; Meyer, Fred W.; ...

2016-11-24

Here, in a magnetic fusion energy (MFE) device, the plasma-facing materials (PFMs) will be subjected to tremendous fluxes of ions, heat, and neutrons. The response of PFMs to the fusion environment is still not well defined. Tungsten metal is the present candidate of choice for PFM applications such as the divertor in ITER. However, tungsten's microstructure will evolve in service, possibly to include recrystallization. How tungsten's response to plasma exposure evolves with changes in microstructure is presently unknown. In this work, we have exposed hot-worked and recrystallized tungsten to an 80 eV helium ion beam at a temperature of 900more » °C to fluences of 2 × 10 23 or 20 × 10 23 He/m 2. This resulted in a faceted surface structure at the lower fluence or short but well-developed nanofuzz structure at the higher fluence. There was little difference in the hot-rolled or recrystallized material's near-surface (≤50 nm) bubbles at either fluence. At higher fluence and deeper depth, the bubble populations of the hot-rolled and recrystallized were different, the recrystallized being larger and deeper. This may explain previous high-fluence results showing pronounced differences in recrystallized material. The deeper penetration in recrystallized material also implies that grain boundaries are traps, rather than high-diffusivity paths.« less

Study of Improved Aluminum Materials for Vehicular Armor

DTIC Science & Technology

1977-04-07

and along cell walls. Dislocations generated during deformation cf the 17 -------------- recrystallized structure interacted with the grain...unrecrystallized (HR) 7475 plate containing dislocations within subgrains and along cell walls. Hot rolling the recrystallized structure at 750OF produced...a structure after solution heat treatment that consisted of elongated recrystallized grains containing polygonized cells . This structure developed

Viscous Flow Causes Weakening in Calcite Nanogouges Sheared at Seismic Velocity

NASA Astrophysics Data System (ADS)

Pozzi, G.; De Paola, N.; Nielsen, S. B.; Holdsworth, R.

2016-12-01

Recent experimental studies have suggested that the activation of diffusion creep at high temperatures (T ≥ 800 °C) and strain rates in nanograin aggregates can weaken faults and facilitate earthquake propagation. However, the frictional properties of nanoscale aggregates at high strain rates and T are still poorly investigated and, in particular, their flow laws at these extreme conditions are poorly constrained due to lack of knowledge about the evolution of grain size and strain localization during seismic slip. Experiments performed in a rotary shear apparatus on micro- and nano-metric calcite gouges (d=63-90 µm and d 200nm, respectively) at seismic (up to 1.4 m/s) and subseismic (<10 cm/s) velocities, arrested at different amounts of slip, show that: (i) onset of dynamic weakening in the nanogouge is faster, with a significantly reduced initial phase of slip hardening, (ii) dynamic weakening of the nanogouge is achieved at velocities and temperatures as low as 1.4 cm/s and <300°C, respectively, compared to >10 cm/s and >500°C in the microgouge, (iii) shear strength shows a rate-dependent weakening. Microstructural analysis of samples shows a three stage evolution: (i) cataclastic comminution and development of Riedel shear bands during the pre-weakening slip-hardening stage, (ii) interconnection of Riedel shears to form a continuous horizontal, localised shear band at the onset of weakening and (iii) evolution of the latter into a thin discrete shear zone with thickness <200 µm composed by a low-porosity aggregate of equigranular recrystallized crystals displaying triple junctions, at the attainment of steady-state weakening stage. Microstructures up to stage (i) are achieved in samples that did not undergo weakening. Despite both gouges show the same microstructural evolution, the initial grainsize of nanoparticles allows a more efficient localisation as the development of a discrete slip zone requires smaller amounts of slip. Our experimental results and microstructural observations shed some light on the critical role that extreme comminution and localisation play on the onset of weakening dominated by viscous flow at high strain rate in carbonate gouges.

Reinforcement of the Cube texture during recrystallization of a 1050 aluminum alloy partially recrystallized and 10% cold-rolled

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Wei; Helbert, Anne-Laure, E-mail: anne-laure.helbert@u-psud.fr; Baudin, Thierry

In high purity Aluminum, very strong {l_brace}100{r_brace}<001> recrystallization texture is developed after 98% cold rolling and annealing at 500 Degree-Sign C. On the contrary, in Aluminum alloys of commercial purity, the Cube component hardly exceeds 30% after complete recrystallization. Parameters controlling Cube orientation development are mainly the solute dragging due to impurities in solid solution and the stored deformation energy. In the present study, besides the 85% cold rolling, two extra annealings and a slight cold rolling are introduced in the processing route to increase the Cube volume fraction. The Cube development was analyzed by X-ray diffraction and Electron BackScatteredmore » Diffraction (EBSD). The nucleation and growth mechanisms responsible for the large Cube growth were investigated using FEG/EBSD in-situ heating experiments. Continuous recrystallization was observed in Cube oriented grains and competed with SIBM (Strain Induced Boundary Migration) mechanism. This latter was favored by the stored energy gap introduced during the additional cold-rolling between the Cube grains and their neighbors. Finally, a Cube volume fraction of 65% was reached after final recrystallization. - Highlights: Black-Right-Pointing-Pointer EBSD in-situ heating experiments of aluminum alloy of commercial purity. Black-Right-Pointing-Pointer A 10% cold-rolling after a partial recrystallization improved Cube nucleation and growth. Black-Right-Pointing-Pointer Annealing before cold-rolling limited the solute drag effect and permitted a large Cube growth. Black-Right-Pointing-Pointer Cube development is enhanced by continuous recrystallization of Cube sub-grains. Black-Right-Pointing-Pointer The preferential Cube growth occurs by SIBM of small Cube grains.« less

Cupric oxide inclusions in cuprous oxide crystals grown by the floating zone method

NASA Astrophysics Data System (ADS)

Frazer, Laszlo; Chang, Kelvin B.; Poeppelmeier, Kenneth R.; Ketterson, John B.

2015-06-01

Phase-pure cuprous oxide (Cu2O) crystals are difficult to grow since cupric oxide can form within the crystal as the crystal is cooled to ambient conditions. Vacancies are the solute which causes precipitation of macroscopic defects. Therefore, even when a mostly phase-pure single crystal is used as a feed rod, cupric oxide inclusions persist in the recrystallized solid. Control of the thermal profile during crystal growth, however, can improve phase-purity; a slow counter-rotation rate of the feed and seed rods results in fewer inclusions. Cupric oxide can be removed by annealing, which produces a factor of 540 ± 70 increase in phase-purity.

Cupric oxide inclusions in cuprous oxide crystals grown by the floating zone method

PubMed Central

Frazer, Laszlo; Chang, Kelvin B; Poeppelmeier, Kenneth R; Ketterson, John B

2015-01-01

Phase-pure cuprous oxide (Cu2O) crystals are difficult to grow since cupric oxide can form within the crystal as the crystal is cooled to ambient conditions. Vacancies are the solute which causes precipitation of macroscopic defects. Therefore, even when a mostly phase-pure single crystal is used as a feed rod, cupric oxide inclusions persist in the recrystallized solid. Control of the thermal profile during crystal growth, however, can improve phase-purity; a slow counter-rotation rate of the feed and seed rods results in fewer inclusions. Cupric oxide can be removed by annealing, which produces a factor of 540 ± 70 increase in phase-purity. PMID:27877798

Combined Effect of Heating Rate and Microalloying Elements on Recrystallization During Annealing of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Bellavoine, Marion; Dumont, Myriam; Drillet, Josée; Hébert, Véronique; Maugis, Philippe

2018-05-01

Adjusting ferrite recrystallization kinetics during annealing is a way to control the final microstructure and thus the mechanical properties of advanced cold-rolled high-strength steels. Two strategies are commonly used for this purpose: adjusting heating rates and/or adding microalloying elements. The present work investigates the effect of heating rate and microalloying elements Ti, Nb, and Mo on recrystallization kinetics during annealing in various cold-rolled Dual-Phase steel grades. The use of combined experimental and modeling approaches allows a deeper understanding of the separate influence of heating rate and the addition of microalloying elements. The comparative effect of Ti, Nb, and Mo as solute elements and as precipitates on ferrite recrystallization is also clarified. It is shown that solute drag has the largest delaying effect on recrystallization in the present case and that the order of solute drag effectiveness of microalloying elements is Nb > Mo > Ti.

Combined Effect of Heating Rate and Microalloying Elements on Recrystallization During Annealing of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Bellavoine, Marion; Dumont, Myriam; Drillet, Josée; Hébert, Véronique; Maugis, Philippe

2018-07-01

Adjusting ferrite recrystallization kinetics during annealing is a way to control the final microstructure and thus the mechanical properties of advanced cold-rolled high-strength steels. Two strategies are commonly used for this purpose: adjusting heating rates and/or adding microalloying elements. The present work investigates the effect of heating rate and microalloying elements Ti, Nb, and Mo on recrystallization kinetics during annealing in various cold-rolled Dual-Phase steel grades. The use of combined experimental and modeling approaches allows a deeper understanding of the separate influence of heating rate and the addition of microalloying elements. The comparative effect of Ti, Nb, and Mo as solute elements and as precipitates on ferrite recrystallization is also clarified. It is shown that solute drag has the largest delaying effect on recrystallization in the present case and that the order of solute drag effectiveness of microalloying elements is Nb > Mo > Ti.

Recrystallization kinetics of warm-rolled tungsten in the temperature range 1150-1350 °C

NASA Astrophysics Data System (ADS)

Alfonso, A.; Juul Jensen, D.; Luo, G.-N.; Pantleon, W.

2014-12-01

Pure tungsten is a potential candidate material for the plasma-facing first wall and the divertor of fusion reactors. Both parts have to withstand high temperatures during service. This will alter the microstructure of the material by recovery, recrystallization and grain growth and will cause degradation in material properties as a loss in mechanical strength and embrittlement. The thermal stability of a pure tungsten plate warm-rolled to 67% thickness reduction was investigated by long-term isothermal annealing in the temperature range between 1150 °C and 1350 °C up to 2200 h. Changes in the mechanical properties during annealing are quantified by Vickers hardness measurements. They are described concisely by classical kinetic models for recovery and recrystallization. The observed time spans for recrystallization and the obtained value for the activation energy of the recrystallization process indicate a sufficient thermal stability of the tungsten plate during operation below 1075 °C.

Boundary migration in a 3D deformed microstructure inside an opaque sample

DOE PAGES

Zhang, Y. B.; Budai, J. D.; Tischler, J. Z.; ...

2017-06-30

How boundaries surrounding recrystallization grains migrate through the 3D network of dislocation boundaries in deformed crystalline materials is unknown and critical for the resulting recrystallized crystalline materials. Furthermore, by using X-ray Laue diffraction microscopy, we show for the first time the migration pattern of a typical recrystallization boundary through a well-characterized deformation matrix. The data provide a unique possibility to investigate effects of both boundary misorientation and plane normal on the migration, information which cannot be accessed with any other techniques. Our results show that neither of these two parameters can explain the observed migration behavior. Instead we suggest thatmore » the subdivision of the deformed microstructure ahead of the boundary plays the dominant role. Our experimental observations challenge the assumptions of existing recrystallization theories, and set the stage for determination of mobilities of recrystallization boundaries.« less

Improvement of seawater salt quality by hydro-extraction and re-crystallization methods

NASA Astrophysics Data System (ADS)

Sumada, K.; Dewati, R.; Suprihatin

2018-01-01

Indonesia is one of the salt producing countries that use sea water as a source of raw materials, the quality of salt produced is influenced by the quality of sea water. The resulting average salt quality contains 85-90% NaCl. The Indonesian National Standard (SNI) for human salt’s consumption sodium chloride content is 94.7 % (dry base) and for industrial salt 98,5 %. In this study developed the re-crystallization without chemical and hydro-extraction method. The objective of this research to choose the best methods based on efficiency. The results showed that re-crystallization method can produce salt with NaCl content 99,21%, while hydro-extraction method content 99,34 % NaCl. The salt produced through both methods can be used as a consumption and industrial salt, Hydro-extraction method is more efficient than re-crystallization method because re-crystallization method requires heat energy.

Tectono-metamorphic evolution of high-P/T and low-P/T metamorphic rocks in the Tia Complex, southern New England Fold Belt, eastern Australia: Insights from K-Ar chronology

NASA Astrophysics Data System (ADS)

Fukui, Shiro; Tsujimori, Tatsuki; Watanabe, Teruo; Itaya, Tetsumaru

2012-10-01

The Tia Complex in the southern New England Fold Belt is a poly-metamorphosed Late Paleozoic accretionary complex. It consists mainly of high-P/low-T type pumpellyite-actinolite facies (rare blueschist facies) schists, phyllite and serpentinite (T = 300 °C and P = 5 kbar), and low-P/high-T type amphibolite facies schist and gneiss (T = 600 °C and P < 5 kbar) associated with granodioritic plutons (Tia granodiorite). White mica and biotite K-Ar ages distinguish Carboniferous subduction zone metamorphism and Permian granitic intrusions, respectively. The systematic K-Ar age mapping along a N-S traverse of the Tia Complex exhibits a gradual change. The white mica ages become younger from the lowest-grade zone (339 Ma) to the highest-grade zone (259 Ma). In contrast, Si content of muscovite changes drastically only in the highest-grade zone. The regional changes of white mica K-Ar ages and chemical compositions of micas indicate argon depletion from precursor high-P/low-T type phengitic white mica during the thermal overprinting and recrystallization by granitoids intrusions. Our new K-Ar ages and available geological data postulate a model of the eastward rollback of a subduction zone in Early Permian. The eastward shift of a subduction zone system and subsequent magmatic activities of high-Mg andesite and adakite might explain formation of S-type granitoids (Hillgrove suite) and coeval low-P/high-T type metamorphism in the Tia Complex.

Controlling microstructure and texture in magnesium alloy sheet by shear-based deformation processing

NASA Astrophysics Data System (ADS)

Sagapuram, Dinakar

Application of lightweight Mg sheet is limited by its low workability, both in production of sheet (typically by multistep hot and cold-rolling) and forming of sheet into components. Large strain extrusion machining (LSEM), a constrained chip formation process, is used to create Mg alloy AZ31B sheet in a single deformation step. The deformation in LSEM is shown to be intense simple shear that is confined to a narrow zone, which results in significant deformation-induced heating up to ~ 200°C and reduces the need for pre-heating to realize continuous sheet forms. This study focuses on the texture and microstructure development in the sheet processed by LSEM. Interestingly, deep, highly twinned steady-state layer develops in the workpiece subsurface due to the compressive field ahead of the shear zone. The shear deformation, in conjunction with this pre-deformed twinned layer, results in tilted-basal textures in the sheet with basal planes tilted well away from the surface. These textures are significantly different from those in rolled sheet, where basal planes are nearly parallel to the surface. By controlling the strain path, the basal plane inclination from the surface could be varied in the range of 32-53°. B-fiber (basal plane parallel to LSEM shear plane), associated with basal slip, is the major texture component in the sheet. An additional minor C2-fiber component appears above 250°C due to the thermal activation of pyramidal slip. Together with these textures, microstructure ranges from severely cold-worked to (dynamically) recrystallized type, with the corresponding grain sizes varying from ultrafine- (~ 200 nm) to fine- (2 mum) grained. Small-scale limiting dome height (LDH) confirmed enhanced formability (~ 50% increase in LDH) of LSEM sheet over the conventional rolled sheet. Premature, twinning-driven shear fractures are observed in the rolled sheet with the basal texture. In contrast, LSEM sheet with a tilted-basal texture favorably oriented for basal slip exhibits ductile tensile-type fracture. A two-fold increase in ductility is also observed for the LSEM sheet under uniaxial tensile testing without significant changes in the strength. Among texture and microstructure (grain size), texture is shown to be more critical for Mg sheet formability. However, in conjunction with a favorable texture, fine recrystallized microstructure provides for additional enhancement of strain-hardening capacity and formability. In-situ imaging of material flow during uniaxial tensile testing revealed new, interesting flow localization phenomena and fracture behavior. It is shown that the deformation behavior of Mg sheet is highly texture dependent, and also radically different from that of conventional ductile metals both in terms of necking and fracture. The implications of these observations for the LDH test results and formability of Mg sheet, in general, are briefly discussed.

Effect of Boron on the Hot Ductility of Resulfurized Low-Carbon Free-Cutting Steel

NASA Astrophysics Data System (ADS)

Liu, Hai-tao; Chen, Wei-qing

2015-09-01

The hot ductility of resulfurized low-carbon free-cutting steel with boron additives is studied in the temperature range 850 - 1200°C with the help of a Gleeble-1500 thermomechanical simulator. The introduction of boron increases hot ductility, especially at 900 - 1050°C. In the single-phase austenitic region, this effect is caused by segregation of boron over grain boundaries, acceleration of dynamic recrystallization, and solid-solution softening of deformed austenite.

Tungsten Inert Gas and Friction Stir Welding Characteristics of 4-mm-Thick 2219-T87 Plates at Room Temperature and -196 °C

NASA Astrophysics Data System (ADS)

Lei, Xuefeng; Deng, Ying; Yin, Zhimin; Xu, Guofu

2014-06-01

2219-T87 aluminum alloy is widely used for fabricating liquid rocket propellant storage tank, due to its admirable cryogenic property. Welding is the dominant joining method in the manufacturing process of aerospace components. In this study, the tungsten inert gas welding and friction stir welding (FSW) characteristics of 4-mm-thick 2219-T87 alloy plate at room temperature (25 °C) and deep cryogenic temperature (-196 °C) were investigated by property measurements and microscopy methods. The studied 2219 base alloy exhibits a low strength plane anisotropy and excellent room temperature and cryogenic mechanical properties. The ultimate tensile strength values of TIG and FSW welding joints can reach 265 and 353 MPa at room temperature, and 342 and 438 MPa at -196 °C, respectively. The base metal consists of elongated deformed grains and many nano-scaled θ (Al2Cu) aging precipitates. Fusion zone and heat-affected zone (HAZ) of the TIG joint are characterized by coarsening dendritic grains and equiaxed recrystallized grains, respectively. The FSW-welded joint consists of the weld nugget zone, thermo-mechanically affected zone (TMAZ), and HAZ. In the weld nugget zone, a micro-scaled sub-grain structure is the main microstructure characteristic. The TMAZ and HAZ are both characterized by coarsened aging precipitates and elongated deformed grains. The excellent FSW welding properties are attributed to the preservation of the working structures and homogenous chemical compositions.

Microstructure, texture, and mechanical properties of friction stir welded commercial brass alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heidarzadeh, A., E-mail: ak.hz62@gmail.com

Microstructural evolution during friction stir welding of single-phase brass and corresponding mechanical properties were investigated. For this purpose, 2 mm thick brass plate was friction stir welded at a rotational speed of 450 rpm and traverse speed of 100 mm/min. The microstructure of the joint was studied using optical microscopy, scanning electron microscopy equipped with electron back scattered diffraction system, and scanning transmission electron microscopy. The mechanical properties were measured using hardness and tensile tests. The formation of subgrains and their transformation into new grains in conjunction with existence of A{sub 1}{sup ⁎}, A{sub 2}{sup ⁎} and C texture componentsmore » revealed that the continuous dynamic recrystallization plays a dominant role in the microstructural evolution. However, grain boundary bulging, along with the formation of twin boundaries, and presence of the G texture component showed that the discontinues dynamic recrystallization may participate in the new grain formation. Furthermore, the different strengthening mechanisms, which caused the higher strength of the joint, were discussed. - Highlights: •Microstructural evolution during FSW of a single phase brass was investigated. •CDRX and DDRX were the main mechanisms of the grain structure formation during FSW. •GDRX and SRX were not contributed in grain structure formation. •The lamellas TBs were formed in the SZ of the joints. •Grain boundary, dislocation, and texture effects resulted in higher strength.« less

Ultrastructural properties of laser-irradiated and heat-treated dentin.

PubMed

Rohanizadeh, R; LeGeros, R Z; Fan, D; Jean, A; Daculsi, G

1999-12-01

Previous studies using scanning electron microscopy and infrared absorption spectroscopy reported that laser irradiation causes compositional changes in enamel. The purpose of this study was to evaluate the ultrastructural and compositional changes in dentin caused by irradiation with a short-pulse laser (Q-switched Nd:YAG). The irradiated and non-irradiated areas of the lased dentin samples were investigated by scanning (SEM) and transmission electron microscopy (TEM), micro-micro electron diffraction, and electron microprobe analysis of dispersive energy (EDX). Heat-treated dentin was similarly investigated. This study demonstrated that laser irradiation resulted in the recrystallization of dentin apatite and in the formation of additional calcium phosphate phases consisting of magnesium-substituted beta-tricalcium phosphate, beta-TCMP, beta-(Ca,Mg)3(PO4)2, and tetracalcium phosphate, TetCP, Ca4(PO4)O. TEM analyses of the modified and unmodified zones of the irradiated areas showed two types of crystal populations: much larger crystals from the modified zone and crystals with size and morphology similar to those of dentin apatite in the unmodified zone. The morphology of crystals in the modified zones in the irradiated dentin resembled those of dentin sintered at 800 or 950 degrees C. In the irradiated areas (modified and unmodified zones), the Ca/P ratio was lower compared with that in the non-irradiated dentin. The Mg/Ca ratio in the modified zones was higher than that in the unmodified zones and in the non-irradiated dentin. In sintered dentin, the Mg/Ca ratio increased as a function of sintering temperature. The ultrastructural and compositional changes observed in laser-irradiated dentin may be attributed to high temperature and high pressure induced by microplasma during laser irradiation. These changes may alter the solubility of the irradiated dentin, making it less susceptible to acid dissolution or to the caries process.

Cellular monotectic model solidification

NASA Technical Reports Server (NTRS)

Kaukler, William F.

1987-01-01

Succinonitrile (sn) was purified to a superior level using a fractional recrystallization method. The melting point of the best twice recrystallized sn was not raised by following with double distillation. This was tested using differential scanning calorimetry. The peak shape on melting also proved that double distillation after double recrystallization did not improve the quality. Stability and phase diagrams for succinonitrile and glycerol are presented.

Effect of one-step recrystallization on the grain boundary evolution of CoCrFeMnNi high entropy alloy and its subsystems.

PubMed

Chen, Bo-Ru; Yeh, An-Chou; Yeh, Jien-Wei

2016-02-29

In this study, the grain boundary evolution of equiatomic CoCrFeMnNi, CoCrFeNi, and FeCoNi alloys after one-step recrystallization were investigated. The special boundary fraction and twin density of these alloys were evaluated by electron backscatter diffraction analysis. Among the three alloys tested, FeCoNi exhibited the highest special boundary fraction and twin density after one-step recrystallization. The special boundary increment after one-step recrystallization was mainly affected by grain boundary velocity, while twin density was mainly affected by average grain boundary energy and twin boundary energy.

Effect of Scandium on the Interaction of Concurrent Precipitation and Recrystallization in Commercial AA3003 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Tu, Yiyou; Qian, Huan; Zhou, Xuefeng; Jiang, Jianqing

2014-04-01

In the current study, the effect of Sc addition on the interaction of concurrent precipitation and recrystallization in commercial AA3003 aluminum alloy was investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. In case of AA3003 alloy, which was cold rolled to a true strain of 2.20 and heated at a heating rate of 150 K/s, the onset of precipitation and ending of recrystallization are signified by the critical temperature, T C ~740 K (467 °C). There is a change in the shape of the recrystallized grains from pancake-like to equiaxed shape, as the annealing temperature increases greater than T C. In case of AA3003 alloy microalloyed with 0.4 wt pct of Sc, the high no. density precipitation of coherent Al3Sc precipitates always occurs before recrystallization because of the small nucleation barrier and high rate of decomposition. This leads to extremely coarse pancake-like recrystallization grains with high fraction of low-angle grain boundaries in the entire annealing temperature range, even at a high brazing temperature of 883 K (610 °C).

Incorporation of Eu(III) into Calcite under Recrystallization conditions.

PubMed

Hellebrandt, S E; Hofmann, S; Jordan, N; Barkleit, A; Schmidt, M

2016-09-13

The interaction of calcite with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three calcite powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu(3+) occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different calcites. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na(+). These findings emphasize the different retention potential of calcite as a primary and secondary mineral e.g. in a nuclear waste disposal site.

Inhibiting ice recrystallization and optimization of cell viability after cryopreservation.

PubMed

Chaytor, Jennifer L; Tokarew, Jacqueline M; Wu, Luke K; Leclère, Mathieu; Tam, Roger Y; Capicciotti, Chantelle J; Guolla, Louise; von Moos, Elisabeth; Findlay, C Scott; Allan, David S; Ben, Robert N

2012-01-01

The ice recrystallization inhibition activity of various mono- and disaccharides has been correlated with their ability to cryopreserve human cell lines at various concentrations. Cell viabilities after cryopreservation were compared with control experiments where cells were cryopreserved with dimethylsulfoxide (DMSO). The most potent inhibitors of ice recrystallization were 220 mM solutions of disaccharides; however, the best cell viability was obtained when a 200 mM d-galactose solution was utilized. This solution was minimally cytotoxic at physiological temperature and effectively preserved cells during freeze-thaw. In fact, this carbohydrate was just as effective as a 5% DMSO solution. Further studies indicated that the cryoprotective benefit of d-galactose was a result of its internalization and its ability to mitigate osmotic stress, prevent intracellular ice formation and/or inhibit ice recrystallization. This study supports the hypothesis that the ability of a cryoprotectant to inhibit ice recrystallization is an important property to enhance cell viability post-freeze-thaw. This cryoprotective benefit is observed in three different human cell lines. Furthermore, we demonstrated that the ability of a potential cryoprotectant to inhibit ice recrystallation may be used as a predictor of its ability to preserve cells at subzero temperatures.

Incorporation of Eu(III) into Calcite under Recrystallization conditions

PubMed Central

Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.

2016-01-01

The interaction of calcite with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three calcite powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu3+ occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different calcites. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na+. These findings emphasize the different retention potential of calcite as a primary and secondary mineral e.g. in a nuclear waste disposal site. PMID:27618958

Anisotropic Morphological Changes in Goethite during Fe(2+)-Catalyzed Recrystallization.

PubMed

Joshi, Prachi; Gorski, Christopher A

2016-07-19

When goethite is exposed to aqueous Fe(2+), rapid and extensive Fe atom exchange can occur between solid-phase Fe(3+) and aqueous Fe(2+) in a process referred to as Fe(2+)-catalyzed recrystallization. This process can lead to the structural incorporation or release of trace elements, which has important implications for contaminant remediation and nutrient biogeochemical cycling. Prior work found that the process did not cause major changes to the goethite structure or morphology. Here, we further investigated if and how goethite morphology and aggregation behavior changed temporally during Fe(2+)-catalyzed recrystallization. On the basis of existing literature, we hypothesized that Fe(2+)-catalyzed recrystallization of goethite would not result in changes to individual particle morphology or interparticle interactions. To test this, we reacted nanoparticulate goethite with aqueous Fe(2+) at pH 7.5 over 30 days and used transmission electron microscopy (TEM), cryogenic TEM, and (55)Fe as an isotope tracer to observe changes in particle dimensions, aggregation, and isotopic composition over time. Over the course of 30 days, the goethite particles substantially recrystallized, and the particle dimensions changed anisotropically, resulting in a preferential increase in the mean particle width. The temporal changes in goethite morphology could not be completely explained by a single mineral-transformation mechanism but rather indicated that multiple transformation mechanisms occurred concurrently. Collectively, these results demonstrate that the morphology of goethite nanoparticles does change during recrystallization, which is an important step toward identifying the driving force(s) of recrystallization.

Modeling the microstructural changes during hot tandem rolling of AA5 XXX aluminum alloys: Part I. Microstructural evolution

NASA Astrophysics Data System (ADS)

Wells, M. A.; Samarasekera, I. V.; Brimacombe, J. K.; Hawbolt, E. B.; Lloyd, D. J.

1998-06-01

A comprehensive mathematical model of the hot tandem rolling process for aluminum alloys has been developed. Reflecting the complex thermomechanical and microstructural changes effected in the alloys during rolling, the model incorporated heat flow, plastic deformation, kinetics of static recrystallization, final recrystallized grain size, and texture evolution. The results of this microstructural engineering study, combining computer modeling, laboratory tests, and industrial measurements, are presented in three parts. In this Part I, laboratory measurements of static recrystallization kinetics and final recrystallized grain size are described for AA5182 and AA5052 aluminum alloys and expressed quantitatively by semiempirical equations. In Part II, laboratory measurements of the texture evolution during static recrystallization are described for each of the alloys and expressed mathematically using a modified form of the Avrami equation. Finally, Part III of this article describes the development of an overall mathematical model for an industrial aluminum hot tandem rolling process which incorporates the microstructure and texture equations developed and the model validation using industrial data. The laboratory measurements for the microstructural evolution were carried out using industrially rolled material and a state-of-the-art plane strain compression tester at Alcan International. Each sample was given a single deformation and heat treated in a salt bath at 400 °C for various lengths of time to effect different levels of recrystallization in the samples. The range of hot-working conditions used for the laboratory study was chosen to represent conditions typically seen in industrial aluminum hot tandem rolling processes, i.e., deformation temperatures of 350 °C to 500 °C, strain rates of 0.5 to 100 seconds and total strains of 0.5 to 2.0. The semiempirical equations developed indicated that both the recrystallization kinetics and the final recrystallized grain size were dependent on the deformation history of the material i.e., total strain and Zener-Hollomon parameter ( Z), where Z = dot \\varepsilon exp left( {{Q_{def} }/{RT_{def }}} right) and time at the recrystallization temperature.

Jurassic to Miocene magmatism and metamorphism in the Mogok metamorphic belt and the India-Eurasia collision in Myanmar

NASA Astrophysics Data System (ADS)

Barley, M. E.; Pickard, A. L.; Zaw, Khin; Rak, P.; Doyle, M. G.

2003-06-01

Situated south of the eastern Himalayan syntaxis at the western margin of the Shan-Thai terrane the high-grade Mogok metamorphic belt (MMB) in Myanmar occupies a key position in the tectonic evolution of Southeast Asia. The first sensitive high-resolution ion microprobe U-Pb in zircon geochronology for the MMB shows that strongly deformed granitic orthogneisses near Mandalay contain Jurassic (˜170 Ma) zircons that have partly recrystallized during ˜43 Ma high-grade metamorphism. A hornblende syenite from Mandalay Hill also contains Jurassic zircons with evidence of Eocene metamorphic recrystallization rimmed by thin zones of 30.9 ± 0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma) I-type granitoids in the MMB, Myeik Archipelago, and Western Myanmar confirm that prior to the collision of India, an up to 200 km wide magmatic belt extended along the Eurasian margin from Pakistan to Sumatra. Metamorphic overgrowths to zircons in the orthogneiss near Mandalay date a period of Eocene (˜43 Ma) high-grade metamorphism possibly during crustal thickening related to the initial collision between India and Eurasia (at 65 to 55 Ma). This was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 Ma. Similar syntectonic syenites and leucogranites intruded the Ailao Shan-Red River shear belt in southern China and Vietnam during the Eocene-Oligocene to Miocene, and the Wang Chao and Three Pagodas faults in northern Thailand (that most likely link with the MMB) were also active at this time. The complex history of Eocene to early Miocene metamorphism, deformation, and magmatism in the MMB provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of India and resulting extrusion or rotation of Indochina.

Crystallographic texture and microstructural changes in fusion welds of recrystallized Zry-4 rolled plates

NASA Astrophysics Data System (ADS)

Moya Riffo, A.; Vicente Alvarez, M. A.; Santisteban, J. R.; Vizcaino, P.; Limandri, S.; Daymond, M. R.; Kerr, D.; Okasinski, J.; Almer, J.; Vogel, S. C.

2017-05-01

This work presents a detailed characterization of the microstructural and crystallographic texture changes observed in the transition region in a weld between two Zircaloy-4 cold rolled and recrystallized plates. The microstructural study was performed by optical microscopy under polarized light and scanning electron microscopy (SEM). Texture changes were characterized at different lengthscales: in the micrometric size, orientation imaging maps (OIM) were constructed by electron backscatter diffraction (EBSD), in the millimetre scale, high energy XRD experiments were done at the Advanced Photon Source (USA) and compared to neutron diffraction texture determinations performed in the HIPPO instrument at Los Alamos National Laboratory. In the heat affected zone (HAZ) we observed the development of Widmanstätten microstructures, typical of the α(hcp) to β(bcc) phase transformation. Associated with these changes a rotation of the c-poles is found in the HAZ and fusion zone. While the base material shows the typical texture of a cold rolled plate, with their c-poles pointing 35° apart from the normal direction of the plate in the normal-transversal line, in the HAZ, c-poles align along the transversal direction of the plate and then re-orient along different directions, all of these changes occurring within a lengthscale in the order of mm. The evolution of texture in this narrow region was captured by both OIM and XRD, and is consistent with previous measurements done by Neutron Diffraction in the HIPPO diffractometer at Los Alamos National Laboratory, USA. The microstructural and texture changes along the HAZ were interpreted as arising due to the effect of differences in the cooling rate and β grain size on the progress of the different α variants during transformation. Fast cooling rates and large β grains are associated to weak variant selection during the β->α transformation, while slow cooling rates and fine β grains result in strong variant selection.

Crystallographic texture and microstructural changes in fusion welds of recrystallized Zry-4 rolled plates

DOE PAGES

Riffo, A. Moya; Vicente Alvarez, M. A.; Santisteban, J. R.; ...

2017-02-08

This study presents a detailed characterization of the microstructural and crystallographic texture changes observed in the transition region in a weld between two Zircaloy-4 cold rolled and recrystallized plates. The microstructural study was performed by optical microscopy under polarized light and scanning electron microscopy (SEM). Texture changes were characterized at different lengthscales: in the micrometric size, orientation imaging maps (OIM) were constructed by electron backscatter diffraction (EBSD), in the millimetre scale, high energy XRD experiments were done at the Advanced Photon Source (USA) and compared to neutron diffraction texture determinations performed in the HIPPO instrument at Los Alamos National Laboratory.more » In the heat affected zone (HAZ) we observed the development of Widmanstätten microstructures, typical of the α( hcp) to β( bcc) phase transformation. Associated with these changes a rotation of the c-poles is found in the HAZ and fusion zone. While the base material shows the typical texture of a cold rolled plate, with their c-poles pointing 35° apart from the normal direction of the plate in the normal-transversal line, in the HAZ, c-poles align along the transversal direction of the plate and then re-orient along different directions, all of these changes occurring within a lengthscale in the order of mm. The evolution of texture in this narrow region was captured by both OIM and XRD, and is consistent with previous measurements done by Neutron Diffraction in the HIPPO diffractometer at Los Alamos National Laboratory, USA. The microstructural and texture changes along the HAZ were interpreted as arising due to the effect of differences in the cooling rate and β grain size on the progress of the different α variants during transformation. Fast cooling rates and large β grains are associated to weak variant selection during the β–>α transformation, while slow cooling rates and fine β grains result in strong variant selection.« less

Crystallographic texture and microstructural changes in fusion welds of recrystallized Zry-4 rolled plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riffo, A. Moya; Vicente Alvarez, M. A.; Santisteban, J. R.

This study presents a detailed characterization of the microstructural and crystallographic texture changes observed in the transition region in a weld between two Zircaloy-4 cold rolled and recrystallized plates. The microstructural study was performed by optical microscopy under polarized light and scanning electron microscopy (SEM). Texture changes were characterized at different lengthscales: in the micrometric size, orientation imaging maps (OIM) were constructed by electron backscatter diffraction (EBSD), in the millimetre scale, high energy XRD experiments were done at the Advanced Photon Source (USA) and compared to neutron diffraction texture determinations performed in the HIPPO instrument at Los Alamos National Laboratory.more » In the heat affected zone (HAZ) we observed the development of Widmanstätten microstructures, typical of the α( hcp) to β( bcc) phase transformation. Associated with these changes a rotation of the c-poles is found in the HAZ and fusion zone. While the base material shows the typical texture of a cold rolled plate, with their c-poles pointing 35° apart from the normal direction of the plate in the normal-transversal line, in the HAZ, c-poles align along the transversal direction of the plate and then re-orient along different directions, all of these changes occurring within a lengthscale in the order of mm. The evolution of texture in this narrow region was captured by both OIM and XRD, and is consistent with previous measurements done by Neutron Diffraction in the HIPPO diffractometer at Los Alamos National Laboratory, USA. The microstructural and texture changes along the HAZ were interpreted as arising due to the effect of differences in the cooling rate and β grain size on the progress of the different α variants during transformation. Fast cooling rates and large β grains are associated to weak variant selection during the β–>α transformation, while slow cooling rates and fine β grains result in strong variant selection.« less

Monte Carlo modeling of recrystallization processes in α-uranium

DOE PAGES

Steiner, M. A.; McCabe, R. J.; Garlea, E.; ...

2017-08-01

In this study, starting with electron backscattered diffraction (EBSD) data obtained from a warm clock-rolled α-uranium deformation microstructure, a Potts Monte Carlo model was used to simulate static site-saturated recrystallization while testing a number of different conditions for the assignment of recrystallized nuclei within the microstructure. The simulations support observations that recrystallized nuclei within α-uranium form preferentially on non-twin high-angle grain boundary sites at 450 °C, and demonstrate that the most likely nucleation sites on these boundaries can be identified by the surrounding degree of Kernel Average Misorientation (KAM), which may be considered as a proxy for the local geometricallymore » necessary dislocation (GND) density.« less

Characterization of thermoplastic polyimide NEW-TPI

NASA Technical Reports Server (NTRS)

Hou, T. H.; Reddy, R. M.

1991-01-01

Thermal and rheological properties of a commercial thermoplastic polyimide, NEW-TPI, were characterized. The as-received material possesses initially a transient crystallite form with a bimodal distribution in peak melting temperatures. After the meltings of the initial crystallite structures, the sample can be recrystallized by various thermal treatments. A bimodal or single-modal melting peak distribution is formed for annealing temperatures below or above 360 C, respectively. The recrystallized crystallinities are all transient in nature. The polymers are unable to be recrystallized after being subjected to elevated temperature annealing above 450 C. The recrystallization mechanism was postulated, and a simple kinetics model was found to describe the behavior satisfactorily under conditions of prolonged thermal annealing.

Effect of one-step recrystallization on the grain boundary evolution of CoCrFeMnNi high entropy alloy and its subsystems

PubMed Central

Chen, Bo-Ru; Yeh, An-Chou; Yeh, Jien-Wei

2016-01-01

In this study, the grain boundary evolution of equiatomic CoCrFeMnNi, CoCrFeNi, and FeCoNi alloys after one-step recrystallization were investigated. The special boundary fraction and twin density of these alloys were evaluated by electron backscatter diffraction analysis. Among the three alloys tested, FeCoNi exhibited the highest special boundary fraction and twin density after one-step recrystallization. The special boundary increment after one-step recrystallization was mainly affected by grain boundary velocity, while twin density was mainly affected by average grain boundary energy and twin boundary energy. PMID:26923713

Geologic setting, sedimentary architecture, and paragenesis of the Mesoproterozoic sediment-hosted Sheep Creek Cu-Co-Ag deposit, Helena embayment, Montana

USGS Publications Warehouse

Graham, Garth; Hitzman, Murray W.; Zieg, Jerry

2012-01-01

The northern margin of the Helena Embayment contains extensive syngenetic to diagenetic massive pyrite horizons that extend over 25 km along the Volcano Valley-Buttress fault zone and extend up to 8 km basinward (south) within the Mesoproterozoic Newland Formation. The Sheep Creek Cu-Co deposit occurs within a structural block along a bend in the fault system, where replacement-style chalcopyrite mineralization is spatially associated mostly with the two stratigraphically lowest massive pyrite zones. These mineralized pyritic horizons are intercalated with debris flows derived from synsedimentary movement along the Volcano Valley-Buttress fault zone. Cominco American Inc. delineated a geologic resource of 4.5 Mt at 2.5% Cu and 0.1% Co in the upper sulfide zone and 4 Mt at 4% Cu within the lower sulfide zone. More recently, Tintina Resources Inc. has delineated an inferred resource of 8.48 Mt at 2.96% Cu, 0.12% Co, and 16.4 g/t Ag in the upper sulfide zone. The more intact upper sulfide zone displays significant thickness variations along strike thought to represent formation in at least three separate subbasins. The largest accumulation of mineralized sulfide in the upper zone occurs as an N-S–trending body that thickens southward from the generally E trending Volcano Valley Fault and probably occupies a paleograben controlled by normal faults in the hanging wall of the Volcano Valley Fault. Early microcrystalline to framboidal pyrite was accompanied by abundant and local barite deposition in the upper and lower sulfide zones, respectively. The sulfide bodies underwent intense (lower sulfide zone) to localized (upper sulfide zone) recrystallization and overprinting by coarser-grained pyrite and minor marcasite that is intergrown with and replaces dolomite. Silicification and paragenetically late chalcopyrite, along with minor tennantite in the upper sulfide zone, replaces fine-grained pyrite, barite, and carbonate. The restriction of chalcopyrite to inferred synsedimentary E- and northerly trending faults and absence of definitive zonation with respect to the Laramide Volcano Valley Fault in the lower sulfide zone suggest a diagenetic age related to basin development for the Sheep Creek Cu-Co-Ag deposit.

Effect of friction stir processing on tribological properties of Al-Si alloys

NASA Astrophysics Data System (ADS)

Aktarer, S. M.; Sekban, D. M.; Yanar, H.; Purçek, G.

2017-02-01

As-cast Al-12Si alloy was processed by single-pass friction stir processing (FSP), and its effect on mainly friction and wear properties of processed alloy was studied in detail. The needle-shaped eutectic silicon particles were fragmented by intense plastic deformation and dynamic recrystallization during FSP. The fragmented and homogenously distributed Si particles throughout the improve the mechanical properties and wear behavior of Al-12Si alloy. The wear mechanisms for this improvement were examined and the possible reasons were discussed.

Computational Analysis of Material Flow During Friction Stir Welding of AA5059 Aluminum Alloys

DTIC Science & Technology

2011-01-01

tool material (AISI H13 tool steel ) is modeled as an isotropic linear-elastic material. Within the analysis, the effects of some of the FSW key process...threads/m; (b) tool 598 material = AISI H13 tool steel ; (c) workpiece material = 599 AA5059; (d) tool rotation speed = 500 rpm; (e) tool travel 600 speed...the strain-hardening term is augmented to take into account for the effect of dynamic recrystallization) while the FSW tool material (AISI H13

The Role of Solvent Reorganization Dynamics in Electron-Transfer Processes. Theory-Experiment Comparisons for Electrochemical and Homogeneous Electron Exchange Involving Metallocene Redox Couples

DTIC Science & Technology

1985-08-01

Kodak) by crystallization from acetone; it was recrystallized twice from ethanol and dried in a vacuum oven. Tetraethylamonium perchlorate (TEAP) (G...the electrooxidation of in(Cp’) 2 , which yielded significantly smaller reverse (cathodic) currents in the most strongly coordinating solvents (DMX...DM50) at slower scan rates (< 0.5 V sec-1). Nevertheless, satisfactory a.c. polarograms were obtained for each of these system=. 5 4 Temperature

Effect of Extrusion Parameters on Texture and Microstructure Evolution of Extruded Mg-1 pctMn and Mg-1 pctMn-Sr Alloys

NASA Astrophysics Data System (ADS)

Borkar, Hemant; Pekguleryuz, Mihriban

2015-01-01

Three Mg alloys Mg-1 pctMn (M1), Mg-1 pctMn-1.3 pctSr, and Mg-1 pctMn-2.1 pctSr were subjected to two different extrusion temperatures and two different extrusion speeds in lab-scale extrusion. The extrusion temperatures of 573 K and 673 K (300 °C and 400 °C) and two ram speeds of 4 and 8 mm/s were used at constant extrusion ratio of 7. M1 exhibited strong basal texture after extrusion at 673 K (400 °C) at higher speed. At 573 K (300 °C), recrystallization in all alloys takes place completely or partially by continuous dynamic recrystallization mechanism, while particle stimulated nucleation (PSN) occurs in all M1-Sr alloys at both extrusion temperatures and speeds. At 673 K (400 °C), grain boundary bulging is the only recrystallization mechanism in alloy M1, while it occurs in combination with PSN in M1-Sr alloys. The effect of texture weakening by PSN is more significant in M1-Sr alloys extruded at 573 K (400 °C). The plant extrusion trials were carried out on Mg-1 pctMn, Mg-1 pctMn-0.3 pctSr, and Mg-1 pctMn-2.1 pctSr at 623 K (350 °C) with different speeds than in lab-scale extrusion. M1 alloy exhibited strong basal texture at both speeds, while Sr additions of 0.3 and 2.1 pct promoted similar amount of texture weakening.

A Mechanistic Thermal Fatigue Model for SnAgCu Solder Joints

NASA Astrophysics Data System (ADS)

Borgesen, Peter; Wentlent, Luke; Hamasha, Sa'd.; Khasawneh, Saif; Shirazi, Sam; Schmitz, Debora; Alghoul, Thaer; Greene, Chris; Yin, Liang

2018-02-01

The present work offers both a complete, quantitative model and a conservative acceleration factor expression for the life span of SnAgCu solder joints in thermal cycling. A broad range of thermal cycling experiments, conducted over many years, has revealed a series of systematic trends that are not compatible with common damage functions or constitutive relations. Complementary mechanical testing and systematic studies of the evolution of the microstructure and damage have led to a fundamental understanding of the progression of thermal fatigue and failure. A special experiment was developed to allow the effective deconstruction of conventional thermal cycling experiments and the finalization of our model. According to this model, the evolution of damage and failure in thermal cycling is controlled by a continuous recrystallization process which is dominated by the coalescence and rotation of dislocation cell structures continuously added to during the high-temperature dwell. The dominance of this dynamic recrystallization contribution is not consistent with the common assumption of a correlation between the number of cycles to failure and the total work done on the solder joint in question in each cycle. It is, however, consistent with an apparent dependence on the work done during the high-temperature dwell. Importantly, the onset of this recrystallization is delayed by pinning on the Ag3Sn precipitates until these have coarsened sufficiently, leading to a model with two terms where one tends to dominate in service and the other in accelerated thermal cycling tests. Accumulation of damage under realistic service conditions with varying dwell temperatures and times is also addressed.

The effect of precipitation on the evolution of recrystallization textures in an AA 8011 aluminum alloy sheet

NASA Astrophysics Data System (ADS)

Ryu, Jong-Ho; Lee, Yoon-Soo; Lee, Dong Nyung

2001-06-01

The texture of an AA 8011 aluminum alloy sheet cold rolled by 95% showed a typical β-fiber, which runs from the copper orientation [C={112}<111>] over S [{123}<634>] to brass [B={011}<112>]. The development of annealing textures depended on annealing temperatures due to the interaction between precipitation and recrystallization. Upon annealing at a low temperature of 275°C, precipitation took place before recrystallization. This led to a weak recrystallization texture consisting of {011}<122>, {001˜<100>, and {hk0}<001>, among which the {011}<122> orientation developed near large FeAl3 particles as the main orientation and the cube [{001}<100>] orientation originating from the matrix was relatively weak. After annealing at 350 and 500°C, a strong cube texture developed along with a weak {011}<122> orientation. When the cube orientation developed, the copper orientation disappeared most rapidly. These results were discussed based on the interaction between precipitation and recrystallization.

Microstructure evolution and texture development of hot form-quench (HFQ) AZ31 twin roll cast (TRC) magnesium alloy

NASA Astrophysics Data System (ADS)

Alias, J.; Zhou, X.; Das, Sanjeev; El-Fakir, Omer; Thompson, G. E.

2017-12-01

The present study on the microstructure evolution of hot form-quench (HFQ) AZ31 twin roll cast magnesium alloy attempt to provide an understanding on the grain structure and heterogeneous intermetallic phase formation in the alloy and texture development following the HFQ process. Grain recrystallization and partial dissolution of eutectic β-Mg17Al12 phase particles were occurred during the solution heat treatment at 450°C, leaving the alloy consists of recrystallized grains and discontinuous or random β-Mg17Al12 phase particles distribution with small volume fraction. The particles act as effective nucleation sites for new grains during recrystallization and variation of recrystallization occurrence contributed to texture alteration. The partial or full β-Mg17Al12 phase dissolution following the HFQ induces void formation that act as fracture nucleation site and the corresponding texture alteration in the recrystallized grains led to poor formability in TRC alloy.

Upper Mantle Anisotropy Under Fast Spreading Mid-ocean Ridges: 2-D Whole Mantle Convection Model With Subduction

NASA Astrophysics Data System (ADS)

Lee, C.; Zhou, Y.; King, S. D.

2008-12-01

Analyses of seismic anisotropy caused by spatial alignments of anisotropic minerals (e.g., olivine) have been widely used to infer mantle flow directions in the upper mantle. Deep seismic anisotropy beneath fast spreading mid-ocean ridges (e.g., East Pacific Rise) has been recently observed at depths of 200-300 km and even down to the transition zone, with polarization changes in radial anisotropy from VSH < VSV (shallow) to VSH < VSV (deep). We investigate the origin of the observed deep seismic anisotropy and polarization changes beneath the EPR in 2-D Cartesian numerical models using both kinematically (prescribed velocity) and dynamically (negative buoyancy) driven ridge spreading. Because subduction is thought to be an important controlling factor in the style of ridge spreading and mantle convection, we consider a subduction zone developing at the prescribed weak zone. A whole mantle domain expressed by a one by four box (2890 by 11560 km) is used to minimize the boundary effects on the subducting slab. For the upper mantle rheology, we consider composite viscosity of diffusion and dislocation creep for dry olivine to evaluate the effects of lateral variation of mantle viscosity and the rheological changes from dislocation to diffusion creep under the mid-ocean ridge. For the lower mantle rheology, we use diffusion creep for dry olivine by increasing grain size to match relevant lower mantle viscosity. We also consider the 660 km phase transition with density and viscosity jump as well as Clapeyron slope. Anisotropy is evaluated using finite-strain ellipses based on the assumption that a-axes of olivine crystals are parallel to the major axes of the finite-strain ellipses. Our preliminary results show 1) in general, the development of VSH < VSV anisotropy is confined only in a narrow region under the ridge axis at depths of 200- 300 km; 2) strong VSH > VSV anisotropy can be found in the 'asthenosphere' beneath the entire spreading oceanic lithosphere; and 3) the dominate creep mechanism changes from dislocation creep to diffusion creep at depths of 300-400 km; indicating a more isotropic lower upper mantle. We conclude that our geodynamical modeling in a passive ridge spreading system does not produce the deep seismic anisotropy recently observed beneath the EPR. However, we do not consider partial melting, dynamic recrystallization and anisotropic viscosity which would change seismic interpretation and mantle flow, and thus further study is required.

The Influence of Interfacial Roughness on Fiber Sliding in Oxide Composites with La-Monazite Interphases

NASA Technical Reports Server (NTRS)

Davis, J. B.; Hay, R. S.; Marshall, D. B.; Morgan, P. E. D.; Sayir, A.; Gray, Hugh R. (Technical Monitor); Farmer, Serene C. (Technical Monitor)

2002-01-01

Room temperature debonding and sliding of La-Monazite coated fibers is assessed using a composite with a polycrystalline alumina matrix and fibers of several different single crystal (mullite, sapphire) and directionally solidified eutectic (Al2O3/Y3Al5O12 and Al2O3/Y-ZrO2) compositions. These fibers provide a range of residual stresses and interfacial roughnesses. Sliding occurred over a debond crack at the fiber-coating interface when the sliding displacement and surface roughness were relatively small. At large sliding displacements with relatively rough interfaces, the monazite coatings were deformed extensively by fracture, dislocations and occasional twinning, whereas the fibers were undamaged. Dense, fine-grained (10 nm) microstructures suggestive of dynamic recrystallization were also observed in the coatings. Frictional heating during sliding is assessed. The possibility of low temperature recrystallization is discussed in the light of the known resistance of monazite to radiation damage. The ability of La-Monazite to undergo plastic deformation relatively easily at low temperatures may be enabling for its use as a composite interface.

Dislocation loop formation by swift heavy ion irradiation of metals.

PubMed

Khara, Galvin S; Murphy, Samuel T; Duffy, Dorothy M

2017-07-19

A coupled two-temperature, molecular dynamics methodology is used to simulate the structural evolution of bcc metals (Fe and W) and fcc metals (Cu and Ni) following irradiation by swift heavy ions. Electronic temperature dependent electronic specific heat capacities and electron-phonon coupling strengths are used to capture the full effects of the variation in the electronic density of states. Tungsten is found to be significantly more resistant to damage than iron, due both to the higher melting temperature and the higher thermal conductivity. Very interesting defect structures, quite different from defects formed in cascades, are found to be created by swift heavy ion irradiation in the bcc metals. Isolated vacancies form a halo around elongated interstitial dislocation loops that are oriented along the ion path. Such configurations are formed by rapid recrystallization of the molten cylindrical region that is created by the energetic ion. Vacancies are created at the recrystallization front, resulting in excess atoms at the core which form interstitial dislocation loops on completion of crystallization. These unique defect structures could, potentially, be used to create metal films with superior mechanical properties and interesting nanostructures.

Dislocation loop formation by swift heavy ion irradiation of metals

NASA Astrophysics Data System (ADS)

Khara, Galvin S.; Murphy, Samuel T.; Duffy, Dorothy M.

2017-07-01

A coupled two-temperature, molecular dynamics methodology is used to simulate the structural evolution of bcc metals (Fe and W) and fcc metals (Cu and Ni) following irradiation by swift heavy ions. Electronic temperature dependent electronic specific heat capacities and electron-phonon coupling strengths are used to capture the full effects of the variation in the electronic density of states. Tungsten is found to be significantly more resistant to damage than iron, due both to the higher melting temperature and the higher thermal conductivity. Very interesting defect structures, quite different from defects formed in cascades, are found to be created by swift heavy ion irradiation in the bcc metals. Isolated vacancies form a halo around elongated interstitial dislocation loops that are oriented along the ion path. Such configurations are formed by rapid recrystallization of the molten cylindrical region that is created by the energetic ion. Vacancies are created at the recrystallization front, resulting in excess atoms at the core which form interstitial dislocation loops on completion of crystallization. These unique defect structures could, potentially, be used to create metal films with superior mechanical properties and interesting nanostructures.

Microstructure Evolution and Flow Stress Model of a 20Mn5 Hollow Steel Ingot during Hot Compression.

PubMed

Liu, Min; Ma, Qing-Xian; Luo, Jian-Bin

2018-03-21

20Mn5 steel is widely used in the manufacture of heavy hydro-generator shaft due to its good performance of strength, toughness and wear resistance. However, the hot deformation and recrystallization behaviors of 20Mn5 steel compressed under high temperature were not studied. In this study, the hot compression experiments under temperatures of 850-1200 °C and strain rates of 0.01/s-1/s are conducted using Gleeble thermal and mechanical simulation machine. And the flow stress curves and microstructure after hot compression are obtained. Effects of temperature and strain rate on microstructure are analyzed. Based on the classical stress-dislocation relation and the kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of 20Mn5 steel. Comparisons between experimental flow stress and predicted flow stress show that the predicted flow stress values are in good agreement with the experimental flow stress values, which indicates that the proposed constitutive model is reliable and can be used for numerical simulation of hot forging of 20Mn5 hollow steel ingot.

Quantifying the effect of diagenetic recrystallization on the Mg isotopic composition of marine carbonates

NASA Astrophysics Data System (ADS)

Chanda, Piyali; Fantle, Matthew S.

2017-05-01

The Mg and Sr isotopic compositions (δ26Mg and 87Sr/86Sr) of pore fluids and bulk carbonates from Ocean Drilling Project Site 1171 (South Tasman Rise; 2148.2 m water depth) are reported, in order to evaluate the potential of diagenesis to alter carbonate-based geochemical proxies in an open marine system. Given the trace amounts of Mg in marine carbonates relative to coexisting pore fluids, diagenesis can alter carbonate δ26Mg, a promising proxy for seawater δ26Mg that may help elucidate long-term changes in the global Mg cycle. Constraints on the effect of diagenetic recrystallization on carbonate δ26Mg are therefore critical for accurate proxy interpretations. This study provides context for assessing the fidelity of geochemical proxy-reconstructions using the primary components (i.e., foraminiferal tests and nannofossils) of bulk carbonate sediments. We find that pore fluid δ26Mg values (on the DSM3 scale) at Site 1171 increase systematically with depth (from -0.72‰ to -0.39‰ in the upper ∼260 m), while the δ26Mg of bulk carbonates decrease systematically with depth (from -2.23‰ to -5.00‰ in the upper ∼260 m). This variability is ascribed primarily to carbonate recrystallization, with a small proportion of the variability due to down-hole changes in nannofossil and foraminiferal species composition. The inferred effect of diagenesis on bulk carbonate δ26Mg correlates with down-core changes in Mg/Ca, Sr/Ca, Na/Ca, and 87Sr/86Sr. A depositional reactive-transport model is employed to validate the hypothesis that calcite recrystallization in this system can generate sizeable shifts in carbonate δ26Mg. Model fits to the data suggest a fractionation factor and a partition coefficient that are consistent with previous work, assuming calcite recrystallization rates of ⩽7%/Ma constrained by Sr geochemistry. In addition, either partial dissolution or a distinctly different previous diagenetic regime must be invoked in order to explain aspects of the elemental chemistry and 87Sr/86Sr of relatively deep sediments from Holes A and C. This study indicates that the dynamics of a given sedimentary system can significantly alter bulk carbonate geochemistry, and presents a framework for considering the potential impact of such alteration on picked archives such as foraminiferal tests and nannofossils. Ultimately, this study contributes to the development of δ26Mg as a proxy for seawater δ26Mg by quantifying the susceptibility of carbonate δ26Mg to diagenetic alteration, particularly in sediments in open marine systems. This study suggests that because of the sensitivity of carbonate δ26Mg to diagenetic recrystallization, it can, in certain systems, be used to quantify the impact of diagenesis on carbonate-based geochemical proxies.

Photoacoustic Imaging.

DTIC Science & Technology

1983-12-01

recrystallization is currently an active area of research. Much effort has been made to grow large grain polysilicon with grain sizes of 100 microns from fine grain... polysilicon using laser recrystallization. The recrystallization process is inherently traumatic, producing large changes in temperature in short...temperature distribution above as the source term in the acoustic field equation, we ol fain r where B1)jwP) The general solution to this equation is given by

A quasi-in-situ EBSD observation of the transformation from rolling texture to recrystallization texture in V-4Cr-4Ti alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, Lixia

Recrystallization texture evolution of rolled V-4Cr-4Ti alloy has been investigated by quasi-in-situ EBSD (electron back-scattering diffraction) method. Concurrently, the precipitates were characterized by SEM (Scanning Electron Microscopy). It was found that both the initial rolling textures and the distribution of the precipitates affected the formation of the recrystallization texture. It was revealed that the texture transformations of (558) 〈110〉 + (665) 〈110〉 to (334) 〈483〉 + (665) 〈1 1 2.4〉 were possibly attributed to the selective drag induced by the sparsely dispersed Ti-rich precipitates. While the densely distributed Ti-rich precipitates were responsible for the randomized recrystallization texture. Finally, when themore » precipitates were absent, the orientation changes from (112) 〈110〉 and (558) 〈110〉 to (111) 〈112〉 and (001) <110> to (001) <520> were observed. - Highlights: • Micro recrystallization texture evolution in V-4Cr-4Ti alloys is reported for the first time. • The volume fraction of Ti-rich precipitates has significant effect on the recrystallization texture evolution. • The dissolution of the Ti-rich precipitates above 1100 °C induces the strengthening of (111) <112> texture.« less

In-situ observation of recrystallization in an AlMgScZr alloy using confocal laser scanning microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taendl, J., E-mail: johannes.taendl@tugraz.atl; Nambu, S.; Orthacker, A.

2015-10-15

In this work we present a novel in-situ approach to study the recrystallization behavior of age hardening alloys. We use confocal laser scanning microscopy (CLSM) at 400 °C to investigate the static recrystallization of an AlMg4Sc0.4Zr0.12 alloy in-situ. The results are combined with electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyses. It was found that CLSM is a powerful tool to visualize both the local initiation and temporal sequence of recrystallization. After fast nucleation and initial growth, the grain growth rate decreases and the grain boundary migration stops after some minutes due to Zener pinning from Al{sub 3}(Sc,Zr)more » precipitates produced during the heat treatment. EBSD and TEM analyses confirm both the boundary movements and the particle-boundary interactions. - Highlights: • First time that CLSM is used to study recrystallization in-situ. • The start and end of recrystallization can be directly observed. • The procedure is easy to apply and requires only simple data interpretation. • In-situ observations on the surface correlate to modifications inside the bulk. • In-situ observations correlate to EBSD and EFTEM analyses.« less

A Comparative Study on the Static Recrystallization Behavior of Cold-Rolled Mg-3Al-1Zn Alloy Stimulated by Electropulse Treatment and Conventional Heat Treatment

NASA Astrophysics Data System (ADS)

Li, Xiaopei; Li, Xiaohui; Kure-Chu, Song-Zhu; Tang, Guoyi

2017-12-01

Cold-rolled AZ31 Mg alloy strips, with a reduction of 33 pct, were subjected to electropulse treatment (EPT) and conventional heat treatment (HT) to evaluate the respective influences of electropulses and temperature on the recrystallization behavior of AZ31. The highest measured temperature during the EPT (543 K) was used in HT. The electron backscattered diffraction results demonstrated that the EPT-stimulated recrystallization was completed within 8 seconds, whereas for HT, recrystallization was still far from completion even after 240 seconds. It was found that both the nucleation and grain growth of these two processes were totally different. In the EPT samples, nucleation tended to occur preferentially near extension twin boundaries and grain boundaries by continuous recrystallization, whereas in the HT samples, nucleation occurred mainly by grain boundaries bulging via discontinuous recrystallization. As grain growth proceeded, the texture intensities of the EPT samples decreased gradually and finally evolved into an obvious transverse-direction-split texture. This is likely attributable to the impact of electropulses on the boundary energy and the contribution of nonbasal dislocations; however, the basal-type textures of the HT samples were notably strengthened, which is associated with a 30 deg〈0001〉 orientation with respect to the deformed texture.

A Comparative Study on the Static Recrystallization Behavior of Cold-Rolled Mg-3Al-1Zn Alloy Stimulated by Electropulse Treatment and Conventional Heat Treatment

NASA Astrophysics Data System (ADS)

Li, Xiaopei; Li, Xiaohui; Kure-Chu, Song-Zhu; Tang, Guoyi

2018-02-01

Cold-rolled AZ31 Mg alloy strips, with a reduction of 33 pct, were subjected to electropulse treatment (EPT) and conventional heat treatment (HT) to evaluate the respective influences of electropulses and temperature on the recrystallization behavior of AZ31. The highest measured temperature during the EPT (543 K) was used in HT. The electron backscattered diffraction results demonstrated that the EPT-stimulated recrystallization was completed within 8 seconds, whereas for HT, recrystallization was still far from completion even after 240 seconds. It was found that both the nucleation and grain growth of these two processes were totally different. In the EPT samples, nucleation tended to occur preferentially near extension twin boundaries and grain boundaries by continuous recrystallization, whereas in the HT samples, nucleation occurred mainly by grain boundaries bulging via discontinuous recrystallization. As grain growth proceeded, the texture intensities of the EPT samples decreased gradually and finally evolved into an obvious transverse-direction-split texture. This is likely attributable to the impact of electropulses on the boundary energy and the contribution of nonbasal dislocations; however, the basal-type textures of the HT samples were notably strengthened, which is associated with a 30 deg〈0001〉 orientation with respect to the deformed texture.

Cube texture formation during the early stages of recrystallization of Al-1%wt.Mn and AA1050 aluminium alloys

NASA Astrophysics Data System (ADS)

Miszczyk, M. M.; Paul, H.

2015-08-01

The cube texture formation during primary recrystallization was analysed in plane strain deformed samples of a commercial AA1050 alloy and an Al-1%wt.Mn model alloy single crystal of the Goss{110}<001> orientation. The textures were measured with the use of X-ray diffraction and scanning electron microscopy equipped with an electron backscattered diffraction facility. After recrystallization of the Al-1%wt.Mn single crystal, the texture of the recrystallized grains was dominated by four variants of the S{123}<634> orientation. The cube grains were only sporadically detected by the SEM/EBSD system. Nevertheless, an increased density of <111> poles corresponding to the cube orientation was observed. The latter was connected with the superposition of four variants of the S{123}<634> orientation. This indicates that the cube texture after the recrystallization was a ‘compromise texture’. In the case of the recrystallized AA1050 alloy, the strong cube texture results from both the increased density of the particular <111> poles of the four variants of the S orientation and the ∼40°(∼< 111>)-type rotation. The first mechanism transforms the Sdef-oriented areas into Srex ones, whereas the second the near S-oriented, as-deformed areas into near cube-oriented grains.

Influence of Heating Rate on Ferrite Recrystallization and Austenite Formation in Cold-Rolled Microalloyed Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Philippot, C.; Bellavoine, M.; Dumont, M.; Hoummada, K.; Drillet, J.; Hebert, V.; Maugis, P.

2018-01-01

Compared with other dual-phase (DP) steels, initial microstructures of cold-rolled martensite-ferrite have scarcely been investigated, even though they represent a promising industrial alternative to conventional ferrite-pearlite cold-rolled microstructures. In this study, the influence of the heating rate (over the range of 1 to 10 K/s) on the development of microstructures in a microalloyed DP steel is investigated; this includes the tempering of martensite, precipitation of microalloying elements, recrystallization, and austenite formation. This study points out the influence of the degree of ferrite recrystallization prior to the austenite formation, as well as the importance of the cementite distribution. A low heating rate giving a high degree of recrystallization, leads to the formation of coarse austenite grains that are homogenously distributed in the ferrite matrix. However, a high heating rate leading to a low recrystallization degree, results in a banded-like structure with small austenite grains surrounded by large ferrite grains. A combined approach, involving relevant multiscale microstructural characterization and modeling to rationalize the effect of the coupled processes, highlights the role of the cold-worked initial microstructure, here a martensite-ferrite mixture: recrystallization and austenite formation commence in the former martensite islands before extending in the rest of the material.

Investigation of the Atypical Glass Transition and Recrystallization Behavior of Amorphous Prazosin Salts

PubMed Central

Kumar, Lokesh; Popat, Dharmesh; Bansal, Arvind K.

2011-01-01

This manuscript studied the effect of counterion on the glass transition and recrystallization behavior of amorphous salts of prazosin. Three amorphous salts of prazosin, namely, prazosin hydrochloride, prazosin mesylate and prazosin tosylate were prepared by spray drying, and characterized by optical-polarized microscopy, differential scanning calorimetry and powder X-ray diffraction. Modulated differential scanning calorimetry was used to determine the glass transition and recrystallization temperature of amorphous salts. Glass transition of amorphous salts followed the order: prazosin mesylate > prazosin tosylate ∼ prazosin hydrochloride. Amorphous prazosin mesylate and prazosin tosylate showed glass transition, followed by recrystallization. In contrast, amorphous prazosin hydrochloride showed glass transition and recrystallization simultaneously. Density Functional Theory, however, suggested the expected order of glass transition as prazosin hydrochloride > prazosin mesylate > prazosin tosylate. The counterintuitive observation of amorphous prazosin hydrochloride having lower glass transition was explained in terms of its lower activation energy (206.1 kJ/mol) for molecular mobility at Tg, compared to that for amorphous prazosin mesylate (448.5 kJ/mol) and prazosin tosylate (490.7 kJ/mol), and was further correlated to a difference in hydrogen bonding strength of the amorphous and the corresponding recrystallized salts. This study has implications in selection of an optimal amorphous salt form for pharmaceutical development. PMID:24310595

Investigation of the atypical glass transition and recrystallization behavior of amorphous prazosin salts.

PubMed

Kumar, Lokesh; Popat, Dharmesh; Bansal, Arvind K

2011-08-25

This manuscript studied the effect of counterion on the glass transition and recrystallization behavior of amorphous salts of prazosin. Three amorphous salts of prazosin, namely, prazosin hydrochloride, prazosin mesylate and prazosin tosylate were prepared by spray drying, and characterized by optical-polarized microscopy, differential scanning calorimetry and powder X-ray diffraction. Modulated differential scanning calorimetry was used to determine the glass transition and recrystallization temperature of amorphous salts. Glass transition of amorphous salts followed the order: prazosin mesylate > prazosin tosylate ~ prazosin hydrochloride. Amorphous prazosin mesylate and prazosin tosylate showed glass transition, followed by recrystallization. In contrast, amorphous prazosin hydrochloride showed glass transition and recrystallization simultaneously. Density Functional Theory, however, suggested the expected order of glass transition as prazosin hydrochloride > prazosin mesylate > prazosin tosylate. The counterintuitive observation of amorphous prazosin hydrochloride having lower glass transition was explained in terms of its lower activation energy (206.1 kJ/mol) for molecular mobility at Tg, compared to that for amorphous prazosin mesylate (448.5 kJ/mol) and prazosin tosylate (490.7 kJ/mol), and was further correlated to a difference in hydrogen bonding strength of the amorphous and the corresponding recrystallized salts. This study has implications in selection of an optimal amorphous salt form for pharmaceutical development.

Inhibition of Recrystallization of Amorphous Lactose in Nanocomposites Formed by Spray-Drying.

PubMed

Hellrup, Joel; Alderborn, Göran; Mahlin, Denny

2015-11-01

This study aims at investigating the recrystallization of amorphous lactose in nanocomposites. In particular, the focus is on the influence of the nano- to micrometer length scale nanofiller arrangement on the amorphous to crystalline transition. Further, the relative significance of formulation composition and manufacturing process parameters for the properties of the nanocomposite was investigated. Nanocomposites of amorphous lactose and fumed silica were produced by co-spray-drying. Solid-state transformation of the lactose was studied at 43%, 84%, and 94% relative humidity using X-ray powder diffraction and microcalorimetry. Design of experiments was used to analyze spray-drying process parameters and nanocomposite composition as factors influencing the time to 50% recrystallization. The spray-drying process parameters showed no significant influence. However, the recrystallization of the lactose in the nanocomposites was affected by the composition (fraction silica). The recrystallization rate constant decreased as a function of silica content. The lowered recrystallization rate of the lactose in the nanocomposites could be explained by three mechanisms: (1) separation of the amorphous lactose into discrete compartments on a micrometer length scale (compartmentalization), (2) lowered molecular mobility caused by molecular interactions between the lactose molecules and the surface of the silica (rigidification), and/or (3) intraparticle confinement of the amorphous lactose. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Preparation and recrystallization behavior of spray-dried co-amorphous naproxen-indomethacin.

PubMed

Beyer, Andreas; Radi, Lydia; Grohganz, Holger; Löbmann, Korbinian; Rades, Thomas; Leopold, Claudia S

2016-07-01

To improve the dissolution properties and the physical stability of amorphous active pharmaceutical ingredients, small molecule stabilizing agents may be added to prepare co-amorphous systems. The objective of the study was to investigate if spray-drying allows the preparation of co-amorphous drug-drug systems such as naproxen-indomethacin and to examine the influence of the process conditions on the resulting initial sample crystallinity and the recrystallization behavior of the drug(s). For this purpose, the process parameters inlet temperature and pump feed rate were varied according to a 2(2) factorial design and the obtained samples were analyzed with X-ray powder diffractometry and Fourier-transformed infrared spectroscopy. Evaluation of the data revealed that the preparation of fully amorphous samples could be achieved depending on the process conditions. The resulting recrystallization behavior of the samples, such as the total recrystallization rate, the individual recrystallization rates of naproxen and indomethacin as well as the polymorphic form of indomethacin that was formed were influenced by these process conditions. For initially amorphous samples, it was found that naproxen and indomethacin recrystallized almost simultaneously, which supports the theory of formation of drug-drug heterodimers in the co-amorphous phase. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of rolling conditions on recrystallization microstructure and texture in magnetostrictive Fe-Ga-Al rolled sheets

NASA Astrophysics Data System (ADS)

Li, Jiheng; Liu, Yangyang; Li, Xiaojuan; Mu, Xing; Bao, Xiaoqian; Gao, Xuexu

2018-07-01

The effects of different rolling conditions on the microstructure and texture of primary and secondary recrystallization in magnetostrictive Fe82Ga9Al9+0.1at%NbC alloy sheets were investigated. After the primary recrystallization annealing at 850 °C for 5 min, the as-rolled sheets prepared by warm-cold rolling with an intermediate annealing, can be fully recrystallized, and obtain the homogeneous matrix in which the fine dispersed NbC precipitate particles are distributed. The primary recrystallization textures of sheets with different rolling conditions consist mostly of strong {1 0 0} textures, γ-fiber textures, {4 1 1}〈1 4 8〉 texture and weak Goss texture. In the primary recrystallized sheets prepared by warm-cold rolling with an intermediate annealing, the high energy grain boundaries and ∑9 boundaries have the highest proportion. After high temperature annealing, the secondary recrystallizations of Goss grains in these sheets are more complete, and the size of abnormal grown Goss grain is up to several centimeters, which results in the strongest Goss texture. Correspondingly, the largest magnetostriction of 183 ppm is observed. The sample prepared by warm-cold rolling with an intermediate annealing, has homogeneous primary matrix, special texture components and grain boundary distribution, all of which provide a better surrounding for the abnormal growth of Goss grains. This work indicates that the control of rolling conditions of Fe-Ga-Al alloy sheets is necessary to achieve the strong Goss texture and obtain a possible high magnetostriction if other appropriate conditions (stress, domain structure) are achieved.

Improvement of physicomechanical properties of carbamazepine by recrystallization at different pH values.

PubMed

Javadzadeh, Yousef; Mohammadi, Ameneh; Khoei, Nazaninossadat Seyed; Nokhodchi, Ali

2009-06-01

The morphology of crystals has an appreciable impact role on the physicochemical properties of drugs. Drug properties such as flowability, dissolution, hardness and bioavailability may be affected by crystallinity behaviours of drugs. The objective of this study was to achieve an improved physicomechanical property of carbamazepine powder through recrystallization from aqueous solutions at different pH values. For this purpose, carbamazapine was recrystallized from aqueous solutions at different pH values (1, 7, 11). The morphology of crystals was investigated using scanning electron microscopy; X-ray powder diffraction (XRPD) was used to identify polymorphism; thermodynamic properties were analyzed using differential scanning calorimetery (DSC). Dissolution rate was determined using USP dissolution apparatus. Mechanical behavior of recrystallized carbamazepine powders was investigated by making tablets under different compaction pressure and measuring their hardness. SEM studies showed that the carbamazepine crystallization in different media affected the morphology and size of carbamazepine crystals. The shape of carbamazepine crystals changed from flaky or thin plate-like to needle shape. XRPD and DSC results ruled out any crystallinity changes occurring due to the temperature during recrystallization procedure or pH of crystallization media. The crushing strength of tablets indicated that all of the recrystallized carbamazepine samples had better compactiblity than the original carbamazepine powder. In vitro dissolution studies of carbamazepine samples showed a higher dissolution rate for carbamazepine crystals obtained from media with pH 11 and 1. Carbamazepine particles recrystallized from aqueous solutions of different pH values (all media) appeared to have superior mechanical properties to those of the original carbamazepine sample.

Two-step recrystallization of water in concentrated aqueous solution of poly(ethylene glycol).

PubMed

Gemmei-Ide, Makoto; Motonaga, Tetsuya; Kasai, Ryosuke; Kitano, Hiromi

2013-02-21

Crystallization behavior of water in a concentrated aqueous solution of poly(ethylene glycol) (PEG) with a water content of 37.5 wt % was investigated by temperature variable mid-infrared (mid-IR) spectroscopy in a temperature range of 298-170 K. The mid-IR spectrum of water at 298 K showed that a large water cluster was not formed and that most of the water molecules were associated with the PEG chain. Ice formation, however, occurred as found in previous studies by differential scanning calorimetory. Ice formations were grouped into three types: crystallization at 231 K during cooling, that at 198 K during heating, and that at 210 K during heating. The latter two were just recrystallization. These ice formations were the direct transition from hydration species to ice without condensation regardless of crystallization or recrystallization. This means that the recrystallized water in the present system was not generated from low-density amorphous solid water. At a low cooling rate, nearly complete crystallization at 231 K during cooling and no recrystallization were observed. At a high cooling rate, no crystallization and two-step recrystallization at 198 and 210 K were observed. The former and latter recrystallizations were found to be generated from water associated with the PEG chains with ttg (the sequence -O-CH(2)-CH(2)-O- having a trans (t) conformation about the -C-O- bond and a gauche (g) conformation about the -C-C- bond) and random conformations, respectively. These results indicate that recrystallizable water does not have a single specific water structure.

Effect of Thermal History on Microstructures and Mechanical Properties of AZ31 Magnesium Alloy Prepared by Friction Stir Processing

PubMed Central

Chai, Fang; Zhang, Datong; Li, Yuanyuan

2014-01-01

Hot-rolled AZ31 (Mg-2.57Al-0.84Zn-0.32Mn, in mass percentage) magnesium alloy is subjected to friction stir processing in air (normal friction stir processing, NFSP) and under water (submerged friction stir processing, SFSP). Thermal history of the two FSP procedures is measured, and its effect on microstructures and mechanical properties of the experimental materials is investigated. Compared with NFSP, the peak temperature during SFSP is lower and the duration time at a high temperature is shorter due to the enhanced cooling effect of water. Consequently, SFSP results in further grain refinement, and the average grain size of the NFSP and SFSP specimens in the stir zone (SZ) are 2.9 μm and 1.3 μm, respectively. Transmission electron microscopy (TEM) examinations confirm that grain refinement is attributed to continuous dynamic recrystallization both for NFSP and SFSP. The average Vickers hardness in the SZ of the NFSP and SFSP AZ31 magnesium alloy are 76 HV and 87 HV. Furthermore, the ultimate tensile strength and the elongation of the SFSP specimen increase from 191 MPa and 31.3% in the NFSP specimen to 210 MPa and 50.5%, respectively. Both the NFSP and SFSP alloys fail through ductile fracture, but the dimples are much more obvious in the SFSP alloy. PMID:28788532

Deformation Mechanism and Recrystallization Relationships in Galfenol Single Crystals: On the Origin of Goss and Cube Orientations

NASA Astrophysics Data System (ADS)

Na, Suok-Min; Smith, Malcolm; Flatau, Alison B.

2018-06-01

In this work, deformation mechanism related to recrystallization behavior in single-crystal disks of Galfenol (Fe-Ga alloy) was investigated to gain insights into the influence of crystal orientations on structural changes and selective grain growth that take place during secondary recrystallization. We started with the three kinds of single-crystal samples with (011)[100], (001)[100], and (001)[110] orientations, which were rolled and annealed to promote the formation of different grain structures and texture evolutions. The initial Goss-oriented (011)[100] crystal mostly rotated into {111}<112> orientations with twofold symmetry and shear band structures by twinning resulted in the exposure of rolled surface along {001}<110> orientation during rolling. In contrast, the Cube-oriented (001)[100] single crystal had no change in texture during rolling with the thickness reduction up to 50 pct. The {123}<111> slip systems were preferentially activated in these single crystals during deformation as well as {112}<111> slip systems that are known to play a role in primary slip of body-centered cubic (BCC) materials such as α-iron and Fe-Si alloys. After annealing, the deformed Cube-oriented single crystal had a small fraction (<10 pct) of recrystallized Goss-oriented grains. The weak Goss component remained in the shear bands of the 50 pct rolled Goss-oriented single crystal, and it appeared to be associated with coalescence of subgrains inside shear band structures during primary recrystallization. Rolling of the (001)[110] single crystal led to the formation of a tilted (001)[100] component close to the <120> orientation, associated with {123}<111> slip systems as well. This was expected to provide potential sites of nucleation for secondary recrystallization; however, no Goss- and Cube-oriented components actually developed in this sample during secondary recrystallization. Those results illustrated how the recrystallization behavior can be influenced by deformed structure and the slip systems.

Evolution of microstructure and grain boundary character distribution of a tin bronze annealed at different temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Weijiu; Chongqing Municipal Key Laboratory of Institutions of Higher Education for Mould Technology, Chongqing University of Technology, Chongqing 400054; Chai, Linjiang, E-mail: chailinjiang@cqut.edu.cn

2016-04-15

Specimens cut from a rolled tin bronze sheet were annealed at 400–800 °C for 1 h and evolution of their microstructures was then characterized in details by electron channeling contrast imaging and electron backscatter diffraction techniques. Particularly, statistics on special boundaries (SBs) with Σ ≤ 29 and network connectivity of random high angle boundaries (HABs) in the annealed specimens were examined to probe optimization potentials of grain boundary character distribution (GBCD) for this material. Results show that the deformed microstructure in the as-received material begins to be recrystallized when the annealing temperature increase to 500 °C and average grain sizesmore » surge with further increasing temperatures. As a result of the recrystallization, a large number of annealing twins (with Σ3 misorientation) are produced, leading to remarkably increased fractions of SBs (f{sub SBs}). Thanks to preexisting dense low angle boundaries, the majority of SBs in the 500 °C specimen with only partial recrystallization are Σ3{sub ic} (incoherent) boundaries, which effectively disrupt connectivity of random HABs network. Although the f{sub SBs} can be further increased (up to 72.5%) in specimens with full recrystallization (at higher temperatures), the Σ3{sub ic} boundaries would be replaced to some extent by Σ3{sub c} (coherent) boundaries which do not contribute directly to optimizing the GBCD. This work should be able to provide clear suggestions on applying the concept of grain boundary engineering to tin bronze alloys. - Highlights: • The rolled tin bronze begins to be recrystallized as temperature increases to 500 °C. • A lot of SBs are produced after recrystallization and the highest f{sub SBs} is 72.5%. • Partially recrystallized specimen has the optimum GBCD due to more Σ3{sub ic} boundaries. • The Σ3{sub ic} boundaries are replaced by Σ3{sub c} boundaries after full recrystallization.« less

User-independent EBSD parameters to study the progress of recovery and recrystallization in Cu-Zn alloy during in situ heating.

PubMed

Sharma, N K; Shekhar, S

2016-12-01

Microstructural evolution of cold-rolled Cu-5%Zn alloy during in situ heating inside field-emission scanning electron microscope was utilized to obtain user-independent parameters in order to trace the progress of static recovery and recrystallization. Electron back-scattered diffraction (EBSD)-based orientation imaging microscopy was used to obtain micrographs at various stages of in situ heating. It is shown that unlike the pre-existing methods, additional EBSD-based parameter can be used to trace the progress of recovery and recrystallization, which is not dependent on user input and hence less prone to error. True strain of 0.3 was imposed during cold rolling of alloy sample. Rolled sample was subjected to in situ heating from room temperature to 500°C (∼0.58 Tm) with soaking time of 10 min, at each of the intermediate temperatures viz. 100, 200, 300, 400 and 450°C. After reaching 500°C, the sample was kept at this temperature for a maximum duration of around 15 h. The sample showed clear signs of recovery for temperature up to 450°C, and at 500°C, recrystallization started to take place. Recrystallization kinetics was moderate, and full recrystallization was achieved in approximately 120 min. We found that EBSD parameter, namely, band contrast intensity can be used as an extra handle to map out the progress of recrystallization occurring in the sample. By contrast, mean angular deviation can be used to understand the evolution of recovery in samples. The parameters mentioned in the current study, unlike other pre-existing methods, can also be used for mapping local microstructural transformations due to recovery and recrystallization. We discuss the benefits and limitations in using these additional handles in understanding the changes taking place in the material during in situ heating. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

Repeated occurrences of methanogenic zones, diagenetic dolomite formation and linked silicate alteration in southern Bering Sea sediments (Bowers Ridge, IODP Exp. 323 Site U1341)

NASA Astrophysics Data System (ADS)

Wehrmann, L. M.; Ockert, C.; Mix, A. C.; Gussone, N.; Teichert, B. M. A.; Meister, P.

2016-03-01

Diagenetic precipitates, such as dolomite, and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments. A 600 m thick sedimentary section, recently drilled at Integrated Ocean Drilling Program (IODP) Site U1341 on Bowers Ridge (southern Bering Sea), provides insight into such a 4.3 Ma old paleo-diagenetic archive. Hard-lithified calcite-dolomite layers, and laminae of disseminated carbonate, were recovered in diatom-rich sediments over a depth range of 400 m. Carbon isotope values of the diagenetic carbonates between -16.6 and -14.4‰ (VPDB) and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon (DIC) during elevated rates of organic carbon mineralization, primarily via sulfate reduction, at shallow sediment depth below the paleo-seafloor. Diagenetic carbonates at 280-440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane (AOM) at sulfate-methane transition zones (SMTZ). These microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2.58-2.51 Ma. A minimum in sulfate concentrations in modern porewaters and low sedimentary Ba/Al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone. The minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations, less radiogenic strontium and isotopically light calcium in the porewater. It is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater. The isotopic composition of porewater calcium was also influenced by ammonium-calcium exchange on clay minerals and carbonate recrystallization. Our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites (>2000 m water depth) over prolonged timescales. It shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization.

Meteoric water in metamorphic core complexes

NASA Astrophysics Data System (ADS)

Teyssier, Christian; Mulch, Andreas

2015-04-01

The trace of surface water has been found in all detachment shear zones that bound the Cordilleran metamorphic core complexes of North America. DeltaD values of mica fish in detachment mylonites demonstrate that these synkinematic minerals grew in the presence of meteoric water. Typically deltaD values are very negative (-120 to -160 per mil) corresponding to deltaD values of water that are < -100 per mil given the temperature of water-mica isotopic equilibration (300-500C). From British Columbia (Canada) to Nevada (USA) detachment systems bound a series of core complexes: the Thor-Odin, Valhalla, Kettle-Okanogan, Bitterroot -Anaconda, Pioneer, Raft River, Ruby Mountain, and Snake Range. The bounding shear zones range in thickness from ~100 m to ~1 km, and within the shear zones, meteoric water signature is recognized over 10s to 100s of meters beneath the detachment fault. The age of shearing ranges generally from Eocene in the N (~50-45 Ma) to Oligo-Miocene in the S (25-15 Ma). DeltaD water values derived from mica fish in shear zones are consistent with supradetachment basin records of the same age brackets and can be used for paleoaltimetry if coeval isotopic records from near sea level are available. Results show that a wave of topography (typically 4000-5000 m) developed from N to S along the Cordillera belt from Eocene to Miocene, accompanied by the propagation of extensional deformation and volcanic activity. In addition, each detachment system informs a particular extensional detachment process. For example, the thick Thor-Odin detachment shear zone provides sufficient age resolution to indicate the downward propagation of shearing and the progressive incorporation of footwall rocks into the hanging wall. The Kettle detachment provides a clear illustration of the dependence of fluid circulation on dynamic recrystallization processes. The Raft River system consists of a thick Eocene shear zone that was overprinted by Miocene shearing; channels of meteoric paleofluids can be traced into a zone of pervasive flow (in the direction of extension from W to E) in which a high transient geotherm is preserved. In the Snake Range the pattern of meteoric signature is consistent with the expected diachronous fluid-rock interaction that would be expected from a rolling-hinge detachment; in the arched section of the detachment meteoric fluid-rock interaction was cut-off early, while the long-lived portion of the E-dipping detachment continued to receive surface fluids. In summary, the hydrology of extending crust involves circulation of surface fluids through the upper crust to the ductile detachment shear zones in the root system of normal faults. Synkinematic hydrous phases encapsulate the signature of meteoric fluids and indicate high-elevation catchment areas for the Cordillera, with development of topography from N to S over Cenozoic time. Meteoric fluids leave a distinct stable isotopic signature that tracks the spatial and temporal interaction among fluid, rock, and structures/ microstructures, and provides useful fingerprints of the inter-relationship between tectonics and crustal hydrology.

The Deformation Behavior and Microstructure Evolution of a Mn- and Cr-Containing Al-Mg-Si-Cu Alloy During Hot Compression and Subsequent Heat Treatment

NASA Astrophysics Data System (ADS)

Xu, Yi; Nagaumi, Hiromi; Han, Yi; Zhang, Gongwang; Zhai, Tongguang

2017-03-01

Hot compression tests on a newly developed Mn- and Cr-containing Al-Mg-Si-Cu alloy were carried out at temperatures ranging from 623 K (350 °C) to 823 K (550 °C) and strain rates between 0.001 and 1 s-1 after casting and subsequent homogenization heat treatment. The true stress-true strain curves of the alloy exhibited a peak stress at a small plastic strain followed by dynamic flow softening. Using the constitutive equation containing the strain rate, peak stress, and temperature, the activation energy for hot deformation in the alloy was determined to be 249.67 kJ/mol, much higher than that (143.4 kJ/mol) for self-diffusion in pure Al. Scanning transmission electron microscopy experiments revealed that Mn- and Cr-containing α-dispersoids formed during homogenization showed a strong pinning effect on dislocations and grain boundaries, which was responsible for the increase in activation energy for hot deformation in the alloy. A threshold stress was consequently introduced and determined in the constitutive equation to count for the dispersoid hardening effect on hot deformation in the alloy. Electron back-scatter diffraction measurements revealed that the softening occurred in the alloy was mainly due to dynamic recovery taking place at relatively large Z values, and that it was dominated by continuous dynamic recrystallization at relatively low Z. In subsequent annealing after hot deformation at large Z, abnormal grain growth could occur, as a result of the critical strain-annealing effect. After upsetting at higher temperatures, the alloy showed superior tensile properties due to a high non-recrystallized area fraction.

Effect of Aluminum on the Microstructure and Properties of Two Refractory High-Entropy Alloys (Postprint)

DTIC Science & Technology

2014-04-01

The chemical compositions of the recrystallized ic release; distribution unlimited. Fig. 5. (a) Equiaxed grain structure of the annealed...deformation bands crossing a grain boundary; (c) fine recrystallized grains formed at grain boundaries; (d) a higher magnification image shows the...presence of nano-precipitates at the boundaries of the recrystallized grains. 220 O.N. Senkov et al. / Acta Materialia 68 (2014) 214–228and non

Research and Process-Optimization on Mixed Crystal Caused Uneven-Performance of High-strength Structural Car Steel QStE500TM

NASA Astrophysics Data System (ADS)

Jian-wen, Li; Hong-yan, Liu

Handan Iron and Steel production of high-strength structural car steel QStE500TM thin gauge products using Nb + Ti composite strengthening, with a small amount of Cr element to improve its hardenability, the process parameter control is inappropriate with Nb + Ti complex steel, it is easy to produce in the mixed crystal phenomenon, resulting in decreasing the toughness and uneven performance. In this paper, Gleeble 3500 thermal simulation testing machine for high-strength structural steel car QStE500TM product deformation austenite recrystallization behavior research, determined completely recrystallized, partial recrystallization and non-recrystallization region, provide theoretical basis and necessary data for reasonable controlled rolling process for production.

Ice-Active Substances from the Infective Juveniles of the Freeze Tolerant Entomopathogenic Nematode, Steinernema feltiae.

PubMed

Ali, Farman; Wharton, David A

2016-01-01

Steinernema feltiae is a moderately freezing tolerant nematode, that can withstand intracellular ice formation. We investigated recrystallization inhibition, thermal hysteresis and ice nucleation activities in the infective juveniles of S. feltiae. Both the splat cooling assay and optical recrystallometry indicate the presence of ice active substances that inhibit recrystallization in the nematode extract. The substance is relatively heat stable and largely retains the recrystallization inhibition activity after heating. No thermal hysteresis activity was detected but the extract had a typical hexagonal crystal shape when grown from a single seed crystal and weak ice nucleation activity. An ice active substance is present in a low concentration, which may be involved in the freezing survival of this species by inhibiting ice recrystallization.

Electron backscatter diffraction study of deformation and recrystallization textures of individual phases in a cross-rolled duplex steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaid, Md; Bhattacharjee, P.P., E-mail: pinakib@iith.ac.in

2014-10-15

The evolution of microstructure and texture during cross-rolling and annealing was investigated by electron backscatter diffraction in a ferritic–austenitic duplex stainless steel. For this purpose an alloy with nearly equal volume fraction of the two phases was deformed by multi-pass cross-rolling process up to 90% reduction in thickness. The rolling and transverse directions were mutually interchanged in each pass by rotating the sample by 90° around the normal direction. In order to avoid deformation induced phase transformation and dynamic strain aging, the rolling was carried out at an optimized temperature of 898 K (625 °C) at the warm-deformation range. Themore » microstructure after cross warm-rolling revealed a lamellar structure with alternate arrangement of the bands of two phases. Strong brass and rotated brass components were observed in austenite in the steel after processing by cross warm-rolling. The ferrite in the cross warm-rolling processed steel showed remarkably strong RD-fiber (RD//< 011 >) component (001)< 011 >. The development of texture in the two phases after processing by cross warm-rolling could be explained by the stability of the texture components. During isothermal annealing of the 90% cross warm-rolling processed material the lamellar morphology was retained before collapse of the lamellar structure to the mutual interpenetration of the phase bands. Ferrite showed recovery resulting in annealing texture similar to the deformation texture. In contrast, the austenite showed primary recrystallization without preferential orientation selection leading to the retention of deformation texture. The evolution of deformation and annealing texture in the two phases of the steel was independent of one another. - Highlights: • Effect of cross warm-rolling on texture formation is studied in duplex steel. • Brass texture in austenite and (001)<110 > in ferrite are developed. • Ferrite shows recovery during annealing retaining the (001)<110 > component. • Austenite shows recrystallization during annealing retaining the deformation texture. • The deformation of recrystallization of two phases is independent of one other.« less

Reconstruction of 3d grain boundaries from rock thin sections, using polarised light

NASA Astrophysics Data System (ADS)

Markus Hammes, Daniel; Peternell, Mark

2016-04-01

Grain boundaries affect the physical and chemical properties of polycrystalline materials significantly by initiating reactions and collecting impurities (Birchenall, 1959), and play an essential role in recrystallization (Doherty et al. 1997). In particular, the shape and crystallographic orientation of grain boundaries reveal the deformation and annealing history of rocks (Kruhl and Peternell 2002, Kuntcheva et al. 2006). However, there is a lack of non-destructive and easy-to-use computer supported methods to determine grain boundary geometries in 3D. The only available instrument using optical light to measure grain boundary angles is still the polarising microscope with attached universal stage; operated manually and time-consuming in use. Here we present a new approach to determine 3d grain boundary orientations from 2D rock thin sections. The data is recorded by using an automatic fabric analyser microscope (Peternell et al., 2010). Due to its unique arrangement of 9 light directions the highest birefringence colour due to each light direction and crystal orientation (retardation) can be determined at each pixel in the field of view. Retardation profiles across grain boundaries enable the calculation of grain boundary angle and direction. The data for all positions separating the grains are combined and further processed. In combination with the lateral position of the grain boundary, acquired using the FAME software (Hammes and Peternell, in review), the data is used to reconstruct a 3d grain boundary model. The processing of data is almost fully automatic by using MATLAB®. Only minor manual input is required. The applicability was demonstrated on quartzite samples, but the method is not solely restricted on quartz grains and other birefringent polycrystalline materials could be used instead. References: Birchenall, C.E., 1959: Physical Metallurgy. McGraw-Hill, New York. Doherty, R.D., Hughes, D.A., Humphreys, F.J., Jonas, J.J., Juul Jensen, D., Kassner, M.E., King, W.E., McNelley, T.R., McQueen, H.J., Rollett, A.D., 1997: Current issues in recrystallization: a review. Materials Science and Engineering A 238, 219-274. Hammes, D.M., Peternell, M., in review. FAME: Software for analysing rock microstructures. Computers & Geoscience. Kruhl, J.H., Peternell, M., 2002. The equilibration of high-angle grain boundaries in dynamically recrystallized quartz: the effect of crystallography and temperature. Journal of Structural Geology 24, 1125-1137. Kuntcheva, B., Kruhl, J.H. & Kunze, K., 2006. Crystallographic orientation of high-angle grain boundaries in dynamically recrystallized quartz: First results. Tectonophysics 421, 331-346. Peternell, M., Hasalová, P., Wilson, J.L., Piaziolo, S., Schulmann, K., 2010. Evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using EBSD and fabric analyser techniques. Journal of Structural Geology 32, 803-817.

Towards the determination of deformation rates - pinch-and-swell structures as a natural and simulated paleo-strain rate gage

NASA Astrophysics Data System (ADS)

Peters, Max; Poulet, Thomas; Karrech, Ali; Regenauer-Lieb, Klaus; Herwegh, Marco

2014-05-01

Layered rocks deformed under viscous deformation conditions frequently show boudinage, a phenomenon that results from differences in effective viscosity between the involved layers. In the case of continuous necking of a mechanically stiffer layer embedded in a weaker matrix, symmetric boudins are interpreted as the result of dominant visco-plastic deformation (Goscombe et al., 2004). However, information on the physical conditions, material properties and deformation processes are yet unknown. Natural samples deformed under low-grade (T<350°C) metamorphic conditions were studied in detail in the Dent de Morcles and Doldenhorn nappes of the Helvetic Alps in order to accurately simulate their deformation styles by numerical models. In these samples, monomineralic calcite (Cc) veins were repeatedly boudinaged on cm- to µm-scale. Remnants of incompletely recrystallized original vein Cc grains in the swells indicate a sequence of deformation twinning, followed by progressive dynamic recrystallization along former twin planes up to complete recrystallization in the pinches (Schmalholz and Maeder, 2012). This sequence suggests dislocation creep to be active as important deformation mechanism. In contrast to the pinch-and-swell structures, the grain size of the Cc in the surrounding matrix is much finer-grained due to pinning by secondary particles, forcing the matrix to deform under viscous granular creep, i.e. by diffusion accommodated grain boundary sliding. The deformation processes observed in the natural samples were incorporated into a numerical model in order to evaluate the rheology of both layer and matrix, using an extension to a user material subroutine (Karrech et al., 2011a) for the finite element solver ABAQUS. We implemented thermo-mechanical coupling allowing elastic, viscous and plastic deformation of Cc (Herwegh et al., in press). We simulate a pure-shear box using finite elements, each representing a grain size distribution, which undergo layer-parallel extension. The box is built up by 3 layers, consisting of a central layer of coarse-grained populations, surrounded by finer-grained populations on bottom and top. The rheology evolves from transient stages (elasticity and strain hardening) to composite viscous flow (GSI & GSS) with increasing shear strain. The small grain sizes in top and bottom layers are strain-invariant and limited in their growth (comparable to Zener pinning) forcing the matrix to deform by exclusively by GSS creep. In contrast, the initially coarse grain sizes of the central layer are allowed to adapt to the physical deformation conditions by either grain growth or grain size reduction following the Paleowattmeter of Austin and Evans (2007) combined with the thermodynamic approach of Regenauer-Lieb and Yuen (2004). Depending on the dissipated energy, grain sizes in these domains vary substantially in space and time. While low strain rates (low stresses) in the swells favor grain growth and GSI dominated deformation, high strain rates in the pinches provoke dramatic grain size reduction with an increasing contribution of GSS as a function of decreasing grain size. The development of symmetric necks observed in nature thus seems to coincide with the transition from dislocation to diffusion creep dominated flow with continuous grain size reduction and growth from swell to neck at relatively high extensional strains. REFERENCES Austin, N. and Evans, B. (2007). Paleowattmeters: A scaling relation for dynamically recrystallized grain size. Geology, 35. Goscombe, B.D., Passchier, C.W. and Hand, M. (2004). Boudinage classification: End-member boudin types and modified boudin structures, Journal of Structural Geology, 26. Herwegh, M., Poulet, T., Karrech, A. and Regenauer-Lieb, K. (in press). From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling. Journal of Geophysical Research. Karrech, A., Regenauer-Lieb, K. and Poulet, T. (2011a). A Damaged visco-plasticity model for pressure and temperature sensitive geomaterials. Journal of Engineering Science 49. Regenauer-Lieb, K. and Yuen, D. (2004). Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics. Physics of the Earth and Planetary Interiors, 142. Schmalholz, S.M. and Maeder, X. (2012). Pinch-and-swell structure and shear zones in viscoplastic layers. Journal of Structural Geology, 34.

Microstructure and crystallographic preferred orientation of polycrystalline microgarnet aggregates developed during progressive creep, recovery, and grain boundary sliding

USGS Publications Warehouse

Massey, M.A.; Prior, D.J.; Moecher, D.P.

2011-01-01

Optical microscopy, electron probe microanalysis, and electron backscatter diffraction methods have been used to examine a broad range of garnet microstructures within a high strain zone that marks the western margin of a major transpression zone in the southern New England Appalachians. Garnet accommodated variable states of finite strain, expressed as low strain porphyroclasts (Type 1), high strain polycrystalline aggregates (Type 2), and transitional morphologies (Type 3) that range between these end members. Type 1 behaved as rigid porphyroclasts and is characterized by four concentric Ca growth zones. Type 2 help define foliation and lineation, are characterized by three Ca zones, and possess a consistent bulk crystallographic preferred orientation of (100) symmetrical to the tectonic fabric. Type 3 show variable degrees of porphyroclast associated with aggregate, where porphyroclasts display complex compositional zoning that corresponds to lattice distortion, low-angle boundaries, and subgrains, and aggregate CPO mimics porphyroclast orientation. All aggregates accommodated a significant proportion of greenschist facies deformation through grain boundary sliding, grain rotation and impingement, and pressure solution, which lead to a cohesive behavior and overall strain hardening of the aggregates. The characteristic CPO could not have been developed in this manner, and was the result of an older phase of partitioned amphibolite facies dislocation creep, recovery including chemical segregation, and recrystallization of porphyroclasts. This study demonstrates the significance of strain accommodation within garnet and its affect on composition under a range of PT conditions, and emphasizes the importance of utilizing EBSD methods with studies that rely upon a sound understanding of garnet. ?? 2010 Elsevier Ltd.

Barite recrystallization in the presence of 226Ra and 133Ba

NASA Astrophysics Data System (ADS)

Heberling, Frank; Metz, Volker; Böttle, Melanie; Curti, Enzo; Geckeis, Horst

2018-07-01

Despite the long history of studies on (Ba,Ra)SO4, various recent investigations aimed at improving our understanding of its formation processes and thermodynamics. Accumulation of natural Ra isotopes (mainly 226Ra and 228Ra) in (Ba,Ra)SO4 plays an important role in many geotechnical applications and water desalination facilities. In the near field of a nuclear waste repository, barite formation may be expected e.g. as a consequence of contact of spent nuclear fuel or vitrified high level waste with sulfate containing ground water, and may control the potential release of Ra from waste forms upon leakage. Here, we present results of long term batch-type barite recrystallization experiments conducted in the simultaneous presence of 226Ra and 133Ba as a function of initial Ra2+ concentration and pH with the same type and charge of barite powder as used in previous studies (Curti et al., 2010; Klinkenberg et al., 2014; Brandt et al., 2015). Due to the simultaneous measurement of 133Ba and 226Ra our data allow for a direct relation of 226Ra uptake with barite recrystallization, which leads to more accurate partition coefficients compared to previous studies. During a reaction period of five years, barite is continuously recrystallizing. Within the investigated radium concentration range (Ba(1-X)RaXSO4 with X < 0.0006), we measure a partition coefficient of D = 2.1 ± 0.5. The partition coefficient is constant within uncertainty during almost five years (1793 days) of experimental duration. This value is in line with a description of (Ba,Ra)SO4 as an ideal solid solution based on the solubility products (KSP) of the endmembers barite (log10(KSP(barite)) = -9.97) and radium sulfate (log10(KSP(RaSO4)) = -10.26; dimensionless Guggenheim parameter, a0 = 0.0 ± 0.3). Apparent discrepancies to previous theoretical results (a0 = 1.0 ± 0.4) may be resolved when the uncertainties related to the solubility of RaSO4 are considered. Compared to results of previous publications, recrystallization is extremely slow in the experiments presented here. While previous authors suggested complete equilibration of bulk microcrystalline barite within less than three years, a recrystallization of less than 7% of the barite mass is observed within five years. We describe the progress of recrystallization with a new modified homogeneous recrystallization model. Observed recrystallization rates are in the range 0.11-1.5 nmol/(m2 s) and increase with decreasing pH. According to this modified homogeneous recrystallization model, complete bulk barite equilibration is expected in about 1400-16,900 years. The strongly decreased recrystallization kinetics in our experiments is likely related to a strongly prolonged pre-equilibration time (0.8 years), which according to XRD investigations, leads to a higher crystallinity (higher crystal domain size and lower Debye-Waller parameters) of the barite powder.

[Comporison Sduty of Microstructure by Metallographicalk on the Polarized Light and Texture by XRD of CC 5083 and CC 5182 Aluminium Alloy after Cold Rolling and Recrystallization].

PubMed

Chen, Ming-biao; Li, Yong-wei; Tan, Yuan-biao; Ma, Min; Wang, Xue-min; Liu, Wen-chang

2015-03-01

At present the study of relation between microstructure, texture and performance of CC 5083 aluminium alloy after cold tolling and recrystallization processes is still finitude. So that the use of the CC 5083 aluminium alloy be influenced. Be cased into electrical furnace, hot up with unlimited speed followed the furnace hot up to different temperature and annealed 2h respectively, and be cased into salt-beth furnace, hot up quickly to different temperature and annealed 30 min respectively for CC 5083 and CC 5182 aluminum alloy after cold roling with 91.5% reduction. The microstructure be watched use metallographic microscope, the texture be inspected by XRD. The start temperature of recrystallization and grain grow up temperature within annealing in the electric furnace of CC 5083 aluminum alloy board is 343 degrees C, and the shap of grain after grow up with long strip (the innovation point ); The start temperature of recrystallization within annealling in the salt bath furnace of CC 5083 is 343 degrees C. The start temperature and end temperature of recrystallization within annealling of CC 5083 and CC 5182 aluminum alloy is 371 degrees C. The grain grow up outstanding of cold rooled CC 5152 aluminum alloy after annealed with 454 degrees C in the electric furnace and salt bath furnace. The start temperature of grain grow up of CC 5083 alluminurn alloy annealed in the electric furnace and salt bath furnace respectively is higher than the start temperature of grain grow up of CC 5182 alluminum alloy annealed in the electric furnace and salt bath furnace respectively. The strat temperature of recrystallization grain grow up is higher than which annealled with other three manner annealing process. The recrystallization temperature of CC 5182 annealed in the salt bath furnace is higher than which annealed in the electric furnace. The recrystallization temperature of the surface layer of CC 5083 and CC 5182 aluminum alloy is higher than the inner layer (the innovation point). There is a difference each other of the structure and the texture of the four manner annealing aluminum alloy (the innovation point). There is a little difference at the recrystallization processes course reflectived by the observe results of structure transform and by the examination results of texture transmission.

Magnetic resonance diffusion and relaxation characterization of water in the unfrozen vein network in polycrystalline ice and its response to microbial metabolic products

NASA Astrophysics Data System (ADS)

Brown, Jennifer R.; Brox, Timothy I.; Vogt, Sarah J.; Seymour, Joseph D.; Skidmore, Mark L.; Codd, Sarah L.

2012-12-01

Polycrystalline ice, as found in glaciers and the ice sheets of Antarctica, is a low porosity porous media consisting of a complicated and dynamic pore structure of liquid-filled intercrystalline veins within a solid ice matrix. In this work, Nuclear Magnetic Resonance measurements of relaxation rates and molecular diffusion, useful for probing pore structure and transport dynamics in porous systems, were used to physically characterize the unfrozen vein network structure in ice and its response to the presence of metabolic products produced by V3519-10, a cold tolerant microorganism isolated from the Vostok ice core. Recent research has found microorganisms that can remain viable and even metabolically active within icy environments at sub-zero temperatures. One potential mechanism of survival for V3519-10 is secretion of an extracellular ice binding protein that binds to the prism face of ice crystals and inhibits ice recrystallization, a coarsening process resulting in crystal growth with ice aging. Understanding the impact of ice binding activity on the bulk vein network structure in ice is important to modeling of frozen geophysical systems and in development of ice interacting proteins for biotechnology applications, such as cryopreservation of cell lines, and manufacturing processes in food sciences. Here, we present the first observations of recrystallization inhibition in low porosity ice containing V3519-10 extracellular protein extract as measured with Nuclear Magnetic Resonance and Magnetic Resonance Imaging.

Recrystallization and grain growth phenomena in a particle-reinforced aluminum composite

NASA Astrophysics Data System (ADS)

van Aken, D. C.; Krajewski, P. E.; Vyletel, G. M.; Allison, J. E.; Jones, J. W.

1995-06-01

Recrystallization and grain growth in a 2219/TiC/15p composite were investigated as functions of the amount of deformation and deformation temperature. Both cold and hot deformed samples were annealed at the normal solution treatment temperature of 535 °C. It was shown that large recrystallized grain diameters, relative to the interparticle spacing, could be produced in a narrow range of deformation for samples cold-worked and those hot-worked below 450 °C. For cold-worked samples, between 4 to 6 pct deformation, the recrystallized grain diameters varied from 530 to 66 μm as the amount of deformation increased. Subsequent grain growth was not observed in these recrystallized materials and noncompact grain shapes were observed. For deformations greater than 15 pct, recrystallized grain diameters less than the interparticle spacing were observed and subsequent grain growth produced a pinned grain diameter of 27 μm. The pinned grain diameter agreed well with an empirical model based on three dimensional (3-D) Monte Carlo simulations of grain growth and particle pinning in a two-phase material. Tensile properties were determined as a function of grain size, and it was shown that grain size had a weak influence on yield strength. A maximum in the yield strength was observed at a grain size larger than the normal grain growth and particle-pinned diameter.

[Investigation of the recrystallization of trehalose as a good glass-former excipient].

PubMed

Katona, Gábor; Orsolya, Jójártné Laczkovich; Szabóné, Révész Piroska

2014-01-01

An amorphous form of trehalose is easy to prepare by using a solvent method. The recrystallization kinetics can be followed well, which is important because of the occurrence of polymorphic forms of trehalose. This is especially significant in the case of dry powder inhalers. Spray-drying was used as a preparation method this being one of the most efficient technologies with which to obtain an amorphous form. This method can result in the required particle size and a monodisperse distribution with excellent flowability and with moreover considerable amorphization. In our work, trehalose was applied as a technological auxiliary agent, and literature data relating to the spray-drying technology of trehalose were collected. Studies were made of the influence of the spraying process on the amorphization of trehalose and on the recrystallization of amorphous trehalose during storage. Amorphous samples were investigated under 3 different conditions during 3 months. The recrystallization process was followed by differential scanning calorimetry and X-ray powder diffraction. The results demonstrated the perfect amorphization of trehalose during the spray-drying process. The glass transition temperature was well measurable in the samples and proved to be the same as the literature data. Recrystallization under normal conditions was very slow but at high relative humidity the process was accelerated greatly. Amorphous trehalose gave rise to dihydrate forms (gamma- and h-trehaloses) during recrystallization, and beta-trehalose was also identified as an anhydrous form.

Composite Magnetite and Protein Containing CaCO3 Crystals. External Manipulation and Vaterite → Calcite Recrystallization-Mediated Release Performance.

PubMed

Sergeeva, Alena; Sergeev, Roman; Lengert, Ekaterina; Zakharevich, Andrey; Parakhonskiy, Bogdan; Gorin, Dmitry; Sergeev, Sergey; Volodkin, Dmitry

2015-09-30

Biocompatibility and high loading capacity of mesoporous CaCO3 vaterite crystals give an option to utilize the polycrystals for a wide range of (bio)applications. Formation and transformations of calcium carbonate polymorphs have been studied for decades, aimed at both basic and applied research interests. Here, composite multilayer-coated calcium carbonate polycrystals containing Fe3O4 magnetite nanoparticles and model protein lysozyme are fabricated. The structure of the composite polycrystals and vaterite → calcite recrystallization kinetics are studied. The recrystallization results in release of both loaded protein and Fe3O4 nanoparticles (magnetic manipulation is thus lost). Fe3O4 nanoparticles enhance the recrystallization that can be induced by reduction of the local pH with citric acid and reduction of the polycrystal crystallinity. Oppositely, the layer-by-layer assembled poly(allylamine hydrochloride)/poly(sodium styrenesulfonate) polyelectrolyte coating significantly inhibits the vaterite → calcite recrystallization (from hours to days) most likely due to suppression of the ion exchange giving an option to easily tune the release kinetics for a wide time scale, for example, for prolonged release. Moreover, the recrystallization of the coated crystals results in formulation of multilayer capsules keeping the feature of external manipulation. This study can help to design multifunctional microstructures with tailor-made characteristics for loading and controlled release as well as for external manipulation.

Recrystallization in Si upon ion irradiation at room temperature in Co/Si(111) thin film systems

NASA Astrophysics Data System (ADS)

Banu, Nasrin; Satpati, B.; Dev, B. N.

2018-04-01

After several decades of research it was concluded that for a constant flux recrystallization in Si upon ion irradiation is possible only at high temperature. At low temperature or at room temperature only amorphization can take place. However we have observed recrystallization in Si upon ion irradiation at room temperature in a Co/Si thin film system. The Co/Si sample was prepared by deposition of 25 nm Co on clean Si(111) substrate. An oxide layer (˜ 2nm) of cobalt at the top of the film due to air exposure. The ion irradiation was done at room temperature under high vacuum with 1MeV Si+ ion with low beam current < 400 nA. Earlier we have shown similar ion induced recrystallization in Si(100) substrate which had a sandwich Si/Ni/Si structure. This system had an epitaxial buffer Si layer on Si substrate. This study also shows that the phenomenon is independent of substrate orientation and buffer layer. We have used transmission electron microscopy (TEM) to study the recrystallization behavior.

Purification and crystal growth of NPB via imidazolium based ionic liquids

NASA Astrophysics Data System (ADS)

Oh, Yong-Taeg; Shin, Dong-Chan

2018-04-01

Here we report the production of high purity and crystallinity organic electronic material of NPB (N,N‧-Di-[(1-naphthyl)-N,N‧-diphenyl]-1,1‧-biphenyl-4,4‧-diamine (C44H32N2) through solution recrystallization within imidazolium based ionic liquids. When low purity NPB was recrystallized at 170 °C within C8MIM[TFSI], its purity was drastically improved from 82% to 99.92%. These recrystallized NPB crystals showed 0.040° FWHM (Full Width Half Maximum) of X-ray (1 1 1) diffraction peak. Such small FWHM angle indicates single-crystal like crystallinity. Initial NPB powder was dissolved at 100 °C and recrystallized at temperature above 110 °C. At higher temperature of 170 °C, a small number of bigger crystals were formed compared to those at 110 °C. This can be well explained by the classical nucleation and growth theory. Therefore, solution recrystallization process using ionic liquid might be promising for mass production of organic electronic materials by replacing the widely-used sublimation purification method.

Microstructural Evolution During Cold Rolling and Subsequent Annealing in Low-Carbon Steel with Different Initial Microstructures

NASA Astrophysics Data System (ADS)

Ogawa, Toshio; Dannoshita, Hiroyuki; Maruoka, Kuniaki; Ushioda, Kohsaku

2017-08-01

Microstructural evolution during cold rolling and subsequent annealing of low-carbon steel with different initial microstructures was investigated from the perspective of the competitive phenomenon between recrystallization of ferrite and reverse phase transformation from ferrite to austenite. Three kinds of hot-rolled sheet specimens were prepared. Specimen P consisted of ferrite and pearlite, specimen B consisted of bainite, and specimen M consisted of martensite. The progress of recovery and recrystallization of ferrite during annealing was more rapid in specimen M than that in specimens P and B. In particular, the recrystallized ferrite grains in specimen M were fine and equiaxed. The progress of ferrite-to-austenite phase transformation during intercritical annealing was more rapid in specimen M than in specimens P and B. In all specimens, the austenite nucleation sites were mainly at high-angle grain boundaries, such as those between recrystallized ferrite grains. The austenite distribution was the most uniform in specimen M. Thus, we concluded that fine equiaxed recrystallized ferrite grains were formed in specimen M, leading to a uniform distribution of austenite.

Cryogenic strength improvement by utilizing room-temperature deformation twinning in a partially recrystallized VCrMnFeCoNi high-entropy alloy

PubMed Central

Jo, Y. H.; Jung, S.; Choi, W. M.; Sohn, S. S.; Kim, H. S.; Lee, B. J.; Kim, N. J.; Lee, S.

2017-01-01

The excellent cryogenic tensile properties of the CrMnFeCoNi alloy are generally caused by deformation twinning, which is difficult to achieve at room temperature because of insufficient stress for twinning. Here, we induced twinning at room temperature to improve the cryogenic tensile properties of the CrMnFeCoNi alloy. Considering grain size effects on the critical stress for twinning, twins were readily formed in the coarse microstructure by cold rolling without grain refinement by hot rolling. These twins were retained by partial recrystallization and played an important role in improving strength, allowing yield strengths approaching 1 GPa. The persistent elongation up to 46% as well as the tensile strength of 1.3 GPa are attributed to additional twinning in both recrystallized and non-recrystallization regions. Our results demonstrate that non-recrystallized grains, which are generally avoided in conventional alloys because of their deleterious effect on ductility, can be useful in achieving high-strength high-entropy alloys. PMID:28604656

Ice-Active Substances from the Infective Juveniles of the Freeze Tolerant Entomopathogenic Nematode, Steinernema feltiae

PubMed Central

Ali, Farman; Wharton, David A.

2016-01-01

Steinernema feltiae is a moderately freezing tolerant nematode, that can withstand intracellular ice formation. We investigated recrystallization inhibition, thermal hysteresis and ice nucleation activities in the infective juveniles of S. feltiae. Both the splat cooling assay and optical recrystallometry indicate the presence of ice active substances that inhibit recrystallization in the nematode extract. The substance is relatively heat stable and largely retains the recrystallization inhibition activity after heating. No thermal hysteresis activity was detected but the extract had a typical hexagonal crystal shape when grown from a single seed crystal and weak ice nucleation activity. An ice active substance is present in a low concentration, which may be involved in the freezing survival of this species by inhibiting ice recrystallization. PMID:27227961

Effect of Segregation of Secondary Phase Particles and "S" Line on Tensile Fracture Behavior of Friction Stir-Welded 2024Al-T351 Joints

NASA Astrophysics Data System (ADS)

Zhang, Z.; Xiao, B. L.; Ma, Z. Y.

2013-09-01

A 5-mm-thick 2024Al-T351 plate was friction stir welded (FSWed) at welding speeds of 100, 200, and 400 mm min-1 with a constant rotation rate of 800 rpm, and the microstructure and tensile fracture behavior of the joints were investigated in detail. FSW resulted in the redistribution of secondary phase particles along the recrystallized grain boundaries at the nugget zone (NZ), forming linear segregation bands consisting of secondary phase particles. The segregation bands, mainly present in the shoulder-driven zone, were believed to result from periodic material flow, with the average band spacing on the longitudinal and horizontal cross sections equal to the tool advancement per revolution. At a low welding speed of 100 mm min-1, in spite of the highest density of segregation bands, the FSWed 2024Al-T351 joint fractured along the low hardness zone (LHZ) of the heat-affected zone because of large hardness gap between NZ and LHZ. Increasing the welding speed to 200 and 400 mm min-1 reduced both the hardness gap between NZ and LHZ and the density of segregation bands. In this case, the segregation bands played a role, resulting in unusual fracture of the joints along the segregation bands. The "S" line originated from the oxide film on the initial butting surfaces and did not affect the fracture behavior of the FSWed 2024Al-T351 joints.

Pairing Heterocyclic Cations with closo-Icosahedral Borane and Carborane Anions. II. Benchtop Alternative Synthetic Methodologies for Binary Triazolium and Tetrazolium Salts with Significant Water Solubility

DTIC Science & Technology

2010-04-01

produced from eutectic melts. Nat. Mater. 2008, 7, 626-630. 9. Any attempt at recrystallizing the 1:1 mixture of cations in (12) is likely to afford... recrystallizations . So, rather than recrystallizing each individual adduct, we concentrated on performing a careful spectroscopic examination of the...suggested. [1] While it is well-known that an admixture of two neutral compounds often affords eutectic behavior, we wondered whether or not the same

Ostwald ripening of clays and metamorphic minerals

USGS Publications Warehouse

Eberl, D.D.; Srodon, J.; Kralik, M.; Taylor, B.E.; Peterman, Z.E.

1990-01-01

Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

Orientation filtering for crystalline films

DOEpatents

Smith, Henry I.; Atwater, Harry A.; Thompson, Carl V.; Geis, Michael W.

1986-12-30

A substrate is coated with a film to be recrystallized. A pattern of crystallization barriers is created in the film, for example, by etching voids in the film. An encapsulation layer is generally applied to protect the film, fill the voids and otherwise enhance a recrystallization process. Recrystallization is carried out such that certain orientations pass preferentially through the barrier, generally as a result of growth-velocity anisotropy. The result is a film of a specific predetermined crystallographic orientation, a range of orientations or a set of discrete orientations.

Effects of annealing and additions on dynamic mechanical properties of SnSb quenched alloy

NASA Astrophysics Data System (ADS)

El-Bediwi, A. B.

2004-08-01

The elastic modulus, internal friction and stiffness values of quenched SnSb bearing alloy have been evaluated using the dynamic resonance technique. Annealing for 2 and 4 h at 120, 140 and 160degreesC caused variations in the elastic modulus. internal friction and stiffness values. This is due to structural changes in the SnSb matrix during isothermal annealing such as coarsening in the phases (Sn, Sb or intermetallic compounds), recrystallization and stress relief. In addition, adding a small amount (1 wt.%) of Cu or Ag improved the bearing mechanical properties of the SnSb bearing alloy. The SnSbCu1 alloy has the best bearing mechanical properties with thermo-mechanical stability for long time at high temperature.

The brittle-viscous-plastic evolution of shear bands in the South Armorican Shear Zone

NASA Astrophysics Data System (ADS)

Bukovská, Zita; Jeřábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf

2014-05-01

Shear bands are microscale shear zones that obliquely crosscut an existing anisotropy such as a foliation. The resulting S-C fabrics are characterized by angles lower than 45° and the C plane parallel to shear zone boundaries. The S-C fabrics typically occur in granitoids deformed at greenschist facies conditions in the vicinity of major shear zones. Despite their long recognition, mechanical reasons for localization of deformation into shear bands and their evolution is still poorly understood. In this work we focus on microscale characterization of the shear bands in the South Armorican Shear Zone, where the S-C fabrics were first recognized by Berthé et al. (1979). The initiation of shear bands in the right-lateral South Armorican Shear Zone is associated with the occurrence of microcracks crosscutting the recrystallized quartz aggregates that define the S fabric. In more advanced stages of shear band evolution, newly formed dominant K-feldspar, together with plagioclase, muscovite and chlorite occur in the microcracks, and the shear bands start to widen. K-feldspar replaces quartz by progressively bulging into the grain boundaries of recrystallized quartz grains, leading to disintegration of quartz aggregates and formation of fine-grained multiphase matrix mixture. The late stages of shear band development are marked by interconnection of fine-grained white mica into a band that crosscuts the original shear band matrix. In its extremity, the shear band widening may lead to the formation of ultramylonites. With the increasing proportion of shear band matrix from ~1% to ~12%, the angular relationship between S and C fabrics increases from ~30° to ~40°. The matrix phases within shear bands show differences in chemical composition related to distinct evolutionary stages of shear band formation. The chemical evolution is well documented in K-feldspar, where the albite component is highest in porphyroclasts within S fabric, lower in the newly formed grains within microcracks and nearly absent in matrix grains in the well developed C bands. The chemical variation between primary and secondary new-formed micas was clearly identified by the Mg-Ti-Na content. The microstructural analysis documents a progressive decrease in quartz grain size and increasing interconnectivity of K-feldspar and white mica towards more mature shear bands. The contact-frequency analysis demonstrates that the phase distribution in shear bands tends to evolve from quartz aggregate distribution via randomization to K-feldspar aggregate distribution. The boundary preferred orientation is absent in quartz-quartz contacts either inside of outside the C bands, while it changes from random to parallel to the C band for the K-feldspar and and K-feldspar-quartz boundaries. The lack of crystallographic preferred orientation of the individual phases in the mixed matrix of the C planes suggests a dominant diffusion-assisted grain boundary sliding deformation mechanism. In the later stages of shear band development, the deformation is accommodated by crystal plasticity of white mica in micaceous bands. The crystallographic and microstructural data thus indicate two important switches in deformation mechanisms, from (i) brittle to Newtonian viscous behavior in the initial stages of shear band evolution and from (ii) Newtonian viscous to power law in the later evolutionary stages. The evolution of shear bands in the South Armorican Shear Zone thus document the interplay between deformation mechanisms and chemical reactions in deformed granitoids.

Importance of ecotone type to landscape dynamics at biome transition zones

USDA-ARS?s Scientific Manuscript database

Landscapes in biome transition zones consist of a mosaic of patches dominated or codominated by species from adjacent biomes. Shifts in the vegetation composition and dynamics of a biome transition zone depend upon the underlying patch dynamics of the ecotones between these dominant species. Landsc...

Behavior of sheets from Ti-alloys by rolling and heat treatment

NASA Astrophysics Data System (ADS)

Isaenkova, M.; Perlovich, Yu.; Fesenko, V.; Gritskevich, M.; Stolbov, S.; Zaripova, M.

2017-10-01

Sheets from single- and two-phase Ti-alloys (VT1-0, Ti-22Nb-9%Zr and VT-16) were rolled at the room temperature up to various deformation degrees and annealed at temperatures 500-900 °C. The regularities of texture formation in both phases were established. In the technically pure Ti (VT1-0) with the single α-Ti phase the final stable texture component is (0001)±30-40°ND-TD<101 ¯0>. In the two-phase alloy the reorientation of basal axes of α-Ti occurs by the same trajectories as in the single phase alloy. However, in the case of two-phase alloy texture development in α-Ti stops at the intermediate stage, when this texture consists of components with rolling planes (0001)±15-20°ND-RD and (0001)±30-40°ND-TD. The stability of the first components can be provided both by the mutually balanced operation of pyramidal and basal slip systems, activity of which remains at the high deformation degree of two-phase alloy, and by the dynamic α↔β phase transformations, taking place in the distorted structures of α- and β-phases in the course of its cold rolling. At recrystallization of technically pure Ti the basal component disappears in its texture. At the same time, prismatic axes turn by angles 20÷30° depending on the heating rate of the rolled sheet and annealing temperature. At recrystallization of the two-phase Ti-alloy prismatic axes of its α-grains doesn't turn relative to their positions in the rolling texture, as it occurs in the single-phase alloy. This fact indicates to some alternative mode of arising new recrystallized grains in two-phase alloys.

REX3DV1.0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holm, Elizabeth A.

2002-03-28

This code is a FORTRAN code for three-dimensional Monte Carol Potts Model (MCPM) Recrystallization and grain growth. A continuum grain structure is mapped onto a three-dimensional lattice. The mapping procedure is analogous to color bitmapping the grain structure; grains are clusters of pixels (sites) of the same color (spin). The total system energy is given by the Pott Hamiltonian and the kinetics of grain growth are determined through a Monte Carlo technique with a nonconserved order parameter (Glauber dynamics). The code can be compiled and run on UNIX/Linux platforms.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Shenyang; Lavender, Curt A.; Joshi, Vineet V.

Recrystallization plays an important role in swelling kinetics of irradiated metallic nuclear fuels. This talk will present a three-dimensional microstructure-dependent swelling model by integrating the evolution of intra-and inter- granular gas bubbles, dislocation loop density, and recrystallization.

Recrystallization characteristics and interfacial oxides on the compression bonding interface

NASA Astrophysics Data System (ADS)

Xie, Bijun; Sun, Mingyue; Xu, Bin; Li, Dianzhong

2018-05-01

Up to now, the mechanism of interface bonding is still not fully understood. This work presents interfacial characteristics of 316LN stainless steel bonding joint after cold compression bonding with subsequent annealing. EBSD analysis shows that fine recrystallization grains preferentially appear near the bonding interface and grow towards both sides of the interface. Transmission electron microscopy reveals that initial cold compression bonding disintegrates the native oxide scales and brings pristine metal from both sides of the interface come into intimate contact, while the broken oxide particles are remained at the original interface. The results indicate that partial bonding can be achieved by cold compression bonding with post-annealing treatment and recrystallization firstly occurs along the bonding interface. However, the interfacial oxides impede the recrystallization grains step over the interface and hinder the complete healing of the bonding interface.

Recrystallization characteristics of oxide dispersion strengthened nickel-base alloys

NASA Technical Reports Server (NTRS)

Hotzler, R. K.; Glasgow, T. K.

1980-01-01

Electron microscopy was employed to study the process of recrystallization in two oxide dispersion strengthened (ODS) mechanically alloyed nickel-base alloys, MA 754 and MA 6000E. MA 754 contained both fine, uniformly dispersed particles and coarser oxides aligned along the working direction. Hot rolled MA 754 had a grain size of 0.5 microns and high dislocation densities. After partial primary recrystallization, the fine grains transformed to large elongated grains via secondary (or abnormal) grain growth. Extruded and rolled MA 6000E contained equiaxed grains of 0.2 micron diameter. Primary recrystallization occurring during working eliminated virtually all dislocations. Conversion from fine to coarse grains was triggered by gamma prime dissolution; this was also a process of secondary or abnormal grain growth. Comparisons were made to conventional and oxide dispersion strengthened nickel-base alloys.

BHQ revisited (1) - Looking at grain size

NASA Astrophysics Data System (ADS)

Heilbronner, Renée; Kilian, Rüdiger; Tullis, Jan

2016-04-01

Black Hills Quartzite (BHQ) has been used extensively in experimental rock deformation for numerous studies. Coaxial and general shear experiments have been carried out, for example, to define the dislocation creep regimes of quartz (Hirth & Tullis, 1992), to determine the effect of annealing (Heilbronner & Tullis, 2002) or to study the development of texture and microstructure with strain (Heilbronner & Tullis, 2006). BHQ was also used to determine the widely used quartz piezometer by Stipp & Tullis (2003). Among the microstructure analyses that were performed in those original papers, grain size was usually determined using CIP misorientation images. However, the CIP method (= computer-integrated polarization microscopy, details in Heilbronner and Barrett, 2014) is only capable of detecting the c-axis orientation of optically uniaxial materials and hence is only capable of detecting grain boundaries between grains that differ in c-axis orientation. One of the puzzling results we found (Heilbronner & Tullis, 2006) was that the recrystallized grain size seemed to depend on the crystallographic preferred orientation of the domain. In other words the grain size did not only depend on the flow stress but also on the orientation of the c-axis w/r to the shear direction. At the time, no EBSD analysis (electron back scatter diffraction) was carried out and hence the full crystallographic orientation was not known. In principle it is therefore possible that we missed some grain boundaries (between grains with parallel c-axes) and miscalculated our grain sizes. In the context of recent shear experiments on quartz gouge at the brittle-viscous transition (see Richter et al., this conference), where EBSD is used to measure the recrystallized grain size, we wanted to re-measure the CIP grain sizes of our 2006 samples (deformed in regime 1, 2 and 3 of dislocation) in exactly the same way. In two companion posters we use EBSD orientation imaging to repeat, refine and expand the microstructure and texture analysis of Heilbronner & Tullis (2006). Here, in poster (1), we focus on the recrystallized grain size with the aim of (a) comparing CIP- and EBSD derived grain size measurements, (b) of comparing the recrystallized grain size of coaxially deformed and sheared BHQ and (c) in order to confirm that the quartz piezometer indeed depends on texture, and (d) to test if it also depends on the type of deformation (irrotational versus rotational deformation). References cited: Heilbronner, R., and S.D. Barrett (2014) Image Analysis in Earth Sciences, Springer. Heilbronner, R., and J. Tullis (2002), The effect of static annealing on micro- structure and crystallographic preferred orientations of quartzites experimentally deformed in axial compression and shear, Geol. Soc. Spec. Publ., 200, 191 - 218. Heilbronner, R., and J. Tullis (2006), Evolution of c axis pole figures and grain size during dynamic recrystallization: Results from experimentally sheared quartzite. JGR, 111, B10202, doi:10.1029/2005JB004194, 2006 Hirth, G., and J. Tullis (1992), Dislocation creep regimes in quartz aggregates, JSG, 14, 145-159. Stipp, M., and J. Tullis (2003), The recrystallized grain size piezometer for quartz, Geophys. Res. Lett., 30(21), 2088, doi:10.1029/2003GL018444.

A cathodoluminescence study on zircons with a complex thermal history traces back Permian crustal events in the Ivrea Zone (South Alpine, Northern Italy)

NASA Astrophysics Data System (ADS)

Peressini, G.; Poller, U.

2003-04-01

In the context of a U-Pb SHRIMP data-set, a cathodoluminescence (CL) study has been performed on zircons from the Ivrea-Verbano Zone; this is a tectonically bounded section of intermediate to deep crust, tilted and obducted in Alpine time, in which a large deep-crustal intrusion of mantle origin, the Mafic Complex (MC), was emplaced in the Early Permian. Zircons from 16 samples from the different units of the MC have been studied using CL. Three samples collected from the Paragneiss Bearing Belt (PBB) yield some partially reset spot-ages, reflecting the field observation that country rock slabs are frequent in that area. On the other side, unlike in zircons from granites, the cores are invisible under CL-imaging, and this makes the U-Pb spot-age results unpredictable, with a continuous range of ages in the same sample, spanning for an interval of over 35 Ma, followed by some much older peaks, up to 600 Ma. A fourth sample, collected 2 km far, but still within the PBB, defines instead a unique, well-defined age at 287±3 Ma, with no older peaks, its zircons showing a CL pattern typical for metamorphic grains. A different case is displayed by a sample collected from the deeper Amphibole Gabbro unit: each single grain records a complex story of magmatic growth with variable diffusivity conditions. All of them show a second major overprint, that lead to both (re)crystallization and resorption, always corresponding to much lower U and Th contents, with no sensible modification of the Th-U ratio. The age of the second event, though, is not distinguishable from that of first crystallization of the grains, and has not been at such a temperature as to obliterate the fine zoning pattern of the primary grain. The CL patterns of each single grain, composed of different domains, allow considerations on the environmental conditions of growth and (re)crystallization. CL is a very powerful tool itself, revealing crystal-chemical processes. The integration of the CL-study with the SHRIMP spot-age determination relates them to the sequence of geologic events. The study, performed on samples coming from all over the Complex, has allowed a better understanding of processes in the Carboniferous-Permian lower crust of the Ivrea Zone: the knowledge of the Complex, its structure and the field relationships has become a key for interpreting the results. Where the CL displays a composite pattern, mechanisms are needed to explain geochemical fingerprints: therefore, trace and REE analyses by ion probe are in progress to integrate the SHRIMP data.

An integrated study on microtectonics, geothermometry and thermochronology of the Çataldaǧ Core Complex (NW Turkey): Implications for cooling, deformation and uplift history

NASA Astrophysics Data System (ADS)

Kamaci, Omer; Altunkaynak, Safak

2017-04-01

We present an integrated study on structure, microstructure, geothermometry and thermochronology of the Çataldaǧ Core Complex (ÇCC) in NW Turkey in order to understand the cooling, deformation and uplift mechanisms. ÇCC is formed from an Eo-Oligocene granite-gneiss-migmatite complex (GGMC) and an Early Miocene I-type granodioritic body (ÇG: Çataldaǧ granodiorite) which were exhumed as a dome-shaped core complex in the footwall of a ring-shaped low-angle detachment zone (The Çataldaǧ Detachment Fault Zone; ÇDFZ) in the Early Miocene. New U-Pb zircon (LA-ICPMS) and monazite ages of GGMC yielded magmatic ages of 33.8 and 30.1 Ma (Latest Eocene-Early Oligocene). 40Ar/39Ar muscovite, biotite and K-feldspar from the GGMC yielded the deformation age span 21.38±0,05 Ma and 20.81±0.04 Ma, which is also the emplacement age (20.84±0.13 Ma and 21.6±0.04 Ma) of ÇG. ÇDFZ is responsible for mainly top-to-the-north sense kinematic processes. The microstructural features of quartz, feldspar and mica indicate that the ÇCC has undergone continuous deformations during its cooling, from submagmatic to cataclastic conditions. Five microstructural grades have been classified under ductile (DZ) and ductile-to-brittle shear zone (SZ), according to the estimated deformation temperature and intensity of the strain. Microcline twinning, marginally replacement myrmekite and flame-perthite are predominant features for feldspar while chessboard extinction, grain boundary migration and subgrain rotation recrystallization is common for quartz in the DZ which has a deformation temperature range of >600°C to 400°C. Grain size reduction is an important factor for the ductile to brittle shear zone (SZ). Feldspar is represented by bulging recrystallization (BLG), feldspar-fish and domino-type microfracture/microfaulting and quartz show more elongated structures such as ribbons with high aspect ratios. Mineral-fish (muscovite, biotite and feldspar) structures indicate a temperature range of 500°C to <250°C. The GGMC and ÇG, which were formed in different periods, suffered continuous ductile-to-brittle deformation and uplifted together along ÇDFZ during Early Miocene when the first major period of N-S extension began in the western Anatolia. Microstructural grades, two-feldspar geothermometry and geochronological data indicate that the GGMC and ÇG, which were formed in different periods, suffered continuous ductile-to-brittle deformation and uplifted together along ÇDFZ during Early Miocene when the first major period of N-S extension began in the western Anatolia.

Dynamic deformation of volcanic ejecta from the Toba caldera: possible relevance to Cretaceous/Tertiary boundary phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carter, N.L.; Officer, C.B.; Chesner, C.A.

1986-05-01

Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development of plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processesmore » may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. 38 references, 3 figures.« less

Recrystallization and grain growth induced by ELMs-like transient heat loads in deformed tungsten samples

NASA Astrophysics Data System (ADS)

Suslova, A.; El-Atwani, O.; Sagapuram, D.; Harilal, S. S.; Hassanein, A.

2014-11-01

Tungsten has been chosen as the main candidate for plasma facing components (PFCs) due to its superior properties under extreme operating conditions in future nuclear fusion reactors such as ITER. One of the serious issues for PFCs is the high heat load during transient events such as ELMs and disruption in the reactor. Recrystallization and grain size growth in PFC materials caused by transients are undesirable changes in the material, since the isotropic microstructure developed after recrystallization exhibits a higher ductile-to-brittle transition temperature which increases with the grain size, a lower thermal shock fatigue resistance, a lower mechanical strength, and an increased surface roughening. The current work was focused on careful determination of the threshold parameters for surface recrystallization, grain growth rate, and thermal shock fatigue resistance under ELM-like transient heat events. Transient heat loads were simulated using long pulse laser beams for two different grades of ultrafine-grained tungsten. It was observed that cold rolled tungsten demonstrated better power handling capabilities and higher thermal stress fatigue resistance compared to severely deformed tungsten. Higher recrystallization threshold, slower grain growth, and lower degree of surface roughening were observed in the cold rolled tungsten.