History-independent cyclic response of nanotwinned metals

NASA Astrophysics Data System (ADS)

Pan, Qingsong; Zhou, Haofei; Lu, Qiuhong; Gao, Huajian; Lu, Lei

2017-11-01

Nearly 90 per cent of service failures of metallic components and structures are caused by fatigue at cyclic stress amplitudes much lower than the tensile strength of the materials involved. Metals typically suffer from large amounts of cumulative, irreversible damage to microstructure during cyclic deformation, leading to cyclic responses that are unstable (hardening or softening) and history-dependent. Existing rules for fatigue life prediction, such as the linear cumulative damage rule, cannot account for the effect of loading history, and engineering components are often loaded by complex cyclic stresses with variable amplitudes, mean values and frequencies, such as aircraft wings in turbulent air. It is therefore usually extremely challenging to predict cyclic behaviour and fatigue life under a realistic load spectrum. Here, through both atomistic simulations and variable-strain-amplitude cyclic loading experiments at stress amplitudes lower than the tensile strength of the metal, we report a history-independent and stable cyclic response in bulk copper samples that contain highly oriented nanoscale twins. We demonstrate that this unusual cyclic behaviour is governed by a type of correlated ‘necklace’ dislocation consisting of multiple short component dislocations in adjacent twins, connected like the links of a necklace. Such dislocations are formed in the highly oriented nanotwinned structure under cyclic loading and help to maintain the stability of twin boundaries and the reversible damage, provided that the nanotwins are tilted within about 15 degrees of the loading axis. This cyclic deformation mechanism is distinct from the conventional strain localizing mechanisms associated with irreversible microstructural damage in single-crystal, coarse-grained, ultrafine-grained and nanograined metals.

Effect of Processing Route on Strain Controlled Low Cycle Fatigue Behavior of Polycrystalline NiAl

NASA Technical Reports Server (NTRS)

Rao, K. Bhanu Sankara; Lerch, B. A.; Noebe, R. D.

1995-01-01

The present investigation examines the effects of manufacturing process on the total axial strain controlled low cycle fatigue behavior of polycrystalline NiAl at 1000 K, a temperature above the monotonic Brittle-to-Ductile Transition Temperature (BDTT). The nickel aluminide samples were produced by three different processing routes: hot isostatic pressing of pre- alloyed powders, extrusion of prealloyed powders, and extrusion of vacuum induction melted ingots. The LCF behavior of the cast plus extruded material was also determined at room temperature (below the BD77) for comparison to the high temperature data. The cyclic stress response, cyclic stress-strain behavior, and strain-life relationships were influenced by the alloy preparation technique and the testing temperature. Detailed characterization of the LCF tested samples was conducted by optical and electron microscopy to determine the variations in fracture and deformation modes and to determine any microstructural changes that occurred during LCF testing. The dependence of LCF properties on processing route was rationalized on the basis of starting microstructure, brittle-to-ductile transition temperature, deformation induced changes in the basic microstructure, deformation substructure, and synergistic interaction between the damage modes.

A natural example of fluid-mediated brittle-ductile cyclicity in quartz veins from Olkiluoto Island, SW Finland

NASA Astrophysics Data System (ADS)

Marchesini, Barbara; Garofalo, Paolo S.; Viola, Giulio; Mattila, Jussi; Menegon, Luca

2017-04-01

Brittle faults are well known as preferential conduits for localised fluid flow in crystalline rocks. Their study can thus reveal fundamental details of the physical-chemical properties of the flowing fluid phase and of the mutual feedbacks between mechanical properties of faults and fluids. Crustal deformation at the brittle-ductile transition may occur by a combination of competing brittle fracturing and viscous flow processes, with short-lived variations in fluid pressure as a viable mechanism to produce this cyclicity switch. Therefore, a detailed study of the fluid phases potentially present in faults can help to better constrain the dynamic evolution of crustal strength within the seismogenic zone, as a function of varying fluid phase characteristics. With the aim to 1) better understand the complexity of brittle-ductile cyclicity under upper to mid-crustal conditions and 2) define the physical and chemical features of the involved fluid phase, we present the preliminary results of a recently launched (micro)structural and geochemical project. We study deformed quartz veins associated with brittle-ductile deformation zones on Olkiluoto Island, chosen as the site for the Finnish deep repository for spent nuclear fuel excavated in the Paleoproterozoic crust of southwestern Finland. The presented results stem from the study of brittle fault zone BFZ300, which is a mixed brittle and ductile deformation zone characterized by complex kinematics and associated with multiple generations of quartz veins, and which serves as a pertinent example of the mechanisms of fluid flow-deformation feedbacks during brittle-ductile cyclicity in nature. A kinematic and dynamic mesostructural study is being integrated with the detailed analysis of petrographic thin sections from the fault core and its immediate surroundings with the aim to reconstruct the mechanical deformation history along the entire deformation zone. Based on the observed microstructures, it was possible to recognize three distinct episodes of ductile deformation alternating with at least three brittle episodes. Preliminary fluid inclusion data show that, during crystallization and brittle-viscous deformation, quartz crystals hosted homogeneous and heterogeneous (boiling) aqueous fluids with a large salinity (11.7-0 wt% NaCleq) and Thtot (410-200 °C) range. Boiling occurred at 200-260 °C. Variations of fluid temperature and density (hence, viscosity) may thus have induced localized cyclic switches between brittle and ductile deformation in quartz, with implications on the bulk regional crustal strength. Preliminary EBSD analysis also supports the hypothesis of cyclic switches between brittle and viscous deformation.

The effect of matrix microstructure on cyclic response and fatigue behavior of particle-reinforced 2219 aluminum: Part II. Behavior at 150 °C

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; van Aken, D. C.; Allison, J. E.

1995-12-01

The 150 °C cyclic response of peak-aged and overaged 2219/TiC/15p and 2219 Al was examined using fully reversed plastic strain-controlled testing. The cyclic response of peak-aged and overaged particle-reinforced materials showed extensive cyclic softening. This softening began at the commencement of cycling and continued until failure. At a plastic strain below 5 × 103, the unreinforced materials did not show evidence of cyclic softening until approximately 30 pct of the life was consumed. In addition, the degree of cyclic softening (†σ) was significantly lower in the unreinforced microstructures. The cyclic softening in both reinforced and unreinforced materials was attributed to the decomposition of the θ' strengthening precipitates. The extent of the precipitate decomposition was much greater in the composite materials due to the increased levels of local plastic strain in the matrix caused by constrained deformation near the TiC particles.

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.

Ratcheting Strain and Microstructure Evolution of AZ31B Magnesium Alloy under a Tensile-Tensile Cyclic Loading

PubMed Central

Wang, Denghui; Wang, Wenxian; Zhou, Jun; He, Xiuli; Dong, Peng; Zhang, Hongxia; Sun, Liyong

2018-01-01

In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material’s fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11−20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11−20} tensile twins. PMID:29597278

Ratcheting Strain and Microstructure Evolution of AZ31B Magnesium Alloy under a Tensile-Tensile Cyclic Loading.

PubMed

Yan, Zhifeng; Wang, Denghui; Wang, Wenxian; Zhou, Jun; He, Xiuli; Dong, Peng; Zhang, Hongxia; Sun, Liyong

2018-03-28

In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material's fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11-20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11-20} tensile twins.

Rapid Assessment of the Role of Microstructural Variability in the Fatigue Behavior of Structural Alloys using Ultrasonic Fatigue

DTIC Science & Technology

2007-06-23

6 %AI-2%Sn- 4 %Zr- 6 %Mo in the very high cycle regime. The microstructure is a two-phase structure with primary a grains (ap grains) in a transformed [3...aluminum [2], magnesium [3], nickel-based [ 4 ], and titanium [5,6] alloy systems. Fatigue crack initiation is known to consume the majority of fatigue...microstructural neighborhood affects this process. In fatigue studies of alpha + beta titanium alloys, [ 6 -9] cyclic deformation localization is first observed in

Computational study of dislocation based mechanisms in FCC materials

NASA Astrophysics Data System (ADS)

Yellakara, Ranga Nikhil

Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechanical behavior of metallic alloys, particularly focusing on face centered cubic (FCC) structured metals through a unique computational methodology called three-dimensional dislocation dynamics (3D-DD). In these simulations, the equations of motion for dislocations are mathematically solved to determine the evolution and interaction of dislocations. Microstructure details and stress-strain curves are a direct observation in the simulation and can be used to validate experimental results. The effect of initial dislocation microstructure on the yield strength has been studied. It has been shown that dislocation density based crystal plasticity formulations only work when dislocation densities/numbers are sufficiently large so that a statistically accurate description of the microstructure can be obtainable. The evolution of the flow stress for grain sizes ranging from 0.5 to 10 mum under uniaxial tension was simulated using an improvised model by integrating dislocation pile-up mechanism at grain boundaries has been performed. This study showed that for a same initial dislocation density, the Hall--Petch relationship holds well at small grain sizes (0.5--2 mum), beyond which the yield strength remains constant as the grain size increases. Various dislocation-particle interaction mechanisms have been introduced and investigations were made on their effect on the uniaxial tensile properties. These studies suggested that increase in particle volume fraction and decrease in particle size has contributed to the strength of these alloys. This work has been successful of capturing complex dislocation mechanisms that involves interactions with particles during the deformation of particle hardened FCC alloys. Finally, the DD model has been extended into studying the cyclic behavior of FCC metallic alloys. This study showed that the strength as well as the cyclic hardening increases due to grain refinement and increase in particle volume fraction. It also showed that the cyclic deformation of ultra-fine grained (UFG) material have undergone cyclic softening at all plastic strain amplitudes. The results provided very useful quantitative information for developing future fatigue models.

Data on processing of Ti-25Nb-25Zr β-titanium alloys via powder metallurgy route: Methodology, microstructure and mechanical properties.

PubMed

Ueda, D; Dirras, G; Hocini, A; Tingaud, D; Ameyama, K; Langlois, P; Vrel, D; Trzaska, Z

2018-04-01

The data presented in this article are related to the research article entitled "Cyclic Shear behavior of conventional and harmonic structure-designed Ti-25Nb-25Zr β-titanium alloy: Back-stress hardening and twinning inhibition" (Dirras et al., 2017) [1]. The datasheet describes the methods used to fabricate two β-titanium alloys having conventional microstructure and so-called harmonic structure (HS) design via a powder metallurgy route, namely the spark plasma sintering (SPS) route. The data show the as-processed unconsolidated powder microstructures as well as the post-SPS ones. The data illustrate the mechanical response under cyclic shear loading of consolidated alloy specimens. The data show how electron back scattering diffraction(EBSD) method is used to clearly identify induced deformation features in the case of the conventional alloy.

Influences of the manufacturing process chain design on the near surface condition and the resulting fatigue behaviour of quenched and tempered SAE 4140

NASA Astrophysics Data System (ADS)

Klein, M.; Eifler, D.

2010-07-01

To analyse interactions between single steps of process chains, variations in material properties, especially the microstructure and the resulting mechanical properties, specimens with tension screw geometry were manufactured with five process chains. The different process chains as well as their parameters influence the near surface condition and consequently the fatigue behaviour in a characteristic manner. The cyclic deformation behaviour of these specimens can be benchmarked equivalently with conventional strain measurements as well as with high-precision temperature and electrical resistance measurements. The development of temperature-values provides substantial information on cyclic load dependent changes in the microstructure.

Microstructure: Property correlation. [multiaxial fatigue damage evolution in waspaloy

NASA Technical Reports Server (NTRS)

Jayaraman, N.

1990-01-01

Strain controlled torsional and biaxial (tension-torsion) low cycle fatigue behavior of Waspaloy was studied at room temperature as a function of heat treatment. Biaxial tests were conducted under proportional (when the axial and torsional strain cycles are in-phase) and non-proportional (when the axial and torsional strain cycles are 90 deg out-of-phase) cyclic conditions. The deformation behavior under these different cyclic conditions were evaluated by slip trace analysis. For this, a Schmidt-type factor was defined for multiaxial loading conditions and it was shown that when the slip deformation is predominant, non-proportional cycles are more damaging than proportional or pure axial or torsional cycles. This was attributed to the fact that under non-proportional cyclic conditions, deformation was through multiple slip as opposed single slip for other loading conditions, which gave rise to increased hardening. The total life for a given test condition was found to be independent of heat treatment. This was interpreted as being due to the differences in the cycles to initiation and propagation of cracks.

Simulation of fatigue fracture of TiNi shape memory alloy samples at cyclic loading in pseudoelastic state

NASA Astrophysics Data System (ADS)

Belyaev, Fedor S.; Volkov, Aleksandr E.; Evard, Margarita E.; Khvorov, Aleksandr A.

2018-05-01

Microstructural simulation of mechanical behavior of shape memory alloy samples at cyclic loading in the pseudoelastic state has been carried out. Evolution of the oriented and scattered deformation defects leading to damage accumulation and resulting in the fatigue fracture has been taken into account. Simulations were performed for the regime of loading imitating that for endovascular stents: preliminary straining, unloading, deformation up to some mean level of the strain and subsequent mechanical cycling at specified strain amplitude. Dependence of the fatigue life on the loading parameters (pre-strain, mean and amplitude values of strain) has been obtained. The results show a good agreement with available experimental data.

Forecasting Low-Cycle Fatigue Performance of Twinning-Induced Plasticity Steels: Difficulty and Attempt

NASA Astrophysics Data System (ADS)

Shao, C. W.; Zhang, P.; Zhang, Z. J.; Liu, R.; Zhang, Z. F.

2017-12-01

We find the existing empirical relations based on monotonic tensile properties and/or hardness cannot satisfactorily predict the low-cycle fatigue (LCF) performance of materials, especially for twinning-induced plasticity (TWIP) steels. Given this, we first identified the different deformation mechanisms under monotonic and cyclic deformation after a comprehensive study of stress-strain behaviors and microstructure evolutions for Fe-Mn-C alloys during tension and LCF, respectively. It is found that the good tensile properties of TWIP steel mainly originate from the large activation of multiple twinning systems, which may be attributed to the grain rotation during tensile deformation; while its LCF performance depends more on the dislocation slip mode, in addition to its strength and plasticity. Based on this, we further investigate the essential relations between microscopic damage mechanism (dislocation-dislocation interaction) and cyclic stress response, and propose a hysteresis loop model based on dislocation annihilation theory, trying to quickly assess the LCF resistance of Fe-Mn-C steels as well as other engineering materials. It is suggested that the hysteresis loop and its evolution can provide significant information on cyclic deformation behavior, e.g., (point) defect multiplication and vacancy aggregation, which may help estimate the LCF properties.

Effect of Heat Treatment Process on Microstructure and Fatigue Behavior of a Nickel-Base Superalloy

PubMed Central

Zhang, Peng; Zhu, Qiang; Chen, Gang; Qin, Heyong; Wang, Chuanjie

2015-01-01

The study of fatigue behaviors for nickel-base superalloys is very significant because fatigue damage results in serious consequences. In this paper, two kinds of heat treatment procedures (Pro.I and Pro.II) were taken to investigate the effect of heat treatment on microstructures and fatigue behaviors of a nickel-base superalloy. Fatigue behaviors were studied through total strain controlled mode at 650 °C. Manson-Coffin relationship and three-parameter power function were used to predict fatigue life. A good link between the cyclic/fatigue behavior and microscopic studies was established. The cyclic deformation mechanism and fatigue mechanism were discussed. The results show that the fatigue resistance significantly drops with the increase of total strain amplitudes. Manson-Coffin relationship can well predict the fatigue life for total strain amplitude from 0.5% to 0.8%. The fatigue resistance is related with heat treatment procedures. The fatigue resistance performance of Pro.I is better than that of Pro.II. The cyclic stress response behaviors are closely related to the changes of the strain amplitudes. The peak stress of the alloy gradually increases with the increase of total strain amplitudes. The main fracture mechanism is inhomogeneous deformation and the different interactions between dislocations and γ′ precipitates. PMID:28793559

Grain boundary engineering: fatigue fracture

NASA Astrophysics Data System (ADS)

Das, Arpan

2017-04-01

Grain boundary engineering has revealed significant enhancement of material properties by modifying the populations and connectivity of different types of grain boundaries within the polycrystals. The character and connectivity of grain boundaries in polycrystalline microstructures control the corrosion and mechanical behaviour of materials. A comprehensive review of the previous researches has been carried out to understand this philosophy. Present research thoroughly explores the effect of total strain amplitude on phase transformation, fatigue fracture features, grain size, annealing twinning, different grain connectivity and grain boundary network after strain controlled low cycle fatigue deformation of austenitic stainless steel under ambient temperature. Electron backscatter diffraction technique has been used extensively to investigate the grain boundary characteristics and morphologies. The nominal variation of strain amplitude through cyclic plastic deformation is quantitatively demonstrated completely in connection with the grain boundary microstructure and fractographic features to reveal the mechanism of fatigue fracture of polycrystalline austenite. The extent of boundary modifications has been found to be a function of the number of applied loading cycles and strain amplitudes. It is also investigated that cyclic plasticity induced martensitic transformation strongly influences grain boundary characteristics and modifications of the material's microstructure/microtexture as a function of strain amplitudes. The experimental results presented here suggest a path to grain boundary engineering during fatigue fracture of austenite polycrystals.

Data related to cyclic deformation and fatigue behavior of direct laser deposited Ti-6Al-4V with and without heat treatment.

PubMed

Sterling, Amanda J; Torries, Brian; Shamsaei, Nima; Thompson, Scott M

2016-03-01

Data is presented describing the strain-controlled, fully-reversed uniaxial cyclic deformation and fatigue behavior of Ti-6Al-4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) - a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their 'as-built', annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the mechanical integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti-6Al-4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their mechanical properties are understood with high certainty.

Data related to cyclic deformation and fatigue behavior of direct laser deposited Ti–6Al–4V with and without heat treatment

PubMed Central

Sterling, Amanda J.; Torries, Brian; Shamsaei, Nima; Thompson, Scott M.

2016-01-01

Data is presented describing the strain-controlled, fully-reversed uniaxial cyclic deformation and fatigue behavior of Ti–6Al–4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) – a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their ‘as-built’, annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the mechanical integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti–6Al–4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their mechanical properties are understood with high certainty. PMID:26949728

Microstructural evaluation of cumulative fatigue damage in a plant component sample

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

Fukuoka, C.; Nakagawa, Y.G.; Yoshida, K.

1996-12-31

Fatigue damage accumulated in a real plant was evaluated in terms of microstructural conditioning. Microstructural damage induced in laboratory by cyclic deformation near and below the fatigue limit was also examined. A Transmission Electron Microscopy (TEM) technique called the Selected Area Diffraction (SAD) method was employed in this study. In earlier studies, it was found that the SAD value indicating a magnitude of crystallographic misorientation in the substructure (dislocation cells) was increasing with the increase of fatigue damage accumulation. Small samples removed from PWR feed water nozzle welds were examined by the SAD. It was found that the damage statemore » measured by the SAD well agreed with the morphological evidence. Cyclic stresses near or below the fatigue limit were applied to samples taken from a SA508 steel plate at various stresses. The SAD value increased even below the fatigue limit, but there was no sign of microstructural conditioning below the stresses of 50% of the fatigue limit. These results suggested that at stresses below the current design curve (below half the fatigue limit) no microstructural conditioning proceeded. It was concluded that the microstructural method was effective to evaluate damage accumulation in real plant components, and also that the current design curve was adequate in terms of microstructural conditioning state.« less

Formation Of Nano Layered Lamellar Structure In a Processed γ-TiAl Based Alloy

NASA Astrophysics Data System (ADS)

Heshmati-Manesh, S.; Shakoorian, H.; Armaki, H. Ghassemi; Ahmadabadi, M. Nili

2009-06-01

In this research, microstructures of an intermetallic alloy based on γ-TiAl has been investigated by optical and transmission electron microscopy. Samples of Ti-47Al-2Cr alloy were subjected to either a cyclic heat treatment or thermomechanical treatment with the aim of microstructural refinement. In both cases it was found that very fine lamellar structure with an interlamellar spacing in the nano scale is formed. Upon cyclic heat treatment, nano layers of α2 and γ ordered intermetallic phases were either formed during rapid cooling cycle in competition with massive structure formation, or formed as secondary lamellar structure during final stages of cyclic heat treatment. Also, TEM observations in hot forged specimens with initial lamellar structure revealed that micro twins form during the deformation within lamellar structure with twinning plates parallel to lamellar interfaces. Concurrent dynamic recrystallisation results in a nano layered structure with an interlamellar spacing of less than 100 nm.

The role of cyclic plastic zone size on fatigue crack growth behavior in high strength steels

NASA Astrophysics Data System (ADS)

Korda, Akhmad A.; Miyashita, Y.; Mutoh, Y.

2015-09-01

The role of cyclic plastic zone in front of the crack tip was studied in high strength steels. Estimated plastic zone size would be compared with actual observation. Strain controlled fatigue tests of the steels were carried out to obtain cyclic stress-strain curves for plastic zone estimation. Observations of plastic zone were carried out using in situ SEM fatigue crack growth tests under a constant-ΔK. Hard microstructures in structural steels showed to inhibit the extent of plastic deformation around the crack tip. The rate of crack growth can be correlated with the size of plastic zone. The smaller the plastic zone size, the slower the fatigue crack growth.

High Cycle Fatigue (HCF) Science and Technology Program 2000 Annual Report

DTIC Science & Technology

2000-01-01

in an area of deep compressive stress. • Results of industry and government testing have indicated the ability to stop crack initiation and...fatigue crack nucleation process with the cyclic deformation behavior of the alloy for different microstructures and crystallographic texture ... texture combinations investigated, bimodal fine uni-rolled and lamellar cross-rolled displayed superior fatigue properties to the remaining four

Production of ultrafine grained aluminum by cyclic severe plastic deformation at ambient temperature

NASA Astrophysics Data System (ADS)

Bereczki, P.; Szombathelyi, V.; Krallics, G.

2014-08-01

In the present study the possibilities of grain refinement was investigated by applying large-scale of cyclic plastic deformation to aluminum at ambient temperature. The specimens are processed by multiaxial forging, which is one of the severe plastic deformation techniques. The aim of the experiments with the aluminum alloy 6082M was the determination of the equivalent stress and strain by multiaxial forging and the investigation of evolution of mechanical properties in relation with the accumulated deformation in the specimen. The mechanical properties of raw material was determined by plane strain compression test as well as by hardness measurements. The forming experiments were carried out on Gleeble 3800 physical simulator with MaxStrain System. The mechanical properties of the forged specimens were investigated by micro hardness measurements and tensile tests. A mechanical model, based on the principle of virtual velocities was developed to calculate the flow curves using the measured dimensional changes of the specimen and the measured force. With respect to the evolution of these curves, the cyclic growth of the flow stress can be observed at every characteristic points of the calculated flow curves. In accordance with this tendency, the evolution of the hardness along the middle cross section of the deformed volume has also a nonmonotonous characteristic and the magnitudes of these values are much smaller than by the specimen after plane strain compression test. This difference between the flow stresses respect to the monotonic and non-monotonic deformation can be also observed. The formed microstructure, after a 10-passes multiaxial forging process, consists of mainly equiaxial grains in the submicron grain scale.

Early stage fatigue damage occurs in bovine tendon fascicles in the absence of changes in mechanics at either the gross or micro-structural level

PubMed Central

Shepherd, Jennifer H.; Riley, Graham P.; Screen, Hazel R.C.

2014-01-01

Many tendon injuries are believed to result from repetitive motion or overuse, leading to the accumulation of micro-damage over time. In vitro fatigue loading can be used to characterise damage during repeated use and investigate how this may relate to the aetiology of tendinopathy. This study considered the effect of fatigue loading on fascicles from two functionally distinct bovine tendons: the digital extensor and deep digital flexor. Micro-scale extension mechanisms were investigated in fascicles before or after a period of cyclic creep loading, comparing two different measurement techniques – the displacement of a photo-bleached grid and the use of nuclei as fiducial markers. Whilst visual damage was clearly identified after only 300 cycles of creep loading, these visual changes did not affect either gross fascicle mechanics or fascicle microstructural extension mechanisms over the 900 fatigue cycles investigated. However, significantly greater fibre sliding was measured when observing grid deformation rather than the analysis of nuclei movement. Measurement of microstructural extension with both techniques was localised and this may explain the absence of change in microstructural deformation in response to fatigue loading. Alternatively, the data may demonstrate that fascicles can withstand a degree of matrix disruption with no impact on mechanics. Whilst use of a photo-bleached grid to directly measure the collagen is the best indicator of matrix deformation, nuclei tracking may provide a better measure of the strain perceived directly by the cells. PMID:25001495

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

PubMed Central

Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

2016-01-01

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

Atomistic-Dislocation Dynamics Modelling of Fatigue Microstructure and Crack Initiation

DTIC Science & Technology

2013-01-01

experimental) Brown 󈧊 (Upper Limit’) DD Results Mughrabi & Pschenitzka 󈧉 (Lower Limit) y = 50 nm d, = 1.2 |lm M I 4 Simulations of... Mughrabi . Introduction to the viewpoint set on: Surface effects in cyclic deformation and fatigue. Scr. Metall. Mater., 26(10): 1499-1504, 1992. [3] E...associated with dislocation cores. Acta Materialia, 53:13131321, 2005. [13] H. Mughrabi . The long-range internal stress field in the dislocation wall

Fatigue Behavior of Ultrafine-Grained 5052 Al Alloy Processed Through Different Rolling Methods

NASA Astrophysics Data System (ADS)

Yogesha, K. K.; Joshi, Amit; Jayaganthan, R.

2017-05-01

In the present study, 5052 Al alloy was processed through different rolling methods to obtain ultrafine grains and its high-cycle fatigue behavior were investigated. The solution-treated Al-Mg alloys (AA 5052) were deformed through different methods such as cryorolling (CR), cryo groove rolling (CGR) and cryo groove rolling followed by warm rolling (CGW), up to 75% thickness reduction. The deformed samples were subjected to mechanical testing such as hardness, tensile and high-cycle fatigue (HCF) test at stress control mode. The CGW samples exhibit better HCF strength when compared to other conditions. The microstructure of the tested samples was characterized by optical microscopy, SEM fractography and TEM to understand the deformation behavior of deformed Al alloy. The improvement in fatigue life of CR and CGR samples is due to effective grain refinement, subgrain formations, and high dislocation density observed in the heavily deformed samples at cryogenic condition as observed from SEM and TEM analysis. However, in case of CGW samples, formation of nanoshear bands accommodates the applied strain during cyclic loading, thereby facilitating dislocation accumulation along with subgrain formations, leading to the high fatigue life. The deformed or broken impurity phase particles found in the deformed samples along with the precipitates that were formed during warm rolling also play a prominent role in enhancing the fatigue strength. These tiny particles hindered the dislocation movement by effectively pinning it at grain boundaries, thereby improving the resistance of crack propagation under cyclic load.

Early stage fatigue damage occurs in bovine tendon fascicles in the absence of changes in mechanics at either the gross or micro-structural level.

PubMed

Shepherd, Jennifer H; Riley, Graham P; Screen, Hazel R C

2014-10-01

Many tendon injuries are believed to result from repetitive motion or overuse, leading to the accumulation of micro-damage over time. In vitro fatigue loading can be used to characterise damage during repeated use and investigate how this may relate to the aetiology of tendinopathy. This study considered the effect of fatigue loading on fascicles from two functionally distinct bovine tendons: the digital extensor and deep digital flexor. Micro-scale extension mechanisms were investigated in fascicles before or after a period of cyclic creep loading, comparing two different measurement techniques - the displacement of a photo-bleached grid and the use of nuclei as fiducial markers. Whilst visual damage was clearly identified after only 300 cycles of creep loading, these visual changes did not affect either gross fascicle mechanics or fascicle microstructural extension mechanisms over the 900 fatigue cycles investigated. However, significantly greater fibre sliding was measured when observing grid deformation rather than the analysis of nuclei movement. Measurement of microstructural extension with both techniques was localised and this may explain the absence of change in microstructural deformation in response to fatigue loading. Alternatively, the data may demonstrate that fascicles can withstand a degree of matrix disruption with no impact on mechanics. Whilst use of a photo-bleached grid to directly measure the collagen is the best indicator of matrix deformation, nuclei tracking may provide a better measure of the strain perceived directly by the cells. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

Effect of severe plastic deformation on microstructure and mechanical properties of magnesium and aluminium alloys in wide range of strain rates

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir; Skripnyak, Evgeniya; Skripnyak, Vladimir; Vaganova, Irina; Skripnyak, Nataliya

2013-06-01

Results of researches testify that a grain size have a strong influence on the mechanical behavior of metals and alloys. Ultrafine grained HCP and FCC metal alloys present higher values of the spall strength than a corresponding coarse grained counterparts. In the present study we investigate the effect of grain size distribution on the flow stress and strength under dynamic compression and tension of aluminium and magnesium alloys. Microstructure and grain size distribution in alloys were varied by carrying out severe plastic deformation during the multiple-pass equal channel angular pressing, cyclic constrained groove pressing, and surface mechanical attrition treatment. Tests were performed using a VHS-Instron servo-hydraulic machine. Ultra high speed camera Phantom V710 was used for photo registration of deformation and fracture of specimens in range of strain rates from 0,01 to 1000 1/s. In dynamic regime UFG alloys exhibit a stronger decrease in ductility compared to the coarse grained material. The plastic flow of UFG alloys with a bimodal grain size distribution was highly localized. Shear bands and shear crack nucleation and growth were recorded using high speed photography.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-01-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-03-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses

PubMed Central

Launey, Maximilien E.; Hofmann, Douglas C.; Johnson, William L.; Ritchie, Robert O.

2009-01-01

The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems. PMID:19289820

Evolution of interphase and intergranular strain in zirconium-niobium alloys during deformation at room temperature

NASA Astrophysics Data System (ADS)

Cai, Song

Zr-2.5Nb is currently used for pressure tubes in the CANDU (CANada Deuterium Uranium) reactor. A complete understanding of the deformation mechanism of Zr-2.5Nb is important if we are to accurately predict the in-reactor performance of pressure tubes and guarantee normal operation of the reactors. This thesis is a first step in gaining such an understanding; the deformation mechanism of ZrNb alloys at room temperature has been evaluated through studying the effect of texture and microstructure on deformation. In-situ neutron diffraction was used to monitor the evolution of the lattice strain of individual grain families along both the loading and Poisson's directions and to track the development of interphase and intergranular strains during deformation. The following experiments were carried out with data interpreted using elasto-plastic modeling techniques: (1) Compression tests of a 100%betaZr material at room temperature. (2) Tension and compression tests of hot rolled Zr-2.5Nb plate material. (3) Compression of annealed Zr-2.5Nb. (4) Cyclic loading of the hot rolled Zr-2.5Nb. (5) Compression tests of ZrNb alloys with different Nb and oxygen contents. The experimental results were interpreted using a combination of finite element (FE) and elasto-plastic self-consistent (EPSC) models. The phase properties and phase interactions well represented by the FE model, the EPSC model successfully captured the evolution of intergranular constraint during deformation and provided reasonable estimates of the critical resolved shear stress and hardening parameters of different slip systems under different conditions. The consistency of the material parameters obtained by the EPSC model allows the deformation mechanism at room temperature and the effect of textures and microstructures of ZrNb alloys to be understood. This work provides useful information towards manufacturing of Zr-2.5Nb components and helps in producing ideal microstructures and material properties for pressure tubes. Also it is helpful in guiding the development of new materials for the next generation of nuclear reactors. Furthermore, the large data set obtained from this study can be used in evaluation and improving current and future polycrystalline deformation models.

Atomic scale characterization of white etching area and its adjacent matrix in a martensitic 100Cr6 bearing steel

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

Li, Y.J., E-mail: y.li@mpie.de

Atom probe tomography was employed to characterize the microstructure and C distribution in the white etching area (WEA) of a martensitic 100Cr6 bearing steel subjected to rolling contact fatigue. Different from its surrounding matrix where a plate-like martensitic structure prevails, the WEA exhibits equiaxed grains with a uniform grain size of about 10 nm. Significant C grain boundary enrichment (>7.5at.%) and an overall higher C concentration than the nominal value are observed in the WEA. These results suggest that the formation of WEA results from severe local plastic deformation that causes dissolution of carbides and the redistribution of C. -more » Highlights: •APT has been applied to characterize the microstructure of white etching area (WEA). •Quantitative analyses of C distribution indicate that carbides are dissolved on the WEA. •WEA contains equiaxed grains with a uniform grain size of 10 nm. •C segregation at grain boundaries stabilizes the nanosized grain structure. •Formation of WEA is explained by severe local plastic deformation introduced by cyclic contact loading.« less

A Fatigue Model for Discontinuous Particulate-Reinforced Aluminum Alloy Composite: Influence of Microstructure

NASA Astrophysics Data System (ADS)

McCullough, R. R.; Jordon, J. B.; Brammer, A. T.; Manigandan, K.; Srivatsan, T. S.; Allison, P. G.; Rushing, T. W.

2014-01-01

In this paper, the use of a microstructure-sensitive fatigue model is put forth for the analysis of discontinuously reinforced aluminum alloy metal matrix composite. The fatigue model was used for a ceramic particle-reinforced aluminum alloy deformed under conditions of fully reversed strain control. Experimental results revealed the aluminum alloy to be strongly influenced by volume fraction of the particulate reinforcement phase under conditions of strain-controlled fatigue. The model safely characterizes the evolution of fatigue damage in this aluminum alloy composite into the distinct stages of crack initiation and crack growth culminating in failure. The model is able to capture the specific influence of particle volume fraction, particle size, and nearest neighbor distance in quantifying fatigue life. The model yields good results for correlation of the predicted results with the experimental test results on the fatigue behavior of the chosen aluminum alloy for two different percentages of the ceramic particle reinforcement. Further, the model illustrates that both particle size and volume fraction are key factors that govern fatigue lifetime. This conclusion is well supported by fractographic observations of the cyclically deformed and failed specimens.

Brittle-viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions

NASA Astrophysics Data System (ADS)

Kjøll, H. J.; Viola, G.; Menegon, L.; Sørensen, B. E.

2015-06-01

We studied by Electron BackScatter Diffraction (EBSD) and optical microscopy a coarse-grained (ca. 0.5-6 mm) quartz vein embedded in a phyllonitic matrix to gain insights into the recrystallization mechanisms and the processes of strain localization in quartz deformed under lower greenschist facies conditions, broadly coincident with the brittle-viscous transition. The vein deformed during faulting along a phyllonitic thrust of Caledonian age within the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The phyllonite hosting the vein formed at the expense of a metabasaltic protolith through feldspar breakdown to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the quartz vein acted as a relatively rigid body. Viscous deformation in the vein was initially accommodated by quartz basal slip. Under the prevailing deformation conditions, however, dislocation glide- and possibly creep-accommodated deformation of quartz was inefficient, and this resulted in localized strain hardening. In response to the (1) hardening, (2) progressive and cyclic increase of the fluid pressure, and (3) increasing competence contrast between the vein and the weakly foliated host phyllonite, vein quartz crystals began to deform by brittle processes along specific, suitably oriented lattice planes, creating microgouges along microfractures. Nucleated new grains rapidly sealed these fractures as fluids penetrated the actively deforming system. The grains grew initially by solution precipitation and later by grain boundary migration. We suggest that the different initial orientation of the vein crystals led to strain accommodation by different mechanisms in the individual crystals, generating remarkably different microstructures. Crystals suitably oriented for basal slip, for example, accommodated strain mainly viscously and experienced only minor fracturing. Instead, crystals misoriented for basal slip hardened and deformed predominantly by domainal fracturing. This study indicates the importance of considering shear zones as dynamic systems wherein the activated deformation mechanisms may vary through time in response to the complex temporal and spatial evolution of the shear zone, often in a cyclic fashion.

Effects of Loading Frequency on Fatigue Behavior, Residual Stress, and Microstructure of Deep-Rolled Stainless Steel AISI 304 at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Nikitin, I.; Juijerm, P.

2018-02-01

The effects of loading frequency on the fatigue behavior of non-deep-rolled (NDR) and deep-rolled (DR) austenitic stainless steel AISI 304 were systematically clarified at elevated temperatures, especially at temperatures exhibiting the dynamic strain aging (DSA) phenomena. Tension-compression fatigue tests were performed isothermally at temperatures of 573 K and 773 K (300 °C and 500 °C) with different loading frequencies of 5, 0.5, 0.05, and 0.005 Hz. For the DR condition, the residual stresses and work-hardening states will be presented. It was found that DSA would be detected at appropriate temperatures and deformation rates. The cyclic deformation curves and the fatigue lives of the investigated austenitic stainless steel AISI 304 are considerably affected by the DSA, especially on the DR condition having high dislocation densities at the surface and in near-surface regions. In the temperature range of the DSA, residual stresses and work-hardening states of the DR condition seem to be stabilized. The microstructural alterations were investigated by transmission electron microscopy (TEM). At an appropriate temperature with low loading frequency, the plastic deformation mechanism shifted from a wavy slip manner to a planar slip manner in the DSA regimes, whereas the dislocation movements were obstructed.

High cycle fatigue in the transmission electron microscope

DOE PAGES

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.; ...

2016-06-28

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

High cycle fatigue in the transmission electron microscope

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

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this paper, the tension–tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were appliedmore » at frequencies from one to several hundred hertz, enabling accumulations of 10 6 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ~10 –12 m·cycle –1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. Finally, these observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.« less

Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

DOE PAGES

Hennessey, Conor; Castelluccio, Gustavo M.; McDowell, David L.

2017-02-01

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT)more » within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

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

Hennessey, Conor; Castelluccio, Gustavo M.; McDowell, David L.

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT)more » within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

State-variable theories for nonelastic deformation

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

Li, C.Y.

The various concepts of mechanical equation of state for nonelastic deformation in crystalline solids, originally proposed for plastic deformation, have been recently extended to describe additional phenomena such as anelastic and microplastic deformation including the Bauschinger effect. It has been demonstrated that it is possible to predict, based on current state variables in a unified way, the mechanical response of a material under an arbitrary loading. Thus, if the evolution laws of the state variables are known, one can describe the behavior of a material for a thermal-mechanical path of interest, for example, during constant load (or stress) creep withoutmore » relying on specialized theories. Some of the existing theories of mechanical equation of state for nonelastic deformation are reviewed. The establishment of useful forms of mechanical equation of state has to depend on extensive experimentation in the same way as that involved in the development, for example, the ideal gas law. Recent experimental efforts are also reviewed. It has been possible to develop state-variable deformation models based on experimental findings and apply them to creep, cyclic deformation, and other time-dependent deformation. Attempts are being made to correlate the material parameters of the state-variable models with the microstructure of a material. 24 figures.« less

Cyclic hardening behavior of extruded ZK60 magnesium alloy with different grain sizes

NASA Astrophysics Data System (ADS)

Zhang, Lixin; Zhang, Wencong; Chen, Wenzhen; Wang, Wenke

2018-04-01

Montonic and fully reversed strain-controlled cyclic deformation experiments were conducted on extruded ZK60 magnesium alloy with two different grain sizes in ambient air. Results revealed that the hardening rates of the ZK60 magnesium alloy rods with fine grain and coarse grain in the monotonic deformation and the fully reversed strain-controlled cyclic deformation were opposite along the extrusion direction. Electron Backscatter Diffration analysis revealed that fine grains were more easily rotated than coarse grains under the cyclic deformation. Under the twinning and detwinning process of the cyclic deformation at a large strain amplitude, the coarse grained ZK60 magnesium alloys were more prone to tension twinning {10-12}<10-11> and more residual twins were observed. Texture hardening of coarse grained magnesium alloy was more obvious in cyclic defromation than fine-grained magnesium alloy.

Influence of Temperature on Fatigue-Induced Martensitic Phase Transformation in a Metastable CrMnNi-Steel

NASA Astrophysics Data System (ADS)

Biermann, Horst; Glage, Alexander; Droste, Matthias

2016-01-01

Metastable austenitic steels can exhibit a fatigue-induced martensitic phase transformation during cyclic loading. It is generally agreed that a certain strain amplitude and a threshold of the cumulated plastic strain must be exceeded to trigger martensitic phase transformation under cyclic loading. With respect to monotonic loading, the martensitic phase transformation takes place up to a critical temperature—the so-called M d temperature. The goal of the present investigation is to determine an M d,c temperature which would be the highest temperature at which a fatigue-induced martensitic phase transformation can take place. For this purpose, fatigue tests controlled by the total strain were performed at different temperatures. The material investigated was a high-alloy metastable austenitic steel X3CrMnNi16.7.7 (16.3Cr-7.2Mn-6.6Ni-0.03C-0.09N-1.0Si) produced using the hot pressing technique. The temperatures were set in the range of 283 K (10 °C) ≤ T ≤ 473 K (200 °C). Depending on the temperature and strain amplitude, the onset of the martensitic phase transformation shifted to different values of the cumulated plastic strain, or was inhibited completely. Moreover, it is known that metastable austenitic CrMnNi steels with higher nickel contents can exhibit the deformation-induced twinning effect. Thus, at higher temperatures and strain amplitudes, a transition from the deformation-induced martensitic transformation to deformation-induced twinning takes place. The fatigue-induced martensitic phase transformation was monitored during cyclic loading using a ferrite sensor. The microstructure after the fatigue tests was examined using the back-scattered electrons, the electron channeling contrast imaging and the electron backscatter diffraction techniques to study the temperature-dependent dislocation structures and phase transformations.

Cyclic Stable-Unstable Slip Preserved along an Appalachian Fault

NASA Astrophysics Data System (ADS)

Wells, R. K.; Newman, J.; Holyoke, C. W., III; Wojtal, S. F.

2017-12-01

The inactive Copper Creek thrust, southern Appalachians, TN, preserves evidence suggesting cyclic aseismic and unstable slip. The Copper Creek thrust is a low-temperature (4-6 km burial depth) foreland thrust with an estimated net slip of 15-20 km. Immediately below the 2 cm thick calcite-shale fault zone, the footwall is composed of shale with cross-cutting calcite veins and is separated from the fault zone by a 300 µm thick layered calcite vein. Optical and electron microscopy indicates that this complex vein layer experienced grain size reduction by plasticity-induced fracturing followed by aseismic diffusion creep. The fault zone calcite exhibits interpenetrating grain boundaries and four-grain junctions suggesting diffusion creep, but also contains nanoscale grains (7 nm), vesicular calcite, and partially-coated clasts indicating unstable, possibly seismic, slip. Well-preserved clasts of deformed calcite vein layer material within the fault zone indicate repeated cycle(s) of aseismic diffusion creep. In addition, nanoscale calcite grains, 30 nm, with straight grain boundaries that form triple junctions, may represent earlier nanoscale grains formed during unstable slip that have experienced grain growth during periods of aseismic creep. Based on the spatial and temporal relations of these preserved microstructures, we propose a sequence of deformation processes consistent with cyclic episodes of unstable slip separated by intervals of aseismic creep. Formation of calcite-filled veins is followed by grain size reduction in vein calcite by plasticity-induced fracturing and aseismic grain-size sensitive diffusion creep deformation in fine-grained calcite. During aseismic creep, the combination of grain growth, resulting in fault strengthening, and an increase in pore fluid pressure, reducing the effective fault strength, leads to new fractures and/or an unstable slip event. During unstable slip, nanograins and vesicular calcite form as a result of thermal decomposition and coated clasts form as a result of fluidization of the fault zone, and are then incorporated within ductilely deforming calcite during a new interval of aseismic creep.

Microstructure and mesh sensitivities of mesoscale surrogate driving force measures for transgranular fatigue cracks in polycrystals

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

Castelluccio, Gustavo M.; McDowell, David L.

The number of cycles required to form and grow microstructurally small fatigue cracks in metals exhibits substantial variability, particularly for low applied strain amplitudes. This variability is commonly attributed to the heterogeneity of cyclic plastic deformation within the microstructure, and presents a challenge to minimum life design of fatigue resistant components. Our paper analyzes sources of variability that contribute to the driving force of transgranular fatigue cracks within nucleant grains. We also employ crystal plasticity finite element simulations that explicitly render the polycrystalline microstructure and Fatigue Indicator Parameters (FIPs) averaged over different volume sizes and shapes relative to the anticipatedmore » fatigue damage process zone. Volume averaging is necessary to both achieve description of a finite fatigue damage process zone and to regularize mesh dependence in simulations. Furthermore, results from constant amplitude remote applied straining are characterized in terms of the extreme value distributions of volume averaged FIPs. Grain averaged FIP values effectively mitigate mesh sensitivity, but they smear out variability within grains. Furthermore, volume averaging over bands that encompass critical transgranular slip planes appear to present the most attractive approach to mitigate mesh sensitivity while preserving variability within grains.« less

Microstructure and mesh sensitivities of mesoscale surrogate driving force measures for transgranular fatigue cracks in polycrystals

DOE PAGES

Castelluccio, Gustavo M.; McDowell, David L.

2015-05-22

The number of cycles required to form and grow microstructurally small fatigue cracks in metals exhibits substantial variability, particularly for low applied strain amplitudes. This variability is commonly attributed to the heterogeneity of cyclic plastic deformation within the microstructure, and presents a challenge to minimum life design of fatigue resistant components. Our paper analyzes sources of variability that contribute to the driving force of transgranular fatigue cracks within nucleant grains. We also employ crystal plasticity finite element simulations that explicitly render the polycrystalline microstructure and Fatigue Indicator Parameters (FIPs) averaged over different volume sizes and shapes relative to the anticipatedmore » fatigue damage process zone. Volume averaging is necessary to both achieve description of a finite fatigue damage process zone and to regularize mesh dependence in simulations. Furthermore, results from constant amplitude remote applied straining are characterized in terms of the extreme value distributions of volume averaged FIPs. Grain averaged FIP values effectively mitigate mesh sensitivity, but they smear out variability within grains. Furthermore, volume averaging over bands that encompass critical transgranular slip planes appear to present the most attractive approach to mitigate mesh sensitivity while preserving variability within grains.« less

Design of novel materials for additive manufacturing - Isotropic microstructure and high defect tolerance.

PubMed

Günther, J; Brenne, F; Droste, M; Wendler, M; Volkova, O; Biermann, H; Niendorf, T

2018-01-22

Electron Beam Melting (EBM) is a powder-bed additive manufacturing technology enabling the production of complex metallic parts with generally good mechanical properties. However, the performance of powder-bed based additively manufactured materials is governed by multiple factors that are difficult to control. Alloys that solidify in cubic crystal structures are usually affected by strong anisotropy due to the formation of columnar grains of preferred orientation. Moreover, processing induced defects and porosity detrimentally influence static and cyclic mechanical properties. The current study presents results on processing of a metastable austenitic CrMnNi steel by EBM. Due to multiple phase transformations induced by intrinsic heat-treatment in the layer-wise EBM process the material develops a fine-grained microstructure almost without a preferred crystallographic grain orientation. The deformation-induced phase transformation yields high damage tolerance and, thus, excellent mechanical properties less sensitive to process-induced inhomogeneities. Various scan strategies were applied to evaluate the width of an appropriate process window in terms of microstructure evolution, porosity and change of chemical composition.

Low cycle fatigue

NASA Technical Reports Server (NTRS)

Solomon, H. D. (Editor); Kaisand, L. R. (Editor); Halford, G. R. (Editor); Leis, B. N. (Editor)

1988-01-01

The papers contained in this volume focus on various aspects of low cycle fatigue, including cyclic deformation, crack propagation, high-temperature low cycle fatigue, microstructural defects, multiaxial and variable amplitude loading, and life prediction. Papers are presented on the low cycle fatigue of some aluminum alloys, prediction of crack growth under creep-fatigue loading conditions, high-temperature low cycle fatigue behavior and lifetime prediction of a nickel-base ODS alloy, and an integrated approach to creep-fatigue life prediction. Other topics discussed include thermal fatigue testing of coated monocrystalline superalloys, low cycle fatigue of Al-Mg-Si alloys, and the effect of superimposed stresses at high frequency on low cycle fatigue.

Review of the Effects of Microstructure on Fatigue in Aluminum Alloys. Ph.D. Thesis - Cincinnati Univ.

NASA Technical Reports Server (NTRS)

Telesman, J.

1984-01-01

Literature survey was conducted to determine the effects of different microstructural features and different load histories on fatigue crack initiation and propagation of aluminum alloys. Comparison of microstructure and monotonic and cyclic properties between powder metallurgy (P/M) and ingot metallurgy (I/M) alloys is presented. The two alloys that are representative of each process on which the comparison is focused are X7091 and 7050. Included is a detailed description of the microstructure produced through the P/M and I/M proesses. The effect of each pertinent microstructural feature on monotonic and cyclic properties, such as yield strength, toughness, crack initiation and propagation is discussed. Also discussed are the proposed mechanisms for crack initiation and propagation, as well as the effects of aggressive environments on these cyclic properties. The effects of variable amplitude loadin on fatigue crack propagation and the various models proposed to predict load interaction effects are discussed.

Deformation-resembling microstructure created by fluid-mediated dissolution-precipitation reactions.

PubMed

Spruzeniece, Liene; Piazolo, Sandra; Maynard-Casely, Helen E

2017-01-27

Deformation microstructures are widely used for reconstructing tectono-metamorphic events recorded in rocks. In crustal settings deformation is often accompanied and/or succeeded by fluid infiltration and dissolution-precipitation reactions. However, the microstructural consequences of dissolution-precipitation in minerals have not been investigated experimentally. Here we conducted experiments where KBr crystals were reacted with a saturated KCl-H 2 O fluid. The results show that reaction products, formed in the absence of deformation, inherit the general crystallographic orientation from their parents, but also display a development of new microstructures that are typical in deformed minerals, such as apparent bending of crystal lattices and new subgrain domains, separated by low-angle and, in some cases, high-angle boundaries. Our work suggests that fluid-mediated dissolution-precipitation reactions can lead to a development of potentially misleading microstructures. We propose a set of criteria that may help in distinguishing such microstructures from the ones that are created by crystal-plastic deformation.

In-Plane Anisotropy in Mechanical Behavior and Microstructural Evolution of Commercially Pure Titanium in Tensile and Cyclic Loading

NASA Astrophysics Data System (ADS)

Sinha, Subhasis; Gurao, N. P.

2017-12-01

Tensile and cyclic deformation behavior of three samples oriented at 0, 45, and 90 deg to the rolling direction in the rolling direction-transverse direction (RD-TD) plane of cold-rolled and annealed plate of commercially pure titanium is studied in the present investigation. The sample along the RD (R0) shows the highest strength but lowest ductility in monotonic tension. Although ultimate tensile strength (UTS) and elongation of samples along 45 and 90 deg to the RD (R45 and R90, respectively) are similar, the former has significantly higher yield strength than the latter, indicating different strain-hardening behavior. It is found that the R90 sample exhibits the highest monotonic ductility as well as fatigue life. This is attributed to a higher propensity for twinning in this sample with the presence of multiple variants and twin intersections. Cyclic life is also influenced by the high tendency for detwinning of contraction twins in this orientation. Elastoplastic self-consistent (EPSC) simulations of one-cycle tension-compression load reversal indicate that the activity of pyramidal 〈 c + a〉 slip and extension twinning oscillates during cyclic loading that builds up damage in a cumulative manner, leading to failure in fatigue.

A crystal plasticity model incorporating the effects of precipitates in superalloys: Application to tensile, compressive, and cyclic deformation of Inconel 718

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

Ghorbanpour, Saeede; Zecevic, Milovan; Kumar, Anil

An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. In using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclicmore » mechanical test data applied in different AM build directions. We demonstrate that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates.« less

A crystal plasticity model incorporating the effects of precipitates in superalloys: Application to tensile, compressive, and cyclic deformation of Inconel 718

DOE PAGES

Ghorbanpour, Saeede; Zecevic, Milovan; Kumar, Anil; ...

2017-09-14

An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. In using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclicmore » mechanical test data applied in different AM build directions. We demonstrate that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates.« 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.

Microstructure characterization based on the type of deformed grains in cold-rolled, Cu-added, bake-hardenable steel

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

Kim, J.S.; Kim, S.I.; Choi, S.-H., E-mail: shihoon@sunchon.ac.kr

2014-06-01

The electron backscatter diffraction technique has been used to characterize the microstructure of deformed grains in cold-rolled, Cu-added, bake-hardenable steel. A new scheme based on the kind and number of average orientations, as determined from a unique grain map of the deformed grains, was developed in order to classify deformed grains by type. The α-fiber components, γ-fiber components and random orientations, those which could not be assigned to either γ-fiber or α-fiber components, were used to define the average orientation of unique grains within individual deformed grains. The microstructures of deformed grains in as-rolled specimens were analyzed based on themore » Taylor factor, stored energy, and misorientation. The relative levels and distributions of the Taylor factor, the stored energy and the misorientation were examined in terms of the types of deformed grains. - Highlights: • We characterized the microstructure of Cu-added BH steel using EBSD. • A new scheme was developed in order to classify deformed grains by type. • Stored energy and misorientation are strongly dependent on the type of deformed grains. • Microstructure was examined in terms of the types of deformed grains.« less

Heavy Deformation of Patented Near-Eutectoid Steel

NASA Astrophysics Data System (ADS)

Khanchandani, Heena; Banerjee, M. K.

2018-01-01

Evolution of microstructure in the patented near-eutectoid steel, forged under varying situations, is critically examined in the present investigation. Steel with 0.74 wt.% carbon is isothermally annealed at 500 °C to obtain fine pearlite microstructure. Steel samples, so patented, are subjected to mechanical deformation by forging at various temperatures with different amount of thickness reduction. Microstructural analyses have revealed that mechanical deformation by forging at lower temperatures brings about partial dissolution of cementite, which is followed by the formation of ɛ-carbide in the microstructures. In contrast, cementite is precipitated within ferrite matrix upon warm or hot forging at higher temperatures. It is further observed that increasing deformation percent during low-temperature forging reduces interlamellar spacing of pearlite, whereas an opposite trend is noticed in case of deformation at higher temperature; moreover, deformation induced the change in interlamellar spacing and formation of fine carbide phases in microstructures has caused appreciable enhancement in hardness of the steel.

Unraveling cyclic deformation mechanisms of a rolled magnesium alloy using in situ neutron diffraction

DOE PAGES

Wu, Wei; An, Ke; Liaw, Peter K.

2014-12-23

In the current study, the deformation mechanisms of a rolled magnesium alloy were investigated under cyclic loading using real-time in situ neutron diffraction under a continuous-loading condition. The relationship between the macroscopic cyclic deformation behavior and the microscopic response at the grain level was established. The neutron diffraction results indicate that more and more grains are involved in the twinning and detwinning deformation process with the increase of fatigue cycles. The residual twins appear in the early fatigue life, which is responsible for the cyclic hardening behavior. The asymmetric shape of the hysteresis loop is attributed to the early exhaustionmore » of the detwinning process during compression, which leads to the activation of dislocation slips and rapid strain-hardening. The critical resolved shear stress for the activation of tensile twinning closely depends on the residual strain developed during cyclic loading. In the cycle before the sample fractured, the dislocation slips became active in tension, although the sample was not fully twinned. The increased dislocation density leads to the rise of the stress concentration at weak spots, which is believed to be the main reason for the fatigue failure. Furthermore, the deformation history greatly influences the deformation mechanisms of hexagonal-close-packed-structured magnesium alloy during cyclic loading.« less

Effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy

NASA Astrophysics Data System (ADS)

Wu, Wenqian; Guo, Lin; Liu, Bin; Ni, Song; Liu, Yong; Song, Min

2017-12-01

The effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy have been investigated. The torsional deformation generates a gradient microstructure distribution due to the gradient torsional strain. Both dislocation activity and deformation twinning dominated the torsional deformation process. With increasing the torsional equivalent strain, the microstructural evolution can be described as follows: (1) formation of pile-up dislocations parallel to the trace of {1 1 1}-type slip planes; (2) formation of Taylor lattices; (3) formation of highly dense dislocation walls; (3) formation of microbands and deformation twins. The extremely high deformation strain (strained to fracture) results in the activation of wavy slip. The tensile strength is very sensitive to the torsional deformation, and increases significantly with increasing the torsional angle.

Fatigue and Creep-Fatigue Deformation of an Ultra-Fine Precipitate Strengthened Advanced Austenitic Alloy

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

M.C. Carroll; L.J. Carroll

An advanced austenitic alloy, HT-UPS (high-temperature ultrafine-precipitation-strengthened), has been identified as an ideal candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS alloys demonstrate improved creep resistance relative to 316 stainless steel (SS) through additions of Ti and Nb, which precipitate to form a widespread dispersion of stable nanoscale metallic carbide (MC) particles in the austenitic matrix. The low-cycle fatigue and creep-fatigue behavior of an HT-UPS alloy have been investigated at 650 °C and a 1.0% total strain, with an R-ratio of -1 and hold times at peak tensile strain as long as 150 min. Themore » cyclic deformation response of HT-UPS is directly compared to that of standard 316 SS. The measured values for total cycles to failure are similar, despite differences in peak stress profiles and in qualitative observations of the deformed microstructures. Crack propagation is primarily transgranular in fatigue and creep-fatigue of both alloys at the investigated conditions. Internal grain boundary damage in the form of fine cracks resulting from the tensile hold is present for hold times of 60 min and longer, and substantially more internal cracks are quantifiable in 316 SS than in HT-UPS. The dislocation substructures observed in the deformed material differ significantly; an equiaxed cellular structure is observed in 316 SS, whereas in HT-UPS the microstructure takes the form of widespread and relatively homogenous tangles of dislocations pinned by the nanoscale MC precipitates. The significant effect of the fine distribution of precipitates on observed fatigue and creep-fatigue response is described in three distinct behavioral regions as it evolves with continued cycling.« less

Fatigue behavior of ULTIMETRTM alloy: Experiment and theoretical modeling

NASA Astrophysics Data System (ADS)

Jiang, Liang

ULTIMETRTM alloy is a commercial Co-26Cr-9Ni (weight percent) superalloy, which possesses excellent resistance to both wear and corrosion. In order to extend the structural applications of this alloy and improve the fundamental understanding of the fatigue damage mechanisms, stress- and strain-controlled fatigue tests were performed at various temperatures and in different environments. The stress- and strain-life data were developed for the structural design and engineering applications of this material. Fractographic studies characterized the crack-initiation and propagation behavior of the alloy. Microstructure evolution during fatigue was revealed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Specifically, it was found that the metastable face-centered-cubic structure of this alloy in the as-received condition could be transformed into a hexagonal-close-packed structure either under the action of plastic deformation at room temperature, or due to the aging and cyclic deformation at intermediate temperatures. This interesting observation constructed a sound basis for the alloy development. The dominant mechanisms, which control the fatigue behavior of ULTIMET alloy, were characterized. High-speed, high-resolution infrared (IR) thermography, as a non-contact, full-field, and nondestructive technique, was used to characterize the damage during fatigue. The temperature variations during each fatigue cycle, which were due to the thermal-elastic-plastic effect, were observed and related to stress-strain analyses. The temperature evolution during fatigue manifested the cumulative fatigue damage process. A constitutive model was developed to predict thermal and mechanical responses of ULTIMET alloy subjected to cyclic deformation. The predicted cyclic stress-strain responses and temperature variations were found to be in good agreement with the experimental results. In addition, a fatigue life prediction model was developed based on the strain-energy consideration, and the measured temperature could be utilized as an index for fatigue-life prediction.

Role of coupled cataclasis-pressure solution deformation in microearthquake activity along the creeping segment of the SAF: Inferences from studies of the SAFOD core samples

NASA Astrophysics Data System (ADS)

Hadizadeh, J.; Gratier, J.; Renard, F.; Mittempregher, S.; di Toro, G.

2009-12-01

Rocks encountered in the SAFOD drill hole represent deformation in the southern-most extent of the creeping segment of the SAF north of the Parkfield. At the site and toward the northwest the SAF is characterized by aseismic creep as well as strain release through repeating microearthquakes M<3. The activity is shown to be mostly distributed as clusters aligned in the slip direction, and occurring at depths of between 3 to 5 kilometers. It has been suggested that the events are due to frequent moment release from high strength asperities constituting only about 1% or less of the total fault surface area within an otherwise weak fault gouge. We studied samples selected from the SAFOD phase 3 cores (3142m -3296m MD) using high resolution scanning electron microscopy, cathodoluminescence imaging, X-ray fluorescence mapping, and energy dispersive X-ray spectroscopy. The observed microstructural deformation that is apparently relevant to the seismological data includes clear evidence of cyclic deformation events, cataclastic flow, and pressure solution creep with attendant vein sealing and fracture healing fabrics. Friction testing of drill cuttings and modeling by others suggest that the overall creep behavior in shale-siltstone gouge may be due to low bulk friction coefficient of 0.2-0.4 for the fault rock. Furthermore, the low resistivity zone extending to about 5km beneath the SAFOD-Middle Mountain area is believed to consist of a pod of fluid-filled fractured and porous rocks. Our microstructural data indicate that the foliated shale-siltstone cataclasites are, in a highly heterogeneous way, more porous and permeable than the host rock and therefore provide for structurally controlled enhanced fluid-rock interactions. This is consistent with the observed pressure solution deformation and the microstructural indications of transiently high fluid pressures. We hypothesize that while the friction laws defining stable sliding are prevalent in bulk deformation of the creeping segment, there exist the possibility of steady conditions for repetitive healing, dilation, and rupture of populations of stress-oriented patches due to operation of pressure solution creep along the fault zone. The limitation on the total area of the locked patches at any given time would be controlled primarily by the imposed tectonic and near field rates of slip and fluid flux within the local permeability structure. The available geophysical data for the creeping section of the SAF including hypocenter cluster distribution, moment release rate, seismic rupture area (∝ healed patch size), stress drop and return time characteristics point to a highly heterogeneous internal structure at the SAFOD site, and could be used to test the proposed coupled cataclasis-pressure solution microstructural model.

Ultrasonic fatigue of a high strength steel

NASA Astrophysics Data System (ADS)

Koster, M.; Wagner, G.; Eifler, D.

2010-07-01

At the Institute of Materials Science and Engineering at the University of Kaiserslautern an ultrasonic testing system for the fatigue assessment of metallic materials in the very high cycle fatigue (VHCF) regime was developed. The ultrasonic testing system allows to control the test and to measure detailed fatigue data. The achieved results can be used to describe the cyclic deformation behaviour of wheel steels at ultrasonic frequencies. In load increase tests (LIT), the critical stress amplitude can be determined, which leads to a defined change of process parameters like generator power, dissipated energy and specimen temperature. With SEM investigations it was proved that the change of the process parameters correlates with irreversible changes in the microstructure. It can be shown that the stress amplitude, leading to first irreversible changes in the microstructure, strongly depends on the depth position within the original wheel rim. New and basic results on the fatigue mechanisms of high strength steels in the VHCF-regime can be achieved.

Low-Cycle Fatigue Behavior of Die-Cast Mg Alloy AZ91

NASA Astrophysics Data System (ADS)

Rettberg, Luke; Anderson, Warwick; Jones, J. Wayne

An investigation has been conducted on the influence of microstructure and artificial aging response (T6) on the low-cycle fatigue behavior of super vacuum die-cast (SVDC) AZ91. Fatigue lifetimes were determined from total strain-controlled fatigue tests for strain amplitudes of 0.2%, 0.4% and 0.6%, under fully reversed loading at a frequency of 5 Hz. Cyclic stress-strain behavior was determined using incremental step test (IST) methods. Two locations in a prototype casting with different thicknesses and, therefore, solidification rates, microstructure and porosity, were examined. In general., at all total strain amplitudes fatigue life was unaffected by microstructure refinement and was attributed to significant levels of porosity. Cyclic softening and a subsequent increased cyclic hardening rate, compared to monotonic tests, were observed, independent of microstructure. These results, fractography and damage accumulation processes, determined from metallographic sectioning, are discussed.

Sulfur Impurities and the Microstructure of Alumina Scales

NASA Technical Reports Server (NTRS)

Smialek, James L.

1997-01-01

The relationship between the microstructure of alumina scales, adhesion, and sulfur content was examined through a series of nickel alloys oxidized in 1100 to 1200 deg. C cyclic or isothermal exposures in air. In cyclic tests of undoped NiCrAl, adhesion was produced when the sulfur content was reduced, without any change in scale microstructure. Although interfacial voids were not observed in cyclic tests of NiCrAl, they were promoted by long-term isothermal exposures, by sulfur doping, and in most exposures of NiAl. Two single crystal superalloys, PWA 1480 and Rene' N5, were also tested, either in the as-received condition or after the sulfur content had been reduced to less than 1 ppmw by hydrogen annealing. The unannealed alloys always exhibited spalling to bare metal, but interfacial voids were not observed consistently. Desulfurized PWA 1480 and Rene' N5 exhibited remarkable adhesion and no voidage for either isothermal or cyclic exposures. The most consistent microstructural feature was that, for the cases where voids did form, the scale undersides exhibited corresponding areas with ridged oxide grain boundaries. Voids were not required for spallation nor were other microstructural features essential for adhesion. These observations are consistent with the model whereby scale spallation is controlled primarily by interfacial sulfur segregation and the consequent degradation of oxide-metal bonding.

Localization in Naturally Deformed Systems - the Default State?

NASA Astrophysics Data System (ADS)

Clancy White, Joseph

2017-04-01

Based on the extensive literature on localized rock deformation, conventional wisdom would interpret it to be a special behaviour within an anticipated background of otherwise uniform deformation. The latter notwithstanding, the rock record is so rife with transient (cyclic), heterogeneous deformation, notably shear localization, as to characterize localization as the anticipated 'normal' behaviour. The corollary is that steady, homogeneous deformation is significantly less common, and if achieved must reflect some special set of conditions that are not representative of the general case. An issue central to natural deformation is then not the existance of localized strain, but rather how the extant deformation processes scale across tectonic phenomena and in turn organize to enable a coherent(?) descripion of Earth deformation. Deformation is fundamentally quantized, discrete (diffusion, glide, crack propagation) and reliant on the defect state of rock-forming minerals. The strain energy distribution that drives thermo-mechanical responses is in the first instance established at the grain-scale where the non-linear interaction of defect-mediated micromechanical processes introduces heterogeneous behaviour described by various gradient theories, and evidenced by the defect microstructures of deformed rocks. Hence, the potential for non-uniform response is embedded within even quasi-uniform, monomineralic materials, seen, for example, in the spatially discrete evolution of dynamic recrystallization. What passes as homogeneous or uniform deformation at various scales is the aggregation of responses at some characteristic dimension at which heterogeneity is not registered or measured. Nevertheless, the aggregate response and associated normalized parameters (strain, strain rate) do not correspond to any condition actually experienced by the deforming material. The more common types of macroscopic heterogeneity promoting localization comprise mechanically contrasting materials typical of most rocks. Such perturbations are of themselves only larger examples of variation in the fundamental defect distribution and response; that is the boundary conditions that induce heterogeneous response are reflections of the microphysical behaviour seen in aggregate as strain accommodating softening or stabilization processes such as grain size reduction and independent grain displacements. Additionally, cyclic interplay between inelastic rupture and subsequent plastic material softening resulting from the concomitant introduction of exogenous material in the form of igneous melts, deformation-induced melts and fluid precipitates (veins). This two-stage process determines the siting and temporary stabilization of the shear phenomena, and indicates that material hardening and non-associated flow over some characteristic time are precursors to any particular instability, with stabilization of localized shear correlated with system softening tied to redistribution of strain energy dissipation within what is effectively a reconstituted material.

Influence of Structure and Microstructure on Deformation Localization and Crack Growth in NiTi Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Paul, Partha P.; Fortman, Margaret; Paranjape, Harshad M.; Anderson, Peter M.; Stebner, Aaron P.; Brinson, L. Catherine

2018-04-01

Porous NiTi shape memory alloys have applications in the biomedical and aerospace fields. Recent developments in metal additive manufacturing have made fabrication of near-net-shape porous products with complicated geometries feasible. There have also been developments in tailoring site-specific microstructures in metals using additive manufacturing. Inspired by these developments, we explore two related mechanistic phenomena in a simplified representation of porous shape memory alloys. First, we computationally elucidate the connection between pore geometry, stress concentration around pores, grain orientation, and strain-band formation during tensile loading of NiTi. Using this, we present a method to engineer local crystal orientations to mitigate the stress concentrations around the pores. Second, we experimentally document the growth of cracks around pores in a cyclically loaded superelastic NiTi specimen. In the areas of stress concentration around holes, cracks are seen to grow in large grains with [1 1 0] oriented along the tensile axis. This combined work shows the potential of local microstructural engineering in reducing stress concentration and increasing resistance to propagation of cracks in porous SMAs, potentially increasing the fatigue life of porous SMA components.

The effect of laser surface melting on microstructure and corrosion behavior of friction stir welded aluminum alloy 2219

NASA Astrophysics Data System (ADS)

Ma, Shengchong; Zhao, Yong; Zou, Jiasheng; Yan, Keng; Liu, Chuan

2017-11-01

This study aimed to explore the electrochemical properties and microstructure of friction stir welds to understand the correlation between their properties and processing. Friction stir welding is a promising solid-state joining process for high-strength aluminum alloys (AA). Although friction stir welding (FSW) eliminates the problems of fusion welding due to the fact that it is performed below Tm, it causes severe plastic deformation in the material. Some AA welded by FSW exhibit relatively poor corrosion resistance. In this research, the corrosion resistance of such welds was enhanced through laser surface melting. A friction stir weld of AA 2219 was laser melted. The melt depth and microstructure were observed using optical and scanning electron microscopy. The melt zone exhibited epitaxially grown columnar grains. The redistribution of elemental composition was analyzed using energy-dispersive spectroscopy. The anticorrosion properties of both laser-melted and original welds were studied in aqueous 3.5% NaCl solution using cyclic potentiodynamic polarization. The results indicated a noticeable increase in the pitting corrosion resistance after the laser treatment on the surface. The repassivation potential was nobler than the corrosion potential after the laser treatment, confirming that the resistance to pitting growth improved.

A Novel Approach for Controlling the Band Formation in Medium Mn Steels

NASA Astrophysics Data System (ADS)

Farahani, H.; Xu, W.; van der Zwaag, S.

2018-06-01

Formation of the microstructural ferrite/pearlite bands in medium Mn steels is an undesirable phenomenon commonly addressed through fast cooling treatments. In this study, a novel approach using the cyclic partial phase transformation concept is applied successfully to prevent microstructural band formation in a micro-chemically banded Fe-C-Mn-Si steel. The effectiveness of the new approach is assessed using the ASTM E1268-01 standard. The cyclic intercritical treatments lead to formation of isotropic microstructures even for cooling rates far below the critical one determined in conventional continuous cooling. In contrast, isothermal intercritical experiments have no effect on the critical cooling rate to suppress microstructural band formation. The origin of the suppression of band formation either by means of fast cooling or a cyclic partial phase transformation is investigated in detail. Theoretical modeling and microstructural observations confirm that band formation is suppressed only if the intercritical annealing treatment leads to partial reversion of the austenite-ferrite interfaces. The resulting interfacial Mn enrichment is responsible for suppression of the band formation upon final cooling at low cooling rates.

A Novel Approach for Controlling the Band Formation in Medium Mn Steels

NASA Astrophysics Data System (ADS)

Farahani, H.; Xu, W.; van der Zwaag, S.

2018-03-01

Formation of the microstructural ferrite/pearlite bands in medium Mn steels is an undesirable phenomenon commonly addressed through fast cooling treatments. In this study, a novel approach using the cyclic partial phase transformation concept is applied successfully to prevent microstructural band formation in a micro-chemically banded Fe-C-Mn-Si steel. The effectiveness of the new approach is assessed using the ASTM E1268-01 standard. The cyclic intercritical treatments lead to formation of isotropic microstructures even for cooling rates far below the critical one determined in conventional continuous cooling. In contrast, isothermal intercritical experiments have no effect on the critical cooling rate to suppress microstructural band formation. The origin of the suppression of band formation either by means of fast cooling or a cyclic partial phase transformation is investigated in detail. Theoretical modeling and microstructural observations confirm that band formation is suppressed only if the intercritical annealing treatment leads to partial reversion of the austenite-ferrite interfaces. The resulting interfacial Mn enrichment is responsible for suppression of the band formation upon final cooling at low cooling rates.

Effect of deformation path on microstructure, microhardness and texture evolution of interstitial free steel fabricated by differential speed rolling

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

Hamad, Kotiba; Chung, Bong Kwon; Ko, Young Gun, E-mail: younggun@ynu.ac.kr

2014-08-15

This paper reports the effect of the deformation path on the microstructure, microhardness, and texture evolution of interstitial free (IF) steel processed by differential speed rolling (DSR) method. For this purpose, total height reductions of 50% and 75% were imposed on the samples by a series of differential speed rolling operations with various height reductions per pass (deformation levels) ranging from 10 to 50% under a fixed roll speed ratio of 1:4 for the upper and lower rolls, respectively. Microstructural observations using transmission electron microscopy and electron backscattered diffraction measurements showed that the samples rolled at deformation level of 50%more » had the finest mean grain size (∼ 0.5 μm) compared to the other counterparts; also the samples rolled at deformation level of 50% showed a more uniform microstructure. Based on the microhardness measurements along the thickness direction of the deformed samples, gradual evolution of the microhardness value and its homogeneity was observed with the increase of the deformation level per pass. Texture analysis showed that, as the deformation level per pass increased, the fraction of alpha fiber and gamma fiber in the deformed samples increased. The textures obtained by the differential speed rolling process under the lubricated condition would be equivalent to those obtained by the conventional rolling. - Highlights: • Effect of DSR deformation path on microstructure of IF steel is significant. • IF steel rolled at deformation level of 50% has the ultrafine grains of ∼ 0.5 μm. • Rolling texture components are pronounced with increasing deformation level.« less

Influence of Nanostructuration on the Sound Velocity in Aluminum Al_99.50

NASA Astrophysics Data System (ADS)

Cazac, A. M.; Alexandru, A.; Baciu, C.; Sandu, A. V.; Bejinariu, C.

2018-06-01

The paper proposes is a multidisciplinary study on the influence of nanostructured material obtained by cyclic closed die forging process, in this case the aluminum with a purity of 99.50% (Al_99.50), on the sound velocity. The study of nanomaterials is a branch of material science on the basis of which nanotechnology can be approached. Severe plastic deformation (SPD) is a generic term describing a group of metal and alloy processing techniques involving very high stresses without including significant changes in the overall dimensions of the model or workpiece. The sample is of a regular quadrangular prism shape with the side square of a = 10 mm and the height of h = 16 mm, so with a dimensional factor h / a = 1.6. For each sample, a number of 7 determinations were performed to establish a mean value for the sound velocity. As a result of the microstructure analysis, it is observed that at the deformation cycle 4 the grains have an average size between 250 and 500 nm.

The effect of strain rate on the evolution of microstructure in aluminium alloys.

PubMed

Leszczyńska-Madej, B; Richert, M

2010-03-01

Intensive deformations influence strongly microstructure. The very well-known phenomenon is the diminishing dimension of grain size by the severe plastic deformation (SPD) methods. The nanometric features of microstructure were discovered after the SPD deformation of various materials, such as aluminium alloys, iron and others. The observed changes depended on the kind of the deformed material, amount of deformation, strain rate, existence of different phases and stacking fault energy. The influence of the strain and strain rate on the microstructure is commonly investigated nowadays. It was found that the high strain rates activate deformation in shear bands, microbands and adiabatic shear bands. It was observed that bands were places of the nucleation of nanograins in the material deformed by SPD methods. In the work, the refinement of microstructure of the aluminium alloys influenced by the high strain rate was investigated. The samples were compressed by a specially designed hammer to the deformation of phi= 0/0.62 with the strain rate in the range of [Formula in text]. The highest reduction of microbands width with the increase of the strain was found in the AlCu4Zr alloy. The influence of the strain rate on the microstructure refinement indicated that the increase of the strain rate caused the reduction of the microbands width in the all investigated materials (Al99.5, AlCu4Zr, AlMg5, AlZn6Mg2.5CuZr). A characteristic feature of the microstructure of the compressed material was large density of the shear bands and microbands. It was found that the microbands show a large misorientation to the surrounds and, except Al99.5, the large density of dislocation.

Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C

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

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatiguemore » tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.« less

Yang Baxter and anisotropic sigma and lambda models, cyclic RG and exact S-matrices

NASA Astrophysics Data System (ADS)

Appadu, Calan; Hollowood, Timothy J.; Price, Dafydd; Thompson, Daniel C.

2017-09-01

Integrable deformation of SU(2) sigma and lambda models are considered at the classical and quantum levels. These are the Yang-Baxter and XXZ-type anisotropic deformations. The XXZ type deformations are UV safe in one regime, while in another regime, like the Yang-Baxter deformations, they exhibit cyclic RG behaviour. The associ-ated affine quantum group symmetry, realized classically at the Poisson bracket level, has q a complex phase in the UV safe regime and q real in the cyclic RG regime, where q is an RG invariant. Based on the symmetries and RG flow we propose exact factorizable S-matrices to describe the scattering of states in the lambda models, from which the sigma models follow by taking a limit and non-abelian T-duality. In the cyclic RG regimes, the S-matrices are periodic functions of rapidity, at large rapidity, and in the Yang-Baxter case violate parity.

Creep deformation in near-γ TiAl: Part 1. the influence of microstructure on creep deformation in Ti-49Al-1V

NASA Astrophysics Data System (ADS)

Worth, Brian D.; Jones, J. Wayne; Allison, John E.

1995-11-01

The influence of microstructure on creep deformation was examined in the near-y TiAl alloy Ti-49A1-1V. Specifically, microstructures with varying volume fractions of lamellar constituent were produced through thermomechanical processing. Creep studies were conducted on these various microstructures under constant load in air at temperatures between 760 °C and 870 °C and at stresses ranging from 50 to 200 MPa. Microstructure significantly influences the creep behavior of this alloy, with a fully lamellar microstructure yielding the highest creep resistance of the microstructures examined. Creep resistance is dependent on the volume fraction of lamellar constituent, with the lowest creep resistance observed at intermediate lamellar volume fractions. Examination of the creep deformation structure revealed planar slip of dislocations in the equiaxed y microstructure, while subboundary formation was observed in the duplex microstructure. The decrease in creep resistance of the duplex microstructure, compared with the equiaxed y microstructure, is attributed to an increase in dislocation mobility within the equiaxed y constituent, that results from partitioning of oxygen from the γ phase to the α2 phase. Dislocation motion in the fully lamellar microstructure was confined to the individual lamellae, with no evidence of shearing of γ/γ or γ/α2 interfaces. This suggests that the high creep resistance of the fully lamellar microstructure is a result of the fine spacing of the lamellar structure, which results in a decreased effective slip length for dislocation motion over that found in the duplex and equiaxed y microstructures.

Low-cycle fatigue behavior of NIMONIC PE16 at room temperature

NASA Astrophysics Data System (ADS)

Singh, V.; Sundararaman, M.; Chen, W.; Wahi, R. P.

1991-02-01

The fatigue behavior of NIMONIC PE16 has been investigated at room temperature as a function of γ' particle size (from 10 to 30 nm) and total strain amplitude (0.44 to 2.60 pct). All specimens initially harden and then soften on further deformation. The degrees of hardening and softening show a marked variation with γ' particle size and strain amplitude. Cyclic stress-strain and Coffin-Manson plots show a bilinear behavior with a change of slope at Δɛp/2, the plastic strain amplitude, of about 0.3 pct. These results are interpreted in terms of microstructural observations, namely, the number of slip systems activated and mutual interaction of dislocations on these systems, as well as their interaction with γ' particles.

Experimental study of microstructure changes due to low cycle fatigue of a steel nanocrystallised by Surface Mechanical Attrition Treatment (SMAT)

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

Sun, Z.

Electron Backscatter Diffraction technique is used to characterize the microstructure of 316L steel generated by Surface Mechanical Attrition Treatment (SMAT) before and after low cycle fatigue tests. A grain size gradient is generated from the top surface to the interior of the samples after SMAT so that three main regions can be distinguished below the treated surface: (i) the ultra-fine grain area within 5 μm under the top surface with preferably oriented grains, (ii) the intermediate area where the original grains are partially transformed, and (iii) the edge periphery area where the original grains are just mechanically deformed with themore » presence of plastic slips. Fatigue tests show that cyclic loading does not change the grain orientation spread and does not activate any plastic slip in the ultra-fine grain top surface area induced by SMAT. On the opposite, in the plastically SMAT affected region including the intermediate area and the edge periphery area, new slip systems are activated by low cycle fatigue while the grain orientation spread is increased. These results represent a first very interesting step towards the characterization and understanding of mechanical mechanisms involved during the fatigue of a grain size gradient material. - Highlights: •LCF tests are carried out on specimens processed by SMAT. •EBSD is used to investigate microstructural changes induced by LCF. •A grain size gradient is generated by SMAT from surface to the bulk of the fatigue samples. •New slip systems are activated by LCF and GOS is increased in plastically deformed region. •However, these phenomena are not observed in the top surface ultra-fine grain area.« less

Compression fatigue behavior and failure mechanism of porous titanium for biomedical applications.

PubMed

Li, Fuping; Li, Jinshan; Huang, Tingting; Kou, Hongchao; Zhou, Lian

2017-01-01

Porous titanium and its alloys are believed to be one of the most attractive biomaterials for orthopedic implant applications. In the present work, porous pure titanium with 50-70% porosity and different pore size was fabricated by diffusion bonding. Compression fatigue behavior was systematically studied along the out-of-plane direction. It resulted that porous pure titanium has anisotropic pore structure and the microstructure is fine-grained equiaxed α phase with a few twins in some α grains. Porosity and pore size have some effect on the S-N curve but this effect is negligible when the fatigue strength is normalized by the yield stress. The relationship between normalized fatigue strength and fatigue life conforms to a power law. The compression fatigue behavior is characteristic of strain accumulation. Porous titanium experiences uniform deformation throughout the entire sample when fatigue cycle is lower than a critical value (N T ). When fatigue cycles exceed N T , strain accumulates rapidly and a single collapse band forms with a certain angle to the loading direction, leading to the sudden failure of testing sample. Both cyclic ratcheting and fatigue crack growth contribute to the fatigue failure mechanism, while the cyclic ratcheting is the dominant one. Porous titanium possesses higher normalized fatigue strength which is in the range of 0.5-0.55 at 10 6 cycles. The reasons for the higher normalized fatigue strength were analyzed based on the microstructure and fatigue failure mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dynamic strain aging in stress controlled creep-fatigue tests of 316L stainless steel under different loading conditions

NASA Astrophysics Data System (ADS)

Jiang, Huifeng; Chen, Xuedong; Fan, Zhichao; Dong, Jie; Jiang, Heng; Lu, Shouxiang

2009-08-01

Stress controlled fatigue-creep tests were carried out for 316L stainless steel under different loading conditions, i.e. different loading levels at the fixed temperature (loading condition 1, LC1) and different temperatures at the fixed loading level (loading condition 2, LC2). Cyclic deformation behaviors were investigated with respect to the evolutions of strain amplitude and mean strain. Abrupt mean strain jumps were found during cyclic deformation, which was in response to the dynamic strain aging effect. Moreover, as to LC1, when the minimum stress is negative at 550 °C, abrupt mean strain jumps occur at the early stage of cyclic deformation and there are many jumps during the whole process. While the minimum stress is positive, mean strain only jumps once at the end of deformation. Similar results were also found in LC2, when the loading level is fixed at -100 to 385 MPa, at higher temperatures (560, 575 °C), abrupt mean strain jumps occur at the early stage of cyclic deformation and there are many jumps during the whole process. While at lower temperature (540 °C), mean strain only jumps once at the end of deformation.

Experimental Investigation on Deformation Failure Characteristics of Crystalline Marble Under Triaxial Cyclic Loading

NASA Astrophysics Data System (ADS)

Yang, Sheng-Qi; Tian, Wen-Ling; Ranjith, P. G.

2017-11-01

The deformation failure characteristics of marble subjected to triaxial cyclic loading are significant when evaluating the stability and safety of deep excavation damage zones. To date, however, there have been notably few triaxial experimental studies on marble under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic tests was conducted to analyze the mechanical damage characteristics of a marble. The post-peak deformation of the marble changed gradually from strain softening to strain hardening as the confining pressure increased from 0 to 10 MPa. Under uniaxial compression, marble specimens showed brittle failure characteristics with a number axial splitting tensile cracks; in the range of σ 3 = 2.5-7.5 MPa, the marble specimens assumed single shear fracture characteristics with larger fracture angles of about 65°. However, at σ 3 = 10 MPa, the marble specimens showed no obvious shear fracture surfaces. The triaxial cyclic experimental results indicate that in the range of the tested confining pressures, the triaxial strengths of the marble specimens under cyclic loading were approximately equal to those under monotonic loading. With the increase in cycle number, the elastic strains of the marble specimens all increased at first and later decreased, achieving maximum values, but the plastic strains of the marble specimens increased nonlinearly. To evaluate quantitatively the damage extent of the marble under triaxial cyclic loading, a damage variable is defined according to the irreversible deformation for each cycle. The evolutions of the elastic modulus for the marble were characterized by four stages: material strengthening, material degradation, material failure and structure slippage. Based on the experimental results of the marble specimens under complex cyclic loading, the cohesion of the marble decreased linearly, but the internal friction angles did not depend on the damage extent. To describe the peak strength characteristics of the marble specimens under complex cyclic loadings with various deformation positions, a revised strength criterion for damaged rocks is offered.

Cyclic deformation of NI/sub 3/(Al,Nb) single crystals at ambient and elevated temperatures

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

Bonda, N.R.

Cyclic tests were performed on Ni/sub 3/(Al,Nb) (..gamma..' phase) single crystals by using a servo-hydraulic machine under fully reversed plastic strain control at a frequency of 0.1-0.2 Hz at room temperature, 400/sup 0/C and 700/sup 0/C. Since the monotonic behavior is orientation dependent, three orientations were studied. Asymmetry in tensile and compressive stresses was observed in the cyclic hardening curves of specimens tested at these temperatures and they were discussed with regard to the model suggested by Paider et al for monotonic behavior. The stress levels in the cyclic stress-strain curves (CSSC) at room temperature depended on orientation and cyclicmore » history. No CSSCs were established at 400/sup 0/C and 700/sup 0/C. The deformation in cyclic tests at small plastic strain amplitudes was found to be different from that in monotonic tests in the microplastic regions in which the deformation is believed to be carried by a small density of edge dislocations. But in cyclic deformation, to and from motion of dislocations trap the edge dislocations into dipoles and therefore screw dislocations will be forced to participate in the deformation. Cracks on the surfaces of specimens tested at room temperature and 400/sup 0/C were found to be of stage I type, whereas at 700/sup 0/C, they were of stage II type.« less

A heat treatment procedure to produce fine-grained lamellar microstructures in a P/M titanium aluminide alloy

NASA Astrophysics Data System (ADS)

Au, Peter

A process for fabricating advanced aerospace titanium aluminide alloys starting from metal powders (the hot isostatically consolidated P/M process) is presented in this thesis. This process does not suffer the difficulties of chemical inhomogeneities and coarse grain structure of castings. In addition heat treatments which take advantage of the refined structure of HIP processed materials are developed to achieve microstructure control and subsequent mechanical property control. It is shown that a better "property balance" is possible after the heat treatment of HIP consolidated materials than it is with alternative processing. It is well understood that the standard microstructures (near-gamma, duplex, nearly lamellar, and fully lamellar) do not have the balanced mechanical properties (tensile, yield, creep and fatigue strength, ductility and fracture toughness) necessary for optimal performance in aero engine and automotive applications. In this work a fine-grained fully lamellar (FGFL) microstructure is developed for property control and in particular for achieving a much improved property balance. A heat treatment procedure for this purpose which consists of cyclic processing in the alpha transus temperature region to achieve an FGFL structure with grain sizes in the range of 50 mum to 150 mum is presented. Compared with conventional duplex structured materials, the minimum creep rate is an order of magnitude lower with only a 10% loss in tensile yield strength. Moreover, a three-fold increase in tensile elongation is possible by converting to an FGFL structure with only a 30% loss in minimum creep rate. These are attractive trade-offs when considering the use of these alloys for aerospace purposes. A thorough literature review of the mechanisms of formation of standard microstructures and their deformation under mechanical loading is contained in the thesis. In addition, conventional techniques to produce FGFL microstructures in wrought and cast materials are discussed in detail. Beyond the review, the results of experiments are described for determining the alpha transus temperature, the phase transformation kinetics in this region and the effects of heat treatment time and cooling rate on microstructure. Based on this preliminary work, a heat treatment to achieve a FGFL microstructure with grain sizes in the range of 50 mum to 150 mum is proposed and confirmed. The room temperature and high temperature mechanical properties of these materials are compared with those of conventional duplex and fully lamellar structures. The results of this experimentation are discussed in terms of the fundamental mechanisms for controlling microstructure and mechanical properties in these materials. The potential for applying cyclic heat treatments to cast and wrought materials to improve the mechanical property balance in engineering practice is discussed.

An investigation of the effects of interfacial microstructure on the fatigue behavior of a four-ply [75]{sub 4} continuous silicon carbide (SCS-6) fiber-reinforced titanium matrix composite

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

Jin, O.; Li, Y.; Rabeeh, B.M.

1997-12-01

The effects of interfacial microstructure/thickness on the strength and fatigue behavior of a model four-ply [75]{sub 4} Ti-15V-3Al-3Cr-3Sn/SiC (SCS-6) composite are examined in this article. Interfacial microstructure was controlled by annealing at 815 C for 10, 50, or 100 hours. The reaction layer and coating thickness were observed to increase with increasing annealing duration. Damage initiation/propagation mechanisms were examined in as-received material and composites annealed at 815 C for 10 and 100 hours. Fatigue behavior was observed to be dependent upon the stress amplitude. At high stress amplitudes, the failure was dominated by overload phenomena. However, at all stress levels,more » fatigue crack initiation occurred by early debonding and matrix deformation by stress-induced precipitation. This was followed by matrix crack growth and fiber fracture prior to the onset of catastrophic failure. Matrix shear failure modes were also observed on the fracture surfaces in addition to fatigue striations in the matrix. Correlations were also established between the observed damage modes and acoustic emission signals that were detected under monotonic and cyclic loading conditions.« less

Visualizing Stress and Temperature Distribution During Elevated Temperature Deformation of IN-617 Using Nanomechanical Raman Spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Yang; Wang, Hao; Tomar, Vikas

2018-04-01

This work presents direct measurements of stress and temperature distribution during the mesoscale microstructural deformation of Inconel-617 (IN-617) during 3-point bending tests as a function of temperature. A novel nanomechanical Raman spectroscopy (NMRS)-based measurement platform was designed for simultaneous in situ temperature and stress mapping as a function of microstructure during deformation. The temperature distribution was found to be directly correlated to stress distribution for the analyzed microstructures. Stress concentration locations are shown to be directly related to higher heat conduction and result in microstructural hot spots with significant local temperature variation.

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

DOE PAGES

Cheng, G.; Choi, K. S.; Hu, X.; ...

2017-04-05

Here in this study, the deformation limits of various DP980 steels are examined with the deformation instability theory. Under uniaxial tension, overall stress–strain curves of the material are estimated based on a simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, an actual microstructure-based finite element (FE) method is used to resolve the deformation compatibilities explicitly between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for themore » various DP980 considered. Under complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Effect of prior deformation on microstructural development and Laves phase precipitation in high-chromium stainless steel.

PubMed

Hsiao, Z-W; Chen, D; Kuo, J-C; Lin, D-Y

2017-04-01

This study investigated the influence of deformation on precipitation behaviour and microstructure change during annealing. Here, the prior deformation of high-chromium stainless steel was tensile deformation of 3%, 6% and 10%, and the specimens were then annealed at 700˚C for 10 h. The specimens were subsequently analyzed using backscattered electron image and electron backscattering diffraction measurements with SEM. Compared with the deformation microstructure, the grains revealed no preferred orientation. The precipitates of TiN and NbC were formed homogenously in the grain interior and at grain boundaries after annealing. Fine Laves phase precipitates were observed in grains and along subgrain boundaries as the deformation increased. Furthermore, the volume fraction of Laves phase increased, but the average particle diameter of precipitate was reduced as the deformation increased. © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society.

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

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

Cheng, G.; Choi, K. S.; Hu, X.

The deformation limits of various DP980 steels are examined in this study with deformation instability theory. Under uniaxial tension, overall stress-strain curves of the material are estimated based on simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, actual microstructure-based finite element (FE) method is used to explicitly resolve the deformation incompatibilities between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for the various DP980 considered. Undermore » complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

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

Cheng, G.; Choi, K. S.; Hu, X.

Here in this study, the deformation limits of various DP980 steels are examined with the deformation instability theory. Under uniaxial tension, overall stress–strain curves of the material are estimated based on a simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, an actual microstructure-based finite element (FE) method is used to resolve the deformation compatibilities explicitly between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for themore » various DP980 considered. Under complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

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.

Effects of load and thermal histories on mechanical behavior of materials; Proceedings of the Symposium, Denver, CO, Feb. 25, 26, 1987

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

Liaw, P.K.; Nicholas, T.

This volume includes topics on fatigue crack propagation; isothermal and thermal-mechanical fatigue; and microstructure, fracture, and damage. Papers are presented on transients in fatigue crack growth, elevated-temperature fatigue crack propagation, the role of crack closure in crack retardation in P/M and I/M aluminum alloys, the acoustic interrogation of fatigue overload effects, and the effects of frequency and environment on crack growth in Inconel 718. Special attention is given to isothermal fatigue failure mechanisms in low-tin lead-based solder, the stress and strain controlled low-cycle fatigue of Pb-Sn solder for electronic packaging applications, load sequence effects on the deformation of isolated microplasticmore » grains, and thermal fatigue of stainless steel. Other papers are on the influence of thermal aging on the creep crack growth behavior of a Cr-Mo steel, the effect of cyclic loading on the fracture toughness of a modified 4340 steel, and the effects of hot rolling condition and boron microalloying on phase transformation and microstructure in niobium-bearing interstitial free steel.« less

Effect of different stages of deformation on the microstructure evolution of Ti-rich NiTi shape memory alloy

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

Tadayyon, Ghazal, E-mail: Ghazal.tadayyon@gmail.co

The main objective of this work was to investigate the thermomechanical behavior and microstructural changes of a Ti-rich NiTi shape memory alloy (SMA). The microstructural and texture evolution of aged NiTi alloy at different degrees of deformation were elicited by transmission electron microscopy (TEM). An effort was made to correlate results obtained from the tensile test with results from microstructure studies. The undeformed sample reveals a self-accommodated morphology with straight and well defined twin boundaries. At different stages of deformation, diverse mechanisms were involved. These mechanisms include marstraining, detwinning accompanied by dislocation movement, and finally, severe plastic deformation, subdivision andmore » amorphization of the matrix. Under increasing strains, high density lattice defects were generated and the morphology of B19’ became disordered. - Graphical abstract: The summary of microstructure changes of the martensite twins during tensile deformation in polycrystalline NiTi SMAs. - Highlights: • Initial elastic response, dislocation avalanche and deformation bands were studied. • < 011 > Type II twin accompanied by detwinned area after 2% cold work was observed. • Visible parallel fine stacking faults showed plastic flow of the material. • At higher strains, subgrains changed to recrystallized, finely amorphous structure.« less

Thermal Microstructural Stability of AZ31 Magnesium after Severe Plastic Deformation

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

Young, John P.; Askari, Hesam A.; Hovanski, Yuri

2015-03-01

Both equal channel angular pressing and friction stir processing have the ability to refine the grain size of twin roll cast AZ31 magnesium and potentially improve its superplastic properties. This work used isochronal and isothermal heat treatments to investigate the microstructural stability of twin roll cast, equal channel angular pressed and friction stir processed AZ31 magnesium. For both heat treatment conditions, it was found that the twin roll casted and equal channel angular pressed materials were more stable than the friction stir processed material. Calculations of the grain growth kinetics showed that severe plastic deformation processing decreased the activation energymore » for grain boundary motion with the equal channel angular pressed material having the greatest Q value of the severely plastically deformed materials and that increasing the tool travel speed of the friction stir processed material improved microstructural stability. The Hollomon-Jaffe parameter was found to be an accurate means of identifying the annealing conditions that will result in substantial grain growth and loss of potential superplastic properties in the severely plastically deformed materials. In addition, Humphreys’s model of cellular microstructural stability accurately predicted the relative microstructural stability of the severely plastically deformed materials and with some modification, closely predicted the maximum grain size ratio achieved by the severely plastically deformed materials.« less

Tensile Deformation Temperature Impact on Microstructure and Mechanical Properties of AISI 316LN Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Xiong, Yi; He, Tiantian; Lu, Yan; Ren, Fengzhang; Volinsky, Alex A.; Cao, Wei

2018-03-01

Uniaxial tensile tests were conducted on AISI 316LN austenitic stainless steel from - 40 to 300 °C at a rate of 0.5 mm/min. Microstructure and mechanical properties of the deformed steel were investigated by optical, scanning and transmission electron microscopies, x-ray diffraction, and microhardness testing. The yield strength, ultimate tensile strength, elongation, and microhardness increase with the decrease in the test temperature. The tensile fracture morphology has the dimple rupture feature after low-temperature deformations and turns to a mixture of transgranular fracture and dimple fracture after high-temperature ones. The dominating deformation microstructure evolves from dislocation tangle/slip bands to large deformation twins/slip bands with temperature decrease. The deformation-induced martensite transformation can only be realized at low temperature, and its quantity increases with the decrease in the temperature.

Improving Tensile and Compressive Properties of an Extruded AZ91 Rod by the Combined Use of Torsion Deformation and Aging Treatment

PubMed Central

Song, Bo; Wang, Chunpeng; Guo, Ning; Pan, Hucheng; Xin, Renlong

2017-01-01

In this study, AZ91 magnesium alloy rods were used to investigate the effects of torsion deformation on microstructure and subsequent aging behavior. Extruded AZ91 rod has a uniform microstructure and typical fiber texture. Torsion deformation can generate a gradient microstructure on the cross-section of the rod. After torsion, from the center to the edge in the cross-section of the rod, both stored dislocations and area fraction of {10-12} twins gradually increase, and the basal pole of the texture tends to rotate in the ED direction. Direct aging usually generates coarse discontinuous precipitates and fine continuous precipitates simultaneously. Both twin structures and dislocations via torsion deformation can be effective microstructures for the nucleation of continuous precipitates during subsequent aging. Thus, aging after torsion can promote continuous precipitation and generate gradient precipitation characteristics. Both aging treatment and torsion deformation can reduce yield asymmetry, and torsion deformation enhances the aging hardening effect by promoting continuous precipitation. Therefore, combined use of torsion deformation and aging treatment can effectively enhance the yield strength and almost eliminate the yield asymmetry of the present extruded AZ91 rod. Finally, the relevant mechanisms are discussed. PMID:28772638

Mechanical Behavior and Microstructure Evolution of Bearing Steel 52100 During Warm Compression

NASA Astrophysics Data System (ADS)

Huo, Yuanming; He, Tao; Chen, Shoushuang; Wu, Riming

2018-05-01

High-performance bearing steel requires a fine and homogeneous structure of carbide particles. Direct deformation spheroidizing of bearing steel in a dual-phase zone can contribute to achieving this important structure. In this work, warm compression testing of 52100 bearing steel was performed at temperatures in the range of 650-850°C and at strain rates of 0.1-10.0 s-1. The effect of deformation temperatures on mechanical behavior and microstructure evolution was investigated to determine the warm deformation temperature window. The effect of deformation rates on microstructure evolution and metal flow softening behavior of the warm compression was analyzed and discussed. Experimental results showed that the temperature range from 750°C to 800°C should be regarded as the critical range separating warm and hot deformation. Warm deformation at temperatures in the range of 650-750°C promoted carbide spheroidization, and this was determined to be the warm deformation temperature window. Metal flow softening during the warm deformation was caused by carbide spheroidization.

Evolution of the viscosity of Earth's upper mantle: Grain-boundary sliding and the role of microstructure in olivine deformation

NASA Astrophysics Data System (ADS)

Hansen, Lars N.

Many features of plate tectonics cannot be explained with standard rheological models of the upper mantle. In particular, the localization of deformation at plate boundaries requires the viscosity of the constituent rocks to evolve spatially and temporally. Such rheological complexity may arise from changing microstructural state variables (e.g., grain size and crystallographic-fabric strength), but the degree to which microstructure contributes to the evolution of viscosity is unclear given our current understanding of deformation mechanisms in mantle minerals. Dislocation-accommodated grain-boundary sliding (GBS) is a potentially critical mechanism for localizing deformation in olivine because it imparts a sensitivity of the viscosity to the state of the microstructure while simultaneously providing mechanisms for changing the microstructure. However, many details of GBS in olivine are currently unknown including 1) the magnitude of the sensitivity of strain rate to crystallographic fabric and grain size, 2) the strength of the crystallographic fabrics produced, and 3) the anisotropy in viscosity of polycrystalline aggregates. Detailed knowledge of these unknowns is necessary to assess the importance of microstructural evolution in the operation of plate tectonics. This dissertation investigates the details of GBS in olivine through four sets of laboratory-based experiments. In Chapter 2, triaxial compressive creep experiments on aggregates of San Carlos olivine are used to develop a flow law for olivine deforming by GBS. Extrapolations of strain rate to geological conditions using the derived flow law indicate that GBS is the dominant deformation mechanism throughout the uppermost mantle. Crystallographic fabrics observed in deformed samples are consistent with upper-mantle seismic anisotropy. In Chapter 3, torsion experiments on iron-rich olivine are used to determine the rheological behavior of olivine deforming by GBS at large strains. The sensitivity of the strain rate to grain size and stress is demonstrated to be consistent with low-strain experiments. Additionally, the sensitivity of strain rate to the development of a crystallographic fabric is determined. Constitutive relationships including microstructural evolution are developed that accurately predict the observed stress as a function of strain. The results of Chapter 3 confirm that significant weakening is associated with both grain-size reduction and crystallographic-fabric development. In Chapter 4, torsion experiments on iron-rich olivine are used to determine if microstructural evolution can lead to strain localization. Experiments were conducted with either constant-strain-rate or constant-stress boundary conditions. Localization is only observed in samples deformed at constant-stress, which suggests boundary conditions affect the critical size of strength perturbation necessary for localization to occur. Strain localization is correlated with fine-grained regions, and a feedback mechanism between grain-size reduction and strain rate is proposed. In Chapter 5, both torsion and tension experiments are used to assess the mechanical anisotropy of previously deformed samples. Based on the direction of the applied stress relative to the orientation of a pre-existing crystallographic fabric, the viscosity is demonstrated to vary by over an order of magnitude. This observation suggests deformation can localize in regions that were previously deformed and retained a strong crystallographic fabric. The results of this dissertation elucidate the interplay between microstructure and deformation of olivine in the GBS regime. Because the viscosity of olivine-rich rocks deforming by GBS is dependent on both grain size and crystallographic fabric, heterogeneities in these microstructural parameters can lead to spatial and temporal variations in viscosity, possibly explaining the large-scale patterns of deformation in the upper mantle. Future numerical simulations can test the importance of microstructure in geodynamic processes by incorporating the constitutive relationships outlined in this dissertation.

Evolution of microstructure and precipitates in 2xxx aluminum alloy after severe plastic deformation

NASA Astrophysics Data System (ADS)

Adamczyk-Cieslak, B.; Zdunek, J.; Mizera, J.

2016-04-01

This paper investigates the influence of precipitation on the microstructure development in a 2xxx aluminum alloy subjected to hydrostatic extrusion. A three step reduction of the diameter was performed using hydrostatic extrusion (HE) process: from 20mm (initial state) to 10 mm, 5 mm and 3 mm, which corresponds to the logarithmic deformations ɛ = 1.4, ɛ = 2.8 and ɛ = 3.8 respectively. The microstructure and precipitation analysis before and after deformation was performed using transmission electron microscope (TEM), and scanning electron microscopy (SEM). As a result of the tests, a very significant influence of precipitation on the degree of refinement and mechanism of microstructure transformation was stated.

An assessment of ultra fine grained 316L stainless steel for implant applications.

PubMed

Muley, Sachin Vijay; Vidvans, Amey N; Chaudhari, Gajanan P; Udainiya, Sumit

2016-01-01

Ultra fine-grained metals obtained by severe plastic deformation exhibit higher specific strength that is useful for many applications and show promise for use as body implants. This work studied the microstructural evolution, mechanical and sliding wear behavior and corrosion behavior of 316L stainless steel warm multi axially forged at 600°C. Microstructural evolution studied using electron backscatter diffraction technique and transmission electron microscopy confirmed the formation of ultra fine-grained structure. Average grain size reduced from 30μm to 0.86μm after nine strain steps. A combination of Hall-Petch strengthening and strain hardening increased the hardness. Improved sliding wear resistance is attributed to a transition from micro cutting to wedge-forming mode of abrasive wear. Load-bearing orthopedic implants often fail from pitting initiated corrosion fatigue. Potentiodynamic tests, cyclic polarization, and FeCl3 immersion tests revealed enhanced pitting resistance of forged steel that is confirmed by Mott-Schottky analysis. This is ascribed to an increase in the grain boundary volume, and homogenization of pit inducing impurities and non-metallic phases due to severe deformation, which influenced the passive film properties. These model studies on 316L steel demonstrate that severely deformed ultra fine-grained metals have potential to deliver improved implant performance. This model study on 316L steel demonstrates that severely deformed ultra fine-grained (UFG) metals have potential to deliver improved load-bearing implant performance. It is as interesting as is unclear as to how such severely deformed UFG material behaves electrochemically in the corrosive body fluids. This work is on studying the inter-relationship between structure, and mechanical, wear, and corrosion behavior of warm multiaxially forged (MAFed) UFG 316L stainless steel. Warm MAF is a bulk processing method capable of yielding large volume of UFG material and is an easily readily adaptable technique in industry. It can be a promising alternative to the expensive metallic alloys available for implant applications. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A continuum dislocation dynamics framework for plasticity of polycrystalline materials

NASA Astrophysics Data System (ADS)

Askari, Hesam Aldin

The objective of this research is to investigate the mechanical response of polycrystals in different settings to identify the mechanisms that give rise to specific response observed in the deformation process. Particularly the large deformation of magnesium alloys and yield properties of copper in small scales are investigated. We develop a continuum dislocation dynamics framework based on dislocation mechanisms and interaction laws and implement this formulation in a viscoplastic self-consistent scheme to obtain the mechanical response in a polycrystalline system. The versatility of this method allows various applications in the study of problems involving large deformation, study of microstructure and its evolution, superplasticity, study of size effect in polycrystals and stochastic plasticity. The findings from the numerical solution are compared to the experimental results to validate the simulation results. We apply this framework to study the deformation mechanisms in magnesium alloys at moderate to fast strain rates and room temperature to 450 °C. Experiments for the same range of strain rates and temperatures were carried out to obtain the mechanical and material properties, and to compare with the numerical results. The numerical approach for magnesium is divided into four main steps; 1) room temperature unidirectional loading 2) high temperature deformation without grain boundary sliding 3) high temperature with grain boundary sliding mechanism 4) room temperature cyclic loading. We demonstrate the capability of our modeling approach in prediction of mechanical properties and texture evolution and discuss the improvement obtained by using the continuum dislocation dynamics method. The framework was also applied to nano-sized copper polycrystals to study the yield properties at small scales and address the observed yield scatter. By combining our developed method with a Monte Carlo simulation approach, the stochastic plasticity at small length scales was studied and the sources of the uncertainty in the polycrystalline structure are discussed. Our results suggest that the stochastic response is mainly because of a) stochastic plasticity due to dislocation substructure inside crystals and b) the microstructure of the polycrystalline material. The extent of the uncertainty is correlated to the "effective cell length" in the sampling procedure whether using simulations and experimental approach.

3D modeling of unconstrained HPT process: role of strain gradient on high deformed microstructure formation

NASA Astrophysics Data System (ADS)

Ben Kaabar, A.; Aoufi, A.; Descartes, S.; Desrayaud, C.

2017-05-01

During tribological contact’s life, different deformation paths lead to the formation of high deformed microstructure, in the near-surface layers of the bodies. The mechanical conditions (high pressure, shear) occurring under contact, are reproduced through unconstrained High Pressure Torsion configuration. A 3D finite element model of this HPT test is developed to study the local deformation history leading to high deformed microstructure with nominal pressure and friction coefficient. For the present numerical study the friction coefficient at the interface sample/anvils is kept constant at 0.3; the material used is high purity iron. The strain distribution in the sample bulk, as well as the main components of the strain gradients according to the spatial coordinates are investigated, with rotation angle of the anvil.

Influence of thermally activated processes on the deformation behavior during low temperature ECAP

NASA Astrophysics Data System (ADS)

Fritsch, S.; Scholze, M.; F-X Wagner, M.

2016-03-01

High strength aluminum alloys are generally hard to deform. Therefore, the application of conventional severe plastic deformation methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low temperature deformation in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically deform a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially deformed from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low temperatures, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic deformation at low temperatures. We then discuss how the deformation temperature and velocity influence the occurrence of PLC effects and the homogeneity of the deformed ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low temperature deformed materials as a function of deformation temperature.

A novel method of multi-scale simulation of macro-scale deformation and microstructure evolution on metal forming

NASA Astrophysics Data System (ADS)

Huang, Shiquan; Yi, Youping; Li, Pengchuan

2011-05-01

In recent years, multi-scale simulation technique of metal forming is gaining significant attention for prediction of the whole deformation process and microstructure evolution of product. The advances of numerical simulation at macro-scale level on metal forming are remarkable and the commercial FEM software, such as Deform2D/3D, has found a wide application in the fields of metal forming. However, the simulation method of multi-scale has little application due to the non-linearity of microstructure evolution during forming and the difficulty of modeling at the micro-scale level. This work deals with the modeling of microstructure evolution and a new method of multi-scale simulation in forging process. The aviation material 7050 aluminum alloy has been used as example for modeling of microstructure evolution. The corresponding thermal simulated experiment has been performed on Gleeble 1500 machine. The tested specimens have been analyzed for modeling of dislocation density, nucleation and growth of recrystallization(DRX). The source program using cellular automaton (CA) method has been developed to simulate the grain nucleation and growth, in which the change of grain topology structure caused by the metal deformation was considered. The physical fields at macro-scale level such as temperature field, stress and strain fields, which can be obtained by commercial software Deform 3D, are coupled with the deformed storage energy at micro-scale level by dislocation model to realize the multi-scale simulation. This method was explained by forging process simulation of the aircraft wheel hub forging. Coupled the results of Deform 3D with CA results, the forging deformation progress and the microstructure evolution at any point of forging could be simulated. For verifying the efficiency of simulation, experiments of aircraft wheel hub forging have been done in the laboratory and the comparison of simulation and experiment result has been discussed in details.

Backtracking Depth-Resolved Microstructures for Crystal Plasticity Identification—Part 1: Backtracking Microstructures

NASA Astrophysics Data System (ADS)

Shi, Qiwei; Latourte, Félix; Hild, François; Roux, Stéphane

2017-12-01

In situ mechanical tests performed on polycrystalline materials in a scanning electron microscope suffer from the lack of information on depth-resolved three-dimensional microstructures. The latter ones can be accessed with focused ion beam technology only postmortem, because it is destructive. The present study considers the challenge of backtracking this deformed microstructure to the reference state. This theoretical question is tackled on a numerical (synthetic) test case. A two-dimensional microstructure with one dimension along the depth is considered, and deformed using a crystal plasticity law. The proposed numerical strategy is shown to retrieve accurately the reference state.

Effect of temperature, microstructure, and stress state on the low cycle fatigue behavior of Waspaloy

NASA Technical Reports Server (NTRS)

Stahl, D. R.; Antolovich, S. D.; Mirdamadi, M.; Zamrik, S. Y.

1988-01-01

Specimens of Waspaloy of two different microstructures were tested in uniaxial and torsional low-cycle fatigue at 24 and 649 C. For all specimens, deformation and failure mechanisms are found to be independent of stress state at 24 C; in both microstructures, failure is associated with the formation of shear cracks. At 649 C, deformation and failure mechanisms for the fine-grain large gamma-prime specimens are independent of stress state, and the mechanisms are similar to those observed at 24 C. For the coarse-grain small gamma-prime specimens, however, failure occurs on principal planes in torsion and on shear plane in uniaxial tension. The results are interpreted in terms of deformation mode and microstructural instability.

3D DDD modelling of dislocation-precipitate interaction in a nickel-based single crystal superalloy under cyclic deformation

NASA Astrophysics Data System (ADS)

Lin, Bing; Huang, Minsheng; Zhao, Liguo; Roy, Anish; Silberschmidt, Vadim; Barnard, Nick; Whittaker, Mark; McColvin, Gordon

2018-06-01

Strain-controlled cyclic deformation of a nickel-based single crystal superalloy has been modelled using three-dimensional (3D) discrete dislocation dynamics (DDD) for both [0 0 1] and [1 1 1] orientations. The work focused on the interaction between dislocations and precipitates during cyclic plastic deformation at elevated temperature, which has not been well studied yet. A representative volume element with cubic γ‧-precipitates was chosen to represent the material, with enforced periodical boundary conditions. In particular, cutting of superdislocations into precipitates was simulated by a back-force method. The global cyclic stress-strain responses were captured well by the DDD model when compared to experimental data, particularly the effects of crystallographic orientation. Dislocation evolution showed that considerably high density of dislocations was produced for [1 1 1] orientation when compared to [0 0 1] orientation. Cutting of dislocations into the precipitates had a significant effect on the plastic deformation, leading to material softening. Contour plots of in-plane shear strain proved the development of heterogeneous strain field, resulting in the formation of shear-band embryos.

Effect of deformation schedule on the microstructure and mechanical properties of a thermomechanically processed C-Mn-Si transformation-induced plasticity steel

NASA Astrophysics Data System (ADS)

Timokhina, I. B.; Hodgson, P. D.; Pereloma, E. V.

2003-08-01

Thermomechanical processing simulations were performed using a hot-torsion machine, in order to develop a comprehensive understanding of the effect of severe deformation in the recrystallized and nonrecrystallized austenite regions on the microstructural evolution and mechanical properties of the 0.2 wt pct C-1.55 wt pct Mn-1.5 wt pct Si transformation-induced plasticity (TRIP) steel. The deformation schedule affected all constituents (polygonal ferrite, bainite in different morphologies, retained austenite, and martensite) of the multiphased TRIP steel microstructure. The complex relationships between the volume fraction of the retained austenite, the morphology and distribution of all phases present in the microstructure, and the mechanical properties of TRIP steel were revealed. The bainite morphology had a more pronounced effect on the mechanical behavior than the refinement of the microstructure. The improvement of the mechanical properties of TRIP steel was achieved by variation of the volume fraction of the retained austenite rather than the overall refinement of the microstructure.

Effect of Low Cu Amounts and Pre-Deformation on the Precipitation in Al-Mg-Si Alloys

NASA Astrophysics Data System (ADS)

Saito, Takeshi; Muraishi, Shinji; Marioara, Calin D.; Holmestad, Randi

Transmission electron microscopy (TEM) studies were performed on two Al-Mg-Si alloys with low Cu additions (0.01 and 0.10 wt%) in order to investigate the effect of Cu and 10% pre-deformation on precipitate microstructure and its connection to mechanical properties. After 300 minutes aging at 190°C, fine microstructures associated with high hardness were observed in the alloy with 0.10% Cu. Pre-deformation led to heterogeneous distributions of precipitates along dislocations, causing microstructure coarsening. This effect was less pronounced in the alloy with the higher Cu amount.

Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones

NASA Astrophysics Data System (ADS)

Yao, D. J.; Zhou, D. R.; Xu, P. Q.; Lu, F. G.

2017-05-01

The as-welded Invar fusion zones were fabricated between cemented carbides and carbon steel using a Fe-Ni Invar interlayer and laser welding method. Three regions in the as-welded Invar fusion zones were defined to compare microstructures, and these were characterized and confirmed by scanning electron microscopy and X-ray diffractometry. The structure and plastic deformation mechanism for initial Invar Fe-Ni alloys and the as-welded Invar fusion zones are discussed. (1) After undergoing high-temperature thermal cycles, the microstructure of the as-welded Invar fusion zones contains γ-(Fe, Ni) solid solution (nickel dissolving in γ-Fe) with a face-centered cubic (fcc) crystal structure and mixed carbides (eutectic colonies, mixed carbides between two adjacent grains). The mixed carbides exhibited larger, coarser eutectic microstructures with a decrease in welding speed and an increase in heat input. (2) The structure of the initial Invar and the as-welded Invar is face-centered cubic γ-(Fe, Ni). (3) The as-welded Invar has a larger plastic deformation than initial Invar with an increase in local strain field and dislocation density. Slip deformation is propagated along the (111) plane. This finding helps us to understand microstructure and the formation of dislocation and plastic deformation when the Invar Fe-Ni alloy undergoes a high-temperature process.

The Effect of Simulated Thermomechanical Processing on the Transformation Behavior and Microstructure of a Low-Carbon Mo-Nb Linepipe Steel

NASA Astrophysics Data System (ADS)

Cizek, P.; Wynne, B. P.; Davies, C. H. J.; Hodgson, P. D.

2015-01-01

The present work investigates the transformation behavior of a low-carbon Mo-Nb linepipe steel and the corresponding transformation product microstructures using deformation dilatometry. The continuous cooling transformation (CCT) diagrams have been constructed for both the fully recrystallized austenite and that deformed in uniaxial compression at 1148 K (875 °C) to a strain of 0.5 for cooling rates ranging from 0.1 to about 100 K/s. The obtained microstructures have been studied in detail using electron backscattered diffraction complemented by transmission electron microscopy. Heavy deformation of the parent austenite has caused a significant expansion of the polygonal ferrite transformation field in the CCT diagram, as well as a shift in the non-equilibrium ferrite transformation fields toward higher cooling rates. Furthermore, the austenite deformation has resulted in a pronounced refinement in both the effective grain (sheaf/packet) size and substructure unit size of the non-equilibrium ferrite microstructures. The optimum microstructure expected to display an excellent balance between strength and toughness is a mix of quasi-polygonal ferrite and granular bainite (often termed "acicular ferrite") produced from the heavily deformed austenite within a processing window covering the cooling rates from about 10 to about 100 K/s.

Some effects of cyclic induced deformation in rocket thrust chambers

NASA Technical Reports Server (NTRS)

Hannum, N. P.; Quentmeyer, R. J.

1979-01-01

A test program to investigate the deformation process observed in the hot gas wall of rocket thrust chambers was conducted using three different liner materials. Five thrust chambers were cycled to failure using hydrogen and oxygen as propellants at a chamber pressure of 4.14 MN/m square (600 psia). The deformation was observed nondestructively at midlife points and destructively after failure occurred. The cyclic life results are presented with an accompanying discussion about the types of failure encountered. Data indicating the deformation of the thrust chamber liner as cycles are accumulated are presented for each of the test thrust chambers.

Mechanical properties of a nitrogen-bearing austenitic steel during static and cycle deformation

NASA Astrophysics Data System (ADS)

Blinov, E. V.; Terent'ev, V. F.; Prosvirnin, D. V.

2016-09-01

The mechanical properties of a nitrogen-bearing corrosion-resistant austenitic steel containing 0.311% nitrogen have been studied during static and cyclic deformation. It is found that the steel having an ultimate strength of 930 MPa exhibits a plasticity of 33%. The endurance limit under repeated tension at 106 loading cycles is 400 MPa. The propagation of a fatigue crack at low and high amplitudes of cyclic deformation follows a ductile fracture mechanism with the presence of fatigue grooves.

The Cyclic Stress-Strain Behavior of a Single Crystal Nickel-Base Superalloy. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Gabb, Timothy P.

1988-01-01

The cyclic stress-strain response and similar deformation structures of the single crystal nickel based superalloy was described under a specific set of conditions. The isothermal low cycle fatigue response and deformation structures were described at a typical intermediate temperature and at high temperature. Specimens oriented near the (001) and (111) crystallographic orientations were tested at 1050 C, where more moderate orientation effects were expected. This enabled the description of the deformation structures at each of the 2 temperatures and their relationship to the observed cyclic stress-strain behavior. The initial yield strength of all specimens tested at 650 C was controlled by the shearing of the gamma prime precipitates by dislocation pairs. Low cycle fatigue tests at 650 C had cyclic hardening, which was associated with dislocation interactions in the gamma matrix. The initial yield strength of specimens tested at 1050 C was associated with dislocation bypassing of the gamma prime precipitates. Low cycle fatigue tests at 1050 C had cyclic softening, associated with extensive dislocation recovery at the gamma-gamma prime interfaces along with some gamma prime precipitate coarsening.

Microstructure-Sensitive Modeling of High Cycle Fatigue (Preprint)

DTIC Science & Technology

2009-03-01

SUBJECT TERMS microplasticity , microstructure-sensitive modeling, high cycle fatigue, fatigue variability 16. SECURITY CLASSIFICATION OF: 17...3Air Force Research Laboratory Wright Patterson Air Force Base, Ohio 45433 Keywords: Microplasticity , microstructure-sensitive modeling, high cycle...cyclic microplasticity ) plays a key role in modeling fatigue resistance. Unlike effective properties such as elastic stiffness, fatigue is

Scaly fabrics and veins of tectonic mélanges in the Shimanto Belt, SW Japan

NASA Astrophysics Data System (ADS)

Ramirez, G. E.; Fisher, D. M.; Smye, A.; Hashimoto, Y.; Yamaguchi, A.

2017-12-01

Mélanges in ancient subduction fault zones provide a microstructural record of the plate boundary deformation associated with underthrusting. These rocks exhibit many of the characteristics associated with exposed ancient subduction fault zones worldwide, including: 1) σ1 is near orthogonal to the deformation fabric, 2) microstructurally pervasive quartz and calcite filled veins concentrated in coarser blocks and along extensional jogs on slip surfaces, 3) evidence for local diffusion of silica sourced from web-like arrays of slip surfaces (i.e., scaly fabrics), and 4) repeated cracking and sealing that record cyclic variations in stress. We present XRD, XRF, and EPMA observations of scaly fabrics from five ancient subduction-related shear zones (Yokonami, Mugi, Kure, Okitsu, and Makimine mélanges) from the Shimanto Belt in Japan that exemplify these characteristics and represent the full temperature range of the seismogenic zone ( 150-340 °C). The scaly fabrics associated with these shear zones display significantly different microstructural and geochemical characteristics. Individual slip surfaces in the scaly fabrics of Mugi mélange, underplated at the updip limit of the seismogenic zone, are characterized by broader (50-300 µm) anastomosing shear zones while the Makimine mélange, underplated at the downdip limit of the seismogenic zone, exhibits thinner (10-20 µm) anastomosing shear zones. XRD analyses also imply geochemical differences such as a decrease in albite concentration and an increase in illite concentration with increasing temperature/depth of underthrusting. Scaly fabrics are sites of silica redistribution in which silica is depleted on the slip surfaces and precipitated as mostly quartz in crack-seal veins. The time to seal, or heal, fractures is mainly temperature-dependent but can also be significantly quickened by fluid salinity, degree of fluid-rock interactions, and geochemical reactions (i.e. incongruent pressure solution). Microstructural and geochemical characteristics that show differences with temperature/depth of underthrusting highlight the importance of establishing the geochemical processes and activation energies that contribute to slip, fracturing, and healing of rocks that underthrust the subduction interface.

Scaly fabrics and veins of the Mugi and Makimine mélanges in the Shimanto belt, SW Japan

NASA Astrophysics Data System (ADS)

Ramirez, G. E.; Fisher, D. M.; Yamaguchi, A.; Kimura, G.

2016-12-01

Two regionally extensive ancient subduction fault zones provide a microstructural record of the plate boundary deformation associated with underthrusting. These rocks exhibit many of the characteristics associated with exposed ancient subduction fault zones worldwide, including: (1) σ1 is near orthogonal to the deformation fabric (2) there are microstructurally pervasive quartz and calcite filled veins concentrated in coarser blocks and along extensional jogs on slip surfaces, (3) evidence for local diffusion of silica sourced from web-like arrays of slip surfaces (i.e., scaly fabrics), and (4) evidence for cycles of cracking and sealing that record cyclic variations in stress. We present new backscatter SEM observations of scaly fabrics from two ancient subduction-related shear zones from the Shimanto Belt in Japan that exemplify these characteristics and represent the full temperature range of the seismogenic zone: 1) the Mugi mélange (lower ( 130-150 °C) and upper ( 170-200 °C) sections) and 2) Makimine mélange (peak temperatures of 340 °C). The Mugi mélange is an underplated duplex consisting of two horses separated by an OOST. The upper section is bounded at the top by a pseudotachylite-bearing paleodécollement. The Makimine mélange was underplated at the downdip limit of the seismogenic zone. The scaly fabrics associated with these shear zones display significantly different microstructural characteristics. A slip surface from along the upper Mugi is characterized by broader ( 20-30 μm), zones of quartz-poor, anastomosing shear zones composed of fine-grained (0.5-2 μm in length) phyllosilicates. The Makimine mélange exhibits thinner (10-20 μm), anastomosing shear zones with coarser (1-4 μm in length) phyllosilicate grains that are more strongly oriented into parallelism with slip surfaces. Quartz veins are pervasively developed in more competent blocks and are oriented at near perpendicular angles to the slip surfaces. Microstructural analyses of ancient subduction-related faults show differences with temperature that highlight the importance of establishing the geochemical processes and activation energies that contribute to slip, fracturing, and healing of rocks that underthrust the subduction interface.

Microstructural evolution of bainitic steel severely deformed by equal channel angular pressing.

PubMed

Nili-Ahmadabadi, M; Haji Akbari, F; Rad, F; Karimi, Z; Iranpour, M; Poorganji, B; Furuhara, T

2010-09-01

High Si bainitic steel has been received much of interest because of combined ultra high strength, good ductility along with high wear resistance. In this study a high Si bainitic steel (Fe-0.22C-2.0Si-3.0Mn) was used with a proper microstructure which could endure severe plastic deformation. In order to study the effect of severe plastic deformation on the microstructure and properties of bainitic steel, Equal Channel Angular Pressing was performed in two passes at room temperature. Optical, SEM and TEM microscopies were used to examine the microstructure of specimens before and after Equal Channel Angular Pressing processing. X-ray diffraction was used to measure retained austenite after austempering and Equal Channel Angular Pressing processing. It can be seen that retained austenite picks had removed after Equal Channel Angular Pressing which could attributed to the transformation of austenite to martensite during severe plastic deformation. Enhancement of hardness values by number of Equal Channel Angular Pressing confirms this idea.

Microstructural evolution and rheology of quartz in a mid-crustal shear zone

NASA Astrophysics Data System (ADS)

Rahl, Jeffrey M.; Skemer, Philip

2016-06-01

We present microstructural and crystallographic preferred orientation (CPO) data on quartz deformed in the middle crust to explore the interaction and feedback between dynamic recrystallization, deformation processes, and CPO evolution. The sample investigated here is a moderately deformed quartz-rich mylonite from the Blue Ridge in Virginia. We have created high-resolution crystallographic orientation maps using electron backscatter diffraction (EBSD) of 51 isolated quartz porphyroclasts with recrystallized grain fractions ranging from 10 to 100%. Recrystallized grains are internally undeformed and display crystallographic orientations dispersed around the orientation of the associated parent porphyroclast. We document a systematic decrease in fabric intensity with recrystallization, suggesting that progressive deformation of the recrystallized domains involves processes that can weaken a pre-existing CPO. Relationships between recrystallization fraction and shear strain suggest that complete microstructural re-equilibration requires strains in excess of γ = 5. Variation in the degree of recrystallization implies that strain was accumulated heterogeneously, and that a steady-state microstructure and rheology were not achieved.

Characterization of a cold-rolled 2101 lean duplex stainless steel.

PubMed

Bassani, Paola; Breda, Marco; Brunelli, Katya; Mészáros, Istvan; Passaretti, Francesca; Zanellato, Michela; Calliari, Irene

2013-08-01

Duplex stainless steels (DSS) may be defined as a category of steels with a two-phase ferritic-austenitic microstructure, which combines good mechanical and corrosion properties. However, these steels can undergo significant microstructural modification as a consequence of either thermo-mechanical treatments (ferrite decomposition, which causes σ- and χ-phase formation and nitride precipitation) or plastic deformation at room temperature [austenite transformation into strain-induced martensite (SIM)]. These secondary phases noticeably affect the properties of DSS, and therefore are of huge industrial interest. In the present work, SIM formation was investigated in a 2101 lean DSS. The material was subjected to cold rolling at various degrees of deformation (from 10 to 80% thickness reduction) and the microstructure developed after plastic deformation was investigated by electron backscattered diffraction, X-ray diffraction measurements, and hardness and magnetic tests. It was observed that SIM formed as a consequence of deformations higher than ~20% and residual austenite was still observed at 80% of thickness reduction. Furthermore, a direct relationship was found between microstructure and magnetic properties.

Microstructure and texture evolution in cold-rolled and annealed alloy MA-956

NASA Astrophysics Data System (ADS)

Hosoda, Takashi

The microstructural and texture development with thermomechanical processing, performed through a combination of cold-rolling and annealing, in MA-956 plate consisting of a layered and inhomogeneous microstructure was systematically assessed. The alloy contained in mass percent, 20 Cr, 4.8 Al, 0.4 Ti, 0.4 Y2O3, and the balance iron. The starting material was as-hot-rolled plate, 9.7 mm thick. The as-hot-rolled plate was subjected to 40%, 60%, and 80% cold-rolling reduction and subsequently annealed at 1000, 1200, or 1380. Assessment of microstructural and texture developments before and after cold-rolling and annealing was performed using light optical microscopy (LOM), Vickers hardness testing, and electron backscatter diffraction (EBSD). Locally introduced misorientations by cold-rolling in each region were evaluated by Kernel Average Misorientation (KAM) maps. The as-hot-rolled condition contained a layered and inhomogeneous microstructure consisting of thin and coarse elongated grains, and aggregated regions which consisted of fine grains and sub-grains with {100} texture parallel to the longitudinal direction. The microstructure of the 40% cold-rolled condition contained deformation bands, and the 60% and 80% cold-rolled conditions also contained highly deformed regions where the deformation bands were intricately tangled. A predominant orientation of (001) parallel to the rolling direction was developed during cold-rolling, becoming more prominent with increasing reduction. The magnitudes of KAM angles varied through the thickness depending on the initial microstructures. Recrystallization occurred in regions where high KAM angles were dense after annealing and nucleation sites were the aggregation regions, deformation bands, and highly deformed regions. The shape and size of the recrystallized grains varied depending on the nucleation sites.

Microstructure and hot compression deformation of the as-cast Mg-5.0Sn-1.5Y-0.1Zr alloy

NASA Astrophysics Data System (ADS)

Luo, Xiaoping; Kang, Li; Li, Qiushu; Chai, Yuesheng

2015-08-01

The hot compression deformation behavior and microstructure of as-cast Mg-5.0Sn-1.5Y-0.1Zr alloy were investigated by performing isothermal hot compression tests. The tests were conducted using a thermal mechanical simulator at 250-450 °C and strain rates ranging from 0.002 to 2 s-1, with a maximum deformation strain of 50 %. The effects of the deformation parameters on the microstructure evolution of the Mg-5.0Sn-1.5Y-0.1Zr alloy were discussed. The study revealed the flow behavior and the deformation mechanism of the Mg-5.0Sn-1.5Y-0.1Zr alloy. The dependence of flow stress on temperature and strain rate was described by a hyperbolic sine constitutive equation. Through regression analysis, the activation energy of 223.26 kJ mol-1 for plastic deformation was determined by considering flow stress at a strain rate of 0.2. Microstructure observation showed that dynamic recrystallization occurred extensively along grain boundaries at temperatures higher than 300 °C and strain rates lower than 0.02 s-1. This observation provides a theoretical basis for the manufacture and application of the Mg-5.0Sn-1.5Y-0.1Zr alloy.

Finite deformation of incompressible fiber-reinforced elastomers: A computational micromechanics approach

NASA Astrophysics Data System (ADS)

Moraleda, Joaquín; Segurado, Javier; LLorca, Javier

2009-09-01

The in-plane finite deformation of incompressible fiber-reinforced elastomers was studied using computational micromechanics. Composite microstructure was made up of a random and homogeneous dispersion of aligned rigid fibers within a hyperelastic matrix. Different matrices (Neo-Hookean and Gent), fibers (monodisperse or polydisperse, circular or elliptical section) and reinforcement volume fractions (10-40%) were analyzed through the finite element simulation of a representative volume element of the microstructure. A successive remeshing strategy was employed when necessary to reach the large deformation regime in which the evolution of the microstructure influences the effective properties. The simulations provided for the first time "quasi-exact" results of the in-plane finite deformation for this class of composites, which were used to assess the accuracy of the available homogenization estimates for incompressible hyperelastic composites.

Evolution of microstructure in stainless martensitic steel for seamless tubing

NASA Astrophysics Data System (ADS)

Pyshmintsev, I. Yu.; Bityukov, S. M.; Pastukhov, V. I.; Danilov, S. V.; Vedernikova, L. O.; Lobanov, M. L.

2017-12-01

Scanning electron microscopy with orientation analysis by the electron backscatter diffraction (EBSD) method is used to study microstructures and textures formed in the 0.08C-13Cr-3Ni-Mo-V-Nb steel through seamless tube production route: after hot deformation by extrusion; after quenching from various temperatures and subsequent high tempering. It is shown that the martensitic microstructure formed both after hot deformation and after quenching is characterized by the presence of deformation crystallographic texture, which is predetermined by the texture of austenite. The effect of heat treatment on texture, packet refinement, lath width, precipitation of carbides and Charpy impact energy is analyzed.

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

NASA Astrophysics Data System (ADS)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

A constitutive model for AS4/PEEK thermoplastic composites under cyclic loading

NASA Technical Reports Server (NTRS)

Rui, Yuting; Sun, C. T.

1990-01-01

Based on the basic and essential features of the elastic-plastic response of the AS4/PEEK thermoplastic composite subjected to off-axis cyclic loadings, a simple rate-independent constitutive model is proposed to describe the orthotropic material behavior for cyclic loadings. A one-parameter memory surface is introduced to distinguish the virgin deformation and the subsequent deformation process and to characterize the loading range effect. Cyclic softening is characterized by the change of generalized plastic modulus. By the vanishing yield surface assumption, a yield criterion is not needed and it is not necessary to consider loading and unloading separately. The model is compared with experimental results and good agreement is obtained.

Material heterogeneity in cancellous bone promotes deformation recovery after mechanical failure.

PubMed

Torres, Ashley M; Matheny, Jonathan B; Keaveny, Tony M; Taylor, David; Rimnac, Clare M; Hernandez, Christopher J

2016-03-15

Many natural structures use a foam core and solid outer shell to achieve high strength and stiffness with relatively small amounts of mass. Biological foams, however, must also resist crack growth. The process of crack propagation within the struts of a foam is not well understood and is complicated by the foam microstructure. We demonstrate that in cancellous bone, the foam-like component of whole bones, damage propagation during cyclic loading is dictated not by local tissue stresses but by heterogeneity of material properties associated with increased ductility of strut surfaces. The increase in surface ductility is unexpected because it is the opposite pattern generated by surface treatments to increase fatigue life in man-made materials, which often result in reduced surface ductility. We show that the more ductile surfaces of cancellous bone are a result of reduced accumulation of advanced glycation end products compared with the strut interior. Damage is therefore likely to accumulate in strut centers making cancellous bone more tolerant of stress concentrations at strut surfaces. Hence, the structure is able to recover more deformation after failure and return to a closer approximation of its original shape. Increased recovery of deformation is a passive mechanism seen in biology for setting a broken bone that allows for a better approximation of initial shape during healing processes and is likely the most important mechanical function. Our findings suggest a previously unidentified biomimetic design strategy in which tissue level material heterogeneity in foams can be used to improve deformation recovery after failure.

Atypical transitions in material response during constant strain rate, hot deformation of austenitic steel

NASA Astrophysics Data System (ADS)

Borah, Utpal; Aashranth, B.; Samantaray, Dipti; Kumar, Santosh; Davinci, M. Arvinth; Albert, Shaju K.; Bhaduri, A. K.

2017-10-01

Work hardening, dynamic recovery and dynamic recrystallization (DRX) occurring during hot working of austenitic steel have been extensively studied. Various empirical models describe the nature and effects of these phenomena in a typical framework. However, the typical model is sometimes violated following atypical transitions in deformation mechanisms of the material. To ascertain the nature of these atypical transitions, researchers have intentionally introduced discontinuities in the deformation process, such as interrupting the deformation as in multi-step rolling and abruptly changing the rate of deformation. In this work, we demonstrate that atypical transitions are possible even in conventional single-step, constant strain rate deformation of austenitic steel. Towards this aim, isothermal, constant true strain rate deformation of austenitic steel has been carried out in a temperature range of 1173-1473 K and strain rate range of 0.01-100 s-1. The microstructural response corresponding to each deformation condition is thoroughly investigated. The conventional power-law variation of deformation grain size (D) with peak stress (σp) during DRX is taken as a typical model and experimental data is tested against it. It is shown that σp-D relations exhibit an atypical two-slope linear behaviour rather than a continuous power law relation. Similarly, the reduction in σp with temperature (T) is found to consist of two discrete linear segments. In practical terms, the two linear segments denote two distinct microstructural responses to deformation. As a consequence of this distinction, the typical model breaks down and is unable to completely relate microstructural evolution to flow behaviour. The present work highlights the microstructural mechanisms responsible for this atypical behavior and suggests strategies to incorporate the two-slope behaviour in the DRX model.

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.

Non-geometric fluxes, quasi-Hopf twist deformations, and nonassociative quantum mechanics

NASA Astrophysics Data System (ADS)

Mylonas, Dionysios; Schupp, Peter; Szabo, Richard J.

2014-12-01

We analyse the symmetries underlying nonassociative deformations of geometry in non-geometric R-flux compactifications which arise via T-duality from closed strings with constant geometric fluxes. Starting from the non-abelian Lie algebra of translations and Bopp shifts in phase space, together with a suitable cochain twist, we construct the quasi-Hopf algebra of symmetries that deforms the algebra of functions and the exterior differential calculus in the phase space description of nonassociative R-space. In this setting, nonassociativity is characterised by the associator 3-cocycle which controls non-coassociativity of the quasi-Hopf algebra. We use abelian 2-cocycle twists to construct maps between the dynamical nonassociative star product and a family of associative star products parametrized by constant momentum surfaces in phase space. We define a suitable integration on these nonassociative spaces and find that the usual cyclicity of associative noncommutative deformations is replaced by weaker notions of 2-cyclicity and 3-cyclicity. Using this star product quantization on phase space together with 3-cyclicity, we formulate a consistent version of nonassociative quantum mechanics, in which we calculate the expectation values of area and volume operators, and find coarse-graining of the string background due to the R-flux.

Modelling of deformation and recrystallisation microstructures in rocks and ice

NASA Astrophysics Data System (ADS)

Bons, Paul D.; Evans, Lynn A.; Gomez-Rivas, Enrique; Griera, Albert; Jessell, Mark W.; Lebensohn, Ricardo; Llorens, Maria-Gema; Peternell, Mark; Piazolo, Sandra; Weikusat, Ilka; Wilson, Chris J. L.

2015-04-01

Microstructures both record the deformation history of a rock and strongly control its mechanical properties. As microstructures in natural rocks only show the final "post-mortem" state, geologists have attempted to simulate the development of microstructures with experiments and later numerical models. Especially in-situ experiments have given enormous insight, as time-lapse movies could reveal the full history of a microstructure. Numerical modelling is an alternative approach to simulate and follow the change in microstructure with time, unconstrained by experimental limitations. Numerical models have been applied to a range of microstructural processes, such as grain growth, dynamic recrystallisation, porphyroblast rotation, vein growth, formation of mylonitic fabrics, etc. The numerical platform "Elle" (www.elle.ws) in particular has brought progress in the simulation of microstructural development as it is specifically designed to include the competition between simultaneously operating processes. Three developments significantly improve our capability to simulate microstructural evolution: (1) model input from the mapping of crystallographic orientation with EBSD or the automatic fabric analyser, (2) measurement of grain size and crystallographic preferred orientation evolution using neutron diffraction experiments and (3) the implementation of the full-field Fast Fourier Transform (FFT) solver for modelling anisotropic crystal-plastic deformation. The latter enables the detailed modelling of stress and strain as a function of local crystallographic orientation, which has a strong effect on strain localisation such as, for example, the formation of shear bands. These models can now be compared with the temporal evolution of crystallographic orientation distributions in in-situ experiments. In the last decade, the possibility to combine experiments with numerical simulations has allowed not only verification and refinement of the numerical simulation technique but also increased significantly the ability to predict and/or interpret natural microstructures. This contribution will present the most recent developments in in-situ and numerical modelling of deformation and recrystallisation microstructures in rocks and in ice.

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

NASA Astrophysics Data System (ADS)

Rokni, M. R.; Nutt, S. R.; Widener, C. A.; Champagne, V. K.; Hrabe, R. H.

2017-08-01

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

In situ, 3D characterization of the deformation mechanics of a superelastic NiTi shape memory alloy single crystal under multiscale constraint

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

Paranjape, Harshad M.; Paul, Partha P.; Amin-Ahmadi, Behnam

Microstructural elements in NiTi shape memory alloys (SMAs) – precipitates, phase boundaries, inclusions, grain boundaries – can be viewed as sources of multiscale constraint that influence their deformation response. In this paper, we characterized in situ, and in 3D, the deformation and the evolution of microstructure during a tension test in a superelastic NiTi specimen containing some of these sources of constraint. The method used was far-field high-energy X-ray diffraction microscopy (ff-HEDM), complemented by electron microscopy. We simulated the local stress state in the specimen using a microstructural model informed by the experimental data. Using these combined microstructure, deformation, andmore » stress data, we report three phenomena, and relate them to specific sources of constraint. During initial elastic loading, axial lattice strain in austenite increased monotonically. On partial stress-induced phase transformation to martensite, the stress redistributed to both phases leading to a stress relaxation in austenite. The specimen contained a dense distribution of inclusions, which led to the activation of martensite habit plane variants that produce less than theoretical maximum transformation strain. Large Ni 4Ti 3 precipitates potentially contributed to the poor transformation response. Under load, proportional gradients in local rotation and elastic stretch developed in the martensite phase, because of the constraint at phase interfaces. Finally, this combined ff-HEDM, electron microscopy, microstructural simulation toolbox provides a versatile method to understand the effect of constraint on inelastic deformation in other alloys with hierarchical microstructure.« less

In situ, 3D characterization of the deformation mechanics of a superelastic NiTi shape memory alloy single crystal under multiscale constraint

DOE PAGES

Paranjape, Harshad M.; Paul, Partha P.; Amin-Ahmadi, Behnam; ...

2017-11-20

Microstructural elements in NiTi shape memory alloys (SMAs) – precipitates, phase boundaries, inclusions, grain boundaries – can be viewed as sources of multiscale constraint that influence their deformation response. In this paper, we characterized in situ, and in 3D, the deformation and the evolution of microstructure during a tension test in a superelastic NiTi specimen containing some of these sources of constraint. The method used was far-field high-energy X-ray diffraction microscopy (ff-HEDM), complemented by electron microscopy. We simulated the local stress state in the specimen using a microstructural model informed by the experimental data. Using these combined microstructure, deformation, andmore » stress data, we report three phenomena, and relate them to specific sources of constraint. During initial elastic loading, axial lattice strain in austenite increased monotonically. On partial stress-induced phase transformation to martensite, the stress redistributed to both phases leading to a stress relaxation in austenite. The specimen contained a dense distribution of inclusions, which led to the activation of martensite habit plane variants that produce less than theoretical maximum transformation strain. Large Ni 4Ti 3 precipitates potentially contributed to the poor transformation response. Under load, proportional gradients in local rotation and elastic stretch developed in the martensite phase, because of the constraint at phase interfaces. Finally, this combined ff-HEDM, electron microscopy, microstructural simulation toolbox provides a versatile method to understand the effect of constraint on inelastic deformation in other alloys with hierarchical microstructure.« less

The influence of matrix microstructure

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; Allison, J. E.; Aken, D. C.

1993-11-01

The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and artificially aged 2219/TiC/15p and unreinforced 2219 Al were investigated utilizing plastic strain-controlled and stress-controlled testing. The cyclic response of both the reinforced and un-reinforced materials was similar for all plastic strain amplitudes tested except that the saturation stress level for the composite was always greater than that of the unreinforced material. The cyclic response of the naturally aged materials exhibited cyclic hardening and, in some cases, cyclic softening, while the cyclic response for the artificially aged materials showed no evidence of either cyclic hardening or softening. The higher ductility of the unreinforced material made it more resistant to fatigue failure at high strains, and thus, at a given plastic strain, it had longer fatigue life. It should be noted that the tensile ductilities of the 2219/TiC/15p were significantly higher than those previously reported for 2XXX-series composites. During stress-controlled test-ing at stresses below 220 MPa, the presence of TiC particles lead to an improvement in fatigue life. Above 220 MPa, no influence of TiC reinforcement on fatigue life could be detected. In both the composite and unreinforced materials, the low-cycle and high-cycle fatigue lives were found to be virtually independent of matrix microstructure.

Deformation Microstructures of the Yugu Peridotites in the Gyeonggi Massif, Korea: Implications for Olivine Fabric Transition in Mantle Shear Zones

NASA Astrophysics Data System (ADS)

Jung, H.; Park, M.

2017-12-01

Large-scale emplaced peridotite bodies may provide insights into plastic deformation process and tectonic evolution in the mantle shear zone. Due to the complexity of deformation microstructures and processes in natural mantle rocks, the evolution of pre-existing olivine fabrics is still not well understood. In this study, we examine well-preserved transitional characteristics of microstructures and olivine fabrics developed in a mantle shear zone from the Yugu peridotite body, the Gyeonggi Massif, Korean Peninsula. The Yugu peridotite body predominantly comprises spinel harzburgite together with minor lherzolite, dunite, and clinopyroxenite. We classified highly deformed peridotites into four textural types based on their microstructural characteristics: proto-mylonite; proto-mylonite to mylonite transition; mylonite; and ultra-mylonite. Olivine fabrics changed from A-type (proto-mylonite) via D-type (mylonite) to E-type (ultra-mylonite). Olivine fabric transition is interpreted as occurring under hydrous conditions at low temperature and high strain, because of characteristics such as Ti-clinohumite defects (and serpentine) and fluid inclusion trails in olivine, and a hydrous mineral (pargasite) in the matrix, especially in the ultra-mylonitic peridotites. Even though the ultra-mylonitic peridotites contained extremely small (24-30 μm) olivine neoblasts, the olivine fabrics showed a distinct (E-type) pattern rather than a random one. Analysis of the lattice preferred orientation strength, dislocation microstructures, recrystallized grain-size, and deformation mechanism maps of olivine suggest that the proto-mylonitic, mylonitic, and ultra-mylonitic peridotites were deformed by dislocation creep (A-type), DisGBS (D-type), and combination of dislocation and diffusion creep (E-type), respectively.

High temperature behavior of B2-based ruthenium aluminide systems

NASA Astrophysics Data System (ADS)

Cao, Fang

Ru-modified NiAl-based bond coats have the potential to improve the durability of Superalloy-Thermal Barrier Coating systems (TBCs) for advanced gas turbine engines. A fundamental understanding of the high temperature mechanical behavior across the Ni-Al-Ru B2 phase field can provide direction for the development of these new bond coats for TBCs. The purpose of this study has been to describe the fundamental processes of creep deformation in single phase B2 Ru-Al-Ni ternary alloys which would form the basis for the bond coats. To accomplish this, five ternary alloys with compositions located within the B2 field across the NiAl-RuAl phase region were fabricated and investigated. Special emphasis was placed on characterizing creep deformation and describing the operative creep mechanisms in these alloys. At room temperature, brittle failure was observed in the Ni-rich alloys in compression, while improved strength and ductility were displayed in two Ru-rich ternary alloys at temperatures up to 700°C. Exceptional creep strength was observed in these alloys, as compared to other high melting temperature B2 intermetallics. A continuous increase of the melting temperature and creep resistance with the increasing of the Ru/Ni ratio in these alloys was observed. Post-creep dislocation analyses identified the presence of <100> and <110> edge dislocations in the Ni-rich alloys, while uniformly distributed jogged <100> screw dislocations predominated in the Ru-rich ternary alloys. A transition of the creep mechanism from viscous glide controlled to jogged screw motion in these Ru-Al-Ni ternary B2 alloys with increasing Ru/Ni ratio is demonstrated by the characteristics of the creep deformation process, stress change creep tests, post-creep dislocation analyses, and numerical modeling. Additionally, the knowledge of the cyclic oxidation behavior of ruthenium aluminide-based alloy is essential, as many high-temperature applications for which this intermetallic might be utilized undergo repeated severe thermal cycling. Thus the second portion of this thesis focuses on the characterization of the cyclic oxidation properties of RuAl-based alloys. The cyclic oxidation behavior of six RuAl-based alloys was studied in air over the temperature range of 1000°C to 1300°C. Oxidation kinetics have been shown to be influenced by microstructure as well as the addition of platinum.

Deformation of the lithosphere and what microstructures can tell us about it (Stephan Mueller Medal Lecture)

NASA Astrophysics Data System (ADS)

Heilbronner, Renée

2016-04-01

The lithosphere is a roughly stratified and heterogeneous rock body that constitutes the outer layer of our planet. It is subdivided into irregularly shaped stiff plates that move with respect to one another deforming each other along their margins. At the large scale the lithosphere is usually modeled as a flat-lying multi-layer, its rheological profile being based on flow laws determined experimentally for key minerals of the crust and upper mantle. At the somewhat smaller scale of field observations, geometrical and physical complexities become apparent: rocks are folded, sheared and fractured, and - in general - quite heterogeneously deformed. And finally, at the even smaller scale of mechanical testing and microscopic investigations, rocks are seen as polycrystalline aggregates or granular composites whose bulk properties depends both on the composition and shape of the individual grains and the spatial arrangement of the crystals with respect to one another. In other words, the physical properties of the lithosphere and the inferred style or type of deformation depend very much on the scale of observation. Microstructures and textures (crystallographic preferred orientations) of deformed rocks provide a wealth of information: when used as archives of the deformation history, they allow us to unravel the tectonic evolution of the lithosphere at plate boundaries. At the same time, they enable us to assess past and/or present geophysical properties. By comparing the microstructures of experimentally and naturally deformed rocks it is possible to infer the active deformation mechanisms and thus to extrapolate flow laws to geological time scales. With the advent of digital image processing, microstructure and texture analysis have taken a great leap forward. By amalgamating methods from neighbouring disciplines such as mathematical morphometry, stereology, geostatistics, material sciences, etc., microstructure and texture analysis have come a long way since the early days of strain analysis and X-ray texture goniometry. During my lecture, I will try to retrace this development: we will start by taking a dive down to the nano-scale, deep into the ductile regime, and inspect the shape, alignments and preferred orientations of sub-grain boundaries during simple shear deformation. What can the microstructure tell us about the deformation mechanism and the amount of strain that the rock material has undergone, and is it really 'strain' we are looking at? We will also look at orientation images and track the development in space and time of crystallographic orientations with temperature, strain rate and strain: do we reach a 'steady state'? We will then come up in scale and look at various definitions of grain size and test the validity of piezometers: how precise is the flow stress that we determine, does it really only depend on grain size, and what do we mean by 'grains size'? Back at the surface, we will look at brittle microstructures and consider distributions: fractal distributions of grain size and spatial distributions of grains: how can we get a handle on the microstructures of cataclastic deformation or granular flow? - At each step, I hope that it becomes apparent that there is more to microstructure and texture than the aspect ratio of an ellipse, the diameter of a grain, or the maximum of a c-axis pole figure...

Strength of the Subduction Plate Interface beneath the Seismogenic Zone: A Microstructural Investigation of Deformation Mechanisms within a Phyllosilicate- and Amphibole-rich Shear Zone

NASA Astrophysics Data System (ADS)

Seyler, C.; Kirkpatrick, J. D.; Šilerová, D.

2017-12-01

Localization of strain at plate boundaries requires rheological weakening of the lithosphere. The rheology of the subduction plate interface is dictated by the dominant grain-scale deformation mechanisms. However, little is known about the deformation mechanisms within phases commonly found in subduction zones, such as phyllosilicates and amphiboles. We investigate the Leech River Shear Zone on Vancouver Island, British Columbia to explore deformation processes downdip of the seismogenic zone and evaluate the bulk rheology of the plate interface. This shear zone juxtaposes a metamorphosed accretionary prism against a metabasaltic oceanic plateau, representing a paleo-plate interface from the ancient Cascadia subduction zone. Preliminary geothermometry results record a prograde deformation temperature of 573.6±11.2 ˚C in the overriding accretionary wedge, and the hornblende-chlorite-epidote-plagioclase mineral assemblage suggests upper greenschist to lower amphibolite facies metamorphism of the downgoing oceanic crust. Detailed mapping of the plate interface documents a 200 m wide mylonitic shear zone developed across the lithologic contact. Asymmetric shear fabrics, isoclinal folding, boudinage, and a steeply plunging, penetrative stretching lineation are consistent with sinistral-oblique subduction. Numerous discordant quartz veins are variably sheared into sigmoidal shapes as well as isoclinally folded and boudinaged, indicating cyclical synkinematic fracture and vein formation. At the grain-scale, interconnected, anastomosing layers of muscovite, chlorite, and graphite in the accretionary prism rocks likely deformed through kinking and dislocation glide. Framework minerals such as quartz and feldspar deformed by dislocation creep. In the metabasalt, hornblende and chlorite form a continuous S—C fabric in which asymmetric hornblende porphyroclasts deformed by rigid grain rotation and dissolution-precipitation creep. The strength of the subduction plate interface beneath the seismogenic zone was therefore controlled by multiple syn-kinematic mechanisms, with overall strength dominated by the rheology of phyllosilicates and amphibole, generating very low viscosities at the plate interface and enhancing strain localization.

Microstructures and Lattice Preferred Orientations in Experimentally Deformed Granulites

NASA Astrophysics Data System (ADS)

Miao, S.; Zhou, Y.

2017-12-01

We analysed microstructures and lattice preferred orientations (LPO) on experimentally deformed natural granulites in order to understand the relationship between deformation processes and evolving microstructures. The LPO was measured using the scanning electron microscope (SEM)-based electron backscatter diffraction (EBSD) technique. Microstructures were observed by polarized light microscopy and by orientation contrast in the SEM. Natural granulite samples were collected in the Archean lower crust terrane of North China Craton. This granulite is composed of 59% plagioclase (PI) + 21% clinopyroxene (Cpx) +14% orthopyroxene + 5% opaque minerals+1% quartz. The water contents of bulk rocks were in the range 0.10-0.26 wt.%. The average grain size of PI and Cpx were 240 μm and 220 μm, respectively. These samples were deformed in axial compress tests up to 7%-15% shorting at temperatures ranged from 900 ° to 1150 °. Microstructures results in conjunction with some other parameters such as stress exponents indicated that the samples deformed mainly by intragranular microcracking, twinning and dislocation glide with very little recrystallization. The natural sample, without any macroscopic foliation visible, has a significant initial LPO in Cpx corresponding to an "S-type" fabric with the b[010]maximum normal to a foliation plane. PI also has a pre-existing fabric. We compared the LPO of Cpx and PI of experimentally deformed samples with that of undeformed natural samples. It shows that no clear LPO evolution apart from the initial LPO could be attributed to deformation. Even if at a temperature range (eg. above 1100 °) where partial melting occurs, "S-type" fabrics of Cpx have been remained effectively. Deformation in the dislocation creep regime does not alter the initial LPO nor produce a new pattern. This is consistent with previous results, which stated that large strains, at least more than 25% shortening are necessary to overprint a pre-existing LPO in clinopyroxenes.

Thermomechanical behavior of tin-rich (lead-free) solders

NASA Astrophysics Data System (ADS)

Sidhu, Rajen Singh

In order to adequately characterize the behavior of ball-grid-array (BGA) Pb-free solder spheres in electronic devices, the microstructure and thermomechanical behavior need to be studied. Microstructure characterization of pure Sn, Sn-0.7Cu, Sn-3.5Ag, and Sn-3.9Ag-0.7Cu alloys was conducted using optical microscopy, scanning electron microscopy, transmission electron microscopy, image analysis, and a novel serial sectioning 3D reconstruction process. Microstructure-based finite-element method (FEM) modeling of deformation in Sn-3.5Ag alloy was conducted, and it will be shown that this technique is more accurate when compared to traditional unit cell models for simulating and understanding material behavior. The effect of cooling rate on microstructure and creep behavior of bulk Sn-rich solders was studied. The creep behavior was evaluated at 25, 95, and 120°C. Faster cooling rates were found to increase the creep strength of the solders due to refinement of the solder microstructure. The creep behavior of Sn-rich single solder spheres reflowed on Cu substrates was studied at 25, 60, 95, and 130°C. Testing was conducted using a microforce testing system, with lap-shear geometry samples. The solder joints displayed two distinct creep behaviors: (a) precipitation-strengthening (Sn-3.5Ag and Sn-3.9Ag-0.7Cu) and (b) power law creep accommodated by grain boundary sliding (GBS) (Sn and Sn-0.7Cu). The relationship between microstructural features (i.e. intermetallic particle size and spacing), stress exponents, threshold stress, and activation energies are discussed. The relationship between small-length scale creep behavior and bulk behavior is also addressed. To better understand the damage evolution in Sn-rich solder joints during thermal fatigue, the local damage will be correlated to the cyclic hysteresis behavior and crystal orientations present in the Sn phase of solder joints. FEM modeling will also be utilized to better understand the macroscopic and local strain response of the lap shear geometry.

Dynamic room temperature precipitation during cyclic deformation of an Al-Zn-Mg-Cu alloy

NASA Astrophysics Data System (ADS)

Hutchinson, C. R.; de Geuser, F.; Deschamps, A.

The effect of pre-straining on a precipitation heat treatment is a well-chartered area and is relevant to a number of Al alloy manufacturing processes. When straining and precipitation occur concurrently, the situation is less clear. This may arise during creep, fatigue or elevated temperature forming operations. Straining introduces dislocations and strain-induced vacancies that may enhance nucleation and growth processes but the dislocations may also shear and/or cause precipitate dissolution. This study reports a systematic characterization of precipitation during room temperature cyclic deformation of the AA7050 (Al-Zn-Mg-Cu) alloy. The mechanical response is monitored using plastic strain controlled cyclic deformation tests and the precipitation state is characterized using small angle x-ray scattering. It is shown that the precipitate volume fraction increases with the number of deformation cycles and is well correlated with the hardening increment observed but the mean precipitate radii remains relatively constant during cycling at 4-5A.

Microstructure, Texture and Mechanical Properties of Titanium Grade 2 Processed by ECAP (Route C)

NASA Astrophysics Data System (ADS)

Wroński, M.; Wierzbanowski, K.; Wojtas, D.; Szyfner, E.; Valiev, R. Z.; Kawałko, J.; Berent, K.; Sztwiertnia, K.

2018-03-01

In the present work the properties of titanium grade 2 after ECAP processing with original route and regimes (route C, channel angle Φ= 120°, deformation temperature 300 °C, number of passes up to 8) were examined. Texture development and microstructure parameters after ECAP processing and after recrystallization were determined using electron back scatter diffraction and analysed. A significant increase of the mechanical strength accompanied by some increase of ductility was observed in the deformed samples. The kernel average misorientation and average grain orientation spread were strongly increased after deformation, which confirms the material refinement and fragmentation. The proportion of low angle boundaries increased after four ECAP passes, but after four consecutive passes high angle grain boundaries became predominant. No deformation twins were observed after four and eight ECAP passes. The material recrystallized after deformation retained a fine grain microstructure. The textures of deformed and recrystallized samples were determined. It was found that texture after 8 passes is more homogeneous that that after 4 passes, which partly explains higher ductility of this first sample.

Deformational Features and Microstructure Evolution of Copper Fabricated by a Single Pass of the Elliptical Cross-Section Spiral Equal-Channel Extrusion (ECSEE) Process

NASA Astrophysics Data System (ADS)

Wang, Chengpeng; Li, Fuguo; Liu, Juncheng

2018-04-01

The objectives of this work are to study the deformational feature, textures, microstructures, and dislocation configurations of ultrafine-grained copper processed by the process of elliptical cross-section spiral equal-channel extrusion (ECSEE). The deformation patterns of simple shear and pure shear in the ECSEE process were evaluated with the analytical method of geometric strain. The influence of the main technical parameters of ECSEE die on the effective strain distribution on the surface of ECSEE-fabricated samples was examined by the finite element simulation. The high friction factor could improve the effective strain accumulation of material deformation. Moreover, the pure copper sample fabricated by ECSEE ion shows a strong rotated cube shear texture. The refining mechanism of the dislocation deformation is dominant in copper processed by a single pass of ECSEE. The inhomogeneity of the micro-hardness distribution on the longitudinal section of the ECSEE-fabricated sample is consistent with the strain and microstructure distribution features.

Effects of thermomechanical processing on the microstructure and mechanical properties of a Ti-V-N steel

NASA Astrophysics Data System (ADS)

Dogan, B.; Collins, L. E.; Boyd, J. D.

1988-05-01

Based on studies of austenite deformation behavior and continuous-cooling-transformation behavior of a Ti-V microalloyed steel by cam plastometer and quench-deformation dilatometer, respectively, plate rolling schedules were designed to produce (i) recrystallized austenite, (ii) unrecrystallized austenite, (iii) deformed ferrite + unrecrystallized austenite. The effects of austenite condition and cooling rate on the final microstructure and mechanical properties were investigated. To rationalize the variation in final ferrite grain size with different thermomechanical processing schedules, it is necessary to consider the kinetics of ferrite grain growth in addition to the density of ferrite nucleation sites. The benefit of dilatometer studies in determining the optimum deformation schedule and cooling rate for a given steel is domonstrated. A wide range of tensile and impact properties results from the different microstructures studied. Yield strength is increased by increasing the amount of deformed ferrite, bainite, or martensite, and by decreasing the ferrite grain size. Impact toughness is most strongly influenced by ferrite grain size and occurrence of rolling plane delaminations.

Deformation microstructures of Barre granite: An optical, Sem and Tem study

USGS Publications Warehouse

Schedl, A.; Kronenberg, A.K.; Tullis, J.

1986-01-01

New scanning electron microscope techniques have been developed for characterizing ductile deformation microstructures in felsic rocks. In addition, the thermomechanical history of the macroscopically undeformed Barre granite (Vermont, U.S.A.) has been reconstructed based on examination of deformation microstructures using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The microstructures reveal three distinct events: 1. (1) a low-stress, high-temperature event that produced subgrains in feldspars, and subgrains and recrystallized grains in quartz; 2. (2) a high-stress, low-temperature event that produced a high dislocation density in quartz and feldspars; and 3. (3) a lowest-temperature event that produced cracks, oriented primarily along cleavage planes in feldspars, and parallel to the macroscopic rift in quartz. The first two events are believed to reflect various stages in the intrusion and cooling history of the pluton, and the last may be related to the last stages of cooling, or to later tectonism. ?? 1986.

Orientation dependence of the dislocation microstructure in compressed body-centered cubic molybdenum

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

Wang, S.; Wang, M.P.; Chen, C., E-mail: chench011-33@163.com

2014-05-01

The orientation dependence of the deformation microstructure has been investigated in commercial pure molybdenum. After deformation, the dislocation boundaries of compressed molybdenum can be classified, similar to that in face-centered cubic metals, into three types: dislocation cells (Type 2), and extended planar boundaries parallel to (Type 1) or not parallel to (Type 3) a (110) trace. However, it shows a reciprocal relationship between face-centered cubic metals and body-centered cubic metals on the orientation dependence of the deformation microstructure. The higher the strain, the finer the microstructure is and the smaller the inclination angle between extended planar boundaries and the compressionmore » axis is. - Highlights: • A reciprocal relationship between FCC metals and BCC metals is confirmed. • The dislocation boundaries can be classified into three types in compressed Mo. • The dislocation characteristic of different dislocation boundaries is different.« less

Micromechanical model of lung parenchyma hyperelasticity

NASA Astrophysics Data System (ADS)

Concha, Felipe; Sarabia-Vallejos, Mauricio; Hurtado, Daniel E.

2018-03-01

Mechanics plays a key role in respiratory physiology, as lung tissue cyclically deforms to bring air in and out the lung, a life-long process necessary for respiration. The study of regional mechanisms of deformation in lung parenchyma has received great attention to date due to its clinical relevance, as local overstretching and stress concentration in lung tissue is currently associated to pathological conditions such as lung injury during mechanical ventilation therapy. This mechanical approach to lung physiology has motivated the development of constitutive models to better understand the relation between stress and deformation in the lung. While material models proposed to date have been key in the development of whole-lung simulations, either they do not directly relate microstructural properties of alveolar tissue with coarse-scale behavior, or they require a high computational effort when based on real alveolar geometries. Furthermore, most models proposed to date have not been thoroughly validated for anisotropic deformation states, which are commonly found in normal lungs in-vivo. In this work, we develop a novel micromechanical model of lung parenchyma hyperelasticity using the framework of finite-deformation homogenization. To this end, we consider a tetrakaidecahedron unit cell with incompressible Neo-Hookean structural elements that account for the alveolar wall tissue responsible for the elastic response, and derive expressions for its effective coarse-scale behavior that directly depend on the alveolar wall elasticity, reference porosity, and two other geometrical coefficients. To validate the proposed model, we simulate the non-linear elastic response of twelve representative volume elements (RVEs) of lung parenchyma with micrometric dimensions, whose geometry is obtained from micrometric computed-tomography reconstructions of murine lungs. We show that the proposed micromechanical model accurately captures the RVEs response not only for isotropic volumetric expansion, but also for three other anisotropic loading conditions for different levels of tissue porosity, while displaying superior computational efficiency and stability in estimating coarse-scale response when compared to direct numerical simulations of RVEs. Further, we find that the most influential microstructural parameters on the response of the micromechanical model are the reference porosity and the alveolar wall elasticity. We also show that the model can reproduce uniaxial experimental tests on lung tissue samples, and estimate the Poisson ratio to be 0.22. We envision that our model will enable predictive and efficient whole-organ simulations useful to study the normal and diseased lung.

Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy

NASA Astrophysics Data System (ADS)

Jung, Jaimyun; Yoon, Jae Ik; Kim, Jung Gi; Latypov, Marat I.; Kim, Jin You; Kim, Hyoung Seop

2017-12-01

Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior, a clear relation among the large aggregate of grains is still lacking. In this work, we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature. Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building. Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation. Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.

Deformation Behavior and Microstructure Evolution of As-Cast 42CrMo Alloy in Isothermal and Non-isothermal Compression

NASA Astrophysics Data System (ADS)

Qin, Fangcheng; Li, Yongtang; Qi, Huiping; Lv, Zhenhua

2016-11-01

The isothermal and non-isothermal multi-pass compression tests of centrifugal casting 42CrMo steel were conducted on a Gleeble-3500 thermal simulation machine. The effects of compression passes and finishing temperatures on deformation behavior and microstructure evolution were investigated. It is found that the microstructure is homogeneous with equiaxed grains, and the flow stress does not show significant change with the increase in passes, while the peak softening coefficient increases first and then decreases during inter-pass. Moreover, the dominant mechanisms of controlled temperature and accumulated static recrystallization for grain refinement and its homogeneous distribution are found after 5 passes deformation. As the finishing temperature increases, the flow stress decreases gradually, but the dynamic recrystallization accelerates and softening effect increases, resulting in the larger grain size and homogeneous microstructure. The microhardness decreases sharply because the sufficient softening occurs in microstructure. When the finishing temperature is 890 °C, the carbide particles are precipitated in the vicinity of the grain boundaries, thus inhibiting the dislocation motion. Thus, the higher finishing temperature (≥970 °C) for centrifugal casting 42CrMo alloy should be avoided in non-isothermal multi-pass deformation, which is beneficial to grain refinement and properties improvement.

Non-destructive and three-dimensional measurement of local strain development during tensile deformation in an aluminium alloy

NASA Astrophysics Data System (ADS)

Kobayashi, M.; Miura, H.; Toda, H.

2015-08-01

Anisotropy of mechanical responses depending on crystallographic orientation causes inhomogeneous deformation on the mesoscopic scale (grain size scale). Investigation of the local plastic strain development is important for discussing recrystallization mechanisms, because the sites with higher local plastic strain may act as potential nucleation sites for recrystallization. Recently, high-resolution X-ray tomography, which is non-destructive inspection method, has been utilized for observation of the materials structure. In synchrotron radiation X-ray tomography, more than 10,000 microstructural features, like precipitates, dispersions, compounds and hydrogen pores, can be observed in aluminium alloys. We have proposed employing these microstructural features as marker gauges to measure local strains, and then have developed a method to calculate the three-dimensional strain distribution by tracking the microstructural features. In this study, we report the development of local plastic strain as a function of the grain microstructure in an aluminium alloy by means of this three-dimensional strain measurement technique. Strongly heterogeneous strain development was observed during tensile loading to 30%. In other words, some parts of the sample deform little whereas another deforms a lot. However, strain in the whole specimen was keeping harmony. Comparing the microstructure with the strain concentration that is obtained by this method has a potential to reveal potential nucleation sites of recrystallization.

Brittle-viscous deformation of vein quartz under fluid-rich low greenschist facies conditions

NASA Astrophysics Data System (ADS)

Kjøll, H. J.; Viola, G.; Menegon, L.; Sørensen, B. E.

2015-01-01

A coarse grained, statically crystallized quartz vein, embedded in a phyllonitic matrix, was studied by EBSD and optical microscopy to gain insights into the processes of strain localization in quartz deformed under low-grade conditions, broadly coincident with the frictional-viscous transition. The vein is from a high strain zone at the front of the Porsa Imbricate Stack in the Paleoproterozoic Repparfjord Tectonic Window in northern Norway. The vein was deformed under lower greenschist facies conditions during deformation along a large out-of-sequence phyllonitic thrust of Caledonian age. The host phyllonite formed at the expense of metabasalt wherein feldspar broke down to form interconnected layers of fine, synkinematic phyllosilicates. In the mechanically weak framework of the phyllonite, the studied quartz vein acted as a relatively rigid body deforming mainly by coaxial strain. Viscous deformation was initially accommodated by basal ⟨a⟩ slip of quartz during the development of a mesoscopic pervasive extensional crenulation cleavage. Under the prevailing boundary conditions, however, dislocation glide-accommodated deformation of quartz resulted inefficient and led to dislocation tangling and strain hardening of the vein. In response to hardening, to the progressive increase of fluid pressure and the increasing competence contrast between the vein and the weak foliated host phyllonite, quartz crystals began to deform frictionally along specific, optimally oriented lattice planes, creating microgouges along microfractures. These were, however, rapidly sealed by nucleation of new grains as transiently over pressured fluids penetrated the deforming system. The new nucleated grains grew initially by solution-precipitation and later by grain boundary migration. Due to the random initial orientation of the vein crystals, strain was accommodated differently in the individual crystals, leading to the development of remarkably different microstructures. Crystals oriented optimally for basal slip accommodated strain mainly viscously and experienced only minor fracturing. Instead, the crystals misoriented for basal slip hardened and deformed by pervasive domainal fracturing. This study indicates the importance of considering shear zones as dynamic systems wherein the activated deformation mechanisms vary transiently in response to the complex temporal and spatial evolution of the shear zone, often in a cyclic fashion.

Dual-phase steel sheets under cyclic tension-compression to large strains: Experiments and crystal plasticity modeling

NASA Astrophysics Data System (ADS)

Zecevic, Milovan; Korkolis, Yannis P.; Kuwabara, Toshihiko; Knezevic, Marko

2016-11-01

In this work, we develop a physically-based crystal plasticity model for the prediction of cyclic tension-compression deformation of multi-phase materials, specifically dual-phase (DP) steels. The model is elasto-plastic in nature and integrates a hardening law based on statistically stored dislocation density, localized hardening due to geometrically necessary dislocations (GNDs), slip-system-level kinematic backstresses, and annihilation of dislocations. The model further features a two level homogenization scheme where the first level is the overall response of a two-phase polycrystalline aggregate and the second level is the homogenized response of the martensite polycrystalline regions. The model is applied to simulate a cyclic tension-compression-tension deformation behavior of DP590 steel sheets. From experiments, we observe that the material exhibits a typical decreasing hardening rate during forward loading, followed by a linear and then a non-linear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals. To predict these effects, we identify the model parameters using a portion of the measured data and validate and verify them using the remaining data. The developed model is capable of predicting all the particular features of the cyclic deformation of DP590 steel, with great accuracy. From the predictions, we infer and discuss the effects of GNDs, the backstresses, dislocation annihilation, and the two-level homogenization scheme on capturing the cyclic deformation behavior of the material.

Grain Nucleation and Growth in Deformed NiTi Shape Memory Alloys: An In Situ TEM Study

NASA Astrophysics Data System (ADS)

Burow, J.; Frenzel, J.; Somsen, C.; Prokofiev, E.; Valiev, R.; Eggeler, G.

2017-12-01

The present study investigates the evolution of nanocrystalline (NC) and ultrafine-grained (UFG) microstructures in plastically deformed NiTi. Two deformed NiTi alloys were subjected to in situ annealing in a transmission electron microscope (TEM) at 400 and 550 °C: an amorphous material state produced by high-pressure torsion (HPT) and a mostly martensitic partly amorphous alloy produced by wire drawing. In situ annealing experiments were performed to characterize the microstructural evolution from the initial nonequilibrium states toward energetically more favorable microstructures. In general, the formation and evolution of nanocrystalline microstructures are governed by the nucleation of new grains and their subsequent growth. Austenite nuclei which form in HPT and wire-drawn microstructures have sizes close to 10 nm. Grain coarsening occurs in a sporadic, nonuniform manner and depends on the physical and chemical features of the local environment. The mobility of grain boundaries in NiTi is governed by the local interaction of each grain with its microstructural environment. Nanograin growth in thin TEM foils seems to follow similar kinetic laws to those in bulk microstructures. The present study demonstrates the strength of in situ TEM analysis and also highlights aspects which need to be considered when interpreting the results.

A Community Database of Quartz Microstructures: Can we make measurements that constrain rheology?

NASA Astrophysics Data System (ADS)

Toy, Virginia; Peternell, Mark; Morales, Luiz; Kilian, Ruediger

2014-05-01

Rheology can be explored by performing deformation experiments, and by examining resultant microstructures and textures as links to naturally deformed rocks. Certain deformation processes are assumed to result in certain microstructures or textures, of which some might be uniquely indicative, while most cannot be unequivocally used to interpret the deformation mechanism and hence rheology. Despite our lack of a sufficient understanding of microstructure and texture forming processes, huge advances in texture measurements and quantification of microstructural parameters have been made. Unfortunately, there are neither standard procedures nor a common consensus on interpretation of many parameters (e.g. texture, grain size, shape preferred orientation). Textures (crystallographic preferred orientations) have been extensively correlated to the interpretation of deformation mechanisms. For example the strength of textures can be measured either from the orientation distribution function (e.g. the J-index (Bunge, 1983) or texture entropy (Hielscher et al., 2007) or via the intensity of polefigures. However, there are various ways to identify a representative volume, to measure, to process the data and to calculate an odf and texture descriptors, which restricts their use as a comparative and diagnostic measurement. Microstructural parameters such as grain size, grain shape descriptors and fabric descriptors are similarly used to deduce and quantify deformation mechanisms. However there is very little consensus on how to measure and calculate some of these very important parameters, e.g. grain size which makes comparison of a vast amount of precious data in the literature very difficult. We propose establishing a community database of a standard set of such measurements, made using typical samples of different types of quartz rocks through standard methods of microstructural and texture quantification. We invite suggestions and discussion from the community about the worth of proposed parameters, methodology and usefulness and willingness to contribute to a database with free access of the community. We further invite institutions to participate on a benchmark analysis of a set of 'standard' thin sections. Bunge, H.J. 1983, Texture Analysis in Materials Science: mathematical methods. Butterworth-Heinemann, 593pp. Hielscher, R., Schaeben, H., Chateigner, D., 2007, On the entropy to texture index relationship in quantitative texture analysis: Journal of Applied Crystallography 40, 371-375.

Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

NASA Astrophysics Data System (ADS)

Maierova, Petra; Lexa, Ondrej; Jeřábek, Petr; Franěk, Jan; Schulmann, Karel

2015-04-01

A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 μm) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 μm grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 μm grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most elaborated and at the same time the most promising descriptions: thermodynamics-based models with and without Zener pinning. For conditions compatible with the S1 and S2 microstructures (~800 °C and strain rate ~10-13 s-1), the calculated stable grain sizes are ~30 μm and >300 μm in the models with and without Zener pinning, respectively. This is in agreement with the contrasting grain sizes associated with S1 and S2 microstructures implying that mainly chemically induced recrystallization of S1 feldspar porphyroclasts must had played a fundamental role in the transition into the diffusion creep. The model with pinning also explains only minor changes of mean grain size associated with S2 microstructure. The S2-S3 switch from the diffusion to dislocation creep is difficult to explain when assuming reasonable temperature and strain rate (or stress). However, a simple incorporation of the effect of melt solidification into the model with pinning can mimic this observed switch. Besides the above mentioned simple models with prescribed temperature and strain rate, we implemented the grain size evolution laws into in a 2D thermo-mechanical model setup, where stress, strain rate and temperature evolve in a more natural manner. This setup simulates a collisional evolution of an orogenic root with anomalous lower crust. The lower-crustal material is a source region for diapirs and it deforms via a combination of dislocation and grain-size-sensitive creeps. We tested the influence of selected parameters in the flow laws and in the grain-size evolution laws on the shape and other characteristics of the growing diapirs. The outputs of our simulations were then compared with the geological record from the Moldanubian granulite massifs.

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

Microstructure and Texture Evolution in Double-Cone Samples of Ti-6Al-4V Alloy with Colony Preform Microstructure

NASA Astrophysics Data System (ADS)

Yang, Kun Vanna; Lim, Chao Voon Samuel; Zhang, Kai; Sun, Jifeng; Yang, Xiaoguang; Huang, Aijun; Wu, Xinhua; Davies, Christopher H.

2015-12-01

Heat-treated Ti-6Al-4V forged bar with colony microstructure was machined into double-cone-shaped samples for a series of isothermal uniaxial compression test at 1223 K (950 °C) with varying constant crosshead speeds of 12.5, 1.25, and 0.125 mms-1 to a height reduction of 70 pct. Another set of samples deformed under the same conditions were heat treated at 1173 K (900 °C) for an hour followed by water quench. Finite element modeling was used to provide the strains, strain rates, and temperature profiles of the hot compression samples, and the microstructure and texture evolution was examined at four positions on each sample, representative of different strain ranges. Lamellae fragmentation and kinking are the dominant microstructural features at lower strain range up to a maximum of 2.0, whereas globularization dominates at strains above 2.0 for the as-deformed samples. The globularization fraction generally increases with strain, or by post-deformation heat treatment, but fluctuates at lower strain. The grain size of the globular α is almost constant with strain and maximizes for samples with the lowest crosshead speed due to the longer deformation time. The globular α grain also coarsens because of post-deformation heat treatment, with its size increasing with strain level. With respect to texture evolution, a basal transverse ring and another component 30 deg from ND is determined for samples deformed at 12.5 mms-1, which is consistent with the temperature increase to close to β-transus from simulation results. The texture type remains unchanged with its intensity increased and spreads with increasing strain.

Relation of cyclic loading pattern to microstructural fracture in creep fatigue

NASA Technical Reports Server (NTRS)

Manson, S. S.; Halford, G. R.; Oldrieve, R. E.

1983-01-01

Creep-fatigue-environment interaction is discussed using the 'strainrange partitioning' (SRP) framework as a basis. The four generic SRP strainrange types are studied with a view of revealing differences in micromechanisms of deformation and fatigue degradation. Each combines in a different manner the degradation associated with slip-plane sliding, grain-boundary sliding, migration, cavitation, void development and environmental interaction; hence the approch is useful in delineating the relative importance of these mechanisms in the different loadings. Micromechanistic results are shown for a number of materials, including 316 SS, wrought heat resistant alloys, several nickel-base superalloys, and a tantalum base alloy, T-111. Although there is a commonality of basic behavior, the differences are useful in delineation several important principles of interpretation. Some quantitative results are presented for 316 SS, involving crack initiation and early crack growth, as well as the interaction of low-cycle fatigue with high-cycle fatigue.

Creep-Fatigue Failure Diagnosis

PubMed Central

Holdsworth, Stuart

2015-01-01

Failure diagnosis invariably involves consideration of both associated material condition and the results of a mechanical analysis of prior operating history. This Review focuses on these aspects with particular reference to creep-fatigue failure diagnosis. Creep-fatigue cracking can be due to a spectrum of loading conditions ranging from pure cyclic to mainly steady loading with infrequent off-load transients. These require a range of mechanical analysis approaches, a number of which are reviewed. The microstructural information revealing material condition can vary with alloy class. In practice, the detail of the consequent cracking mechanism(s) can be camouflaged by oxidation at high temperatures, although the presence of oxide on fracture surfaces can be used to date events leading to failure. Routine laboratory specimen post-test examination is strongly recommended to characterise the detail of deformation and damage accumulation under known and well-controlled loading conditions to improve the effectiveness and efficiency of failure diagnosis. PMID:28793676

Cyclic deformation-induced solute transport in tissue scaffolds with computer designed, interconnected, pore networks: experiments and simulations.

PubMed

Den Buijs, Jorn Op; Dragomir-Daescu, Dan; Ritman, Erik L

2009-08-01

Nutrient supply and waste removal in porous tissue engineering scaffolds decrease from the periphery to the center, leading to limited depth of ingrowth of new tissue into the scaffold. However, as many tissues experience cyclic physiological strains, this may provide a mechanism to enhance solute transport in vivo before vascularization of the scaffold. The hypothesis of this study was that pore cross-sectional geometry and interconnectivity are of major importance for the effectiveness of cyclic deformation-induced solute transport. Transparent elastic polyurethane scaffolds, with computer-programmed design of pore networks in the form of interconnected channels, were fabricated using a 3D printing and injection molding technique. The scaffold pores were loaded with a colored tracer for optical contrast, cyclically compressed with deformations of 10 and 15% of the original undeformed height at 1.0 Hz. Digital imaging was used to quantify the spatial distribution of the tracer concentration within the pores. Numerical simulations of a fluid-structure interaction model of deformation-induced solute transport were compared to the experimental data. The results of experiments and modeling agreed well and showed that pore interconnectivity heavily influences deformation-induced solute transport. Pore cross-sectional geometry appears to be of less relative importance in interconnected pore networks. Validated computer models of solute transport can be used to design optimal scaffold pore geometries that will enhance the convective transport of nutrients inside the scaffold and the removal of waste, thus improving the cell survivability deep inside the scaffold.

Effects of the Heterogeneity in the Electron Beam Welded Joint on Mechanical Properties of Ti6Al4V Alloy

NASA Astrophysics Data System (ADS)

Liu, Jing; Gao, Xiao-Long; Zhang, Lin-Jie; Zhang, Jian-Xun

2015-01-01

The aim of this investigation was to evaluate the effect of microstructure heterogeneity on the tensile and low cycle fatigue properties of electron beam welded (EBW) Ti6Al4V sheets. To achieve this goal, the tensile and low cycle fatigue property in the EBW joints and base metal (BM) specimens is compared. During the tensile testing, digital image correlation technology was used to measure the plastic strain field evolution within the specimens. The experimental results showed that the tensile ductility and low cycle fatigue strength of EBW joints are lower than that of BM specimens, mainly because of the effect of microstructure heterogeneity of the welded joint. Moreover, the EBW joints exhibit the cyclic hardening behavior during low fatigue process, while BM specimens exhibit the cyclic softening behavior. Compared with the BM specimens with uniform microstructure, the heterogeneity of microstructure in the EBW joint is found to decrease the mechanical properties of welded joint.

Microstructural Characteristics of High Rate Plastic Deformation in Elektron™ WE43 Magnesium Alloy

NASA Astrophysics Data System (ADS)

Hamilton, Joseph; Brennan, Sarah T.; Sohn, Yongho; Davis, Bruce; DeLorme, Rick; Cho, Kyu

High strain rate deformation of WE43 magnesium alloy was carried out by high velocity impacts, and the characteristics and mechanisms of microstructural damage were examined. Six samples were subjected to a variety of high velocity impact loadings that resulted in both partial and full damage. Optical, scanning and transmission electron microscopy analyses were performed in order to identify regions of shear localization. These regions were used to map, both quantitatively and qualitatively, the effects of deformation on the microstructure. Shear localization was observed in every sample, and its depth was measured. Evidence of shear localization was observed to a greater extent in samples with partial damage while fracturing was observed more frequently in samples with full damage.

Deformation mechanisms in negative Poisson's ratio materials - Structural aspects

NASA Technical Reports Server (NTRS)

Lakes, R.

1991-01-01

Poisson's ratio in materials is governed by the following aspects of the microstructure: the presence of rotational degrees of freedom, non-affine deformation kinematics, or anisotropic structure. Several structural models are examined. The non-affine kinematics are seen to be essential for the production of negative Poisson's ratios for isotropic materials containing central force linkages of positive stiffness. Non-central forces combined with pre-load can also give rise to a negative Poisson's ratio in isotropic materials. A chiral microstructure with non-central force interaction or non-affine deformation can also exhibit a negative Poisson's ratio. Toughness and damage resistance in these materials may be affected by the Poisson's ratio itself, as well as by generalized continuum aspects associated with the microstructure.

Kinetics of Sub-Micron Grain Size Refinement in 9310 Steel

NASA Astrophysics Data System (ADS)

Kozmel, Thomas; Chen, Edward Y.; Chen, Charlie C.; Tin, Sammy

2014-05-01

Recent efforts have focused on the development of novel manufacturing processes capable of producing microstructures dominated by sub-micron grains. For structural applications, grain refinement has been shown to enhance mechanical properties such as strength, fatigue resistance, and fracture toughness. Through control of the thermo-mechanical processing parameters, dynamic recrystallization mechanisms were used to produce microstructures consisting of sub-micron grains in 9310 steel. Starting with initial bainitic grain sizes of 40 to 50 μm, various levels of grain refinement were observed following hot deformation of 9310 steel samples at temperatures and strain rates ranging from 755 K to 922 K (482 °C and 649 °C) and 1 to 0.001/s, respectively. The resulting deformation microstructures were characterized using scanning electron microscopy and electron backscatter diffraction techniques to quantify the extent of carbide coarsening and grain refinement occurring during deformation. Microstructural models based on the Zener-Holloman parameter were developed and modified to include the effect of the ferrite/carbide interactions within the system. These models were shown to effectively correlate microstructural attributes to the thermal mechanical processing parameters.

Primary combination of phase-field and discrete dislocation dynamics methods for investigating athermal plastic deformation in various realistic Ni-base single crystal superalloy microstructures

NASA Astrophysics Data System (ADS)

Gao, Siwen; Rajendran, Mohan Kumar; Fivel, Marc; Ma, Anxin; Shchyglo, Oleg; Hartmaier, Alexander; Steinbach, Ingo

2015-10-01

Three-dimensional discrete dislocation dynamics (DDD) simulations in combination with the phase-field method are performed to investigate the influence of different realistic Ni-base single crystal superalloy microstructures with the same volume fraction of {γ\\prime} precipitates on plastic deformation at room temperature. The phase-field method is used to generate realistic microstructures as the boundary conditions for DDD simulations in which a constant high uniaxial tensile load is applied along different crystallographic directions. In addition, the lattice mismatch between the γ and {γ\\prime} phases is taken into account as a source of internal stresses. Due to the high antiphase boundary energy and the rare formation of superdislocations, precipitate cutting is not observed in the present simulations. Therefore, the plastic deformation is mainly caused by dislocation motion in γ matrix channels. From a comparison of the macroscopic mechanical response and the dislocation evolution for different microstructures in each loading direction, we found that, for a given {γ\\prime} phase volume fraction, the optimal microstructure should possess narrow and homogeneous γ matrix channels.

Deformation-related microstructures in magmatic zircon and implications for diffusion

NASA Astrophysics Data System (ADS)

Reddy, Steven Michael; Timms, Nicholas E.; Hamilton, Patrick Joseph; Smyth, Helen R.

2009-02-01

An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common <100> misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of <001>{100} and <100>{010} slip systems. The restriction of deformation microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon grains, indicate that zircon deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic microstructures in zircon is not restricted to high-strain rocks. Such microstructures have previously been shown to enhance bulk diffusion of trace elements (U, Th and REE) in zircon. The development of deformation microstructures, and therefore multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion and dissolution rates.

Influence of Secondary Cyclic Hardening on the Low Cycle Fatigue Behavior of Nitrogen Alloyed 316LN Stainless Steel

NASA Astrophysics Data System (ADS)

Prasad Reddy, G. V.; Sandhya, R.; Mathew, M. D.; Sankaran, S.

2013-12-01

In this article, the occurrence of secondary cyclic hardening (SCH) and its effect on high-temperature cyclic deformation and fatigue life of 316LN Stainless steel are presented. SCH is found to result from planar slip mode of deformation and enhance the degree of hardening over and above that resulted from dynamic strain aging. The occurrence of SCH is strongly governed by the applied strain amplitude, test temperature, and the nitrogen content in the 316LN SS. Under certain test conditions, SCH is noticed to decrease the low cycle fatigue life with the increasing nitrogen content.

Microstructure-based modelling of arbitrary deformation histories of filler-reinforced elastomers

NASA Astrophysics Data System (ADS)

Lorenz, H.; Klüppel, M.

2012-11-01

A physically motivated theory of rubber reinforcement based on filler cluster mechanics is presented considering the mechanical behaviour of quasi-statically loaded elastomeric materials subjected to arbitrary deformation histories. This represents an extension of a previously introduced model describing filler induced stress softening and hysteresis of highly strained elastomers. These effects are referred to the hydrodynamic reinforcement of rubber elasticity due to strain amplification by stiff filler clusters and cyclic breakdown and re-aggregation (healing) of softer, already damaged filler clusters. The theory is first developed for the special case of outer stress-strain cycles with successively increasing maximum strain. In this more simple case, all soft clusters are broken at the turning points of the cycle and the mechanical energy stored in the strained clusters is completely dissipated, i.e. only irreversible stress contributions result. Nevertheless, the description of outer cycles involves already all material parameters of the theory and hence they can be used for a fitting procedure. In the general case of an arbitrary deformation history, the cluster mechanics of the material is complicated due to the fact that not all soft clusters are broken at the turning points of a cycle. For that reason additional reversible stress contributions considering the relaxation of clusters upon retraction have to be taken into account for the description of inner cycles. A special recursive algorithm is developed constituting a frame of the mechanical response of encapsulated inner cycles. Simulation and measurement are found to be in fair agreement for CB and silica filled SBR/BR and EPDM samples, loaded in compression and tension along various deformation histories.

Material heterogeneity in cancellous bone promotes deformation recovery after mechanical failure

PubMed Central

Torres, Ashley M.; Matheny, Jonathan B.; Keaveny, Tony M.; Taylor, David; Rimnac, Clare M.; Hernandez, Christopher J.

2016-01-01

Many natural structures use a foam core and solid outer shell to achieve high strength and stiffness with relatively small amounts of mass. Biological foams, however, must also resist crack growth. The process of crack propagation within the struts of a foam is not well understood and is complicated by the foam microstructure. We demonstrate that in cancellous bone, the foam-like component of whole bones, damage propagation during cyclic loading is dictated not by local tissue stresses but by heterogeneity of material properties associated with increased ductility of strut surfaces. The increase in surface ductility is unexpected because it is the opposite pattern generated by surface treatments to increase fatigue life in man-made materials, which often result in reduced surface ductility. We show that the more ductile surfaces of cancellous bone are a result of reduced accumulation of advanced glycation end products compared with the strut interior. Damage is therefore likely to accumulate in strut centers making cancellous bone more tolerant of stress concentrations at strut surfaces. Hence, the structure is able to recover more deformation after failure and return to a closer approximation of its original shape. Increased recovery of deformation is a passive mechanism seen in biology for setting a broken bone that allows for a better approximation of initial shape during healing processes and is likely the most important mechanical function. Our findings suggest a previously unidentified biomimetic design strategy in which tissue level material heterogeneity in foams can be used to improve deformation recovery after failure. PMID:26929343

Cyclic Deformation and Fatigue of Monocrystalline Ni-Base Superalloys.

DTIC Science & Technology

1983-12-16

understanding crack nucleation (Laird et al at Pennsylvania, Fine et al at Northwestern, Neumann et al at Dusseldorf and Mughrabi et al at Stuttgart...hardened alloy in a project supported by the army. This work concentrated on the stability of precipitates under cyclic deformation ( Al -Ag, Al -Cu systems...and the strain-localization behavior of alloys containing shearable precipitates ( Al -Cu, e") and non-shearable precipitates ( Al -Cu, e’). Furthermore

Microstructural effects on the deformation and fracture of the alloy Ti-25Al-10Nb-3B-1Mo. Final report, 1 July 1988-15 December 1992

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

Ward, C.H.

1992-12-01

The effects of microstructure and temperature on tensile and fracture behavior were explored for the titanium aluminide alloy Ti-25Al-lONb-3V-lMo (atomic percent). Three microstructures were selected for this study in an attempt to determine the role of the individual microstructural constituents. the three microstructures studied were an alpha-2 + beta processed microstructure with a fine Widmanstaetten microstructure, a beta processed microstructure with a fine Widmanstaetten microstructure, and a beta processed microstructure with a coarse Widmanstaetten microstructure. Tensile testing of both round and flat specimens was conducted in vacuum at elevated temperature and in air at room and elevated temperatures. Extensive fractographymore » and specimen sectioning were used to study tensile deformation and the effects of environment on this alloy. Room temperature fracture toughness testing using compact tension specimens was conducted. Elevated temperature toughness testing was performed using J-bend bar specimens in an air environment. Again, extensive fractography and specimen sectioning were used to study the elevated temperature toughening mechanisms of this alloy.... Titanium, Titanium aluminide, Intermetallic, Fracture toughness, Tensile behavior, Fractography environmental interaction.« less

Microstructural Evolution and Mechanical Properties of Ti-22Al-25Nb (At.%) Orthorhombic Alloy with Three Typical Microstructures

NASA Astrophysics Data System (ADS)

Wang, Wei; Zeng, Weidong; Liu, Yantao; Xie, Guoxin; Liang, Xiaobo

2018-01-01

Microstructural evolution, tensile and creep behavior of Ti-22Al-25Nb (at.%) orthorhombic alloy with three typical microstructures were investigated. The three typical microstructures were obtained by different solution and age treatment temperatures and analyzed by the BSE technique. The tensile strengths of the alloy at room temperature and 650 °C were investigated. The creep behaviors of the three typical microstructures were also studied at 650 °C/150 MPa for 100 h in air. The phase transformation mechanisms in creep deformation were also found. The experimental results showed that the formations of the three typical microstructures were decided by the isothermal forging and heat treatment. It was supposed that the high-temperature solution treatment might be dominant for the volume fraction and diameter of the equiaxed particles. While the double age treatment would lead to lamellar O phases. Due to grain refinement strengthening, the equiaxed microstructure presented the best tensile strength and ductility. The fully lamellar microstructure had the best creep resistance than that of other microstructures. In this paper, the phenomenon of creep-induced α 2 phase decomposition was occurred during creep deformation of the equiaxed microstructure.

Fine grained 304 ASS processed by a severe plastic deformation and subsequent annealing; microstructure and mechanical properties evaluation

NASA Astrophysics Data System (ADS)

Salout, Shima Ahmadzadeh; Shirazi, Hasan; Nili-Ahmadabadi, Mahmoud

2018-01-01

The current research is an attempt to study the effect of a novel severe plastic deformation technique so called "repetitive corrugation and straightening by rolling" (RCSR) and subsequent annealing on the microstructure and mechanical properties of AISI type 304 austenitic stainless steel. In this study, RCSR process was carried out at 200 °C on the 304 austenitic stainless steel (above Md30 temperature that is about 50 °C for this stainless steel) in order to avoid the formation of martensite phase when a high density of dislocations was introduced into the austenite phase and also high density of mechanical twins was induced in the deformed 304 austenitic stainless steel. Because of relationship between deformation temperature, stacking fault energy (SFE) and mechanisms of deformation. Thereafter subsequently, annealing treatment was applied into deformed structure in order to refine the microstructure of 304 stainless s teel. The specimens were examined by means of optical microscopy (OM), scanning electron microscopy (SEM), tensile and micro-hardness tests. The results indicate that by increasing the cycles of RCSR process (increasing applied strain), further mechanical twins are induced, the hardness and in particular, the yield stress of specimens have been increased.

Hidden secrets of deformation: Impact-induced compaction within a CV chondrite

NASA Astrophysics Data System (ADS)

Forman, L. V.; Bland, P. A.; Timms, N. E.; Collins, G. S.; Davison, T. M.; Ciesla, F. J.; Benedix, G. K.; Daly, L.; Trimby, P. W.; Yang, L.; Ringer, S. P.

2016-10-01

The CV3 Allende is one of the most extensively studied meteorites in worldwide collections. It is currently classified as S1-essentially unshocked-using the classification scheme of Stöffler et al. (1991), however recent modelling suggests the low porosity observed in Allende indicates the body should have undergone compaction-related deformation. In this study, we detail previously undetected evidence of impact through use of Electron Backscatter Diffraction mapping to identify deformation microstructures in chondrules, AOAs and matrix grains. Our results demonstrate that forsterite-rich chondrules commonly preserve crystal-plastic microstructures (particularly at their margins); that low-angle boundaries in deformed matrix grains of olivine have a preferred orientation; and that disparities in deformation occur between chondrules, surrounding and non-adjacent matrix grains. We find heterogeneous compaction effects present throughout the matrix, consistent with a highly porous initial material. Given the spatial distribution of these crystal-plastic deformation microstructures, we suggest that this is evidence that Allende has undergone impact-induced compaction from an initially heterogeneous and porous parent body. We suggest that current shock classifications (Stöffler et al., 1991) relying upon data from chondrule interiors do not constrain the complete shock history of a sample.

Roles of microstructures on deformation response of 316 stainless steel made by 3D printing

NASA Astrophysics Data System (ADS)

Pham, Minh-Son; Hooper, Paul

2017-10-01

One of the main challenges in additive manufacturing (AM) of metals is to manufacture high quality materials and ensure the performance of AM materials in service duties. This challenge can only be solved when the relationships between build process parameters, microstructure and deformation behaviour are understood. This present study is part of holistic efforts at Imperial College to reveal such relationships. In this study, we present our study of porosity condition, grain morphology, texture and metastable phases in AM stainless steel 316. To provide samples for mechanical and microstructural study, cylindrical samples of stainless steel 316 were printed by powder-bed laser melting with a bi-directional hatch pattern. Scanning electron microscopy and electron backscattered diffraction were used to investigate fine microstructures (such as grain morphology, texture and crystal phases) after 3D printing and deformation. Subsequently, a detailed 3D structure of columnar grains in as-printed 316 steel is constructed thanks to microscopic observation. Most of grains in as-built samples have a spherical bowl morphology, and being stacked on others to form the columnar structure. Examinations on microstructures show that the small sub-grains in as-printed samples is likely responsible for high yield strength at room temperature (significantly higher than that of conventional steel). In addition, residual stresses after rapid cooling probably promote the deformation-induced twinning that assists the plasticity during deformation, leading to a good ductility of the AM steel (almost as same as that of conventional 316 steel). Currently, a more detailed study is being undertaken to confirm this hypothesis.

FIB–SEM tomography of 4th generation PWA 1497 superalloy

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

Ziętara, Maciej, E-mail: zietara@agh.edu.pl; Kruk, Adam, E-mail: kruczek@agh.edu.pl; Gruszczyński, Adam, E-mail: gruszcz@agh.edu.pl

2014-01-15

The effect of creep deformation on the microstructure of the PWA 1497 single crystal Ni-base superalloy developed for turbine blade applications was investigated. The aim of the present study was to characterize quantitatively a superalloy microstructure and subsequent development of rafted γ′ precipitates in the PWA 1497 during creep deformation at 982 °C and 248 MPa up to rupture. The PWA1497 microstructure was characterized by scanning electron microscopy and FIB–SEM electron tomography. The 3D reconstruction of the PWA1497 microstructure is presented and discussed. - Highlights: • The microstructure of PWA1497 superalloy was examined using FIB–SEM tomography. • In case ofmore » modern single crystal superalloys, measurements of A{sub A} are adequate for V{sub V}. • During creep the γ channel width increases from 65 to 193 nm for ruptured specimen. • Tomography is a useful technique for quantitative studies of material microstructure.« less

Microstructure and mechanical properties of Al-3Fe alloy processed by equal channel angular extrusion

NASA Astrophysics Data System (ADS)

Fuxiao, Yu; Fang, Liu; Dazhi, Zhao; Toth, Laszlo S.

2014-08-01

Al-Fe alloys are attractive for applications at temperatures beyond those normally associated with the conventional aluminum alloys. Under proper solidification condition, a full eutectic microstructure can be generated in Al-Fe alloys at Fe concentration well in excess of the eutectic composition of 1.8 wt.% Fe. The microstructure in this case is characterized by the metastable regular eutectic Al-Al6Fe fibers of nano-scale in diameter, instead of the equilibrium eutectic Al-Al3Fe phase. In this study, the microstructure and mechanical properties of the Al-3Fe alloy with metastable Al6Fe particles deformed by equal channel angular extrusion were investigated. Severe plastic deformation results in a microstructure consisting of submicron equiaxed Al grains with a uniform distribution of submicron Al6Fe particles on the grain boundaries. The room temperature tensile properties of the alloy with this microstructure will be presented.

Study on Dynamic Strain Aging and Low-Cycle Fatigue of Stainless Steel in Ultra-Supercritical Unit

NASA Astrophysics Data System (ADS)

Hongwei, Zhou; Yizhu, He; Jizu, Lv; Sixian, Rao

Dynamic strain aging (DSA) and low-cycle fatigue (LCF) behavior of TP347H stainless steel in ultra-supercritical unit were investigated at 550-650 °C. All the LCF tests were carried out under a fully-reversed, total axial strain control mode at the total strain amplitude from ±0.2% to ±1.0%. The effects of DSA in cyclic stress response, microstructure evolution and fatigue fracture surfaces and fatigue life were investigated in detail. The results show that DSA occurs during tensile, which is manifested as serrated flow in tensile stress-strain curves. The apparent activation energy for appearing of serrations in tensile stress-strain curves was 270 kJ/mol. Pipe diffusion of substitutional solutes such as Cr and Nb along the dislocation core, and strong interactions between segregated solutes and dislocations are considered as the mechanism of DSA. DSA partly restricts dislocation cross-slip, and dislocation cross-slip and planar-slip happen simultaneously during LCF. A lot of planar structures form, which is due to dislocation gliding on the special plane. This localized deformation structures result in many crack initiation sites. Meanwhile, DSA hardening increases cyclic stress response, accelerating crack propagation, which reduces high temperature strain fatigue life of steel.

Effect of cold deformation on the electrochemical behaviour of 304L stainless steel in contaminated sulfuric acid environment

NASA Astrophysics Data System (ADS)

Luo, Hong; Su, Huaizhi; Ying, Guobing; Dong, Chaofang; Li, Xiaogang

2017-12-01

The effect of cold deformation on the microstructure and electrochemical corrosion behaviour of 304L stainless steel in contaminated sulfuric acid solutions (simulated proton exchange membrane fuel cells environments) were evaluated using electron backscatter diffraction analyses, electrochemical measurements, and surface analyses. The internal microstructure,including the grain sizes, angles of the grain boundaries, low coincidence site lattice boundaries, and phase transformations, was changed due to the cold deformation. No noticeable modifications of the pitting corrosion potential were observed during the various deformations, except for a slight enhancement in the passive current density with an increase in the deformation. The CrO3 and metal Ni species in the passive film were investigated after deformation. After heavy deformation (greater than 60%), nickel oxides were detected. Moreover, the Cr/Fe and O2-/OH- ratios in the passive film were higher before deformation, and they decreased with an increase in the deformation level.

Simulating Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi

NASA Technical Reports Server (NTRS)

Manchiraju, Sivom; Gaydosh, Darrell J.; Noebe, Ronald D.; Anderson, Peter M.

2011-01-01

A microstructure-based FEM model that couples crystal plasticity, crystallographic descriptions of the B2-B19' martensitic phase transformation, and anisotropic elasticity is used to simulate thermal cycling and isothermal deformation in polycrystalline NiTi (49.9at% Ni). The model inputs include anisotropic elastic properties, polycrystalline texture, DSC data, and a subset of isothermal deformation and load-biased thermal cycling data. A key experimental trend is captured.namely, the transformation strain during thermal cycling is predicted to reach a peak with increasing bias stress, due to the onset of plasticity at larger bias stress. Plasticity induces internal stress that affects both thermal cycling and isothermal deformation responses. Affected thermal cycling features include hysteretic width, two-way shape memory effect, and evolution of texture with increasing bias stress. Affected isothermal deformation features include increased hardening during loading and retained martensite after unloading. These trends are not captured by microstructural models that lack plasticity, nor are they all captured in a robust manner by phenomenological approaches. Despite this advance in microstructural modeling, quantitative differences exist, such as underprediction of open loop strain during thermal cycling.

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

Phase Transformation Study in Nb-Mo Microalloyed Steels Using Dilatometry and EBSD Quantification

NASA Astrophysics Data System (ADS)

Isasti, Nerea; Jorge-Badiola, Denis; Taheri, Mitra L.; Uranga, Pello

2013-08-01

A complete microstructural characterization and phase transformation analysis has been performed for several Nb and Nb-Mo microalloyed low-carbon steels using electron backscattered diffraction (EBSD) and dilatometry tests. Compression thermomechanical schedules were designed resulting in the undeformed and deformed austenite structures before final transformation. The effects of microalloying additions and accumulated deformation were analyzed after CCT diagram development and microstructural quantification. The resulting microstructures ranged from polygonal ferrite and pearlite at slow cooling ranges, to a combination of quasipolygonal ferrite and granular ferrite for intermediate cooling rates, and finally, to bainitic ferrite with martensite for fast cooling rates. The addition of Mo promotes a shift in the CCT diagrams to lower transformation start temperatures. When the amount of Nb is increased, CCT diagrams show little variations for transformations from the undeformed austenite and higher initial transformation temperatures in the transformations from the deformed austenite. This different behavior is due to the effect of niobium on strain accumulation in austenite and its subsequent acceleration of transformation kinetics. This article shows the complex interactions between chemical composition, deformation, and the phases formed, as well as their effect on microstructural unit sizes and homogeneity.

Microstructure, accumulated strain, and mechanical behavior of AA6061 Al alloy severely deformed at cryogenic temperatures

NASA Astrophysics Data System (ADS)

Magalhães, D. C.; Kliauga, A. M.; Ferrante, M.; Sordi, V. L.

2017-05-01

The combination of Severe Plastic Deformation (SPD) and cryogenic temperatures can be an efficient way to obtain metals and alloys with very refined microstructure and thus optimize the strength-ductility pair. However, there is still a lack of studies on cryogenic SPD process and their effects on microstructure and mechanical properties, especially in precipitation-hardenable aluminum alloys. This study describes the effect of low temperature processing on microstructure, aging kinetic and tensile properties of AA6061 Al alloy after cryo-SPD. Samples of AA6061 Al alloy in the solutionized state was processed by Equal-channel angular pressing (ECAP) at 77 K and 298 K, up to accumulate true strains up to 4.2. Results indicated that the aging kinetic is accelerated when deformation is performed at cryogenic temperature, dislocation density measurement by x-ray and diffraction analysis at TEM achieved a saturation level of 2×1015 m-2 by ECAP at 298K and 5×1015 m-2 after cryogenic ECAP plus precipitation hardening. The same level of yield strength was observed in both deformation procedures but an improvement in uniform elongation was achieved by cryogenic ECAP followed by a T6 treatment

Microstructure based hygromechanical modelling of deformation of fruit tissue

NASA Astrophysics Data System (ADS)

Abera, M. K.; Wang, Z.; Verboven, P.; Nicolai, B.

2017-10-01

Quality parameters such as firmness and susceptibility to mechanical damage are affected by the mechanical properties of fruit tissue. Fruit tissue is composed of turgid cells that keep cell walls under tension, and intercellular gas spaces where cell walls of neighboring cells have separated. How the structure and properties of these complex microstructures are affecting tissue mechanics is difficult to unravel experimentally. In this contribution, a modelling methodology is presented to calculate the deformation of apple fruit tissue affected by differences in structure and properties of cells and cell walls. The model can be used to perform compression experiments in silico using a hygromechanical model that computes the stress development and water loss during tissue deformation, much like in an actual compression test. The advantage of the model is that properties and structure can be changed to test the influence on the mechanical deformation process. The effect of microstructure, turgor pressure, cell membrane permeability, wall thickness and damping) on the compressibility of the tissue was simulated. Increasing the turgor pressure and thickness of the cell walls results in increased compression resistance of apple tissue increases, as do decreasing cell size and porosity. Geometric variability of the microstructure of tissues plays a major role, affecting results more than other model parameters. Different fruit cultivars were compared, and it was demonstrated, that microstructure variations within a cultivar are so large that interpretation of cultivar-specific effects is difficult.

Interpreting U-Pb data from primary and secondary features in lunar zircon

NASA Astrophysics Data System (ADS)

Grange, M. L.; Pidgeon, R. T.; Nemchin, A. A.; Timms, N. E.; Meyer, C.

2013-01-01

In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U-Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th-U-Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal-plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U-Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal-plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U-Pb isotopic systems.

Evolution of Mechanical and Electrical Properties During Annealing of the Copper Wire Drawn

NASA Astrophysics Data System (ADS)

Zidani, M.; Messaoudi, S.; Baudin, T.; Derfouf, C.; Boulagroun, A.; Mathon, M. H.

2011-12-01

In this work, the evolution of mechanical and electrical properties and microstructure of industrial copper wire used for electrical cabling was characterized. This work is not limited to the interpretation of the microstructural characteristics of the wire-drawn state but also after different annealing treatments. For the lowest temperatures (160 °C and 200 °C), significant changes are not observed in the microstructure (grain size) in the weak deformed wire (28.5%). Instead, variations of some properties of the metal were observed (hardness and electrical resistivity). For strong deformation (61.4% and 84.59%), annealing, leads to recrystallization with a softening material. Let us note that the resistivity increases with deformation level and becomes higher after annealing at low temperature (200 °C).

Strengthening Mechanisms in Thermomechanically Processed NbTi-Microalloyed Steel

NASA Astrophysics Data System (ADS)

Kostryzhev, Andrii G.; Marenych, Olexandra O.; Killmore, Chris R.; Pereloma, Elena V.

2015-08-01

The effect of deformation temperature on microstructure and mechanical properties was investigated for thermomechanically processed NbTi-microalloyed steel with ferrite-pearlite microstructure. With a decrease in the finish deformation temperature at 1348 K to 1098 K (1075 °C to 825 °C) temperature range, the ambient temperature yield stress did not vary significantly, work hardening rate decreased, ultimate tensile strength decreased, and elongation to failure increased. These variations in mechanical properties were correlated to the variations in microstructural parameters (such as ferrite grain size, solid solution concentrations, precipitate number density and dislocation density). Calculations based on the measured microstructural parameters suggested the grain refinement, solid solution strengthening, precipitation strengthening, and work hardening contributed up to 32 pct, up to 48 pct, up to 25 pct, and less than 3 pct to the yield stress, respectively. With a decrease in the finish deformation temperature, both the grain size strengthening and solid solution strengthening increased, the precipitation strengthening decreased, and the work hardening contribution did not vary significantly.

The cyclic stress-strain behavior of a nickel-base superalloy at 650 C

NASA Technical Reports Server (NTRS)

Gabb, T. P.; Welsch, G. E.

1986-01-01

It is pointed out that examinations of the monotonic tensile and fatigue behaviors of single crystal nickel-base superalloys have disclosed orientation-dependent tension-compression anisotropies and significant differences in the mechanical response of octahedral and cube slip at intermediate temperatures. An examination is conducted of the cyclic hardening response of the single crystal superalloy PWA 1480 at 650 C. In the considered case, tension-compression anisotropy is present, taking into account primarily conditions under which a single slip system is operative. Aspects of a deformation by single slip are considered along with cyclic hardening anisotropy in tension and compression. It is found that specimens deforming by octahedral slip on a single slip system have similar hardening responses in tensile and low cycle fatigue loading. Cyclic strain hardening is very low for specimens displaying single slip.

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

DOE PAGES

Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; ...

2015-10-19

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. We demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. Furthermore, this “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising frommore » increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. Our results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.« less

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

PubMed Central

Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; Liu, Zhan-Li; Ma, Evan; Li, Ju; Sun, Jun; Zhuang, Zhuo; Dao, Ming; Shan, Zhi-Wei; Suresh, Subra

2015-01-01

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen. PMID:26483463

Stablization of Nanotwinned Microstructures in Stainless Steels Through Alloying and Microstructural Design

DTIC Science & Technology

2013-08-23

REPORT Stablization of Nanotwinned Microstructures in Stainless Steels Through Alloying and Microstructural Design 14. ABSTRACT 16. SECURITY...15. SUBJECT TERMS materials design, stainless steels , plastic deformation by twinning, computational materials science, experimental characterization...Standard Form 298 (Rev 8/98) Prescribed by ANSI Std. Z39.18 - 30-Jun-2013 Stablization of Nanotwinned Microstructures in Stainless Steels Through

Cyclic Deformation-Induced Solute Transport in Tissue Scaffolds with Computer Designed, Interconnected, Pore Networks: Experiments and Simulations

PubMed Central

Op Den Buijs, Jorn; Dragomir-Daescu, Dan; Ritman, Erik L.

2014-01-01

Nutrient supply and waste removal in porous tissue engineering scaffolds decrease from the periphery to the center, leading to limited depth of ingrowth of new tissue into the scaffold. However, as many tissues experience cyclic physiological strains, this may provide a mechanism to enhance solute transport in vivo before vascularization of the scaffold. The hypothesis of this study was that pore cross-sectional geometry and interconnectivity are of major importance for the effectiveness of cyclic deformation-induced solute transport. Transparent elastic polyurethane scaffolds, with computer-programmed design of pore networks in the form of interconnected channels, were fabricated using a 3D printing and injection molding technique. The scaffold pores were loaded with a colored tracer for optical contrast, cyclically compressed with deformations of 10 and 15% of the original undeformed height at 1.0 Hz. Digital imaging was used to quantify the spatial distribution of the tracer concentration within the pores. Numerical simulations of a fluid–structure interaction model of deformation-induced solute transport were compared to the experimental data. The results of experiments and modeling agreed well and showed that pore interconnectivity heavily influences deformation-induced solute transport. Pore cross-sectional geometry appears to be of less relative importance in interconnected pore networks. Validated computer models of solute transport can be used to design optimal scaffold pore geometries that will enhance the convective transport of nutrients inside the scaffold and the removal of waste, thus improving the cell survivability deep inside the scaffold. PMID:19466547

Cyclic strain rate effects in fatigued face-centred and body-centred cubic metals

NASA Astrophysics Data System (ADS)

Mughrabi, Haël

2013-09-01

The present work deals mainly with the effect and the use of strain rate and temperature changes during cyclic deformation as a means to obtain valuable information on the thermally activated dislocation glide processes, based on the assessment of reversible changes of the thermal effective stress and of transient changes of the athermal stress. The importance of closed-loop testing in true plastic strain control with constant cyclic plastic strain rate throughout the cycle is explained and emphasized, especially with respect to the case of strain rate sensitive materials. Stress responses of face-centred cubic and body-centred cubic (bcc) metals to cyclic strain rate changes are presented to illustrate that the deformation modes of these two classes of materials differ characteristically at temperatures below that the so-called knee temperature of bcc metals. When such tests are performed in cyclic saturation, the temperature and strain rate dependence of bcc metals can be measured very accurately on one and the same specimen, permitting a thorough analysis of thermal activation.

Assessment of Shape Memory Alloys - From Atoms To Actuators - Via In Situ Neutron Diffraction

NASA Technical Reports Server (NTRS)

Benafan, Othmane

2014-01-01

As shape memory alloys (SMAs) become an established actuator technology, it is important to identify the fundamental mechanisms responsible for their performance by understanding microstructure performance relationships from processing to final form. Yet, microstructural examination of SMAs at stress and temperature is often a challenge since structural changes occur with stress and temperature and microstructures cannot be preserved through quenching or after stress removal, as would be the case for conventional materials. One solution to this dilemma is in situ neutron diffraction, which has been applied to the investigation of SMAs and has offered a unique approach to reveal the fundamental micromechanics and microstructural aspects of bulk SMAs in a non-destructive setting. Through this technique, it is possible to directly correlate the micromechanical responses (e.g., internal residual stresses, lattice strains), microstructural evolutions (e.g., texture, defects) and phase transformation properties (e.g., phase fractions, kinetics) to the macroscopic actuator behavior. In this work, in situ neutron diffraction was systematically employed to evaluate the deformation and transformation behavior of SMAs under typical actuator conditions. Austenite and martensite phases, yield behavior, variant selection and transformation temperatures were characterized for a polycrystalline NiTi (49.9 at. Ni). As the alloy transforms under thermomechanical loading, the measured textures and lattice plane-level variations were directly related to the cyclic actuation-strain characteristics and the dimensional instability (strain ratcheting) commonly observed in this alloy. The effect of training on the shape memory characteristics of the alloy and the development of two-way shape memory effect (TWSME) were also assessed. The final conversion from a material to a useful actuator, typically termed shape setting, was also investigated in situ during constrained heatingcooling and subsequent shape recovery experiments. Neutron diffraction techniques are also being applied to the investigation of novel high temperature SMAs with the objective of designing alloys with better stability, higher transition temperatures and ultimately superior durability.

The nature of the Ailao Shan-Red River (ASRR) shear zone: Constraints from structural, microstructural and fabric analyses of metamorphic rocks from the Diancang Shan, Ailao Shan and Day Nui Con Voi massifs

NASA Astrophysics Data System (ADS)

Liu, Junlai; Tang, Yuan; Tran, My-Dung; Cao, Shuyun; Zhao, Li; Zhang, Zhaochong; Zhao, Zhidan; Chen, Wen

2012-03-01

The structural geology, timing of shearing, and tectonic implications of the ASRR shear zone, one of the most striking lineaments in Southeast Asia, have been the topics of extensive studies over the past few decades. The Xuelong Shan (XLS), Diancang Shan (DCS), Ailao Shan (ALS) and Day Nui Con Voi (DNCV) metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution. Our field structural analysis, detailed microstructural and fabric analysis, as well as the quartz, sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during Cenozoic tectonic evolution in the shear zone. Among the contrasting structural and microstructural associations in the shear zone, D2 structures, which were formed at the brittle to ductile transition during large-scale left-lateral shearing in the second deformation episode, predominate over the structural styles of the other two deformation episodes. Discrete micro-shear zones with intensive grain size reduction compose the characteristic structural style of D2 deformation. In addition, several types of folds (early shearing folds, F21, and late-shearing folds, F22) were formed in the sheared rocks, including discrete to distributed mylonitic foliation, stretching lineation and shear fabrics (e.g., mica fish, domino structures, as well as sigma and delta fabrics). A sequence of microstructures from syn-kinematic magmatic flow, high-temperature solid-state deformation, to brittle-ductile shearing is well-preserved in the syn-kinematic leucocratic intrusions. Deformation structures from the first episode (D1) are characterized by F1 folds and distributed foliations (S1) in rocks due to pure shearing at high temperatures. They are preserved in weakly sheared (D2) rocks along the eastern margin of the ALS belt or in certain low-strain tectonic enclaves within the shear zone. Furthermore, semi-brittle deformation structures, such as hot striae and discrete retrogression zones, are attributed to normal-slip shearing in the third deformation episode (D3), which was probably locally active, along the eastern flank of the DCS range, for example. There are four quartz c-axis fabric patterns in the mylonitic rocks, including type A point maxima, type B Y point maxima with crossed girdles superimposition, type C quadrant maxima, as well as type D point and quadrant maxima combination. They are consistent with microscopic observations of microstructures of high-temperature pure shearing, low-temperature simple shearing and their superimposition. Integrated microstructural analysis and fabric thermometer studies provide information on both high temperature (up to 750 °C) and dominant low-temperature (300-600 °C) deformations of quartz grains in different rock types. Sillimanite and garnet fabrics, especially the latter, were primarily formed at the peak metamorphism during high-temperature pure shearing. The above structural, microstructural and fabric associations were generated in the tectonic framework of the Indian-Eurasian collision. The low-temperature microstructures and fabrics are attributed to left-lateral shearing along the ASRR shear zone from 27 to 21 Ma during the southeastward extrusion of the Indochina block, which postdated high-temperature deformation at the peak metamorphism during the collision.

Microstructural analysis of the thermal annealing of ice-Ih using EBSD

NASA Astrophysics Data System (ADS)

Hidas, Károly; Tommasi, Andréa; Mainprice, David; Chauve, Thomas; Barou, Fabrice; Montagnat, Maurine

2017-04-01

Rocks deformed in the middle crust and deeper in the Earth typically remain at high temperature for extended time spans after the cessation of deformation. This results in annealing of the deformation microstructure by a series of thermally activated, diffusion-based processes, namely: recovery and static recrystallization, which may also modify the crystal preferred orientation (CPO) or texture. Understanding the effects of annealing on the microstructure and CPO is therefore of utmost importance for the interpretation of the microstructures and for the estimation of the anisotropy of physical properties of lower crustal and mantle rocks. Ice-Ih -the typical form of water ice on the Earth's surface, with hexagonal crystal symmetry- deforms essentially by glide of dislocations on the basal plane [1], thus it has high viscoplastic anisotropy, which induces strong heterogeneity of stresses and strains at both the intra- and intergranular scales [2-3]. This behavior makes ice-Ih an excellent analog material for silicate minerals that compose the Earth. In situ observations of the evolution of the microstructures and CPO during annealing enable the study of the interplay between the various physical processes involved in annealing (recovery, nucleation, grain growth). They also allow the analysis of the impact of the preexisting deformation microstructures on the microstructural and CPO evolution during annealing. Here we studied the evolution of the microstructure of ice-Ih during static recrystallization by stepwise annealing experiments. We alternated thermal annealing and electron backscatter diffraction (EBSD) analyses on polycrystalline columnar ice-Ih pre-deformed in uniaxial compression at temperature of -7 °C to strains of 3.0-5.2. Annealing experiments were carried out at -5 °C and -2 °C up to a maximum of 3.25 days, typically in 5-6 steps. EBSD crystal orientation maps obtained after each annealing step permit the description of microstructural changes. Decrease in average intragranular misorientation at the sample scale and modification of the misorientation across subgrain boundaries provide evidence for recovery from the earliest stages of annealing. This evolution is similar for all studied samples irrespective of their initial strain or annealing temperature. After an incubation period up to 2 hours, recovery is accompanied by recrystallization (nucleation and grain boundary migration). Grain growth proceeds at the expense of domains with high intra-granular misorientations and its kinetics fits the parabolic growth law. Deformation-induced microstructures (tilt boundaries and kink bands) are stable features during early stages of static recrystallization and locally slow down grain boundary migration, pinning grain growth. REFERENCES 1. Duval, P., Ashby, M.F., Anderman, I., 1983. Rate-controlling processes in the creep of polycrystalline ice. Journal of Physical Chemistry 87, 4066-4074. 2. Grennerat, F., Montagnat, M., Castelnau, O., Vacher, P., Moulinec, H., Suquet, P., Duval, P., 2012. Experimental characterization of the intragranular strain field in columnar ice during transient creep. Acta Materialia 60, 3655-3666. 3. Chauve, T., Montagnat, M., Vacher, P., 2015. Strain field evolution during dynamic recrystallization nucleation: A case study on ice. Acta Materialia 101, 116-124. Funding: Research leading to these results was funded by the EU-FP7 Marie Curie postdoctoral grant PIEF-GA-2012-327226 to K.H.

Effects of hot compression deformation temperature on the microstructure and properties of Al-Zr-La alloys

NASA Astrophysics Data System (ADS)

Yue, Xian-hua; Liu, Chun-fang; Liu, Hui-hua; Xiao, Su-fen; Tang, Zheng-hua; Tang, Tian

2018-02-01

The main goal of this study is to investigate the microstructure and electrical properties of Al-Zr-La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al3Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.

Microstructural and mechanical responses to various rolling speeds determined in multi-pass break-down rolling of AZ31B alloy

NASA Astrophysics Data System (ADS)

Jia, Weitao; Tang, Yan; Ning, Fangkun; Le, Qichi; Cui, Jianzhong

2018-04-01

Different rolling operations of as-cast AZ31B alloy were performed under different rolling speed (18 ∼ 72 m min‑1) and rolling pass conditions at 400 °C. Microstructural studies, tensile testing and formability evaluation relevant to each rolling operation were investigated. For 1-pass rolling, coarse average grain size (CAGS) region gradually approached the center layer as the rolling speed increased. Moreover, twins, shear bands and coarse-grain structures were the dominant components in the microstructure of plates rolled at 18, 48 and 72 m min‑1, respectively, indicating the severe deformation inhomogeneity under the high reduction per pass condition. For 2-pass rolling and 4-pass rolling, dynamic recrystallization was observed to be well and CAGS region has substantially disappeared, indicating the significant improvement in deformation uniformity and further the grain homogenization under the conditions. Microstructure uniformity degree of 2-pass rolled plates did not vary much as the rolling speed varied. On this basis, shear band distribution dominated the deformation behavior during the uniaxial tension of the 2-pass rolled plates. However, microstructure uniformity accompanied by twin distribution played a leading role in stretching the 4-pass rolled plates.

The effect of microstructure, temperature, and hold-time on low-cycle fatigue of As HIP P/M Rene 95

NASA Technical Reports Server (NTRS)

Bashir, S.; Antolovich, S. D.

1984-01-01

The effects of microstructure, temperature, plastic strain range, and hold time on the low-cycle fatigue (LCF) life were studied for Rene 95, an important Ni base superalloy used in jet engine disks. It was shown that the life could be varied by approximately an order of magnitude at elevated temperatures by simple heat treatments. The life was largest for the microstructure that promoted the most homogeneous deformation mode. The results are explained using the concept of a synergistic interaction between the deformation mode and boundary oxidation.

Quantifying the influence of twin boundaries on the deformation of nanocrystalline copper using atomistic simulations

DOE PAGES

Tucker, Garritt J.; Foiles, Stephen Martin

2014-09-22

Over the past decade, numerous efforts have sought to understand the influence of twin boundaries on the behavior of polycrystalline materials. Early results suggested that twin boundaries within nanocrystalline face-centered cubic metals have a considerable effect on material behavior by altering the activated deformation mechanisms. In this work, we employ molecular dynamics simulations to elucidate the role of twin boundaries on the deformation of <100> columnar nanocrystalline copper at room temperature under uniaxial strain. We leverage non-local kinematic metrics, formulated from continuum mechanics theory, to compute atomically-resolved rotational and strain fields during plastic deformation. These results are then utilized tomore » compute the distribution of various nanoscale mechanisms during straining, and quantitatively resolve their contribution to the total strain accommodation within the microstructure, highlighting the fundamental role of twin boundaries. Our results show that nanoscale twins influence nanocrystalline copper by altering the cooperation of fundamental deformation mechanisms and their contributed role in strain accommodation, and we present new methods for extracting useful information from atomistic simulations. The simulation results suggest a tension–compression asymmetry in the distribution of deformation mechanisms and strain accommodation by either dislocations or twin boundary mechanisms. In highly twinned microstructures, twin boundary migration can become a significant deformation mode, in comparison to lattice dislocation plasticity in non-twinned columnar microstructures, especially during compression.« less

Finite element analysis of the cyclic indentation of bilayer enamel

NASA Astrophysics Data System (ADS)

Jia, Yunfei; Xuan, Fu-zhen; Chen, Xiaoping; Yang, Fuqian

2014-04-01

Tooth enamel is often subjected to repeated contact and often experiences contact deformation in daily life. The mechanical strength of the enamel determines the biofunctionality of the tooth. Considering the variation of the rod arrangement in outer and inner enamel, we approximate enamel as a bilayer structure and perform finite element analysis of the cyclic indentation of the bilayer structure, to mimic the repeated contact of enamel during mastication. The dynamic deformation behaviour of both the inner enamel and the bilayer enamel is examined. The material parameters of the inner and outer enamel used in the analysis are obtained by fitting the finite element results with the experimental nanoindentation results. The penetration depth per cycle at the quasi-steady state is used to describe the depth propagation speed, which exhibits a two-stage power-law dependence on the maximum indentation load and the amplitude of the cyclic load, respectively. The continuous penetration of the indenter reflects the propagation of the plastic zone during cyclic indentation, which is related to the energy dissipation. The outer enamel serves as a protective layer due to its great resistance to contact deformation in comparison to the inner enamel. The larger equivalent plastic strain and lower stresses in the inner enamel during cyclic indentation, as calculated from the finite element analysis, indicate better crack/fracture resistance of the inner enamel.

Inelastic Deformation of Metal Matrix Composites. Part 1; Plasticity and Damage Mechanisms

NASA Technical Reports Server (NTRS)

Majumdar, B. S.; Newaz, G. M.

1992-01-01

The deformation mechanisms of a Ti 15-3/SCS6 (SiC fiber) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and to confirm the mechanisms by rigorous microstructural evaluations. The results of room temperature experiments performed on 0 degree and 90 degree systems primarily are reported in this report. Results of experiments performed on other laminate systems and at high temperatures will be provided in a forthcoming report. Inelastic deformation of the 0 degree MMC (fibers parallel to load direction) was dominated by the plasticity of the matrix. In contrast, inelastic deformations of the 90 degree composite (fibers perpendicular to loading direction) occurred by both damage and plasticity. The predictions of a continuum elastic plastic model were compared with experimental data. The model was adequate for predicting the 0 degree response; however, it was inadequate for predicting the 90 degree response largely because it neglected damage. The importance of validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out. The deformation mechanisms, and the likely sequence of events associated with the inelastic deformation of MMCs, are indicated in this paper.

Microstructural Evolution and Deformation Behavior of a Hot-Rolled and Heat Treated Fe-8Mn-4Al-0.2C Steel

NASA Astrophysics Data System (ADS)

Cai, Zhihui; Ding, Hua; Ying, Zhengyan; Misra, R. D. K.

2014-04-01

The microstructural evolution following tensile deformation of a hot-rolled and heat treated Fe-8Mn-4Al-0.2C steel was studied. Quenching in the range of 750-800 °C followed by tempering at 200 °C led to a ferrite-austenite mixed microstructure that was characterized by excellent combination of tensile strength of 800-1000 MPa and elongation of 30-40%, and a three-stage work hardening behavior. During the tensile deformation, the retained austenite transformed into martensite and delayed the onset of necking, thus leading to a higher ductility via the transformation-induced plasticity (TRIP) effect. The improvement of elongation is attributed to diffusion of carbon from δ-ferrite to austenite during tempering, which improves the stability of austenite, thus contributing to enhanced tensile ductility.

Macroscopic and Microstructural Aspects of the Transformation Behavior in a Polycrystalline NiTi Shape Memory Alloy

NASA Technical Reports Server (NTRS)

Benafan, Othmane; Noebe, Ronald D.; Padula, Santo A., II; Lerch, Bradley A.; Bigelow, Glen S.; Gaydosh, Darrell J.; Garg, Anita; An, Ke; Vaidyanathan, Raj

2013-01-01

The mechanical and microstructural behavior of a polycrystalline Ni(49.9)Ti(50.1) (at.%) shape memory alloy was investigated as a function of temperature around the transformation regime. The bulk macroscopic responses, measured using ex situ tensile deformation and impulse excitation tests, were compared to the microstructural evolution captured using in situ neutron diffraction. The onset stress for inelastic deformation and dynamic Young's modulus were found to decrease with temperature, in the martensite regime, reaching a significant minimum at approximately 80 C followed by an increase in both properties, attributed to the martensite to austenite transformation. The initial decrease in material compliance during heating affected the ease with which martensite reorientation and detwinning could occur, ultimately impacting the stress for inelastic deformation prior to the start of the reverse transformation.

Comparison of mechanical compressive properties of commercial and autologous fibrin glues for tissue engineering applications.

PubMed

Cravens, Matthew G; Behn, Anthony W; Dragoo, Jason L

2017-11-01

Fibrin glues are widely used in orthopedic surgery as adhesives and hemostatic agents. We evaluated the compressive properties of selected fibrin glues in order to identify which are appropriate for tissue regeneration applications subject to compression. Uniaxial unconfined compression tests were performed on fibrin gels prepared from commercial and autologous products: (1) Evicel (Ethicon), (2) Tisseel (Baxter), (3) Angel (Arthrex), and (4) ProPlaz (Biorich). Cyclic loads were applied from 0 to 30% strain for 100cycles at 0.5Hz. Following cyclic testing, specimens were subjected to ramp displacement of 1% strain per second to 80% strain. Throughout cyclic loading, Evicel and Tisseel deformed (shortened) less than Angel at all but one time point, and deformed less than ProPlaz at cycles 10 and 20. The dynamic moduli, peak stress, and strain energy were significantly greater in Tisseel than all other groups. Evicel displayed significantly greater dynamic moduli, peak stress, and strain energy than Angel and ProPlaz. Following cyclic testing, Tisseel and Evicel were significantly less deformed than Angel. No specimens exhibited gross failure during ramp loading to 80% strain. Ramp loading trends mirrored those of cyclic loading. The tested commercial glues were significantly more resistant to compression than the autologous products. The compressive properties of Tisseel were approximately twice those of Evicel. All preparations displayed moduli multiple orders of magnitude less than that of native articular cartilage. We conclude that in knee surgeries requiring fibrin glue to undergo compression of daily activity, commercial products are preferable to autologous preparations from platelet-poor plasma, though both will deform significantly. Copyright © 2017 Elsevier Ltd. All rights reserved.

Microstructure and Mechanical Properties of Extruded Gamma Microstructure Met PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Das, G.; Locci, J.; Whittenberger, J. D.; Lerch, B. A.; Kestler, H.

2003-01-01

A gamma TiAl alloy with a high Nb content is being assessed as a compressor blade material. The microstructure and mechanical properties of extruded Ti-45Al-X(Nb,B,C) (at.%) were evaluated in both an as-extruded condition and after a lamellar heat treatment. Tensile behavior of both as-extruded and lamellar heat treated specimens was studied in the temperature range of RT to 926 C. In general, the yield stress and ultimate tensile strength reached relatively high values at room temperature and decreased with increasing deformation temperature. The fatigue strength of both microstructures was characterized at 650 C and compared to a baseline TiAl alloy and to a Ni-base superalloy. Tensile and fatigue specimens were also exposed to 800 C for 200 h in air to evaluate the alloy's environmental resistance. A decrease in ductility was observed at room temperature due to the 800 C. exposure but the 650 C fatigue properties were unaffected. Compressive and tensile creep testing between 727 and 1027 C revealed that the creep deformation was reproducible and predictable. Creep strengths reached superalloy-like levels at fast strain rates and lower temperatures but deformation at slower strain rates and/or higher temperature indicated significant weakening for the as-extruded condition. At high temperatures and low stresses, the lamellar microstructure had improved creep properties when compared to the as-extruded material. Microstructural evolution during heat treatment, identification of various phases, and the effect of microstructure on the tensile, fatigue, and creep behaviors is discussed.

Hierarchically-driven Approach for Quantifying Materials Uncertainty in Creep Deformation and Failure of Aerospace Materials

DTIC Science & Technology

2016-07-01

characteristics and to examine the sensitivity of using such techniques for evaluating microstructure. In addition to the GUI tool, a manual describing its use has... Evaluating Local Primary Dendrite Arm Spacing Characterization Techniques Using Synthetic Directionally Solidified Dendritic Microstructures, Metallurgical and...driven approach for quanti - fying materials uncertainty in creep deformation and failure of aerspace materials, Multi-scale Structural Mechanics and

Experimental study of cyclic creep and high-cycle fatigue of welded joints of St3 steel by the DIC technique

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

Kibitkin, Vladimir V., E-mail: vvk@ispms.tsc.ru; Solodushkin, Andrey I., E-mail: s.ai@sibmail.com; Pleshanov, Vasily S., E-mail: vsp@ispms.tsc.ru

In the paper the mechanisms of plastic deformation and fracture of welded joints of steel St3 were investigated at high-cycle fatigue and cyclic creep by the digital image correlation (DIC) technique. The evolution of strain rate is studied for the following regions: base metal, HAZ, and fusion zone. This strain rate evolution can be considered as a mechanical response of material. Three stages of deformation evolution are shown: deformation hardening (I), fatigue crack initiation (II), and the last stage is related to main crack (III). Two criteria are offered to evaluate the current mechanical state of welded joints.

Microstructural analysis and calcite piezometry on hydrothermal veins: Insights into the deformation history of the Cocos Plate at Site U1414 (IODP Expedition 344)

NASA Astrophysics Data System (ADS)

Brandstätter, Jennifer; Kurz, Walter; Rogowitz, Anna

2017-08-01

In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e-twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal-plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low-angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high-temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity.

Microstructural analysis and calcite piezometry on hydrothermal veins: Insights into the deformation history of the Cocos Plate at Site U1414 (IODP Expedition 344).

PubMed

Brandstätter, Jennifer; Kurz, Walter; Rogowitz, Anna

2017-08-01

In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e-twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal-plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low-angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high-temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity.

Microstructural analysis and calcite piezometry on hydrothermal veins: Insights into the deformation history of the Cocos Plate at Site U1414 (IODP Expedition 344)

PubMed Central

Kurz, Walter; Rogowitz, Anna

2017-01-01

Abstract In this study we present microstructural data from hydrothermal veins in the sedimentary cover and the igneous basement recovered from Hole U1414A, Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project), to constrain deformation mechanism operating in the subducting Cocos Plate. Cathodoluminescence studies, mechanical e‐twin piezometry and electron backscatter diffraction (EBSD) analyses of carbonate veins were used to give insights into the deformation conditions and to help to understand the tectonic deformation history of the Cocos Plate offshore Costa Rica. Analyses of microstructures in the sedimentary rocks and in the basalt of the igneous basement reveal brittle deformation, as well as crystal‐plastic deformation of the host rock and the vein material. Cathodoluminescence images showed that in the basalt fluid flow and related precipitation occurred over several episodes. The differential stresses, obtained from two different piezometers using the same parameter (twin density), indicate various mean differential stresses of 49 ± 11 and 69 ± 30 MPa and EBSD mapping of calcite veins reveals low‐angle subgrain boundaries. Deformation temperatures are restricted to the range from 170°C to 220°C, due to the characteristics of the existing twins and the lack of high‐temperature intracrystalline deformation mechanisms (>220°C). The obtained results suggest that deformation occurred over a period associated with changes of ambient temperatures, occurrence of fluids and hydrofracturing, induced differential stresses due to the bending of the plate at the trench, and related seismic activity. PMID:29081570

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.

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

Deformation Behavior of Recycled Concrete Aggregate during Cyclic and Dynamic Loading Laboratory Tests

PubMed Central

Sas, Wojciech; Głuchowski, Andrzej; Gabryś, Katarzyna; Soból, Emil; Szymański, Alojzy

2016-01-01

Recycled concrete aggregate (RCA) is a relatively new construction material, whose applications can replace natural aggregates. To do so, extensive studies on its mechanical behavior and deformation characteristics are still necessary. RCA is currently used as a subbase material in the construction of roads, which are subject to high settlements due to traffic loading. The deformation characteristics of RCA must, therefore, be established to find the possible fatigue and damage behavior for this new material. In this article, a series of triaxial cyclic loading and resonant column tests is used to characterize fatigue in RCA as a function of applied deviator stress after long-term cyclic loading. A description of the shakedown phenomenon occurring in the RCA and calculations of its resilient modulus (Mr) as a function of fatigue are also presented. Test result analysis with the stress-life method on the Wohler S-N diagram shows the RCA behavior in accordance with the Basquin law. PMID:28773905

Microcracking and Healing in Semibrittle Salt-Rock: Elastic and Plastic Behavior

NASA Astrophysics Data System (ADS)

Ding, J.; Chester, F. M.; Chester, J. S.; Shen, X.; Arson, C. F.

2017-12-01

Microcracking and healing during semibrittle deformation are important processes that affect physical properties such as elastic moduli and permeability. We study these processes through triaxial compression tests involving cyclic differential loading and isostatic-holds on synthetic salt-rock at room temperature and low confining pressure (Pc, 1 to 4 MPa). The salt samples are produced by uniaxial pressing of granular (300 µm dia.) halite to 75 MPa at 150˚C for 10^3 s, to create low-porosity ( 5%) aggregates of nearly equant, work-hardened grains. Alternating large- and small-load cycles are performed to track the evolution of plastic and elastic properties, respecitively, with progressive strain to 8% axial shortening. 24-hour holds are carried out at about 4% axial shortening followed by renewed cyclic loading to investigate healing. During large load cycles samples yield and exhibit distributed flow with dilatancy and small work hardening. Young's Modulus (YM) decreases and then tends to stabilize, while Poisson's Ratio (PR) increases at a reducing rate, with progressive strain. Microstructures at sequential stages show that opening-mode grain-boundary cracking, grain-boundary sliding, and some intracrystalline plasticity are the dominant deformation processes. Opening and shear occur preferentially on boundaries that are parallel and inclined to the shortening axis, respectively, leading to progressive redistribution of porosity. Opening-mode grain-boundary cracks increase in number and aperature with strain, and are linked by sliding grain-boundaries to form en echelon arrays. After a 24-hour hold, samples show yielding and flow behavior consistent with that prior to the hold, whereas YM and PR are reset to the same values documented at zero strain and subsequently evolve with additional strain similar to that documented at smaller strains prior to the hold. Open grain-boundary cracks are not closed or healed during the hold. Observations suggest that changes in elastic properties in the semibrittle salt-rock reflect weakening and healing of grain-boundaries undergoing sliding rather than progressive dilatancy or healing of opening-mode cracks. Findings are being used to inform and develop continuum damage mechanics models of semibrittle deformation in polycrystalline aggregates

Microstructures imply cataclasis and authigenic mineral formation control geomechanical properties of New Zealand's Alpine Fault

NASA Astrophysics Data System (ADS)

Schuck, B.; Janssen, C.; Schleicher, A. M.; Toy, V. G.; Dresen, G.

2018-05-01

The Alpine Fault is capable of generating large (MW > 8) earthquakes and is the main geohazard on South Island, NZ, and late in its 250-291-year seismic cycle. To minimize its hazard potential, it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength-evolution of the fault. High-resolution microstructural, mineralogical and geochemical analyses of the Alpine Fault's core demonstrate wall rock fragmentation, assisted by mineral dissolution, and cementation resulting in the formation of a fine-grained principal slip zone (PSZ). A complex network of anastomosing and mutually cross-cutting calcite veins implies that faulting occurred during episodes of dilation, slip and sealing. Fluid-assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core. Undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the Earth's surface. Microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling, particularly influenced by abundant nanoparticles, play a key role in the fault core's velocity-weakening behavior rather than frictional sliding. This is further supported by the absence of smectite, which is reasonable given recently measured geothermal gradients of more than 120 °C km-1 and the impermeable nature of the PSZ, which both limit the growth of this phase and restrict its stability to shallow depths. Our observations demonstrate that high-temperature fluids can influence authigenic mineral formation and thus control the fault's geomechanical behavior and the cyclic evolution of its strength.

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.

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

Binder, I.

TiC/Ni compositions with 10, 20, and 40 percent nickel were tested for transverse rupture strengths up to 1600 deg C. Transverse bend, cantilever beam, hot deformation, and hot extrusion experiments were performed in order to study the onset of plastic deformation. These materials were plastically deformed, and their microstructures were studied to learn about the mode of deiormation, plastic flow of the nickel binder, and alignment of the carbide grains. Other refractory hardmetal compositions, both single phase and cemented, were tested in transverse rupture up to 1600 deg C and were also subjected to various forms of hot deformation. Transversemore » strength peaks, versus temperature, were found for each material in the range 800 to 1500 deg C. Reasons for this behavior are developed. Microstructures of these materials were examined in connection with the strength tests and deformation studies. (auth)« less

Influence of deformation ageing treatment on microstructure and properties of aluminum alloy 2618

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

Wang Jianhua; Yi Danqing; Su Xuping

2008-07-15

The effects of deformation ageing treatment (DAT) on the microstructure and properties of aluminum alloy 2618 were investigated. The alloy was subjected to deformation ageing treatment which included solution treating at 535 deg. C quenching into water at room-temperature, cold rolling (10%) and further ageing to peak hardness level at 200 deg. C. The electron microscopic studies revealed that the treatment affects the ageing characteristics and the coarsening of ageing phase (S') at elevated-temperature. The dislocation-precipitate tangles substructure couldn't be found in alloy 2618. The tensile and hardness tests showed that deformation-ageing treatment causes a significant improvement in tensile strengthmore » and hardness to alloy 2618 at room- and elevated-temperature.« less

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

NASA Astrophysics Data System (ADS)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

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).

Influence of Al on the Microstructural Evolution and Mechanical Behavior of Low-Carbon, Manganese Transformation-Induced-Plasticity Steel

NASA Astrophysics Data System (ADS)

Suh, Dong-Woo; Park, Seong-Jun; Lee, Tae-Ho; Oh, Chang-Seok; Kim, Sung-Joon

2010-02-01

Microstructural design with an Al addition is suggested for low-carbon, manganese transformation-induced-plasticity (Mn TRIP) steel for application in the continuous-annealing process. With an Al content of 1 mass pct, the competition between the recrystallization of the cold-rolled microstructure and the austenite formation cannot be avoided during intercritical annealing, and the recrystallization of the deformed matrix does not proceed effectively. The addition of 3 mass pct Al, however, allows nearly complete recrystallization of the deformed microstructure by providing a dual-phase cold-rolled structure consisting of ferrite and martensite and by suppressing excessive austenite formation at a higher annealing temperature. An optimized annealing condition results in the room-temperature stability of the intercritical austenite in Mn TRIP steel containing 3 mass pct Al, permitting persistent transformation to martensite during tensile deformation. The alloy presents an excellent strength-ductility balance combining a tensile strength of approximately 1 GPa with a total elongation over 25 pct, which is comparable to that of Mn TRIP steel subjected to batch-type annealing.

Impact of Martensite Spatial Distribution on Quasi-Static and Dynamic Deformation Behavior of Dual-Phase Steel

NASA Astrophysics Data System (ADS)

Singh, Manpreet; Das, Anindya; Venugopalan, T.; Mukherjee, Krishnendu; Walunj, Mahesh; Nanda, Tarun; Kumar, B. Ravi

2017-12-01

The effects of microstructure parameters of dual-phase steels on tensile high strain dynamic deformation characteristic were examined in this study. Cold-rolled steel sheets were annealed using three different annealing process parameters to obtain three different dual-phase microstructures of varied ferrite and martensite phase fraction. The volume fraction of martensite obtained in two of the steels was near identical ( 19 pct) with a subtle difference in its spatial distribution. In the first microstructure variant, martensite was mostly found to be situated at ferrite grain boundaries and in the second variant, in addition to at grain boundaries, in-grain martensite was also observed. The third microstructure was very different from the above two with respect to martensite volume fraction ( 67 pct) and its morphology. In this case, martensite packets were surrounded by a three-dimensional ferrite network giving an appearance of core and shell type microstructure. All the three steels were tensile deformed at strain rates ranging from 2.7 × 10-4 (quasi-static) to 650 s-1 (dynamic range). Field-emission scanning electron microscope was used to characterize the starting as well as post-tensile deformed microstructures. Dual-phase steel consisting of small martensite volume fraction ( 19 pct), irrespective of its spatial distribution, demonstrated high strain rate sensitivity and on the other hand, steel with large martensite volume fraction ( 67 pct) displayed a very little strain rate sensitivity. Interestingly, total elongation was found to increase with increasing strain rate in the dynamic regime for steel with core-shell type of microstructure containing large martensite volume fraction. The observed enhancement in plasticity in dynamic regime was attributed to adiabatic heating of specimen. To understand the evolving damage mechanism, the fracture surface and the vicinity of fracture ends were studied in all the three dual-phase steels.

Impact of Martensite Spatial Distribution on Quasi-Static and Dynamic Deformation Behavior of Dual-Phase Steel

NASA Astrophysics Data System (ADS)

Singh, Manpreet; Das, Anindya; Venugopalan, T.; Mukherjee, Krishnendu; Walunj, Mahesh; Nanda, Tarun; Kumar, B. Ravi

2018-02-01

The effects of microstructure parameters of dual-phase steels on tensile high strain dynamic deformation characteristic were examined in this study. Cold-rolled steel sheets were annealed using three different annealing process parameters to obtain three different dual-phase microstructures of varied ferrite and martensite phase fraction. The volume fraction of martensite obtained in two of the steels was near identical ( 19 pct) with a subtle difference in its spatial distribution. In the first microstructure variant, martensite was mostly found to be situated at ferrite grain boundaries and in the second variant, in addition to at grain boundaries, in-grain martensite was also observed. The third microstructure was very different from the above two with respect to martensite volume fraction ( 67 pct) and its morphology. In this case, martensite packets were surrounded by a three-dimensional ferrite network giving an appearance of core and shell type microstructure. All the three steels were tensile deformed at strain rates ranging from 2.7 × 10-4 (quasi-static) to 650 s-1 (dynamic range). Field-emission scanning electron microscope was used to characterize the starting as well as post-tensile deformed microstructures. Dual-phase steel consisting of small martensite volume fraction ( 19 pct), irrespective of its spatial distribution, demonstrated high strain rate sensitivity and on the other hand, steel with large martensite volume fraction ( 67 pct) displayed a very little strain rate sensitivity. Interestingly, total elongation was found to increase with increasing strain rate in the dynamic regime for steel with core-shell type of microstructure containing large martensite volume fraction. The observed enhancement in plasticity in dynamic regime was attributed to adiabatic heating of specimen. To understand the evolving damage mechanism, the fracture surface and the vicinity of fracture ends were studied in all the three dual-phase steels.

Resistance of a directionally solidified gamma/gamma prime-delta eutectic alloy to recrystallization. [Ni-base alloy

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Scheuermann, C. M.; Andrews, C. W.

1976-01-01

A lamellar nickel-base directionally-solidified eutectic gamma/gamma prime-delta alloy has potential as an advanced gas turbine blade material. The microstructural stability of this alloy was investigated. Specimens were plastically deformed by uniform compression or Brinell indentation, then annealed between 750 and 1120 C. Microstructural changes observed after annealing included gamma prime coarsening, pinch-off and spheroidization of delta lamellae, and appearance of an unidentified blocky phase in surface layers. All but the first of these was localized in severely deformed regions, suggesting that microstructural instability may not be a serious problem in the use of this alloy.

Resistance of a gamma/gamma prime - delta directionally solidified eutectic alloy to recrystallization

NASA Technical Reports Server (NTRS)

Tewari, S. N.; Scheuermann, C. M.; Andrews, C. W.

1975-01-01

The lamellar directionally solidified nickel-base eutectic alloy gamma/gamma prime-delta has potential as an advanced turbine blade material. The microstructural stability of this alloy was investigated. Specimens were plastically deformed by uniform compression or Brinell indentation, then annealed between 705 and 1120 C. Microstructural changes observed after annealing included gamma prime coarsening, pinch-off and spheroidization of delta lamellae, and the appearance of an unidentified blocky phase in surface layers. All but the first of these was localized in severely deformed regions, suggesting that microstructural instability is not a serious problem in the use of this alloy.

Deformability of shredded tires

DOT National Transportation Integrated Search

1999-01-01

This report describes three separate studies that examine the deformability of shredded tire fill material. The first study determined the response of shredded tires to cyclic loading. These tests were conducted in a load frame on both constrained an...

Microstructure and Mechanical Properties of Bulk Nanostructured Cu-Ta Alloys Consolidated by Equal Channel Angular Extrusion

DTIC Science & Technology

2014-07-01

5,9], W [16], Zr [17] and Nb [18]. These systems have shown moderate to extraordinarily high microstructural stability at elevated temperatures...cans were then either serial sectioned for shear punch testing or cut into compression samples using wire electric discharge machining. Through SEM...to resist deformation, but do not necessarily alter the dislocation mechanism operating during plastic deformation. There are a number of challenges

Tunable Microfluidic Devices for Hydrodynamic Fractionation of Cells and Beads: A Review

PubMed Central

Alvankarian, Jafar; Majlis, Burhanuddin Yeop

2015-01-01

The adjustable microfluidic devices that have been developed for hydrodynamic-based fractionation of beads and cells are important for fast performance tunability through interaction of mechanical properties of particles in fluid flow and mechanically flexible microstructures. In this review, the research works reported on fabrication and testing of the tunable elastomeric microfluidic devices for applications such as separation, filtration, isolation, and trapping of single or bulk of microbeads or cells are discussed. Such microfluidic systems for rapid performance alteration are classified in two groups of bulk deformation of microdevices using external mechanical forces, and local deformation of microstructures using flexible membrane by pneumatic pressure. The main advantage of membrane-based tunable systems has been addressed to be the high capability of integration with other microdevice components. The stretchable devices based on bulk deformation of microstructures have in common advantage of simplicity in design and fabrication process. PMID:26610519

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

PubMed Central

Kim, J. T.; Hong, S. H.; Park, H. J.; Kim, Y. S.; Suh, J. Y.; Lee, J. K.; Park, J. M.; Maity, T.; Eckert, J.; Kim, K. B.

2017-01-01

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition. PMID:28067248

On the critical parameters that regulate the deformation behaviour of tooth enamel.

PubMed

Xie, Zonghan; Swain, Michael; Munroe, Paul; Hoffman, Mark

2008-06-01

Tooth enamel is the hardest tissue in the human body with a complex hierarchical structure. Enamel hypomineralisation--a developmental defect--has been reported to cause a marked reduction in the mechanical properties of enamel and loss of dental function. We discover a distinctive difference in the inelastic deformation mechanism between sound and hypomineralised enamels that is apparently controlled by microstructural variation. For sound enamel, when subjected to mechanical forces the controlling deformation mechanism was distributed shearing within nanometre thick protein layer between its constituent mineral crystals; whereas for hypomineralised enamel microcracking and subsequent crack growth were more evident in its less densely packed microstructure. We develop a mechanical model that not only identifies the critical parameters, i.e., the thickness and shear properties of enamels, that regulate the mechanical behaviour of enamel, but also explains the degradation of hypomineralised enamel as manifested by its lower resistance to deformation and propensity for catastrophic failure. With support of experimental data, we conclude that for sound enamel an optimal microstructure has been developed that endows enamel with remarkable structural integrity for durable mechanical function.

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

NASA Astrophysics Data System (ADS)

Zhao, H.; Palmiere, E. J.

2017-07-01

Although there has been much research regarding the effect of austenite deformation on accelerated cooled microstructures in microalloyed steels, there is still a lack of accurate data on boundary densities and effective grain sizes. Previous results observed from optical micrographs are not accurate enough, because, for displacive transformation products, a substantial part of the boundaries have disorientation angles below 15 deg. Therefore, in this research, a niobium microalloyed steel was used and electron backscattering diffraction mappings were performed on all of the transformed microstructures to obtain accurate results on boundary densities and grain refinement. It was found that with strain rising from 0 to 0.5, a transition from bainitic ferrite to acicular ferrite occurs and the effective grain size reduces from 5.7 to 3.1 μm. When further increasing strain from 0.5 to 0.7, dynamic recrystallization was triggered and postdynamic softening occurred during the accelerated cooling, leading to an inhomogeneous and coarse transformed microstructure. In the entire strain range, the density changes of boundaries with different disorientation angles are distinct, due to different boundary formation mechanisms. Finally, the controversial influence of austenite deformation on effective grain size of low-temperature transformation products was argued to be related to the differences in transformation conditions and final microstructures.

Cryomilled and spark plasma sintered titanium: the evolution of microstructure

NASA Astrophysics Data System (ADS)

Kozlík, Jiří; Becker, Hanka; Harcuba, Petr; Stráský, Josef; Janeček, Milos

2017-05-01

Bulk ultra-fine grained (UFG) commercially pure Ti was prepared by cryogenic milling in liquid argon and subsequent spark plasma sintering (SPS). During cryogenic milling, individual powder particles are repetitively severely deformed by attrition forces. Powder particles were not significantly refined, but due to severe repetitive plastic deformation, ultra-fine grained microstructure emerges within each powder particle. Cryogenic milling can be therefore considered as a specific severe plastic deformation (SPD) method. Compactization of cryomilled powder by SPS technique (also referred to as field assisted sintering technique - FAST) requires significantly lower sintering temperatures and shorter sintering times for successful compaction when compared to any other sintering technique. This is crucial for maintaining the UFG microstructure due to its limited thermal stability. Several specimens were prepared by varying processing parameters, in particular the sintering temperature. The microstructure of powders and compacted samples was observed by scanning electron microscopy (SEM). Increased sintering temperature results in recrystallization and grain growth. A trade-off relationship between the density of compacted material and grain size was identified. Microhardness of the material was found to depend on residual porosity rather than grain size. This contribution presents cryogenic milling and spark plasma sintering as a viable alternative for achieving UFG microstructure in commercially pure Ti.

Microstructural record of pressure solution and crystal plastic deformation in carbonate fault rocks from a shallow crustal strike-slip fault, Northern Calcareous Alps (Austria)

NASA Astrophysics Data System (ADS)

Bauer, Helene; Rogowitz, Anna; Grasemann, Benhard; Decker, Kurt

2017-04-01

This study presents microstructural investigations of natural carbonate fault rocks that formed by a suite of different deformation processes, involving hydro-fracturing, dissolution-precipitation creep and cataclasis. Some fault rocks show also clear indications of crystal plastic deformation, which is quite unexpected, as the fault rocks were formed in an upper crustal setting, raising the question of possible strongly localised, low temperature ductile deformation in carbonate rocks. The investigated carbonate fault rocks are from an exhumed, sinistral strike-slip fault at the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps (Austria). The SEMP fault system formed during eastward lateral extrusion of the Eastern Alps in the Oligocene to Lower Miocene. Based on vitrinite reflectance data form intramontane Teritary basins within the Northern Calcareous Alps, a maximum burial depth of 4 km for the investigated fault segment is estimated. The investigated fault accommodated sinistral slip of several hundreds of meters. Microstructural analysis of fault rocks includes scanning electron microscopy, optical microscopy and electron backscattered diffraction mapping. The data show that fault rocks underwent various stages of evolution including early intense veining (hydro-fracturing) and stylolite formation reworked by localised shear zones. Cross cutting relationship reveals that veins never cross cut clay seams accumulated along stylolites. We conclude that pressure solution processes occured after hydro-fracturing. Clay enriched zones localized further deformation, producing a network of small-scale clay-rich shear zones of up to 1 mm thickness anastomosing around carbonate microlithons, varying from several mm down to some µm in size. Clay seams consist of kaolinit, chlorite and illite matrix and form (sub) parallel zones in which calcite was dissolved. Beside pressure solution, calcite microlithons show also ductile deformation microstructures, including deformation twinning, undulose extinction, subgrain rotation recrystallization and even grain boundary migration. Especially coarse grained calcites from veins localized ductile deformation and record dislocation glide. The investigated fault rocks are excellent examples of frictional, pressure solution and crystal plastic deformation processes. We speculated that crystal plastic deformation typical for higher metamorphic shear zones in marbles, can be either produced under much lower temperature conditions or the temperature necessary for crystal plastic deformation was generated by frictional slip or strain heating within the fault zone.

Features of the Kaiser effect in coal specimens at different stages of the triaxial axisymmetric deformation

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

Shkuratnik, V.L.; Filimonov, Y.L.; Kuchurin, S.V.

2007-01-15

The experimental data are presented for the features of formation and manifestation of the acoustic-emission and deformation memory effects in specimens of anthracite at different stages of the triaxial cyclic deformation by the Karman scheme in the pre-limiting and post-limiting zones.

Effect of upsetting deformation temperature on the formation of the fine-grained cast alloy structure of the Ni-Mn-Ga system

NASA Astrophysics Data System (ADS)

Musabirov, I. I.; Safarov, I. M.; Sharipov, I. Z.; Nagimov, M. I.; Koledov, V. V.; Khovailo, V. V.; Mulyukov, R. R.

2017-08-01

The plastic behavior during deformation by upsetting and its effect on the microstructure in the polycrystalline Ni2.19Fe0.04Mn0.77Ga alloy are studied. The temperatures of martensitic and magnetic phase transformations were determined by the method for analyzing the temperature dependence of the specific magnetization as M F = 320 K, A S = 360 K, and T C = 380 K. Using differential scanning calorimetry, it is shown that the phase transition from the ordered phase L21 to the disordered phase B2 is observed in the alloy during sample heating in the temperature range of 930-1070 K. The melting temperature is 1426 K. An analysis of the load curves constructed for sample deposition at temperatures of 773, 873, and 973 K shows that the behavior of the stress-strain curve at a temperature of 773 K is inherent to cold deformation. The behavior of the dependences for 873 and 973 K is typical of hot deformation. After deforming the alloy, its microstructure is studied using backscattered scanning electron microscopy. Plastic deformation of the alloy at study temperatures results in grain structure fragmentation in the localized deformation region. At all temperatures, a recrystallized grain structure is observed. It is found that the structure is heterogeneously recrystallized after upsetting at 973 K due to the process intensity at such a high temperature. The alloy microstructure after plastic deformation at a temperature of 873 K is most homogeneous in terms of the average grain size.

Detecting thermally driven cyclic deformation of an exfoliation sheet with lidar and radar

USGS Publications Warehouse

Collins, Brian D.; Stock, Greg M.

2014-01-01

Rock falls from steep, exfoliating cliffs are common in many landscapes. Of the many mechanisms known to trigger rock falls, thermally driven deformation is among the least quantified, despite potentially being a prevalent trigger due to its occurrence at all times of year. Here we present the results of a field-based monitoring program using instrumentation, ground-based lidar, and ground-based radar to investigate the process of thermally driven deformation of an exfoliation sheet, and the ability of remote sensing tools to capture cyclic expansion and contraction patterns. Our results indicate that thermally driven exfoliation occurs on diurnal cycles and can be measured at the submillimeter to centimeter scale using high-resolution strain gauges, short-range (2 km) radar interfer-ometry.

Deformation and Fabric in Compacted Clay Soils

NASA Astrophysics Data System (ADS)

Wensrich, C. M.; Pineda, J.; Luzin, V.; Suwal, L.; Kisi, E. H.; Allameh-Haery, H.

2018-05-01

Hydromechanical anisotropy of clay soils in response to deformation or deposition history is related to the micromechanics of platelike clay particles and their orientations. In this article, we examine the relationship between microstructure, deformation, and moisture content in kaolin clay using a technique based on neutron scattering. This technique allows for the direct characterization of microstructure within representative samples using traditional measures such as orientation density and soil fabric tensor. From this information, evidence for a simple relationship between components of the deviatoric strain tensor and the deviatoric fabric tensor emerge. This relationship may provide a physical basis for future anisotropic constitutive models based on the micromechanics of these materials.

Effects of freezing-induced cell-fluid-matrix interactions on the cells and extracellular matrix of engineered tissues.

PubMed

Teo, Ka Yaw; DeHoyos, Tenok O; Dutton, J Craig; Grinnell, Frederick; Han, Bumsoo

2011-08-01

The two most significant challenges for successful cryopreservation of engineered tissues (ETs) are preserving tissue functionality and controlling highly tissue-type dependent preservation outcomes. In order to address these challenges, freezing-induced cell-fluid-matrix interactions should be understood, which determine the post-thaw cell viability and extracellular matrix (ECM) microstructure. However, the current understanding of this tissue-level biophysical interaction is still limited. In this study, freezing-induced cell-fluid-matrix interactions and their impact on the cells and ECM microstructure of ETs were investigated using dermal equivalents as a model ET. The dermal equivalents were constructed by seeding human dermal fibroblasts in type I collagen matrices with varying cell seeding density and collagen concentration. While these dermal equivalents underwent an identical freeze/thaw condition, their spatiotemporal deformation during freezing, post-thaw ECM microstructure, and cellular level cryoresponse were characterized. The results showed that the extent and characteristics of freezing-induced deformation were significantly different among the experimental groups, and the ETs with denser ECM microstructure experienced a larger deformation. The magnitude of the deformation was well correlated to the post-thaw ECM structure, suggesting that the freezing-induced deformation is a good indicator of post-thaw ECM structure. A significant difference in the extent of cellular injury was also noted among the experimental groups, and it depended on the extent of freezing-induced deformation of the ETs and the initial cytoskeleton organization. These results suggest that the cells have been subjected to mechanical insult due to the freezing-induced deformation as well as thermal insult. These findings provide insight on tissue-type dependent cryopreservation outcomes, and can help to design and modify cryopreservation protocols for new types of tissues from a pre-developed cryopreservation protocol. Copyright © 2011 Elsevier Ltd. All rights reserved.

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).

Dislocation model of nucleation and development of slip bands and their effect on service life of structural materials subject to cyclic loading

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

Shetulov, D. I.; Andreev, V. V., E-mail: vyach.andreev@mail.ru; Myasnikov, A. M.

Most of the destructions of machine parts are of fatigue character. Under cyclic loading, the surface layer, in which hardening–softening processes rapidly occur, is formed almost at once after its beginning. The interaction of plastic-deformation traces with each other and with other structural elements, such as grains, results in the formation of a characteristic microstructure of the machine-part surface subject to cyclic loadings. The character of accumulation of slip bands and their shape (narrow, wide, twisting, and broken) depends on the conditions under which (under what factors) the cyclic loading occurs. The fatigue-resistance index expressed in terms of the slopemore » of left portion of the fatigue curve linearized in logarithmic coordinates also depends on the set of relevant factors. The dependence of the surface damageability on the fatigue resistance index makes it possible to implement the method of predicting the fatigue curve by the description of the factors acting on a detail or construction. The position of the inflection point on the curve in the highcycle fatigue region (the endurance limit and the number of loading cycles, the ordinate and abscissa of the inflection point on the fatigue curve, respectively) also depends on the set of relevant factors. In combination with the previously obtained value of the slope of the left portion of the curve in the high-cycle fatigue region, this makes it possible to construct an a priori fatigue curve, thus reducing the scope of required fatigue tests and, hence, high expenses because of their long duration and high cost. The scope of tests upon using the developed method of prediction may be reduced to a minimum of one or two samples at the predicted level of the endurance limit.« less

Cyclic Axial-Torsional Deformation Behavior of a Cobalt-Base Superalloy

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

1995-01-01

The cyclic, high-temperature deformation behavior of a wrought cobalt-base super-alloy, Haynes 188, is investigated under combined axial and torsional loads. This is accomplished through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue database has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gage section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. The fatigue behavior of Haynes 188 at 760 C under axial, torsional, and combined axial-torsional loads and the monotonic and cyclic deformation behaviors under axial and torsional loads have been previously reported. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress ,versus engineering shear strain, axial strain versus engineering shear strain. and axial stress versus shear stress spaces are presented for cyclic in-phase and out-of-phase axial-torsional tests. For in-phase tests, three different values of the proportionality constant lambda (the ratio of engineering shear strain amplitude to axial strain amplitude, are examined, viz. 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 degrees with lambda equals 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress-strain and the maximum shear stress-maximum engineering shear strain (Tresca) curves. Comparisons are also made between the hardening behaviors of cyclic axial, torsional, and combined in-phase (lambda = 1.73 and phi = 0) and out-of-phase (lambda = 1.73 and phi = 90') axial-torsional fatigue tests. These comparisons are accomplished through simple Ramberg-Osgood type stress-strain functions for cyclic, axial stress-strain and shear stress-engineering shear strain curves.

Grain-scale investigations of deformation heterogeneities in aluminum alloys

NASA Astrophysics Data System (ADS)

Güler, Baran; Şimşek, Ülke; Yalçınkaya, Tuncay; Efe, Mert

2018-05-01

The anisotropic deformation of Aluminum alloys at micron scale exhibits localized deformation, which has negative implications on the macroscale mechanical and forming behavior. The scope of this work is twofold. Firstly, micro-scale deformation heterogeneities affecting forming behavior of aluminum alloys is investigated through experimental microstructure analysis at large strains and various strain paths. The effects of initial texture, local grain misorientation, and strain paths on the strain localizations are established. In addition to uniaxial tension condition, deformation heterogeneities are also investigated under equibiaxial tension condition to determine the strain path effects on the localization behavior. Secondly, the morphology and the crystallographic data obtained from the experiments is transferred to Abaqus software, in order to predict both macroscopic response and the microstructure evolution though crystal plasticity finite element simulations. The model parameters are identified through the comparison with experiments and the capability of the model to capture real material response is discussed as well.

Post Deformation Annealing Behaviour of Mg-Al-Sn Alloys

NASA Astrophysics Data System (ADS)

Kabir, Abu Syed Humaun; Su, Jing; Sanjari, Mehdi; Jung, In-Ho; Yue, Stephen

In this study, effects of dynamically formed precipitates on the microstructure and texture evolutions were investigated after the post deformation annealing for various times. Two ternary alloys of Mg, Al and Sn were designed, produced and deformed at 300°C at a strain rate of 0.01s-1 to form different amounts of strain induced precipitates during deformation. Subsequent annealing at deformation temperature was performed for up to 4 hours. Microstructures and precipitation were investigated by optical and scanning electron microscopes and macro and micro-texture were measured by X-ray diffraction (XRD) and Electron Back-Scattered Diffraction (EBSD) techniques, respectively. It was found that certain amount of strain induced precipitates was necessary to prevent grain growth for a certain time during annealing by grain boundary pinning effect. Also, texture randomization was possible with the presence of precipitates after certain time of annealing.

High-temperature deformation and microstructural analysis for Si3N4-Sc2O3

NASA Technical Reports Server (NTRS)

Cheong, Deock-Soo; Sanders, William A.

1990-01-01

It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at triple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

High-temperature deformation and microstructural analysis for silicon nitride-scandium(III) oxide

NASA Technical Reports Server (NTRS)

Cheong, Deock-Soo; Sanders, William A.

1992-01-01

It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at tripple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

Cyclic density functional theory: A route to the first principles simulation of bending in nanostructures

NASA Astrophysics Data System (ADS)

Banerjee, Amartya S.; Suryanarayana, Phanish

2016-11-01

We formulate and implement Cyclic Density Functional Theory (Cyclic DFT) - a self-consistent first principles simulation method for nanostructures with cyclic symmetries. Using arguments based on Group Representation Theory, we rigorously demonstrate that the Kohn-Sham eigenvalue problem for such systems can be reduced to a fundamental domain (or cyclic unit cell) augmented with cyclic-Bloch boundary conditions. Analogously, the equations of electrostatics appearing in Kohn-Sham theory can be reduced to the fundamental domain augmented with cyclic boundary conditions. By making use of this symmetry cell reduction, we show that the electronic ground-state energy and the Hellmann-Feynman forces on the atoms can be calculated using quantities defined over the fundamental domain. We develop a symmetry-adapted finite-difference discretization scheme to obtain a fully functional numerical realization of the proposed approach. We verify that our formulation and implementation of Cyclic DFT is both accurate and efficient through selected examples. The connection of cyclic symmetries with uniform bending deformations provides an elegant route to the ab-initio study of bending in nanostructures using Cyclic DFT. As a demonstration of this capability, we simulate the uniform bending of a silicene nanoribbon and obtain its energy-curvature relationship from first principles. A self-consistent ab-initio simulation of this nature is unprecedented and well outside the scope of any other systematic first principles method in existence. Our simulations reveal that the bending stiffness of the silicene nanoribbon is intermediate between that of graphene and molybdenum disulphide - a trend which can be ascribed to the variation in effective thickness of these materials. We describe several future avenues and applications of Cyclic DFT, including its extension to the study of non-uniform bending deformations and its possible use in the study of the nanoscale flexoelectric effect.

Effect of Production Process on Microstructure and Mechanical Properties of Copper Coatings of Jet Charges

NASA Astrophysics Data System (ADS)

Gleener, R. E.; Cheerova, M. N.; Shadiev, B. Sh.; Katyukhin, E. B.

2017-07-01

Special features of formation of the grain structure and mechanical properties of copper during recrystallization annealing after cold deformation with a wide range of reduction are studied. The constants of the Hall-Petch equation are determined for copper, the microstructure of which forms in the course of plastic deformation and subsequent heat treatment. The results of the study are allowed for in the process of production of claddings for jet charges.

Rheological properties of the lower crust and upper mantle beneath Baja California: a microstructural study of xenoliths from San Quintin

NASA Astrophysics Data System (ADS)

Van der Werf, Thomas F.; Chatzaras, Vasileios; Tikoff, Basil; Drury, Martyn R.

2016-04-01

Baja California is an active transtensional rift zone, which links the San Andreas Fault with the East Pacific Rise. The erupted basalts of the Holocene San Quintin volcanic field contain xenoliths, which sample the lower crust and upper mantle beneath Baja California. The aim of this research is to gain insight in the rheology of the lower crust and the upper mantle by investigating the xenolith microstructure. Microstructural observations have been used to determine the dominant deformation mechanisms. Differential stresses were estimated from recrystallized grain size piezometry of plagioclase and clinopyroxene for the lower crust and olivine for the upper mantle. The degree of deformation can be inferred from macroscopic foliations and the deformation microstructures. Preliminary results show that both the lower crust and the upper mantle have been affected by multiple stages of deformation and recrystallization. In addition the dominant deformation mechanism in both the lower crust and the upper mantle is dislocation creep based on the existence of strong crystallographic preferred orientations. The differential stress estimates for the lower crust are 10-29 MPa using plagioclase piezometry and 12-35 MPa using clinopyroxene piezometry. For the upper mantle, differential stress estimates are 10-20 MPa. These results indicate that the strength of the lower crust and the upper mantle are very similar. Our data do not fit with the general models of lithospheric strength and may have important implications for the rheological structure of the lithosphere in transtensional plate margins and for geodynamic models of the region.

Effect of Composition and Deformation on Coarse-Grained Austenite Transformation in Nb-Mo Microalloyed Steels

NASA Astrophysics Data System (ADS)

Isasti, N.; Jorge-Badiola, D.; Taheri, M. L.; López, B.; Uranga, P.

2011-12-01

Thermomechanical processing of microalloyed steels containing niobium can be performed to obtain deformed austenite prior to transformation. Accelerated cooling can be employed to refine the final microstructure and, consequently, to improve both strength and toughness. This general rule is fulfilled if the transformation occurs on a quite homogeneous austenite microstructure. Nevertheless, the presence of coarse austenite grains before transformation in different industrial processes is a usual source of concern, and regarding toughness, the coarsest high-angle boundary units would determine its final value. Sets of deformation dilatometry tests were carried out using three 0.06 pct Nb microalloyed steels to evaluate the effect of Mo alloying additions (0, 0.16, and 0.31 pct Mo) on final transformation from both recrystallized and unrecrystallized coarse-grained austenite. Continuous cooling transformation (CCT) diagrams were created, and detailed microstructural characterization was achieved through the use of optical microscopy (OM), field emission gun scanning electron microscopy (FEGSEM), and electron backscattered diffraction (EBSD). The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling ranges to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformation, moving the CCT curves to higher temperatures and shorter times. However, an increase in the final heterogeneity was observed when BF packets were formed, creating coarse high-angle grain boundary units.

Erosion and Modifications of Tungsten-Coated Carbon and Copper Under High Heat Flux

NASA Astrophysics Data System (ADS)

Liu, Xiang; S, Tamura; K, Tokunaga; N, Yoshida; Zhang, Fu; Xu, Zeng-yu; Ge, Chang-chun; N, Noda

2003-08-01

Tungsten-coated carbon and copper was prepared by vacuum plasma spraying (VPS) and inert gas plasma spraying (IPS), respectively. W/CFC (Tungsten/Carbon Fiber-Enhanced material) coating has a diffusion barrier that consists of W and Re multi-layers pre-deposited by physical vapor deposition on carbon fiber-enhanced materials, while W/Cu coating has a graded transition interface. Different grain growth processes of tungsten coatings under stable and transient heat loads were observed, their experimental results indicated that the recrystallizing temperature of VPS-W coating was about 1400 °C and a recrystallized columnar layer of about 30 μm thickness was formed by cyclic heat loads of 4 ms pulse duration. Erosion and modifications of W/CFC and W/Cu coatings under high heat load, such as microstructure changes of interface, surface plastic deformations and cracks, were investigated, and the erosion mechanism (erosion products) of these two kinds of tungsten coatings under high heat flux was also studied.

Fatigue stress concentration and notch sensitivity in nanocrystalline metals

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

Furnish, Timothy A.; Boyce, Brad L.; Sharon, John A.

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zonesmore » underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.« less

Fatigue stress concentration and notch sensitivity in nanocrystalline metals

DOE PAGES

Furnish, Timothy A.; Boyce, Brad L.; Sharon, John A.; ...

2016-03-11

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zonesmore » underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.« less

Grain refinement and Lattice Imperfections in Commercial Aluminum Alloy Processed by Severe Plastic Deformation

NASA Astrophysics Data System (ADS)

Charfeddine, Saifeddine; Zehani, Karim; Besais, Lotfi; Korchef, Atef

2014-08-01

In the present work, investigations on the microstructure of an aluminum alloy that had been subjected to severe plastic deformation (SPD) by equal channel angular pressing (ECAP), filing and ball milling, were carried out using X-ray diffraction and scanning electron microscopy. SPD leads to lattice distortions, increased dislocation density and an intensive refinement of the microstructure. The refinement and lattice imperfections of the material are greatly affected by the deformation modes and loading performance occurring during SPD. During the milling, the dislocation annihilation increases at higher strains thereby resulting in a smaller crystallite size. After ECAP, the material manifests a strong shear texture and anisotropy of the deformation behavior. Strain anisotropy is less pronounced in filed and ball milled powder particles.

Microstructural and Microanalytical Study on Concrete Exposed to the Sulfate Environment

NASA Astrophysics Data System (ADS)

Qing, Fang; Beixing, Li; Jiangang, Yin; Xiaolu, Yuan

2017-11-01

Microstructural properties have been examined to investigate the effect of mineral admixtures on the sulfate resistance of concrete. Concrete and cement paste specimens made with ordinary Portland cement (OPC) or ordinary Portland cement incorporating 20% fly ash (FA) or 30% ground blast furnace slag (GBFS), were made and exposed to 250 cycles of the cyclic sulfate environment. Microstructural and Microanalytical study was conducted by means of x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and mercury intrusion porosimetry (MIP). Results indicate that the pore structure of concrete after sulfate exposure possesses the fractal feature. The OPC concrete presents more complex pore internal surface, higher porosity and less micro-pores than the concrete incorporating fly ash and GBFS. Portlandite in OPC concrete and OPC-FA concrete is mainly converted to gypsum; while for OPC-GBFS concrete, both gypsum and ettringite are formed. In the cyclic sulfate environment, repeated hydration and dehydration of sulfates produce the expansive stress in pores, aggravating the demolishment of concrete structure.

Hardening mechanisms in olivine single crystal deformed at 1090 °C: an electron tomography study

NASA Astrophysics Data System (ADS)

Mussi, Alexandre; Cordier, Patrick; Demouchy, Sylvie; Hue, Benoit

2017-11-01

The dislocation microstructures in a single crystal of olivine deformed experimentally in uniaxial compression at 1090 °C and under a confining pressure of 300 MPa, have been investigated by transmission electron tomography in order to better understand deformation mechanisms at the microscale relevant for lithospheric mantle deformations. Investigation by electron tomography reveals microstructures, which are more complex than previously described, composed of ? and ? dislocations commonly exhibiting 3D configurations. Numerous mechanisms such as climb, cross-slip, double cross-slip as well as interactions like junction formations and collinear annihilations are the source of this complexity. The diversity observed advocates for microscale deformation of olivine significantly less simple than classic dislocation creep reported in metals or ice close to melting temperature. Deciphering mechanism of hardening in olivine at temperatures where ionic diffusion is slow and is then expected to play very little role is crucial to better understand and thus model deformation at larger scale and at temperatures (900-1100 °C) highly relevant for the lithospheric mantle.

Effect of Deformation Parameters on Microstructure and Properties During DIFT of X70HD Pipeline Steel

NASA Astrophysics Data System (ADS)

Wang, Jian; Zhu, Wei; Xiao, Hong; Zhang, Liang-liang; Qin, Hao; Yu, Yue

2018-02-01

Grain refinement is a critical approach to improve the strength of materials without damaging the toughness. The grains of deformation-induced ferrite are considerably smaller than those of proeutectoid ferrite. Grain refinement is crucial to the application of deformation-induced ferrite. The composition of ferrite and bainite or martensite is important in controlling the performance of X70HD pipeline steel, and cooling significantly influences the control of their ratio and grain size. By analyzing the static and dynamic phase-transition points using Gleeble-3800 thermal simulator, thermal simulations were performed through two-stage deformations in the austenite zone. Ferrite transformation rules were studied with thermal simulation tests under different deformation and cooling parameters based on the actual production of cumulative deformation. The influence of deformation parameters on the microstructure transformation was analyzed. Numerous fine-grain deformation-induced ferrites were obtained by regulating various parameters, including deformation temperature, strain rate, cooling rate, final cooling temperature and other parameters. Results of metallographic observation and microtensile testing revealed that the selection of appropriate parameters can refine the grains and improve the performance of the X70HD pipeline steel.

Crystal plasticity assisted prediction on the yield locus evolution and forming limit curves

NASA Astrophysics Data System (ADS)

Lian, Junhe; Liu, Wenqi; Shen, Fuhui; Münstermann, Sebastian

2017-10-01

The aim of this study is to predict the plastic anisotropy evolution and its associated forming limit curves of bcc steels purely based on their microstructural features by establishing an integrated multiscale modelling approach. Crystal plasticity models are employed to describe the micro deformation mechanism and correlate the microstructure with mechanical behaviour on micro and mesoscale. Virtual laboratory is performed considering the statistical information of the microstructure, which serves as the input for the phenomenological plasticity model on the macroscale. For both scales, the microstructure evolution induced evolving features, such as the anisotropic hardening, r-value and yield locus evolution are seamlessly integrated. The predicted plasticity behaviour by the numerical simulations are compared with experiments. These evolutionary features of the material deformation behaviour are eventually considered for the prediction of formability.

Microstructure and Mechanical Properties of Extruded Gamma Met PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Das, G.; Locci, I.; Whittenberger, J. D.; Lerch, B. A.; Kestler, H.

2003-01-01

A gamma TiAl alloy with a high Nb content is being assessed as a compressor blade material. The microstructure and mechanical properties of extruded Ti-45Al-X(Nb,B,C) (at %) were evaluated in both an as-extruded condition and after a lamellar heat treatment. Tensile behavior of both as-extruded and lamellar heat treated specimens was studied in the temperature range of RT to 926 C. In general, the yield stress and ultimate tensile strength reached relatively high values at room temperature and decreased with increasing deformation temperature. The fatigue strength of both microstructures was characterized at 650 C and compared to a baseline TiAl alloy and to a Ni-base superalloy. Tensile and fatigue specimens were also exposed to 800 C for 200 h in air to evaluate the alloy's environmental resistance. A decrease in ductility was observed at room temperature due to the 800 C exposure but the 650 C fatigue properties were unaffected. Compressive and tensile creep testing between 727 and 1027 C revealed that the creep deformation was reproducible and predictable. Creep strengths reached superalloy-like levels at fast strain rates and lower temperatures but deformation at slower strain rates and/or higher temperature indicated significant weakening for the as-extruded condition. At high temperatures and low stresses, the lamellar microstructure had improved creep properties when compared to the as-extruded material. Microstructural evolution during heat treatment, identification of various phases, and the effect of microstructure on the tensile, fatigue, and creep behaviors is discussed.

Competing Grain Boundary and Interior Deformation Mechanisms with Varying Sizes

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

Zhang, Wei; Gao, Yanfei; Nieh, T. G.

In typical coarse-grained alloys, the dominant plastic deformations are dislocation gliding or climbing, and material strengths can be tuned by dislocation interactions with grain boundaries, precipitates, solid solutions, and other defects. With the reduction of grain size, the increase of material strengths follows the classic Hall-Petch relationship up to nano-grained materials. Even at room temperatures, nano-grained materials exhibit strength softening, or called the inverse Hall-Petch effect, as grain boundary processes take over as the dominant deformation mechanisms. On the other hand, at elevated temperatures, grain boundary processes compete with grain interior deformation mechanisms over a wide range of the appliedmore » stress and grain sizes. This book chapter reviews and compares the rate equation model and the microstructure-based finite element simulations. The latter explicitly accounts for the grain boundary sliding, grain boundary diffusion and migration, as well as the grain interior dislocation creep. Therefore the explicit finite element method has clear advantages in problems where microstructural heterogeneities play a critical role, such as in the gradient microstructure in shot peening or weldment. Furthermore, combined with the Hall-Petch effect and its breakdown, the above competing processes help construct deformation mechanism maps by extending from the classic Frost-Ashby type to the ones with the dependence of grain size.« less

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.

Microstructural characterization of high-manganese austenitic steels with different stacking fault energies

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

Sato, Shigeo, E-mail: s.sato@imr.tohoku.ac.jp; Kwon, Eui-Pyo; Imafuku, Muneyuki

Microstructures of tensile-deformed high-manganese austenitic steels exhibiting twinning-induced plasticity were analyzed by electron backscatter diffraction pattern observation and X-ray diffraction measurement to examine the influence of differences in their stacking fault energies on twinning activity during deformation. The steel specimen with the low stacking fault energy of 15 mJ/m{sup 2} had a microstructure with a high population of mechanical twins than the steel specimen with the high stacking fault energy (25 mJ/m{sup 2}). The <111> and <100> fibers developed along the tensile axis, and mechanical twinning occurred preferentially in the <111> fiber. The Schmid factors for slip and twinning deformationsmore » can explain the origin of higher twinning activity in the <111> fiber. However, the high stacking fault energy suppresses the twinning activity even in the <111> fiber. A line profile analysis based on the X-ray diffraction data revealed the relationship between the characteristics of the deformed microstructures and the stacking fault energies of the steel specimens. Although the variation in dislocation density with the tensile deformation is not affected by the stacking fault energies, the effect of the stacking fault energies on the crystallite size refinement becomes significant with a decrease in the stacking fault energies. Moreover, the stacking fault probability, which was estimated from a peak-shift analysis of the 111 and 200 diffractions, was high for the specimen with low stacking fault energy. Regardless of the difference in the stacking fault energies of the steel specimens, the refined crystallite size has a certain correlation with the stacking fault probability, indicating that whether the deformation-induced crystallite-size refinement occurs depends directly on the stacking fault probability rather than on the stacking fault energies in the present steel specimens. - Highlights: {yields} We studied effects of stacking fault energies on deformed microstructures of steels. {yields} Correlations between texture and occurrence of mechanical twinning are discussed. {yields} Evolutions of dislocations and crystallite are analyzed by line profile analysis.« less

Concurrent multiscale modeling of microstructural effects on localization behavior in finite deformation solid mechanics

DOE PAGES

Alleman, Coleman N.; Foulk, James W.; Mota, Alejandro; ...

2017-11-06

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. In order to resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. Here, the authors demonstrate the use of concurrent multiscale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeled withmore » a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J 2 plasticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. In this study, the framework is applied to model incipient localization in tensile specimens during necking.« less

Concurrent multiscale modeling of microstructural effects on localization behavior in finite deformation solid mechanics

NASA Astrophysics Data System (ADS)

Alleman, Coleman N.; Foulk, James W.; Mota, Alejandro; Lim, Hojun; Littlewood, David J.

2018-02-01

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. To resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. In this study, the authors demonstrate the use of concurrent multiscale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeled with a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J2 plasticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. In this study, the framework is applied to model incipient localization in tensile specimens during necking.

Concurrent multiscale modeling of microstructural effects on localization behavior in finite deformation solid mechanics

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

Alleman, Coleman N.; Foulk, James W.; Mota, Alejandro

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. In order to resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. Here, the authors demonstrate the use of concurrent multiscale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeled withmore » a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J 2 plasticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. In this study, the framework is applied to model incipient localization in tensile specimens during necking.« less

Inferring Spatial Variations of Microstructural Properties from Macroscopic Mechanical Response

PubMed Central

Liu, Tengxiao; Hall, Timothy J.; Barbone, Paul E.; Oberai, Assad A.

2016-01-01

Disease alters tissue microstructure, which in turn affects the macroscopic mechanical properties of tissue. In elasticity imaging, the macroscopic response is measured and is used to infer the spatial distribution of the elastic constitutive parameters. When an empirical constitutive model is used these parameters cannot be linked to the microstructure. However, when the constitutive model is derived from a microstructural representation of the material, it allows for the possibility of inferring the local averages of the spatial distribution of the microstructural parameters. This idea forms the basis of this study. In particular, we first derive a constitutive model by homogenizing the mechanical response of a network of elastic, tortuous fibers. Thereafter, we use this model in an inverse problem to determine the spatial distribution of the microstructural parameters. We solve the inverse problem as a constrained minimization problem, and develop efficient methods for solving it. We apply these methods to displacement fields obtained by deforming gelatin-agar co-gels, and determine the spatial distribution of agar concentration and fiber tortuosity, thereby demonstrating that it is possible to image local averages of microstructural parameters from macroscopic measurements of deformation. PMID:27655420

Recent advances in the deformation processing of titanium alloys

NASA Astrophysics Data System (ADS)

Tamirisakandala, S.; Bhat, R. B.; Vedam, B. V.

2003-12-01

Titanium (Ti) alloys are special-purpose materials used for several critical applications in aerospace as well as non-aerospace industries, and extensive deformation processing is necessary to shape-form these materials, which poses many challenges due to the microstructural complexities. Some of the recent developments in the deformation processing of Ti alloys and usefulness of integrating the material behavior information with simulation schemes while designing and optimizing manufacturing process schedules are discussed in this paper. Discussions are primarily focused on the most important alloy, Ti-6Al-4V and on developing a clear understanding on the influence of key parameters (e.g., oxygen content, starting microstructure, temperature, and strain rate) on the deformation behavior during hot working. These studies are very useful not only for obtaining controlled microstructures but also to design complex multi-step processing sequences to produce defect-free components. Strain-induced porosity (SIP) has been a serious problem during titanium alloy processing, and improved scientific understanding helps in seeking elegant solutions to avoid SIP. A novel high-speed processing technique for microstructural conversion in titanium has been described, which provides several benefits over the conventional slow-speed practices. The hot working behavior of some of the affordable α+β and β titanium alloys being developed recently—namely, Ti-5.5Al-1Fe, Ti-10V-2Fe-3Al, Ti-6.8Mo-4.5Fe-1.5Al, and Ti-10V-4.5Fe-1.5Al—has been analyzed, and the usefulness of the processing maps in optimizing the process parameters and design of hot working schedules in these alloys is demonstrated. Titanium alloys modified with small additions of boron are emerging as potential candidates for replacing structural components requiring high specific strength and stiffness. Efforts to understand the microstructural mechanisms during deformation processing of Ti-B alloys and the issues associated with their processing are discussed.

A Microstructure Study on an AZ31 Magnesium Alloy Tube after Hot Metal Gas Forming Process

NASA Astrophysics Data System (ADS)

Liu, Yi; Wu, Xin

2007-06-01

An AZ31 magnesium alloy tube has been deformed by the hot metal gas forming (HMGF) technique. Microstructures before and after deformation have been investigated by using Electron Backscattered Diffraction (EBSD) and Electron Microscopy. Due to the inhomogeneous distribution by induction heating, there is a temperature gradient distribution along the tube axis. Accordingly, the deformation mechanism is also different. In the middle area of deformation zone where the temperature is ˜410 °C, almost no twinning has been found, whereas at the edge areas of deformation zone where the temperature is ˜200 °C, a high density of twins has been found. EBSD experiments show a weak (0001) fiber texture along the radial direction of the tube before and after deformation in the high-temperature zone. EBSD experiments on the low temperature deformation region were not successful due to the high stored energy. Schmid factor analysis on the EBSD data shows that, despite the (0001) fiber texture, there are still many grains favoring basal slip along both the axis direction and hoop direction.

A technique for recording polycrystalline structure and orientation during in situ deformation cycles of rock analogues using an automated fabric analyser.

PubMed

Peternell, M; Russell-Head, D S; Wilson, C J L

2011-05-01

Two in situ plane-strain deformation experiments on norcamphor and natural ice using synchronous recording of crystal c-axis orientations have been performed with an automated fabric analyser and a newly developed sample press and deformation stage. Without interrupting the deformation experiment, c-axis orientations are determined for each pixel in a 5 × 5 mm sample area at a spatial resolution of 5 μm/pixel. In the case of norcamphor, changes in microstructures and associated crystallographic information, at a strain rate of ∼2 × 10(-5) s(-1), were recorded for the first time during a complete in situ deformation-cycle experiment that consisted of an annealing, deformation and post-deformation annealing path. In the case of natural ice, slower external strain rates (∼1 × 10(-6) s(-1)) enabled the investigation of small changes in the polycrystal aggregate's crystallography and microstructure for small amounts of strain. The technical setup and first results from the experiments are presented. © 2010 The Authors Journal of Microscopy © 2010 Royal Microscopical Society.

Formation of nano-laminated structures in a dry sliding wear-induced layer under different wear mechanisms of 20CrNi2Mo steel

NASA Astrophysics Data System (ADS)

Yin, Cun-hong; Liang, Yi-long; Jiang, Yun; Yang, Ming; Long, Shao-lei

2017-11-01

The microstructures of 20CrNi2Mo steel underneath the contact surface were examined after dry sliding. Scanning Electronic Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Backscattered Diffraction (EBSD) and an ultra-micro-hardness tester were used to characterize the worn surface and dry sliding wear-induced layer. Martensite laths were ultra-refined due to cumulative strains and a large strain gradient that occurred during cyclic loading in wear near the surface. The microstructure evolution in dominant abrasive wear differs from that in adhesive wear. In dominant abrasive wear, only bent martensite laths with high-density deformation dislocations were observed. In contrast, in dominant adhesive wear, gradient structures were formed along the depth from the wear surface. Cross-sectional TEM foils were prepared in a focused ion beam (FIB) to observe the gradient structures in a dry sliding wear-induced layer at depths of approximately 1-5 μm and 5-20 μm. The gradient structures contained nano-laminated structures with an average thickness of 30-50 nm and bent martensite laths. We found that the original martensite laths coordinated with the strain energy and provided origin boundaries for the formation of gradient structures. Geometrically necessary boundaries (GNBs) and isolated dislocation boundaries (IDBs) play important roles in forming the nano-laminated structures.

Microstructural controls on the viscoplasticity of Carbopol, and possible applications to shale deformation studies

NASA Astrophysics Data System (ADS)

Hayman, N. W.; Shafiei, M.; Balhoff, M.; Daigle, H.

2017-12-01

To a first order, sedimentary materials behave in an elastic-plastic manner for most experimental and natural conditions at short time scales. However, long-term patterns of leakage from carbon-capture and storage efforts, and reduced efficiency during unconventional hydrocarbon production, point to a broader range of subsurface behaviors. Our analyses of microstructural and porosity responses to experimental deformation of shale suggest that sedimentary rock deformation is not strictly elastic-plastic. For example, organic matter (OM) in mudrocks can fracture during failure, but elsewhere may be more viscous in the same rock volume. The fracture of OM can be accompanied by some combination of frictional and poroelastic deformation in the surrounding clay aggregates, potentially described by critical-state-line soil mechanics. What is less clear is the possible role of viscoplasticity in sedimentary rock deformation. Though not a good analog material for all rock deformation, the cross-linked polymer Carbopol provides an excellent opportunity to explore controls on viscoplasticity. Above the yield stress, carbopol plastic deformation follows a Herschel-Bulkley model wherein shear stress varies as function of strain rate to a power that is generally <1; i.e. it is a shear-thinning material. The rheology can then be tuned by changing the pH of the gel. Using images obtained from scanning electron microscopy, including using a cryogenic system, we found that a structural transition from a dilute neutralized dispersion to an aggregate of closely packed particulates occurs as the pH of the polymer solution increases. This closely packed microstructure thus controls the yield strength which in turn follows approximately a non-linear relationship with porosity. This "analog material" thus has allowed us to quantify the microstructural length-scales that govern viscoplasticity in this material. Future experiments and numerical modeling can evaluate if a viscoplastic component to sedimentary rock deformation is important during engineering efforts. Such an exploration might focus on porosity-yield stress relationships and the monitoring fracture propagation for a wide range of stress conditions, including those which enhance ductility.

Effect of Cooling Mode on Microstructure and Mechanical Properties of Pipeline Steel for Strain Based Design and Research on its Deformation Mechanism

NASA Astrophysics Data System (ADS)

Hesong, Zhang; Yonglin, Kang

With the rapid development of oil and gas industry long distance pipelines inevitably pass through regions with complex geological activities. In order to avoid large deformation the pipelines must be designed based on strain criteria. In this paper the alloy system of X80 high deformability pipeline steel was designed which was 0.25%Mo-0.05%C-1.75%Mn. The effect of controlled cooling process on microstructure and mechanical properties of X80 high deformability pipeline steel were systematically investigated. Through the two-stage controlled cooling process the microstructure of the X80 high deformability pipeline steel were ferrite, bainite and M/A island. There were two kinds of ferrite which were polygonal ferrite (PF) and quasi-polygonal ferrite (QF). The bainite was granular bainite ferrite (GF). Along with the decrease of the start cooling temperature, the volume fraction of ferrite and M/A both increased, the yield ratio (Y/T) decreased, the uniform elongation (uEl) increased firstly with the content of ferrite increased but then decreased with the content and size of M/A increased. When the finish cooling temperature decreasing, the size of M/A became finer. As the start cooling temperature was 690 °C and the finish cooling temperature was 450 °C the volume fraction of ferrite was 23%, the size of ferrite grain was 5μm, the size of M/A island was below 1μm and the structure uniformity was the best. The deformation mechanism of X80 high deformability pipeline steel was analyzed. The best way to improve the work hardening rate was reducing the size of M/A islands on the premise of a certain volume fraction. The decreasing path of instantaneous strain hardening index (n*-value) showed three stages in the deformation process. The n*-value kept stable in the second stage, the reason was that the retained austenite transformed into martensite and the phase transition improved the strain hardening ability of the microstructure. This phenomenon was called transformation induced plasticity effect (TRIP).

Effect of oxide particles on the stabilization and final microstructure in aluminium

PubMed Central

Bachmaier, Andrea; Pippan, Reinhard

2011-01-01

Bulk aluminium samples containing alumina particles have been produced by different severe plastic deformation methods. Aluminium foils with different initial foil thicknesses were cold rolled to different amounts of strain and aluminium powders were consolidated and deformed by high pressure torsion (HPT). During processing, alumina particles from the foil or particle surface are easily incorporated and dispersed in the bulk material. The influence of these alumina particles on the developing microstructures and the mechanical properties has been studied. PMID:21976787

Surface integrity and fatigue behaviour of electric discharged machined and milled austenitic stainless steel

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

Lundberg, Mattias, E-mail: mattias.lundberg@liu.se

Machining of austenitic stainless steels can result in different surface integrities and different machining process parameters will have a great impact on the component fatigue life. Understanding how machining processes affect the cyclic behaviour and microstructure are of outmost importance in order to improve existing and new life estimation models. Milling and electrical discharge machining (EDM) have been used to manufacture rectangular four-point bend fatigue test samples; subjected to high cycle fatigue. Before fatigue testing, surface integrity characterisation of the two surface conditions was conducted using scanning electron microscopy, surface roughness, residual stress profiles, and hardness profiles. Differences in cyclicmore » behaviour were observed between the two surface conditions by the fatigue testing. The milled samples exhibited a fatigue limit. EDM samples did not show the same behaviour due to ratcheting. Recrystallized nano sized grains were identified at the severely plastically deformed surface of the milled samples. Large amounts of bent mechanical twins were observed ~ 5 μm below the surface. Grain shearing and subsequent grain rotation from milling bent the mechanical twins. EDM samples showed much less plastic deformation at the surface. Surface tensile residual stresses of ~ 500 MPa and ~ 200 MPa for the milled and EDM samples respectively were measured. - Highlights: •Milled samples exhibit fatigue behaviour, but not EDM samples. •Four-point bending is not suitable for materials exhibiting pronounced ratcheting. •LAGB density can be used to quantitatively measure plastic deformation. •Grain shearing and rotation result in bent mechanical twins. •Nano sized grains evolve due to the heat of the operation.« less

Microstructural evolution and deformation behavior of Al-Cu alloys: A Transmission X-ray Microscopy (TXM) and micropillar compression study

DOE PAGES

Kaira, C. Shashank; Kantzos, Christopher; Williams, Jason J.; ...

2017-11-07

In this paper, a unique approach to correlating an evolving 3D microstructure in an Al-Cu alloy and its micro-scale mechanical properties has been introduced. Using these nanoscale three-dimensional microstructures derived from Transmission X-ray Microscopy (TXM), individual contributions from different strengthening mechanisms were quantified. The spatial distribution and morphology of the individual θ' and θ phases were seen to play an important role in influencing dislocation storage. Uniaxial micro-compression experiments were used to quantify the stress-strain response of the alloy at different aging times. Transmission electron microscopy (TEM) aided in discerning dislocation activity at these precipitates. A model is proposed tomore » accurately predict the variation in yield stress by using appropriate morphological parameters from the 3D microstructure and its validity has been corroborated using experimental measurements. Distributions of 2D and 3D inter-precipitate spacing were seen to provide crucial insights on influencing deformation in such precipitation-strengthened alloys. In conclusion, the transition in deformation behavior and origin of numerous strain bursts were investigated using in situ micropillar compression testing.« less

In-depth quantitative analysis of the microstructures produced by Surface Mechanical Attrition Treatment (SMAT)

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

Samih, Y., E-mail: youssef.samih@univ-lorraine.fr; Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures; Beausir, B.

2013-09-15

Electron BackScattered Diffraction (EBSD) maps are used to characterize quantitatively the graded microstructure formed by Surface Mechanical Attrition Treatment (SMAT) and applied here to the 316L stainless steel. In particular, the analysis of GNDs – coupled with relevant and reliable criteria – was used to depict the thickness of each zone identified in the SMAT-affected layers: (i) the “ultrafine grain” (UFG) zone present at the extreme top surface, (ii), the “transition zone” where grains were fragmented under the heavy plastic deformation and, finally, (iii) the “deformed zone” where initial grains are simply deformed. The interest of this procedure is illustratedmore » through the comparative analysis of the effect of some SMAT processing parameters (amplitude of vibration and treatment duration). The UFG and transition zones are more significantly modified than the overall affected thickness under our tested conditions. - Highlights: • EBSD maps are used to characterize quantitatively the microstructure of SMAT treated samples. • Calculation of the GND density to quantify strain gradients • A new method to depict the different zone thicknesses in the SMAT affected layer • Effects of SMAT processing parameters on the surface microstructure evolution.« less

The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions

PubMed Central

Chen, Tao-Hsing; Tsai, Chih-Kai

2015-01-01

In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles. PMID:28788034

Microstructural evolution and deformation behavior of Al-Cu alloys: A Transmission X-ray Microscopy (TXM) and micropillar compression study

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

Kaira, C. Shashank; Kantzos, Christopher; Williams, Jason J.

In this paper, a unique approach to correlating an evolving 3D microstructure in an Al-Cu alloy and its micro-scale mechanical properties has been introduced. Using these nanoscale three-dimensional microstructures derived from Transmission X-ray Microscopy (TXM), individual contributions from different strengthening mechanisms were quantified. The spatial distribution and morphology of the individual θ' and θ phases were seen to play an important role in influencing dislocation storage. Uniaxial micro-compression experiments were used to quantify the stress-strain response of the alloy at different aging times. Transmission electron microscopy (TEM) aided in discerning dislocation activity at these precipitates. A model is proposed tomore » accurately predict the variation in yield stress by using appropriate morphological parameters from the 3D microstructure and its validity has been corroborated using experimental measurements. Distributions of 2D and 3D inter-precipitate spacing were seen to provide crucial insights on influencing deformation in such precipitation-strengthened alloys. In conclusion, the transition in deformation behavior and origin of numerous strain bursts were investigated using in situ micropillar compression testing.« less

Microstructure and Texture of Al-2.5wt.%Mg Processed by Combining Accumulative Roll Bonding and Conventional Rolling

NASA Astrophysics Data System (ADS)

Gatti, J. R.; Bhattacharjee, P. P.

2014-12-01

Evolution of microstructure and texture during severe deformation and annealing was studied in Al-2.5%Mg alloy processed by two different routes, namely, monotonic Accumulative Roll Bonding (ARB) and a hybrid route combining ARB and conventional rolling (CR). For this purpose Al-2.5%Mg sheets were subjected to 5 cycles of monotonic ARB (equivalent strain (ɛeq) = 4.0) processing while in the hybrid route (ARB + CR) 3 cycle ARB-processed sheets were further deformed by conventional rolling to 75% reduction in thickness (ɛeq = 4.0). Although formation of ultrafine structure was observed in the two processing routes, the monotonic ARB—processed material showed finer microstructure but weak texture as compared to the ARB + CR—processed material. After complete recrystallization, the ARB + CR-processed material showed weak cube texture ({001}<100>) but the cube component was almost negligible in the monotonic ARB-processed material-processed material. However, the ND-rotated cube components were stronger in the monotonic ARB-processed material-processed material. The observed differences in the microstructure and texture evolution during deformation and annealing could be explained by the characteristic differences of the two processing routes.

The influence of cell morphology on the compressive fatigue behavior of Ti-6Al-4V meshes fabricated by electron beam melting.

PubMed

Zhao, S; Li, S J; Hou, W T; Hao, Y L; Yang, R; Misra, R D K

2016-06-01

Additive manufacturing technique is a promising approach for fabricating cellular bone substitutes such as trabecular and cortical bones because of the ability to adjust process parameters to fabricate different shapes and inner structures. Considering the long term safe application in human body, the metallic cellular implants are expected to exhibit superior fatigue property. The objective of the study was to study the influence of cell shape on the compressive fatigue behavior of Ti-6Al-4V mesh arrays fabricated by electron beam melting. The results indicated that the underlying fatigue mechanism for the three kinds of meshes (cubic, G7 and rhombic dodecahedron) is the interaction of cyclic ratcheting and fatigue crack growth on the struts, which is closely related to cumulative effect of buckling and bending deformation of the strut. By increasing the buckling deformation on the struts through cell shape design, the cyclic ratcheting rate of the meshes during cyclic deformation was decreased and accordingly, the compressive fatigue strength was increased. With increasing bending deformation of struts, fatigue crack growth in struts contributed more to the fatigue damage of meshes. Rough surface and pores contained in the struts significantly deteriorated the compressive fatigue strength of the struts. By optimizing the buckling and bending deformation through cell shape design, Ti-6Al-4V alloy cellular solids with high fatigue strength and low modulus can be fabricated by the EBM technique. Copyright © 2016 Elsevier Ltd. All rights reserved.

Observations of grain boundary structures and inclusions in the NEEM ice core by combination of light and scanning electron microscopy

NASA Astrophysics Data System (ADS)

Shigeyama, Wataru; Nagatsuka, Naoko; Homma, Tomoyuki; Takata, Morimasa; Goto-Azuma, Kumiko; Weikusat, Ilka; Drury, Martyn R.; Kuiper, Ernst-Jan N.; Pennock, Gill M.; Mateiu, Ramona V.; Azuma, Nobuhiko; Dahl-Jensen, Dorthe

2017-04-01

Dynamics of ice sheets is governed by the flow of the ice and this flow results from the internal deformation of the ice aggregate. The deformation properties of the ice are known to be dependent on several factors, such as microstructure (e.g. crystal grain size and orientation) and impurities. It is well known that ice from glacial periods in ice sheets has a high impurity concentration, and the deformation is reported to be faster than that of non-glacial ice (Faria et al., 2014). However, the mechanisms of the deformation are still not well understood. For a better understanding of ice sheet dynamics, it is a prerequisite to elucidate deformation mechanisms of such impurity-rich ice. The microstructure of a material is a factor that influences mechanical properties and is also an indicator of the dominant deformation mechanisms. The effects of impurities on the deformation and the microstructure depend on chemical compositions, states (viz. insoluble inclusions or soluble ions) and locations of the impurities in the crystal lattice. Therefore, in order to better understand the deformation mechanisms in ice, investigation of relationship between the microstructure and characteristics of the impurities is important. We examined the relationship between grain boundaries and inclusions. Light microscopy (LM) is commonly used to map grain boundary structures on a large area of the ice samples (up to 10 × 10 cm); however, observation of small inclusions < 1 µm is limited due to the spatial resolution of LM. For observations of small impurities in ice cores, scanning electron microscopy (SEM) is useful although limited area (1 × 1 cm) can be examined, and sublimation/surface diffusion on ice in the SEM could move the impurities from their original locations. In order to examine the relationship between the grain boundary and the inclusions, we have combined LM and SEM. We first mapped large areas of the ice samples with LM, and then chose several smaller areas within the mapped area for SEM observations. Energy dispersive X-ray spectroscopy (EDS) was also performed during SEM observations to characterize the chemical composition. Our approach was applied to NEEM glacial ice (1548 m depth, 19.2 kyr BP). The initial results show inclusions observed by LM formed aggregates of sub-micrometer-sized particles, whose main constituents were silicates. Reference Faria, S. H., I. Weikusat and N. Azuma (2014). The microstructure of polar ice. Part II: State of the art, Journal of Structural Geology 61: 21-49.

Microstructural characterization of pipe bomb fragments

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

Gregory, Otto, E-mail: gregory@egr.uri.edu; Oxley, Jimmie; Smith, James

2010-03-15

Recovered pipe bomb fragments, exploded under controlled conditions, have been characterized using scanning electron microscopy, optical microscopy and microhardness. Specifically, this paper examines the microstructural changes in plain carbon-steel fragments collected after the controlled explosion of galvanized, schedule 40, continuously welded, steel pipes filled with various smokeless powders. A number of microstructural changes were observed in the recovered pipe fragments: deformation of the soft alpha-ferrite grains, deformation of pearlite colonies, twin formation, bands of distorted pearlite colonies, slip bands, and cross-slip bands. These microstructural changes were correlated with the relative energy of the smokeless powder fillers. The energy of themore » smokeless powder was reflected in a reduction in thickness of the pipe fragments (due to plastic strain prior to fracture) and an increase in microhardness. Moreover, within fragments from a single pipe, there was a radial variation in microhardness, with the microhardness at the outer wall being greater than that at the inner wall. These findings were consistent with the premise that, with the high energy fillers, extensive plastic deformation and wall thinning occurred prior to pipe fracture. Ultimately, the information collected from this investigation will be used to develop a database, where the fragment microstructure and microhardness will be correlated with type of explosive filler and bomb design. Some analyses, specifically wall thinning and microhardness, may aid in field characterization of explosive devices.« less

Three sets of crystallographic sub-planar structures in quartz formed by tectonic deformation

NASA Astrophysics Data System (ADS)

Derez, Tine; Pennock, Gill; Drury, Martyn; Sintubin, Manuel

2016-05-01

In quartz, multiple sets of fine planar deformation microstructures that have specific crystallographic orientations parallel to planes with low Miller-Bravais indices are commonly considered as shock-induced planar deformation features (PDFs) diagnostic of shock metamorphism. Using polarized light microscopy, we demonstrate that up to three sets of tectonically induced sub-planar fine extinction bands (FEBs), sub-parallel to the basal, γ, ω, and π crystallographic planes, are common in vein quartz in low-grade tectonometamorphic settings. We conclude that the observation of multiple (2-3) sets of fine scale, closely spaced, crystallographically controlled, sub-planar microstructures is not sufficient to unambiguously distinguish PDFs from tectonic FEBs.

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response

PubMed Central

Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-01-01

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process. PMID:29027925

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response.

PubMed

Hu, Li; Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-10-13

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

Toward an MRI-based method to measure non-uniform cartilage deformation: an MRI-cyclic loading apparatus system and steady-state cyclic displacement of articular cartilage under compressive loading.

PubMed

Neu, C P; Hull, M L

2003-04-01

Recent magnetic resonance imaging (MRI) techniques have shown potential for measuring non-uniform deformations throughout the volume (i.e. three-dimensional (3D) deformations) in small orthopedic tissues such as articular cartilage. However, to analyze cartilage deformation using MRI techniques, a system is required which can construct images from multiple acquisitions of MRI signals from the cartilage in both the underformed and deformed states. The objectives of the work reported in this article were to 1) design an apparatus that could apply highly repeatable cyclic compressive loads of 400 N and operate in the bore of an MRI scanner, 2) demonstrate that the apparatus and MRI scanner can be successfully integrated to observe 3D deformations in a phantom material, 3) use the apparatus to determine the load cycle necessary to achieve a steady-state deformation response in normal bovine articular cartilage samples using a flat-surfaced and nonporous indentor in unconfined compression. Composed of electronic and pneumatic components, the apparatus regulated pressure to a double-acting pneumatic cylinder so that (1) load-controlled compression cycles were applied to cartilage samples immersed in a saline bath, (2) loading and recovery periods within a cycle varied in time duration, and (3) load magnitude varied so that the stress applied to cartilage samples was within typical physiological ranges. In addition the apparatus allowed gating for MR image acquisition, and operation within the bore of an MRI scanner without creating image artifacts. The apparatus demonstrated high repeatability in load application with a standard deviation of 1.8% of the mean 400 N load applied. When the apparatus was integrated with an MRI scanner programmed with appropriate pulse sequences, images of a phantom material in both the underformed and deformed states were constructed by assembling data acquired through multiple signal acquisitions. Additionally, the number of cycles to reach a steady-state response in normal bovine articular cartilage was 49 for a total cycle duration of 5 seconds, but decreased to 33 and 27 for increasing total cycle durations of 10 and 15 seconds, respectively. Once the steady-state response was achieved, 95% of all displacements were within +/- 7.42 microns of the mean displacement, indicating that the displacement response to the cyclic loads was highly repeatable. With this performance, the MRI-loading apparatus system meets the requirements to create images of articular cartilage from which 3D deformation can be determined.

Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Laffont, Lydia; Lafont, Marie-Christine; Tanguy, Benoit; Andrieu, Eric

2013-02-01

The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δɛp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown.

Detecting the Extent of Cellular Decomposition after Sub-Eutectoid Annealing in Rolled UMo Foils

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

Kautz, Elizabeth J.; Jana, Saumyadeep; Devaraj, Arun

2017-07-31

This report presents an automated image processing approach to quantifying microstructure image data, specifically the extent of eutectoid (cellular) decomposition in rolled U-10Mo foils. An image processing approach is used here to be able to quantitatively describe microstructure image data in order to relate microstructure to processing parameters (time, temperature, deformation).

Effect of Post-deformation Annealing Treatment on the Microstructural Evolution of a Cold-Worked Corrosion-Resistant Superalloy (CRSA) Steel

NASA Astrophysics Data System (ADS)

Mirzaei, A.; Zarei-Hanzaki, A.; Mohamadizadeh, A.; Lin, Y. C.

2018-03-01

The post-deformation annealing treatments of a commercial cold-worked corrosion-resistant superalloy steel (Sanicro 28 steel) were carried out at different temperatures in the range of 900-1100 °C for different holding durations of 5, 10, and 15 min. The effects of post-deformation annealing time and temperature on the microstructural evolution and subsequent mechanical properties of the processed Sanicro 28 steel were investigated. The observations indicated that twin-twin hardening in cold deformation condition mainly correlates with abundant nucleation of mechanical twins in multiple directions resulting in considerable strain hardening behavior. Microstructural investigations showed that the static recrystallization takes place after isothermal holding at 900 °C for 5 min. Increasing the annealing temperature from 900 to 1050 °C leads to recrystallization development and grain refinement in the as-recrystallized state. In addition, an increase in annealing duration from 5 to 15 min leads to subgrain coarsening and subsequently larger recrystallized grains size. The occurrence of large proportion of the grain refinement, which is achieved in the first annealing stage at 1050 °C after 5 min, is considered as the main factor for the maximum elongation at this stage.

Capability of X-ray diffraction for the study of microstructure of metastable thin films

PubMed Central

Rafaja, David; Wüstefeld, Christina; Dopita, Milan; Motylenko, Mykhaylo; Baehtz, Carsten

2014-01-01

Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species. PMID:25485125

An electron back-scattered diffraction study on the microstructure evolution of severely deformed aluminum AI6061 alloy

NASA Astrophysics Data System (ADS)

Vaseghi, M.; Karimi Taheri, A.; Kim, H. S.

2014-08-01

In this paper dynamic strain ageing behavior in an Al-Mg-Si alloy related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation and ageing effects on microstructure evolutions and strengthening characteristics, the Al6061 alloy were subjected to phi=90° ECAP die for up to 4 passes via route Bc at high temperatures. For investigating the effects of ageing temperature and strain rate in ECAP, Vickers hardness tests were performed. The combination of the ECAP process with dynamic ageing at higher temperatures resulted in a significant increase in hardness. The microstructural evolution of the samples was studied using electron back-scattering diffraction (EBSD). The grains of Al6061 aluminum alloy were refined significantly at 100 and 150 °C with greater pass numbers and the distributions of grain size tended to be more uniform with pass number increasing. Frequency of sub-boundaries and low angle grain boundaries (LAGBs) increased at initial stage of deformation, and sub-boundaries and LAGBs evolved into highangle grain boundaries (HAGBs) with further deformation, which resulted in the high frequency of HAGBs in the alloy after ECAP 4 passes.

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.

Strain Characterization and Microstructure Evolution Under Deformation in 2060 Alloy

NASA Astrophysics Data System (ADS)

Jin, X.; Zhang, G. D.; Zhao, Y. F.; Xue, F.

2018-05-01

A new method of DIC combined with EBSD is developed for the characterization of strain and microstructure evolution during bending. The traditional microhardness point and DIC methods are used to study the microstructure evolution in 2060 alloy during bending; the interested area suffers under tensile stress, the microstructure evolution is collected by SEM, EBSD, digital image correlation (DIC) method during bending. The results shows that the DIC method can both realize the strain tensor characterization of the interested area, and can also express the local strain tensor in the micro-area even more. The degree of grain division in the process of deformation is related to the strain in this region; the grains have larger strain of small angle grain boundary (SLGBs), which results in a new micro-organizational structure. The misorientation is smaller with larger strain degree while the misorientation is larger with smaller strain.

Micro-mechanisms of Surface Defects Induced on Aluminum Alloys during Plastic Deformation at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Gali, Olufisayo A.

Near-surface deformed layers developed on aluminum alloys significantly influence the corrosion and tribological behavior as well as reduce the surface quality of the rolled aluminum. The evolution of the near-surface microstructures induced on magnesium containing aluminum alloys during thermomechanical processing has been investigated with the aim generating an understanding of the influence of individual forming parameters on its evolution and examine the microstructure of the roll coating induced on the mating steel roll through material transfer during rolling. The micro-mechanisms related to the various features of near-surface microstructure developed during tribological conditions of the simulated hot rolling process were identified. Thermomechanical processing experiments were performed with the aid of hot rolling (operating temperature: 550 to 460 °C, 4, 10 and 20 rolling pass schedules) and hot forming (operating temperature: 350 to 545 °C, strain rate: 4 x 10-2 s-1) tribo-simulators. The surface, near-surface features and material transfer induced during the elevated temperature plastic deformation were examined and characterized employing optical interferometry, SEM/EDS, FIB and TEM. Near-surface features characterized on the rolled aluminum alloys included; cracks, fractured intermetallic particles, aluminum nano-particles, oxide decorated grain boundaries, rolled-in oxides, shingles and blisters. These features were related to various individual rolling parameters which included, the work roll roughness, which induced the formation of shingles, rolling marks and were responsible for the redistribution of surface oxide and the enhancements of the depth of the near-surface damage. The enhanced stresses and strains experienced during rolling were related to the formation and propagation of cracks, the nanocrystalline structure of the near-surface layers and aluminum nano-particles. The mechanism of the evolution of the near-surface microstructure were determined to include grain boundary sliding which induced the cracks at the surface and subsurface of the alloy, magnesium diffusion to free surfaces, crack propagation from shear stresses and the shear strains inducing the nanocrystalline grain structure, the formation of shingles by the shear deformation of micro-wedges induced by the work roll grooves, and the deformation of this oxide covered micro-wedges inducing the rolled-in oxides. Magnesium diffusion to free surfaces was identified as inducing crack healing due to the formation of MgO within cracks and was responsible for the oxide decorated grain boundaries. An examination of the roll coating revealed a complex layered microstructure that was induced through tribo-chemical and mechanical entrapment mechanisms. The microstructure of the roll coating suggested that the work roll material and the rolled aluminum alloy were essential in determining its composition and structure. Subsequent hot forming processes revealed the rich oxide-layer of the near-surface microstructure was beneficial for reducing the coefficient of friction during tribological contact with the steel die. Damage to the microstructure include cracks induced from grain boundary sliding of near-surface grains and the formation of oxide fibres within cracks of the near-surface deformed layers.

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.

Applications for evaluation of physical properties - An example of siliceous rock permeability -

NASA Astrophysics Data System (ADS)

Ojima, T.

2015-12-01

ODP Leg. 186, two sites (Site 1150 and Site 1151) were drilled on the continental slope of the deep-sea forearc basin of northern Japan. Diatomaceous sediments were recovered Site 1150 and Site 1151, and the depth of each site is 1181.60 mbsf and 1113.60 mbsf, respectively. This area is under the influence of the Oyashio current and is one of the highly bio-productive regions of the North Pacific Ocean (Motoyama et al., 2004). The combination of high productivity and active tectonic deformation that often caused high rate accumulating of fossil and organic rich sediments. Likewise, IODP Exp. 341 was implemented on off South Alaska. Pelagic and MTD 's layer were recognized with IRD(Ice Rafted Debris). In Tohoku, The onboard results of porosity measurements show high value (50-70 %) down to 1000 mbsf, and obviously higher than nearby subduction trench, Nankai Trough (Taylor and Fisher, 1993). There is a possibility that diatomaceous shell keep a frame structure from effective stress and load pressure. On another drilling site result, DSDP Leg. 19 located 60 km to the north of ODP sites, was reported high value of porosity, but recognized only shallow range (>500 mbsf) (Shephard and Bryant, 1980). Also, South Alaska sediments show high sedimentation rate and cyclic MTD's Layer. Permeability was lower than Tohoku sediments in spite of upper depth. We focused on the relationships between physical property, microstructure, and logging data at deep range(-1000 mbsf). Logging data were collected using wireline logging (Sacks and Suyehiro, 2003; IODP Prel. Rept., 341., 2014). Based on these results, it is expected that microstructure and logging can be integrated into a general model of core-log correlation. In this presentation, We show results of microstructure using SEM, measured physical properties, and wireline logging data, respectively.

Multiaxial mechanical response and constitutive modeling of esophageal tissues: Impact on esophageal tissue engineering.

PubMed

Sommer, Gerhard; Schriefl, Andreas; Zeindlinger, Georg; Katzensteiner, Andreas; Ainödhofer, Herwig; Saxena, Amulya; Holzapfel, Gerhard A

2013-12-01

Congenital defects of the esophagus are relatively frequent, with 1 out of 2500 babies suffering from such a defect. A new method of treatment by implanting tissue engineered esophagi into newborns is currently being developed and tested using ovine esophagi. For the reconstruction of the biological function of native tissues with engineered esophagi, their cellular structure as well as their mechanical properties must be considered. Since very limited mechanical and structural data for the esophagus are available, the aim of this study was to investigate the multiaxial mechanical behavior of the ovine esophagus and the underlying microstructure. Therefore, uniaxial tensile, biaxial tensile and extension-inflation tests on esophagi were performed. The underlying microstructure was examined in stained histological sections through standard optical microscopy techniques. Moreover, the uniaxial ultimate tensile strength and residual deformations of the tissue were determined. Both the mucosa-submucosa and the muscle layers showed nonlinear and anisotropic mechanical behavior during uniaxial, biaxial and inflation testing. Cyclical inflation of the intact esophageal tube caused marked softening of the passive esophagi in the circumferential direction. The rupture strength of the mucosa-submucosa layer was much higher than that of the muscle layer. Overall, the ovine esophagus showed a heterogeneous and anisotropic behavior with different mechanical properties for the individual layers. The intact and layer-specific multiaxial properties were characterized using a well-known three-dimensional microstructurally based strain-energy function. This novel and complete set of data serves the basis for a better understanding of tissue remodeling in diseased esophagi and can be used to perform computer simulations of surgical interventions or medical-device applications. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Microstructural evidence of melting in crustal rocks (Invited)

NASA Astrophysics Data System (ADS)

Holness, M. B.; Cesare, B.; Sawyer, E. W.

2010-12-01

The signature of the former presence of melt on a microscopic scale is highly variable, subject to modification both during the melting event and during its subsequent history. Static pyrometamorphism results in melt films on grain boundaries between reactant phases. If a volume increase is involved, melting results in hydrofracture. On a longer timescale, as demonstrated by fragments of the crustal source in lava flows at El Hoyazo (SE Spain), melt occurs throughout the rock. These examples are highly unusual: the great majority of rocks that underwent melting cooled more slowly, permitting microstructural modification driven by a combination of textural equilibration, reaction and deformation. In the absence of deformation, and at constant temperature, melt-bearing rocks approach textural equilibrium, characterised by uniform grain size, smoothly curved grain boundaries and the establishment at all three-grain junctions of the equilibrium dihedral angle. The dihedral angle controls melt connectivity, with consequences for melt mobility and rock rheology. However, deformation is the rule rather than the exception in regional metamorphic terrains with profound effects on melt distribution. If deformation occurs predominantly by diffusive processes, textural equilibration can keep pace. At higher deformation rates melt is squeezed into planar pockets aligned parallel to the shearing direction or perpendicular to the extensional stress. Microstructures formed during solidification are controlled by cooling rate, H2O, and the size of the melt pockets. Large pockets solidify to look like igneous rocks. In small pores the supersaturation required for crystal growth is high and melt persist to lower temperatures, even being preserved as tiny glassy inclusions (“nanogranites”) in regional terranes. The pore size effect changes crystallization order, resulting in small, highly cuspate grains on grain boundaries with low dihedral angles. Crystallisation microstructures of poly-component liquids are highly dependent on diffusion rates, and therefore H2O content. Dry conditions result in diffusion-limited crystallisation to form intergrowths and symplectites (e.g. granophyre). The cooling rate must be slow in order to nucleate and grow individual grains from the melt. If the melt was primarily concentrated in thick films on grain boundaries this results in the “string of beads” texture. If there is sufficient water, and the rocks stay sufficiently hot, the microstructures will move towards a granular texture, driven by the reduction in interfacial energy. Highly cuspate pseudomorphs of melt at three-grain junctions will become rounded as the dihedral angle increases (generally towards the range 110-140°). Melt-related microstructures are more likely to be retained in dry rocks: in migmatite terranes in which melting was driven by infiltration of aqueous fluids and where melt extraction wasn’t pervasive, microstructures are likely to have been significantly modified by sub-solidus recrystallisation, especially likely if the rock underwent intense deformation on the retrograde path.

Comparison of thermal modeling, microstructural analysis, and Ti-in-quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA

NASA Astrophysics Data System (ADS)

Nevitt, Johanna M.; Warren, Jessica M.; Kidder, Steven; Pollard, David D.

2017-03-01

Granitic plutons commonly preserve evidence for jointing, faulting, and ductile fabric development during cooling. Constraining the spatial variation and temporal evolution of temperature during this deformation could facilitate an integrated analysis of heterogeneous deformation over multiple length-scales through time. Here, we constrain the evolving temperature of the Lake Edison granodiorite within the Mount Abbot Quadrangle (central Sierra Nevada, CA) during late Cretaceous deformation by combining microstructural analysis, titanium-in-quartz thermobarometry (TitaniQ), and thermal modeling. Microstructural and TitaniQ analyses were applied to 12 samples collected throughout the pluton, representative of either the penetrative "regional" fabric or the locally strong "fault-related" fabric. Overprinting textures and mineral assemblages indicate the temperature decreased from 400-500°C to <350°C during faulting. TitaniQ reveals consistently lower Ti concentrations for partially reset fault-related fabrics (average: 12 ± 4 ppm) than for regional fabrics (average: 31 ± 12 ppm), suggesting fault-related fabrics developed later, following a period of pluton cooling. Uncertainties, particularly in TiO2 activity, significantly limit further quantitative thermal estimates using TitaniQ. In addition, we present a 1-D heat conduction model that suggests average pluton temperature decreased from 585°C at 85 Ma to 332°C at 79 Ma, consistent with radiometric age data for the field. Integrated with the model results, microstructural temperature constraints suggest faulting initiated by ˜83 Ma, when the temperature was nearly uniform across the pluton. Thus, spatially heterogeneous deformation cannot be attributed to a persistent temperature gradient, but may be related to regional structures that develop in cooling plutons.

Microstructural, textural and thermal evolution of an exhumed strike-slip fault and insights into localization and rheological transition

NASA Astrophysics Data System (ADS)

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

2016-04-01

The presence of deep exhumed crustal rocks with a dominant but contrasting mineralogy results in shear concentration in the rheological weakest layer, which exhibits contrasting patterns of fabrics and thermal conditions during their formation. We tested a combination of methodologies including microstructural and textural investigations, geochronology and geothermometry on deformed rocks from exhumed strike-slip fault, Ailao Shan-Red River, SE, Asian. Results indicate that the exhumed deep crustal rocks since late Oligocene (ca. 28 Ma) to Pliocene (ca. 4 Ma) typically involve dynamic microstructural, textural and thermal evolution processes, which typically record a progressive deformation and syn-kinematic reactions from ductile to semi-ductile and brittle behavior during exhumation. This transformation also resulted in dramatic strength reduction that promoted strain localization along the strike-slip and transtensional faults. Detailed analysis has revealed the co-existence of microfabrics ranging from high-temperatures (granulite facies conditions) to overprinting low-temperatures (lower greenschist facies conditions). The high-temperature microstructures and textures are in part or entirely altered by subsequent, overprinting low-temperature shearing. In quartz-rich rocks, quartz was deformed in the dislocation creep regime and records transition of microfabrics and slip systems during decreasing temperature, which lasted until retrogression related to final exhumation. As a result, grain-size reduction associated by fluids circulating within the strike-slip fault zone at brittle-ductile transition leads to rock softening, which resulted in strain localization, weak rock rheology and the overall hot thermal structure of the crust. Decompression occurred during shearing and as a result of tectonic exhumation. All these results demonstrate that the ductile to ductile-brittle transition involves a combination of different deformation mechanisms, rheological transition features and feedbacks between deformation, decreasing temperature and fluids.

Crack tip field and fatigue crack growth in general yielding and low cycle fatigue

NASA Technical Reports Server (NTRS)

Minzhong, Z.; Liu, H. W.

1984-01-01

Fatigue life consists of crack nucleation and crack propagation periods. Fatigue crack nucleation period is shorter relative to the propagation period at higher stresses. Crack nucleation period of low cycle fatigue might even be shortened by material and fabrication defects and by environmental attack. In these cases, fatigue life is largely crack propagation period. The characteristic crack tip field was studied by the finite element method, and the crack tip field is related to the far field parameters: the deformation work density, and the product of applied stress and applied strain. The cyclic carck growth rates in specimens in general yielding as measured by Solomon are analyzed in terms of J-integral. A generalized crack behavior in terms of delta is developed. The relations between J and the far field parameters and the relation for the general cyclic crack growth behavior are used to analyze fatigue lives of specimens under general-yielding cyclic-load. Fatigue life is related to the applied stress and strain ranges, the deformation work density, crack nucleus size, fracture toughness, fatigue crack growth threshold, Young's modulus, and the cyclic yield stress and strain. The fatigue lives of two aluminum alloys correlate well with the deformation work density as depicted by the derived theory. The general relation is reduced to Coffin-Manson low cycle fatigue law in the high strain region.

Deformation mechanisms in experimentally deformed Boom Clay

NASA Astrophysics Data System (ADS)

Desbois, Guillaume; Schuck, Bernhard; Urai, Janos

2016-04-01

Bulk mechanical and transport properties of reference claystones for deep disposal of radioactive waste have been investigated since many years but little is known about microscale deformation mechanisms because accessing the relevant microstructure in these soft, very fine-grained, low permeable and low porous materials remains difficult. Recent development of ion beam polishing methods to prepare high quality damage free surfaces for scanning electron microscope (SEM) is opening new fields of microstructural investigation in claystones towards a better understanding of the deformation behavior transitional between rocks and soils. We present results of Boom Clay deformed in a triaxial cell in a consolidated - undrained test at a confining pressure of 0.375 MPa (i.e. close to natural value), with σ1 perpendicular to the bedding. Experiments stopped at 20 % strain. As a first approximation, the plasticity of the sample can be described by a Mohr-Coulomb type failure envelope with a coefficient of cohesion C = 0.117 MPa and an internal friction angle ϕ = 18.7°. After deformation test, the bulk sample shows a shear zone at an angle of about 35° from the vertical with an offset of about 5 mm. We used the "Lamipeel" method that allows producing a permanent absolutely plane and large size etched micro relief-replica in order to localize and to document the shear zone at the scale of the deformed core. High-resolution imaging of microstructures was mostly done by using the BIB-SEM method on key-regions identified after the "Lamipeel" method. Detailed BIB-SEM investigations of shear zones show the following: the boundaries between the shear zone and the host rock are sharp, clay aggregates and clastic grains are strongly reoriented parallel to the shear direction, and the porosity is significantly reduced in the shear zone and the grain size is smaller in the shear zone than in the host rock but there is no evidence for broken grains. Comparison of microstructures within the host rock and the undeformed sample shows that the sample underwent compaction prior shearing that results in a change of power law exponent of the pore size distribution within the clay matrix and a slight reorientation of clastic grains' long axis perpendicular to σ1. Microstructures in the shear zone indicate ductile behavior before the specimen's failure. Deformation mechanisms are bending of clay plates and sliding along clay-clay contacts. Strain is strongly localised in thin, anastomosing zones of strong preferred orientation, producing slickensided shear surfaces common in shallow clays. There is no evidence for intragranular cracking.We propose that the deformation localizes in regions without hard quartz grains.

Structural and microstructural evolution of fault zones in Cretaceous poorly lithified sandstones of the Rio do Peixe basin, Paraiba, NE Brazil

NASA Astrophysics Data System (ADS)

Balsamo, Fabrizio; Nogueira, Francisco; Storti, Fabrizio; Bezerra, Francisco H. R.; De Carvalho, Bruno R.; André De Souza, Jorge

2017-04-01

In this contribution we describe the structural architecture and microstructural features of fault zones developed in Cretaceous, poorly lithified sandstones of the Rio do Peixe basin, NE Brazil. The Rio do Peixe basin is an E-W-trending, intracontinental half-graben basin developed along the Precambrian Patos shear zone where it is abutted by the Porto Alegre shear zone. The basin formed during rifting between South America and Africa plates and was reactivated and inverted in a strike-slip setting during the Cenozoic. Sediments filling the basin consist of an heterolithic sequence of alternating sandstones, conglomerates, siltstone and clay-rich layers. These lithologies are generally poorly lithified far from the major fault zones. Deformational structures in the basin mostly consist of deformation band-dominated fault zones. Extensional and strike-slip fault zones, clusters of deformation bands, and single deformation bands are commonly well developed in the proximity of the basin-boundary fault systems. All deformation structures are generally in positive relief with respect to the host rocks. Extensional fault zones locally have growth strata in their hangingwall blocks and have displacement generally <10 m. In map view, they are organized in anastomosed segments with high connectivity. They strike E-W to NE-SW, and typically consist of wide fault cores (< 1 m in width) surrounded by up to few-meter wide damage zones. Fault cores are characterized by distributed deformation without pervasive strain localization in narrow shear bands, in which bedding is transposed into foliation imparted by grain preferred orientation. Microstructural observations show negligible cataclasis and dominant non-destructive particulate flow, suggesting that extensional fault zones developed in soft-sediment conditions in a water-saturated environment. Strike-slip fault zones commonly overprint the extensional ones and have displacement values typically lower than about 2 m. They are arranged in conjugate system consisting of NNW-SSE- and WNW-ESE-trending fault zones with left-lateral and right-lateral kinematics, respectively. Compared to extensional fault zones, strike-slip fault zones have narrow fault cores (few cm thick) and up to 2-3 m-thick damage zones. Microstructural observations indicate that cataclasis with pervasive grain size reduction is the dominant deformation mechanisms within the fault core, thus suggesting that late-stage strike-slip faulting occurred when sandstones were partially lithified by diagenetic processes. Alternatively, the change in deformation mechanisms may indicate faulting at greater depth. Structural and microstructural data suggest that fault zones in the Rio do Peixe basin developed in a progression from "ductile" (sensu Rutter, 1986) to more "brittle" deformation during changes from extensional to strike-slip kinematic fields. Such rheological and stress configuration evolution is expected to impact the petrophysical and permeability structure of fault zones in the study area.

Prediction of microstructure, residual stress, and deformation in laser powder bed fusion process

NASA Astrophysics Data System (ADS)

Yang, Y. P.; Jamshidinia, M.; Boulware, P.; Kelly, S. M.

2018-05-01

Laser powder bed fusion (L-PBF) process has been investigated significantly to build production parts with a complex shape. Modeling tools, which can be used in a part level, are essential to allow engineers to fine tune the shape design and process parameters for additive manufacturing. This study focuses on developing modeling methods to predict microstructure, hardness, residual stress, and deformation in large L-PBF built parts. A transient sequentially coupled thermal and metallurgical analysis method was developed to predict microstructure and hardness on L-PBF built high-strength, low-alloy steel parts. A moving heat-source model was used in this analysis to accurately predict the temperature history. A kinetics based model which was developed to predict microstructure in the heat-affected zone of a welded joint was extended to predict the microstructure and hardness in an L-PBF build by inputting the predicted temperature history. The tempering effect resulting from the following built layers on the current-layer microstructural phases were modeled, which is the key to predict the final hardness correctly. It was also found that the top layers of a build part have higher hardness because of the lack of the tempering effect. A sequentially coupled thermal and mechanical analysis method was developed to predict residual stress and deformation for an L-PBF build part. It was found that a line-heating model is not suitable for analyzing a large L-PBF built part. The layer heating method is a potential method for analyzing a large L-PBF built part. The experiment was conducted to validate the model predictions.

XRD and EBSD analysis of anisotropic microstructure development in cold rolled F138 stainless steel

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

De Vincentis, N.S., E-mail: devincentis@ifir-conic

The microstructural characteristics of deformation-processed materials highly influence their mechanical properties. For a complete characterization of a microstructure both local and global information must be gathered, which requires the combination of different analysis techniques. X-ray and Electron Backscatter Diffraction were used in the present paper to characterize the deformation induced in a cold rolled F138 austenitic stainless steel sample. The results obtained using laboratory and synchrotron X-ray sources were compared and combined with EBSD quantitative results, allowing the global and local characterization and orientation dependence of the deformation microstructure. A particular behavior was observed in the XRD data corresponding tomore » the planes with < 220 >∥ ND, likely due to a smaller amount of defects accumulated in the crystals with that particular orientation. EBSD was used to separate the scans data into partitions and to calculate misorientation variables and parameters, showing that this behavior can be attributed to a combination of larger grain sizes, lower local boundary misorientations and dislocation densities for crystals having < 220 >∥ ND. Several conclusions, of general validity for the evaluation of microstructure anisotropy, can be extracted from the results. - Highlights: •Combined XRD and EBSD for studying microstructure gave a superb insight on anisotropic accumulation of defects. •W-H and CMWP methods were applied for checking consistency of results. •XRD showed that a smaller accumulation of defects occurred in crystals with < 220 >∥ ND. •High brilliance X-ray beam allowed to study the anisotropy of defect accumulation.« less

Prediction of microstructure, residual stress, and deformation in laser powder bed fusion process

NASA Astrophysics Data System (ADS)

Yang, Y. P.; Jamshidinia, M.; Boulware, P.; Kelly, S. M.

2017-12-01

Laser powder bed fusion (L-PBF) process has been investigated significantly to build production parts with a complex shape. Modeling tools, which can be used in a part level, are essential to allow engineers to fine tune the shape design and process parameters for additive manufacturing. This study focuses on developing modeling methods to predict microstructure, hardness, residual stress, and deformation in large L-PBF built parts. A transient sequentially coupled thermal and metallurgical analysis method was developed to predict microstructure and hardness on L-PBF built high-strength, low-alloy steel parts. A moving heat-source model was used in this analysis to accurately predict the temperature history. A kinetics based model which was developed to predict microstructure in the heat-affected zone of a welded joint was extended to predict the microstructure and hardness in an L-PBF build by inputting the predicted temperature history. The tempering effect resulting from the following built layers on the current-layer microstructural phases were modeled, which is the key to predict the final hardness correctly. It was also found that the top layers of a build part have higher hardness because of the lack of the tempering effect. A sequentially coupled thermal and mechanical analysis method was developed to predict residual stress and deformation for an L-PBF build part. It was found that a line-heating model is not suitable for analyzing a large L-PBF built part. The layer heating method is a potential method for analyzing a large L-PBF built part. The experiment was conducted to validate the model predictions.

Analysis of Plastic Flow Instability During Superplastic Deformation of the Zn-Al Eutectoid Alloy Modified with 2 wt.% Cu

NASA Astrophysics Data System (ADS)

Ramos-Azpeitia, Mitsuo; Elizabeth Martínez-Flores, E.; Hernandez-Rivera, Jose Luis; Torres-Villaseñor, Gabriel

2017-11-01

The aim of this work is to analyze the plastic flow instability in Zn-21Al-2Cu alloy deformed under 10-3 s-1 and 513 K, which are optimum conditions for inducing superplastic behavior in this alloy. An evaluation using the Hart and Wilkinson-Caceres criteria showed that the limited stability of plastic flow observed in this alloy is related to low values of the strain-rate sensitivity index ( m) and the strain-hardening coefficient ( γ), combined with the tendency of these parameters to decrease depending on true strain ( ɛ). The reduction in m and γ values could be associated with the early onset of plastic instability and with microstructural changes observed as function of the strain. Grain growth induced by deformation seems to be important during the first stage of deformation of this alloy. However, when ɛ > 0.4 this growth is accompanied by other microstructural rearrangements. These results suggest that in this alloy, a grain boundary sliding mechanism acts to allow a steady superplastic flow only for ɛ < 0.4. For ɛ values between 0.4 and 0.7, observed occurrences of microstructural changes and severe neck formation lead to the supposition that there is a transition in the deformation mechanism. These changes are more evident when ɛ > 0.7 as another mechanism is thought to take over.

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

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

Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling,more » are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the harmonic generation method to tubular mechanical test specimens and pipes for nondestructive evaluation. Tubular specimens and pipes act as waveguides, thus we applied the acoustic harmonic generation method to guided waves in both plates and shells. Magnetostrictive transducers were used to generate and receive guided wave modes in the shell sample and the received signals were processed to show the sensitivity of higher harmonic generation to microstructure evolution. Modeling was initiated to correlate higher harmonic generation with the microstructure that will lead to development of a life prediction model that is informed by the nonlinear acoustics measurements.« less

The Fatigue Behavior of Built-Up Welded Beams of Commercially Pure Titanium

NASA Astrophysics Data System (ADS)

Patnaik, Anil; Poondla, Narendra; Bathini, Udaykar; Srivatsan, T. S.

2011-10-01

In this article, the results of a recent study aimed at evaluating, understanding, and rationalizing the extrinsic influence of fatigue loading on the response characteristics of built-up welded beams made from commercially pure titanium (Grade 2) are presented and discussed. The beams were made from welding plates and sheets of titanium using the pulsed gas metal arc welding technique to form a structural beam having an I-shaped cross section. The welds made for the test beams of the chosen metal were fillet welds using a matching titanium filler metal wire. The maximum and minimum load values at which the built-up beams were cyclically deformed were chosen to be within the range of 22-45% of the maximum predicted flexural static load. The beams were deformed in fatigue at a stress ratio of 0.1 and constant frequency of 5 Hz. The influence of the ratio of maximum load with respect to the ultimate failure load on fatigue performance, quantified in terms of fatigue life, was examined. The percentage of maximum load to ultimate load that resulted in run-out of one million cycles was established. The overall fracture behavior of the failed beam sample was characterized by scanning electron microscopy observations to establish the conjoint influence of load severity, intrinsic microstructural effects, and intrinsic fracture surface features in governing failure by fracture.

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

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

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Creep mechanisms of a new Ni-Co-base disc superalloy at an intermediate temperature.

PubMed

Yuan, Y; Gu, Y F; Zhong, Z H; Osada, T; Cui, C Y; Tetsui, T; Yokokawa, T; Harada, H

2012-10-01

The microstructures of a new Ni-Co-base disc superalloy, TMW-4M3, before and after the creep test at 725 °C/630 MPa have been systematically investigated by transmission electron microscopy (TEM). The crept microstructures were marked as three different deformation stages (I, II and III) corresponding to the gradually increased strain. At stage I, stacking fault (SF) shearing was the main deformation mechanism. The SF was extrinsic and lay on {111} plane. However, deformation microtwinning became the dominant mode at stage II and III. The average spacing of deformation twins decreased from 109 ± 15 nm at stage II to 76 ± 12 nm at stage III, whereas the twin thickness did not change significantly. The influence of stacking fault energy (SFE) of γ matrix on the deformation mechanism is discussed. It is suggested that lower SFE in TMW-4M3 is partly responsible for the enhanced creep resistance. © 2012 The Authors Journal of Microscopy © 2012 Royal Microscopical Society.

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

DOE PAGES

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.; ...

2017-11-30

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Effects of neutron irradiation on deformation behavior of nickel-base fastener alloys

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

Bajaj, R.; Mills, W.J.; Kammenzind, B.F.

1999-07-01

This paper presents the effects of neutron irradiation on the fracture behavior and deformation microstructure of high-strength nickel-base alloy fastener materials, Alloy X-750 and Alloy 625. Alloy X-750 in the HTH condition, and Alloy 625 in the direct aged condition were irradiated to a fluence of 2.4x10{sup 20} n/cm{sup 2} at 264 C in the Advanced Test Reactor. Deformation structures at low strains were examined. It was previously shown that Alloy X-750 undergoes hardening, a significant degradation in ductility and an increase in intergranular fracture. In contrast, Alloy 625 had shown softening with a concomitant increase in ductility and transgranularmore » failure after irradiation. The deformation microstructures of the two alloys were also different. Alloy X-750 deformed by a planar slip mechanism with fine microcracks forming at the intersections of slip bands with grain boundaries. Alloy 625 showed much more homogeneous deformation with fine, closely spaced slip bands and an absence of microcracks. The mechanism(s) of irradiation assisted stress corrosion cracking (IASCC) are discussed.« less

Deformation mechanisms and resealing of damage zones in experimentally deformed cemented and un-cemented clay-rich geomaterials, at low bulk strain

NASA Astrophysics Data System (ADS)

Desbois, Guillaume; Urai, Janos L.; Schuck, Bernhardt; Hoehne, Nadine; Oelker, Anne; Bésuelle, Pierre; Viggiani, Gioacchino; Schmatz, Joyce; Klaver, Jop

2017-04-01

A microphysics-based understanding of mechanical and fluid flow properties in clay-rich geomaterials is required for extrapolating better constitutive equations beyond the laboratory's time scales, so that predictions over the long term can be made less uncertain. In this contribution, we present microstructural investigations of rocks specimens sheared in triaxial compression at low bulk strain, by using the combination of broad-ion-beam (BIB) milling and scanning electron microscopy (SEM) to infer deformation mechanisms based on microstructures imaged at sub-micron resolution. Two end-member clay-rich geomaterials from European Underground Laboratories (URL) were analysed: (i) the poorly cemented Boom Clay sediment (BC from URL at Mol/Dessel, Belgium; confining pressure [CP] = 0.375 & 1.5 MPa) and (ii) the Callovo-Oxfordian claystone (COx from the URL at Bure, France; CP = 2 & 10 MPa). Although as a first approximation the inelastic bahvior of cemented and uncemented clay-rich geomaterials can be described by similar pressure-dependent hardening plasticity models, deformed samples in this contribution show very contrasting micro-scale behaviour: microstructures reveal brittle-ductile transitional behaviour in BC, whereas deformation in COx is dominantly cataclastic. In Boom Clay, at meso-scale, shear bands exhibit characteristics that are typical of uncemented small-grained clay-rich materials deformed at high shear strains, consisting of anastomosing shears interpreted as Y- and B-shears, which bound the passively deformed microlithons. At micro- down to nano-scale, the strong shape preferential orientation of clay aggregates in the anastomosing shears is interpreted to be responsible of the shear weakness. More over, the reworking of clay aggregates during deformation contributes to the collapsing of porosity in the shear band. Ductile deformation mechanisms represented by grain-rotation, grain-sliding, bending and granular flow mechanisms are strongly involved for the development of the shear band. At the same time, evidence for dilatancy at low confining pressure indicates that deformation involves also brittle deformation. Our observations strongly suggest that the deformation mostly localizes in those regions of the specimen, where the original grain sizes are smaller. In COx, microstructures show evidence for dominantly cataclastic deformation involving intergranular - transgranular - and - intragranular micro fracturing, grain rotation and clay particle bending mechanisms, down to nm- scale. Micro fracturing of the original fabric results in fragments at a range of scales, which are reworked into a clay-rich cataclastic gouge during frictional flow. Intergranular and minor intragranular micro fracturing occur in regions of non localized deformation, whereas transgranular micro fracturing occurs at regions of localized deformation. These processes are accompanied by dilatancy, but also by progressive decrease of porosity and pore size in the gouge with the non-clay particles embedded in reworked clay. The mechanism of this compaction during shearing is interpreted to be a combination of cataclasis of the cemented clay matrix, and shear-induced rearrangement of clay particles around the fragments of non-clay particles.

Fundamental mechanisms of fatigue and fracture.

PubMed

Christ, Hans-Jürgen

2008-01-01

A brief overview is given in this article on the main design philosophies and the resulting description concepts used for components which undergo monotonic and cyclic loading. Emphasis is put on a mechanistic approach avoiding a plain reproduction of empirical laws. After a short consideration of fracture as a result of monotonic loading using fracture mechanics basics, the phenomena taking place as a consequence of cyclic plasticity are introduced. The development of fatigue damage is treated by introducing the physical processes which (i) are responsible for microstructural changes, (ii) lead to crack initiation and (iii) determine crack propagation. From the current research topics within the area of metal fatigue, two aspects are dealt with in more detail because of their relevance to biomechanics. The first one is the growth behaviour of microstructural short cracks, which controls cyclic life of smooth parts at low stress amplitudes. The second issue addresses the question of the existence of a true fatigue limit and is of particular interest for components which must sustain a very high number of loading cycles (very high cycle fatigue).

Effect of cooling rate during hot stamping on low cyclic fatigue of boron steel sheet

NASA Astrophysics Data System (ADS)

Suh, Chang Hee; Jang, Won Seok; Oh, Sang Kyun; Lee, Rac Gyu; Jung, Yun-Chul; Kim, Young Suk

2012-08-01

Boron steel is widely used throughout the automobile industry due to its high tensile strength and hardenability. When boron steel is used for body parts, only high strength is required for crashworthiness. However, when boron steel is used for chassis parts, a high fatigue life is needed. The microstructure of boron steel is mainly affected by the cooling rate during hot stamping. Therefore, this study investigated the low cyclic fatigue life according to the cooling rate. The fatigue life increased at a low strain amplitude when the cooling rate was fast. However, at a high strain amplitude, the fatigue life decreased, due to the low ductility and fracture toughness of the martensite formed by rapid cooling. Martensite formed by a fast cooling rate shows excellent fatigue life at a low total strain amplitude; however, a multiphase microstructure formed by a slow cooling rate is recommended if the parts experience high and low total strain amplitudes alternately. In addition, the cooling rate has little effect on the distribution of solute boron and boron precipitations, so it is expected that boron rarely affects low cyclic fatigue.

Microstructural change in electroformed copper liners of shaped charges upon plastic deformation at ultra-high strain rate

NASA Astrophysics Data System (ADS)

Tian, W. H.; Hu, S. L.; Fan, A. L.; Wang, Z.

2002-01-01

Transmission electron microscopy (TEM) observations were carried out for examining the as-formed and post-deformed microstructures in a variety of electroformed copper liners of shaped charges. The deformation was carried out at an ultra-high strain rate. Specifically, the electron backscattering Kikuchi pattern (EBSP) technique was utilized to examine the micro-texture of these materials. TEM observations revealed that these electroformed copper liners of shaped charges have a grain size of about 1-3 mum, EBSP analysis demonstrated that the as-grown copper liners of shaped charges exhibit a l 10) fiber micro-texture which is parallel to the normal direction of the surface of the liners of shaped charges. Having undergone plastic deformation at ultra-high strain rate (10(7) s(-1)), the specimens which were recovered from the copper slugs were found to have grain size of the same order as that before deformation. EBSP analysis revealed that the (110) fiber texture existed in the as-formed copper liners disappears in the course of deformation. TEM examination results indicate that dynamic recovery and recrystallization play a significant role in this deformation process.

Accumulative Roll Bonding and Post-Deformation Annealing of Cu-Al-Mn Shape Memory Alloy

NASA Astrophysics Data System (ADS)

Moghaddam, Ahmad Ostovari; Ketabchi, Mostafa; Afrasiabi, Yaser

2014-12-01

Accumulative roll bonding is a severe plastic deformation process used for Cu-Al-Mn shape memory alloy. The main purpose of this study is to investigate the possibility of grain refinement of Cu-9.5Al-8.2Mn (in wt.%) shape memory alloy using accumulative roll bonding and post-deformation annealing. The alloy was successfully subjected to 5 passes of accumulative roll bonding at 600 °C. The microstructure, properties as well as post-deformation annealing of this alloy were investigated by optical microscopy, scanning electron microscopy, x-ray diffraction, differential scanning calorimeter, and bend and tensile testing. The results showed that after 5 passes of ARB at 600 °C, specimens possessed α + β microstructure with the refined grains, but martensite phases and consequently shape memory effect completely disappeared. Post-deformation annealing was carried out at 700 °C, and the martensite phase with the smallest grain size (less than 40 μm) was obtained after 150 s of annealing at 700 °C. It was found that after 5 passes of ARB and post-deformation annealing, the stability of SME during thermal cycling improved. Also, tensile properties of alloys significantly improved after post-deformation annealing.

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

Characterization of the Hot Deformation Behavior of a Newly Developed Nickel-Based Superalloy

NASA Astrophysics Data System (ADS)

Shi, Zhaoxia; Yan, Xiaofeng; Duan, Chunhua; Tang, Cunjiang; Pu, Enxiang

2018-03-01

To clarify the microstructural evolution and hot workability of GH4282 during hot forming processes, the hot deformation behavior of this superalloy was investigated by isothermal compression tests in the temperature interval of 950-1210 °C and the strain rate range of 0.01-10 s-1 with a true strain of 0.7. The results show that the flow stresses decrease with an increase in the deformation temperature and a decrease in the strain rate. The characteristic of dynamic recrystallization is revealed by the flow curves. The variation rule of the flow stress can be well described by the hyperbolic sine type equation, and the thermal deformation activation energy is determined to be 498.118 kJ/mol. The optimum hot working parameters are 1100-1180 °C and 0.01-0.1 s-1, under which the fine and uniform microstructure can be obtained.

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

Lattice defects affecting moisture-induced embrittlement of Ni-based L1{sub 2} ordered intermetallics

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

Takasugi, T.; Hanada, S.

1997-12-31

Moisture-induced embrittlement of L1{sub 2} alloys (such as Ni{sub 3}(Si,Ti) and Ni{sub 3}Al) is observed by tensile test and SEM fractography. A variety of microstructures were prepared by selecting pre-deformation and heat treatment conditions. It is shown that tensile ductility and the associated fractography depend on structure as well as test atmosphere. Well-annealed specimens are susceptible to moisture-induced embrittlement while pre-deformed specimens are resistive to moisture-induced embrittlement. Also, this embrittlement is generally sensitive to the heat treatment scheme preceded by the pre-deformation. Results indicate that the embrittlement occurs when hydrogen is enriched on grain boundaries. On the other hand, themore » embrittlement can be suppressed when hydrogen is trapped at lattice defects such as dislocations and vacancies. These results are discussed in association with the kinetics of hydrogen in the pre-deformed microstructure.« less

Predicting Hot Deformation of AA5182 Sheet

NASA Astrophysics Data System (ADS)

Lee, John T.; Carpenter, Alexander J.; Jodlowski, Jakub P.; Taleff, Eric M.

Aluminum 5000-series alloy sheet materials exhibit substantial ductilities at hot and warm temperatures, even when grain size is not particularly fine. The relatively high strain-rate sensitivity exhibited by these non-superplastic materials, when deforming under solute-drag creep, is a primary contributor to large tensile ductilities. This active deformation mechanism influences both plastic flow and microstructure evolution across conditions of interest for hot- and warm-forming. Data are presented from uniaxial tensile and biaxial bulge tests of AA5182 sheet material at elevated temperatures. These data are used to construct a material constitutive model for plastic flow, which is applied in finite-element-method (FEM) simulations of plastic deformation under multiaxial stress states. Simulation results are directly compared against experimental data to explore the usefulness of this constitutive model. The effects of temperature and stress state on plastic response and microstructure evolution are discussed.

Microstructural Analysis of Severe Plastic Deformed Twin Roll Cast AZ31 for the Optimization of Superplastic Properties

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

Young, John P.; Askari, Hesam A.; Heiden, Michael J.

2013-07-08

In recent years magnesium alloys have attracted significant attention as potential candidates to replace many of the heavier metals used in some automotive applications. However, the limited formability of magnesium and its alloys at room temperature has driven interest in the superplastic forming magnesium as an alternative shaping method. Severe plastic deformation techniques have become a well studied method of refining the grain size and modifying the microstructural characteristics of many magnesium alloys to achieve greater superplastic properties. In this study twin roll cast (TRC) AZ31 magnesium alloy was subjected to equal channel angular pressing (ECAP) and friction stir weldingmore » (FSW). The influence of these severe plastic deformation processes on the grain size, texture and grain boundary character distribution was investigated to identify the optimum severe plastic deformation process for the superplastic forming of AZ31.« less

Orientation Dependence of the Deformation Microstructure of Ta-4%W after Cold-Rolling

NASA Astrophysics Data System (ADS)

Zhang, J.; Ma, G. Q.; Godfrey, A.; Shu, D. Y.; Chen, Q.; Wu, G. L.

2017-07-01

One of the common features of deformed face-centered cubic metals with medium to high stacking fault energy is the formation of geometrically necessary dislocation boundaries. The dislocation boundary arrangements in refractory metals with body-centered cubic crystal structure are, however, less well known. To address this issue a Ta-4%W alloy was cold rolled up to 70% in thickness in the present work. The resulting deformation microstructures were characterized by electron back-scattering diffraction and the dislocation boundary arrangements in each grain were revealed using sample-frame misorientation axis maps calculated using an in-house code. The maps were used to analyze the slip pattern of individual grains after rolling, revealing an orientation dependence of the slip pattern.

Effects of Rolling and Cooling Conditions on Microstructure of Umbrella-Bone Steel

NASA Astrophysics Data System (ADS)

Wu, Yan-Xin; Fu, Jian-Xun; Zhang, Hua; Xu, Jie; Zhai, Qi-Jie

2017-10-01

The effects of deformation temperature and cooling rate on the micro-structure evolution of umbrella-bone steel was investigated using a Gleeble thermal-mechanical testing machine and dynamic continuous cooling transformation (CCT) curves. The results show that fast cooling which lowers the starting temperature of ferrite transformation leads to finer ferrite grains and more pearlite. Low temperature deformation enhances the hardening effect of austenite and reduces hardenability, allowing a wider range of cooling rates and thus avoiding martensite transformation after deformation. According to the phase transformation rules, the ultimate tensile strength and reduction in area of the wire rod formed in the optimized industrial trial are 636 MPa and 73.6 %, respectively, showing excellent strength and plasticity.

Measuring in-vivo and in-situ ex-vivo the 3D deformation of the lamina cribrosa microstructure under elevated intraocular pressure

NASA Astrophysics Data System (ADS)

Wei, Junchao; Yang, Bin; Voorhees, Andrew P.; Tran, Huong; Brazile, Bryn; Wang, Bo; Schuman, Joel; Smith, Matthew A.; Wollstein, Gadi; Sigal, Ian A.

2018-02-01

Elevated intraocular pressure (IOP) deforms the lamina cribrosa (LC), a structure within the optic nerve head (ONH) in the back of the eye. Evidence suggests that these deformations trigger events that eventually cause irreversible blindness, and have therefore been studied in-vivo using optical coherence tomography (OCT), and ex-vivo using OCT and a diversity of techniques. To the best of our knowledge, there have been no in-situ ex-vivo studies of LC mechanics. Our goal was two-fold: to introduce a technique for measuring 3D LC deformations from OCT, and to determine whether deformations of the LC induced by elevated IOP differ between in-vivo and in-situ ex-vivo conditions. A healthy adult rhesus macaque monkey was anesthetized and IOP was controlled by inserting a 27- gauge needle into the anterior chamber of the eye. Spectral domain OCT was used to obtain volumetric scans of the ONH at normal and elevated IOPs. To improve the visibility of the LC microstructure the scans were first processed using a novel denoising technique. Zero-normalized cross-correlation was used to find paired corresponding locations between images. For each location pair, the components of the 3D strain tensor were determined using non-rigid image registration. A mild IOP elevation from 10 to 15mmHg caused LC effective strains as large as 3%, and about 50% larger in-vivo than in-situ ex-vivo. The deformations were highly heterogeneous, with substantial 3D components, suggesting that accurate measurement of LC microstructure deformation requires high-resolution volumes. This technique will help improve understanding of LC biomechanics and how IOP contributes to glaucoma.

A microstructural study of fault rocks from the SAFOD: Implications for the deformation mechanisms and strength of the creeping segment of the San Andreas Fault

NASA Astrophysics Data System (ADS)

Hadizadeh, Jafar; Mittempergher, Silvia; Gratier, Jean-Pierre; Renard, Francois; Di Toro, Giulio; Richard, Julie; Babaie, Hassan A.

2012-09-01

The San Andreas Fault zone in central California accommodates tectonic strain by stable slip and microseismic activity. We study microstructural controls of strength and deformation in the fault using core samples provided by the San Andreas Fault Observatory at Depth (SAFOD) including gouge corresponding to presently active shearing intervals in the main borehole. The methods of study include high-resolution optical and electron microscopy, X-ray fluorescence mapping, X-ray powder diffraction, energy dispersive X-ray spectroscopy, white light interferometry, and image processing. The fault zone at the SAFOD site consists of a strongly deformed and foliated core zone that includes 2-3 m thick active shear zones, surrounded by less deformed rocks. Results suggest deformation and foliation of the core zone outside the active shear zones by alternating cataclasis and pressure solution mechanisms. The active shear zones, considered zones of large-scale shear localization, appear to be associated with an abundance of weak phases including smectite clays, serpentinite alteration products, and amorphous material. We suggest that deformation along the active shear zones is by a granular-type flow mechanism that involves frictional sliding of microlithons along phyllosilicate-rich Riedel shear surfaces as well as stress-driven diffusive mass transfer. The microstructural data may be interpreted to suggest that deformation in the active shear zones is strongly displacement-weakening. The fault creeps because the velocity strengthening weak gouge in the active shear zones is being sheared without strong restrengthening mechanisms such as cementation or fracture sealing. Possible mechanisms for the observed microseismicity in the creeping segment of the SAF include local high fluid pressure build-ups, hard asperity development by fracture-and-seal cycles, and stress build-up due to slip zone undulations.

Microprobe monazite geochronology: new techniques for dating deformation and metamorphism

NASA Astrophysics Data System (ADS)

Williams, M.; Jercinovic, M.; Goncalves, P.; Mahan, K.

2003-04-01

High-resolution compositional mapping, age mapping, and precise dating of monazite on the electron microprobe are powerful additions to microstructural and petrologic analysis and important tools for tectonic studies. The in-situ nature and high spatial resolution of the technique offer an entirely new level of structurally and texturally specific geochronologic data that can be used to put absolute time constraints on P-T-D paths, constrain the rates of sedimentary, metamorphic, and deformational processes, and provide new links between metamorphism and deformation. New analytical techniques (including background modeling, sample preparation, and interference analysis) have significantly improved the precision and accuracy of the technique and new mapping and image analysis techniques have increased the efficiency and strengthened the correlation with fabrics and textures. Microprobe geochronology is particularly applicable to three persistent microstructural-microtextural problem areas: (1) constraining the chronology of metamorphic assemblages; (2) constraining the timing of deformational fabrics; and (3) interpreting other geochronological results. In addition, authigenic monazite can be used to date sedimentary basins, and detrital monazite can fingerprint sedimentary source areas, both critical for tectonic analysis. Although some monazite generations can be directly tied to metamorphism or deformation, at present, the most common constraints rely on monazite inclusion relations in porphyroblasts that, in turn, can be tied to the deformation and/or metamorphic history. Examples will be presented from deep-crustal rocks of northern Saskatchewan and from mid-crustal rocks from the southwestern USA. Microprobe monazite geochronology has been used in both regions to deconvolute overprinting deformation and metamorphic events and to clarify the interpretation of other geochronologic data. Microprobe mapping and dating are powerful companions to mass spectroscopic dating techniques. They allow geochronology to be incorporated into the microstructural analytical process, resulting in a new level of integration of time (t) into P-T-D histories.

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.

Effect of Hierarchical Microstructures of Lath Martensite on the Transitional Behavior of Fatigue Crack Growth Rate

NASA Astrophysics Data System (ADS)

Yang, Ming; Zhong, Yi; Liang, Yi-long

2018-04-01

In this study, the fatigue-crack growth (FCG) behavior of 20CrMTiH steel with different substructure sizes was investigated. The results showed that coarsen microstructures exhibit excellent growth resistance. Moreover, two transitional behaviors were observed in the FCG curves of all specimens. The first transition point occurs in the near-threshold regime, whereas the second transition point occurs in the Paris regime. A comparison of substructure size to cyclic plastic size showed that the block size is almost equal to cyclic plastic size at ΔKT1, indicating that block size is an effective grain size to control the first transitional behavior of fatigue-crack propagation, whereas the second transitional behavior is related to the packet width or grain size. According to the fracture morphology, the fracture mechanism above and below the transition point responsible for the above phenomenon were distinguished. In addition, two prediction models based on microstructure size were established for lath martensite to evaluate the threshold and stress intensity factor range at the transition point.

Fabrication of fine-grain tantalum diffusion barrier tube for Nb3Sn conductors

NASA Astrophysics Data System (ADS)

Hartwig, K. T.; Balachandran, S.; Mezyenski, R.; Seymour, N.; Robinson, J.; Barber, R. E.

2014-01-01

Diffusion barriers used in Nb3Sn wire are often fabricated by wrapping Ta sheet into a tube with an overlap seam. A common result of such practice is non-uniform deformation in the Ta sheet as it thins by wire drawing because of non-uniform grain size and texture in the original Ta sheet. Seamless Ta tube with a fine-grain and uniform microstructure would be much better for the diffusion barrier application, but such material is expensive and difficult to manufacture. This report presents results on a new fabrication strategy for Ta tube that shows promise for manufacture of less costly tube with an improved microstructure. The fabrication method begins with seam-welded tube but gives a fine-grain uniform microstructure with little difference between the longitudinal seam weld region and the parent metal after post-weld processing. Severe plastic deformation processing (SPD) applied by area reduction extrusion and tube equal channel angular extrusion (tECAE) are used to refine and homogenize the microstructure. Microstructure and mechanical property results are presented for Ta tubes fabricated by this new processing strategy.

Properties of Ti-6Al-4V spun formed fuze supports

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

Moody, N.R.; Gates, G.

1985-05-01

Spin forming is designated as the primary fabrication process for the Ti-6A1-4V, W-87 fuze support. This process reduces the amount of rough machining during production, the cost of the starting material and the lead time from order to delivery of finished parts compared with parts made from forgings. However, because the amount of deformation from the spin forming process varies greatly within the part, the properties resulting from spin forming the fuze supports are unknown. This study shows that the properties and microstructure of the highly deformed walls of the fuze support are similar to those of forgings, while themore » properties and microstructure of the lightly deformed nose are similar to those of the parent plate. A solution treatment at 1750/sup 0/F/1h/WQ (954/sup 0/C) followed by a 900/sup 0/F (482/sup 0/C) four hour age gives the desired properties. Additionally, microstructural evaluation shows that the temperatures during spin forming are maintained within desired limits and that no significant microstructural changes occur during subsequent elevated temperature processing of the finished part. This study shows that solution treated and aged parts meet all required properties for all conditions to which the fuze supports will be subjected.« less

Comparison of isothermal and cyclic oxidation behavior of twenty-five commercial sheet alloys at 1150 C

NASA Technical Reports Server (NTRS)

Barrett, C. A.; Lowell, C. E.

1975-01-01

Twenty-five commercial nickel-, iron-, and cobalt-base sheet alloys incorporating chromium or chromium and aluminum additions for oxidation resistance were tested at 1150 C in air for 100 hr in both isothermal and 1-hr cyclic furnace exposures. The alloys were evaluated by sample specific weight change, by type of scale formed, by amount and type of spall, and by sample thickness change and microstructure.-

Cyclic creep and fatigue of TD-NiCr (thoria-dispersion-strengthened nickel-chromium), TD-Ni, and NiCr sheet at 1200 C

NASA Technical Reports Server (NTRS)

Hirschberg, M. H.; Spera, D. A.; Klima, S. J.

1972-01-01

The resistance of thin TD-NiCr sheet to cyclic deformation was compared with that of TD-Ni and a conventional nickel-chromium alloy. Strains were determined by a calibration technique which combines room-temperature strain gage and deflection measurements with high-temperature deflection measurements. Analyses of the cyclic tests using measured tensile and creep-rupture data indicated that the TD-NiCr and NiCr alloy specimens failed by a cyclic creep mechanism. The TD-Ni specimens, on the other hand, failed by a fatigue mechanism.

Microstructure, strengthening mechanisms and hot deformation behavior of an oxide-dispersion strengthened UFG Al6063 alloy

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

Asgharzadeh, H.; Kim, H.S.; Simchi, A., E-mail: simchi@sharif.edu

2013-01-15

An ultrafine-grained Al6063/Al{sub 2}O{sub 3} (0.8 vol.%, 25 nm) nanocomposite was prepared via powder metallurgy route through reactive mechanical alloying and hot powder extrusion. Scanning electron microcopy, transmission electron microscopy, and back scattered electron diffraction analysis showed that the grain structure of the nanocomposite is trimodal and composed of nano-size grains (< 0.1 {mu}m), ultrafine grains (0.1-1 {mu}m), and micron-size grains (> 1 {mu}m) with random orientations. Evaluation of the mechanical properties of the nanocomposite based on the strengthening-mechanism models revealed that the yield strength of the ultrafine-grained nanocomposite is mainly controlled by the high-angle grain boundaries rather than nanometricmore » alumina particles. Hot deformation behavior of the material at different temperatures and strain rates was studied by compression test and compared to coarse-grained Al6063 alloy. The activation energy of the hot deformation process for the nanocomposite was determined to be 291 kJ mol{sup -1}, which is about 64% higher than that of the coarse-grained alloy. Detailed microstructural analysis revealed that dynamic recrystallization is responsible for the observed deformation softening in the ultrafine-grained nanocomposite. - Highlights: Black-Right-Pointing-Pointer The strengthening mechanisms of Al6063/Al{sub 2}O{sub 3} nanocomposite were evaluated. Black-Right-Pointing-Pointer Hot deformation behavior of the nanocomposite was studied. Black-Right-Pointing-Pointer The hot deformation activation energy was determined using consecutive models. Black-Right-Pointing-Pointer The restoration mechanisms and microstructural changes are presented.« less

Spatial distribution of quartz recrystallization microstructures across the Aar massif (Swiss Central Alps)

NASA Astrophysics Data System (ADS)

Peters, M.; Herwegh, M.

2012-04-01

In the Aar massif, main foliation and major deformation structures were developed during NW-SE compression associated with the Alpine orogeny (Steck 1968). To be precise, shearing at the brittle to ductile transition may have initiated at different stages between 22-20 Ma and 14-12 Ma, followed by purely brittle deformation at around 10 Ma (Rolland et al. 2009). In light of the onset of dynamic recrystallization in quartz, Bambauer et al. (2009) defined a quartz recrystallization isograd in the northern part of the Aar massif. To the south, the grain size of recrystallized grains increases due to an increase of metamorphic temperatures from N to S. The aim of the current project is to carry out quantitative analysis on changes of the dynamic and static recrystallization behavior of quartz. Across the Aar massif, two general types of microstructures have to be discriminated: (i) weakly to moderately deformed host rocks and (ii) intensely deformed mylonites to ultramylonites out of high strain shear zones. In (i), volume fraction and size of recrystallized quartz grains increase towards the S showing grain size changes from around 5 µm up to ca. 200 µm. Southern microstructures are characterized by complete recrystallization. In terms of recrystallization processes, a transition from bulging recrystallization in the N to subgrain rotation recrystallization in the S occurs. Such a change in dynamic recrystallization processes combined with a grain size increase points towards reduced differential stresses with increasing temperature. This temperature gradient is also corroborated by a switch in the active glide systems in quartz from basal to rhomb dominated glide. In contrast to the granitic host rocks, the mylonites and ultramylonites (ii) show smaller recrystallized grain sizes due to enhanced strain rates. However, they also reveal a general increase of recrystallized grain sizes from N to S. In the S, microstructures from (i) and (ii) show equidimensional grains with 120° triple junctions and straight grain boundaries. Such microstructures are typical for static annealing. For that reason, we propose a post-deformational temperature pulse mainly affecting the southern part of the Aar massif. This annealing stage might correlate with the fluid pulse between 12-10 Ma suggested by Challandes et al. (2008). We will present constraints on the grade of deformation based on grain size data and CPO analyses, supporting the hypothesis that various deformation stages are well preserved in statically recrystallized structures.

Electron Backscatter Diffraction (EBSD) Analysis and U-Pb Geochronology of the Oldest Lunar Zircon: Constraining Early Lunar Differentiation and Dating Impact-Related Deformation

NASA Technical Reports Server (NTRS)

Timms, Nick; Nemchin, Alexander; Grange, Marion; Reddy, Steve; Pidgeon, Bob; Geisler, Thorsten; Meyer, Chuck

2009-01-01

The evolution of the early moon was dominated by two processes (i) crystallization of the Lunar Magma Ocean (LMO) and differentiation of potassium-rare earth element-phosphorous-rich residual magma reservoir referred to as KREEP, and (ii) an intense meteorite bombardment referred to as lunar cataclysm . The exact timing of these processes is disputed, and resolution relies on collection and interpretation of precise age data. This study examines the microstructure and geochronology of zircon from lunar impact breccias collected during the Apollo 17 mission. A large zircon clast within lunar breccia 72215,195 shows sector zoning in optical microscopy, cathodoluminescence (CL) imaging and Raman mapping, and indicates that it was a relict fragment of a much larger magmatic grain. Sensitive high resolution ion microprobe (SHRIMP) U-Pb analysis of the zircon shows that U and Th concentration correlate with sector zoning, with darkest CL domains corresponding with high-U and Th (approx.150 and approx.100 ppm respectively), and the brightest-CL sectors containing approx.30-50 ppm U and approx.10-20 ppm Th. This indicates that variations in optical CL and Raman properties correspond to differential accumulation of alpha-radiation damage in each sector. Electron backscatter diffraction (EBSD) mapping shows that the quality of electron backscatter patterns (band contrast) varies with sector zoning, with the poorest quality patterns obtained from high-U and Th, dark-CL zones. EBSD mapping also reveals a deformation microstructure that is cryptic in optical, CL and Raman imaging. Two orthogonal sets of straight discrete and gradational low-angle boundaries accommodate approx.12 misorientation across the grain. The deformation bands are parallel to the crystallographic {a}-planes of the zircon, have misorientation axes parallel to the c-axis, and are geometrically consistent with formation by dislocation creep associated with <100>{010} slip. The deformation bands are unlike curved morphology of crystal-plastic microstructures in tectonically deformed terrestrial zircon, and geometrically similar to dislocation microstructures reported in experimentally shocked zircon. We interpret these crystal-plastic deformation microstructures to have resulted from a significant impact, either directly from impact shock, or during ductile flow directly following the impact. The deformation bands appear to continue undeflected through the non-indexed, radiation-damaged areas of the grain, which suggests that the orientation variation predates any significant mechanical weakening from radiation damage in the grain, and therefore occurred early in its history.

Three Microstructural Exercises for Students.

ERIC Educational Resources Information Center

Means, Winthrop D.

1986-01-01

Describes laboratory exercises which demonstrate a new simplified technique for deforming thin samples of crystalline materials on the stage of a petrographic microscope. Discusses how this process allows students to see the development of microstructures resulting from cracking, slipping, thinning, and recrystallization. References and sources of…

Strain Localization on Different Scales and their Related Microstructures - Comparison of Microfabrics of Calcite Mylonites from Naxos (Greece) and Helvetic Nappes (Switzerland)

NASA Astrophysics Data System (ADS)

Ebert, A.; Herwegh, M.; Karl, R.; Edwin, G.; Decrouez, D.

2007-12-01

In the upper crust, shear zones are widespread and appear at different scales. Although deformation conditions, shear zone history, and displacements vary in time and space between shear zones and also within them, in all shear zones similar trends in the evolution of large- to micro-scale fabrics can be observed. The microstructural analyses of calcite mylonites from Naxos and various Helvetic nappes show that microstructures from different metamorphic zones vary considerably on the outcrop- and even on the sample- scale. However, grain sizes tend to increase with metamorphic degree in case of Naxos and the Helvetic nappes. Although deformation conditions (e.g. deformation temperature, strain rate, and shear zone geometry, i.e. shear zone width and rock type above/below thrust) vary between the different tectonic settings, microstructural trends (e.g. grain size) correlate with each other. This is in contrast to many previous studies, where no corrections for second phase contents have been applied. In an Arrhenius-type diagram, the grain growth trends of calcite of all studied shear zones fit on a single trend, independent of the dimensions of localized large-scale structures, which is in the dm to m- and km-range in case of the Helvetic thrusts and the marble suite of Naxos, respectively. The calcite grain size increases continuously from few μm to >2mm with a temperature increase from <300°C to >700°C. In a field geologist's point of view, this is an important observation because it shows that natural dynamically stabilized steady state microfabrics can be used to estimate temperature conditions during deformation, although the tectonic settings are different (e.g. strain rate, fluid flow). The reason for this agreement might be related to a scale-dependence of the shear zone dimensions, where the widths increase with increasing metamorphic conditions. In this sense, the deformation volumes affected by localization must closely be linked to the strength of the affected rocks. In comparison to experiments, similar microstructural trends are observed. Here, however, shifts of these trends occur due to the higher strain rates.

Hot isostatic pressing (HIP) of powder mixtures and composites: Packing, densification, and microstructural effects

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

Li, E.K.H.; Funkenbusch, P.D.

1993-06-01

Hot isostatic pressing (HIP) of powder mixtures (containing differently sized components) and of composite powders is analyzed. Recent progress, including development of a simple scheme for estimating radial distribution functions, has made modeling of these systems practical. Experimentally, powders containing bimodal or continuous size distributions are observed to hot isostatically press to a higher density tinder identical processing conditions and to show large differences in the densification rate as a function of density when compared with the monosize powders usually assumed for modeling purposes. Modeling correctly predicts these trends and suggests that they can be partially, but not entirely, attributedmore » to initial packing density differences. Modeling also predicts increased deformation in the smaller particles within a mixture. This effect has also been observed experimentally and is associated with microstructural changes, such as preferential recrystallization of small particles. Finally, consolidation of a composite mixture containing hard, but deformable, inclusions has been modeled for comparison with existing experimental data. Modeling results match both the densification and microstructural observations reported experimentally. Densification is retarded due to contacts between the reinforcing particles which support a significant portion of the applied pressure. In addition, partitioning of deformation between soft matrix and hard inclusion powders results in increased deformation of the softer material.« less

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.

On the Process-Related Rivet Microstructural Evolution, Material Flow and Mechanical Properties of Ti-6Al-4V/GFRP Friction-Riveted Joints.

PubMed

Borba, Natascha Z; Afonso, Conrado R M; Blaga, Lucian; Dos Santos, Jorge F; Canto, Leonardo B; Amancio-Filho, Sergio T

2017-02-15

In the current work, process-related thermo-mechanical changes in the rivet microstructure, joint local and global mechanical properties, and their correlation with the rivet plastic deformation regime were investigated for Ti-6Al-4V (rivet) and glass-fiber-reinforced polyester (GF-P) friction-riveted joints of a single polymeric base plate. Joints displaying similar quasi-static mechanical performance to conventional bolted joints were selected for detailed characterization. The mechanical performance was assessed on lap shear specimens, whereby the friction-riveted joints were connected with AA2198 gussets. Two levels of energy input were used, resulting in process temperatures varying from 460 ± 130 °C to 758 ± 56 °C and fast cooling rates (178 ± 15 °C/s, 59 ± 15 °C/s). A complex final microstructure was identified in the rivet. Whereas equiaxial α-grains with β-phase precipitated in their grain boundaries were identified in the rivet heat-affected zone, refined α' martensite, Widmanstätten structures and β-fleck domains were present in the plastically deformed rivet volume. The transition from equiaxed to acicular structures resulted in an increase of up to 24% in microhardness in comparison to the base material. A study on the rivet material flow through microtexture of the α-Ti phase and β-fleck orientation revealed a strong effect of shear stress and forging which induced simple shear deformation. By combining advanced microstructural analysis techniques with local mechanical testing and temperature measurement, the nature of the complex rivet plastic deformational regime could be determined.

A thermally activated dislocation-based constitutive flow model of nanostructured FCC metals involving microstructural evolution

NASA Astrophysics Data System (ADS)

Zhang, J. Y.; Li, J.; Wu, K.; Liu, G.; Sun, J.

2017-03-01

Due to their interface and nanoscale effects associated with structural peculiarities of nanostructured, face-centered-cubic (FCC) ultrafine-grained/nanocrystalline (UFG/NC) metals, in particular nanotwinned (NT) metals exhibit unexpected deformation behaviours fundamentally different from their coarse-grained (CG) counterparts. These internal boundaries, including grain boundaries and twin boundaries in UFG/NC metals, strongly interact with dislocations as deformation barriers to enhance the strength and strain rate sensitivity (SRS) of materials on the one hand, and play critical roles in their microstructural evolution as dislocation sources/sinks to sustain plastic deformation on the other. In this work, building on the findings of twin softening and (de)twinning-mediated grain growth/refinement in stretched free-standing NT-Ni foils, a constitutive model based on the thermally activated depinning process of dislocations residing in boundaries has been proposed to predict the steady-state grain size and simulate the plastic flow of NT-Ni, by considering the blocking effects of nanotwins on the absorption of dislocations emitted from boundaries. It is uncovered that the stress ratio (ηstress) of effective-to-internal stress can be taken as a signature to estimate the stability of microstructures during plastic deformation. This model not only reproduces well the plastic flow of the stretched NT-Ni foils as well as reported NT-Cu and the steady-state grain size, but also sheds light on the size-dependent SRS and failure of FCC UFG/NC metals. This theoretical framework offers the opportunity to tune the microstructures in the polycrystalline materials to synthesise high performance engineering materials with high strength and great ductility.

Dynamic shaping of cellular membranes by phospholipids and membrane-deforming proteins.

PubMed

Suetsugu, Shiro; Kurisu, Shusaku; Takenawa, Tadaomi

2014-10-01

All cellular compartments are separated from the external environment by a membrane, which consists of a lipid bilayer. Subcellular structures, including clathrin-coated pits, caveolae, filopodia, lamellipodia, podosomes, and other intracellular membrane systems, are molded into their specific submicron-scale shapes through various mechanisms. Cells construct their micro-structures on plasma membrane and execute vital functions for life, such as cell migration, cell division, endocytosis, exocytosis, and cytoskeletal regulation. The plasma membrane, rich in anionic phospholipids, utilizes the electrostatic nature of the lipids, specifically the phosphoinositides, to form interactions with cytosolic proteins. These cytosolic proteins have three modes of interaction: 1) electrostatic interaction through unstructured polycationic regions, 2) through structured phosphoinositide-specific binding domains, and 3) through structured domains that bind the membrane without specificity for particular phospholipid. Among the structured domains, there are several that have membrane-deforming activity, which is essential for the formation of concave or convex membrane curvature. These domains include the amphipathic helix, which deforms the membrane by hemi-insertion of the helix with both hydrophobic and electrostatic interactions, and/or the BAR domain superfamily, known to use their positively charged, curved structural surface to deform membranes. Below the membrane, actin filaments support the micro-structures through interactions with several BAR proteins as well as other scaffold proteins, resulting in outward and inward membrane micro-structure formation. Here, we describe the characteristics of phospholipids, and the mechanisms utilized by phosphoinositides to regulate cellular events. We then summarize the precise mechanisms underlying the construction of membrane micro-structures and their involvements in physiological and pathological processes. Copyright © 2014 the American Physiological Society.

Effects of Cyclic Loading on the Deformation and Elastic-Plastic Fracture Behavior of a Cast Stainless Steel

DTIC Science & Technology

1991-10-01

23 8. High Cycle Fatigue Crack Growth Data for Cast Stainless Steel Showing Comparison with Rolfe and Barsom Fit .......... 24 9. Cyclic Load...compared to the Rolfe /Barsom4 fatigue crack propagation equation for austenitic stainless steels in Fig. 8. ELASTIC-PLASTIC Cyclic J-testing was...place during both the compression and tensile loadings. The J-integral was calculated on each cycle using the Merkle -Corten 9 J equation as modified by

High-temperature deformation and processing maps of Zr-4 metal matrix with dispersed coated surrogate nuclear fuel particles

NASA Astrophysics Data System (ADS)

Chen, Jing; Liu, Huiqun; Zhang, Ruiqian; Li, Gang; Yi, Danqing; Lin, Gaoyong; Guo, Zhen; Liu, Shaoqiang

2018-06-01

High-temperature compression deformation of a Zr-4 metal matrix with dispersed coated surrogate nuclear fuel particles was investigated at 750 °C-950 °C with a strain rate of 0.01-1.0 s-1 and height reduction of 20%. Scanning electron microscopy was utilized to investigate the influence of the deformation conditions on the microstructure of the composite and damage to the coated surrogate fuel particles. The results indicated that the flow stress of the composite increased with increasing strain rate and decreasing temperature. The true stress-strain curves showed obvious serrated oscillation characteristics. There were stable deformation ranges at the initial deformation stage with low true strain at strain rate 0.01 s-1 for all measured temperatures. Additionally, the coating on the surface of the surrogate nuclear fuel particles was damaged when the Zr-4 matrix was deformed at conditions of high strain rate and low temperature. The deformation stability was obtained from the processing maps and microstructural characterization. The high-temperature deformation activation energy was 354.22, 407.68, and 433.81 kJ/mol at true strains of 0.02, 0.08, and 0.15, respectively. The optimum deformation parameters for the composite were 900-950 °C and 0.01 s-1. These results are expected to provide guidance for subsequent determination of possible hot working processes for this composite.

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

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

Wu, Wei; An, Ke

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Understanding Low-cycle Fatigue Life Improvement Mechanisms in a Pre-twinned Magnesium Alloy

DOE PAGES

Wu, Wei; An, Ke

2015-10-03

The mechanisms of fatigue life improvement by pre-twinning process in a commercial rolled magnesium (Mg) alloy have been investigated using real-time in situ neutron diffraction under a continuous-loading condition. It is found that by introducing the excess twinned grains through pre-compression along the rolling direction the fatigue life was enhanced approximately 50%, mainly resulting from the prolonged detwinning process and inhibited dislocation slip during reverse tension. Moreover, after pre-twinning process, the removal of the rapid strain hardening during reverse tension leads to a compressive mean stress value and more symmetric shape of stress-strain hysteresis loop. The pre-twinning has significant impactsmore » on the twinning-detwinning characteristics and deformation modes during cyclic loading and greatly facilitates the twinning-detwinning activities in plastic deformation. The cyclic straining leads to the increase of contribution of tensile twinning deformation in overall plastic deformation in both the as-received and pre-deformed sample. The mechanisms of load partitioning in different groups of grains are closely related to the deformation modes in each deformation stage, while the fatigue cycling has little influence on the load sharing. The pre-twinning process provides an easy and cost-effective route to improve the low-cycle fatigue life through manufacturing and processing, which would advance the wide application of light-weight wrought Mg alloys as structural materials.« less

Mechanism of Martensitic to Equiaxed Microstructure Evolution during Hot Deformation of a Near-Alpha Ti Alloy

NASA Astrophysics Data System (ADS)

Shams, Seyed Amir Arsalan; Mirdamadi, Shamsoddin; Abbasi, Seyed Mahdi; Kim, Daehwan; Lee, Chong Soo

2017-06-01

In this study, mechanisms of microstructural evolution during hot deformation of Ti-1100 were investigated by EBSD analysis. Misorientation angle distribution of initial microstructure showed that diffusionless martensitic phase transformation in Ti-1100 obeys Burgers orientation relationship, and most of the high-angle-grain boundaries consist of angles of 60 and 63 deg. Calculated activation energy of hot deformation ( 338 kJ/mol) and EBSD grain boundary maps revealed that continuous dynamic recrystallization (CDRX) is the dominant mechanism during hot compression at 1073 K (800 °C) and strain rate of 0.005 s-1. At a temperature range of 1073 K to 1173 K (800 °C to 900 °C), not only the array of variants lying perpendicular to compression axis but also CDRX contributes to flow softening. Increasing the rolling temperature from 1123 K to 1273 K (850 °C to 1000 °C) brought about changes in spheroidization mechanism from CDRX to conventional boundary splitting and termination migration correlated with the higher volume fraction of beta phase at higher temperatures.

Micropillar compression study of the influence of size and internal boundary on the strength of HT9 tempered martensitic steel

NASA Astrophysics Data System (ADS)

Lim, Sangyeob; Shin, Chansun; Heo, Jungwoo; Kim, Sangeun; Jin, Hyung-Ha; Kwon, Junhyun; Guim, Hwanuk; Jang, Dongchan

2018-05-01

HT9, a ferritic/martensitic steel, is a candidate structural material for next-generation advanced reactors. Its microstructure is a typical tempered martensite showing a hierarchical lath-block-and-packet structure. We investigate the specimen size effect and strengthening contribution of various microstructural boundaries manifested in the compression tests of micropillars with diameters ranging from 0.5 to 17 μm. It is observed that micropillars with diameters larger than 3 μm show uniform deformation and plastic flow curves comparable to the bulk flow curve. Localized deformation by a few pronounced slip bands occurs in micropillars with diameters smaller than 1 μm, and the yield strength is reduced. Careful examination of the sizes of the microstructural features and cross-sections of the micropillars shows that the block boundaries are the most effective strengthening boundaries in tempered martensitic microstructure. The bulk mechanical properties of HT9 can be evaluated from a micropillar with diameter as low as 3 μm.

The production of fine grained magnesium alloys through thermomechanical processing for the optimization of microstructural and mechanical properties

NASA Astrophysics Data System (ADS)

Young, John Paul

The low density and high strength to weight ratio of magnesium alloys makes them ideal candidates to replace many of the heavier steel and aluminum alloys currently used in the automotive and other industries. Although cast magnesium alloys components have a long history of use in the automotive industry, the integration of wrought magnesium alloys components has been hindered by a number of factors. Grain refinement through thermomechanical processing offers a possible solution to many of the inherent problems associated with magnesium alloys. This work explores the development of several thermomechanical processing techniques and investigates their impact on the microstructural and mechanical properties of magnesium alloys. In addition to traditional thermomechanical processing, this work includes the development of new severe plastic deformation techniques for the production of fine grain magnesium plate and pipe and develops a procedure by which the thermal microstructural stability of severely plastically deformed microstructures can be assessed.

Microstructure and Strain Rate-Dependent Tensile Deformation Behavior of Fiber Laser-Welded Butt Joints of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Liu, Yang; Dong, Danyang; Han, Zhiqiang; Yang, Zhibin; Wang, Lu; Dong, Qingwei

2018-05-01

The microstructure and tensile deformation behavior of the fiber laser-welded similar and dissimilar dual-phase (DP) steel joints over a wide range of strain rates from 10-3 to 103 s-1 were investigated for the further applications on the lightweight design of vehicles. The high strain rate dynamic tensile deformation process and full-field strain distribution of the base metals and welded joints were examined using the digital image correlation method and high-speed photography. The strain rate effects on the stress-strain responses, tensile properties, deformation, and fracture behavior of the investigated materials were analyzed. The yield stress (YS) and ultimate tensile strength (UTS) of the dissimilar DP780/DP980 welded joints were lying in-between those of the DP780 and DP980 base metals, and all materials exhibited positive strain rate dependence on the YS and UTS. Owing to the microstructure heterogeneity, the welded joints showed relatively lower ductility in terms of total elongation (TE) than those of the corresponding base metals. The strain localization started before the maximum load was reached, and the strain localization occurred earlier during the whole deformation process with increasing strain rate. As for the dissimilar welded joint, the strain localization tended to occur in the vicinity of the lowest hardness value across the welded joint, which was in the subcritical HAZ at the DP780 side. As the strain rate increased, the typical ductile failure characteristic of the investigated materials did not change.

Microstructure and Strain Rate-Dependent Tensile Deformation Behavior of Fiber Laser-Welded Butt Joints of Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Liu, Yang; Dong, Danyang; Han, Zhiqiang; Yang, Zhibin; Wang, Lu; Dong, Qingwei

2018-04-01

The microstructure and tensile deformation behavior of the fiber laser-welded similar and dissimilar dual-phase (DP) steel joints over a wide range of strain rates from 10-3 to 103 s-1 were investigated for the further applications on the lightweight design of vehicles. The high strain rate dynamic tensile deformation process and full-field strain distribution of the base metals and welded joints were examined using the digital image correlation method and high-speed photography. The strain rate effects on the stress-strain responses, tensile properties, deformation, and fracture behavior of the investigated materials were analyzed. The yield stress (YS) and ultimate tensile strength (UTS) of the dissimilar DP780/DP980 welded joints were lying in-between those of the DP780 and DP980 base metals, and all materials exhibited positive strain rate dependence on the YS and UTS. Owing to the microstructure heterogeneity, the welded joints showed relatively lower ductility in terms of total elongation (TE) than those of the corresponding base metals. The strain localization started before the maximum load was reached, and the strain localization occurred earlier during the whole deformation process with increasing strain rate. As for the dissimilar welded joint, the strain localization tended to occur in the vicinity of the lowest hardness value across the welded joint, which was in the subcritical HAZ at the DP780 side. As the strain rate increased, the typical ductile failure characteristic of the investigated materials did not change.

Properties of a Ni(sub 19.5)Pd(sub 30)Ti(sub 50.5) high-temperature shape memory alloy in tension and compression

NASA Technical Reports Server (NTRS)

Noebe, Ronald; Padula, Santo, II; Bigelow, Glen; Rios, Orlando; Garg, Anita; Lerch, Brad

2006-01-01

Potential applications involving high-temperature shape memory alloys have been growing in recent years. Even in those cases where promising new alloys have been identified, the knowledge base for such materials contains gaps crucial to their maturation and implementation in actuator and other applications. We begin to address this issue by characterizing the mechanical behavior of a Ni19.5Pd30Ti50.5 high-temperature shape memory alloy in both uniaxial tension and compression at various temperatures. Differences in the isothermal uniaxial deformation behavior were most notable at test temperatures below the martensite finish temperature. The elastic modulus of the material was very dependent on strain level; therefore, dynamic Young#s Modulus was determined as a function of temperature by an impulse excitation technique. More importantly, the performance of a thermally activated actuator material is dependent on the work output of the alloy. Consequently, the strain-temperature response of the Ni19.5Pd30Ti50.5 alloy under various loads was determined in both tension and compression and the specific work output calculated and compared in both loading conditions. It was found that the transformation strain and thus, the specific work output were similar regardless of the loading condition. Also, in both tension and compression, the strain-temperature loops determined under constant load conditions did not close due to the fact that the transformation strain during cooling was always larger than the transformation strain during heating. This was apparently the result of permanent plastic deformation of the martensite phase with each cycle. Consequently, before this alloy can be used under cyclic actuation conditions, modification of the microstructure or composition would be required to increase the resistance of the alloy to plastic deformation by slip.

Effects of plaque lengths on stent surface roughness.

PubMed

Syaifudin, Achmad; Takeda, Ryo; Sasaki, Katsuhiko

2015-01-01

The physical properties of the stent surface influence the effectiveness of vascular disease treatment after stent deployment. During the expanding process, the stent acquires high-level deformation that could alter either its microstructure or the magnitude of surface roughness. This paper constructed a finite element simulation to observe the changes in surface roughness during the stenting process. Structural transient dynamic analysis was performed using ANSYS, to identify the deformation after the stent is placed in a blood vessel. Two types of bare metal stents are studied: a Palmaz type and a Sinusoidal type. The relationship between plaque length and the changes in surface roughness was investigated by utilizing three different length of plaque; plaque length longer than the stent, shorter than the stent and the same length as the stent. In order to reduce computational time, 3D cyclical and translational symmetry was implemented into the FE model. The material models used was defined as a multilinear isotropic for stent and hyperelastic for the balloon, plaque and vessel wall. The correlation between the plastic deformation and the changes in surface roughness was obtained by intermittent pure tensile test using specimen whose chemical composition was similar to that of actual stent material. As the plastic strain is achieved from FE simulation, the surface roughness can be assessed thoroughly. The study found that the plaque size relative to stent length significantly influenced the critical changes in surface roughness. It was found that the length of stent which is equal to the plaque length was preferable due to the fact that it generated only moderate change in surface roughness. This effect was less influential to the Sinusoidal stent.

Cyclic Spin Testing of Superalloy Disks With a Dual Grain Microstructure

NASA Technical Reports Server (NTRS)

Gayda, John; Kantzos, Pete

2005-01-01

An aggressive cyclic spin test program was run to verify the reliability of superalloy disks with a dual grain structure, fine grain bore and coarse grain rim, utilizing a disk design with web holes bisecting the grain size transition zone. Results of these tests were compared with conventional disks with uniform grain structures. Analysis of the test results indicated the cyclic performance of disks with a dual grain structure could be estimated to a level of accuracy which does not appear to prohibit the use of this technology in advanced gas turbine engines, although further refinement of lifing methodology is clearly warranted.

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.

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.

Aseismic creep along the North Anatolian Fault quantified by coupling microstructural strain and chemical analyses

NASA Astrophysics Data System (ADS)

Kaduri, Maor; Gratier, Jean-Pierre; Renard, François; Çakir, Ziyadin; Lasserre, Cécile

2017-04-01

In the last decade aseismic creep has been noted as one of the key processes along tectonic plate boundaries. It contributes to the energy budget during the seismic cycle, delaying or triggering the occurrence of large earthquakes. Several major continental active faults show spatial alternation of creeping and locked segments. A great challenge is to understand which parameters control the transition from seismic to aseismic deformation in fault zones, such as the lithology, the degree of deformation from damage rocks to gouge, and the stress driven fault architecture transformations at all scales. The present study focuses on the North Anatolian Fault (Turkey) and characterizes the mechanisms responsible for the partition between seismic and aseismic deformation. Strain values were calculated using various methods, e.g. Fry, R-φs from microstructural measurements in gouge and damage samples collected on more than 30 outcrops along the fault. Maps of mineral composition were reconstructed from microprobe measurements of gouge and damage rock microstructure, in order to calculate the relative mass changes due to stress driven processes during deformation. Strain values were extracted, in addition to the geometrical properties of grain orientation and size distribution. Our data cover subsamples in the damage zones that were protected from deformation and are reminiscent of the host rock microstructure and composition, and subsamples that were highly deformed and recorded both seismic and aseismic deformations. Increase of strain value is linked to the evolution of the orientation of the grains from random to sheared sub-parallel and may be related to various parameters: (1) relative mass transfer increase with increasing strain indicating how stress driven mass transfer processes control aseismic creep evolution with time; (2) measured strain is strongly related with the initial lithology and with the evolution of mineral composition: monomineralic rocks are stronger (less deformed) than polymineralic ones; (3) strain measurements allow to evaluate the cumulated geological displacement accommodated by aseismic creep and the relative ratio between seismic and aseismic displacement for each section of an active fault. These relations allow to quantify more accurately the aseismic creep processes and their evolution with time along the North Anatolian Fault which are controlled by a superposition of two kinds of mechanisms: (1) stress driven mass transfer (pressure solution and metamorphism) that control local and regional mass transfer and associated rheology evolution and (2) grain boundary sliding along weak mineral interfaces (initially weak minerals or more often transformed by deformation-related reactions).

Cyclic axial-torsional deformation behavior of a cobalt-base superalloy

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

1992-01-01

Multiaxial loading, especially at elevated temperature, can cause the inelastic response of a material to differ significantly from that predicted by simple flow rules, i.e., von Mises or Tresca. To quantify some of these differences, the cyclic high-temperature, deformation behavior of a wrought cobalt-based superalloy, Haynes 188, is investigated under combined axial and torsional loads. Haynes 188 is currently used in many aerospace gas turbine and rocket engine applications, e.g., the combustor liner for the T800 turboshaft engine for the RAH-66 Comanche helicopter and the liquid oxygen posts in the main injector of the space shuttle main engine. The deformation behavior of this material is assessed through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue data base has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gauge section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress versus engineering shear strain, axial strain versus engineering shear strain, and axial stress versus shear stress spaces are presented for cyclic, in-phase and out-of-phase, axial torsional tests. For in-phase tests three different values of the proportionality constant, lambda (ratio of engineering shear strain amplitude to axial strain amplitude), are examined, viz., 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 deg with lambda = 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress-strain and the maximum shear stress-maximum engineering shear strain (Tresca) curves. Comparisons are also made between the hardening behaviors of cyclic axial, torsional, and combined in-phase and out-of-phase axial-torsional fatigue tests. These comparisons are accomplished through simple Ramberg-Osgood type stress-strain functions for cyclic, axial stress-strain and shear stress-engineering shear strain curves.

Acoustic emission during tensile deformation of M250 grade maraging steel

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Chandan Kumar; Rajkumar, Kesavan Vadivelu; Chandra Rao, Bhaghi Purna; Jayakumar, Tamanna

2012-05-01

Acoustic emission (AE) generated during room temperature tensile deformation of varyingly heat treated (solution annealed and thermally aged) M250 grade maraging steel specimens have been studied. Deformation of microstructure corresponding to different heat treated conditions in this steel could be distinctly characterized using the AE parameters such as RMS voltage, counts and peak amplitude of AE hits (events).

Microstructure stability during creep deformation of hard-oriented polysynthetically twinned crystal of TiAl alloy

NASA Astrophysics Data System (ADS)

Kim, Hee Y.; Maruyama, K.

2003-10-01

The hard-orientated polysynthetically twinned (PST) crystal with the lamellar plates oriented parallel to the compression axis was deformed at 1150 K under the applied stress of 158 to 316 MPa. Microstructural changes were examined quantitatively for the PST crystal during creep deformation. In the as-grown PST crystal of the present study, proportions of α 2/ γ, true twin, pseudotwin, and 120 deg rotational fault interfaces were 12, 59, 12, and 17 pct, respectively. After creep deformation, lamellar coarsening by dissolution of α 2 lamellae and migration of γ/γ interfaces were observed. The acceleration of creep rate after the minimum strain rate in the creep curve was attributed to the lamellar coarsening and destruction of lamellar structure during the creep deformation. Thirty-two percent of α 2/ γ interfaces, 51 pct of true twin interfaces, 74 pct of pseudotwin interfaces, and 80 pct of 120 deg rotational faults disappeared after 4 pct creep strain at 1150 K. The α 2/ γ interface was more stable than γ/γ interfaces during the creep deformation. The pseudotwin interface and 120 deg rotational fault were less thermally stable than the true twin interface for γ/γ interfaces.

3-Dimensional Microstructure of Al-Al3Ti Alloy Severely Deformed by ECAP

NASA Astrophysics Data System (ADS)

Sato, Hisashi; Hishikawa, Takahisa; Makino, Yuuki; Kunimine, Takahiro; Watanabe, Yoshimi

Microstructure of Al-Al3Ti alloy deformed by Equal-Channel-Angular Pressing (ECAP) is 3-dimensionally investigated. Especially, distribution of Al3Ti particles is focused in this study. The Al-Al3Ti alloy has coarse Al3Ti platelet particles in α-Al matrix. When the Al-Al3Ti alloy is deformed by ECAP under route A, fine Al3Ti platelet particles are observed. These Al3Ti platelet particles are aligned along to deformation axis, and its plane normal is perpendicular to the deformation axis. On the other hand, Al-Al3Ti alloy ECAPed under route Bc forms several groups consisted of fine Al3Ti platelet particles. Moreover, longitudinal size of the Al3Ti particle groups is close to that of initial Al3Ti particles with 4-pass ECAP specimen. These distribution behaviors of the Al3Ti particle can be explained by plastic flow of α-Al matrix. Finally, it is concluded that distribution of Al3Ti particle in Al-Al3Ti alloy by ECAP is controlled by plastic deformation of α-Al matrix.

Microstructural record of cataclastic and dissolution-precipitation processes from shallow crustal carbonate strike-slip faults, Northern Calcareous Alps (Austria)

NASA Astrophysics Data System (ADS)

Bauer, Helene; Grasemann, Bernhard; Decker, Kurt

2015-04-01

The concept of coseismic slip and aseismic creep deformation along faults is supported by the variability of natural fault rocks and their microstructures. Faults in carbonate rocks are characterized by very narrow principal slip zones (cm to mm wide) containing (ultra)cataclastic fault rocks that accommodate most of the fault displacement. Fluidization of ultracataclastic sub layers and thermal decomposition of calcite due to frictional heating have been proposed as possible indicators for seismic slip. Dissolution-precipitation (DP) processes are possible mechanism of aseismic sliding, resulting in spaced cleavage solution planes and associated veins, indicating diffusive mass transfer and precipitation in pervasive vein networks. We investigated exhumed, sinistral strike-slip faults in carbonates of the Northern Calcareous Alps. The study presents microstructural investigations of natural carbonate fault rocks that formed by cataclastic and dissolution-precipitation related deformation processes. Faults belong to the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system that was formed during eastward lateral extrusion of the Eastern Alps in Oligocene to Lower Miocene. The investigated faults accommodated sinistral slip between several tens and few hundreds of meters. Microstructural analysis of fault rocks was done with scanning electron microscopy and optical microscopy. Deformation experiments of natural fault rocks are planned to be conducted at the Sapienza University of Roma and should be available at the meeting. The investigated fault rocks give record of alternating cataclastic deformation and DP creep. DP fault rocks reveal various stages of evolution including early stylolites, pervasive pressure solution seams and cleavage, localized shear zones with syn-kinematic calcite fibre growth and mixed DP/cataclastic microstructures, involving pseudo sc- and scc'-fabrics. Pressure solution seams host fine grained kaolinit, chlorite and illite while the protolith shows only weak evidence of detrital clay content. Our studies suggest that velocity weakening and strengthening mechanisms alternated during the accumulation of displacement along the SEMP fault zone.

Thermal Stability of Microstructure and Microhardness of Heterophase BCC-Alloys After Torsional Deformation on Bridgman Anvils

NASA Astrophysics Data System (ADS)

Ditenberg, I. A.; Tyumentsev, A. N.

2018-03-01

The results of investigations of thermal stability of microstructure and microhardness of alloys of the V-4Ti-4Cr and Mo-47Re systems, subjected to torsional deformation by high quasi-hydrostatic pressure at room temperature, are reported. It is shown that submicrocrystalline and nanocrystalline states, and the respective high values of microhardness, persist up to the upper bound ( 0.4 Tmelt) of the temperature interval of their recovery and polygonization in a single-phase state. The main factors ensuring thermal stability of highlydefective states in heterophase alloys are discussed.

Twinning and martensite in a 304 austenitic stainless steel

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

Shen, Yongfeng; Li, Xi; Sun, Xin

2012-08-30

The microstructure characteristics and deformation behavior of 304L stainless steel during tensile deformation at two different strain rates have been investigated by means of interrupted tensile tests, electron-backscatter-diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The volume fractions of transformed martensite and deformation twins at different stages of the deformation process were measured using X-ray diffraction method and TEM observations. It is found that the volume fraction of martensite monotonically increases with increasing strain but decreases with increasing strain rate. On the other hand, the volume fraction of twins increases with increasing strain for strain level less than 57%. Beyondmore » that, the volume fraction of twins decreases with increasing strain. Careful TEM observations show that stacking faults (SFs) and twins preferentially occur before the nucleation of martensite. Meanwhile, both {var_epsilon}-martensite and {alpha}{prime}-martensite are observed in the deformation microstructures, indicating the co-existence of stress induced- transformation and strain-induced-transformation. We also discussed the effects of twinning and martensite transformation on work-hardening as well as the relationship between stacking faults, twinning and martensite transformation.« less

The mechanical properties of austenite stainless steel 304 after structural deformation through cold work

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

Mubarok, Naila; Manaf, Azwar, E-mail: azwar@ui.ac.id; Notonegoro, Hamdan Akbar

The 304 stainless steel (SS) type is widely used in oil and gas operations due to its excellent corrosion resistance. However, the presence of the fine sand particles and H{sub 2}S gas contained in crude oil could lead the erosion and abrasion in steel. In this study, cold rolled treatments were conducted to the 304 SS in order to increase the wear resistance of the steel. The cold work has resulted in thickness reduction to 20%, 40% and 60% of the original. Various microstructural characterizations were used to analyze the effect of deformation. The hardness characterization showed that the initialmore » hardness value increased from 145 HVC to 395 HVC as the level of deformation increase. Further, the wear resistance increased with the deformation rate from 0% to 40% and subsequently decreased from 40% to 60% deformation rate. Microstructural characterization shows that the boundary change to coincide by 56 µm, 49 µm, 45 µm, and 43 µm width and the grain go to flatten and being folded like needles. The effect of deformation on the grain morphology and structure was also studied by optical metallography and X-Ray Diffraction. It is shown that the deformation by means of a cold rolled process has transformed the austenite structure into martensitic structure.« less

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.

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

2018-01-01

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes

DOE PAGES

Ghassemi-Armaki, Hassan; Leff, Asher C.; Taheri, Mitra L.; ...

2017-06-22

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C ismore » compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less

Fatigueless response of spider draglines in cyclic torsion facilitated by reversible molecular deformation

NASA Astrophysics Data System (ADS)

Kumar, Bhupesh; Singh, Kamal P.

2014-11-01

We demonstrate that spider draglines exhibit a fatigueless response in extreme cyclic torsion up to its breaking limit. The well defined Raman bands at 1095 and 1245 cm-1 shifted linearly towards lower wavenumbers versus increasing twist in both clockwise and counter-clockwise directions. Under thousands of continuous loading cycles of twist strain approaching its breaking limit, all the Raman bands were preserved and the characteristic Raman peak shifts were found to be reversible. Besides, nanoscale surface profile of the worked silk appeared as good as the pristine silk. This unique fatigueless twist response of draglines, facilitated by reversible deformation of protein molecules, could find applications in durable miniatured devices.

Microstructural observations on hydrothermal veins of Site U1414, IODP Expedition 344 (CRISP 2)

NASA Astrophysics Data System (ADS)

Brandstätter, Jennifer; Kurz, Walter; Rogowitz, Anna

2017-04-01

The erosive active margin offshore Osa Peninsula (Costa Rica) is characterized by the subducting Cocos Plate with its topographic height, the aseismic Cocos Ridge, which has lifted the seismogenic zone in the reach of scientific drilling. To understand the processes occurring in the subducting Cocos Plate in the vicinity to the Middle America Trench, we investigated microstructures in hydrothermal veins, transecting the lithified sediments and the igneous basement of IODP Hole U-1414A. Mechanical e-twinning occurred mainly in the blocky calcite veins in the lithified sediments, rather than in the fibrous calcite veins within the Cocos Ridge basalt. The differential stress, obtained from two different piezometers, indicate mean differential stresses of approximately 53 and 82 MPa. The majority of the twins show a significant thickness (up to 120 µm), straight twin boundaries and are indicative for deformation temperatures between 150 to 300°C. The presence of additional deformation structures, such as undulose extinction and subgrain boundaries, indicates intracrystalline-plastic deformation by dislocation creep. The comparison of the EBSD data from two samples within the lithified sedimentary unit indicates diverse deformation temperatures. Variation in subgrain size observed for the different samples can be related to local variations in differential stress. The results of different microstructural observations showed, that the deformational history of Site 344-U1414 is characterized by distinct tectonic phases, occurring during the movement of the Cocos Ridge from its location of origin (the Galapagos hotspot) to the convergent margin offshore Costa Rica. The causes for these changes in deformation mechanisms in the studied rocks are ascribed to magmatic advection resulting in an increase of temperature and decrease of critical resolved shear stresses, as well as the bending of the Cocos plate adjacent to the Middle American trench.

Ductile to Brittle Shear Localization in the Upper Crust During Thermal Anomaly: the Calamita Complex (Elba Island, Italy)

NASA Astrophysics Data System (ADS)

Papeschi, S.

2016-12-01

A field and microstructural study of contemporaneous pluton-related thermal anomaly and thrust faulting highlights the mutual interaction between active regional tectonics, magma emplacement and contact metamorphism. The Calamita Complex is composed of highly strained HT/LP schists, metarenites and metacarbonates. HT metamorphism was caused by the emplacement of the buried Porto Azzurro intrusion occurred at pressures below 0.2 GPa. Thermal anomaly was associated to top-to-NE shearing that produced multiple mylonitic shear zones, a HT/LP W-dipping foliation and E-W trending lineations. Strain markers provided by metaconglomerates suggest that deformation occurred in a constrictional regime, independent from the geometry of the magmatic system. Pluton emplacement and shearing were not caused by each other but they interacted producing an entirely new fabric that transposed the previous regional features. Deformation outlasted cooling causing the progressive localization of shearing along a main cataclastic zone localized at the contact between mylonitic metacarbonates and schists. The interaction between shearing and the emplacement of late leucogranitic sills caused also the development of mylonitic to cataclastic fabrics within the sills, depending on temperature and strain rate at the time of emplacement. At the microscale synkinematic blastesis of andalusite plus cordierite and the progressive switch from GBM- to SGR- to BLG- microstructures of quartz, locally overprinted by cataclastic fabrics. The analysis of microstructures suggest that in the Calamita Complex regional deformation affected the host rocks and the late magmatic products of the pluton that registered the switch from ductile to brittle conditions. This switch was generally due to the progressive cooling of the system; however multiple microstructures suggest that deformation in the Calamita was heterogeneous in time and space and possibly subject to different strain rates in different portions that may have produced coeval ductile and brittle deformation.

Microstructural and strain rate effects on plastic deformation in aluminum 2219-T87

NASA Astrophysics Data System (ADS)

Rincon, Carlos D.

A fundamental investigation has been conducted on the effects of microstructure and strain rate on the plastic deformation of theta-prime-strengthened 2219 aluminum. The motivation for this work is based upon a previous study which showed inhomogeneous and locally extreme work hardening in the HAZ regions in VPPA 2219-T87 butt welds. This strongly suggests that the HAZ microstructure plays a major role in the deformation and fracture process in precipitation hardened aluminum alloy 2219. Tensile specimens of the weld joint exhibited more rapid work hardening in the heat-affected-zone (HAZ) at higher strain levels. Microhardness contour maps for these welds illustrated that late stage deformation was concentrated in two crossing bands at about 45sp° to the tensile axis. The width of the deformation bands and the ultimate tensile strength seemed to be dictated by the amount of work hardening in the HAZ. In this study, three different heat treatments were used to produce samples with different particle sizes and particle spacings, but all hardened by copper aluminide precipitates of the thetasp' structure. The heat treatments were categorized as being (A) as-received T87 condition, (B) T87 condition aged at approximately 204sp°C for 3 hours and (C) T87 over-aged at 204sp°C for 7 days. Uniaxial tensile tests consisted of two sets of experiments: (1) three heat treatments (A, B, and C) at two strain rates (0.02 minsp{-1} and 0.2 minsp{-1}) and (2) three heat treatments that were interrupted at select stress-strain levels (0.8% and 2% total strain) during the tensile tests at strain rate equal to 0.02 minsp{-1} at room temperature. Furthermore, a detailed transmission electron microscopy (TEM) study demonstrates the microstructural development during tensile deformation. The Voce equation of strain-hardening provides a slightly better fit to the tensile curves than the Ludwik-Hollomon equation. At higher strains, localized areas showed strain fields around thetasp' platelets had diminished. Lastly, in every treatment, both the yield and tensile strength were slightly higher for the higher strain rate, but only by 0.5 to 2.0 ksi.

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

NASA Astrophysics Data System (ADS)

Cui, Z.; Patel, J.; Palmiere, E. J.

The recrystallisation behaviour of medium carbon steels with dilute Nb addition was investigated by means of plane strain compression tests and the observation of prior austenite microstructures during different deformation conditions. It was found that complete suppression of recrystallisation did not occur in the deformation temperature range investigated. At lower deformation temperatures, partial recrystallisation occurred in the higher Nb sample. This gives the potential to obtain a full suppression of recrystallisation at lower deformation temperatures.

Dynamic Response and Microstructure Evolution of AA2219-T4 and AA2219-T6 Aluminum Alloys

NASA Astrophysics Data System (ADS)

Olasumboye, A.; Owolabi, G.; Odeshi, A.; Zeytinci, A.; Yilmaz, N.

2018-02-01

In this study, the dynamic deformation behavior of AA2219 aluminum alloy was investigated in two different temper conditions: T4 and T6, with a view to determining the effect of heat treatment on the microstructure and flow behavior of the material under high strain rates. Split Hopkinson pressure bar experiment was used in determining the dynamic response of the alloy while a digital image correlation system was employed in visualizing and tracking the surface deformation of the specimens. Optical microscopy and scanning electron microscopy were used to assess the microstructure of the material after following standard metallographic specimen preparation techniques. The results obtained showed heterogeneous deformation of the alloy in the two temper conditions. It was observed that the dynamic mechanical behavior of each sample preparation was dependent on its strength properties due to aging type, which in turn controls the metamorphosis of the strengthening precipitates and the initial microstructure. At the maximum strain rate of 3500 s-1, transformed bands leading to crack nucleation was observed in the AA2219-T4 aluminum alloy while AA2219-T6 had fractured at the same strain rate. The modes of crack formation and growth in the two alloys were found to be similar: nucleation, growth and coalescence of voids. However, shear band bifurcation phenomenon was observed only in the AA2219-T6 alloy.

Effect of composition and austenite deformation on the transformation characteristics of low-carbon and ultralow-carbon microalloyed steels

NASA Astrophysics Data System (ADS)

Cizek, P.; Wynne, B. P.; Davies, C. H. J.; Muddle, B. C.; Hodgson, P. D.

2002-05-01

Deformation dilatometry has been used to simulate controlled hot rolling followed by controlled cooling of a group of low- and ultralow-carbon microalloyed steels containing additions of boron and/or molybdenum to enhance hardenability. Each alloy was subjected to simulated recrystallization and nonrecrystallization rolling schedules, followed by controlled cooling at rates from 0.1 °C/s to about 100 °C/s, and the corresponding continuous-cooling-transformation (CCT) diagrams were constructed. The resultant microstructures ranged from polygonal ferrite (PF) for combinations of slow cooling rates and low alloying element contents, through to bainitic ferrite accompanied by martensite for fast cooling rates and high concentrations of alloying elements. Combined additions of boron and molybdenum were found to be most effective in increasing steel hardenability, while boron was significantly more effective than molybdenum as a single addition, especially at the ultralow carbon content. Severe plastic deformation of the parent austenite (>0.45) markedly enhanced PF formation in those steels in which this microstructural constituent was formed, indicating a significant effective decrease in their hardenability. In contrast, in those steels in which only nonequilibrium ferrite microstructures were formed, the decreases in hardenability were relatively small, reflecting the lack of sensitivity to strain in the austenite of those microstructural constituents forming in the absence of PF.

Micromechanics of plastic deformation and phase transformation in a three-phase TRIP-assisted advanced high strength steel: Experiments and modeling

NASA Astrophysics Data System (ADS)

Srivastava, Ankit; Ghassemi-Armaki, Hassan; Sung, Hyokyung; Chen, Peng; Kumar, Sharvan; Bower, Allan F.

2015-05-01

The micromechanics of plastic deformation and phase transformation in a three-phase advanced high strength steel are analyzed both experimentally and by microstructure-based simulations. The steel examined is a three-phase (ferrite, martensite and retained austenite) quenched and partitioned sheet steel with a tensile strength of 980 MPa. The macroscopic flow behavior and the volume fraction of martensite resulting from the austenite-martensite transformation during deformation were measured. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress-strain curves were obtained. Finite element simulations idealize the microstructure as a composite that contains ferrite, martensite and retained austenite. All three phases are discretely modeled using appropriate crystal plasticity based constitutive relations. Material parameters for ferrite and martensite are determined by fitting numerical predictions to the micropillar data. The constitutive relation for retained austenite takes into account contributions to the strain rate from the austenite-martensite transformation, as well as slip in both the untransformed austenite and product martensite. Parameters for the retained austenite are then determined by fitting the predicted flow stress and transformed austenite volume fraction in a 3D microstructure to experimental measurements. Simulations are used to probe the role of the retained austenite in controlling the strain hardening behavior as well as internal stress and strain distributions in the microstructure.

Dynamic Response and Microstructure Evolution of AA2219-T4 and AA2219-T6 Aluminum Alloys

NASA Astrophysics Data System (ADS)

Olasumboye, A.; Owolabi, G.; Odeshi, A.; Zeytinci, A.; Yilmaz, N.

2018-06-01

In this study, the dynamic deformation behavior of AA2219 aluminum alloy was investigated in two different temper conditions: T4 and T6, with a view to determining the effect of heat treatment on the microstructure and flow behavior of the material under high strain rates. Split Hopkinson pressure bar experiment was used in determining the dynamic response of the alloy while a digital image correlation system was employed in visualizing and tracking the surface deformation of the specimens. Optical microscopy and scanning electron microscopy were used to assess the microstructure of the material after following standard metallographic specimen preparation techniques. The results obtained showed heterogeneous deformation of the alloy in the two temper conditions. It was observed that the dynamic mechanical behavior of each sample preparation was dependent on its strength properties due to aging type, which in turn controls the metamorphosis of the strengthening precipitates and the initial microstructure. At the maximum strain rate of 3500 s-1, transformed bands leading to crack nucleation was observed in the AA2219-T4 aluminum alloy while AA2219-T6 had fractured at the same strain rate. The modes of crack formation and growth in the two alloys were found to be similar: nucleation, growth and coalescence of voids. However, shear band bifurcation phenomenon was observed only in the AA2219-T6 alloy.

Characterization of ultra-fine grained aluminum produced by accumulative back extrusion (ABE)

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

Alihosseini, H., E-mail: hamid.alihossieni@gmail.com; Materials Science and Engineering Department, Engineering School, Amirkabir University, Tehran; Faraji, G.

2012-06-15

In the present work, the microstructural evolutions and microhardness of AA1050 subjected to one, two and three passes of accumulative back extrusion (ABE) were investigated. The microstructural evolutions were characterized using transmission electron microscopy. The results revealed that applying three passes of accumulative back extrusion led to significant grain refinement. The initial grain size of 47 {mu}m was refined to the grains of 500 nm after three passes of ABE. Increasing the number of passes resulted in more decrease in grain size, better microstructure homogeneity and increase in the microhardness. The cross-section of ABEed specimen consisted of two different zones:more » (i) shear deformation zone, and (ii) normal deformation zone. The microhardness measurements indicated that the hardness increased from the initial value of 31 Hv to 67 Hv, verifying the significant microstructural refinement via accumulative back extrusion. - Highlights: Black-Right-Pointing-Pointer A significant grain refinement can be achieved in AA1050, Al alloy by applying ABE. Black-Right-Pointing-Pointer Microstructural homogeneity of ABEed samples increased by increasing the number of ABE cycles. Black-Right-Pointing-Pointer A substantial increase in the hardness, from 31 Hv to 67 Hv, was recorded.« less

Low-Cycle Fatigue Properties of P92 Ferritic-Martensitic Steel at Elevated Temperature

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Hu, ZhengFei; Schmauder, Siegfried; Mlikota, Marijo; Fan, KangLe

2016-04-01

The low-cycle fatigue behavior of P92 ferritic-martensitic steel and the corresponding microstructure evolution at 873 K has been extensively studied. The test results of fatigue lifetime are consistent with the Coffin-Manson relationship over a range of controlled total strain amplitudes from 0.15 to 0.6%. The influence of strain amplitude on the fatigue crack initiation and growth has been observed using optical microscopy and scanning electron microscopy. The formation mechanism of secondary cracks is established according to the observation of fracture after fatigue process and there is an intrinsic relationship between striation spacing, current crack length, and strain amplitude. Transmission electron microscopy has been employed to investigate the microstructure evolution after fatigue process. It indicates the interaction between carbides and dislocations together with the formation of cell structure inhibits the cyclic softening. The low-angle sub-boundary elimination in the martensite is mainly caused by the cyclic stress.

Effect of Cyclic Thermal Process on Ultrafine Grain Formation in AISI 304L Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Ravi Kumar, B.; Mahato, B.; Sharma, Sailaja; Sahu, J. K.

2009-12-01

As-received hot-rolled commercial grade AISI 304L austenitic stainless steel plates were solution treated at 1060 °C to achieve chemical homogeneity. Microstructural characterization of the solution-treated material revealed polygonal grains of about 85- μm size along with annealing twins. The solution-treated plates were heavily cold rolled to about 90 pct of reduction in thickness. Cold-rolled specimens were then subjected to thermal cycles at various temperatures between 750 °C and 925 °C. X-ray diffraction showed about 24.2 pct of strain-induced martensite formation due to cold rolling of austenitic stainless steel. Strain-induced martensite formed during cold rolling reverted to austenite by the cyclic thermal process. The microstructural study by transmission electron microscope of the material after the cyclic thermal process showed formation of nanostructure or ultrafine grain austenite. The tensile testing of the ultrafine-grained austenitic stainless steel showed a yield strength 4 to 6 times higher in comparison to its coarse-grained counterpart. However, it demonstrated very poor ductility due to inadequate strain hardenability. The poor strain hardenability was correlated with the formation of strain-induced martensite in this steel grade.

Mechanism of slip and twinning

NASA Technical Reports Server (NTRS)

Rastani, Mansur

1992-01-01

The objectives are to: (1) demonstrate the mechanisms of deformation in body centered cubic (BCC), face centered cubic (FCC), and hexagonal close-packed (HCP)-structure metals and alloys and in some ceramics as well; (2) examine the deformed microstructures (slip lines and twin boundaries) in different grains of metallic and ceramic specimens; and (3) study visually the deformed macrostructure (slip and twin bands) of metals and alloys. Some of the topics covered include: deformation behavior of materials, mechanisms of plastic deformation, slip bands, twin bands, ductile failure, intergranular fracture, shear failure, slip planes, crystal deformation, and dislocations in ceramics.

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.

Thermomechanical deformation behavior of a dynamic strain aging alloy, Hastelloy X

NASA Technical Reports Server (NTRS)

Castelli, Michael G.; Miner, Robert V.; Robinson, David N.

1992-01-01

An experimental study was performed to identify the effects of dynamic strain aging (solute drag) and metallurgical instabilities under thermomechanical loading conditions. The study involved a series of closely controlled thermomechanical deformation tests on the solid-solution-strenghened nickel-base superalloy, Hastelloy X. This alloy exhibits a strong isothermal strain aging peak at approximately 600 C, promoted by the effects of solute drag and precipitation hardening. Macroscopic thermomechanical hardening trends are correlated with microstructural characteristics through the use of transmission electron microscopy. These observations are compared and contrasted with isothermal conditions. Thermomechanical behavior unique to the isothermal database is identified and discussed. The microstructural characteristics were shown to be dominated by effects associated with the highest temperature of the thermomechanical cycle. Results indicate that the deformation behavior of Hastelloy X is thermomechanically path dependent. In addition, guidance is given pertaining to deformation modeling in the context of macroscopic unified theory. An internal state variable is formulated to qualitatively reflect the isotropic hardening trends identified in the TMD experiments.

Dependence of stress-induced omega transition and mechanical twinning on phase stability in metastable β Ti–V alloys

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

Wang, X.L.; Li, L.; Mei, W.

2015-09-15

Tensile properties and deformation microstructures of a series of binary β Ti–16–22V alloys have been investigated. The results show that the plastic deformation mode changes from the plate-like stress-induced ω phase transformation with a special habit plane of (− 5052){sub ω}//(3 − 3 − 2){sub β} to (332)<113> type deformation twinning with increasing the content of vanadium in the β Ti–16–22 wt.% V alloys. The plate-like stress-induced ω phase has a special orientation relationship with the β phase matrix, i.e., [110]{sub β}//[− 12 − 10]{sub ω}, (3 − 3 − 2){sub β}//(− 5052){sub ω} and (− 55 − 4){sub β}//(30more » − 31){sub ω}. The alloys plastically deformed by stress-induced ω phase transformation exhibit relatively higher yield strength than those deformed via (332)<113> type deformation twinning. It can be concluded that the stability of β phase plays a significant role in plastic deformation mode, i.e., stress-induced ω phase transformation or (332)<113> type deformation twinning, which governs the mechanical property of the β Ti–16–22 wt.% V alloys. - Highlights: • Tensile properties and deformed microstructures of β Ti–16–22V alloys were studied. • Stress-induced ω phase transformation and (332)<113> twinning occur in the alloys. • Stability of β phase plays a significant role in plastic deformation mode. • Plastic deformation mode governs the mechanical property of the alloys.« less

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.

Liquefaction, ground oscillation, and soil deformation at the Wildlife Array, California

USGS Publications Warehouse

Holzer, T.L.; Youd, T.L.

2007-01-01

Excess pore-water pressure and liquefaction at the Wildlife Liquefaction Array in 1987 were caused by deformation associated with both high-frequency strong ground motion and 5.5-second-period Love waves. The Love waves produced large (???1.5%) cyclic shear strains well after the stronger high-frequency ground motion abated. These cyclic strains generated approximately from 13 to 35% of the excess pore-water pressure in the liquefied layer and caused excess pore-water pressures ultimately to reach effective overburden stress. The deformation associated with the Love waves explains the "postearthquake" increase of pore-water pressure that was recorded at the array. This explanation suggests that conventional methods for predicting liquefaction based on peak ground acceleration are incomplete and may need to consider cyclic strains associated with long-period surface waves. A post-earthquake survey of an inclinometer casing indicated permanent shear strain associated with lateral spreading primarily occurred in the upper part of the liquefied layer. Comparison of cone penetration test soundings conducted after the earthquake with pre-earthquake soundings suggests sleeve friction increased. Natural lateral variability of the liquefied layer obscured changes in tip resistance despite a ???1% reduction in volume. The large oscillatory motion associated with surface waves explains ground oscillation that has been reported at some liquefaction sites during earthquakes.

[A microstructural approach to fatigue crack processes in poly crystalline BCC materials]. Progress report

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

Gerberich, W.W.

1992-12-31

Objective was to study fatigue where a combination of low temperature and cyclic loading produced cyclic cleavage in bcc Fe-base systems. Both dislocation dynamics and quasi-statics of crack growth were probed. This document reviews progress over the past 6 years: hydrogen embrittlement and cleavage, computations (stress near crack tip), dislocation emission from grain boundaries, fracture process zones, and understanding brittle fracture at the atomistic/dislocation scales and at the microscopic/macroscopic scale.

Deformation, static recrystallization, and reactive melt transport in shallow subcontinental mantle xenoliths (Tok Cenozoic volcanic field, SE Siberia)

NASA Astrophysics Data System (ADS)

Tommasi, Andréa; Vauchez, Alain; Ionov, Dmitri A.

2008-07-01

Partial melting and reactive melt transport may change the composition, microstructures, and physical properties of mantle rocks. Here we explore the relations between deformation and reactive melt transport through detailed microstructural analysis and crystallographic orientation measurements in spinel peridotite xenoliths that sample the shallow lithospheric mantle beneath the southeastern rim of the Siberian craton. These xenoliths have coarse-grained, annealed microstructures and show petrographic and chemical evidence for variable degrees of reaction with silicate melts and fluids, notably Fe-enrichment and crystallization of metasomatic clinopyroxene (cpx). Olivine crystal preferred orientations (CPO) range from strong to weak. [010]-fiber patterns, characterized by a point concentration of [010] normal to the foliation and by dispersion of [100] in the foliation plane with a weak maximum parallel to the lineation, predominate relative to the [100]-fiber patterns usually observed in lithospheric mantle xenoliths and peridotite massifs. Variations in olivine CPO patterns or intensity are not correlated with modal and chemical compositions. This, together with the analysis of microstructures, suggests that reactive melt percolation postdated both deformation and static recrystallization. Preferential crystallization of metasomatic cpx along (010) olivine grain boundaries points to an influence of the preexisting deformation fabrics on melt transport, with higher permeability along the foliation. Similarity between orthopyroxene (opx) and cpx CPO suggests that cpx orientations may be inherited from those of opx during melt-rock reaction. As observed in previous studies, reactive melt transport does not weaken olivine CPO and seismic anisotropy in the upper mantle, except in melt accumulation domains. In contrast, recovery and selective grain growth during static recrystallization may lead to development of [010]-fiber olivine CPO and, if foliations are horizontal, result in apparent isotropy for vertically propagating SKS waves, but strong anisotropy for horizontally propagating surface waves.

Fluid distribution in grain boundaries of natural fine-grained rock salt deformed at low differential stress (Qom Kuh salt fountain, central Iran): Implications for rheology and transport properties

NASA Astrophysics Data System (ADS)

Desbois, Guillaume; Urai, Janos L.; de Bresser, Johannes H. P.

2012-10-01

We used a combination of broad ion beam cross-sectioning and cryogenic SEM to image polished surfaces and corresponding pairs of fractured grain boundaries in an investigation of grain boundary microstructures and fluid distribution in naturally deformed halite from the Qom Kuh salt glacier (central Iran). At the scale of observations, four types of fluid-filled grain boundary can be distinguished by morphology (from straight to wavy), thickness (from 5000 to 50 nm) and the presence of fluid inclusions. The mobility of the brine is shown after cutting the inclusions by broad ion beam (BIB) in vacuum and fine-grained halite forms efflorescence and precipitates on internal walls of inclusions. At cryogenic temperature, grain boundary brine is shown either as continuous film or in isolated inclusions. The halite-halite grain boundary between isolated fluid inclusions is interpreted to have formed by fluid-assisted grain boundary healing. Preliminary experiments on the samples at shear stress conditions of natural salt glacier show very slow strain rates (7.4 × 10-10 s-1 and 1 × 10-9 s-1), which are less than expected for pressure solution creep. Both microstructures and deformation experiments suggest interfacial energy-driven grain boundary healing and therefore rendering inactive the pressure solution creep in our samples. This result disagrees with previous microstructural studies of the same sample, which showed microstructural evidence for pressure solution (and dislocation creep). Different explanations are discussed, which imply that both healing and reactivation of grain boundaries are important in salt glaciers, leading to heterogeneous distribution of deformation mechanisms and strain rates in both space and time.

On the Process-Related Rivet Microstructural Evolution, Material Flow and Mechanical Properties of Ti-6Al-4V/GFRP Friction-Riveted Joints

PubMed Central

Borba, Natascha Z.; Afonso, Conrado R. M.; Blaga, Lucian; dos Santos, Jorge F.; Canto, Leonardo B.; Amancio-Filho, Sergio T.

2017-01-01

In the current work, process-related thermo-mechanical changes in the rivet microstructure, joint local and global mechanical properties, and their correlation with the rivet plastic deformation regime were investigated for Ti-6Al-4V (rivet) and glass-fiber-reinforced polyester (GF-P) friction-riveted joints of a single polymeric base plate. Joints displaying similar quasi-static mechanical performance to conventional bolted joints were selected for detailed characterization. The mechanical performance was assessed on lap shear specimens, whereby the friction-riveted joints were connected with AA2198 gussets. Two levels of energy input were used, resulting in process temperatures varying from 460 ± 130 °C to 758 ± 56 °C and fast cooling rates (178 ± 15 °C/s, 59 ± 15 °C/s). A complex final microstructure was identified in the rivet. Whereas equiaxial α-grains with β-phase precipitated in their grain boundaries were identified in the rivet heat-affected zone, refined α′ martensite, Widmanstätten structures and β-fleck domains were present in the plastically deformed rivet volume. The transition from equiaxed to acicular structures resulted in an increase of up to 24% in microhardness in comparison to the base material. A study on the rivet material flow through microtexture of the α-Ti phase and β-fleck orientation revealed a strong effect of shear stress and forging which induced simple shear deformation. By combining advanced microstructural analysis techniques with local mechanical testing and temperature measurement, the nature of the complex rivet plastic deformational regime could be determined. PMID:28772545

Microstructural Damage During High-Strain Torsion Experiments on Calcite-Anhydrite Aggregates

NASA Astrophysics Data System (ADS)

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

2016-12-01

Ductile shear zones play a critical role in localising deformation in the Earth's crust and mantle. Severe grain size reduction - a ubiquitous feature of natural mylonites - is commonly thought to cause strain weakening via a transition to grain size sensitive deformation mechanisms. Although grain size reduction is modulated by grain growth in single-phase aggregates, grain boundary pinning in well-mixed poly-phase composites can inhibit grain growth, leading to microstructural `damage' which is likely a critical element of strain localization in the lithosphere. While dynamic recrystallization has been widely explored in rock mechanics and materials science, the mechanisms behind phase-mixing remain poorly understood. In this contribution we present results from high-strain, deformation experiments on calcite-anhydrite composites. Experiments were conducted in torsion at T = 500-700°C and P 1.5 GPa, using the new Large Volume Torsion (LVT) solid-medium apparatus, to shear strains of 0.5-30. As shear strain increases, progressive thinning and necking of initially large (≤ 1 mm) calcite domains is observed, resulting in an increase in the proportion of interphase boundaries. Grain-size is negatively correlated with the fraction of interphase boundaries, such that calcite grains in well-mixed regions are significantly smaller than those in single-phase domains. Crucially, progressive deformation leads to a reduction in grain-size beyond the lower limit established by the grain size piezometer for mono-phase calcite, implying microstructural damage. These data therefore demonstrate continued microstructural evolution in two-phase composites that is not possible in single-phase aggregates. These observations mark a new `geometric' mechanism for phase mixing, complementing previous models for phase mixing involving chemical reactions, material diffusion, and/or grain boundary sliding.

Effect of Thermomechanical Processing on the Microstructure and Mechanical Properties of Nb-Ti-V Microalloyed Steel

NASA Astrophysics Data System (ADS)

Opiela, M.

2014-09-01

The paper presents the results of thermomechanical treatment via forging on the microstructure and mechanical properties of newly obtained microalloyed steel containing 0.28% C, 1.41% Mn, 0.027% Nb, 0.028% Ti, and 0.019% V. The investigated steel is assigned to the production of forged elements for the automotive industry. Conditions of forging using the thermomechanical processing method were developed based on plastometric tests. Continuous and double-hit compression tests were conducted using the Gleeble 3800 thermomechanical simulator. The samples were investigated in a temperature range from 900 to 1100 °C and a strain rate of 1 and 10 s-1. To determine the recrystallization kinetics of plastically deformed austenite, discontinuous compression tests of samples using the applied deformation were conducted in a temperature range from 900 to 1100 °C with isothermal holding of the specimens between successive deformations for 2-100 s. Observations of the microstructures of thin foils were conducted using a TITAN80-300 FEI transmission electron microscope. The applied thermomechanical treatment allows to obtain a fine-grained microstructure of the austenite during hot-working and production of forged parts. These acquire advantageous mechanical properties and guaranteed crack resistance after controlled cooling from the end plastic deformation temperature and successive tempering. Forgings produced using the thermomechanical treatment method, consecutively subjected to tempering in a temperature range from 550 to 650 °C, reveal values of YS0.2 which equal from 994 to 892 MPa, UTS from 1084 to 958 MPa, KV from 69 to 109 J, KV-40 from 55 to 83 J, and a hardness ranging from 360 to 300 HBW.

On the effect of hydrogen on the mechanical behavior of Beta-C titanium in aged condition

NASA Astrophysics Data System (ADS)

Alvarez, Anna-Maria

The effect of hydrogen in solid solution on the mechanical behavior of the metastable beta-titanium alloy Beta-C was studied. The samples were aged at 482°C for 28 h prior to hydrogen charging in order to obtain a microstructure of alpha-precipitates in a beta-phase matrix. The kinetics and thermodynamics of hydrogen uptake in the alloy were studied in order to determine the required parameters to gas charge the samples with hydrogen, without altering the microstructure. The mechanical samples were hydrogen charged at 350°C to hydrogen concentrations between 0.6 and 24 at%. The samples were thereafter tested under tensile and alternating loading in order to study the effect of hydrogen on the tensile properties, fatigue properties and crack propagation rate. The fracture surfaces were then studied by using SEM, TEM and X-ray diffraction techniques. The macroscopic mechanical properties were compared with the micromechanisms of deformation and fracture in order to obtain information about the operating hydrogen-enhanced fracture mechanism. It was found that the tensile behavior was sensitive to hydrogen. A sharp ductile-to-brittle transition (DBT) occurred when hydrogen in solid solution reached a concentration of about 3.5 at%. TEM and X-ray analysis showed that stress-induced hydrides form in areas of low stress intensities at hydrogen concentrations above the DBT, and it is therefore believed that this is the cause of the hydrogen embrittlement in this alloy. However, at higher stress intensities, slip localization and enhanced slip band fracture were observed. Since slip localization and hydrogen-induced slip band fracture have previously been connected with a large decrease in ductility it can not be excluded that these effects of hydrogen affects the DBT. The cyclic stress strain behavior was not affected by hydrogen; the non-linear elastic behavior and the cyclic softening did not change with introduction of hydrogen up to a level of 10.8 at%. The fatigue life was, however, reduced when hydrogen charged samples were tested at low frequency (0.00032 Hz).

Asymptotic analysis of hierarchical martensitic microstructure

NASA Astrophysics Data System (ADS)

Cesana, Pierluigi; Porta, Marcel; Lookman, Turab

2014-12-01

We consider a hierarchical nested microstructure, which also contains a point of singularity (disclination) at the origin, observed in lead orthovanadate. We show how to exactly compute the energy cost and associated displacement field within linearized elasticity by enforcing geometric compatibility of strains across interfaces of the three-phase mixture of distortions (variants) in the microstructure. We prove that the mechanical deformation is purely elastic and discuss the behavior of the system close to the origin.

Effect of Plastic Deformation on the Structure and Properties of Alloy IMV7-1 of the Mg - Y - Gd - Zr System

NASA Astrophysics Data System (ADS)

Rokhlin, L. L.; Dobatkina, T. V.; Luk'yanova, E. A.; Korol'kova, I. G.; Choporov, V. F.

2016-07-01

The microstructure and strength properties of hot-pressed alloy IMV7-1 of the Mg - Y - Gd - Zr system are studied after additional cold and hot rolling deformation. It is shown that the strength properties of the pressed alloy can be elevated by cold deformation at an admissible level of ductility.

Cyclic deformations in the Opalinus clay: a laboratory experiment

NASA Astrophysics Data System (ADS)

Huber, Emanuel; Huggenberger, Peter; Möri, Andreas; Meier, Edi

2015-04-01

The influence of tunnel climate on deformation cycles of joint openings and closings is often observed immediately after excavation. At the EZ-B niche in the Mt. Terri rock laboratory (Switzerland), a cyclic deformation of the shaly Opalinus clay has been monitored for several years. The deformation cycles of the joints parallel to the clay bedding planes correlate with seasonal variations in relative humidity of the air in the niche. In winter, when the relative humidity is the lowest (down to 65%), the joints open as the clay volume decreases, whereas they tend to close in the summer when the relative humidity reaches up to 100%. Furthermore, in situ measurements have shown the trend of an increasingly smaller aperture of joints with time. A laboratory experiment was carried out to reproduce the observed cyclic deformation in a climate chamber using a core sample of Opalinus clay. The main goal of the experiment was to investigate the influence of the relative humidity on the deformation of the Opalinus clay while excluding the in situ effects (e.g. confining stress). The core sample of Opalinus clay was put into a closed ended PVC tube and the space between the sample and the tube was filled with resin. Then, the sample (size: 28 cm × 14 cm × 6.5 cm) was cut in half lengthways and the open end was cut, so that the half-core sample could move in one direction. The mounted sample was exposed to wetting and drying cycles in a climate chamber. Air temperature, air humidity and sample weight were continuously recorded. Photographs taken at regular time intervals by a webcam allowed the formation/deformation of cracks on the surface of the sample to be monitored. A crackmeter consisting of a double-plate capacitor attached to the core sample was developed to measure the dynamics of the crack opening and closing. Preliminary results show that: - Deformation movements during different climate cycles can be visualized with the webcam - The crackmeter signal gives a relatively precise response for relative humidity below 80% - The sample weight variations are clearly related to the climatic conditions (temperature and relative humidity) and associated with deformation of the sample (widening and narrowing of the cracks) - The control of the relative humidity in the climate chamber turned out to be difficult in a laboratory without climate conditioning, especially during summer time

The deformation record of olivine in mylonitic peridotites from the Finero Complex, Ivrea Zone: Separate deformation cycles during exhumation

NASA Astrophysics Data System (ADS)

Matysiak, Agnes K.; Trepmann, Claudia A.

2015-12-01

Mylonitic peridotites from the Finero complex are investigated to detect characteristic olivine microfabrics that can resolve separate deformation cycles at different metamorphic conditions. The heterogeneous olivine microstructures are characterized by deformed porphyroclasts surrounded by varying amounts of recrystallized grains. A well-developed but only locally preserved foam structure is present in recrystallized grain aggregates. This indicates an early stage of dynamic recrystallization and subsequent recovery and recrystallization at quasi-static stress conditions, where the strain energy was reduced such that a reduction in surface energy controlled grain boundary migration. Ultramylonites record a renewed stage of localized deformation and recrystallization by a second generation of recrystallized grains that do not show a foam structure. This second generation of recrystallized grains as well as sutured grain and kink band boundaries of porphyroclasts indicate that these microstructures developed during a stage of localized deformation after development of the foam structure. The heterogeneity of the microfabrics is interpreted to represent several (at least two) cycles of localized deformation separated by a marked hiatus with quasi-static recrystallization and recovery and eventually grain growth. The second deformation cycle did not only result in reactivation of preexisting shear zones but instead also locally affected the host rock that was not deformed in the first stage. Such stress cycles can result from sudden increases in differential stress imposed by seismic events, i.e., high stress-loading rates, during exhumation of the Finero complex.

Effect of temperature on the anisotropy of AZ31 magnesium alloy rolling sheet under high strain rate deformation

NASA Astrophysics Data System (ADS)

Liu, Yanyu; Mao, Pingli; Zhang, Feng; Liu, Zheng; Wang, Zhi

2018-04-01

In order to investigate the effect of temperature on the anisotropic behaviour of AZ31 magnesium alloy rolling sheet under high strain rate deformation, the Split Hopkinson Pressure Bar was used to analyse the dynamic mechanical properties of AZ31 magnesium alloy rolling sheet in three directions, rolling direction(RD), transverse direction (TD) and normal direction (ND). The texture of the rolling sheet was characterised by X-ray analysis and the microstructure prior and after high strain rate deformation was observed by optical microscope (OM). The results demonstrated that AZ31magnesium alloy rolling sheet has strong initial {0 0 0 2} texture, which resulted at the obvious anisotropy in high strain rate deformation at 20 °C. The anisotropy reflected in stress-strain curve, yield stress, peak stress and microstructure. The anisotropy became much weaker when the deformation temperature increased up to 250 °C. Continuing to increase the deformation temperature to 350 °C the anisotropy of AZ31 rolling sheet essentially disappeared. The decreasing tendency of anisotropy with increasing temperature was due to the fact that when the deformation temperature increased, the critical resolved shear stress (CRSS) for pyramidal 〈c + a〉 slip, which was the predominant slip mechanism for ND, decreased close to that of twinning, which was the predominant deformation mechanism for RD and TD. The deformation mechanism at different directions and temperatures and the Schmid factor (SF) at different directions were discussed in the present paper.

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

Deformability and size-based cancer cell separation using an integrated microfluidic device.

PubMed

Pang, Long; Shen, Shaofei; Ma, Chao; Ma, Tongtong; Zhang, Rui; Tian, Chang; Zhao, Lei; Liu, Wenming; Wang, Jinyi

2015-11-07

Cell sorting by filtration techniques offers a label-free approach for cell separation on the basis of size and deformability. However, filtration is always limited by the unpredictable variation of the filter hydrodynamic resistance due to cell accumulation and clogging in the microstructures. In this study, we present a new integrated microfluidic device for cell separation based on the cell size and deformability by combining the microstructure-constricted filtration and pneumatic microvalves. Using this device, the cell populations sorted by the microstructures can be easily released in real time for subsequent analysis. Moreover, the periodical sort and release of cells greatly avoided cell accumulation and clogging and improved the selectivity. Separation of cancer cells (MCF-7, MDA-MB-231 and MDA231-LM2) with different deformability showed that the mixture of the less flexible cells (MCF-7) and the flexible cells (MDA-MB-231 and MDA231-LM2) can be well separated with more than 75% purity. Moreover, the device can be used to separate cancer cells from the blood samples with more than 90% cell recovery and more than 80% purity. Compared with the current filtration methods, the device provides a new approach for cancer cell separation with high collection recovery and purity, and also, possesses practical potential to be applied as a sample preparation platform for fundamental studies and clinical applications.

Microstructural Evolution and Constitutive Relationship of M350 Grade Maraging Steel During Hot Deformation

NASA Astrophysics Data System (ADS)

Chakravarthi, K. V. A.; Koundinya, N. T. B. N.; Narayana Murty, S. V. S.; Nageswara Rao, B.

2017-03-01

Maraging steels exhibit extraordinary strength coupled with toughness and are therefore materials of choice for critical structural applications in defense, aerospace and nuclear engineering. Thermo-mechanical processing is an important step in the manufacture of these structural components. This process assumes significance as these materials are expensive and the mechanical properties obtained depend on the microstructure evolved during thermo-mechanical processing. In the present study, M350 grade maraging steel specimens were hot isothermally compressed in the temperature range of 900-1200 °C and in the strain rate range of 0.001-100 s-1, and true stress-true strain curves were generated. The microstructural evolution as a function of strain rate and temperature in the deformed compression specimens was studied. The effect of friction between sample and compression dies was evaluated, and the same was found to be low. The measured flow stress data was used for the development of a constitutive model to represent the hot deformation behavior of this alloy. The proposed equation can be used as an input in the finite element analysis to obtain the flow stress at any given strain, strain rate, and temperature useful for predicting the flow localization or fracture during thermo-mechanical simulation. The activation energy for hot deformation was calculated and is found to be 370.88 kJ/mol, which is similar to that of M250 grade maraging steel.

Plastic Flow and Microstructure Evolution during Thermomechanical Processing of a PM Nickel-Base Superalloy

NASA Astrophysics Data System (ADS)

Semiatin, S. L.; McClary, K. E.; Rollett, A. D.; Roberts, C. G.; Payton, E. J.; Zhang, F.; Gabb, T. P.

2013-06-01

Plastic flow and microstructure evolution during sub- and supersolvus forging and subsequent supersolvus heat treatment of the powder-metallurgy superalloy LSHR (low-solvus, high-refractory) were investigated to develop an understanding of methods that can be used to obtain a moderately coarse gamma grain size under well-controlled conditions. To this end, isothermal, hot compression tests were conducted over broad ranges of temperature [(1144 K to 1450 K) 871 °C to 1177 °C] and constant true strain rate (0.0005 to 10 s-1). At low temperatures, deformation was generally characterized by flow softening and dynamic recrystallization that led to a decrease in grain size. At high subsolvus temperatures and low strain rates, steady-state flow or flow hardening was observed. These latter behaviors were ascribed to superplastic deformation and microstructure evolution characterized by a constant grain size or concomitant dynamic grain growth, respectively. During supersolvus heat treatment following subsolvus deformation, increases in grain size whose magnitude was a function of the prior deformation conditions were noted. A transition in flow behavior from superplastic to nonsuperplastic and the development during forging at a high subsolvus temperature of a wide (possibly bi- or multimodal) gamma-grain-size distribution having some large grains led to a substantially coarser grain size during supersolvus annealing in comparison to that produced under all other forging conditions.

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.

Experimental study of grain interactions on rolling texture development in face-centered cubic metals

NASA Astrophysics Data System (ADS)

Kumar Ray, Atish

There exists considerable debate in the texture community about whether grain interactions are a necessary factor to explain the development of deformation textures in polycrystalline metals. Computer simulations indicate that grain interactions play a significant role, while experimental evidence shows that the material type and starting orientation are more important in the development of texture and microstructure. A balanced review of the literature on face-centered cubic metals shows that the opposing viewpoints have developed due to the lack of any complete experimental study which considers both the intrinsic (material type and starting orientation) and extrinsic (grain interaction) factors. In this study, a novel method was developed to assemble ideally orientated crystalline aggregates in 99.99% aluminum (Al) or copper (Cu) to experimentally evaluate the effect of grain interactions on room temperature deformation texture. Ideal orientations relevant to face-centered cubic rolling textures, Cube {100} <001>, Goss {110} <001>, Brass {110} <11¯2> and Copper {112} <111¯> were paired in different combinations and deformed by plane strain compression to moderate strain levels of 1.0 to 1.5. Orientation dependent mechanical behavior was distinguishable from that of the neighbor-influenced behavior. In interacting crystals the constraint on the rolling direction shear strains (gammaXY , gammaXZ) was found to be most critical to show the effect of interactions via the evolution of local microstructure and microtexture. Interacting crystals with increasing deformations were observed to gradually rotate towards the S-component, {123} <634>. Apart from the average lattice reorientations, the interacting crystals also developed strong long-range orientation gradients inside the bulk of the crystal, which were identified as accumulating misorientations across the deformation boundaries. Based on a statistical procedure using quaternions, the orientation and interaction related heterogeneous deformations were characterized by three principal component vectors and their respective eigenvalues for both the orientation and misorientation distributions. For the case of a medium stacking fault energy metal like Cu, the texture and microstructure development depends wholly on the starting orientations. Microstructural instabilities in Cu are explained through a local slip clustering process, and the possible role of grain interactions on such instabilities is proposed. In contrast, the texture and microstructure development in a high stacking fault energy metal like Al is found to be dependent on the grain interactions. In general, orientation, grain interaction and material type were found to be key factors in the development of rolling textures in face-centered cubic metals and alloys. Moreso, in the texture development not any single parameter can be held responsible, rather, the interdependency of each of the three parameters must be considered. In this frame-work polycrystalline grains can be classified into four types according to their stability and susceptibility during deformation.

Disturbed Dreaming and the Instability of Sleep: Altered Nonrapid Eye Movement Sleep Microstructure in Individuals with Frequent Nightmares as Revealed by the Cyclic Alternating Pattern

PubMed Central

Simor, Péter; Bódizs, Róbert; Horváth, Klára; Ferri, Raffaele

2013-01-01

Study Objectives: Nightmares are disturbing mental experiences during sleep that usually result in abrupt awakenings. Frequent nightmares are associated with poor subjective sleep quality, and recent polysomnographic data suggest that nightmare sufferers exhibit impaired sleep continuity during nonrapid eye movement (NREM) sleep. Because disrupted sleep might be related to abnormal arousal processes, the goal of this study was to examine polysomnographic arousal-related activities in a group of nightmare sufferers and a healthy control group. Design: Sleep microstructure analysis was carried out by scoring the cyclic alternating pattern (CAP) in NREM sleep and the arousal index in rapid eye movement (REM) sleep on the second night of the polysomnographic examination. Setting: Hospital-based sleep research laboratory. Participants: There were 17 in the nightmare (NMs) group and 23 in the healthy control (CTLs) group. Interventions: N/A. Measurements and Results: The NMs group exhibited reduced amounts of CAP A1 subtype and increased CAP A2 and A3 subtypes, as well as longer duration of CAP A phases in comparison with CTLs. Moreover, these differences remained significant after controlling for the confounding factors of anxious and depressive symptoms. The absolute number and frequency of REM arousals did not differ significantly between the two groups. Conclusions: The results of our study indicate that NREM sleep microstructure is altered during nonsymptomatic nights of nightmares. Disrupted sleep in the NMs group seems to be related to abnormal arousal processes, specifically an imbalance in sleep-promoting and arousing mechanisms during sleep. Citation: Simor P; Bódizs R; Horváth K; Ferri R. Disturbed dreaming and the instability of sleep: altered nonrapid eye movement sleep microstructure in individuals with frequent nightmares as revealed by the cyclic alternating pattern. SLEEP 2013;36(3):413-419. PMID:23449753

On the cyclic stress-strain behavior and low cycle fatigue of aerospace materials

NASA Technical Reports Server (NTRS)

Burbach, J.

1972-01-01

The elastic-plastic deformation behavior under cyclic stress of a number of different engineering materials was experimentally investigated with the aid of high-precision methods of measuring, some of which had been newly developed. Experiments made with a variety of steels, the titanium alloy Ti-A16-V4, a cobalt (tungsten) alloy, the high-temperature material Nimonic 90 and Dural (A1-Cu) are reported. The theory given in an attempt to explain these experiments is aimed at finding general formulas for the cyclic stress-strain behavior materials.

Estimation of cyclic interstory drift capacity of steel framed structures and future applications for seismic design.

PubMed

Bojórquez, Edén; Reyes-Salazar, Alfredo; Ruiz, Sonia E; Terán-Gilmore, Amador

2014-01-01

Several studies have been devoted to calibrate damage indices for steel and reinforced concrete members with the purpose of overcoming some of the shortcomings of the parameters currently used during seismic design. Nevertheless, there is a challenge to study and calibrate the use of such indices for the practical structural evaluation of complex structures. In this paper, an energy-based damage model for multidegree-of-freedom (MDOF) steel framed structures that accounts explicitly for the effects of cumulative plastic deformation demands is used to estimate the cyclic drift capacity of steel structures. To achieve this, seismic hazard curves are used to discuss the limitations of the maximum interstory drift demand as a performance parameter to achieve adequate damage control. Then the concept of cyclic drift capacity, which incorporates information of the influence of cumulative plastic deformation demands, is introduced as an alternative for future applications of seismic design of structures subjected to long duration ground motions.

Estimation of Cyclic Interstory Drift Capacity of Steel Framed Structures and Future Applications for Seismic Design

PubMed Central

Bojórquez, Edén; Reyes-Salazar, Alfredo; Ruiz, Sonia E.; Terán-Gilmore, Amador

2014-01-01

Several studies have been devoted to calibrate damage indices for steel and reinforced concrete members with the purpose of overcoming some of the shortcomings of the parameters currently used during seismic design. Nevertheless, there is a challenge to study and calibrate the use of such indices for the practical structural evaluation of complex structures. In this paper, an energy-based damage model for multidegree-of-freedom (MDOF) steel framed structures that accounts explicitly for the effects of cumulative plastic deformation demands is used to estimate the cyclic drift capacity of steel structures. To achieve this, seismic hazard curves are used to discuss the limitations of the maximum interstory drift demand as a performance parameter to achieve adequate damage control. Then the concept of cyclic drift capacity, which incorporates information of the influence of cumulative plastic deformation demands, is introduced as an alternative for future applications of seismic design of structures subjected to long duration ground motions. PMID:25089288

Real-time, high-resolution study of nanocrystallization and fatigue cracking in a cyclically strained metallic glass.

PubMed

Wang, Cheng-Cai; Mao, Yun-Wei; Shan, Zhi-Wei; Dao, Ming; Li, Ju; Sun, Jun; Ma, Evan; Suresh, Subra

2013-12-03

Metallic glasses (MGs) exhibit greater elastic limit and stronger resistance to plastic deformation than their crystalline metal counterparts. Their capacity to withstand plastic straining is further enhanced at submicrometer length scales. For a range of microelectromechanical applications, the resistance of MGs to damage and cracking from thermal and mechanical stress or strain cycling under partial or complete constraint is of considerable scientific and technological interest. However, to our knowledge, no real-time, high-resolution transmission electron microscopy observations are available of crystallization, damage, and failure from the controlled imposition of cyclic strains or displacements in any metallic glass. Here we present the results of a unique in situ study, inside a high-resolution transmission electron microscope, of glass-to-crystal formation and fatigue of an Al-based MG. We demonstrate that cyclic straining progressively leads to nanoscale surface roughening in the highly deformed region of the starter notch, causing crack nucleation and formation of nanocrystals. The growth of these nanograins during cyclic straining impedes subsequent crack growth by bridging the crack. In distinct contrast to this fatigue behavior, only distributed nucleation of smaller nanocrystals is observed with no surface roughening under monotonic deformation. We further show through molecular dynamics simulation that these findings can be rationalized by the accumulation of strain-induced nonaffine atomic rearrangements that effectively enhances diffusion through random walk during repeated strain cycling. The present results thus provide unique insights into fundamental mechanisms of fatigue of MGs that would help shape strategies for material design and engineering applications.

Stress evolution and associated microstructure during transient creep of olivine at 1000-1200 °C

NASA Astrophysics Data System (ADS)

Thieme, M.; Demouchy, S.; Mainprice, D.; Barou, F.; Cordier, P.

2018-05-01

We study the mechanical response and correlated microstructure of axial deformed fine-grained olivine aggregates as a function of incremental finite strains. Deformation experiments were conducted in uniaxial compression in an internally heated gas-medium deformation apparatus at temperatures of 1000 and 1200 °C, at strain rates of 10-6 s-1 to 10-5 s-1 and at confining pressure of 300 MPa. Sample volumes are around 1.2 cm3. Finite strains range from 0.1 to 8.6% and corresponding maximal (final) differential stresses range from 80 to 1073 MPa for deformation at 1000 °C and from 71 to 322 MPa for deformation at 1200 °C. At 1200 °C, samples approach steady state deformation after about 8% of strain. At 1000 °C, significant strain hardening leads to stresses exceeding the confining pressure by a factor of 3.5 with brittle deformation after 3% of strain. Deformed samples were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD maps with step sizes as low as 50 nm were acquired without introducing analytical artifacts for the first time. The grain size of deformed samples ranges from 2.1 to 2.6 μm. Despite clear strain hardening, texture or microstructure do not change as a function of stress or finite strain. This observation is supported by a constant texture strength (J-index) and symmetry (BA-index), constant grain shape and aspect ratio, constant density of geometrically necessary dislocations, grain orientation spread, and constant subgrain boundary spacing and misorientation in between samples. TEM shows that all samples exhibit unambiguous dislocation activity but with a highly heterogeneous dislocation distribution. Olivine grains display evidence of [1 0 0] and [0 0 1] slip activity, but there is no evidence of interaction between the dislocations from the different slip systems. Several observations of grain boundaries acting as dislocation sources have been found. We find no confirmation of increasing dislocation densities as the cause for strain hardening during transient creep. This suggests other, yet not fully understood mechanisms affecting the strength of deformed olivine. These mechanisms could possibly involve grain boundaries. Such mechanisms are relevant for the deformation of uppermost mantle rocks, where the Si diffusion rate is too slow and dislocation glide must be accommodated in another way to fulfill the von Mises criterion.

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

Ghassemi-Armaki, Hassan; Leff, Asher C.; Taheri, Mitra L.

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C ismore » compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less

Stress recovery and cyclic behaviour of an Fe-Mn-Si shape memory alloy after multiple thermal activation

NASA Astrophysics Data System (ADS)

Hosseini, E.; Ghafoori, E.; Leinenbach, C.; Motavalli, M.; Holdsworth, S. R.

2018-02-01

The stress recovery and cyclic deformation behaviour of Fe-17Mn-5Si-10Cr-4Ni-1(V,C) shape memory alloy (Fe-SMA) strips, which are often used for pre-stressed strengthening of structural members, were studied. The evolution of recovery stress under different constraint conditions was studied. The results showed that the magnitude of the tensile stress in the Fe-SMA member during thermal activation can have a signification effect on the final recovery stress. The higher the tensile load in the Fe-SMA (e.g., caused by dead load or thermal expansion of parent structure during heating phase), the lower the final recovery stress. Furthermore, this study investigated the cyclic behaviour of the activated SMA followed by a second thermal activation. Although the magnitude of the recovery stress decreased during the cyclic loading, the second thermal activation could retrieve a significant part of the relaxed recovery stress. This observation suggests that the relaxation of recovery stress during cyclic loading is due to a reversible phase transformation-induced deformation (i.e., forward austenite-to-martensite transformation) rather than an irreversible dislocation-induced plasticity. Retrieval of the relaxed recovery stress by the reactivation process has important practical implications as the prestressing loss in pre-stressed civil structures can be simply recovered by reheating of the Fe-SMA elements.

FinalReport-DOE BES DMSE-UNR-QLi

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

Li, Qizhen

The primary goal of this project is to explore the fundamental deformation and failure mechanisms for magnesium with a hexagonal close packed (HCP) crystal structure. It is critical to perform this project for a number of reasons. First, magnesium is the lightest structural metal and its application in various structural components can save the final component weight. Second, the weight reduction from the usage of magnesium-based structural components in transportation vehicles such as automobiles and aircrafts can improve fuel efficiency and reduce the greenhouse gas emissions. Third, structural components often experience dynamic loading such as cyclic loading conditions. Fourth, magnesiummore » with a HCP crystal structure generally has its special deformation responses under loading conditions. This project investigated magnesium based materials (magnesium single crystal, pure polycrystalline magnesium, and some magnesium alloys) under various loading conditions, and also explored some processing routes to manipulate the microstructure and mechanical properties of magnesium. The research results were published in a number of articles and also disseminated through presentations in various conferences such as TMS annual meetings, MRS meetings, the international Plasticity conferences, the Pacific Rim International Congress on Advanced Materials and Processing, and AeroMat. In addition to the contribution to the research/academic community, this project is also beneficial to the general public. With the actual usage of magnesium in the passenger cars, the weight reduction and fuel consumption reduction will save the fuel bill of individual owners.« less

History Dependence of the Microstructure on Time-Dependent Deformation During In-Situ Cooling of a Nickel-Based Single-Crystal Superalloy

NASA Astrophysics Data System (ADS)

Panwisawas, Chinnapat; D'Souza, Neil; Collins, David M.; Bhowmik, Ayan; Roebuck, Bryan

2018-05-01

Time-dependent plastic deformation through stress relaxation and creep deformation during in-situ cooling of the as-cast single-crystal superalloy CMSX-4® has been studied via neutron diffraction, transmission electron microscopy, electro-thermal miniature testing, and analytical modeling across two temperature regimes. Between 1000 °C and 900 °C, stress relaxation prevails and gives rise to softening as evidenced by a decreased dislocation density and the presence of long segment stacking faults in γ phase. Lattice strains decrease in both the γ matrix and γ' precipitate phases. A constitutive viscoplastic law derived from in-situ isothermal relaxation test under-estimates the equivalent plastic strain in the prediction of the stress and strain evolution during cooling in this case. It is thereby shown that the history dependence of the microstructure needs to be taken into account while deriving a constitutive law and which becomes even more relevant at high temperatures approaching the solvus. Higher temperature cooling experiments have also been carried out between 1300 °C and 1150 °C to measure the evolution of stress and plastic strain close to the γ' solvus temperature. In-situ cooling of samples using ETMT shows that creep dominates during high-temperature deformation between 1300 °C and 1220 °C, but below a threshold temperature, typically 1220 °C work hardening begins to prevail from increasing γ' fraction and resulting in a rapid increase in stress. The history dependence of prior accumulated deformation is also confirmed in the flow stress measurements using a single sample while cooling. The saturation stresses in the flow stress experiments show very good agreement with the stresses measured in the cooling experiments when viscoplastic deformation is dominant. This study demonstrates that experimentation during high-temperature deformation as well as the history dependence of the microstructure during cooling plays a key role in deriving an accurate viscoplastic constitutive law for the thermo-mechanical process during cooling from solidification.

Evolution of Mechanical Properties and Microstructures in the Inner Accretionary Prism of the Nankai Subduction Zone

NASA Astrophysics Data System (ADS)

Kuo, S. T.; Kitamura, M.; Kitajima, H.

2016-12-01

Mechanical properties and microstructural characteristics of accretionary prism sediments can provide detailed deformation history and processes in subduction zones. The IODP Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Expedition 348 has extended the deep riser hole down to 3058.5 meters below sea floor (mbsf) to the inner accretionary wedge at Site C0002 located 35 km landward from the trench. Here, we conducted deformation experiments on the core samples recovered from 2185 msbf at Site C0002 to understand mechanical behaviors and deformation of inner prism sediments. We deformed the siltstone samples with a porosity of 20% at 25°C or 60°C under isotropic loading path (S1=S2=S3) and triaxial compression (S1>S2=S3). In the isotropic loading test, we step-wisely increased confining pressure (Pc) from 11.5 to 194 MPa and kept pore pressure (Pp) at 10 MPa. In a series of triaxial compression loading tests, we first increased Pc to the targeting 42-78 MPa and Pp to 20 MPa, and then applied the differential load at a constant displacement rate of 0.005 μm/s while keeping Pc and Pp constant. We will analyze the microstructures of the experimentally deformed samples to understand deformation mechanism. We define yield points based on slope changes in relationships between volumetric strain and effective mean stress (p') for isotropic loading and those between differential stress (q) and axial strain for triaxial loading. The sample yields at p' of 100 MPa (q = 0 MPa) in isotropic loading test. In triaxial loading, the samples at effective pressure (Pe) of 22, 28, and 58 MPa yield at q = 30 MPa (p' = 32 MPa), q = 30 MPa (p' = 38 MPa) and q = 45 MPa (p' = 73 MPa), respectively. Upon yield, the samples deformed at Pe of 22 MPa and 28 MPa show brittle behavior with a peak q of 50 MPa and 55 MPa followed by strain weakening to reach q of 36 and 46 MPa at steady state. Both samples show single fracture planes with angles of 30° to S1. On the other hand, the sample at Pe of 58 MPa shows strain hardening after the yield and exhibits barreling. In triaxial loading experiments, all samples show an increase in volumetric strain with increasing Pe. Our experiment results at different Pe are consistent with a critical state soil mechanics theory. We will further correlate the microstructural features of the deformed samples with the mechanical data.

Dynamic Torsional and Cyclic Fracture Behavior of ProFile Rotary Instruments at Continuous or Reciprocating Rotation as Visualized with High-speed Digital Video Imaging.

PubMed

Tokita, Daisuke; Ebihara, Arata; Miyara, Kana; Okiji, Takashi

2017-08-01

This study examined the dynamic fracture behavior of nickel-titanium rotary instruments in torsional or cyclic loading at continuous or reciprocating rotation by means of high-speed digital video imaging. The ProFile instruments (size 30, 0.06 taper; Dentsply Maillefer, Ballaigues, Switzerland) were categorized into 4 groups (n = 7 in each group) as follows: torsional/continuous (TC), torsional/reciprocating (TR), cyclic/continuous (CC), and cyclic/reciprocating (CR). Torsional loading was performed by rotating the instruments by holding the tip with a vise. For cyclic loading, a custom-made device with a 38° curvature was used. Dynamic fracture behavior was observed with a high-speed camera. The time to fracture was recorded, and the fractured surface was examined with scanning electron microscopy. The TC group initially exhibited necking of the file followed by the development of an initial crack line. The TR group demonstrated opening and closing of a crack according to its rotation in the cutting and noncutting directions, respectively. The CC group separated without any detectable signs of deformation. In the CR group, initial crack formation was recognized in 5 of 7 samples. The reciprocating rotation exhibited a longer time to fracture in both torsional and cyclic fatigue testing (P < .05). The scanning electron microscopic images showed a severely deformed surface in the TR group. The dynamic fracture behavior of NiTi rotary instruments, as visualized with high-speed digital video imaging, varied between the different modes of rotation and different fatigue testing. Reciprocating rotation induced a slower crack propagation and conferred higher fatigue resistance than continuous rotation in both torsional and cyclic loads. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

A microstructure sensitive study of rolling contact fatigue in bearing steels: A numerical and experimental approach

NASA Astrophysics Data System (ADS)

Pandkar, Anup Surendra

Bearings are an integral part of machine components that transmit rotary power such as cars, motors, engines etc. Safe bearing operation is essential to avoid serious failures and accidents, which necessitates their timely replacement. This calls for an accurate bearing life prediction methods. Based on the Lundberg-Palmgen (LP) model, current life models consistently under predict bearings lives. Improvement in life prediction requires understanding of the bearing failure mechanism i.e. Rolling Contact Fatigue (RCF). The goal of this research is to develop a mechanistic framework required for an improved bearing life prediction model. Such model should account for metal plasticity, influence of microstructural features and cyclically evolving stressstrain fields induced during RCF. To achieve this, elastic-plastic finite element (FE) study is undertaken to investigate the response of M50-NiL bearing steel during RCF. Specifically, a microstructure sensitive study of the influence of non-metallic inclusions on RCF response of bearings is presented. M50-NiL microstructure consists of carbides which are orders of magnitude smaller than bearing dimensions. To account for this size difference, a multi-scale FE modeling approach is employed. The FE results reveal that hard carbide particles act as local stress risers, alter surrounding stressstrain fields and cause micro-scale yielding of steel matrix. Moreover, they introduce a shear stress cycle with non-zero mean stress, which promotes micro-plastic strain accumulation via ratcheting mechanism. Localized ratcheting is primarily responsible for cyclic hardening within the RCF affected region. Such evolution of subsurface hardness can be used to quantify RCF induced damage. To investigate this further, cyclic hardening response of the RCF affected region is simulated. The results show good agreement with the experimental observations. The cyclic stress-strain fields obtained from these simulations and the knowledge of hardness evolution can prove useful for future improvements to life models. The material parameters required for FE simulations are not available for many bearing steels. A novel method is presented to estimate these parameters for M50-NiL using the experimental results. Based on logical assumptions, this method provides meaningful estimates of material parameters. Modeling techniques and conclusions drawn from this research are helpful for improvements in life models.

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.

Representation and Management of the Knowledge of Brittle Deformation in Shear Zones Using Microstructural Data From the SAFOD Core Samples

NASA Astrophysics Data System (ADS)

Babaie, H. A.; Broda, C. M.; Kumar, A.; Hadizadeh, J.

2010-12-01

Web access to data that represent knowledge acquired by investigators studying the microstructures in the core samples of the SAFOD (San Andreas Observatory at Depth) project can help scientists efficiently integrate and share knowledge, query the data, and update the knowledge base on the Web. To achieve this, we have used OWL (Web Ontology Language) to build the brittle deformation ontology for the microstructures observed in the SAFOD core samples, by explicitly formalizing the knowledge about deformational processes, geological objects undergoing deformation, and the underlying mechanical and environmental conditions in brittle shear zones. The developed Web-based ‘SAFOD Brittle Microstructure and Mechanics Knowledge base’ (SAFOD BM2KB), which instantiates this ontology and is available at http://codd.cs.gsu.edu:9999/safod/index.jsp, will host and serve data that pertains to spatial objects, such as microstructure, gouge, fault, and SEM image, acquired by the SAFOD investigators through the studies of the SAFOD core samples. Deformation in shear zones involves complex brittle and ductile processes that alter, create, and/or destroy a wide variety of one- to three-dimensional, multi-scale spatial entities such as rocks and their constituent minerals and structure. These processes occur through a series of sub-processes that happen in different time intervals, and affect the spatial objects at granular to regional scales within shear zones. The processes bring about qualitative change to the spatial entities over time intervals that start and end with events. Processes, such as mylonitization and cataclastic flow, change the spatial location, distribution, dimension, size, shape, and orientation of some objects through translation, rotation and strain. These processes may also result in newly formed entities, such as a new mineral, gouge, vein, or fault, during one or more phases of deformation. Deformation processes may also destroy entities, such as a mineral, fossil, or original structure. Laboratory investigations by the SAFOD scientists result in ever-increasing volumes of complex data related to different tectonic processes, deformed rocks, and structures. These data are often published in the tables of scientific articles or are stored in personal Excel worksheets or, in rare cases, in a network community database. It is extremely hard to integrate autonomously built databases distributed on the Web because of their heterogeneous schemas. As a closed world model, databases can only store and serve a finite set of static data that are known to be true. They cannot represent knowledge in a constantly changing, open world. In contrast, integration of scientific data and presentation of their underlying knowledge can be achieved through the use of Semantic Web technologies. These technologies are capable of handling an infinite supply of known and yet to be known facts due to their open world model. The inference rules of OWL and its underlying RDFS and RDF semantic languages allow formal and explicit specification of the theories and knowledge of a particular domain such as brittle deformation in shear zone.

Microstructural characterization of ultrasonic impact treated aluminum-magnesium alloy

NASA Astrophysics Data System (ADS)

Tran, Kim Ngoc Thi

Aluminum 5456-H116 has high as-welded strength, is formable, and highly corrosion resistant, however, it can become sensitized when exposed to elevated temperatures for a prolonged time. Sensitization results in the formation of a continuous β phase at the grain boundaries that is anodic to the matrix. Thus the grain boundaries become susceptible to stress corrosion cracking (SCC) and intergranular corrosion cracking (IGC). Cracking issues on aluminum superstructures have prompted the use of a severe plastic deformation processes, such as ultrasonic impact treatment (UIT), to improve SCC resistance. This study correlated the effects of UIT on the properties of 5456-H116 alloy to the microstructural evolution of the alloy and helped develop a fundamental understanding of the mechanisms that cause the microstructural evolution. Ultrasonic impact treatment produces a deformed layer at the surface ˜ 10 to 18 µm thick that is characterized by micro-cracks, tears, and voids. Ultrasonic impact treatment results in grain refinement within the deformation layer and extending below the deformed layer. The microstructure exhibits weak crystallographic texture with larger fraction of high angle grain boundaries. Nanocrystalline grains within the deformation layer vary in size from 2 to 200 nm in diameter and exhibit curved or wavy grain boundaries. The nanocrystalline grains are thermally stable up to 300°C. Above 300°C, grain growth occurs with an activation energy of ˜ 32 kJ/mol. Below the deformation layer, the microstructure is characterized by submicron grains, complex structure of dislocations, sub-boundaries, and Moiré fringes depicting overlapping grains. The deformation layer does not exhibit the presence of a continuous β phase, however below the deformation layer; a continuous β phase along the grain boundaries is present. In general the highest hardness and yield strength is at the UIT surface which is attributed to the formation of nanocrystalline grains. Although the highest hardness and yield strength was observed at the UIT surface, the results were mixed with some lower values. The lower hardness and yield strength values at the UIT surface are attributed to the voids and micro cracking/micro voids observed in the deformation layer. The fracture mode was transgranular ductile fracture with micro void coalescence and dimples. Both UIT and untreated material exhibit similar levels of intergranular corrosion susceptibility. Corrosive attack was intergranular with slightly deeper attack in the untreated material. Numerical simulation modeling showed that the calculated residual stress under the tool, ˜80 MPa, is of the same order of magnitude as the compressive residual stresses measured by XRD measurements near the surface. Modeling also showed that high effective strains were induced almost immediately. The UIT process also resulted in rapid localized heating to a maximum temperature of ˜32°C during the first eleven pin tool cycles. The model also showed that during UIT processing, the material undulates as the pin tool impacts and retracts from the surface of the material. The undulations represent the elastic response of the surface to the compressive stresses built up during a pin tool cycle.

Micromechanical modelling of polyethylene

NASA Astrophysics Data System (ADS)

Alvarado Contreras, Jose Andres

2008-10-01

The increasing use of polyethylene in diverse applications motivates the need for understanding how its molecular properties relate to the overall behaviour of the material. Although microstructure and mechanical properties of polymers have been the subject of several studies, the irreversible microstructural rearrangements occurring at large deformations are not completely understood. The purpose of this thesis is to describe how the concepts of Continuum Damage Mechanics can be applied to modelling of polyethylene materials under different loading conditions. The first part of the thesis consists of the theoretical formulation and numerical implementation of a three-dimensional micromechanical model for crystalline polyethylene. Based on the theory of shear slip on crystallographic planes, the proposed model is expressed in the framework of viscoplasticity coupled with degradation at large deformations. Earlier models aid in the interpretation of the mechanical behaviour of crystalline polyethylene under different loading conditions; however, they cannot predict the microstructural damage caused by deformation. The model, originally due to Parks and Ahzi (199o), was further developed in the light of the concept of Continuum Damage Mechanics to consider the original microstructure, the particular irreversible rearrangements, and the deformation mechanisms. Damage mechanics has been a matter of intensive research by many authors, yet it has not been introduced to the micromodelling of semicrystalline polymeric materials such as polyethylene. Regarding the material representation, the microstructure is simplified as an aggregate of randomly oriented and perfectly bonded crystals. To simulate large deformations, the new constitutive model attempts to take into account existence of intracrystalline microcracks. The second part of the work presents the theoretical formulation and numerical implementation of a three-dimensional constitutive model for the mechanical behaviour of semicrystalline polyethylene. The model proposed herein attempts to describe the deformation and degradation process in semicrystalline polyethylene following the approach of damage mechanics. Structural degradation, an important phenomenon at large deformations, has not received sufficient attention in the literature. The modifications to the constitutive equations consist essentially of introducing the concept of Continuum Damage Mechanics to describe the rupture of the intermolecular (van der Waals) bonds that hold crystals as coherent structures. In order to model the mechanical behaviour, the material morphology is simplified as a collection of inclusions comprising the crystalline and amorphous phases with their characteristic average volume fractions. In the spatial arrangement, each inclusion consists of crystalline material lying in a thin lamella attached to an amorphous layer. To consider microstructural damage, two different approaches are analyzed. The first approach assumes damage occurs only in the crystalline phase, i.e., degradation of the amorphous phase is ignored. The second approach considers the effect of damage on the mechanical behaviour of both the amorphous and crystalline phases. To illustrate the proposed constitutive formulations, the models were used to predict the responses of crystalline and semicrystalline polyethylene under uniaxial tension and simple shear. The numerical simulations were compared with experimental data previously obtained by Bartczak et al. (1994), G'Sell and Jonas (1981), G'Sell et al. (1983), Hillmansen et al. (2000), and Li et al. (2001). Our model's predictions show a consistently good agreement with the experimental results and a significant improvement with respect to the ones obtained by Parks and Ahzi (1990), Schoenfeld et al. (1995), Yang and Chen (2001), Lee et al. (i993b), Lee et al. (1993a), and Nikolov et al. (2006). The newly proposed formulations demonstrate that these types of constitutive models based on Continuum Damage Mechanics are appropriate for predicting large deformations and failure in polyethylene materials.

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.

Effects of varying material properties on the load deformation characteristics of heel cushions.

PubMed

Sun, Pi-Chang; Wei, Hung-Wen; Chen, Chien-Hua; Wu, Chun-Hao; Kao, Hung-Chan; Cheng, Cheng-Kung

2008-07-01

Various insole materials were used in attenuation of heel-strike impact. This study presented a compression test to investigate the deformation characteristics of common heel cushions. There were two materials (thermoplastic elastomer "TPE" and silicone) with three hardness and six thickness being analyzed. They underwent consecutive loading-unloading cycles with a load control mode. The displacement of material thickness was recorded during cyclic compression being applied and released from 0 to 1050 N. The energy input, return and dissipation were evaluated based on the load deformation curves when new and after repeated compression. The TPE recovered more deformed energy and thickness than the silicone after the first loading cycle. The silicone would preserve more strain energy with increasing its hardness for the elastic recovery in the unloading process. The deformed energy was decreased as the original thickness did not completely recover under cyclic tests. The reduction in hysteresis area was gradually converged within 20 cycles. The silicone attenuated more impact energy in the initial cycles, but its energy dissipation was reduced after repeated loading. To increase hardness or thickness should be considered to improve resilience or accommodate persistent compression without flattening. The careful selection of cushion materials is imperative to meet individual functional demands.

Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

NASA Astrophysics Data System (ADS)

Satheesh Kumar, S. S.; Raghu, T.

2015-02-01

Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

The effects of CuO particle size on microstructure evolution of AgCuO compo-sites in plastic deformation process: finite element simulation and experimental study

NASA Astrophysics Data System (ADS)

Li, Zhiguo; Cao, Hanxing; Zhou, Xiaolong; Zhou, Zhaobo; Cao, Jianchun

2018-04-01

The effects of CuO with different particle sizes on the microstructure evolution of AgCuO composite material during plastic deformation process were investigated by finite element (FE) analysis and experiment. The results are as follows: with the decrease of CuO particle size, the degree of radial compression and axial elongation of CuO particle cluster increase gradually, as well as the dispersion of CuO also increase. Meanwhile, the shape of CuO particles is constantly transformed from polygonal to fibrous, which makes the number of linear fibrous CuO increase continuously while bent fibrous CuO reduce gradually. By comparing the simulation and experiment results we find that there are four different typical microstructure regions, which caused by the interaction between monoclinic and cubic CuO during the extrusion process.

Effect of Morphological Differences on the Cold Formability of an Isothermally Heat-Treated Advanced High-Strength Steel

NASA Astrophysics Data System (ADS)

Weißensteiner, Irmgard; Suppan, Clemens; Hebesberger, Thomas; Winkelhofer, Florian; Clemens, Helmut; Maier-Kiener, Verena

2018-04-01

Steel sheets of Fe-0.2C-2Mn-0.2Si-0.03Ti-0.003B (m%) for the automotive industry were isothermally heat-treated, comprising austenitizing and subsequent isothermal annealing at temperatures between 300°C and 500°C. As a consequence, microstructures ranging from granular bainite over lower bainite to auto-tempered and untempered martensite were obtained. In tensile, hole expansion and bending tests, the performances in different forming conditions were compared and the changes of microstructure and texture were studied by complementary electron backscatter diffraction (EBSD) analyses. Samples with granular bainitic microstructures exhibited high total elongations but lower hole expansion ratios; in subsequent EBSD and texture analyses, evidence for inhomogeneous deformation was found. In contrast, the lath-like bainitic/martensitic microstructure showed higher strength and lower elongation to fracture. This results in a reduced bendability, but also in a high tolerance against damage induced by the shearing of edges, and, thus, allows homogeneous deformation to higher strains in the hole expansion test.

Characterization and modeling of mechanical behavior of single crystal titanium deformed by split-Hopkinson pressure bar

DOE PAGES

Morrow, B. M.; Lebensohn, R. A.; Trujillo, C. P.; ...

2016-03-28

Single crystal titanium samples were dynamically loaded using split-Hopkinson pressure bar (SHPB) and the resulting microstructures were examined. Characterization of the twins and dislocations present in the microstructure was conducted to understand the pathway for observed mechanical behavior. Electron backscatter diffraction (EBSD) was used to measure textures and quantify twinning. Microstructures were profusely twinned after loading, and twin variants and corresponding textures were different as a function of initial orientation. Focused ion beam (FIB) foils were created to analyze dislocation content using transmission electron microscopy (TEM). Large amounts of dislocations were present, indicating that plasticity was achieved through slip andmore » twinning together. Viscoplastic self-consistent (VPSC) modeling was used to confirm the complex order of operations during deformation. The activation of different mechanisms was highly dependent upon crystal orientation. For [0001] and View the MathML source[101¯1]-oriented crystals, compressive twinning was observed, followed by secondary tensile twinning. Furthermore, dislocations though prevalent in the microstructure, contributed to final texture far less than twinning.« less

Scanning and Transmission Electron Microscopy of High Temperature Materials

NASA Technical Reports Server (NTRS)

1994-01-01

Software and hardware updates to further extend the capability of the electron microscope were carried out. A range of materials such as intermetallics, metal-matrix composites, ceramic-matrix composites, ceramics and intermetallic compounds, based on refractory elements were examined under this research. Crystal structure, size, shape and volume fraction distribution of various phases which constitute the microstructures were examined. Deformed materials were studied to understand the effect of interfacial microstructure on the deformation and fracture behavior of these materials. Specimens tested for a range of mechanical property requirements, such as stress rupture, creep, low cycle fatigue, high cycle fatigue, thermomechanical fatigue, etc. were examined. Microstructural and microchemical stability of these materials exposed to simulated operating environments were investigated. The EOIM Shuttle post-flight samples were also examined to understand the influence of low gravity processing on microstructure. In addition, fractographic analyses of Nb-Zr-W, titanium aluminide, molybdenum silicide and silicon carbide samples were carried out. Extensive characterization of sapphire fibers in the fiber-reinforced composites made by powder cloth processing was made. Finally, pressure infiltration casting of metal-matrix composites was carried out.

Mechanical Behavior of Additive Manufactured Layered Materials, Part 2: Stainless Steels

DTIC Science & Technology

2015-04-30

and/or excellent cyclic fatigue behavior: stainless - steel 316L and 17-4PH. Additive materials were fabricated at a leading-edge facility using their...Tensile deformation Representative engineering stress- strain data from measurements obtained with our stainless steel specimens are shown in... fatigue behavior Cyclic fatigue strengths demonstrated by the DMLS stainless steels fabricated in the horizontal orientation were almost equal to

Microstructural Evolution during the Dynamic Deformation of High Strength Navy Steels

DTIC Science & Technology

2008-05-19

phase particles (Figures 23d,e). These include carbides as well as copper precipitates that are of the order of 10 nm or less in size. These particles ...Microstructure and kinetics of martensite transformations in splat-quenched Fe and Fe-Ni alloys - I pure Fe: Acta Metallurgica 30(1982)323. 22. Y. Inokuti...and B. Cantor, Microstructure and kinetics of martensite transformations in splat-quenched Fe and Fe-Ni alloys - II Fe-Ni alloys : Acta

Anisotropic and Heterogeneous Development of Microstructures. Combining Laboratory/Synchrotron X-rays and EBSD on a few SPD Metallic Systems

NASA Astrophysics Data System (ADS)

Bolmaro, Raúl E.; De Vincentis, Natalia S.; Benatti, Emanuel; Kliauga, Andrea M.; Avalos, Martina C.; Schell, Norbert; Brokmeier, Heinz-Günter

2014-08-01

The onset of Severe Plastic Deformation (SPD) regime is quite instructive on the possible origins of the nano-microstructures developed in metals and alloys. It is known that grain fragmentation and dislocation accumulation, among other defects, proceed at different paces depending fundamentally on grain orientations and active deformation mechanisms. There have been many attempts to characterize nano-microstructure anisotropy, leading all of them to sometimes contradictory conclusions. Moreover, the characterizations rely on different measurements techniques and pos-processing approaches, which can be observing different manifestations of the same phenomena. On the current presentation we show a few experimental and computer pos-processing and simulation approaches, applied to some SPD/alloy systems. Williamson-Hall and Convolutional Multiple Whole Profile (CMWP) techniques will be applied to peak broadening analysis on experimental results stemming from laboratory Cu Ka X-rays, and synchrotron radiation from LNLS (Laboratório Nacional de Luz Síncrotron, Campinas, Brazil) and Petra III line (HEMS station, at DESY, Hamburg, Germany). Taking advantage of the EBSD capability of giving information on orientational and topological characteristics of grain boundaries, microstructures, grain sizes, etc., we also performed investigations on dislocation density and Geometrically Necessary Dislocation Boundaries (GNDB) and their correlation with texture components. Orientation dependent nano-microstructures and domain sizes are shown on the scheme of generalized pole figures and discussions provide some hints on nano-microstructure anisotropy.

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.

Thermo-Mechanical Analyses of Dynamically Loaded Rubber Cylinders

NASA Technical Reports Server (NTRS)

Johnson, Arthur R.; Chen, Tzi-Kang

2002-01-01

Thick rubber components are employed by the Army to carry large loads. In tanks, rubber covers road wheels and track systems to protect roadways. It is difficult for design engineers to simulate the details of the hysteretic heating for large strain viscoelastic deformations. In this study, an approximation to the viscoelastic energy dissipated per unit time is investigated for use in estimating mechanically induced viscoelastic heating. Coupled thermo-mechanical simulations of large cyclic deformations of rubber cylinders are presented. The cylinders are first compressed axially and then cyclically loaded about the compressed state. Details of the algorithm and some computational issues are discussed. The coupled analyses are conducted for tall and short rubber cylinders both with and without imbedded metal disks.

Training and shape retention in conducting polymer artificial muscles

NASA Astrophysics Data System (ADS)

Tominaga, Kazuo; Hashimoto, Hikaru; Takashima, Wataru; Kaneto, Keiichi

2011-12-01

Electrochemomechanical deformation (ECMD) of the conducting polymer polyaniline film is studied to investigate the behaviour of actuation under tensile loads. The ECMD was induced by the strains due to the insertion of ionic species (cyclic strain) and a creep due to applied loads during the redox cycle. The cyclic strain was enhanced by the experience of high tensile loads, indicating a training effect. The training effect was explained by the enhanced electrochemical activity of the film. The creep was recovered by removal of the tensile load and several electrochemical cycles. This fact indicates that the creep results from the one-dimensional anisotropic deformation, and is retained (shape retention) by the ionic crosslink. The recovery of creep results from the elastic relaxation of the polymer conformation.

A Review of Texture Evolution Mechanisms During Deformation by Rolling in Aluminum Alloys

NASA Astrophysics Data System (ADS)

Li, Shasha; Zhao, Qi; Liu, Zhiyi; Li, Fudong

2018-06-01

The current understanding of texture evolution during deformation by rolling in aluminum alloys was summarized. This included understanding the evolution mechanisms and several key factors of initial texture, microstructure, alloy composition, deformation temperature, stress-strain condition, and rolling geometry. Related models on predicting texture evolution during rolling were also discussed. Finally, for this research field, the recommendations for controlling the formation of rolling textures were proposed.

ARL Summer Student Research Symposium Compendium of Abstracts. Volume 2

DTIC Science & Technology

2015-12-01

to withstand ballistic/blast impact. The mechanical response of these materials is primarily determined by the active deformation modes operating...atomic scale deformation mechanisms such as basal, prismatic, pyramidal slip and twinning on the microstructure of the system (i.e., loading orientation...deformation, the dependence of peak strength on grain size, and the mechanisms of failure are discussed. I wish to acknowledge the mentorship of Dr

THE EFFECTS OF HYDROGEN, TRITIUM, AND HEAT TREATMENT ON THE DEFORMATION AND FRACTURE TOUGHNESS PROPERTIES OF STAINLESS STEEL

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

Morgan, M.; Tosten, M.; Chapman, G.

2013-09-06

The deformation and fracture toughness properties of forged stainless steels pre-charged with tritium were compared to the deformation and fracture toughness properties of the same steels heat treated at 773 K or 873 K and precharged with hydrogen. Forged stainless steels pre-charged with tritium exhibit an aging effect: Fracture toughness values decrease with aging time after precharging because of the increase in concentration of helium from tritium decay. This study shows that forged stainless steels given a prior heat treatment and then pre-charged with hydrogen also exhibit an aging effect: Fracture toughness values decrease with increasing time at temperature. Amore » microstructural analysis showed that the fracture toughness reduction in the heat-treated steels was due to patches of recrystallized grains that form within the forged matrix during the heat treatment. The combination of hydrogen and the patches of recrystallized grains resulted in more deformation twinning. Heavy deformation twinning on multiple slip planes was typical for the hydrogen-charged samples; whereas, in the non-charged samples, less twinning was observed and was generally limited to one slip plane. Similar effects occur in tritium pre-charged steels, but the deformation twinning is brought on by the hardening associated with decay helium bubbles in the microstructure.« less

Room temperature creep behavior of Ti–Nb–Ta–Zr–O alloy

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

Zhang, Wei-dong

The room temperature creep behavior and deformation mechanisms of a Ti–Nb–Ta–Zr–O alloy, which is also called “gum metal”, were investigated with the nanoindentation creep and conventional creep tests. The microstructure was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the creep stress exponent of the alloy is sensitive to cold deformation history of the alloy. The alloy which was cold swaged by 85% shows high creep resistance and the stress exponent is approximately equal to 1. Microstructural observation shows that creep process of the alloy without cold deformation is controlled by dislocationmore » mechanism. The stress-induced α' martensitic phase transformation also occurs. The EBSD results show that the grain orientation changes after the creep tests, and thus, the creep of the cold-worked alloy is dominated by the shear deformation of giant faults without direct assistance from dislocations. - Highlights: •Nanoindentation was used to investigate room temperature creep behavior of gum metal. •The creep stress exponent of gum metal is sensitive to the cold deformation history. •The creep stress exponent of cold worked gum metal is approximately equal to 1. •The creep of the cold-worked gum metal is governed by the shear deformation of giant faults.« less

Simultaneous measurements of photoemission and morphology of various Al alloys during mechanical deformation

NASA Astrophysics Data System (ADS)

Cai, M.; Li, W.; Dickinson, J. T.

2006-11-01

We report simultaneous measurements of strain and photoelectron emission from high purity Al (1350), Al-Mg (5052), Al-Mn (3003), Al-Cu (2024), and Al-Mg-Si (6061) alloys under uniaxial tension due to pulsed excimer laser radiation (248nm). The emission of low-energy photoelectrons is sensitive to deformation-induced changes in surface morphology, including the formation of slip lines and slip bands. Alloy composition and surface treatment significantly influence the photoemission during deformation. Surface oxide enhances the signal-to-noise level during photoemission measurement. In the early stage of deformation (strain ⩽0.04), photoemission intensity increases gradually in a nonlinear fashion. While subsequent photoemission increases almost linearly with strain until failure in samples with thin oxide layer (˜31Å), there are two linear segments of photoemission for the samples with oxide of 45Å. The onset of strain localization corresponds to the intersection point of two linear segments, usually at a strain of 0.08-0.20. A constitutive model incorporating microstructure evolution and work hardening during tensile deformation is proposed to qualitatively interpret the growth of the photoemission as a function of strain. Photoemissions from various alloys are interpreted in the light of surface treatment, work function, composition, and microstructural development during deformation.

A study of the effects of rare-earth elements on the microstructural evolution and deformation behavior of magnesium alloys at temperatures up to 523K

NASA Astrophysics Data System (ADS)

Chakkedath, Ajith

Due to their high specific strength, lightweight magnesium (Mg) alloys are being increasingly used for applications, such as the automotive industry, where weight savings are critical. In order to develop new alloys and processing methods to achieve higher strength and better formability to compete with currently used metal alloys, it is important to understand the effects of alloying elements, processing, and temperature on the microstructure, mechanical properties, and the deformation behavior. In this dissertation, a systematic investigation on the effects of Nd additions (0-1wt.%) and temperature (298-523K) on the microstructure and the activity of different deformation modes in as-cast and cast-then-extruded Mg-1Mn (wt.%) alloys were performed. For this study, an in-situ testing technique which combines tension and compression testing inside a scanning electron microscope (SEM) with electron backscatter diffraction (EBSD) analysis was employed. The main findings of this work were that the microstructure, strength, and the distribution of the deformation modes varied significantly as a function of Nd content, temperature, and processing. An increase in the Nd content resulted in a weaker texture after extrusion in Mg-1Mn alloys. A combination of slip and twinning mechanisms controlled the tensile deformation in the extruded alloys at ambient temperatures. With an increase in temperature, the twinning activity decreased, and slip mechanisms dominated the deformation. In the extruded Nd-containing alloys, basal slip dominated the deformation, especially at elevated temperatures, suggesting that Nd additions strengthen basal slip. This resulted in excellent elevated-temperature strength retention in extruded Mg-1Mn-1Nd alloy, and a decrease in the Nd content to 0-0.3wt.% resulted in a decrease in the tensile strength at elevated temperatures. In extruded Mg-1Mn, contraction twinning dominated the tensile deformation and this alloy exhibited a lower elongation-to-failure (epsilon f) than the other alloys at 323K. With an increase in strain, these twins evolved into {101¯1} - {101¯2} double twins. Crystal plasticity modeling and simulation of the contraction twins and double twins showed that the activity of these twin modes is detrimental to the epsilon f of Mg alloys due to the strain localization that happens within the twinned volume due to the enhanced activity of basal slip. This agreed with the experimental observations. Compared to the extruded materials, the as-cast alloys exhibited significantly larger grain sizes and lower tensile strengths. The deformation in the as-cast alloys was dominated by a combination of basal slip and extension twinning at all test temperatures. A novel methodology which combines in-situ annealing inside a SEM with EBSD analysis was developed and employed to understand the effects of dilute Ce additions (0.2-0.6wt.%) on the recrystallization behavior in Mg-2Zn (wt.%) alloys. Texture weakening in these alloys resulted from the formation of an enhanced number of grain boundaries with rotation axis during recrystallization. The developed testing methodology will be valuable for future recrystallization studies on Mg and other alloy systems. Overall, the insights gained from this dissertation will have a broad impact on understanding the deformation behavior and microstructural evolution of RE-containing Mg alloys, and such insights can serve as guidance for the development of new alloys and processes. The information and data provided in this dissertation can also serve as inputs for the development of accurate crystal plasticity models.

Biaxial deformation of collagen and elastin fibers in coronary adventitia

PubMed Central

Chen, Huan; Slipchenko, Mikhail N.; Liu, Yi; Zhao, Xuefeng; Cheng, Ji-Xin; Lanir, Yoram

2013-01-01

The microstructural deformation-mechanical loading relation of the blood vessel wall is essential for understanding the overall mechanical behavior of vascular tissue in health and disease. We employed simultaneous mechanical loading-imaging to quantify in situ deformation of individual collagen and elastin fibers on unstained fresh porcine coronary adventitia under a combination of vessel inflation and axial extension loading. Specifically, the specimens were imaged under biaxial loads to study microscopic deformation-loading behavior of fibers in conjunction with morphometric measurements at the zero-stress state. Collagen fibers largely orientate in the longitudinal direction, while elastin fibers have major orientation parallel to collagen, but with additional orientation angles in each sublayer of the adventitia. With an increase of biaxial load, collagen fibers were uniformly stretched to the loading direction, while elastin fibers gradually formed a network in sublayers, which strongly depended on the initial arrangement. The waviness of collagen decreased more rapidly at a circumferential stretch ratio of λθ = 1.0 than at λθ = 1.5, while most collagen became straightened at λθ = 1.8. These microscopic deformations imply that the longitudinally stiffer adventitia is a direct result of initial fiber alignment, and the overall mechanical behavior of the tissue is highly dependent on the corresponding microscopic deformation of fibers. The microstructural deformation-loading relation will serve as a foundation for micromechanical models of the vessel wall. PMID:24092692

The effect of postprocessing on tensile property and microstructure evolution of friction stir welding aluminum alloy joint

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

Hu, Z.L., E-mail: zhilihuhit@163.com; State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001; State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology

Friction stir welding is an efficient manufacturing method for joining aluminum alloy and can dramatically reduce grain size conferring excellent plastic deformation properties. Consequently, friction stir welding is used to manufacture tailor welded blanks to optimize weight or performance in the final component. In the study, the microstructural evolution and mechanical properties of friction stir welding joint during plastic forming and subsequent heat treatment were investigated. The microstructural characteristics of the friction stir welding joints were studied by Electron Backscattered Diffraction and Transmission Electron Microscopy. The mechanical properties were evaluated by tensile and microhardness tests. It is found that themore » tensile and yield strengths of friction stir welding joints are significantly improved after severe plastic deformation due to the grain refinement. Following heat treatment, the strength of the friction stir welding joints significantly decrease due to the obvious abnormal grain growth. Careful attention must be given to the processing route of any friction stir welding joint intended for plastic forming, especially the annealing between forming passes. Severe plastic deforming of the friction stir welding joint leads to a high level of stored energy/dislocation density, which causes the abnormal grain growth during subsequent heat treatment, and consequently reduce the mechanical properties of the friction stir welding joint. - Highlights: • Great changes are observed in the microstructure of FSW joint after postprocessing. • Postprocessing shows great effect on the microstructure stability of FSW joint. • The weld shows more significant decrease in strength than the BM due to the AGG. • Attention must be given to the processing route of FSW joint for plastic forming.« less

Effet Bauschinger lors de la plasticité cyclique de l'aluminium pur monocristallin

NASA Astrophysics Data System (ADS)

Alhamany, A.; Chicois, J.; Fougères, R.; Hamel, A.

1992-08-01

This paper is concerned with the study of microscopic mechanisms which control the cyclic deformation of pure aluminium and especially with the analysis of the Bauschinger effect which appears in aluminium single crystals deformed by cyclic straining. Fatigue tests are performed on Al single crystals with the crystal axis parallel to [ overline{1}23] at room temperature, at plastic shear strain amplitudes in the range from 10^{-4} to 3× 10^{-3}. Mechanical saturation is not obtained at any strain level. Instead, a hardening-softening-secondary hardening sequence is found. The magnitude of the Bauschinger effect as the difference between yield stresses in traction and in compression, changes all along the fatigue loop and during the fatigue test. The Bauschinger effect disappears at two points of the fatigue loop, one in the traction part, the other in the compression one. At these points, the Bauschinger effect is inverted. Dislocation arrangement evolutions with fatigue conditions can explain the cyclic behaviour of Al single crystals. An heterogeneous dislocation distribution can be observed in the cyclically strained metal : dislocation tangles, long dislocation walls and dislocation cell walls, separated by dislocation poor channels appear in the material as a function of the cycle number. The long range internal stress necessary to ensure the compatibility of deformation between the hard and soft regions controls the observed Bauschinger effect. Ce travail s'inscrit dans le cadre de l'étude des mécanismes microsocopiques intervenant lors de la déformation cyclique de l'aluminium pur et concerne en particulier l'analyse de l'effet Bauschinger apparaissant au cours de la solliciation cyclique des monocristaux. L'étude a été menée à température ambiante sur des monocristaux d'aluminium pur orientés pour un glissement simple (axe [ overline{1}23] ), à des amplitudes de déformation plastique comprise entre 10^{-4} et quelques 10^{-3}. Nous n'avons pas obtenu de véritable saturation mécanique. Nous sommes en présence d'une séquence durcissement-adoucissement-durcissement secondaire. L'amplitude de l'effet Bauschinger considéré comme la différence entre les limites élastiques en traction et en compression mesurées selon une procédure appropriée, évolue le long d'une boucle de fatigue, s'annule pour deux points particuliers l'un en traction l'autre en compression. De part et d'autre de ces points, le signe de l'effet Bauschinger est inversé. Les microstructures des états fatigués sont caractérisés par une répartition hétérogène des dislocations constituée d'amas, de murs ou des parois, suivant le degré de déformation cyclique, séparés par des zones à faible densité de dislocations. Les contraintes internes liées aux incompatibilités de déformation résultant de cette répartition hétérogène des dislocations sont à l'origine de l'effet Bauschinger observé dans les monocristaux. Ces contraintes et l'évolution de la quantité de cellules de dislocations avec la fatigue expliquent le durcissement secondaire.

Microstructural characterisation of friction stir welding joints of mild steel to Ni-based alloy 625

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

Rodriguez, J.; University of Campinas; Ramirez, A.J., E-mail: ramirezlondono.1@osu.edu

2015-12-15

In this study, 6-mm-thick mild steel and Ni-based alloy 625 plates were friction stir welded using a tool rotational speed of 300 rpm and a travel speed of 100 mm·min{sup −1}. A microstructural characterisation of the dissimilar butt joint was performed using optical microscopy, scanning and transmission electron microscopy, and energy dispersive X-ray spectroscopy (XEDS). Six different weld zones were found. In the steel, the heat-affected zone (HAZ) was divided into three zones and was composed of ferrite, pearlite colonies with different morphologies, degenerated regions of pearlite and allotriomorphic and Widmanstätten ferrite. The stir zone (SZ) of the steel showedmore » a coarse microstructure consisting of allotriomorphic and Widmanstätten ferrite, degenerate pearlite and MA constituents. In the Ni-based alloy 625, the thermo-mechanically affected zone (TMAZ) showed deformed grains and redistribution of precipitates. In the SZ, the high deformation and temperature produced a recrystallised microstructure, as well as fracture and redistribution of MC precipitates. The M{sub 23}C{sub 6} precipitates, present in the base material, were also redistributed in the stir zone of the Ni-based alloy. TMAZ in the steel and HAZ in the Ni-based alloy could not be identified. The main restorative mechanisms were discontinuous dynamic recrystallisation in the steel, and discontinuous and continuous dynamic recrystallisation in the Ni-based alloy. The interface region between the steel and the Ni-based alloy showed a fcc microstructure with NbC carbides and an average length of 2.0 μm. - Highlights: • Comprehensive microstructural characterisation of dissimilar joints of mild steel to Ni-based alloy • Friction stir welding of joints of mild steel to Ni-based alloy 625 produces sound welds. • The interface region showed deformed and recrystallised fcc grains with NbC carbides and a length of 2.0 μm.« less

Microstructural and mechanical challenges in biomedical NiTi

NASA Astrophysics Data System (ADS)

Franz-Xaver Wagner, Martin

2010-07-01

The mechanical behaviour of NiTi shape memory alloys superficially resembles that of certain biomaterials, such as bones or tissues: By virtue of a reversible martensitic phase transformation, NiTi alloys can recover relatively large strains; uniaxial stress-strain curves exhibit constant stress-plateaus (at several hundreds of MPa, depending on alloy composition and testing temperature) associated with the phase transition. These novel functional properties, in combination with high mechanical strength in ultra-fine grained NiTi and good biocompatibility, are utilized in various implants and medical devices. Yet - and quite similar to hierarchically structured biomaterials - the deformation behaviour of NiTi is intricately linked to distinct deformation processes on several length scales, and there remain significant gaps in our understanding of the microstructure-property relations. In the present paper, recent experimental and theoretical results from first-principles calculations, micromechanical modelling and nanoindentation are discussed with a focus on the role of inelastic deformation processes, twin boundaries and the interaction of plastic deformation and stress-induced phase transformations. These novel findings challenge our understanding of the fundamental mechanical properties of NiTi. They highlight the importance of inelastic deformation mechanisms for the overall mechanical properties and strength of NiTi.

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

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

Estrada Rodas, Ernesto A.; Neu, Richard W.

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformationmore » on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.« less

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

DOE PAGES

Estrada Rodas, Ernesto A.; Neu, Richard W.

2017-09-11

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformationmore » on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.« less

A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys

PubMed Central

Hamad, Kotiba; Ko, Young Gun

2016-01-01

Magnesium alloys have recently attracted great interest due their lightweight and high specific strength. However, because of their hexagonal close-packed structure, they have few active slip systems, resulting in poor ductility and high mechanical anisotropy at room temperature. In the present work, we used a cross-shear deformation imposed by a differential speed rolling (DSR) technique to improve the room temperature strength and ductility of AZ31 magnesium alloy sheets. To introduce the cross-shear deformation, the sheets were rotated 180° around their longitudinal axis between the adjacent passes of DSR. The sheets of the AZ31 alloy subjected to the cross-shear deformation showed a uniform fine microstructure (1.2 ± 0.1 μm) with weak basal textures. The fabricated sheets showed a simultaneous high ultimate tensile strength and elongation-to-failure, i.e., ~333 MPa and ~21%, respectively. These were explained based on the structural features evolved due to the cross-shear deformation by DSR. The high strength was attributed to the uniform fine microstructure, whereas the high ductility was explained based on the basal texture weakening. PMID:27406685

Plastic deformation behaviors of Ni- and Zr-based bulk metallic glasses subjected to nanoindentation

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

Weizhong, Liang, E-mail: wzliang1966@126.com; Zhiliang, Ning; Zhenqian, Dang

2013-12-15

Plastic deformation behaviors of Ni{sub 42}Ti{sub 20}Zr{sub 21.5}Al{sub 8}Cu{sub 5}Si{sub 3.5} and Zr{sub 51}Ti{sub 5}Ni{sub 10}Cu{sub 25}Al{sub 9} bulk metallic glasses at room temperature were studied by nanoindentation testing and atomic force microscopy under equivalent indentation experimental conditions. The different chemical composition of these two bulk metallic glasses produced variant tendencies for displacement serrated flow to occur during the loading process. The nanoindentation strain rate was calculated as a function of indentation displacement in order to verify the occurrence of displacement serrated flow at different loading rates. Atomic force microscopy revealed decreasing numbers of discrete shear bands around the indentationmore » sites as loading rates increased from 0.025 to 2.5 mNs{sup −1}. Variations in plastic deformation behaviors between Ni and Zr-based glasses materials can be explained by the different metastable microstructures and thermal stabilities of the two materials. The mechanism governing plastic deformation of these metallic glasses was analyzed in terms of an established model of the shear transformation zone. - Highlights: • Plastic deformation of Ni- and Zr-based BMG is studied under identical conditions • Zr-based BMG undergoes a greater extent of plastic deformation than Ni-based BMG • Nanoindentation strain rate is studied to clarify variation in plastic deformation • Metastable microstructure, thermal stability affect BMG plastic deformation.« less

Non-singular and cyclic universe from the modified GUP

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

Salah, Maha; Hammad, Fayçal; Faizal, Mir

In this paper, we investigate the effects of a new version of the generalized uncertainty principle (modified GUP) on the dynamics of the Universe. As the modified GUP will modify the relation between the entropy and area of the apparent horizon, it will also deform the Friedmann equations within Jacobson's approach. We explicitly find these deformed Friedmann equations governing the modified GUP-corrected dynamics of such a Universe. It is shown that the modified GUP-deformed Jacobson's approach implies an upper bound for the density of such a Universe. The Big Bang singularity can therefore also be avoided using the modified GUP-correctionsmore » to horizons' thermodynamics. In fact, we are able to analyze the pre Big Bang state of the Universe. Furthermore, the equations imply that the expansion of the Universe will come to a halt and then will immediately be followed by a contracting phase. When the equations are extrapolated beyond the maximum rate of contraction, a cyclic Universe scenario emerges.« less

Non-singular and cyclic universe from the modified GUP

NASA Astrophysics Data System (ADS)

Salah, Maha; Hammad, Fayçal; Faizal, Mir; Farag Ali, Ahmed

2017-02-01

In this paper, we investigate the effects of a new version of the generalized uncertainty principle (modified GUP) on the dynamics of the Universe. As the modified GUP will modify the relation between the entropy and area of the apparent horizon, it will also deform the Friedmann equations within Jacobson's approach. We explicitly find these deformed Friedmann equations governing the modified GUP-corrected dynamics of such a Universe. It is shown that the modified GUP-deformed Jacobson's approach implies an upper bound for the density of such a Universe. The Big Bang singularity can therefore also be avoided using the modified GUP-corrections to horizons' thermodynamics. In fact, we are able to analyze the pre Big Bang state of the Universe. Furthermore, the equations imply that the expansion of the Universe will come to a halt and then will immediately be followed by a contracting phase. When the equations are extrapolated beyond the maximum rate of contraction, a cyclic Universe scenario emerges.

A comprehensive study of layer-specific morphological changes in the microstructure of carotid arteries under uniaxial load.

PubMed

Krasny, Witold; Morin, Claire; Magoariec, Hélène; Avril, Stéphane

2017-07-15

The load bearing properties of large blood vessels are principally conferred by collagen and elastin networks and their microstructural organization plays an important role in the outcomes of various arterial pathologies. In particular, these fibrous networks are able to rearrange and reorient spatially during mechanical deformations. In this study, we investigate for the first time whether these well-known morphological rearrangements are the same across the whole thickness of blood vessels, and subsequently if the underlying mechanisms that govern these rearrangements can be predicted using affine kinematics. To this aim, we submitted rabbit carotid samples to uniaxial load in three distinct deformation directions, while recording live images of the 3D microstructure using multiphoton microscopy. Our results show that the observed realignment of collagen and elastin in the media layer, along with elastin of the adventitia layer, remained limited to small angles that can be predicted by affine kinematics. We show also that collagen bundles of fibers in the adventitia layer behaved in significantly different fashion. They showed a remarkable capacity to realign in the direction of the load, whatever the loading direction. Measured reorientation angles of the fibers were significantly higher than affine predictions. This remarkable property of collagen bundles in the adventitia was never observed before, it shows that the medium surrounding collagen in the adventitia undergoes complex deformations challenging traditional hyperelastic models based on mixture theories. The biomechanical properties of arteries are conferred by the rearrangement under load of the collagen and elastin fibers making up the arterial microstructure. Their kinematics under deformation is not yet characterized for all fiber networks. In this respect we have submitted samples of arterial tissue to uniaxial tension, simultaneously to confocal imaging of their microstructure. Our method allowed identifying for the first time the remarkable ability of adventitial collagen fibers to reorient in the direction of the load, achieving reorientation rotations that exceeded those predicted by affine kinematics, while all other networks followed the affine kinematics. Our results highlight new properties of the microstructure, which might play a role in the outcomes of vascular pathologies like aneurysms. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Creep of Bridgmanite Analog, Neighborite (NaMgF3), and Implications for Viscous Flow in the Lower Mantle

NASA Astrophysics Data System (ADS)

Kaercher, P. M.; Mecklenburgh, J.; Mariani, E.; Wheeler, J.

2016-12-01

The rheology of the lower mantle directly influences mantle viscosity and strength and therefore affects a number of geophysical processes including mantle mixing, formation of mantle plumes and hotspots, slab subduction and stagnation, and plate motion. Experimental flow laws of lower mantle minerals, which quantify rheology of the lower mantle, are needed to help resolve discrepancies in estimates of lower mantle viscosity, better constrain geophysical models, and answer a number of outstanding questions such as, why slabs descend to different depths, and why the lower mantle is mostly isotropic despite large strains predicted by convection models. However, we lack natural lower mantle samples from which to infer deformation history. Furthermore, deformation experiments at lower mantle pressures and temperatures are challenging, and strain rates and stress cannot always be precisely controlled or measured. As a valuable alternative we have synthesized and deformed neighborite (NaMgF3), a low pressure analog of bridgmanite (MgSiO3), the most abundant mineral in the lower mantle and the Earth. Neighborite was deformed at 200 MPa confining pressure and between 500-700°C in compression using a fluid-medium deformation apparatus, and in torsion using a Patterson rig. In these experiments strain rate and stress can be accurately controlled and measured, and flow laws reliably determined. In addition we have recovered samples and examined deformation microstructures in a scanning electron microscope using electron backscatter diffraction. Preliminary mechanical results show a switch from linear-viscous deformation at lower stress (<50 MPa) to power law creep accommodated by grain boundary sliding at higher stress (>50 MPa). We also see strain weakening. Microstructures of samples deformed at a range of stress steps show grain boundary migration recrystallization (likely from lower stress) and crystallographic preferred orientation with poles to (100) planes parallel to compression (likely from higher stress). Further work is in progress to obtain microstructures that can be univocally associated with the observed mechanical behavior. We compare our results to those of other bridgmanite analogs and bridgmanite itself and extrapolate to geologic strain rates.

Microstructural changes and strain hardening effects in abrasive contacts at different relative velocities and temperatures

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

Rojacz, H., E-mail: rojacz@ac2t.at

2016-08-15

Strain hardening is commonly used to reach the full potential of materials and can be beneficial in tribological contacts. 2-body abrasive wear was simulated in a scratch test, aimed at strain hardening effects in various steels. Different working conditions were examined at various temperatures and velocities. Strain hardening effects and microstructural changes were analysed with high resolution scanning electron microscopy (HRSEM), electron backscatter diffraction (EBSD), micro hardness measurements and nanoindentation. Statistical analysing was performed quantifying the influence of different parameters on microstructures. Results show a crucial influence of temperature and velocity on the strain hardening in tribological contacts. Increased velocitymore » leads to higher deformed microstructures and higher increased surface hardness at a lower depth of the deformed zones at all materials investigated. An optimised surface hardness can be achieved knowing the influence of velocity (strain rate) and temperature for a “tailor-made” surface hardening in tribological systems aimed at increased wear resistance. - Highlights: •Hardening mechanisms and their intensity in tribological contacts are dependent on relative velocity and temperature. •Beneficial surface hardened zones are formed at certain running-in conditions; the scientific background is presented here. •Ferritic-pearlitic steels strain hardens via grain size reduction and decreasing interlamellar distances in pearlite. •Austenitic steels show excellent surface hardening (120% hardness increase) by twinning and martensitic transformation. •Ferritic steels with hard phases harden in the ferrite phase as per Hall-Petch equation and degree of deformation.« less

Development of ultrafine-grained microstructure in Al-Cu-Mg alloy through equal-channel angular pressing

NASA Astrophysics Data System (ADS)

Sai Anuhya, Danam; Gupta, Ashutosh; Nayan, Niraj; Narayana Murty, S. V. S.; Manna, R.; Sastry, G. V. S.

2014-08-01

Al-Cu-Mg alloys are extensively used for riveting applications in aerospace industries due to their relatively high shear strength coupled with high plasticity. The significant advantage of using V65 aluminum alloy ((Al-4Cu-0.2Mg) for rivet application also stems from its significantly slower natural aging kinetics, which gives operational flexibility to carryout riveting operation even after 4 days of solution heat treatment, in contrast to its equivalent alloy AA2024.Rivets are usually made by cold heading of wire rods. In order to form a defect free rivet head, grain size control in wire rods is essential at each and every stage of processing right from casting onwards upto the final wire drawing stage. Wire drawing is carried out at room temperature to reduce diameter as well as impart good surface finish. In the present study, different microstructures in V65 alloy bars were produced by rolling at different temperatures (room temperature to 523K) and subsequently deformed by equal channel angular pressing (ECAP) at 423K upto an equivalent strain of 7. ECAP was carried out to study the effect of initial microstructure on grain refinement and degree of deformation on the evolution of ultrafine grain structure. The refinement of V65 alloy by ECAP is significantly influenced by Initial microstructure but amount of deformation strongly affects the evolution processes as revealed by optical microscopy and transmission electron microscopy.

Microstructures and Mechanical Properties of Two-Phase Alloys Based on NbCr(2)

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

Cady, C.M.; Chen, K.C.; Kotula, P.G.

A two-phase, Nb-Cr-Ti alloy (bee+ C15 Laves phase) has been developed using several alloy design methodologies. In effort to understand processing-microstructure-property relationships, diffment processing routes were employed. The resulting microstructure and mechanical properties are discussed and compared. Plasma arc-melted samples served to establish baseline, . . . as-cast properties. In addition, a novel processing technique, involving decomposition of a supersaturated and metastable precursor phase during hot isostatic pressing (HIP), was used to produce a refined, equilibrium two-phase microstructure. Quasi-static compression tests as a ~ function of temperature were performed on both alloy types. Different deformation mechanisms were encountered based uponmore » temperature and microstructure.« less

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

Mechanisms of Earth activity forsed by external celestial bodies:energy budjet and nature of cyclicity

NASA Astrophysics Data System (ADS)

Barkin, Yu. V.; Ferrandiz, J. M.

2003-04-01

In given report we discuss tidal and non-tidal mechanisms of forced tectonic (endogenous) activity of the Earth caused by gravitational attraction of the Moon, Sun and the planets. On the base of the classical solution of the problem of elasticity for model of the Earth with concentric mass distribution the evaluations of the tidal energy and power of Earth lunar-solar deformations, including their joint effect, were obtained. Important role of the joint energetic effect of rotational deformation of the Earth with lunar and solar tides was illustrated. Gravitational interaction of the Moon and Sun with non-spherical, non-homogeneous shells of the Earth generates big additional mechanical forces and moments of the interaction of the neighboring shells (rigid core, liquid core, mantle, lithosphere and separate plates). Acting of these forces and moments in the different time scales on the corresponding sells generates cyclic perturbations of the tensional state of the shells, their deformations, small relative translational displacements and small relative rotational oscillations of the shells. In geological period of time it leads to a fundamental tectonic reconstruction of the Earth. These additional forces and moments of the cyclic celestial-mechanical nature produce cyclic deformations of the all layers of the body and organize and control practically all natural processes. The additional force between mantle and core is cyclic and characterized by the wide basis of frequencies typical for orbital motions (of the Sun, Moon and planets), for rotational motion of the Earth, Moon and Sun and for many from observed natural processes. The problem about small relative translatory-rotary motion of the two shells separated by the thin viscous-elastic layer is studied. The differential equations of motion were obtained and have been studied in particular cases (plane motion of system; case of two axisymmetrical interacting shells and oth.) by approximate methods of small parameter and methods of averaging. Some regimes of the relative translatory-rotary motions of the shells were described in analytical form. Wide set observed geodynamical and geophysical phenomena can be illustrated as results or as reflections of the small and slow relative displacements of the shells in corresponding time-scales. Barkin's work was accepted and financed by RFBR grant 02-05-64176 and by grant SAB2000-0235 of Ministry of Education of Spain (Secretaria de Estado de Educacion y Universidades).

The effect of matrix microstructure on cyclic response and fatigue behavior of particle- reinforced 2219 aluminum: Part I. room temperature behavior

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; Allison, J. E.; van Aken, D. C.

1995-12-01

The low-cycle and high-cycle fatigue behavior and cyclic response of naturally aged and overaged 2219/TiC/15p and unreinforced 2219 Al were investigated using plastic strain-controlled and stress-controlled testing. In addition, the influence of grain size on the particle-reinforced materials was examined. In both reinforced and unreinforced materials, the naturally aged conditions were cyclically unstable, exhibiting an initial hardening behavior followed by an extended region of cyclic stability and ultimately a softening region. The overaged reinforced material was cyclically stable for the plastic strains examined, while the overaged unreinforced material exhibited cyclic hardening at plastic strains greater than 2.5 × 10-4. Decreasing grain size of particle-reinforced materials modestly increased the cyclic flow stress of both naturally aged and overaged materials. Reinforced and unreinforced materials exhibited similar fatigue life behaviors; however, the reinforced and unreinforced naturally aged materials had superior fatigue lives in comparison to the overaged materials. Grain size had no effect on the fatigue life behavior of the particle-reinforced materials. The fatigue lives were strongly influenced by the presence of clusters of TiC particles and exogenous Al3Ti intermetallics.

Characteristics of aluminum alloy microplastic deformation in different structural states

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

Seregin, G.V.; Efimenko, L.L.; Leonov, M.V.

The solution to the problem of improving the mechanical properties (including cyclic strength) of structural materials is largely dependent on our knowledge of the laws governing the development of microplastic deformations in them. The effect of heat and mechanical treatment on the elastoplastic properties and fatigue resistance of the commercial aluminum alloys AK4-1 and D16 is analyzed.

Effect of Rolling on High-Cycle Fatigue and Fracture of an Al - Mg - Sc Alloy

NASA Astrophysics Data System (ADS)

Zhemchuzhnikova, D. A.; Petrov, A. P.; Eremeev, N. V.; Eremeev, V. V.; Kaibyshev, R. O.

2016-07-01

The tensile strength and fatigue properties of alloy 1575 of the Al - Mg - Sc system are studied after hot deformation (at 360°C) and subsequent cold rolling with different reduction ratios. The effect of the deformed structure on the properties and mechanisms of fracture of the alloy under cyclic tests is determined.

Deformations of temporary wooden supports used to reduce building deflections in mining areas

NASA Astrophysics Data System (ADS)

Gromysz, Krzysztof

2018-04-01

Temporary supports, consisting of a stack of wooden elements and a hydraulic jack, are used in the process of removing deflections in buildings with one to three aboveground floors in mining areas. During uneven raising, the supports are loaded monotonically, unloaded and loaded cyclically. Laboratory tests were designed for the supports. For the investigated range of loads of 0 to 400 kN, under a growing load, a linear relationship exists between a load and the change in the stack length, which signifies that the deformations of wooden elements and displacements related to their mutual interactions increase proportionally. A seemingly higher stack stiffness is seen at the beginning of the unloading process and for cyclical loads, meaning that in this phase of loading, the material deformation of the wooden elements and the jack is responsible for changing the jack length in this load phase, with a negligible presence of mutual displacements of wooden elements. The support, after being unloaded, returns to the initial position and its permanent deformations are not observed. The stiffness of a temporary support decreases as the height of the stack of wooden elements increases.

Finite element analysis of the upsetting of a 5056 aluminum alloy sample with consideration of its microstructure

NASA Astrophysics Data System (ADS)

Voronin, S. V.; Chaplygin, K. K.

2017-12-01

Computer simulation of upsetting the finite element models (FEMs) of an isotropic 5056 aluminum alloy sample and a 5056 aluminum alloy sample with consideration of microstructure is carried out. The stress and strain distribution patterns at different process stages are obtained. The strain required for the deformation of the FEMs of 5056 alloy samples is determined. The influence of the material microstructure on the stress-strain behavior and technological parameters are demonstrated.

Effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK).

PubMed

Simsiriwong, Jutima; Shrestha, Rakish; Shamsaei, Nima; Lugo, Marcos; Moser, Robert D

2015-11-01

In this study, the effects of microstructural inclusions on fatigue life of polyether ether ketone (PEEK) was investigated. Due to the versatility of its material properties, the semi-crystralline PEEK polymer has been increasingly adopted in a wide range of applications particularly as a biomaterial for orthopedic, trauma, and spinal implants. To obtain the cyclic behavior of PEEK, uniaxial fully-reversed strain-controlled fatigue tests were conducted at ambient temperature and at 0.02 mm/mm to 0.04 mm/mm strain amplitudes. The microstructure of PEEK was obtained using the optical and the scanning electron microscope (SEM) to determine the microstructural inclusion properties in PEEK specimen such as inclusion size, type, and nearest neighbor distance. SEM analysis was also conducted on the fracture surface of fatigue specimens to observe microstructural inclusions that served as the crack incubation sites. Based on the experimental strain-life results and the observed microstructure of fatigue specimens, a microstructure-sensitive fatigue model was used to predict the fatigue life of PEEK that includes both crack incubation and small crack growth regimes. Results show that the employed model is applicable to capture microstructural effects on fatigue behavior of PEEK. Copyright © 2015 Elsevier Ltd. All rights reserved.

Fatigue strength of a magnesium MA2-1 alloy after equal-channel angular pressing

NASA Astrophysics Data System (ADS)

Terent'ev, V. F.; Dobatkin, S. V.; Prosvirnin, D. V.; Bannykh, I. O.; Kopylov, V. I.; Serebryany, V. N.

2010-09-01

The fatigue strength of a magnesium MA2-1 alloy is studied after annealing and equal-channel angular pressing (ECAP). The ultrafine-grained structure formed upon ECAP is shown to increase the plasticity of the material during static tension, to decrease the cyclic life to failure, and not to decrease the fatigue limit. The mechanisms of crack nucleation and growth during cyclic deformation are investigated.

Microstructure and Mechanical Properties Evolution of the Al, C-Containing CoCrFeNiMn-Type High-Entropy Alloy during Cold Rolling.

PubMed

Klimova, Margarita; Stepanov, Nikita; Shaysultanov, Dmitry; Chernichenko, Ruslan; Yurchenko, Nikita; Sanin, Vladimir; Zherebtsov, Sergey

2017-12-29

The effect of cold rolling on the microstructure and mechanical properties of an Al- and C-containing CoCrFeNiMn-type high-entropy alloy was reported. The alloy with a chemical composition (at %) of (20-23) Co, Cr, Fe, and Ni; 8.82 Mn; 3.37 Al; and 0.69 C was produced by self-propagating high-temperature synthesis with subsequent induction. In the initial as-cast condition the alloy had an face centered cubic single-phase coarse-grained structure. Microstructure evolution was mostly associated with either planar dislocation glide at relatively low deformation during rolling (up to 20%) or deformation twinning and shear banding at higher strain. After 80% reduction, a heavily deformed twinned/subgrained structure was observed. A comparison with the equiatomic CoCrFeNiMn alloy revealed higher dislocation density at all stages of cold rolling and later onset of deformation twinning that was attributed to a stacking fault energy increase in the program alloy; this assumption was confirmed by calculations. In the initial as-cast condition the alloy had low yield strength of 210 MPa with yet very high uniform elongation of 74%. After 80% rolling, yield strength approached 1310 MPa while uniform elongation decreased to 1.3%. Substructure strengthening was found to be dominated at low rolling reductions (<40%), while grain (twin) boundary strengthening prevailed at higher strains.

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.

Examining the microtexture evolution in a hole-edge punched into 780 MPa grade hot-rolled steel

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

Shin, J.H.; Kim, M.S.

The deformation behavior in the hole-edge of 780 MPa grade hot-rolled steel during the punching process was investigated via microstructure characterization and computational simulation. Microstructure characterization was conducted to observe the edges of punched holes through the thickness direction, and electron back-scattered diffraction (EBSD) was used to analyze the heterogeneity of the deformation. Finite element analysis (FEA) that could account for a ductile fracture criterion was conducted to simulate the deformation and fracture behaviors of 780 MPa grade hot-rolled steel during the punching process. Calculation of rotation rate fields at the edges of the punched holes during the punching processmore » revealed that metastable orientations in Euler space were confined to specific orientation groups. Rotation-rate fields effectively explained the stability of the initial texture components in the hole-edge region during the punching process. A visco-plastic self-consistent (VPSC) polycrystal model was used to calculate the microtexture evolution in the hole-edge region during the punching process. FEA revealed that the heterogeneous effective strain was closely related to the heterogeneity of the Kernel average misorientation (KAM) distribution in the hole-edge region. A simulation of the deformation microtexture evolution in the hole-edge region using a VPSC model was in good agreement with the experimental results. - Highlights: •We analyzed the microstructure in a hole-edge punched in HR 780HB steel. •Rotation rate fields revealed the stability of the initial texture components. •Heterogeneous effective stain was closely related to the KAM distribution. •VPSC model successfully simulated the deformation microtexture evolution.« less

Deformation behavior of migmatites: insights from microstructural analysis of a garnet-sillimanite-mullite-quartz-feldspar-bearing anatectic migmatite at Rampura-Agucha, Aravalli-Delhi Fold Belt, NW India

NASA Astrophysics Data System (ADS)

Prakash, Abhishek; Piazolo, Sandra; Saha, Lopamudra; Bhattacharya, Abhijit; Pal, Durgesh Kumar; Sarkar, Saheli

2018-03-01

In the present study we investigate the microstructural development in mullite, quartz and garnet in an anatectic migmatite hosted within a Grenvillian-age shear zone in the Aravalli-Delhi Fold Belt. The migmatite exhibits three main deformation structures and fabrics (S1, S2, S3). Elongated garnet porphyroblasts are aligned parallel to the metatexite S2 layers and contain crenulation hinges defined by biotite-sillimanite-mullite-quartz (with S1 axial planar foliation). Microstructural evidence and phase equilibrium relations establish the garnet as a peritectic phase of incongruent melting by breakdown of biotite, sillimanite ± mullite and quartz at peak P-T of 8 kbar, 730 °C along a tight-loop, clockwise P-T path. Monazite dating establishes that the partial melting occurred between 1000 and 870 Ma. The absence of subgrains and systematic crystal lattice distortions in these garnets despite their elongation suggests growth pseudomorphing pre-existing 3-D networks of S1 biotite aggregates rather than high-temperature crystal plastic deformation which is noted in the S1 quartz grains that exhibit strong crystallographic preferred orientation (CPO), undulatory extinction and subgrains. Mode-I fractures in these garnet porphyroblasts induced by high melt pressure during late stage of partial melt crystallization are filled by retrograde biotite-sillimanite. Weak CPO and non-systematic crystal lattice distortions in the coarse quartz grains within the S2 leucosome domains indicate these crystallized during melt solidification without later crystal plastic deformation overprint. In the later stages of deformation (D3), strain was mostly accommodated in the mullite-biotite-sillimanite-rich restite domains forming S3 which warps around garnet and leucosome domains; consequently, fine-grained S3 quartz does not exhibit strong CPOs.

Improving Cull Cow Meat Quality Using Vacuum Impregnation.

PubMed

Leal-Ramos, Martha Y; Alarcón-Rojo, Alma D; Gutiérrez-Méndez, Néstor; Mújica-Paz, Hugo; Rodríguez-Almeida, Felipe; Quintero-Ramos, Armando

2018-05-07

Boneless strip loins from mature cows (50 to 70 months of age) were vacuum impregnated (VI) with an isotonic solution (IS) of sodium chloride. This study sought to determine the vacuum impregnation and microstructural properties of meat from cull cows. The experiments were conducted by varying the pressure, p 1 (20.3, 71.1 kPa), and time, t 1 (0.5, 2.0, 4.0 h), of impregnation. After the VI step, the meat was kept for a time, t 2 (0.0, 0.5, 2.0, 4.0 h), in the IS under atmospheric pressure. The microstructural changes, impregnation, deformation, and porosity of the meat were measured in all the treatments. Impregnation and deformation levels in terms of volume fractions of the initial sample at the end of the vacuum step and the VI processes were calculated according to the mathematical model for deformation-relaxation and hydrodynamic mechanisms. Scanning electron microscopy (SEM) was used to study the microstructure of the vacuum-impregnated meat samples. Results showed that both the vacuum and atmospheric pressures generated a positive impregnation and deformation. The highest values of impregnation X (10.5%) and deformation γ (9.3%) were obtained at p 1 of 71.1 kPa and t 1 of 4.0 h. The sample effective porosity ( ε e ) exhibited a significant interaction ( p < 0.01) between p 1 × t 1 . The highest ε e (14.0%) was achieved at p 1 of 20.3 kPa and t 1 of 4.0 h, whereas the most extended distension of meat fibers (98 μm) was observed at the highest levels of p ₁, t ₁, and t ₂. These results indicate that meat from mature cows can undergo a vacuum-wetting process successfully, with an IS of sodium chloride to improve its quality.

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

Study of cyclic thermal aging of tube type receivers as a function of the duration of the cycle

NASA Astrophysics Data System (ADS)

Setien, Eneko; Fernández-Reche, Jesús; Ariza, María Jesús; Álvarez-de-Lara, Mónica

2017-06-01

The tube type receivers are exposed to variable duration cyclic operating conditions, which can jeopardize its reliability, and make it hard to estimate its long term performance. The designers have to deal with this problem and estimate the receiver long term performance based on the poor available litterature and the data sheets of the material. In order to help the designer better estimate the performance of the receivers, in this paper the cyclic thermal aging is analyzed as a function of the cycle duration. For this purpose, coated and uncoated Inconel alloy 625 tubular samples, similar to those used in the commercial receivers, are cyclically aged with different thermal cycle duration. The aging of these samples has been analyzed by means of oxidation kinetics, microstructure examination and mechanical and optical properties. The effect of the thermal cycle duration is studied and discussed by comparison of the results.

Highly stable multi-wall carbon nanotubes@poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) core-shell composites with three-dimensional porous nano-network for electrochemical capacitors

NASA Astrophysics Data System (ADS)

Zhou, Haihan; Han, Gaoyi; Chang, Yunzhen; Fu, Dongying; Xiao, Yaoming

2015-01-01

A facile and feasible electrochemical polymerization method has been used to construct the multi-wall carbon nanotubes@poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (MWCNTs@PEDOT/PSS) core-shell composites with three-dimensional (3D) porous nano-network microstructure. The composites are characterized with Fourier transform infrared spectroscopy, scanning electron microscope, and transmission electron microscopy. This special core-shell nanostructure can significantly reduce the ions diffusion distance and the 3D porous nano-network microstructure effectively enlarges the electrode/electrolyte interface. The electrochemical tests including cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy tests are performed, the results manifest the MWCNTs@PEDOT/PSS core-shell composites have superior capacitive behaviors and excellent cyclic stability, and a high areal capacitance of 98.1 mF cm-2 is achieved at 5 mV s-1 cyclic voltammetry scan. Furthermore, the MWCNTs@PEDOT/PSS composites exhibit obviously superior capacitive performance than that of PEDOT/PSS and PEDOT/Cl electrodes, indicating the effective composite of MWCNTs and PEDOT noticeably boosts the capacitive performance of PEDOT-based electrodes for electrochemical energy storage. Such a highly stable core-shell 3D network structural composite is very promising to be used as electrode materials for the high-performance electrochemical capacitors.

Cyclic Degradation Behavior of < 001 > -Oriented Fe-Mn-Al-Ni Single Crystals in Tension

NASA Astrophysics Data System (ADS)

Vollmer, M.; Kriegel, M. J.; Krooß, P.; Martin, S.; Klemm, V.; Weidner, A.; Chumlyakov, Y.; Biermann, H.; Rafaja, D.; Niendorf, T.

2017-12-01

In the present study, functional fatigue behavior of a near 〈001〉-oriented Fe-Mn-Al-Ni single crystal was investigated under tensile load. An incremental strain test up to 3.5% strain and cyclic tests up to 25 cycles revealed rapid pseudoelastic degradation. Progressive microstructural degradation was studied by in situ scanning electron microscopy. The results show a partially inhibited reactivation of previously formed martensite and proceeding activation of untransformed areas in subsequent cycles. The preferentially formed martensite variants were identified by means of Schmid factor calculation and the Kurdjumov-Sachs relationship. Post mortem transmission electron microscopy investigations shed light on the prevailing degradation mechanisms. Different types of dislocations were found promoting the progressive degradation during cyclic loading.