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Sample records for microstructural evolution based

  1. Microstructure Evolution of Gas Atomized Iron Based ODS Alloys

    SciTech Connect

    Rieken, J.R.; Anderson, I.E.; Kramer, M.J.; Anderegg, J.W.; Shechtman, D.

    2009-12-01

    In a simplified process to produce precursor powders for oxide dispersion-strength- ened (ODS) alloys, gas-atomization reaction synthesis (GARS) was used to induce a surface oxide layer on molten droplets of three differing erritic stainless steel alloys during break-up and rapid solidification. The chemistry of the surface oxide was identified using auger electron spectroscopy (AES) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The precursor iron-base powders were consolidated at 850 C and 1,300 C using hot isostatic pressing (HIPing). Consolidation at the lower temperature resulted in a fully dense microstructure, while preventing substantial prior particle-boundary-oxide dissociation. Microstructural analysis of the alloys consolidated at the higher temperature confirmed a significant reduction in prior-particle-boundary-oxide volume fraction, in comparison with the lower-temperature-consolidated sample. This provided evidence that a high-temperature internal oxygen-exchange reaction occurred between the metastable prior particle-boundary-oxide phase (chromium oxide) and the yttrium contained within each prior particle. This internal oxygen-exchange reaction is shown to result in the formation of yttrium-enriched oxide dispersoids throughout the alloy microstructure. The evolving microstructure was characterized using transmission electron microscopy (TEM) and high-energy X-ray diffraction (HE-XRD).

  2. Microstructure Evolution of Gas Atomized Iron Based ODS Alloys

    SciTech Connect

    Rieken, J.R.; Anderson, I.E.; Kramer, M.J.

    2011-08-09

    In a simplified process to produce precursor powders for oxide dispersion-strengthened (ODS) alloys, gas-atomization reaction synthesis (GARS) was used to induce a surface oxide layer on molten droplets of three differing erritic stainless steel alloys during break-up and rapid solidification. The chemistry of the surface oxide was identified using auger electron spectroscopy (AES) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The precursor iron-base powders were consolidated at 850 C and 1,300 C using hot isostatic pressing (HIPing). Consolidation at the lower temperature resulted in a fully dense microstructure, while preventing substantial prior particle-boundary-oxide dissociation. Microstructural analysis of the alloys consolidated at the higher temperature confirmed a significant reduction in prior-particle-boundary-oxide volume fraction, in comparison with the lower-temperature-consolidated sample. This provided evidence that a high-temperature internal oxygen-exchange reaction occurred between the metastable prior particle-boundary-oxide phase (chromium oxide) and the yttrium contained within each prior particle. This internal oxygen-exchange reaction is shown to result in the formation of yttrium-enriched oxide dispersoids throughout the alloy microstructure. The evolving microstructure was characterized using transmission electron microscopy (TEM) and high-energy X-ray diffraction (HE-XRD).

  3. Plastic Flow and Microstructure Evolution During Thermomechanical Processing of a PM Nickel-Base Superalloy (Preprint)

    DTIC Science & Technology

    2012-07-01

    creep and creep-crack growth under dwell- fatigue loading in service, final heat treatment above the solvus temperature of the strengthening...supersolvus furnace heat treatment were used to evaluate plastic flow and microstructure evolution during thermomechanical processing (TMP) of the...AFRL-RX-WP-TP-2012-0368 PLASTIC FLOW AND MICROSTRUCTURE EVOLUTION DURING THERMOMECHANICAL PROCESSING OF A PM NICKEL-BASE SUPERALLOY

  4. Mesoscale modeling and simulation of microstructure evolution during dynamic recrystallization of a Ni-based superalloy

    NASA Astrophysics Data System (ADS)

    Chen, Fei; Cui, Zhenshan; Ou, Hengan; Long, Hui

    2016-10-01

    Microstructural evolution and plastic flow characteristics of a Ni-based superalloy were investigated using a simulative model that couples the basic metallurgical principle of dynamic recrystallization (DRX) with the two-dimensional (2D) cellular automaton (CA). Variation of dislocation density with local strain of deformation is considered for accurate determination of the microstructural evolution during DRX. The grain topography, the grain size and the recrystallized fraction can be well predicted by using the developed CA model, which enables to the establishment of the relationship between the flow stress, dislocation density, recrystallized fraction volume, recrystallized grain size and the thermomechanical parameters.

  5. In-Situ Resistivity Monitoring of Microstructure Evolution in IN718 Nickel-Base Superalloy

    NASA Astrophysics Data System (ADS)

    Madhi, E.; Nagy, P. B.

    2009-03-01

    This work is aimed at characterizing the irreversible changes in electrical resistivity caused by microstructure evolution in IN718 nickel-base superalloy. Of course, the electric resistivity also exhibits a strong reversible change that is a function of the instantaneous temperature, therefore realtime assessment of microstructure evolution also requires accurate monitoring of temperature. In-situ resistivity monitoring was conducted throughout various heating cycles using the Alternating Current Potential Drop (ACPD) technique. Using thermocouple wires for connections, measurement of the DC potential difference between the connecting electrodes without current injection allows parallel monitoring of the local temperature. It was found that this method can be readily used both to record the thermal history experienced by the material and to assess the resulting irreversible microstructural changes.

  6. Microstructural Evolution During Friction Stir Welding of Mild Steel and Ni-Based Alloy 625

    NASA Astrophysics Data System (ADS)

    Fernandez, Johnnatan Rodriguez; Ramirez, Antonio J.

    2017-01-01

    Microstructure evolution during friction stir welding (FSW) of mild steel and Ni-based alloy 625 was studied. Regarding the Ni-based alloy, the welding process led to grain refinement caused by discontinuous and continuous dynamic recrystallization, where bulging of the pre-existing grains and subgrain rotation were the primary mechanisms of recrystallization. In the steel, discontinuous dynamic recrystallization was identified as the recovery process experienced by the austenite. Simple shear textures were observed in the regions affected by the deformation of both materials. Although the allotropic transformation obscured the deformation history, the thermo-mechanically affected zone was identified in the steel by simple shear texture components. A new methodology for the study of texture evolution based on rotations of the slip systems using pole figures is presented as an approximation to describe the texture evolution in FSW.

  7. Microstructural Evolution During Friction Stir Welding of Mild Steel and Ni-Based Alloy 625

    NASA Astrophysics Data System (ADS)

    Fernandez, Johnnatan Rodriguez; Ramirez, Antonio J.

    2017-03-01

    Microstructure evolution during friction stir welding (FSW) of mild steel and Ni-based alloy 625 was studied. Regarding the Ni-based alloy, the welding process led to grain refinement caused by discontinuous and continuous dynamic recrystallization, where bulging of the pre-existing grains and subgrain rotation were the primary mechanisms of recrystallization. In the steel, discontinuous dynamic recrystallization was identified as the recovery process experienced by the austenite. Simple shear textures were observed in the regions affected by the deformation of both materials. Although the allotropic transformation obscured the deformation history, the thermo-mechanically affected zone was identified in the steel by simple shear texture components. A new methodology for the study of texture evolution based on rotations of the slip systems using pole figures is presented as an approximation to describe the texture evolution in FSW.

  8. Microstructurally Based Cross-slip Mechanisms and Their Effects on Dislocation Microstructure Evolution in fcc Crystals

    DTIC Science & Technology

    2015-01-01

    nickel microcrystals, Acta Mater. 56 (13) (2008) 2008. [58] G Makov P Landau , R Z Shneck, A. Venkert, Evolution of dislocation patterns in fcc metals, IOP...orientation: I. disloca- tion arrangement and cell structure of crystals deformed in tension, Philos. Mag. 28 (1973) 1057–1976. [61] P. Landau , R.Z. Shneck

  9. Microstructure evolution and mechanical property of pulsed laser welded Ni-based superalloy

    NASA Astrophysics Data System (ADS)

    Ma, Guangyi; Wu, Dongjiang; Niu, Fangyong; Zou, Helin

    2015-09-01

    For evaluating the microstructure evolution and mechanical property of Ni-based Hastelloy C-276 weld joint by the pulsed laser welding, the influence of pulsed laser welding on the microstructure and mechanical property of the weld joint is investigated by the analysis of the microstructure morphology, microhardness, phase structure and tensile property. The results indicate that, in the fusion zone three sections are divided on the basis of the patterns of grain structures. In the weld joint, the element segregation is found, but the trend of brittle phase's formation is weakened. The weld microhardness presents just a little higher than that of base metal, and there is no obvious the softened heat affected zone. Meanwhile in the weld joint, the phase structure is still the face-center cubic with the tiny shift of peak positions and widened Full Width at Half-Maximum. The yield strength of weld joint is the same as that of base metal, and the tensile strength is nearly 90% of that of base metal. The decreased tensile strength is mainly attributed to the dislocation piling-up.

  10. An incremental-iterative method for modeling damage evolution in voxel-based microstructure models

    NASA Astrophysics Data System (ADS)

    Zhu, Qi-Zhi; Yvonnet, Julien

    2015-02-01

    Numerical methods motivated by rapid advances in image processing techniques have been intensively developed during recent years and increasingly applied to simulate heterogeneous materials with complex microstructure. The present work aims at elaborating an incremental-iterative numerical method for voxel-based modeling of damage evolution in quasi-brittle microstructures. The iterative scheme based on the Lippmann-Schwinger equation in the real space domain (Yvonnet, in Int J Numer Methods Eng 92:178-205, 2012) is first cast into an incremental form so as to implement nonlinear material models efficiently. In the proposed scheme, local strain increments at material grid points are computed iteratively by a mapping operation through a transformation array, while local stresses are determined using a constitutive model that accounts for material degradation by damage. For validation, benchmark studies and numerical simulations using microtomographic data of concrete are performed. For each test, numerical predictions by the incremental-iterative scheme and the finite element method, respectively, are presented and compared for both global responses and local damage distributions. It is emphasized that the proposed incremental-iterative formulation can be straightforwardly applied in the framework of other Lippmann-Schwinger equation-based schemes, like the fast Fourier transform method.

  11. Microstructure Evolution during Supersolvus Heat Treatment of a Powder Metallurgy 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.

    2012-05-01

    Microstructure evolution during the supersolvus heat treatment of a powder-metallurgy, low-solvus, high-refractory (LSHR) superalloy was established. For this purpose, three lots of LSHR with varying initial carbon/boron composition and thermomechanical history were subjected to a series of short-time (induction) and long-time (furnace) heat treatments followed by scanning electron microscopy/electron backscatter diffraction and quantitative metallography. The size of the (pinned) gamma grains exhibited a limited dependence on heating rate and soak time at peak temperature, and it was generally smaller than the predictions based on the classic Smith-Zener model. The differences were rationalized in terms of stereological and pinning-particle location effects. Observations of limited coarsening of the carbide/boride pinning particles were interpreted in the context of prior experimental observations and a modified Lifshitz-Slyosov-Wagner model applied previously for the coarsening of compound phases in steels.

  12. Evolution of microstructure and defect structure in manganese-aluminum-based permanent magnet alloys

    NASA Astrophysics Data System (ADS)

    Yanar, Cagatay

    In this study, the transformation behavior of MnAl-based ferromagnetic alloys was investigated. The low-cost and availability of the Mn-Al base metals along with their high mechanical strength, machineability and high magnetic energy product (BH) per unit weight make these materials attractive candidates for permanent magnet applications. These alloys derive their magnetic properties from the metastable L10 tau-phase, which generally appears towards the Mn-rich side of the near equiatomic composition. The magnetic properties of these materials are strongly influenced by the microstructure and characteristic defect structure of the tau-phase. The tau-phase exhibits a unique defect structure, which includes twins, stacking faults, anti-phase domain boundaries and dislocations. Understanding the true nature of defect generation is necessary in order to be able to develop processing techniques to enhance and optimize the properties of these materials. The tau-phase derives from a phase mixture of ε(hcp) and ε '(B19) phases through various heat treatment processes. Controversial mechanisms are reported in the literature regarding the nature of the ε + ε' → tau transformation. Phase transformation mechanisms that are displacive and those involving a massive transformation have been reported. In this study, the true nature of the tau-phase formation was investigated experimentally by utilizing techniques such as transmission electron microscopy (TEM), high-resolution electron microscopy (HREM) and in-situ TEM heating experiments. It was shown that both of the transformation modes, i.e. massive and displacive mechanisms, can operate and result in tau-phase formation. The atomic nature of the displacive transformation was studied in detail to elucidate the viability of transformation of a two-phase mixture into a single phase through a shear transformation. In the absence of stress, the massive mode was shown to dominate microstructural evolution in bulk materials

  13. Prediction of microstructure evolution during high temperature blade forging of a Ni-Fe based superalloy, Alloy 718

    NASA Astrophysics Data System (ADS)

    Na, Young-Sang; Yeom, Jong-Taek; Park, Nho-Kwang; Lee, Jai-Young

    2003-02-01

    The mechanical properties of the Ni-Fe-based Alloy 718 depend very much on grain size, as well as the strengthening phases, γ' and γ. The grain structure of the superalloy components is mainly controlled during thermo-mechanical processes by the dynamic, meta-dynamic recrystallization and grain growth. In this investigation, the evolution of the grain structure in the process of two-step blade forging was experimentally and numerically dealt with. The evolution of the grain structure in Alloy 718 during blade forging was predicted using a 2-DFE simulator with implemented constitutive models on dynamic recrystallization and grain growth. The comparison of the simulated microstructure with the actual grain structure of the forged parts validated the prediction of the grain structure evolution. The effect of dynamic recrystallization on the evolution of grain structure is highlighted in this article.

  14. Microstructural and continuum evolution modeling of sintering.

    SciTech Connect

    Braginsky, Michael V.; Olevsky, Eugene A.; Johnson, D. Lynn; Tikare, Veena; Garino, Terry J.; Arguello, Jose Guadalupe, Jr.

    2003-12-01

    deformation during. The continuum portion is based on a finite element formulation that allows 3D components to be modeled using SNL's nonlinear large-deformation finite element code, JAS3D. This tool provides a capability to model sintering of complex three-dimensional components. The model was verified by comparing to simulations results published in the literature. The model was validated using experimental results from various laboratory experiments performed by Garino. In addition, the mesoscale simulations were used to study anisotropic shrinkage in aligned, elongated powder compacts. Anisotropic shrinkage occurred in all compacts with aligned, elongated particles. However, the direction of higher shrinkage was in some cases along the direction of elongation and in other cases in the perpendicular direction depending on the details of the powder compact. In compacts of simple-packed, mono-sized, elongated particles, shrinkage was higher in the direction of elongation. In compacts of close-packed, mono-sized, elongated particles and of elongated particles with a size and shape distribution, the shrinkage was lower in the direction of elongation. We also explored the concept of a sintering stress tensor rather than the traditional sintering stress scalar concept for the case of anisotropic shrinkage. A thermodynamic treatment of this is presented. A method to calculate the sintering stress tensor is also presented. A user-friendly code that can simulate microstructural evolution during sintering in 2D and in 3D was developed. This code can run on most UNIX platforms and has a motif-based GUI. The microstructural evolution is shown as the code is running and many of the microstructural features, such as grain size, pore size, the average grain boundary length (in 2D) and area (in 3D), etc. are measured and recorded as a function of time. The overall density as the function of time is also recorded.

  15. Oxidation and microstructure evolution of Al-Si coated Ni3Al based single crystal superalloy with high Mo content

    NASA Astrophysics Data System (ADS)

    Tu, Xiaolu; Peng, Hui; Zheng, Lei; Qi, Wenyan; He, Jian; Guo, Hongbo; Gong, Shengkai

    2015-01-01

    A Si modified aluminide (Al-Si) coating was prepared on a Ni3Al based single crystal superalloy with high Mo content by high-activity pack cementation. Cyclic oxidation test at 1150 °C was carried out and the microstructure evolution of the coating was investigated. The results show that the oxidation resistance of the substrate was greatly increased by applying an Al-Si coating. During oxidation, outward diffusion of Mo was effectively blocked due to its high affinity with Si. Besides, a layered structure was formed as a result of the elements inter-diffusion. An obvious degradation of the Al-Si coating was observed after 100 h oxidation. Possible mechanisms related to the oxidation and elements inter-diffusion behaviours were also discussed.

  16. Microstructure evolution characteristics induced by oxygen vacancy generation in anatase TiO2 based resistive switching devices

    NASA Astrophysics Data System (ADS)

    Liu, Chen; Gao, Bin; Huang, Peng; Kang, Jinfeng

    2017-03-01

    In this work, first principle calculations are employed to study the microstructure characteristics of the anatase TiO2 resistive switching material associated with the generation of oxygen vacancy (V o) based nanofilaments during the switching process. The calculations indicate that both the magnéli phase Ti4O7 and V o-defect phase of anatase TiO2 may be formed with the generation of oxygen vacancies during the forming and SET processes. Based on the calculations, a new physical insight is proposed to clarify the microstructure evolution characteristics of the anatase TiO2 resistive switching material and the correlation with resistive switching behaviors. During the forming or SET process, the anatase TiO2 is first excited to a transition state with the generation of oxygen vacancies, then fully relaxes to a stable V o-defect state. This V o-defect state may either recover to the original state with the recombination of the oxygen vacancies, which causes the reversible resistive switching behavior, or further transform to a much more stable state—the magnéli phase Ti4O7, through a phase transition process with the generation of many more oxygen vacancies. The phase transition from V o- defective anatase phase to magnéli phase Ti4O7 causes the failure of the resistive switching due to the significantly reduced possibility of the reversible phase transition from the magnéli phase to the anatase phase, compared with the possibility of the recombination from the V o-defective anatase.

  17. Microstructural evolution and mechanical behavior of nickel-based superalloy 625 made by selective laser melting

    NASA Astrophysics Data System (ADS)

    Witkin, David B.; Adams, Paul; Albright, Thomas

    2015-03-01

    The mechanical properties and microstructures of Selective Laser Melted (SLM) alloy 625 procured from different suppliers were compared. The post-SLM process of hot isostatic pressing (HIP) led to a relatively coarse recrystallized gamma matrix phase that was similar in all the suppliers' materials, resulting in nearly identical tensile properties. These similarities obscure significant differences between them with respect to the population of second phase particles, which consisted of carbides or Laves phase. During solidification, the final liquid phase is concentrated in Nb, Mo, Si and C, and leads to L --> γ + carbide/Laves eutectic reactions. Secondary particles are very small prior to HIP and their composition has not been analyzed yet, but are limited to the fine-grained eutectic regions of the material prior to HIP. During HIP the gamma phase recrystallizes to remove the original as-solidified SLM microstructure, but secondary particles nucleate and grow where their elemental constituents first solidified, leading to a non-homogeneous distribution. Quasi-static tensile properties do not appear to be sensitive to these differences, but it is likely that other mechanical properties will be affected, especially fatigue and fracture behavior. Surface roughness, large grain size, and pores and voids left unhealed by the HIP cycle will also influence fatigue and fracture. Surface roughness and porosity in particular are features that could be improved by implementing novel approaches to laser processing in SLM.

  18. Micro-structure evolution of wall based crystals after casting of model suspensions as obtained from Bragg microscopy.

    PubMed

    Palberg, Thomas; Maaroufi, Martin R; Stipp, Andreas; Schöpe, Hans Joachim

    2012-09-07

    Growth of heterogeneously nucleated, wall based crystals plays a major role in determining the micro-structure during melt casting. This issue is here addressed using a model system of charged colloidal spheres in deionized aqueous suspension observed by Bragg microscopy which is a combination of light scattering and microscopy. We examine the evolution of the three-dimensional size, shape, and orientation of twin domains in monolithic crystals growing from two opposing planar walls into a meta-stable (shear-) melt. At each wall crystal orientation and twinning emerges during nucleation with small domains. During growth these widen and merge. From image analysis we observe the lateral coarsening velocities to follow a power law behaviour L(XY) ∝ t(1/2) as long as the vertical growth continues at constant speed. Lateral coarsening terminates upon intersection of the two solids and hardly any further ripening is seen. Initial lateral coarsening velocities show a Wilson Frenkel type dependence on the melt meta-stability.

  19. Understanding the solidification and microstructure evolution during CSC-MIG welding of Fe–Cr–B-based alloy

    SciTech Connect

    Sorour, A.A. Chromik, R.R. Gauvin, R. Jung, I.-H. Brochu, M.

    2013-12-15

    The present is a study of the solidification and microstructure of Fe–28.2%Cr–3.8%B–1.5%Si–1.5%Mn (wt.%) alloy deposited onto a 1020 plain carbon steel substrate using the controlled short-circuit metal inert gas welding process. The as-solidified alloy was a metal matrix composite with a hypereutectic microstructure. Thermodynamic calculation based on the Scheil–Gulliver model showed that a primary (Cr,Fe){sub 2}B phase formed first during solidification, followed by an eutectic formation of the (Cr,Fe){sub 2}B phase and a body-centered cubic Fe-based solid solution matrix, which contained Cr, Mn and Si. Microstructure analysis confirmed the formation of these phases and showed that the shape of the (Cr,Fe){sub 2}B phase was irregular plate. As the welding heat input increased, the weld dilution increased and thus the volume fraction of the (Cr,Fe){sub 2}B plates decreased while other microstructural characteristics were similar. - Highlights: • We deposit Fe–Cr–B-based alloy onto plain carbon steel using the CSC-MIG process. • We model the solidification behavior using thermodynamic calculation. • As deposited alloy consists of (Cr,Fe){sub 2}B plates embedded in Fe-based matrix. • We study the effect of the welding heat input on the microstructure.

  20. Microstructure evolution in irradiated materials

    SciTech Connect

    Caturla, M

    1999-11-30

    Study the interaction of defects produced during irradiation or deformation of a metal with the microstructure of that particular material, such as dislocations and grain boundaries. In particular we will study the interaction of dislocation with interstitial loops and stacking fault tetrahedral, and the production of displacement cascades close to dislocations and grain boundaries. The data obtained from these simulations will be used as input to diffusion models and dislocation dynamics models.

  1. The evolution of dinosaur tooth enamel microstructure.

    PubMed

    Hwang, Sunny H

    2011-02-01

    The evolution of tooth enamel microstructure in both extinct and extant mammalian groups has been extensively documented, but is poorly known in reptiles, including dinosaurs. Previous intensive sampling of dinosaur tooth enamel microstructure revealed that: (1) the three-dimensional arrangement of enamel types and features within a tooth-the schmelzmuster-is most useful in diagnosing dinosaur clades at or around the family level; (2) enamel microstructure complexity is correlated with tooth morphology complexity and not necessarily with phylogenetic position; and (3) there is a large amount of homoplasy within Theropoda but much less within Ornithischia. In this study, the examination of the enamel microstructure of 28 additional dinosaur taxa fills in taxonomic gaps of previous studies and reinforces the aforementioned conclusions. Additionally, these new specimens reveal that within clades such as Sauropodomorpha, Neotheropoda, and Euornithopoda, the more basal taxa have simpler enamel that is a precursor to the more complex enamel of more derived taxa and that schmelzmusters evolve in a stepwise fashion. In the particularly well-sampled clade of Euornithopoda, correlations between the evolution of dental and enamel characters could be drawn. The ancestral schmelzmuster for Genasauria remains ambiguous due to the dearth of basal ornithischian teeth available for study. These new specimens provide new insights into the evolution of tooth enamel microstructure in dinosaurs, emphasizing the importance of thorough sampling within broadly inclusive clades, especially among their more basal members.

  2. Phase Transformations and Microstructural Evolution: Part I

    DOE PAGES

    Clarke, Amy Jean

    2015-08-29

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance, including in extreme environments, of structural metal alloys. In this paper, aspects of phase transformations and microstructural evolution aremore » highlighted from the atomic to the microscopic scale for ferrous and non-ferrous alloys. Many papers from this issue are highlighted with small summaries of their scientific achievements given.« less

  3. Phase Transformations and Microstructural Evolution: Part II

    DOE PAGES

    Clarke, Amy Jean

    2015-10-30

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance. In this issue, aspects of liquid–solid and solid-state phase transformations and microstructural evolution are highlighted. Many papers in thismore » issue are highlighted by this paper, giving a brief summary of what they bring to the scientific community.« less

  4. Phase Transformations and Microstructural Evolution: Part II

    SciTech Connect

    Clarke, Amy Jean

    2015-10-30

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance. In this issue, aspects of liquid–solid and solid-state phase transformations and microstructural evolution are highlighted. Many papers in this issue are highlighted by this paper, giving a brief summary of what they bring to the scientific community.

  5. Phase Transformations and Microstructural Evolution: Part I

    SciTech Connect

    Clarke, Amy Jean

    2015-08-29

    The activities of the Phase Transformations Committee of the Materials Processing & Manufacturing Division (MPMD) of The Minerals, Metals & Materials Society (TMS) are oriented toward understanding the fundamental aspects of phase transformations. Emphasis is placed on the thermodynamic driving forces for phase transformations, the kinetics of nucleation and growth, interfacial structures and energies, transformation crystallography, surface reliefs, and, above all, the atomic mechanisms of phase transformations. Phase transformations and microstructural evolution are directly linked to materials processing, properties, and performance, including in extreme environments, of structural metal alloys. In this paper, aspects of phase transformations and microstructural evolution are highlighted from the atomic to the microscopic scale for ferrous and non-ferrous alloys. Many papers from this issue are highlighted with small summaries of their scientific achievements given.

  6. Microstructural evolution and mechanical properties of an Fe-18Ni-16Cr-4Al base alloy during aging at 950°C

    NASA Astrophysics Data System (ADS)

    Wang, Man; Sun, Yong-duo; Feng, Jing-kai; Zhang, Rui-qian; Tang, Rui; Zhou, Zhang-jian

    2016-03-01

    The development of Gen-IV nuclear systems and ultra-supercritical power plants proposes greater demands on structural materials used for key components. An Fe-18Ni-16Cr-4Al (316-base) alumina-forming austenitic steel was developed in our laboratory. Its microstructural evolution and mechanical properties during aging at 950°C were investigated subsequently. Micro-structural changes were characterized by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Needle-shaped NiAl particles begin to precipitate in austenite after ageing for 10 h, whereas round NiAl particles in ferrite are coarsened during aging. Precipitates of NiAl with different shapes in different matrices result from differences in lattice misfits. The tensile plasticity increases by 32.4% after aging because of the improvement in the percentage of coincidence site lattice grain boundaries, whereas the tensile strength remains relatively high at approximately 790 MPa.

  7. Stress Rupture Fracture Model and Microstructure Evolution for Waspaloy

    NASA Astrophysics Data System (ADS)

    Yao, Zhihao; Zhang, Maicang; Dong, Jianxin

    2013-07-01

    Stress rupture behavior and microstructure evolution of nickel-based superalloy Waspaloy specimens from tenon teeth of an as-received 60,000-hour service-exposed gas turbine disk were studied between 923 K and 1088 K (650 °C and 815 °C) under initial applied stresses varying from 150 to 840 MPa. Good microstructure stability and performance were verified for this turbine disk prior to stress rupture testing. Microstructure instability, such as the coarsening and dissolution of γ' precipitates at the varying test conditions, was observed to be increased with temperature and reduced stress. Little microstructure variation was observed at 923 K (650 °C). Only secondary γ' instability occurred at 973 K (700 °C). Four fracture mechanisms were obtained. Transgranular creep fracture was exhibited up to 923 K (650 °C) and at high stress. A mixed mode of transgranular and intergranular creep fracture occurred with reduced stress as a transition to intergranular creep fracture (ICF) at low stress. ICF was dominated by grain boundary sliding at low temperature and by the nucleation and growth of grain boundary cavities due to microstructure instability at high temperature. The fracture mechanism map and microstructure-related fracture model were constructed. Residual lifetime was also evaluated by the Larson-Miller parameter method.

  8. Microstructural Evolution and Bonding Behavior during Transient Liquid-Phase Bonding of a Duplex Stainless Steel using two Different Ni-B-Based Filler Materials

    NASA Astrophysics Data System (ADS)

    Yuan, Xinjian; Kim, Myung Bok; Kang, Chung Yun

    2011-05-01

    Microstructural evolution and bonding behavior of transient liquid-phase (TLP) bonded joint for a duplex stainless steel using MBF-30 (Ni -4.5Si -3.2B [wt pct]) and MBF-50 (Ni -7.5Si -1.4B -18.5Cr [wt pct]) were investigated. Using MBF-30, the microstructure of the athermally solidified zone was dependent on B diffusion at 1333.15 K (1060 °C). Ni3B and a supersaturated γ-Ni phase were observed in this zone. BN appeared in the bonding-affected zone. However, using MBF-50, the influences of base metal alloying elements, particularly N and Cr as well as Si in the filler material, on the bond microstructure development were more pronounced at 1448.15 K (1175 °C). BN and (Cr, Ni)3Si phase were present in the bond centerline. The formation of BN precipitates in the bonding-affected zone was suppressed. A significant deviation in the isothermal solidification rate from the conventional TLP bonding diffusion models was observed in the joints prepared at 1448.15 K (1175 °C) using MBF-50.

  9. Effect of Initial Microstructure on the Microstructural Evolution and Joint Efficiency of a WE43 Alloy During Friction Stir Welding

    DTIC Science & Technology

    2013-04-01

    microstructure during friction stir welding ( FSW ). The overall kinetics of microstructural evolution is location sensitive and the effect of the...determining the spatial and temporal evolution of the microstructure during friction stir welding ( FSW ). The overall kinetics of microstructural...strength, contributing factors and evolution path as a function of alloy chemistry during FSW . The thermal stability of the precipitates strongly

  10. A Markov random field approach for modeling spatio-temporal evolution of microstructures

    NASA Astrophysics Data System (ADS)

    Acar, Pinar; Sundararaghavan, Veera

    2016-10-01

    The following problem is addressed: ‘Can one synthesize microstructure evolution over a large area given experimental movies measured over smaller regions?’ Our input is a movie of microstructure evolution over a small sample window. A Markov random field (MRF) algorithm is developed that uses this data to estimate the evolution of microstructure over a larger region. Unlike the standard microstructure reconstruction problem based on stationary images, the present algorithm is also able to reconstruct time-evolving phenomena such as grain growth. Such an algorithm would decrease the cost of full-scale microstructure measurements by coupling mathematical estimation with targeted small-scale spatiotemporal measurements. The grain size, shape and orientation distribution statistics of synthesized polycrystalline microstructures at different times are compared with the original movie to verify the method.

  11. Compositional and Microstructural Evolution of Olivine During Pulsed Laser Irradiation: Insights Based on a FIB/Field-Emission TEM Study

    NASA Astrophysics Data System (ADS)

    Christoffersen, R.; Loeffler, M. J.; Dukes, C. A.; Baragiola, R. A.

    2015-11-01

    Field-emission TEM shows multi-layer vapor and melt deposits produced on olivine by pulsed laser irradiation contain abundant nanophase metallic Fe and have some microstructural similarities to melt deposits in micrometeorite impact craters.

  12. Relationship between Microstructural Evolution and Electrical Properties in Ba(Ti, Zr)O3-Based Materials for Ni-MLCC

    NASA Astrophysics Data System (ADS)

    Mizuno, Youichi; Morita, Koichiro; Hagiwara, Tomoya; Kishi, Hiroshi; Ohnuma, Kenji; Ohsato, Hitoshi

    2004-09-01

    The influence of the microstructural evolution induced by increasing firing temperature on the change in dielectric properties induced by re-oxidation treatment in the Ba(Ti, Zr)O3(BTZ)-Ho-Mn system was investigated. The microstructural observation of as-fired disk samples revealed gradual grain growth with firing temperature. From the temperature characteristic (TC) measurement, the shift to higher temperatures of dielectric maximum (Tmax) due to re-oxidation treatment became larger with grain growth although the chemical compositions were quite the same. It was found that grain growth accelerated the valence change of Mn by re-oxidation treatment and the substitution of dopants in a grain in this system. Microstructural evolutions, such as compositional distribution and the concentration of additives in a grain, had an influence on the changes in dielectric properties induced by re-oxidation treatment.

  13. Microstructural evolution of eutectic Au-Sn solder joints

    SciTech Connect

    Song, Ho Geon

    2002-05-01

    Current trends toward miniaturization and the use of lead(Pb)-free solder in electronic packaging present new problems in the reliability of solder joints. This study was performed in order to understand the microstructure and microstructural evolution of small volumes of nominally eutectic Au-Sn solder joints (80Au-20Sn by weight), which gives insight into properties and reliability.

  14. Fusion boundary microstructure evolution in aluminum alloys

    NASA Astrophysics Data System (ADS)

    Kostrivas, Anastasios Dimitrios

    2000-10-01

    A melting technique was developed to simulate the fusion boundary of aluminum alloys using the GleebleRTM thermal simulator. Using a steel sleeve to contain the aluminum, samples were heated to incremental temperatures above the solidus temperature of a number of alloys. In alloy 2195, a 4wt%Cu-1wt%Li alloy, an equiaxed non-dendritic zone (EQZ) could be formed by heating in the temperature range from approximately 630 to 640°C. At temperatures above 640°C, solidification occurred by the normal epitaxial nucleation and growth mechanism. Fusion boundary behavior was also studied in alloys 5454-H34, 6061-T6, and 2219-T8. Additionally, experimental alloy compositions were produced by making bead on plate welds using an alloy 5454-H32 base metal and 5025 or 5087 filler metals. These filler metals contain zirconium and scandium additions, respectively, and were expected to influence nucleation and growth behavior. Both as-welded and welded/heat treated (540°C and 300°C) substrates were tested by melting simulation, resulting in dendritic and EQZ structures depending on composition and substrate condition. Orientation imaging microscopy (OIM(TM)) was employed to study the crystallographic character of the microstructures produced and to verify the mechanism responsible for EQZ formation. OIM(TM) proved that grains within the EQZ have random orientation. In all other cases, where the simulated microstructures were dendritic in nature, it was shown that epitaxy was the dominant mode of nucleation. The lack of any preferred crystallographic orientation relationship in the EQZ supports a theory proposed by Lippold et al that the EQZ is the result of heterogeneous nucleation within the weld unmixed zone. EDS analysis of the 2195 on STEM revealed particles with ternary composition consisted of Zr, Cu and Al and a tetragonal type crystallographic lattice. Microdiffraction line scans on EQZ grains in the alloy 2195 showed very good agreement between the measured Cu

  15. Microstructure and texture evolution of Cu–Nb composite wires

    SciTech Connect

    Deng, Liping; Yang, Xiaofang; Han, Ke; Lu, Yafeng; Liang, Ming; Liu, Qing

    2013-07-15

    The evolution of microstructure and texture in Cu–Nb composite wires fabricated by an accumulative drawing and bundling process was investigated by backscattered electron (BSE), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results indicate the onset of severe curling and shape changing occurred at the size of Nb ∼ 400 nm with a surface increase of about 6.91 μm{sup 2}/μm{sup 3} (the area per unit volume). Two kinds of grain boundaries in Nb are suggested: one is 20°–50° boundary with a rotate/tilt axis around <110> parallel to drawing direction (DD), and another is > 50° boundary with the axis perpendicular to DD. The curling phenomenon occurred at the Cu–Nb interface and is related not only to the deformation mechanism of Nb but also to the presence of interface. This result is distinct from reported works showing that curling takes place when BCC metals are heavily drawn (Area reduction > 73%). The variation in microstructure and texture evolution between Cu and Nb filaments was discussed based on the differences in deformation mechanisms of these two metals. - Highlights: • Microstructure and texture evolution were studied systematically by EBSD. • In Nb, grain boundaries of 20°–50° have a rotate/tile axis around <110>//DD. • The rotation axes of above 50° boundaries are concentrated around <111> ⊥ DD in Nb. • Curling is related to not only deformation mode of BCC but also Cu–Nb interface.

  16. Monitoring microstructural evolution in irradiated steel with second harmonic generation

    SciTech Connect

    Matlack, Kathryn H.; Kim, Jin-Yeon; Jacobs, Laurence J.; Wall, James J.; Qu, Jianmin

    2015-03-31

    Material damage in structural components is driven by microstructural evolution that occurs at low length scales and begins early in component life. In metals, these microstructural features are known to cause measurable changes in the acoustic nonlinearity parameter. Physically, the interaction of a monochromatic ultrasonic wave with microstructural features such as dislocations, precipitates, and vacancies, generates a second harmonic wave that is proportional to the acoustic nonlinearity parameter. These nonlinear ultrasonic techniques thus have the capability to evaluate initial material damage, particularly before crack initiation and propagation occur. This paper discusses how the nonlinear ultrasonic technique of second harmonic generation can be used as a nondestructive evaluation tool to monitor microstructural changes in steel, focusing on characterizing neutron radiation embrittlement in nuclear reactor pressure vessel steels. Current experimental evidence and analytical models linking microstructural evolution with changes in the acoustic nonlinearity parameter are summarized.

  17. Compositional and Microstructural Evolution of Olivine During Pulsed Laser Irradiation: Insights Based on a FIB/Field-Emission TEM Study

    NASA Technical Reports Server (NTRS)

    Christoffersen, R.; Loeffler, M. J.; Dukes, C. A.; Baragiola, R. A.

    2015-01-01

    Introduction: The use of pulsed laser irradiation to simulate the short duration, high-energy conditions characteristic of micrometeorite impacts is now an established approach in experimental space weathering studies. The laser generates both melt and vapor deposits that contain nanophase metallic Fe (npFe(sup 0)) grains with size distributions and optical properties similar to those in natural impact-generated melt and vapor deposits. There remains uncertainty, however, about how well lasers simulate the mechanical work and internal (thermal) energy partitioning that occurs in actual impacts. We are currently engaged in making a direct comparison between the products of laser irradiation and experimental/natural hypervelocity impacts. An initial step reported here is to use analytical TEM is to attain a better understanding of how the microstructure and composition of laser deposits evolve over multiple cycles of pulsed laser irradiation. Experimental Methods: We irradiated pressed-powder pellets of San Carlos olivine (Fo(sub 90)) with up to 99 rastered pulses of a GAM ArF excimer laser. The irradiated surface of the sample were characterized by SEM imaging and areas were selected for FIB cross sectioning for TEM study using an FEI Quanta dual-beam electron/focused ion beam instrument. FIB sections were characterized using a JEOL2500SE analytical field-emission scanning transmission electron microscope (FE-STEM) optimized for quantitative element mapping at less than 10 nm spatial resolutions. Results: In the SEM the 99 pulse pressed pellet sample shows a complex, inhomogeneous, distribution of laser-generated material, largely concentrated in narrow gaps and larger depressions between grains. Local concentrations of npFe0 spherules 0.1 to 1 micrometers in size are visible within these deposits in SEM back-scatter images. Fig. 1 shows bright-field STEM images of a FIB cross-section of a one of these deposits that continuously covers the top and sloping side of an

  18. Microstructural Evolution and interfacial motion in systems with diffusion barriers

    SciTech Connect

    Perry H. Leo

    2009-03-05

    This research program was designed to model and simulate phase transformations in systems containing diffusion barriers. The modeling work included mass flow, phase formation, and microstructural evolution in interdiffusing systems. Simulation work was done by developing Cahn-Hilliard and phase field equations governing both the temporal and spatial evolution of the composition and deformation fields and other important phase variables.

  19. Horizontal evolution of tidally modulated buoyant plumes and the subsequent genesis of non linear internal waves as observed with an AUV based microstructure profiler.

    NASA Astrophysics Data System (ADS)

    toberman, matthew; Inall, Mark; Boyd, Tim

    2013-04-01

    The tidally modulated outflow of brackish water from a sea loch forms a thin stable surface layer that propagates into the coastal ocean as a buoyant gravity current, transporting nutrients and sediments, as well as fresh water, heat and momentum. The fresh intrusion propagates as an undular bore, and the introduced stratification supports trains of non-linear internal waves (NLIWs). In February 2011 an Autonomous Underwater Vehicle (AUV) was used on repeated reciprocal transects to make simultaneous CTD, ADCP and shear microstructure measurements of the evolution of these phenomena in conjunction with conventional mooring measurements. AUV-based temperature and salinity signals of NLIWs of depression were observed together with increased turbulent kinetic energy dissipation rates of over two orders of magnitude within and in the wake of the NLIWs. Repeated measurements over several tidal cycles allow a unique opportunity to investigate the horizontal structure of these phenomena, the interaction of each tidally driven pulse with ambient stratification and the remnants of previous plumes, as well as the genesis of and subsequent mixing induced by the NLIWs.

  20. Mechanical Properties and Microstructural Evolution of Welded Eglin Steel

    NASA Astrophysics Data System (ADS)

    Leister, Brett M.

    Eglin steel is a new ultra-high strength steel that has been developed at Eglin Air Force Base in the early 2000s. This steel could be subjected to a variety of processing steps during fabrication, each with its own thermal history. This article presents a continuous cooling transformation diagram developed for Eglin steel to be used as a guideline during processing. Dilatometry techniques performed on a Gleeble thermo-mechanical simulator were combined with microhardness results and microstructural characterization to develop the diagram. The results show that four distinct microstructures form within Eglin steel depending on the cooling rate. At cooling rates above about 1 °C/s, a predominately martensitic microstructure is formed with hardness of ˜520 HV. Intermediate cooling rates of 1 °C/s to 0.2 °C/s produce a mixed martensitic/bainitic microstructure with a hardness that ranges from 520 - 420 HV. Slower cooling rates of 0.1 °C/s to 0.03 °C/s lead to the formation of a bainitic microstructure with a hardness of ˜420 HV. The slowest cooling rate of 0.01 °C/s formed a bainitic microstructure with pearlite at the prior austenite grain boundaries. A comprehensive study was performed to correlate the mechanical properties and the microstructural evolution in the heat affected zone of thermally simulated Eglin steel. A Gleeble 3500 thermo-mechanical simulator was used to resistively heat samples of wrought Eglin steel according to calculated thermal cycles with different peak temperatures at a heat input of 1500 J/mm. These samples underwent mechanical testing to determine strength and toughness, in both the `as-simulated' condition and also following post-weld heat treatments. Mechanical testing has shown that the inter-critical heat affected zone (HAZ) has the lowest strength following thermal simulation, and the fine-grain and coarse-grain heat affected zone having an increased strength when compared to the inter-critical HAZ. The toughness of the heat

  1. General introduction to microstructural evolution under cascade damage conditions

    SciTech Connect

    Wiedersich, H.

    1993-06-01

    A short overview of the processes that affect the evolution of the microstructure during irradiation is given. The processes include defect production with an emphasis on the effects of the dynamic cascade events, defect clustering, irradiation-enhanced diffusion, radiation-induced segregation, phase decompositions and phase transformations. A simple model for the description of the development of the defect microstructure in a pure metal during cascade producing irradiation is also outlined which can provide, in principle, defect fluxes required for the description of the microstructural processes such as phase decomposition and irradiation-induced precipitation.

  2. Microstructural Evolution in the 2219 Aluminum Alloy During Severe Plastic Deformation

    SciTech Connect

    Kaibyshev, R.O.; Safarov, I.M.; Lesuen, D.R.

    2000-03-29

    Numerous investigations have demonstrated that intense plastic deformation is an attractive procedure for producing an ultrafine grain size in metallic materials. Torsional deformation under high pressure and equal-channel angular extrusion are two techniques that can produce microstructures with grain sizes in the submicrometer and nanometer range. Materials with these microstructures have many attractive properties. The microstructures formed by these two processing techniques are essentially the same and thus the processes occurring during deformation should be the same. Most previous studies have examined the final microstructures produced as a result of severe plastic deformation and the resulting properties. Only a limited number of studies have examined the evolution of microstructure. As a result, some important aspects of ultra-fine grain formation during severe plastic deformation remain unknown. There is also limited data on the influence of the initial state of the material on the microstructural evolution and mechanisms of ultra-fine grain formation. This limited knowledge base makes optimization of processing routes difficult and retards commercial application of these techniques. The objective of the present work is to examine the microstructure evolution during severe plastic deformation of a 2219 aluminum alloy. Specific attention is given to the mechanism of ultrafine grain formation as a result of severe plastic deformation.

  3. Microstructural evolution and grain morphology of ZrN pellets

    NASA Astrophysics Data System (ADS)

    Park, Sungho; Han, Ilsu; Lee, Hyunjun; Huh, Sunchul; Park, Wonjo

    2009-04-01

    Improvements in the mechanical integrity of zirconium nitride (ZrN) inert matrixes in advanced nuclear fuels were addressed in this work. This was done by first better understanding and then controlling texture and microstructural evolution of the former. Several samples were examined via orientation imaging microscopy: several monolithic specimens were hot isostatically pressed (HIP), and two sintered specimens with 80 % and 85 % density Grain size and crystallographic orientation studies revealed sample microstructure and their evolution during sintering. A correlation between larger grains and orientations near to <111> parallel to the compression axis during cold pressing was present for the 85 % density sample.

  4. Microstructural evolution and surface properties of nanostructured Cu-based alloy by ultrasonic nanocrystalline surface modification technique

    NASA Astrophysics Data System (ADS)

    Amanov, Auezhan; Cho, In-Sik; Pyun, Young-Sik

    2016-12-01

    A nanostructured surface layer with a thickness of about 180 μm was successfully produced in Cu-based alloy using an ultrasonic nanocrystalline surface modification (UNSM) technique. Cu-based alloy was sintered onto low carbon steel using a powder metallurgy (P/M) method. Transmission electron microscope (TEM) characterization revealed that the severe plastic deformation introduced by UNSM technique resulted in nano-sized grains in the topmost surface layer and deformation twins. It was also found by atomic force microscope (AFM) observations that the UNSM technique provides a significant reduction in number of interconnected pores. The effectiveness of nanostructured surface layer on the tribological and micro-scratch properties of Cu-based alloy specimens was investigated using a ball-on-disk tribometer and micro-scratch tester, respectively. Results exhibited that the UNSM-treated specimen led to an improvement in tribological and micro-scratch properties compared to that of the sintered specimen, which may be attributed to the presence of nanostructured surface layer having an increase in surface hardness and reduction in surface roughness. The findings from this study are expected to be implemented to the automotive industry, in particular connected rod bearings and bushings in order to increase the efficiency and performance of internal combustion engines (ICEs).

  5. Macrosegregation and Microstructural Evolution in a Pressure-Vessel Steel

    NASA Astrophysics Data System (ADS)

    Pickering, E. J.; Bhadeshia, H. K. D. H.

    2014-06-01

    This work assesses the consequences of macrosegregation on microstructural evolution during solid-state transformations in a continuously cooled pressure-vessel steel (SA508 Grade 3). Stark spatial variations in microstructure are observed following a simulated quench from the austenitization temperature, which are found to deliver significant variations in hardness. Partial-transformation experiments are used to show the development of microstructure in segregated material. Evidence is presented which indicates the bulk microstructure is not one of upper bainite, as it has been described in the past, but one comprised of Widmanstätten ferrite and pockets of lower bainite. Segregation is observed on three different length scales, and the origins of each type are proposed. Suggestions are put forward for how the segregation might be minimized, and its detrimental effects suppressed by heat treatments.

  6. Numerical Study of Microstructural Evolution During Homogenization of Al-Si-Mg-Fe-Mn Alloys

    NASA Astrophysics Data System (ADS)

    Priya, Pikee; Johnson, David R.; Krane, Matthew J. M.

    2016-09-01

    Microstructural evolution during homogenization of Al-Si-Mg-Fe-Mn alloys occurs in two stages at different length scales: while holding at the homogenization temperature (diffusion on the scale of the secondary dendrite arm spacing (SDAS) in micrometers) and during quenching to room temperature (dispersoid precipitation at the nanometer to submicron scale). Here a numerical study estimates microstructural changes during both stages. A diffusion-based model developed to simulate evolution at the SDAS length scale predicts homogenization times and microstructures matching experiments. That model is coupled with a Kampmann Wagner Neumann-based precipitate nucleation and growth model to study the effect of temperature, composition, as-cast microstructure, and cooling rates during posthomogenization quenching on microstructural evolution. A homogenization schedule of 853 K (580 °C) for 8 hours, followed by cooling at 250 K/h, is suggested to optimize microstructures for easier extrusion, consisting of minimal α-Al(FeMn)Si, no β-AlFeSi, and Mg2Si dispersoids <1 μm size.

  7. Microstructural evolution of eutectic gold-tin solder joints

    NASA Astrophysics Data System (ADS)

    Song, Ho Geon

    Current trends toward miniaturization and the use of lead (Pb)-free solders in electronic packaging present new problems in the reliability of solder joints. This study was performed in order to understand the microstructure and microstructural evolution of small volumes of nominally eutectic Au-Sn solder joints (80Au-20Sn by weight), which gives insight into properties and reliability. The study particularly concentrated on the effects that the joint size and the type of substrate metallization have on both the bulk and interface microstructures of the joints. The systems studied were eutectic Au-Sn on Cu and Cu/electroless Ni/Au and for each system, two sets of sample geometries were used. Eutectic Au-Sn solder joints on Cu have microstructures that are very coarse on the scale of the joint, where the microstructure is strongly affected by the amount of Cu dissolution during reflow process. During aging, steady diffusion of Cu leads to the growth of Cu-rich interfacial intermetallic layers, significant consumption of substrate Cu, and formation of Kirkendall pores along the interface. Thermal cycling of the joints caused decomposition of the thick zeta(Cu)-phase into a fine-grained multiphase microstructure. The microstructures of eutectic Au-Sn solder joints on Cu/electroless Ni/Au are also very coarse due to the dissolution of Au used as a protective layer during soldering. Electroless Ni is shown to effectively act as a diffusion barrier for Cu. The electroless Ni near the interface evolves into a complicated structure due to the interfacial reaction. The solubility characteristics and diffusional behavior of substrate metals into eutectic Au-Sn solder determines the detailed microstructure and microstructural evolution of the ultrafine eutectic Au-Sn joints. Two important things to be noted from the results are as follows: First, the overall microstructures of these joints are very coarse with respect to the size of joint, and hence the properties of the

  8. Evolution of microstructural disorder in annealed bismuth telluride nanowires

    DOE PAGES

    Erickson, Kristopher J.; Limmer, Steven J.; Yelton, W. Graham; ...

    2017-03-01

    Controlling the distribution of structural defects in nanostructures is important since such defects can strongly affect critical properties, including thermal and electronic transport. However, characterizing the defect arrangements in individual nanostructures is difficult because of the small length scales involved. Here, we investigate the evolution of microstructural disorder with annealing in electrochemically deposited Bi2Te3 nanowires, which are of interest for thermoelectrics. We combine Convergent Beam Electron Diffraction (CBED) and Scanning Transmission Electron Microscopy (STEM) to provide the necessary spatial and orientational resolution. We find that despite their large initial grain sizes and strong Formula crystallographic texturing, the as-deposited nanowires stillmore » exhibit significant intragranular orientational disorder. Annealing drives both grain growth and a significant reduction in the intragranular disorder. The results are discussed in the context of the existing understanding of the initial microstructure of electrodeposited materials and the understanding of annealing microstructures in both electrochemically deposited and bulk-deformed materials. Finally, this analysis highlights the importance of assessing both the grain size and intragranular disorder in understanding the microstructural evolution of individual nanostructures.« less

  9. The effect of microstructural evolution on superplasticity in Ni{sub 3}Si(V,Mo)

    SciTech Connect

    Stoner, S.L.; Mukherjee, A.K.

    1992-10-01

    To further the understanding of superplasticity in intermetallics, this paper presents results of experimental investigations on an intermetallic alloy based on nickel silicide. Specifically, the evolution of the microstructure and its influence on superplastic performance is discussed. In the duplex microstructure, one phase showed grain growth, and the other, grain refinement. Cavitation occurred at interphase boundaries and final failure was by interlinkage of these cavities. Annealing the material improved the homogeneity of the microstructure. The annealed material showed improved strain rate sensitivity values and enhanced superplasticity. Microstructural features and ductility were also influenced by changing the orientation of the tensile axis. Though a transverse orientation showed more cavitation than longitudinal, it yielded greater elongation. An increased resistance to cavity coalescence in the transverse direction played a role in the enhanced ductility.

  10. Microstructural evolution in fast-neutron-irradiated austenitic stainless steels

    SciTech Connect

    Stoller, R.E.

    1987-12-01

    The present work has focused on the specific problem of fast-neutron-induced radiation damage to austenitic stainless steels. These steels are used as structural materials in current fast fission reactors and are proposed for use in future fusion reactors. Two primary components of the radiation damage are atomic displacements (in units of displacements per atom, or dpa) and the generation of helium by nuclear transmutation reactions. The radiation environment can be characterized by the ratio of helium to displacement production, the so-called He/dpa ratio. Radiation damage is evidenced microscopically by a complex microstructural evolution and macroscopically by density changes and altered mechanical properties. The purpose of this work was to provide additional understanding about mechanisms that determine microstructural evolution in current fast reactor environments and to identify the sensitivity of this evolution to changes in the He/dpa ratio. This latter sensitivity is of interest because the He/dpa ratio in a fusion reactor first wall will be about 30 times that in fast reactor fuel cladding. The approach followed in the present work was to use a combination of theoretical and experimental analysis. The experimental component of the work primarily involved the examination by transmission electron microscopy of specimens of a model austenitic alloy that had been irradiated in the Oak Ridge Research Reactor. A major aspect of the theoretical work was the development of a comprehensive model of microstructural evolution. This included explicit models for the evolution of the major extended defects observed in neutron irradiated steels: cavities, Frank faulted loops and the dislocation network. 340 refs., 95 figs., 18 tabs.

  11. Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process

    SciTech Connect

    Das, D.K.; Joshi, S.V.; Singh, V.

    1998-08-01

    This study deals with the aluminizing of a directionally cast Ni-base superalloy, namely CM-247, by a single-step process using a high-activity pack. It is observed that significant incorporation of Al into the substrate surface during aluminizing continues over a period of about 1 hour and is not restricted merely to the first few minutes, as reported in the literature. Based on the microstructural details of the coatings formed at various stages of aluminizing, it is concluded that the coating growth in the above process takes place primarily by inward Al diffusion initially, followed by an intermediate stage when the growth involves both inward Al and outward Ni diffusion. In the final stages, the outward diffusion of Ni dominates the coating formation process. The above mechanism of coating formation is different from the one that prevails in the conventional two-step high-activity coating process in that the reaction front for the formation of NiAl remains spatially stationary despite the outward diffusion of nickel during the intermediate stage. It is also shown in the present study that the content of the Al source in the pack affects the coating structure significantly. It is further demonstrated that the microstructure of the aluminide coatings depends not only on the amount of Al incorporated in the sample during aluminizing but also on the time over which the uptake of this Al takes place.

  12. Evolution of microstructure and mechanical properties of VVER-1000 RPV steels under re-irradiation

    NASA Astrophysics Data System (ADS)

    Gurovich, B.; Kuleshova, E.; Shtrombakh, Ya.; Fedotova, S.; Erak, D.; Zhurko, D.

    2015-01-01

    This is a comprehensive study of microstructure and mechanical properties evolution at re-irradiation after recovery annealing of VVER-1000 RPV weld and base metals as well as the effect of annealing on the microstructure and properties of base metal in the zone of the temperature gradient that is implemented during annealing using special heating device. It is shown that the level of radiation-induced microstructural changes under accelerated re-irradiation of weld and base metal is not higher than for the primary irradiation. Thus, we can predict that re-embrittlement of VVER-1000 RPV materials considering the flux effect will not exceed the typical embrittlement rate for the primary irradiation.

  13. The strength and dislocation microstructure evolution in superalloy microcrystals

    NASA Astrophysics Data System (ADS)

    Hussein, Ahmed M.; Rao, Satish I.; Uchic, Michael D.; Parthasarathay, Triplicane A.; El-Awady, Jaafar A.

    2017-02-01

    In this work, the evolution of the dislocations microstructure in single crystal two-phase superalloy microcrystals under monotonic loading has been studied using the three-dimensional discrete dislocation dynamics (DDD) method. The DDD framework has been extended to properly handle the collective behavior of dislocations and their interactions with large collections of arbitrary shaped precipitates. Few constraints are imposed on the initial distribution of the dislocations or the precipitates, and the extended DDD framework can support experimentally-obtained precipitate geometries. Full tracking of the creation and destruction of anti-phase boundaries (APB) is accounted for. The effects of the precipitate volume fraction, APB energy, precipitate size, and crystal size on the deformation of superalloy microcrystals have been quantified. Correlations between the precipitate microstructure and the dominant deformation features, such as dislocation looping versus precipitate shearing, are also discussed. It is shown that the mechanical strength is independent of the crystal size, increases linearly with increasing the volume fraction, follows a near square-root relationship with the APB energy and an inverse square-root relationship with the precipitate size. Finally, the flow strength in simulations having initial dislocation pair sources show a flow strength that is about one half of that predicted from simulations starting with single dislocation sources. The method developed can be used, with minimal extensions, to simulate dislocation microstructure evolution in general multiphase materials.

  14. Modeling of Microstructural Evolution in an MCrAlY Overlay Coating on Different Superalloy Substrates

    NASA Astrophysics Data System (ADS)

    Karunaratne, M. S. A.; di Martino, I.; Ogden, S. L.; Oates, D. L.; Thomson, R. C.

    2012-02-01

    A multicomponent, one-dimensional diffusion model that was developed for simulating microstructure evolution in coated gas turbine blade systems has been used to compare the phase structures of three MCrAlY coated superalloy systems. The model is based on finite differences and incorporates oxidation and equilibrium thermodynamic computations. The superalloy substrates considered were the nickel-based superalloy CMSX-4, a high-Cr single-crystal superalloy, and a cobalt-based MAR-M509, and these were all coated with an MCrAlY bond coat of similar composition. The results predicted by the model have been compared with similar experimental systems. The model can predict many features observed experimentally and therefore can be expected to be a useful tool in lifetime prediction and microstructural assessment of turbine blade systems based on superalloys. The work also highlighted the fact that for a given coating, the phase evolution within system is dependent on the substrate material.

  15. Nonlinear acoustics experimental characterization of microstructure evolution in Inconel 617

    SciTech Connect

    Yao, Xiaochu; Liu, Yang; Lissenden, Cliff J.

    2014-02-18

    Inconel 617 is a candidate material for the intermediate heat exchanger in a very high temperature reactor for the next generation nuclear power plant. This application will require the material to withstand fatigue-ratcheting interaction at temperatures up to 950°C. Therefore nondestructive evaluation and structural health monitoring are important capabilities. Acoustic nonlinearity (which is quantified in terms of a material parameter, the acoustic nonlinearity parameter, β) has been proven to be sensitive to microstructural changes in material. This research develops a robust experimental procedure to track the evolution of damage precursors in laboratory tested Inconel 617 specimens using ultrasonic bulk waves. The results from the acoustic non-linear tests are compared with stereoscope surface damage results. Therefore, the relationship between acoustic nonlinearity and microstructural evaluation can be clearly demonstrated for the specimens tested.

  16. Nonlinear acoustics experimental characterization of microstructure evolution in Inconel 617

    NASA Astrophysics Data System (ADS)

    Yao, Xiaochu; Liu, Yang; Lissenden, Cliff J.

    2014-02-01

    Inconel 617 is a candidate material for the intermediate heat exchanger in a very high temperature reactor for the next generation nuclear power plant. This application will require the material to withstand fatigue-ratcheting interaction at temperatures up to 950°C. Therefore nondestructive evaluation and structural health monitoring are important capabilities. Acoustic nonlinearity (which is quantified in terms of a material parameter, the acoustic nonlinearity parameter, β) has been proven to be sensitive to microstructural changes in material. This research develops a robust experimental procedure to track the evolution of damage precursors in laboratory tested Inconel 617 specimens using ultrasonic bulk waves. The results from the acoustic non-linear tests are compared with stereoscope surface damage results. Therefore, the relationship between acoustic nonlinearity and microstructural evaluation can be clearly demonstrated for the specimens tested.

  17. Tectonic Evolution of the Cretaceous Sava-Klepa Massif, Former Yugoslav Republic of Macedonia, based on field observations and microstructural analysis - Towards a new geodynamic Model

    NASA Astrophysics Data System (ADS)

    Altmeyer, Tobias; Peternell, Mark; Prelević, Dejan; Köpping, Jonas

    2016-04-01

    The Balkan Peninsula was formed during the Mesozoic collision of Gondwana and Eurasia, associated with the closure of the Neo-Tethyan Ocean. As a result, two ophiolitic belts were formed: Dinaride-Hellenide ophiolitic belt in the southwest and the Vardar ophiolitic belt in the northeast. The bulk of Balkan ophiolites originated in the Jurassic (Robertson & Karamata, 1994), and only recently the Late Cretaceous Sava-zone ophiolites are discovered. Ophiolit-like outcrops of Mount Klepa in the Central Macedonia represents a part of Late Cretaceous oceanic lithosphere within the Sava Zone, comprising of pillow lavas, sheet flows, columns, hyaloclastites, dikes as well as cumulates. In this study we investigate the geodynamic setting and evolution of the Late Cretaceous Klepa Massif. Our working hypotheses we want to test is that Klepa Massif represents a new ocean opened through rifting after the closure of Tethyan ocean(s) and collision of Europe and Gondwana already in the Late Jurassic to Early Cretaceous. This hypothesis contradicts the accepted model suggesting that Sava ophiolites represent a relic of the Neo-Tethyan Ocean that closed in the Late Cretaceous. During detailed structural geology field studies, the ophiolitic rock sequence of Klepa Mountain area was mapped in several profiles and about 60 rock samples were taken. These field data in addition to the north-south trending outcrops of the Klepa ophiolite and the north-south trending shear zones which bound the Klepa basalt, lead to the assumption of the existence of a pull apart basin. With the help of microstructural analyses we will determine the deformation history and temperatures which also will be confirmed by the analyses of calcite twins (Ferril et al., 2004). Quartz grain size analysis of quartz bearing rocks, were used for stress piezometry. Furthermore, quartz crystal geometry and crystallographic orientations, which were measured with the Fabric Analyser G60 (Peternell et al., 2010), reveal

  18. Microstructural evolution during dynamic deformation of cubic metals: copper

    SciTech Connect

    Cerreta, Ellen K; Koller, Darcie D; Bronkhorst, Curt A; Excobedo, Juan P; Hansen, Benjamin L; Patterson, Brian M; Lebensohn, Ricardo A; Livescu, Veronica; Tonks, Davis; Mourad, Hashem M; Germann, Timothy C; Perez - Bergquist, Alex; Gray Ill, George T

    2010-12-22

    Shockwave shape can influence dynamic damage evolution. Features such as rise time, pulse duration, peak shock pressure, pull back, and release rate are influenced as wave shape changes. However, their individual influence on dynamic damage evolution is not well understood. Specifically, changing from a square to triangular or Taylor wave loading profile can alter the release kinetics from peak shock pressure and the volume of material sampled during release. This creates a spatial influence. In high purity metals, because damage is often linked to boundaries within the microstructure (grain or twin), changing the volume of material sampled during release, can have a drastic influence on dynamic damage evolution as the number of boundaries or defects sampled is altered. In this study, model-driven dynamic experiments have been conducted on eu with four different grain sizes to examine, for a given shockwave shape, how the spatial effect of boundary distribution influences dynamic damage evolution. Both two and three dimensional damage characterization techniques have been utilized. This study shows the critical influence of spatial effects, in this case boundary density, on dynamic damage evolution. As the boundary density decreases, the damage evolution transitions from nucleation controlled to growth controlled. It also shows that specific boundaries, those with high Schmid factor orientations on either side, maybe a necessary condition for void formation.

  19. Epitaxy and Microstructure Evolution in Metal Additive Manufacturing

    NASA Astrophysics Data System (ADS)

    Basak, Amrita; Das, Suman

    2016-07-01

    Metal additive manufacturing (AM) works on the principle of incremental layer-by-layer material consolidation, facilitating the fabrication of objects of arbitrary complexity through the controlled melting and resolidification of feedstock materials by using high-power energy sources. The focus of metal AM is to produce complex-shaped components made of metals and alloys to meet demands from various industrial sectors such as defense, aerospace, automotive, and biomedicine. Metal AM involves a complex interplay between multiple modes of energy and mass transfer, fluid flow, phase change, and microstructural evolution. Understanding the fundamental physics of these phenomena is a key requirement for metal AM process development and optimization. The effects of material characteristics and processing conditions on the resulting epitaxy and microstructure are of critical interest in metal AM. This article reviews various metal AM processes in the context of fabricating metal and alloy parts through epitaxial solidification, with material systems ranging from pure-metal and prealloyed to multicomponent materials. The aim is to cover the relationships between various AM processes and the resulting microstructures in these material systems.

  20. Microstructural and textural evolution during hot deformation of dilute Zr-Sn alloy

    NASA Astrophysics Data System (ADS)

    Jha, S. K.; Keskar, N.; Vishnu Narayan, K. I.; Mani Krishna, K. V.; Srivastava, D.; Dey, G. K.; Saibaba, N.

    2016-12-01

    A dilute Zr alloy containing 0.3% Sn (a potential material for liner applications of composite fuel claddings of thermal nuclear power reactors) was subjected to controlled uniaxial compression over a wide range of strain rates and temperatures in a thermo-mechanical simulator. The evolved microstructures were characterized using SEM based EBSD technique and the texture evolution was analysed by bulk X-ray diffraction method. The study had brought out the systematic changes brought out in microstructure and texture as a function of temperature and strain rate. The results indicate that a temperature of 750 °C is the optimum temperature for hot deformation of this alloy in terms of achieving a homogenous and well recrystallized microstructure.

  1. Microstructural evolution of carbon nanotube fibers: deformation and strength mechanism.

    PubMed

    Liu, Xia; Lu, Weibang; Ayala, Orlando M; Wang, Lian-Ping; Karlsson, Anette M; Yang, Qingsheng; Chou, Tsu-Wei

    2013-03-07

    A comprehensive investigation of the mechanical behavior and microstructural evolution of carbon nanotube (CNT) continuous fibers under twisting and tension is conducted using coarse-grained molecular dynamics simulations. The tensile strength of CNT fibers with random CNT stacking is found to be higher than that of fibers with regular CNT stacking. The factor dominating the mechanical response of CNT fibers is identified as individual CNT stretching. A simplified twisted CNT fiber model is studied to illustrate the structural evolution mechanisms of CNT fibers under tension. Moreover, it is demonstrated that CNT fibers can be reinforced by enhancing intertube interactions. This study would be helpful not only in the general understanding of the nano- and micro-scale factors affecting CNT fibers' mechanical behavior, but also in the optimal design of CNT fibers' architecture and performance.

  2. Microstructural evolution in an austenitic stainless steel fusion reactor first wall

    SciTech Connect

    Stoller, R.E.; Odette, G.R.

    1986-01-01

    A detailed rate-theory-based model of microstructural evolution under fast neutron irradiation has been developed. The prominent new aspect of this model is a treatment of dislocation evolution in which Frank faulted loops nucleate, grow and unfault to provide a source for network dislocations while the dislocation network can be simultaneously annihilated by a climb/glide process. The predictions of this model compare very favorably with the observed dose and temperature dependence of these key microstructural features over a broad range. This new description of dislocation evolution has been coupled with a previously developed model of cavity evolution and good agreement has been obtained between the predictions of the composite model and fast reactor swelling data as well. The results from the composite model also reveal that the various components of the irradiation-induced microstructure evolve in a highly coupled manner. The predictions of the composite model are more sensitive to parametric variations than more simple models. Hence, its value as a tool in data analysis and extrapolation is enhanced.

  3. Microstructural evolution during the thermomechanical fatigue of solder joints

    SciTech Connect

    Frear, D R

    1991-01-01

    Solder joints in electronic packages are electrical interconnections that also function as mechanical bonds. The solder often constrains materials of different coefficients of thermal expansion that, when thermal fluctuations are encountered, causes the solder joint to experience cyclical deformation. Due to the catastrophic consequences of electrical or mechanical failure of solder joints, a great deal of work has been performed to develop a better understanding of the metallurgical response of solder joints subjected to thermomechanical fatigue. This work reviews the microstructural and mechanical evolution that occurs in solder joints during thermomechanical fatigue. The eutectic Sn-Pb solder alloy is highlighted. Unlike most materials that experience thermomechanical fatigue, solder is commonly used at temperatures of up to nine-tenths of its melting point. Therefore extensive creep, solid state diffusion, recrystallization and grain growth occur in this alloy resulting in the evolution of a heterogeneous coarsened band through which failure eventually takes place. Two other solder alloys are compared with the Sn-Pb eutectic, a Pb-rich Sn-Pb alloy and a ternary near eutectic (40In-40Sn-20Pb, all alloys are given in wt. %). The Pb-rich alloy is a precipitated single phase matrix that does not evolve during thermomechanical fatigue and subsequently has a shorter lifetime. Conversely, the 40In-40Sn-20Pb solder is a two phase eutectic in which the microstructures refines during thermomechanical fatigue giving it a longer lifetime than the eutectic Sn-Pb solder. The microstructural processes that occur during thermomechanical fatigue and final fracture behavior are discussed for the three solder alloys. 47 refs., 14 figs.

  4. Microstructure evolution of 7050 Al alloy during age-forming

    SciTech Connect

    Chen, Junfeng; Zou, Linchi; Li, Qiang; Chen, Yulong

    2015-04-15

    The microstructure evolution of the 7050 Al alloy treated by age-forming was studied using a designed device which can simulate the age-forming process. The grain shape, grain boundary misorientation and grain orientation evolution of 7050 Al alloy during age-forming have been quantitatively characterized by electron backscattering diffraction technique. The results show that age-forming produced abundant low-angle boundaries and elongated grains, which attributed to stress induced dislocation movement and grain boundary migration during the age-forming process. On the other side, the stress along rolling direction caused some unstable orientation grains to rotate towards the Brass and S orientations during the age-forming process. Hence, the intensity of the rolling texture orientation in age-formed samples is enhanced. But this effect decays gradually with increasing aging time, since stress decreases and precipitation hardening occurs during the age-forming process. - Highlights: • Quantitative analysis of grain evolution of 7050 Al alloys during age-forming • Stress induces some grain rotation of 7050 Al alloys during age-forming. • Creep leads to elongate grain of 7050 Al alloys during age-forming. • Obtains a trend on texture evolution during age-forming applied stress.

  5. Microstructural evolution in the HAZ of Inconel 718 and correlation with the hot ductility test

    NASA Technical Reports Server (NTRS)

    Thompson, R. G.; Genculu, S.

    1983-01-01

    The nickel-base alloy 718 was evaluated to study the role of preweld heat treatment in reducing or eliminating heat-affected zone hot cracking. Three heat treatments were studied using the Gleeble hot ductility test. A modified hot ductility test was also used to follow the evolution of microstructure during simulated welding thermal cycles. The microstructural evolution was correlated with the hot ductility data in order to evaluate the mechanism of hot cracking in alloy 718. The correlation of hot ductility with microstructure showed that recrystallization, grain growth, and dissolution of precipitates did not in themselves cause any loss of ductility during cooling. Ductility loss during cooling was not initiated until the constitutional liquation of NbC particles was observed in the microstructure. Laves-type phases were found precipitated in the solidified grain boundaries but were not found to correlate with any ductility loss parameter. Mechanisms are reviewed which help to explain how heat treatment controls the hot crack susceptibility of alloy 718 as measured in the hot ductility test.

  6. Microstructural evolution in joining of TiAl with a liquid Ti alloy

    SciTech Connect

    Blue, C.A.; Blue, R.A.; Lin, R.Y. . Dept. of Materials Science and Engineering)

    1995-01-01

    In this study, the reaction between titanium aluminide and a liquid titanium alloy, 70Ti-15Cu-15Ni in wt%, was investigated in order to reveal the behavior of TiAl during joining. The microstructural evolution of the reacted melt during solidification was also studied. Issues of concern in this study include: (1) the solidification process of the melt upon termination of heating, and (2) the diffusion of Cu and Ni into the substrate during processing. To accurately control the extent of reaction, an innovative infrared processing technique was used. Infrared processing can produce heating rates exceeding 100 C/s up to the processing temperature and cooling to below 500 C in a few seconds. Such rapid rates of processing decreases or eliminates the adverse effects associated with prolonged heating. In this study, experiments were conducted at various heating times in order to investigate the solidified zone microstructure, melt affected zone thickness, and base material microstructure. The system investigated in this study is directly related to joining of titanium aluminide with a titanium brazing alloy. Meanwhile, the evolution of the microstructure may be applied to other solid-liquid reactions of titanium alloys.

  7. Microstructural Evolution and Interfacial Motion in Systems with Diffusion Barriers

    SciTech Connect

    William C. Johnson

    2007-06-30

    The initial goal of this research program was to model and to simulate phase transformations in systems containing diffusion barriers. The modeling work included the development and testing of code to describe mass flow, the kinetics of phase formation, elastic deformation, and subsequent microstructural evolution occurring during interdiffusion. The primary simulation tools to be used were a class of diffuse interface methods described by the Cahn-Hilliard and phase field equations for the temporal and spatial evolution of the composition and deformation fields and other relevant phase variables. One-dimensional analytical solutions were also to be developed both to test the numerical methods and to establish connections to physical systems. During the early stages of the research program, two new areas of research related to systems with diffusion barriers were identified. The first area concerned phase formation and diffusional phase transformations in reacting systems subject to high electric current densities. Such high-current environments are common in lead-free solders, for example, and have important technological applications. The second area was an offshoot of the present work, and concerned theoretical modeling of phase evolution and cyclical amorphization of metallic alloys during ball milling.

  8. Microstructure evolution of compressible granular systems under large deformations

    NASA Astrophysics Data System (ADS)

    Gonzalez, Marcial; Cuitiño, Alberto M.

    2016-08-01

    We report three-dimensional particle mechanics static calculations that predict the microstructure evolution during die-compaction of elastic spherical particles up to relative densities close to one. We employ a nonlocal contact formulation that remains predictive at high levels of confinement by removing the classical assumption that contacts between particles are formulated locally as independent pair-interactions. The approach demonstrates that the coordination number depends on the level of compressibility, i.e., on Poisson's ratio, of the particles. Results also reveal that distributions of contact forces between particles and between particles and walls, although similar at jamming onset, are very different at full compaction. Particle-wall forces are in remarkable agreement with experimental measurements reported in the literature, providing a unifying framework for bridging experimental boundary observations with bulk behavior.

  9. Laser assisted high entropy alloy coating on aluminum: Microstructural evolution

    SciTech Connect

    Katakam, Shravana; Joshi, Sameehan S.; Mridha, Sanghita; Mukherjee, Sundeep; Dahotre, Narendra B.

    2014-09-14

    High entropy alloy (Al-Fe-Co-Cr-Ni) coatings were synthesized using laser surface engineering on aluminum substrate. Electron diffraction analysis confirmed the formation of solid solution of body centered cubic high entropy alloy phase along with phases with long range periodic structures within the coating. Evolution of such type of microstructure was a result of kinetics associated with laser process, which generates higher temperatures and rapid cooling resulting in retention of high entropy alloy phase followed by reheating and/or annealing in subsequent passes of the laser track giving rise to partial decomposition. The partial decomposition resulted in formation of precipitates having layered morphology with a mixture of high entropy alloy rich phases, compounds, and long range ordered phases.

  10. Microstructure Evolution in a New Refractory High-Entropy Alloy W-Mo-Cr-Ti-Al

    NASA Astrophysics Data System (ADS)

    Gorr, Bronislava; Azim, Maria; Christ, Hans-Juergen; Chen, Hans; Szabo, Dorothee Vinga; Kauffmann, Alexander; Heilmaier, Martin

    2016-02-01

    The microstructure of a body-centered cubic 20W-20Mo-20Cr-20Ti-20Al alloy in the as-cast condition as well as its microstructural evolution during heat treatment was investigated. Different characterization techniques, such as focused ion beam-scanning electron microscope, X-ray diffraction, and transmission electron microscope, were applied. Experimental observations were supported by thermodynamic calculations. The alloy exhibits a pronounced dendritic microstructure in the as-cast condition with the respective dendritic and interdendritic regions showing significant fluctuations of the element concentrations. Using thermodynamic calculations, it was possible to rationalize the measured element distribution in the dendritic and the interdendritic regions. Observations of the microstructure evolution reveal that during heat treatment, substantial homogenization takes place leading to the formation of a single-phase microstructure. Driving forces for the microstructural evolution were discussed from a thermodynamic point of view.

  11. Processing, microstructure evolution and properties of nanoscale aluminum alloys

    NASA Astrophysics Data System (ADS)

    Han, Jixiong

    In this project, phase transformations and precipitation behavior in age-hardenable nanoscale materials systems, using Al-Cu alloys as model materials, were first studied. The Al-Cu nanoparticles were synthesized by a Plasma Ablation process and found to contain a 2˜5 nm thick adherent aluminum oxide scale, which prevented further oxidation. On aging of the particles, a precipitation sequence consisting of, nearly pure Cu precipitates to the metastable theta' to equilibrium theta was observed, with all three forming along the oxide-particle interface. The structure of theta' and its interface with the Al matrix has been characterized in detail. Ultrafine Al-Cu nanoparticles (5˜25 nm) were also synthesized by inert gas condensation (IGC) and their aging behavior was studied. These particles were found to be quite stable against precipitation. Secondly, pure Al nanoparticles were prepared by the Exploding Wire process and their sintering and consolidation behavior were studied. It was found that nanopowders of Al could be processed to bulk structures with high hardness and density. Sintering temperature was found to have a dominant effect on density, hardness and microstructure. Sintering at temperatures >600°C led to breakup of the oxide scale, leading to an interesting nanocomposite composed of 100˜200 nm Al oxide dispersed in a bimodal nanometer-micrometer size Al matrix grains. Although there was some grain growth, the randomly dispersed oxide fragments were quite effective in pinning the Al grain boundaries, preventing excessive grain growth and retaining high hardness. Cold rolling and hot rolling were effective methods for attaining full densification and high hardness. Thirdly, the microstructure evolution and mechanical behavior of Al-Al 2O3 nanocomposites were studied. The composites can retain high strength at elevated temperature and thermal soaking has practically no detrimental effect on strength. Although the ductility of the composite remains

  12. Microstructure Evolution in Alpha Iron during High Temperature Tensile Deformation

    NASA Astrophysics Data System (ADS)

    Thanh, Phi Hung Xuan

    The microstructural evolution of alpha iron under tensile deformation at high temperature (TH 0.5) and slow strain-rate (10-5 s-1 to 10-5 s-1) was investigated. The impetus for this study was the recent observation of Dynamic Abnormal Grain Growth (DAGG) in pure molybdenum under the same testing conditions. A high temperature tensile testing system was refurbished and assembled for this study. The testing system consists of an Centorr 2229 furnace system mounted on an Instron 1331 load frame. I designed the tensile grip and programmed the testing program to obtain data in the stress and strain regime of interest. Testing were done at both UC Davis and Los Alamos National Labs (LANL). Metallography techniques and electron backscattering diffraction (EBSD) technique in a scanning electron microscope were used to characterize the samples after testing. In addition to normal tensile tests at constant strain-rates where DAGG is proposed to occur, a series of strain-rate change tests were designed and performed. Strain-rate change tests were employed to extract activation area information that provided insight into the active mechanism of deformation of the material in addition to the information obtained from analysis of the stress-strain curve and the microstructure via optical microscopy and EBSD. The obtained stress-train curve data were compared with the stress-strain curves data in the literature for alpha iron in similar regime of deformation indicating that the dominant mechanism of deformation is dynamic recovery. The comparison includes past stress-strain curves and the data recorded in the Ashby Map. Optical and EBSD analysis showed that normal grain growth occurred in alpha iron during this testing regime. This lack of grain boundary pinning by impurity differs from that observed in Mo that exhibited DAGG. Activation area analysis showed that the activation area values of Fe are consistent with friction drag from the lattice being the active deformation

  13. Conventional and Multiscale Modeling of Microstructure Evolution During Laminar Cooling of DP Steel Strips

    NASA Astrophysics Data System (ADS)

    Pietrzyk, Maciej; Kusiak, Jan; Kuziak, Roman; Madej, Łukasz; Szeliga, Danuta; Gołąb, Rafał

    2014-12-01

    Physical and numerical simulations of the hot rolling and laminar cooling of DP steel strips are presented in the paper. The objectives of the paper were twofold. Physical simulations of hot plastic deformation were used to identify and validate numerical models. Validated models were applied to simulate the manufacturing of DP steel strips. Conventional flow stress model and microstructure evolution model were used in the hot deformation part. The approach to the complex systems analysis based on global thermodynamic characterization and detailed microstructure characterization was applied to determine equilibrium state at various temperatures. Finally, two numerical models were used to simulate kinetics of austenite decomposition at varying temperatures: the first, conventional model based on the Avrami equation, and the second, the discrete Cellular Automata approach. Plastometric tests and stress relaxation tests were used for identification of the hot rolling model for the DP steel. Dilatometric tests were performed to identify the phase transformation models. Verification confirmed good accuracy of all models. Validated models were applied to simulate the manufacturing of DP steel strips. Influence of technological parameters ( e.g., strip thickness and velocity, active sections in the laminar cooling, and water flux in the sections) on the DP microstructure was analyzed. The cooling schedules, which give required microstructures were proposed. The numerical tool, which simulates manufacturing chain for DP steel strips is the main output of the paper.

  14. Microstructure evolution and densification of alumina in liquid phase sintering

    NASA Astrophysics Data System (ADS)

    Dong, Weimin

    The microstructure evolution and densification of alumina during liquid phase sintering were quantified. Quantification included the evolution of pore-size distribution, the redistribution of liquid phase, the densification kinetics, and the fraction of closed and open pores. The results revealed that the small and large pores were filled simultaneously. This is inconsistent with Shaw's model in which liquid fills preferentially the smaller low-coordination-number pores in order to reach a low-energy configuration. The results also recommended that the pressure build-up of the trapped gases in pores due to the closure of open pores might have a significantly negative contribution to the driving force, and consequently cause the termination of the densification of alumina. To demonstrate whether the trapped gases played an important role in the microstructure evolution and the densification of alumina during liquid phase sintering, the following two experiments have been conducted. First, alumina preforms containing artificial pores were penetrated by glass. The results indicated that the trapped gases in pores had a considerable influence on the pore filling process, and ultimately caused the termination of the densification of the alumina preforms. Second, alumina compacts containing different amount of glass were sintered in vacuum. The alumina compact containing 20 vol. % reached full density during vacuum sintering, indicating that the pressure build-up of the trapped gases in pores was the main factor causing the termination of the densification of alumina in the final stage of liquid phase sintering. The limiting relative densities of compacts were calculated theoretically on the basis of a comprehensive analysis of the variation of the capillary pressure and gas pressure in pores with pore size and pore number. The capillary pressure and gas pressure in alumina compact during liquid phase sintering were analyzed on the basis of the above theoretical models

  15. Subtask 12F2: Microstructural evolution of V-4Cr-4Ti during neutron irradiation

    SciTech Connect

    Chung, H.M.; Gazda, J.; Loomis, B.A.

    1995-03-01

    The objective of this work is to characterize the microstructural evolution of V-4Cr-4Ti alloy during irradiation by fast neutrons, and thereby to provide a better understanding of long-term performance of the alloy under fusion conditions. Microstructural evolution of V-4Cr-4Ti, an alloy recently shown to exhibit excellent tensile and creep properties, virtual immunity to irradiation embrittlement, and good resistance to swelling, was characterized after irradiation in a lithium environment in the Fast Flux Test Facility (FFTF) (a sodium-cooled fast reactor located in Richland, Washington) at 420, 520, and 600{degrees}C to 24-34 dpa. The primary feature of microstructural evolution during irradiation at 520 and 600{degrees}C was high-density formation of ultrafine Ti{sub 5}Si{sub 3} precipitates and short dislocations. For irradiation at 420{degrees}C, precipitation of Ti{sub 5}Si{sub 3} was negligible, and {open_quotes}black-dot{close_quotes} defects and dislocations were observed in significantly higher densities. In spite of their extremely high densities, neither the {open_quotes}black-dot{close_quotes} defects nor Ti{sub 5}Si{sub 3} precipitates are overly detrimental to ductility and toughness of the alloy, yet they very effectively suppress irradiation-induced swelling. Therefore, these features, normally observed in V-base alloys containing Ti and Si, are considered stable. Unstable microstructural modifications that are likely to degrade mechanical properties significantly were not observed, e.g., irradiation-induced formation of fine oxides, carbides, nitrides, or Cr-rich clusters. 18 refs., 4 figs., 1 tab.

  16. Application of morphological synthesis for understanding electrode microstructure evolution as a function of applied charge/discharge cycles

    NASA Astrophysics Data System (ADS)

    Glazoff, Michael V.; Dufek, Eric J.; Shalashnikov, Egor V.

    2016-10-01

    Morphological synthesis operations were employed for understanding electrode microstructure transformations and evolution accompanying the application of charge/discharge cycles to electrochemical storage systems (batteries). Using state-of-the-art morphological algorithms, it was possible to predict microstructure evolution in porous Si electrodes for Li-ion batteries with reasonable accuracy. The developed techniques could be considered supplementary to a phase-field mesoscopic approach to microstructure evolution that is based upon clear and definitive changes in the appearance of microstructure. However, unlike in phase field, the governing equations for the morphological approach are geometry, not physics, based. A similar non-physics-based approach to understanding different phenomena was attempted with the introduction of cellular automata. It is anticipated that morphological synthesis will represent a useful supplementary tool to phase field and will render assistance to unraveling the underlying microstructure-property relationships. The paper contains data on electrochemical characterization of different electrode materials that was conducted in parallel to the morphological study.

  17. Microstructural evolution of Ti-added interstitial free steel in high strain deformation by hot torsion

    NASA Astrophysics Data System (ADS)

    Gholizadeh, R.; Shibata, A.; Terada, D.; Tsuji, N.

    2015-08-01

    The dynamically evolved microstructure under high strain deformation condition does still have many debatable aspects, particularly in the case of easy-recovery metals like bcc-iron. In this research, microstructural evolution in high strain deformation by hot torsion of Ti-added interstitial free (IF) steel was systematically investigated. Torsion specimens were deformed up to an equivalent strain of ∼ 7 at different temperatures (650 °C - 850 °C) and strain rates (0.01 s-1 - 1.0 s-1), i.e., under various values of the Zener-Hollomon (Z) parameter. Immediately after the deformation, samples were water-quenched and microstructures were investigated by electron backscattering diffraction (EBSD) measurements and electron channelling contrast imaging (ECCI). Flow stress-strain curves of the IF steel under various deformation conditions showed typical flow curves of high stacking fault energy metals at low Z values, i.e., a peak stress followed by slight softening. On the other hand, under the high-Z deformation conditions, the specimens showed a larger stress drop after a certain amount of deformation. EBSD-based quantitative analysis was used to study the microstructural transition between high and low Z values. At low Z values, the occurrence of strain induced boundary migration (SIBM) as an initiation of dynamic recrystallization (DRX) was clearly observed. On the other hand, at high Z values, grain subdivision phenomena led to very fine and elongated structures.

  18. Microstructural Evolution During Multi-Pass Friction Stir Processing of a Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Tripathi, A.; Tewari, A.; Kanjarla, A. K.; Srinivasan, N.; Reddy, G. M.; Zhu, S. M.; Nie, J. F.; Doherty, R. D.; Samajdar, I.

    2016-05-01

    A commercial magnesium alloy was processed through multi-pass and multi-directional (unidirectional, reverse, and transverse tool movements) friction stir processing (FSP). Based on the FSP location, the dominant prior-deformation basal texture was shifted along the arc of a hypothetical ellipse. The patterns of deformation texture developments were captured by viscoplastic self-consistent modeling with appropriate velocity gradients. The simulated textures, however, had two clear deficiencies. The simulations involved shear strains of 0.8 to 1.0, significantly lower than those expected in the FSP. Even at such low shear, the simulated textures were significantly stronger. Microstructural observations also revealed the presence of ultra-fine grains with relatively weak crystallographic texture. Combinations of ultra-fine grain superplasticity followed by grain coarsening were proposed as the possible mechanism for the microstructural evolution during FSP.

  19. Microstructure evolution of electron beam welded Ti{sub 3}Al-Nb joint

    SciTech Connect

    Feng Jicai; Wu Huiqiang . E-mail: huiqiang_wu@hit.edu.cn; He Jingshan; Zhang Bingang

    2005-02-15

    The microstructure evolution characterization in high containing Nb, low Al titanium aluminide alloy of electron beam welded joints was investigated by means of OM, SEM, XRD, TEM and microhardness analysis. The results indicated that the microstructure of the weld metal made with electron beam under the welding conditions employed in this work was predominantly metastable, retaining ordered {beta} phase (namely B2 phase), and was independent of the welding parameters but independent of the size and the orientation of the weld solidification structures. As the heat input is decreased, the cellular structure zone is significantly reduced, and then the crystallizing morphology of fusion zone presented dendritically columnar structure. There existed grain growth coarsening in heat affected zone (HAZ) for insufficient polygonization. Both fusion zone (FZ) and the HAZ had higher microhardness than the base metal.

  20. Numerical simulation of temperature field, microstructure evolution and mechanical properties of HSS during hot stamping

    SciTech Connect

    Shi, Dongyong; Liu, Wenquan; Ying, Liang Hu, Ping Shen, Guozhe

    2013-12-16

    The hot stamping of boron steels is widely used to produce ultra high strength automobile components without any spring back. The ultra high strength of final products is attributed to the fully martensitic microstructure that is obtained through the simultaneous forming and quenching of the hot blanks after austenization. In the present study, a mathematical model incorporating both heat transfer and the transformation of austenite is presented. A FORTRAN program based on finite element technique has been developed which permits the temperature distribution and microstructure evolution of high strength steel during hot stamping process. Two empirical diffusion-dependent transformation models under isothermal conditions were employed respectively, and the prediction capability on mechanical properties of the models were compared with the hot stamping experiment of an automobile B-pillar part.

  1. Microstructural effects on damage evolution in shocked copper polycrystals

    DOE PAGES

    Lieberman, Evan J.; Lebensohn, Ricardo A.; Menasche, David B.; ...

    2016-07-01

    Three-dimensional crystal orientation fields of a copper sample, characterized before and after shock loading using High Energy Diffraction Microscopy, are used for input and validation of direct numerical simulations using a Fast Fourier Transform (FFT)-based micromechanical model. The locations of the voids determined by X-ray tomography in the incipiently-spalled sample, predominantly found near grain boundaries, were traced back and registered to the pre-shocked microstructural image. Using FFT-based simulations with direct input from the initial microstructure, micromechanical fields at the shock peak stress were obtained. Statistical distributions of micromechanical fields restricted to grain boundaries that developed voids after the shock aremore » compared with corresponding distributions for all grain boundaries. Distributions of conventional measures of stress and strain (deviatoric and mean components) do not show correlation with the locations of voids in the post-shocked image. Neither does stress triaxiality, surface traction or grain boundary inclination angle, in a significant way. On the other hand, differences in Taylor factor and accumulated plastic work across grain boundaries do correlate with the occurrence of damage. As a result, damage was observed to take place preferentially at grain boundaries adjacent to grains having very different plastic response.« less

  2. Microstructural effects on damage evolution in shocked copper polycrystals

    SciTech Connect

    Lieberman, Evan J.; Lebensohn, Ricardo A.; Menasche, David B.; Bronkhorst, Curt Allan; Rollett, Anthony D.

    2016-07-01

    Three-dimensional crystal orientation fields of a copper sample, characterized before and after shock loading using High Energy Diffraction Microscopy, are used for input and validation of direct numerical simulations using a Fast Fourier Transform (FFT)-based micromechanical model. The locations of the voids determined by X-ray tomography in the incipiently-spalled sample, predominantly found near grain boundaries, were traced back and registered to the pre-shocked microstructural image. Using FFT-based simulations with direct input from the initial microstructure, micromechanical fields at the shock peak stress were obtained. Statistical distributions of micromechanical fields restricted to grain boundaries that developed voids after the shock are compared with corresponding distributions for all grain boundaries. Distributions of conventional measures of stress and strain (deviatoric and mean components) do not show correlation with the locations of voids in the post-shocked image. Neither does stress triaxiality, surface traction or grain boundary inclination angle, in a significant way. On the other hand, differences in Taylor factor and accumulated plastic work across grain boundaries do correlate with the occurrence of damage. As a result, damage was observed to take place preferentially at grain boundaries adjacent to grains having very different plastic response.

  3. Phase-Field Modeling of Microstructure Evolution in Electron Beam Additive Manufacturing

    NASA Astrophysics Data System (ADS)

    Gong, Xibing; Chou, Kevin

    2015-05-01

    In this study, the microstructure evolution in the powder-bed electron beam additive manufacturing (EBAM) process is studied using phase-field modeling. In essence, EBAM involves a rapid solidification process and the properties of a build partly depend on the solidification behavior as well as the microstructure of the build material. Thus, the prediction of microstructure evolution in EBAM is of importance for its process optimization. Phase-field modeling was applied to study the microstructure evolution and solute concentration of the Ti-6Al-4V alloy in the EBAM process. The effect of undercooling was investigated through the simulations; the greater the undercooling, the faster the dendrite grows. The microstructure simulations show multiple columnar-grain growths, comparable with experimental results for the tested range.

  4. Effect of solidification rate on microstructure evolution in dual phase microalloyed steel

    PubMed Central

    Kostryzhev, A. G.; Slater, C. D.; Marenych, O. O.; Davis, C. L.

    2016-01-01

    In steels the dependence of ambient temperature microstructure and mechanical properties on solidification rate is not well reported. In this work we investigate the microstructure and hardness evolution for a low C low Mn NbTi-microalloyed steel solidified in the cooling rate range of 1–50 Cs−1. The maximum strength was obtained at the intermediate solidification rate of 30 Cs−1. This result has been correlated to the microstructure variation with solidification rate. PMID:27759109

  5. Effects of the primary recoil spectrum on microstructural evolution

    SciTech Connect

    Wiedersich, H.

    1989-11-01

    For quantitative predictions and comparisons of microstructures that evolve during exposure to different radiation environments at elevated temperature one needs to develop methods that go beyond those based on the number of displacements per atom. The number of freely migrating defects that contribute to the microstructural development is far less than the total number of defects produced, as has been recognized for some time from measurements of radiation-induced segregation and of radiation-enhanced diffusion. One major reason for the small amount of defects available for long range migration is the high concentration and close spatial correlation of vacancies and, to a somewhat lesser degree, of interstitials in cascades produced by high energy knock-ons. As a consequence, many defects either recombine or form immobile defect clusters during the defect formation and cooling phases of the cascades. After doses exceeding a few tenths of a displacement per atom, the residue of small clusters and dislocation loops of vacancy type remaining in the central portions of energetic cascades and subscascades, is the second major reason for the reduction of the mean free path of defects between creation and annihilation. Defect production in various neutron and ion irradiation environments is discussed in light of these facts. A method to calculate the fraction of freely migrating defects from the cluster size distribution of defects produced in cascades is suggested. The results are in good agreement with available data. 22 refs., 5 figs.

  6. Microstructural Evolution of Chloride-Cleaned Silicon Carbide Aluminum Composites

    NASA Astrophysics Data System (ADS)

    Adeosun, S. O.; Akpan, E. I.; Gbenebor, O. P.; Balogun, S. A.

    2016-02-01

    This study examines the synergy between reinforcement surface modifications on the evolution of microstructures of AA6011-silicon carbide particle (SiCp) composites in multidirectional solidification. Silicon carbide particles (SiCp) were cleaned with ammonium chloride, tin(II) chloride, sodium chloride, and palladium(II) chloride and used as reinforcement to cast AA6011-SiCp composites by applying the stir casting method. A scanning electron microscope and x-ray diffractometer were used to investigate the morphology and phases present, respectively, in the composite material. Results show that wetting agents were effective as they inhibited the formation of Al4C3 in all modified composites. The modified SiCp was found to have varying effects on the morphology, dendrite arm size and direction, size and configuration of AlFeSi, and the amount of eutectic silicon depending on the concentration of the reagent and cleaning time. The highest effect was shown by the use of 40 g/L of tin(II) chloride. The composites had short dendritic arms, good interfacial interaction, and only a few crystals of AlFeSi.

  7. Study on the microstructural evolution of AZ31 magnesium alloy in a vertical twin-roll casting process

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Hu, Xiao-Dong; Han, Bing; Deng, Xiao-Hu; Ju, Dong-Ying

    2016-02-01

    Finite element method was employed to calculate the macroflow velocity and temperature distribution of the pool domain's biting zone in twin-roll casting. Macroanalysis results were inducted as boundary conditions into microanalysis. Phase field method (PFM) was adopted to investigate the microstructure evolution. Based on the Kim-Kim-Suzuki model, the effect of metal flow velocity was coupled on the solute gradient item, and the real physical parameters of AZ31 were inducted into the numerical calculation. We used the marker and cell method in the discrete element solution of microstructural pattern prediction of AZ31 magnesium alloys. The different flow velocity values that predicted the columnar dendrite evolution were discussed in detail. Numerical simulation results were also compared with the experiment analysis. The microstructure obtained by PFM agrees with the actual pattern observed via optical microscopy.

  8. Computational Modeling of Microstructural-Evolution in AISI 1005 Steel During Gas Metal Arc Butt Welding

    DTIC Science & Technology

    2013-05-01

    of the commercially available metallic materials, in particular, steels (including stainless steels ), super alloys, aluminum alloys, etc.; (b) welding...REPORT Computational Modeling of Microstructural-Evolution in AISI 1005 Steel During Gas Metal Arc Butt Welding 14. ABSTRACT 16. SECURITY...Computational Modeling of Microstructural-Evolution in AISI 1005 Steel During Gas Metal Arc Butt Welding Report Title ABSTRACT A fully coupled (two-way

  9. Microstructural Evolution of Ti-6Al-4V during High Strain Rate Conditions of Metal Cutting

    NASA Technical Reports Server (NTRS)

    Dong, Lei; Schneider, Judy

    2009-01-01

    The microstructural evolution following metal cutting was investigated within the metal chips of Ti-6Al-4V. Metal cutting was used to impose a high strain rate on the order of approx.10(exp 5)/s within the primary shear zone as the metal was removed from the workpiece. The initial microstructure of the parent material (PM) was composed of a bi-modal microstructure with coarse prior grains and equiaxed primary located at the boundaries. After metal cutting, the microstructure of the metal chips showed coarsening of the equiaxed primary grains and lamellar. These metallographic findings suggest that the metal chips experienced high temperatures which remained below the transus temperature.

  10. Mechanical modeling of battery separator based on microstructure image analysis and stochastic characterization

    NASA Astrophysics Data System (ADS)

    Xu, Hongyi; Zhu, Min; Marcicki, James; Yang, Xiao Guang

    2017-03-01

    A microstructure-based modeling method is developed to predict the mechanical behaviors of lithium-ion battery separators. Existing battery separator modeling methods cannot capture the structural features on the microscale. To overcome this issue, we propose an image-based microstructure Representative Volume Element (RVE) modeling method, which facilitates the understanding of the separators' complex macro mechanical behaviors from the perspective of microstructural features. A generic image processing workflow is developed to identify different phases in the microscopic image. The processed RVE image supplies microstructural information to the Finite Element Analysis (FEA). Both mechanical behavior and microstructure evolution are obtained from the simulation. The evolution of microstructure features is quantified using the stochastic microstructure characterization methods. The proposed method successfully captures the anisotropic behavior of the separator under tensile test, and provides insights into the microstructure deformation, such as the growth of voids. We apply the proposed method to a commercially available separator as the demonstration. The analysis results are validated using experimental testing results that are reported in literature.

  11. Cow-eye microstructure evolution of laser pulse processed for ductile iron

    NASA Astrophysics Data System (ADS)

    Ba, Fahai; Gan, Cuihua; Yu, Gang

    2003-04-01

    Pulsed laser beam with lattice distribution was used to modify surface processing for ductile iron. The microstructures around the graphite were observed using OM, and Nanoindentation and micro-hardness of that measured from surface to inner of sample. The result shows that the graphite ball has an important effect on cow-eye microstructure evolution either in light molten area or in phase change hardened are. It is not true that assuming the material is uniform during laser rapid heating and fast cooling for the graphite ball as a dependant composition phase. The microstructures of cow-eye is made up of fine remnant austenite in light molten area, and consisted of martensite and bainite in laser modified are. The cow-eye microstructure has a transformation from martensite and bainite to pearlite with the distance increasing from surfce. At last, the microstructure evolution of cow-eye has been discussed.

  12. Final Report: A Transport Phenomena Based Approach to Probe Evolution of Weld Macro and Microstructures and A Smart Bi-directional Model of Fusion Welding

    SciTech Connect

    Dr. Tarasankar DebRoy

    2009-12-11

    In recent years, applications of numerical heat transfer and fluid flow models of fusion welding have resulted in improved understanding of both the welding processes and welded materials. They have been used to accurately calculate thermal cycles and fusion zone geometry in many cases. Here we report the following three major advancements from this project. First, we show how microstructures, grain size distribution and topology of welds of several important engineering alloys can be computed starting from better understanding of the fusion welding process through numerical heat transfer and fluid flow calculations. Second, we provide a conclusive proof that the reliability of numerical heat transfer and fluid flow calculations can be significantly improved by optimizing several uncertain model parameters. Third, we demonstrate how the numerical heat transfer and fluid flow models can be combined with a suitable global optimization program such as a genetic algorithm for the tailoring of weld attributes such as attaining a specified weld geometry or a weld thermal cycle. The results of the project have been published in many papers and a listing of these are included together with a list of the graduate thesis that resulted from this project. The work supported by the DOE award has resulted in several important national and international awards. A listing of these awards and the status of the graduate students are also presented in this report.

  13. Evolution of the microstructure during the process of consolidation and bonding in soft granular solids.

    PubMed

    Yohannes, B; Gonzalez, M; Abebe, A; Sprockel, O; Nikfar, F; Kiang, S; Cuitiño, A M

    2016-04-30

    The evolution of microstructure during powder compaction process was investigated using a discrete particle modeling, which accounts for particle size distribution and material properties, such as plasticity, elasticity, and inter-particle bonding. The material properties were calibrated based on powder compaction experiments and validated based on tensile strength test experiments for lactose monohydrate and microcrystalline cellulose, which are commonly used excipient in pharmaceutical industry. The probability distribution function and the orientation of contact forces were used to study the evolution of the microstructure during the application of compaction pressure, unloading, and ejection of the compact from the die. The probability distribution function reveals that the compression contact forces increase as the compaction force increases (or the relative density increases), while the maximum value of the tensile contact forces remains the same. During unloading of the compaction pressure, the distribution approaches a normal distribution with a mean value of zero. As the contact forces evolve, the anisotropy of the powder bed also changes. Particularly, during loading, the compression contact forces are aligned along the direction of the compaction pressure, whereas the tensile contact forces are oriented perpendicular to direction of the compaction pressure. After ejection, the contact forces become isotropic.

  14. The layered evolution of fabric and microstructure of snow at Point Barnola, Central East Antarctica

    NASA Astrophysics Data System (ADS)

    Calonne, Neige; Montagnat, Maurine; Matzl, Margret; Schneebeli, Martin

    2017-02-01

    Snow fabric, defined as the distribution of the c-axis orientations of the ice crystals in snow, is poorly known. So far, only one study exits that measured snow fabric based on a statistically representative technique. This recent study has revealed the impact of temperature gradient metamorphism on the evolution of fabric in natural snow, based on cold laboratory experiments. On polar ice sheets, snow properties are currently investigated regarding their strong variability in time and space, notably because of their potential influence on firn processes and consequently on ice core analysis. Here, we present measurements of fabric and microstructure of snow from Point Barnola, East Antarctica (close to Dome C). We analyzed a snow profile from 0 to 3 m depth, where temperature gradients occur. The main contributions of the paper are (1) a detailed characterization of snow in the upper meters of the ice sheet, especially by providing data on snow fabric, and (2) the study of a fundamental snow process, never observed up to now in a natural snowpack, namely the role of temperature gradient metamorphism on the evolution of the snow fabric. Snow samples were scanned by micro-tomography to measure continuous profiles of microstructural properties (density, specific surface area and pore thickness). Fabric analysis was performed using an automatic ice texture analyzer on 77 representative thin sections cut out from the samples. Different types of snow fabric could be identified and persist at depth. Snow fabric is significantly correlated with snow microstructure, pointing to the simultaneous influence of temperature gradient metamorphism on both properties. We propose a mechanism based on preferential grain growth to explain the fabric evolution under temperature gradients. Our work opens the question of how such a layered profile of fabric and microstructure evolves at depth and further influences the physical and mechanical properties of snow and firn. More generally

  15. Evolution of the microstructure of a VT6 alloy during friction stir welding

    NASA Astrophysics Data System (ADS)

    Mironov, S. Yu.

    2015-04-01

    The evolution of the microstructure of a VT6 alloy during friction stir welding (FSW) is studied. The β-α phase transformation that takes place after FSW is found to obey the Burgers orientation relationship. The granular structure and the crystallographic texture of the high-temperature β phase are reconstructed. The mechanisms of structural evolution during FSW are discussed.

  16. Spatially dependent cluster dynamics modeling of microstructure evolution in low energy helium irradiated tungsten

    NASA Astrophysics Data System (ADS)

    Faney, T.; Wirth, B. D.

    2014-09-01

    In fusion reactors, plasma facing components (PFC) and in particular the divertor will be irradiated with high fluxes of low energy (˜100 eV) helium and hydrogen ions. Tungsten is one of the leading candidate divertor materials for ITER and DEMO fusion reactors. However, the behavior of tungsten under high dose, coupled helium/hydrogen exposure remains to be fully understood. The PFC response and performance changes are intimately related to microstructural changes, such as the formation of point defect clusters, helium and hydrogen bubbles or dislocation loops. Computational materials modeling has been used to investigate the mechanisms controlling microstructural evolution in tungsten following high dose, high temperature helium exposure. The aim of this study is to understand and predict helium implantation, primary defect production and defect diffusion, helium-defect clustering and interactions below a tungsten surface exposed to low energy helium irradiation. The important defects include interstitial clusters, vacancy clusters, helium interstitials and helium-vacancy clusters. We report results from a one-dimensional, spatially dependent cluster dynamics model based on the continuum reaction-diffusion rate theory to describe the evolution in space and time of all these defects. The key parameter inputs to the model (diffusion coefficients, migration and binding energies, initial defect production) are determined from a combination of atomistic materials modeling and available experimental data.

  17. Microstructure evolution with varied layer thickness in magnetron-sputtered Ni/C multilayer films

    PubMed Central

    Peng, Jichang; Li, Wenbin; Huang, Qiushi; Wang, Zhanshan

    2016-01-01

    The microstructure evolution of magnetron-sputtered Ni/C multilayers was investigated by varying the Ni and C layer thickness in the region of a few nanometers. For the samples having 2.6-nm-thick C layers, the interface width increases from 0.37 to 0.81 nm as the Ni layer thickness decreases from 4.3 to 1.3 nm. Especially for the samples with Ni layers less than 2.0 nm, the interface width changes significantly due to the discontinuously distributed Ni crystallites. For the samples having 2.8-nm-thick Ni layers, the interface width increases from 0.37 to 0.59 nm when the C layer thickness decreases from 4.3 to 0.7 nm. The evolution of interface microstructures with varied Ni and C layers is explained based on a proposed simple growth model of Ni and C layers. PMID:27515586

  18. Chemical and microstructural evolution on ODS Fe-14CrWTi steel during manufacturing stages

    NASA Astrophysics Data System (ADS)

    Olier, P.; Malaplate, J.; Mathon, M. H.; Nunes, D.; Hamon, D.; Toualbi, L.; de Carlan, Y.; Chaffron, L.

    2012-09-01

    Oxide Dispersion Strengthened (ODS) steels are promising candidate materials for fission and fusion applications thanks to their improved properties related to both their fine grained microstructure and high density of Y-Ti-O nanoscale clusters (NCs). The Fe-14Cr-1 W-0.3Ti-0.3Y2O3 ODS ferritic steel was produced by powder metallurgy: Iron-base gas atomized powders were mechanically alloyed with 0.3% Y2O3 particles in an attritor. Then, the ODS powders were encapsulated in a soft steel can, consolidated by hot extrusion and cold rolled under the shape of tube cladding. The present work investigates the evolution of the chemical composition and the microstructure after each stage of the fabrication route (i.e. mechanical alloying, extrusion and cold rolling). Chemical analysis indicates a significant increase of the carbon content and a moderate increase of oxygen and nitrogen after mechanical alloying compared to initial atomized powders. After extrusion, the measured oxygen content corresponds mainly to the oxygen coming from yttria addition during MA process. In addition, electron microprobe analyses are performed after hot extrusion to determine the concentration and the distribution of the constitutive elements (Cr, Ti, W, Y, O). The microstructure was investigated by transmission electron microscopy (TEM) and small angle neutron scattering (SANS) in order to characterize the size distribution of Y-Ti-O particles. TEM results reveal a fine microstructure (average grain size of 600 nm in the transverse direction) including Y-Ti-O NCs with a mean diameter close to 3 nm after extrusion. A slight coarsening of Y-Ti-O NCs is evidenced by SANS after cold rolling and heat treatments.

  19. Microstructural and Chemical Rejuvenation of a Ni-Based Superalloy

    NASA Astrophysics Data System (ADS)

    Yao, Zhiqi; Degnan, Craig C.; Jepson, Mark A. E.; Thomson, Rachel C.

    2016-12-01

    The microstructural evolution of the Ni-based superalloy CMSX-4 including the change in gamma prime morphology, size, and distribution after high-temperature degradation and subsequent rejuvenation heat treatments has been examined using field emission gun scanning electron microscopy and transmission electron microscopy. In this paper, it is shown that there are significant differences in the size of the `channels' between gamma prime particles, the degree of rafting, and the size of tertiary gamma prime particles in each of the different microstructural conditions studied. Chemical analysis has been carried out to compare rejuvenated and pre-service samples after the same subsequent degradation procedure. The results indicate that although the microstructures of pre-service and rejuvenated samples are similar, chemical differences are more pronounced in the rejuvenated samples, suggesting that chemical segregation from partitioning of the elements was not completely eliminated through the applied rejuvenation heat treatment. A number of modified rejuvenation heat treatment trials were carried out to reduce the chemical segregation prior to creep testing. The creep test results suggest that chemical segregation has an immeasurable influence on the short-term mechanical properties under the test conditions used here, indicating that further work is required to fully understand the suitability of specific rejuvenation heat treatments and their role in the extension of component life in power plant applications.

  20. Microstructural evolution of type 304 and 316 stainless steels under neutron irradiation at LWR relevant conditions

    SciTech Connect

    Tan, Lizhen; Stoller, Roger E.; Field, Kevin G.; Yang, Ying; Morgan, Dane; Wirth, Brian D.; Gussev, Maxim N.; Busby, Jeremy T.; Nam, H.

    2015-12-11

    Extension of light water reactors' useful life will expose austenitic internal core components to irradiation damage levels beyond 100 displacements per atom (dpa), which will lead to profound microstructural evolution and consequent degradation of macroscopic properties. Microstructural evolution, including Frank loops, cavities, precipitates, and segregation at boundaries and the resultant radiation hardening in type 304 and 316 stainless steel (SS) variants, were studied in this work via experimental characterization and multiple simulation methods. Experimental data for up to 40 heats of type 304SS and 316SS variants irradiated in different reactors to 0.6–120 dpa at 275–375°C were either generated from this work or collected from literature reports. These experimental data were then combined with models of Frank loop and cavity evolution, computational thermodynamics and precipitation, and ab initio and rate theory integrated radiation-induced segregation models to provide insights into microstructural evolution and degradation at higher radiation doses.

  1. Microstructural Evolution of Type 304 and 316 Stainless Steels Under Neutron Irradiation at LWR Relevant Conditions

    NASA Astrophysics Data System (ADS)

    Tan, L.; Stoller, R. E.; Field, K. G.; Yang, Y.; Nam, H.; Morgan, D.; Wirth, B. D.; Gussev, M. N.; Busby, J. T.

    2016-02-01

    Life extension of light water reactors will expose austenitic internal core components to irradiation damage levels beyond 100 displacements per atom (dpa), leading to profound microstructural evolution and consequent degradation of macroscopic properties. Microstructural evolution, including Frank loops, cavities, precipitates, and segregation at boundaries and the resultant radiation hardening in type 304 and 316 stainless steel (SS) variants were studied in this work via experimental characterization and multiple simulation methods. Experimental data for up to 40 heats of type 304SS and 316SS variants irradiated in different reactors to 0.6-120 dpa at 275-375°C were generated from this work or collected from literature reports. These experimental data were then combined with models of Frank loop and cavity evolution, computational thermodynamics and precipitation, and ab initio and rate theory integrated radiation-induced segregation models to provide insights into microstructural evolution and degradation at higher doses.

  2. Microstructural evolution of the Yugu peridotites in the Gyeonggi Massif, Korea

    NASA Astrophysics Data System (ADS)

    Park, M.; Jung, H.

    2015-12-01

    The Yugu peridotite is the largest and freshest ultramafic body in the Gyeonggi Massif, Korean Peninsula, which potentially has a tectonic affinity to the eastward extension of the Qinling-Dabie-Sulu collision belt in China. In spite of its tectonic and rheological importance, only few mineralogical and petrological studies have been reported from Yugu peridotite. In order to understand the microstructural evolution of the Yugu peridotites, we conducted a detailed analysis of the microstructures and petro-fabrics. The majority of Yugu peridotite body is significantly serpentinized, and it consists predominantly of spinel harzburgite together with minor lherzolite, dunite, and clinopyroxenite. We collected peridotites from mainly two areas (northwestern and southwestern parts) of the Yugu ultramafic body, and all samples are spinel harzburgites consisting of olivine, orthopyroxene, clinopyroxene, spinel, and amphibole. These samples have similar mineralogy except for the varied amount of clinopyroxene and amphibole. These mineral contents are generally increasing from proto-mylonite peridotites to mylonite peridotites. Based on microstructural characteristics of highly deformed peridotites (especially grain-size of olivine), we classified the samples into four textural types, which are proto-mylonite, proto-mylonite to mylonite transition, mylonite, and ultra-mylonite. Depending on the texture of specimen, it is found that the lattice-preferred orientation (LPO) of olivine varies from A-type (proto-mylonite) via D-type like (mylonite) to E-type (ultra-mylonite). The fabric strength of olivine (M-index and J-index) systematically decreases with decreasing grain-size of olivine from proto-mylonite via mylonite to ultra-mylonite. The cause of fabric evolution in the Yugu peridotites will be discussed.

  3. Full-field Model and Experimental Validation of Subgrain Texture and Microstructure Evolution of Polycrystalline Copper

    SciTech Connect

    Lebensohn, Ricardo A.; Brenner, Renald; Castelnau, Olivier

    2007-05-17

    An efficient full-field formulation based on Fast Fourier Transforms (FFT) for the prediction of the viscoplastic deformation of polycrystals is applied to the study of the subgrain texture and microstructure evolution in a copper aggregate deformed under tension. Direct input from OIM images is used in the construction of the initial unit cell. Average orientations and misorientations predicted with the FFT-based approach after 11% tensile strain are directly compared with OIM measurements, showing a reasonable agreement. The differences between misorientations of surface grains compared with bulk grains are estimated, and the orientation-dependence of grain's misorientations is studied. Measurements and simulations agree in that grains with initial orientation near (110) tend to develop higher misorientations, as deformation proceeds. This behavior can be explained in terms of attraction towards the two different stable orientations and grain interaction. Only models that account for grain interaction, like the FFT-based formulation, are able to capture these effects.

  4. Evolution of Local Microstructures: Spatial Instabilities in Coarsening Clusters

    NASA Technical Reports Server (NTRS)

    2003-01-01

    Diffusion-limited capillarity-driven coarsening of precipitates is an important and intensively studied phenomenon. The classic coarsening theory developed by Lifshitz and Syozov and Wagner (LSW theory) is limited to infinitesimally small volume fractions, V(sub nu), therefore neglects all direct interparticle interactions. This work uses modeling and holographic imaging to compare coarsening rates in "high" volume fraction versus low volume fraction microstructures by observing mixed-dimensional droplets (spherical caps on a surface coarsening by two-dimensional diffusion) during ground-based investigations. The method involves filling a cell with selected homogeneous parent phase, and cooling below the consolute temperature to the isopycnic temperature in the two-phase region of a monotectic system. A microgravity holographic experiment is required for three-dimensional observations to minimize sedimentation during long-term coarsening. Determination of sizes and positions of the many droplets in the holographic images requires automation. We have developed software for automated data analysis, and demonstrated good agreement between regenerated maps and scaled photographs of the original holograms for mixed dimensional coarsening. The results of these experiments were presented in a formal microgravity Science Concept Review (SCR) on December 18, 2000.

  5. Effects of shape anisotropy on microstructural evolution of diblock copolymers

    NASA Astrophysics Data System (ADS)

    Panday, Ashoutosh

    This dissertation discusses the effects of shape anisotropy on the evolved microstructure of diblock copolymers at various levels. Due to chain connectivity and microphase separation, the diblock copolymers self-assemble into ellipsoidal grains of lamellar and cylindrical morphologies. A grain-structure related phenomenon, Excluded Volume Epitaxy (E.V.E.) is explored in Chapter 2. E.V.E. is a local, inter-grain azimuthal orientational correlations effect, which results from a combination of sporadic nucleation and impingement of growing anisotropic shaped grains. Due to E.V.E., the ellipsoidal grains have a propensity for similar orientations in a local neighborhood, despite complete absence of global orientation in the sample. Simulations and experiments have verified this effect. The Avrami kinetics of anisotropic shaped grains is discussed in Chapter 3. Traditionally Avrami equation is used to model the growth kinetics of volume filling isotropic shaped grains. The probabilistic nature of Avrami kinetics produces a coupling between the grain shape and Poisson distribution. The Poisson-shape coupling remains latent for isotropic grains but becomes operative for anisotropic grains in random orientations scheme leading to inhibited growth kinetics. For unidirectional orientation of anisotropic grains, the growth kinetics remains uninhibited due to absence of Poisson-shape coupling. For two-dimensional case in simultaneous and continuous nucleation regimes, the inhibited kinetics scales as L1/2 where L is the shape anisotropy. The blends of highly shape anisotropic nanoclay, montmorillonite (MMT) and lamellar poly(styrene-b-isoprene), PS-PI are discussed in Appendix A. Annealing and cooling is sufficient to produce long-range lamellar order at 1 wt % clay loading. However at 5 wt % clay loading, shear force is additionally required. This system reveals the effect of shape anisotropy on evolution of long-range order in clay-block copolymer blends. The effect of shape

  6. Evolution of microstructure at hot band annealing of ferritic FeSi steels

    NASA Astrophysics Data System (ADS)

    Schneider, Jürgen; Li, Guangqiang; Franke, Armin; Zhou, Bowen

    2017-02-01

    The magnetic properties of the finally fabricated nonoriented FeSi steels critically depend on the microstructure and on the occurring crystallographic texture. The fabrication route comprises hot rolling, coiling and cooling, hot band annealing before cold rolling (optional), cold rolling and the final thermal treatment. As well known there is an interplay between the microstructure and texture during the various processing steps. For that reason, it is of interest to know more on the evolution of the microstructure at hot band annealing of hot band prepared in different ways. In this paper we will summarize our recent results on the evolution of microstructure during thermal annealing of hot band: thermal treatment following immediately the last pass of hot rolling or a hot band annealing as a separate processing step before cold rolling.

  7. Microstructural evolution of fusion zone in laser beam welds of pure titanium

    SciTech Connect

    Liu, H.; Nakata, K.; Zhang, J.X.; Yamamoto, N.; Liao, J.

    2012-03-15

    Microstructural evolution of fusion zone in laser beam welds of pure titanium was studied by means of electron backscattering diffraction. The microstructural evolution is strongly affected by the {beta} {yields} {alpha} transformation mechanism dependent on the cooling rate during phase transformation. The long-range diffusional transformation mainly occurs in the fusion zone at the low cooling rate, and the massive transformation dominantly takes place at the high cooling rate. For this reason, the grain morphologies probably change from the granular-like to columnar-like grains with the cooling rate increasing. - Highlights: Black-Right-Pointing-Pointer Microstructures of fusion zone in laser beam welds of pure titanium are studied. Black-Right-Pointing-Pointer Increasing cooling rate changes grain morphology from granular to columnar one. Black-Right-Pointing-Pointer Final microstructures depend on the {beta}{yields}{alpha} transformation mechanisms.

  8. Influence of various heat treatment stages on evolution of microstructure and grain in H407 steel

    NASA Astrophysics Data System (ADS)

    Sun, Jian; Ji, Kai; Jiang, Chen Wei; Zhang, Yun Chang

    2016-09-01

    Regarding heat treatment as one of the main methods for improving property of die steel, dead annealing, quenching, once tempering, twice tempering, and thrice tempering treatment of H407 die steel were conducted in this thesis. Microstructure conversion and grain size development in various stages of heat treatment were analyzed, and then magnitude, shape, and distribution of secondary phase during heat treatment were investigated to explore the function mechanism of microalloyed elements on evolution of microstructure and grain during heat treatment. The steel achieves homogeneous microstructure and composition after this heat treatment. The final phase constituent is α and γ phase as well as the final microstructure consists of tempered martensite, trace retained austenite and granular carbides. A large number of fine and dispersive MC as well as M7C3 type granular carbides containing V, Mo and Cr precipitate in trice tempered microstructure. After this heat treatment grain is finer with grain size of 5.96 μm.

  9. Persistence and variation in microstructural design during the evolution of spider silk

    PubMed Central

    Madurga, R.; Blackledge, T. A.; Perea, B.; Plaza, G. R.; Riekel, C.; Burghammer, M.; Elices, M.; Guinea, G.; Pérez-Rigueiro, J.

    2015-01-01

    The extraordinary mechanical performance of spider dragline silk is explained by its highly ordered microstructure and results from the sequences of its constituent proteins. This optimized microstructural organization simultaneously achieves high tensile strength and strain at breaking by taking advantage of weak molecular interactions. However, elucidating how the original design evolved over the 400 million year history of spider silk, and identifying the basic relationships between microstructural details and performance have proven difficult tasks. Here we show that the analysis of maximum supercontracted single spider silk fibers using X ray diffraction shows a complex picture of silk evolution where some key microstructural features are conserved phylogenetically while others show substantial variation even among closely related species. This new understanding helps elucidate which microstructural features need to be copied in order to produce the next generation of biomimetic silk fibers. PMID:26438975

  10. Persistence and variation in microstructural design during the evolution of spider silk

    NASA Astrophysics Data System (ADS)

    Madurga, R.; Blackledge, T. A.; Perea, B.; Plaza, G. R.; Riekel, C.; Burghammer, M.; Elices, M.; Guinea, G.; Pérez-Rigueiro, J.

    2015-10-01

    The extraordinary mechanical performance of spider dragline silk is explained by its highly ordered microstructure and results from the sequences of its constituent proteins. This optimized microstructural organization simultaneously achieves high tensile strength and strain at breaking by taking advantage of weak molecular interactions. However, elucidating how the original design evolved over the 400 million year history of spider silk, and identifying the basic relationships between microstructural details and performance have proven difficult tasks. Here we show that the analysis of maximum supercontracted single spider silk fibers using X ray diffraction shows a complex picture of silk evolution where some key microstructural features are conserved phylogenetically while others show substantial variation even among closely related species. This new understanding helps elucidate which microstructural features need to be copied in order to produce the next generation of biomimetic silk fibers.

  11. A Monte Carlo-finite element model for strain energy controlled microstructural evolution - 'Rafting' in superalloys

    NASA Technical Reports Server (NTRS)

    Gayda, J.; Srolovitz, D. J.

    1989-01-01

    This paper presents a specialized microstructural lattice model, MCFET (Monte Carlo finite element technique), which simulates microstructural evolution in materials in which strain energy has an important role in determining morphology. The model is capable of accounting for externally applied stress, surface tension, misfit, elastic inhomogeneity, elastic anisotropy, and arbitrary temperatures. The MCFET analysis was found to compare well with the results of analytical calculations of the equilibrium morphologies of isolated particles in an infinite matrix.

  12. In situ, laser-ultrasonic monitoring of stainless steel microstructure evolution during heat treatment

    SciTech Connect

    Spicer, J.B.

    1997-02-01

    A laser ultrasonic method is described by which the microstructural evolution of a material may be monitored in situ during thermal processing. The method employs analysis of laser ultrasonic data that includes only those measurable quantities obtained from the ultrasonic data itself. Various microstructural changes, including the magnetic Curie transition and the dissolution of carbide structures in stainless-steel alloys, are investigated. These changes may be identified without specific knowledge of the sample temperature, thereby allowing for the possibility of direct microstructure analysis and control using laser-ultrasonic methods.

  13. Predicting mesoscale microstructural evolution in electron beam welding

    SciTech Connect

    Rodgers, Theron M.; Madison, Jonathan D.; Tikare, Veena; Maguire, Michael C.

    2016-03-16

    Using the kinetic Monte Carlo simulator, Stochastic Parallel PARticle Kinetic Simulator, from Sandia National Laboratories, a user routine has been developed to simulate mesoscale predictions of a grain structure near a moving heat source. Here, we demonstrate the use of this user routine to produce voxelized, synthetic, three-dimensional microstructures for electron-beam welding by comparing them with experimentally produced microstructures. When simulation input parameters are matched to experimental process parameters, qualitative and quantitative agreement for both grain size and grain morphology are achieved. The method is capable of simulating both single- and multipass welds. As a result, the simulations provide an opportunity for not only accelerated design but also the integration of simulation and experiments in design such that simulations can receive parameter bounds from experiments and, in turn, provide predictions of a resultant microstructure.

  14. Predicting Mesoscale Microstructural Evolution in Electron Beam Welding

    NASA Astrophysics Data System (ADS)

    Rodgers, T. M.; Madison, J. D.; Tikare, V.; Maguire, M. C.

    2016-05-01

    Using the kinetic Monte Carlo simulator, Stochastic Parallel PARticle Kinetic Simulator, from Sandia National Laboratories, a user routine has been developed to simulate mesoscale predictions of a grain structure near a moving heat source. Here, we demonstrate the use of this user routine to produce voxelized, synthetic, three-dimensional microstructures for electron-beam welding by comparing them with experimentally produced microstructures. When simulation input parameters are matched to experimental process parameters, qualitative and quantitative agreement for both grain size and grain morphology are achieved. The method is capable of simulating both single- and multipass welds. The simulations provide an opportunity for not only accelerated design but also the integration of simulation and experiments in design such that simulations can receive parameter bounds from experiments and, in turn, provide predictions of a resultant microstructure.

  15. Predicting mesoscale microstructural evolution in electron beam welding

    DOE PAGES

    Rodgers, Theron M.; Madison, Jonathan D.; Tikare, Veena; ...

    2016-03-16

    Using the kinetic Monte Carlo simulator, Stochastic Parallel PARticle Kinetic Simulator, from Sandia National Laboratories, a user routine has been developed to simulate mesoscale predictions of a grain structure near a moving heat source. Here, we demonstrate the use of this user routine to produce voxelized, synthetic, three-dimensional microstructures for electron-beam welding by comparing them with experimentally produced microstructures. When simulation input parameters are matched to experimental process parameters, qualitative and quantitative agreement for both grain size and grain morphology are achieved. The method is capable of simulating both single- and multipass welds. As a result, the simulations provide anmore » opportunity for not only accelerated design but also the integration of simulation and experiments in design such that simulations can receive parameter bounds from experiments and, in turn, provide predictions of a resultant microstructure.« less

  16. A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials.

    PubMed

    Nag, S; Banerjee, R; Fraser, H L

    2007-05-01

    The new generation of metallic biomaterials for prosthesis implantation (orthopedic and dental) typically have a Ti base with fully biocompatible alloying additions such as Nb, Ta, Zr, Mo, Fe and Sn. While the binary Ti-Ta and the ternary Ti-Nb-Ta systems are promising, the large composition space afforded by these systems offers tremendous scope in terms of alloy design via optimization of alloy composition and thermomechanical treatment. In the present paper a novel combinatorial approach has been developed for rapidly exploring the microstructural evolution and microstructure-microhardness (or elastic modulus) relationships in these systems. Using directed laser deposition, compositionally graded alloy samples have been fabricated and subsequently heat-treated to affect different microstructures in terms of the volume fraction and distribution of the alpha phase in the beta matrix as a function of composition. Subsequently, composition-specific indentation-based hardness and modulus information has been obtained from these graded samples, and the resulting data have been used to develop relationships between the composition, microstructure and mechanical properties. Such rapid combinatorial assessments can be very useful in optimizing not only the alloy composition but also the desired microstructure for achieving the best combination of properties for specific orthopedic or dental applications.

  17. Shear band evolution and accumulated microstructural development in Cosserat media

    NASA Astrophysics Data System (ADS)

    Tordesillas, A.; Peters, J. F.; Gardiner, B. S.

    2004-08-01

    This paper prepares the ground for the continuum analysis of shear band evolution using a Cosserat/micropolar constitutive equation derived from micromechanical considerations. The nature of the constitutive response offers two key advantages over other existing models. Firstly, its non-local character obviates the mathematical difficulties of traditional analyses, and facilitates an investigation of the shear band evolution (i.e. the regime beyond the onset of localization). Secondly, the constitutive model parameters are physical properties of particles and their interactions (e.g. particle stiffness coefficients, coefficients of inter-particle rolling friction and sliding friction), as opposed to poorly understood fitting parameters. In this regard, the model is based on the same material properties used as model inputs to a discrete element (DEM) analysis, therefore, the micromechanics approach provides the vehicle for incorporating results not only from physical experiments but also from DEM simulations. Although the capabilities of such constitutive models are still limited, much can be discerned from their general rate form. In this paper, an attempt is made to distinguish between those aspects of the continuum theory of localization that are independent of the constitutive model, and those that require significant advances in the understanding of micromechanics. Copyright

  18. Microstructural Evolution and Creep-Rupture Behavior of A-USC Alloy Fusion Welds

    NASA Astrophysics Data System (ADS)

    Bechetti, Daniel H.; DuPont, John N.; Siefert, John A.; Shingledecker, John P.

    2016-09-01

    Characterization of the microstructural evolution of fusion welds in alloys slated for use in advanced ultrasupercritical (A-USC) boilers during creep has been performed. Creep-rupture specimens involving INCONEL® 740, NIMONIC® 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and Haynes® 282® (Haynes and 282 are registered trademarks of Haynes International) have been analyzed via light optical microscopy, scanning electron microscopy, X-ray diffraction, and thermodynamic and kinetic modeling. Focus has been given to the microstructures that develop along the grain boundaries in these alloys during creep at temperatures relevant to the A-USC process cycle, and particular attention has been paid to any evidence of the formation of local γ'-denuded or γ'-free zones. This work has been performed in an effort to understand the microstructural changes that lead to a weld strength reduction factor (WSRF) in these alloys as compared to solution annealed and aged alloy 740 base metal. γ' precipitate-free zones have been identified in alloy 740 base metal, solution annealed alloy 740 weld metal, and alloy 263 weld metal after creep. Their development during long-term thermal exposure is correlated with the stabilization of phases that are rich in γ'-forming elements ( e.g., η and G) and is suppressed by precipitation of phases that do not contain the γ' formers ( e.g., M23C6 and μ). The location of failure and creep performance in terms of rupture life and WSRF for each welded joint is presented and discussed.

  19. Microstructure Evolution of a Platinum-Modified Nickel-Aluminide Coating During Thermal and Thermo-mechanical Fatigue

    NASA Astrophysics Data System (ADS)

    Sallot, Pierre; Maurel, Vincent; Rémy, Luc; N'Guyen, Franck; Longuet, Arnaud

    2015-10-01

    The microstructure evolution of a platinum-modified nickel-aluminide coating on single-crystal nickel-based superalloy was investigated for various thermal cycling and thermo-mechanical fatigue (TMF) conditions in air for a long-term exposure. An increase in roughness and in β→γ' transformation rate depends similarly on maximum temperature, holding time at maximum temperature and applied stress. Moreover, the evolution of the interdiffusion zone (IDZ) is analyzed by making the distinction between two layers, according to the major phases observed within these layers, namely β-(Ni,Pt)Al and γ'-Ni3Al. This distinction highlighted that the respective thickness evolution of these two layers are sensitive to each parameter of TMF tests with similar increase in evolution rate when increasing time, temperature, as well as applied stress. The distinctive features of phase transformation are finally discussed together with localization of phase transformation and measured evolution of phase transformation within the external coating and β- and γ'-IDZ layer thicknesses under thermal and thermo-mechanical fatigue. This analysis leads to a conclusion that grain boundaries within the external coating as well as interfaces, between thermally grown oxide, external coating, and IDZ, respectively, play a major role in diffusion, phase transformation, and microstructure evolution of typical platinum-modified nickel-aluminide coating.

  20. Microstructural engineering applied to the controlled cooling of steel wire rod: Part II. Microstructural evolution and mechanical properties correlations

    NASA Astrophysics Data System (ADS)

    Campbell, P. C.; Hawbolt, E. B.; Brimacombe, J. K.

    1991-11-01

    In the second part of this paper, the microstructural evolution and mechanical properties of plain-carbon steel rods which have been subjected to known cooling conditions are described. Specifically, the isothermal phase transformation kinetics for the decomposition of austenite into ferrite and pearlite have been determined with a diametral dilatometer and characterized in terms of empirical coefficients in the Avrami equation. The continuous cooling transformation (CCT) start time, fraction ferrite, ferrite grain diameter, and pearlite interlamellar spacing have been quantified and correlated with steel composition and cooling rate. Tensile tests have been conducted to obtain yield strength (YS) and ultimate tensile strength (UTS), which, with literature data, have been related to the microstructure and composition of the steels. These correlations, which apply to both hypoeutectoid and eutectoid steels, have been incorporated in a mathematical model of the Stelmor process, to be described in Part III of this article.[441

  1. Microstructure evolution of a multiphase superalloy processed by severe plastic deformation

    NASA Astrophysics Data System (ADS)

    Sauvage, Xavier; Mukhtarov, Shamil

    2014-08-01

    This paper presents an overview and some original results about the microstructure evolution of an Ultra Fine Grained (UFG) nickel-iron based alloy INCONEL 718 processed by Severe Plastic Deformation (SPD). The ultrafine grain structure of this alloy that contains a high density of γ" and γ' precipitates was characterized by Scanning Transmission Electron Microscopy (STEM). We propose a comparison between two SPD processes, High Pressure Torsion (HPT) and Multiple Forging (MF). The grain refinement is much more pronounced by HPT but intermetallic particles are partly dissolved during SPD. The UFG structure after MF is obviously very different and exhibits a much better thermal stability especially because second phase particles do not reprecipitate during post-deformation annealing.

  2. Composite model of microstructural evolution in austenitic stainless steel under fast neutron irradiation

    SciTech Connect

    Stoller, R.E.; Odette, G.R.

    1986-01-01

    A rate-theory-based model has been developed which includes the simultaneous evolution of the dislocation and cavity components of the microstructure of irradiated austenitic stainless steels. Previous work has generally focused on developing models for void swelling while neglecting the time dependence of the dislocation structure. These models have broadened our understanding of the physical processes that give rise to swelling, e.g., the role of helium and void formation from critically-sized bubbles. That work has also demonstrated some predictive capability by successful calibration to fit the results of fast reactor swelling data. However, considerable uncertainty about the values of key parameters in these models limits their usefulness as predictive tools. Hence the use of such models to extrapolate fission reactor swelling data to fusion reactor conditions is compromised.

  3. Modeling Of Microstructure Evolution Of BCC Metals Subjected To Severe Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Svyetlichnyy, Dmytro; Majta, Janusz; Muszka, Krzysztof; Łach, Łukasz

    2011-01-01

    Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant, current problems in materials science. Several advanced methods of analysis can be applied for this issue: vertex models, phase field models, Monte Carlo Potts, finite element method (FEM) discrete element method (DEM) and finally cellular automata (CA). The main asset of the CA is ability for a close correlation of the microstructure with the mechanical properties in micro- and meso-scale simulation. Joining CA with the DEM undoubtedly improves accuracy of modeling of coupled phenomena during the innovative forming processes in both micro- and macro-scale. Deformation in micro-scale shows anisotropy, which connected with that the polycrystalline material contains grains with different crystallographic orientation, and grain deformation is depended from configuration of directions of main stresses and axis of grain. Then, CA and DEM must be joint solutions of crystal plasticity theory. In the present model, deformation in macro-scale is transferred to meso-sale, where a block contains several, score or hundreds grains, and then is applied in micro-scale to each grain. Creation of low-angle boundaries and their development into high-angle boundaries are simulated by the cellular automata on the base of calculations using finite element method and crystal plasticity theory. The idea proposed in this study and particular solutions are discussed for the case of ultrafine-grained low-carbon steel.

  4. Modeling Of Microstructure Evolution Of BCC Metals Subjected To Severe Plastic Deformation

    SciTech Connect

    Svyetlichnyy, Dmytro; Majta, Janusz; Muszka, Krzysztof; Lach, Lukasz

    2011-01-17

    Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant, current problems in materials science. Several advanced methods of analysis can be applied for this issue: vertex models, phase field models, Monte Carlo Potts, finite element method (FEM) discrete element method (DEM) and finally cellular automata (CA). The main asset of the CA is ability for a close correlation of the microstructure with the mechanical properties in micro- and meso-scale simulation. Joining CA with the DEM undoubtedly improves accuracy of modeling of coupled phenomena during the innovative forming processes in both micro- and macro-scale. Deformation in micro-scale shows anisotropy, which connected with that the polycrystalline material contains grains with different crystallographic orientation, and grain deformation is depended from configuration of directions of main stresses and axis of grain. Then, CA and DEM must be joint solutions of crystal plasticity theory. In the present model, deformation in macro-scale is transferred to meso-sale, where a block contains several, score or hundreds grains, and then is applied in micro-scale to each grain. Creation of low-angle boundaries and their development into high-angle boundaries are simulated by the cellular automata on the base of calculations using finite element method and crystal plasticity theory. The idea proposed in this study and particular solutions are discussed for the case of ultrafine-grained low-carbon steel.

  5. Modeling of microstructure evolution of magnesium alloy during the high pressure die casting process

    NASA Astrophysics Data System (ADS)

    Wu, Mengwu; Xiong, Shoumei

    2012-07-01

    Two important microstructure characteristics of high pressure die cast magnesium alloy are the externally solidified crystals (ESCs) and the fully divorced eutectic which form at the filling stage of the shot sleeve and at the last stage of solidification in the die cavity, respectively. Both of them have a significant influence on the mechanical properties and performance of magnesium alloy die castings. In the present paper, a numerical model based on the cellular automaton (CA) method was developed to simulate the microstructure evolution of magnesium alloy during cold-chamber high pressure die casting (HPDC) process. Modeling of dendritic growth of magnesium alloy with six-fold symmetry was achieved by defining a special neighbourhood configuration and calculating of the growth kinetics from complete solution of the transport equations. Special attention was paid to establish a nucleation model considering both of the nucleation of externally solidified crystals in the shot sleeve and the massive nucleation in the die cavity. Meanwhile, simulation of the formation of fully divorced eutectic was also taken into account in the present CA model. Validation was performed and the capability of the present model was addressed by comparing the simulated results with those obtained by experiments.

  6. Effects of solute elements on irradiation hardening and microstructural evolution in low alloy steels

    NASA Astrophysics Data System (ADS)

    Fujii, Katsuhiko; Ohkubo, Tadakatsu; Fukuya, Koji

    2011-10-01

    The effects of the elements Mn, Ni, Si and Cu on irradiation hardening and microstructural evolution in low alloy steels were investigated in ion irradiation experiments using five kinds of alloys prepared by removing Mn, Ni and Si from, and adding 0.05 wt.%Cu to, the base alloy (Fe-1.5Mn-0.5Ni-0.25Si). The alloy without Mn showed less hardening and the alloys without Ni or Si showed more hardening. The addition of Cu had hardly any influence on hardening. These facts indicated that Mn enhanced hardening and that Ni and Si had some synergetic effects. The formation of solute clusters was not confirmed by atom probe (AP) analysis, whereas small dislocation loops were identified by TEM observation. The difference in hardening between the alloys with and without Mn was qualitatively consistent with loop formation. However, microstructural components that were not detected by the AP and TEM were assumed to explain the hardening level quantitatively.

  7. Phase-field modeling of microstructure evolutions in magnetic materials

    PubMed Central

    Koyama, Toshiyuki

    2008-01-01

    Recently, the phase-field method has been extended and utilized across many fields of materials science. Since this method can incorporate, systematically, the effect of the coherency induced by lattice mismatch and the applied stress as well as the external electrical and magnetic fields, it has been applied to many material processes including solidification, solid-state phase transformations and various types of complex microstructure changes. In this paper, we focus on the recent phase-field simulations of real magnetic materials, and the simulation method for magnetic materials is explained comprehensively. Several applications of the phase-field method to clarifying the microstructure changes in magnetic materials, such as Ni2MnGa ferromagnetic shape memory alloy, FePt nanogranular thin film, Co–Sm–Cu rare-earth magnet, Fe–Cr–Co spinodal magnet, and Fe–C steel with external magnetic field, are demonstrated. Furthermore, the general concept of the effective strategy for controlling microstructure in magnetic materials is proposed. PMID:27877924

  8. Connecting grain boundary properties to microstructural evolution in polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Holm, Elizabeth

    2013-03-01

    Within the last decade, both computational and experimental methods have evolved to the point that large-scale surveys of grain boundary properties have become tractable. Such studies have provided new information and insight about boundary structure, energetics, motion mechanisms, and mobility on a scale that invites application to polycrystalline systems. However, the complex behavior revealed in these studies often generates as many questions as it answers. This presentation will review pertinent computational and experimental studies of grain boundary properties in FCC metals, concentrating on boundary energy and mobility. The goal will be to identify the microstructural signatures of boundary properties in polycrystalline grain boundary networks. Topics will include how boundary energy and mobility trends manifest in real microstructures; the effects of shear coupling on boundary motion in bicrystals and polycrystals; the significance of boundaries that move in a non-thermally-activated manner to low temperature grain growth; and the consequences of the thermal roughening transition on grain stagnation. In each case, individual grain boundary properties couple with the characteristics of the grain boundary network to generate diverse microstructural outcomes. Supported in part by the US Department of Energy Office of Basic Energy Sciences.

  9. Calculation of the evolution of the fuel microstructure in UMo alloys and implications for fuel swelling.

    SciTech Connect

    Rest, J.; Hofman, G. L.; Konovalov, I.; Maslov, A.

    1999-10-01

    The evolution of a cellular dislocation structure and subsequent recrystallization have been identified as important aspects of the irradiated UMo alloy microstructure that can have a strong impact on dispersion fuel swelling. Dislocation kinetics depends on the preferential bias of dislocations for interstitial compared to vacancies. This paper presents theoretical calculations for the evolution of a cellular dislocation structure, and recrystallization in U-10Mo. Implications for fuel swelling are discussed.

  10. Modeling of Microstructure Evolution During the Thermomechanical Processing of Titanium Alloys (Preprint)

    DTIC Science & Technology

    2008-07-01

    misorientation across grain boundaries . As such, microstructure and texture evolution are coupled and must be treated simultaneously during modeling... grain - boundary grooving developed originally by Mullins [23, 24]. In the original work, grooving was assumed to be controlled by volume diffusion...in which deformation is accomplished largely by grain - boundary sliding and secondarily by dislocation-glide processes. Thus, the enhancement of

  11. Supersoft lithography: candy-based fabrication of soft silicone microstructures.

    PubMed

    Moraes, Christopher; Labuz, Joseph M; Shao, Yue; Fu, Jianping; Takayama, Shuichi

    2015-01-01

    We designed a fabrication technique able to replicate microstructures in soft silicone materials (E < 1 kPa). Sugar-based 'hard candy' recipes from the confectionery industry were modified to be compatible with silicone processing conditions, and used as templates for replica molding. Microstructures fabricated in soft silicones can then be easily released by dissolving the template in water. We anticipate that this technique will be of particular importance in replicating physiologically soft, microstructured environments for cell culture, and demonstrate a first application in which intrinsically soft microstructures are used to measure forces generated by fibroblast-laden contractile tissues.

  12. Direct handling of sharp interfacial energy for microstructural evolution

    DOE PAGES

    Hernández–Rivera, Efraín; Tikare, Veena; Noirot, Laurence; ...

    2014-08-24

    In this study, we introduce a simplification to the previously demonstrated hybrid Potts–phase field (hPPF), which relates interfacial energies to microstructural sharp interfaces. The model defines interfacial energy by a Potts-like discrete interface approach of counting unlike neighbors, which we use to compute local curvature. The model is compared to the hPPF by studying interfacial characteristics and grain growth behavior. The models give virtually identical results, while the new model allows the simulator more direct control of interfacial energy.

  13. Microstructurally based finite element simulation of solder joint behavior

    SciTech Connect

    Frear, D.R.; Burchett, S.N.; Neilsen, M.K.; Stephens, J.J.

    1996-01-01

    The most commonly used solder for electrical interconnects in electronic packages is the near eutectic 60Sn-40Pb alloy. This alloy has a number of processing advantages (suitable melting point of 183C and good wetting behavior). However, under conditions of cyclic strain and temperature (thermomechanical fatigue) the microstructure of this alloy undergoes a heterogeneous coarsening and failure process that makes the prediction of solder joint lifetime complex. A finite element simulation methodology to predict solder joint mechanical behavior, that includes microstructural evolution, has been developed. The mechanical constitutive behavior was incorporated into the time dependent internal state variable viscoplastic model through experimental creep tests. The microstructural evolution is incorporated through a series of mathematical relations that describe mass flow in a temperature/strain environment. The model has been found to simulate observed thermomechanical fatigue behavior in solder joints.

  14. Microstructural and phase evolution in metakaolin geopolymers with different activators and added aluminosilicate fillers

    NASA Astrophysics Data System (ADS)

    Sarkar, Madhuchhanda; Dana, Kausik; Das, Sukhen

    2015-10-01

    This work aims to investigate the microstructural and phase evolution of alkali activated metakaolin products with different activators and added aluminosilicate filler phases. The added filler phases have different reactivity to the alkali activated metakaolin system. Microstructural evolution in the alkali activated products has been investigated by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Field Emission Scanning Electron Microscope (FESEM). Variation in strength development in alkali activated metakaolin products was followed by compressive strength measurement test. Microstructural study shows that in case of metakaolin with NaOH activator crystalline sodalite formed in all the product samples irrespective of the added filler phases. The microstructure of these NaOH activated products investigated by FESEM showed crystalline and inhomogeneous morphology. Mixed activator containing both NaOH and sodium silicate in a fixed mass ratio formed predominantly amorphous phase. Microstructure of these samples showed more homogeneity than that of NaOH activated metakaolin products. The study further shows that addition of α-Al2O3 powder, non reactive phase to the alkali activated metakaolin system when used in larger amount increased crystalline phase in the matrix. α-Al2O3 powder addition increased the compressive strength of the product samples for both the activator compositions. Added phase of colloidal silica, reactive to the alkali activated metakaolin system when used in larger amount was found to increase amorphous nature of the matrix. Addition of colloidal silica influenced the compressive strength property differently with different activator compositions.

  15. Modeling of microstructure evolution in direct metal laser sintering: A phase field approach

    NASA Astrophysics Data System (ADS)

    Nandy, Jyotirmoy; Sarangi, Hrushikesh; Sahoo, Seshadev

    2017-02-01

    Direct Metal Laser Sintering (DMLS) is a new technology in the field of additive manufacturing, which builds metal parts in a layer by layer fashion directly from the powder bed. The process occurs within a very short time period with rapid solidification rate. Slight variations in the process parameters may cause enormous change in the final build parts. The physical and mechanical properties of the final build parts are dependent on the solidification rate which directly affects the microstructure of the material. Thus, the evolving of microstructure plays a vital role in the process parameters optimization. Nowadays, the increase in computational power allows for direct simulations of microstructures during materials processing for specific manufacturing conditions. In this study, modeling of microstructure evolution of Al-Si-10Mg powder in DMLS process was carried out by using a phase field approach. A MATLAB code was developed to solve the set of phase field equations, where simulation parameters include temperature gradient, laser scan speed and laser power. The effects of temperature gradient on microstructure evolution were studied and found that with increase in temperature gradient, the dendritic tip grows at a faster rate.

  16. On the effect of natural convection on the thermal-microstructural evolution in gray cast-iron solidification

    NASA Astrophysics Data System (ADS)

    Celentano, Diego J.; Cruchaga, Marcela A.; Schulz, Bernd J.

    2006-04-01

    A coupled analysis involving natural convection, thermal balance, and microstructural evolution that take place in the solidification process of a hypoeutectic gray cast iron is presented in this work. The microstructural formulation used in this study includes classical models of primary-austenite and eutectic (gray and white) transformations. The influence of both natural convection and heat-transfer conditions on the thermal-microstructural response is particularly assessed in a simple cylindrical casting system. The evolutions of temperature and different microstructural variables are compared and validated with available experimental measurements.

  17. Hybrid models for the simulation of microstructural evolution influenced by coupled, multiple physical processes.

    SciTech Connect

    Tikare, Veena; Hernandez-Rivera, Efrain; Madison, Jonathan D.; Holm, Elizabeth Ann; Patterson, Burton R.; Homer, Eric R.

    2013-09-01

    Most materials microstructural evolution processes progress with multiple processes occurring simultaneously. In this work, we have concentrated on the processes that are active in nuclear materials, in particular, nuclear fuels. These processes are coarsening, nucleation, differential diffusion, phase transformation, radiation-induced defect formation and swelling, often with temperature gradients present. All these couple and contribute to evolution that is unique to nuclear fuels and materials. Hybrid model that combines elements from the Potts Monte Carlo, phase-field models and others have been developed to address these multiple physical processes. These models are described and applied to several processes in this report. An important feature of the models developed are that they are coded as applications within SPPARKS, a Sandiadeveloped framework for simulation at the mesoscale of microstructural evolution processes by kinetic Monte Carlo methods. This makes these codes readily accessible and adaptable for future applications.

  18. Microstructure evolution and mechanical behavior of a high strength dual-phase steel under monotonic loading

    SciTech Connect

    Nesterova, E.V.; Bouvier, S.; Bacroix, B.

    2015-02-15

    Transmission electron microscopy (TEM) microstructures of a high-strength dual-phase steel DP800 have been examined after moderate plastic deformations in simple shear and uniaxial tension. Special attention has been paid to the effect of the intergranular hard phase (martensite) on the microstructure evolution in the near-grain boundary regions. Quantitative parameters of dislocation patterning have been determined and compared with the similar characteristics of previously examined single-phase steels. The dislocation patterning in the interiors of the ferrite grains in DP800 steel is found to be similar to that already observed in the single-phase IF (Interstitial Free) steel whereas the martensite-affected zones present a delay in patterning and display very high gradients of continuous (gradual) disorientations associated with local internal stresses. The above stresses are shown to control the work-hardening of dual-phase materials at moderate strains for monotonic loading and are assumed to influence their microstructure evolution and mechanical behavior under strain-path changes. - Highlights: • The microstructure evolution has been studied by TEM in a DP800 steel. • It is influenced by both martensite and dislocations in the initial state. • The DP800 steel presents a high work-hardening rate due to internal stresses.

  19. Microstructural evolution and trace element mobility in Witwatersrand pyrite

    NASA Astrophysics Data System (ADS)

    Reddy, Steven M.; Hough, Robert M.

    2013-11-01

    Microstructural analysis of pyrite from a single sample of Witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation. Internal deformation associated with dislocation creep is heterogeneously developed within grains, shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the Central Rand conglomerates. In contrast, brittle deformation, manifest by grain fragmentation that transects dislocation-related microstructures, is spatially related to grain contacts and is interpreted to represent post-depositional deformation of the Central Rand conglomerates. Analysis of the low-angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of <010>{100} slip systems. However, some orientation boundaries have geometrical characteristics that are not consistent with simple <010>{100} deformation. These boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized <001>{120} slip system. These boundaries are associated with order of magnitude enrichments in As, Ni and Co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast-diffusion pathways. The results confirm the importance of grain-scale elemental remobilization within pyrite prior to their incorporation into the Witwatersrand gold-bearing conglomerates. Since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite, the results have implications for the application of minor element geochemistry to ore deposit formation, suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for

  20. A hierarchical framework for the multiscale modeling of microstructure evolution in heterogeneous materials.

    SciTech Connect

    Luscher, Darby J.

    2010-04-01

    All materials are heterogeneous at various scales of observation. The influence of material heterogeneity on nonuniform response and microstructure evolution can have profound impact on continuum thermomechanical response at macroscopic “engineering” scales. In many cases, it is necessary to treat this behavior as a multiscale process thus integrating the physical understanding of material behavior at various physical (length and time) scales in order to more accurately predict the thermomechanical response of materials as their microstructure evolves. The intent of the dissertation is to provide a formal framework for multiscale hierarchical homogenization to be used in developing constitutive models.

  1. Modeling of microstructure evolution, residual stresses and distortions in 6082-T6 aluminum weldments

    SciTech Connect

    Myhr, O.R.; Kluken, A.O.; Klokkehaug, S.; Fjaer, H.G.; Grong, O.

    1998-07-01

    This article illustrates the applications of process modeling for prediction of microstructure evolution, residual stresses and distortions in welding of hollow AA6082-T6 extrusions. The model consists of three components, i.e., a numerical heat flow model, a microstructure model and a mechanical model that are sequentially coupled. It is shown that the model adequately predicts the temperature and local strength distribution. The calculated distortions were found to depend strongly on the welding sequence. Moreover, the local softening of the heat-affected zone was shown to have a significant effect on the simulated residual stress distribution.

  2. Microstructurally based model of fatigue initiation and growth

    NASA Technical Reports Server (NTRS)

    Brockenbrough, J. R.; Hinkle, A. J.; Magnusen, P. E.; Bucci, R. J.

    1994-01-01

    A model to calculate fatigue life is developed based on the assumption that fatigue life is entirely composed of crack growth from an initial microstructural inhomogeneity. Specifically, growth is considered to start from either an ellipsoidal void, a cracked particle, or a debonded particle. The capability of predicting fatigue life from material microstructure is based on linear elastic fracture mechanics principles, the sizes of the crack-initiating microstructural inhomogeneities, and an initiation parameter that is proportional to the cyclic plastic zone size. A key aspect of this modeling approach is that it is linked with a general purpose probability program to analyze the effect of the distribution of controlling microstructural features within the material. This enables prediction of fatigue stress versus life curves for various specimen geometries using distributional statistics obtained from characterizations of the microstructure. Results are compared to experimental fatigue data from an aluminum alloy.

  3. Microstructure-based modelling of multiphase materials and complex structures

    NASA Astrophysics Data System (ADS)

    Werner, Ewald; Wesenjak, Robert; Fillafer, Alexander; Meier, Felix; Krempaszky, Christian

    2016-09-01

    Micromechanical approaches are frequently employed to monitor local and global field quantities and their evolution under varying mechanical and/or thermal loading scenarios. In this contribution, an overview on important methods is given that are currently used to gain insight into the deformational and failure behaviour of multiphase materials and complex structures. First, techniques to represent material microstructures are reviewed. It is common to either digitise images of real microstructures or generate virtual 2D or 3D microstructures using automated procedures (e.g. Voronoï tessellation) for grain generation and colouring algorithms for phase assignment. While the former method allows to capture exactly all features of the microstructure at hand with respect to its morphological and topological features, the latter method opens up the possibility for parametric studies with respect to the influence of individual microstructure features on the local and global stress and strain response. Several applications of these approaches are presented, comprising low and high strain behaviour of multiphase steels, failure and fracture behaviour of multiphase materials and the evolution of surface roughening of the aluminium top metallisation of semiconductor devices.

  4. Microstructure evolution during annealing of TiAl/NiCoCrAl multilayer composite prepared by EB-PVD

    SciTech Connect

    Zhang, Rubing; Zhang, Deming; Chen, Guiqing; Wang, Yuesheng

    2014-07-01

    TiAl/NiCoCrAl laminate composite sheet with a thickness of 0.4–0.6 mm as well as a dimension of 150 mm × 100 mm was fabricated successfully by using electron beam physical vapor deposition (EB-PVD) method. The annealing treatment was processed at 1123 and 1323 K for 3 h in a high vacuum atmosphere, respectively. The phase composition and microstructure of TiAl/NiCoCrAl microlaminated sheet have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on the sheet characterization and results of the microstructure evolution during annealing treatment process, the diffusion mechanism of interfacial reaction in TiAl/NiCoCrAl microlaminate was investigated and discussed.

  5. Microstructural evolution of type 304 and 316 stainless steels under neutron irradiation at LWR relevant conditions

    DOE PAGES

    Tan, Lizhen; Stoller, Roger E.; Field, Kevin G.; ...

    2015-12-11

    Extension of light water reactors' useful life will expose austenitic internal core components to irradiation damage levels beyond 100 displacements per atom (dpa), which will lead to profound microstructural evolution and consequent degradation of macroscopic properties. Microstructural evolution, including Frank loops, cavities, precipitates, and segregation at boundaries and the resultant radiation hardening in type 304 and 316 stainless steel (SS) variants, were studied in this work via experimental characterization and multiple simulation methods. Experimental data for up to 40 heats of type 304SS and 316SS variants irradiated in different reactors to 0.6–120 dpa at 275–375°C were either generated from thismore » work or collected from literature reports. These experimental data were then combined with models of Frank loop and cavity evolution, computational thermodynamics and precipitation, and ab initio and rate theory integrated radiation-induced segregation models to provide insights into microstructural evolution and degradation at higher radiation doses.« less

  6. Evolution of microstructure, strain and physical properties in oxide nanocomposite films

    DOE PAGES

    Chen, Aiping; Weigand, Marcus; Bi, Zhenxing; ...

    2014-06-24

    Using LSMO:ZnO nanocomposite films as a model system, we have researched the effect of film thickness on the physical properties of nanocomposites. It shows that strain, microstructure, as well as magnetoresistance strongly rely on film thickness. The magnetotransport properties have been fitted by a modified parallel connection channel model, which is in agreement with the microstructure evolution as a function of film thickness in nanocomposite films on sapphire substrates. The strain analysis indicates that the variation of physical properties in nanocomposite films on LAO is dominated by strain effect. These results confirm the critical role of film thickness on microstructures,more » strain states, and functionalities. Furthermore, it shows that one can use film thickness as a key parameter to design nanocomposites with optimum functionalities.« less

  7. Microstructure Evolution of Biphasic TiNi1+ x Sn Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Verma, Nisha; Douglas, Jason E.; Krämer, Stephan; Pollock, Tresa M.; Seshadri, Ram; Levi, Carlos G.

    2016-08-01

    The effects of thermal treatment on the microstructure of biphasic materials comprising half-Heusler (hH) and full-Heusler (fH) phases, as well as on their associated thermal conductivity, are discussed. The focus of this study was on a biphasic hH/fH alloy of nominal stoichiometry TiNi1.2Sn, synthesized by containerless (magnetic levitation) induction melting. The alloy samples were exposed to various heat treatments to generate microstructures containing second-phase precipitates ranging in size from ~10 nm to a few micrometers. The materials were characterized with regard to morphology, size, shape, and orientation relationship of the fH and hH phases, both of which were present as precipitates within larger regions of the counterpart phase. The solidification path of the alloy and its implications for the subsequent microstructure evolution during heat treatment were elucidated, and relationships with the ensuing thermal conductivity were characterized.

  8. Evolution of microstructure, strain and physical properties in oxide nanocomposite films

    PubMed Central

    Chen, Aiping; Weigand, Marcus; Bi, Zhenxing; Zhang, Wenrui; Lü, Xuejie; Dowden, Paul; MacManus-Driscoll, Judith L.; Wang, Haiyan; Jia, Quanxi

    2014-01-01

    We, using LSMO:ZnO nanocomposite films as a model system, have studied the effect of film thickness on the physical properties of nanocomposites. It shows that strain, microstructure, as well as magnetoresistance strongly rely on film thickness. The magnetotransport properties have been fitted by a modified parallel connection channel model, which is in agreement with the microstructure evolution as a function of film thickness in nanocomposite films on sapphire substrates. The strain analysis indicates that the variation of physical properties in nanocomposite films on LAO is dominated by strain effect. These results confirm the critical role of film thickness on microstructures, strain states, and functionalities. It further shows that one can use film thickness as a key parameter to design nanocomposites with optimum functionalities. PMID:24958206

  9. Evolution of microstructure, strain and physical properties in oxide nanocomposite films

    SciTech Connect

    Chen, Aiping; Weigand, Marcus; Bi, Zhenxing; Zhang, Wenrui; Lü, Xuejie; Dowden, Paul; MacManus-Driscoll, Judith L.; Wang, Haiyan; Jia, Quanxi

    2014-06-24

    Using LSMO:ZnO nanocomposite films as a model system, we have researched the effect of film thickness on the physical properties of nanocomposites. It shows that strain, microstructure, as well as magnetoresistance strongly rely on film thickness. The magnetotransport properties have been fitted by a modified parallel connection channel model, which is in agreement with the microstructure evolution as a function of film thickness in nanocomposite films on sapphire substrates. The strain analysis indicates that the variation of physical properties in nanocomposite films on LAO is dominated by strain effect. These results confirm the critical role of film thickness on microstructures, strain states, and functionalities. Furthermore, it shows that one can use film thickness as a key parameter to design nanocomposites with optimum functionalities.

  10. Investigation of microstructure thermal evolution in nanocrystalline Cu

    NASA Astrophysics Data System (ADS)

    Zhou, Kai; Li, Hui; Pang, JinBiao; Wang, Zhu

    2011-02-01

    The microstructure of nanocrystalline Cu prepared by compacting nanoparticles (50-60 nm in diameter) under high pressures has been studied by means of positron lifetime spectroscopy and X-ray diffraction. These nanoparticles were produced by two different methods. We found that there are order regions interior to the grains and disorder regions at the grain boundaries with a wide distribution of interatomic distances. The mean grain sizes of the nanocrystalline Cu samples decrease after being annealed at 900 °C and increase during aging at 180 °C, which are observed by X-ray diffraction, revealing that the atoms exchange between the two regions. The positron lifetime results clearly indicate that the vacancy clusters formed in the annealing process are unstable and decomposed at the aging time below 6 hours. In addition, the partially oxidized surfaces of the nanoparticles hinder grain growth when the samples age at 180 °C, and the vacancy clusters inside the disorder regions, which are related to Cu 2O, need longer aging time to decompose. The disorder regions remain after the heat treatment in this work, in spite of the grain growth, which will be good for the samples keeping the properties of nanocrystalline material.

  11. Microstructure evolution in Zr under equal channel angular pressing

    NASA Astrophysics Data System (ADS)

    Choi, W. S.; Ryoo, H. S.; Hwang, S. K.; Kim, M. H.; Kwun, S. I.; Chae, S. W.

    2002-03-01

    Pure polycrystalline Zr was deformed by equal channel angular pressing (ECAP), and the microstructural characteristics were analyzed. By repeated alternating ECAP, it was possible to refine the grain size from 200 to 0.2 µm. Subsequent annealing heat treatment at 550 °C resulted in a grain growth of up to 6 µm. Mechanical twinning was an important deformation mechanism, particularly during the early stage of deformation. The most active twinning system was identified as 85.2 deg {10bar 12} tensile twinning, followed by 57.1 deg {10bar 11} compressive twinning. Crystal texture as well as grain-boundary misorientation distribution of deformed Zr were analyzed by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The ECAP-deformed Zr showed a considerable difference in the crystallographic attributes from those of cold-rolled Zr or Ti, in that texture and boundary misorientation-angle distribution tend toward more even distribution with a slightly preferential distribution of boundaries of a 20 to 30 deg misorientation angle. Furthermore, unlike the case of cold rolling, the crystal texture was not greatly altered by subsequent annealing heat treatment. Overall, the present work suggests ECAP as a viable method to obtain significant grain refining in hexagonal close-packed (hcp) metals.

  12. Synthetic Microstructure-Based Lifing of Nickel-Based Superalloys

    NASA Astrophysics Data System (ADS)

    Tucker, Joseph C.

    This work focuses on the root cause of life limiting behavior in Ni-based superalloys for high pressure and temperature turbine disks applications in low cycle fatigue (LCF) by generating statistical volume elements (SVEs) of directly measured 3D microstructures for finite element method (FEM) simulations with crystal plasticity. Synthetic microstructures with experimentally determined microstructurally small fatigue crack (MSFC) weakest link features of as large as (ALA) grains and long annealing twins comprise the test cases. Upper limit truncated log-normal distributions account for the log-normal upper tail departure in grain size distributions of Ni-based superalloys more accurately representing ALA grains. Probability plots quantify the log-normality of grain sizes more effectively than traditional histograms. Twins are inserted into synthetic microstructures according to the coherent Sigma3 orientation relationship. A 3D measured dataset of the Inconel 100 (IN100) validates the Saltykov method stereology technique for estimating 3D grain size distributions from 2D; the 3D grain size distribution mean field and upper tail of IN100 is accurately predicted. The Saltykov method gave 3D grain sizes from a Rene 88 Damage Tolerant (R88DT) 2D dataset resulting in fatigue SVEs of approximately 1.5 million elements and 200 grains from FEM sensitivity studies. Changing mesh resolution minimally impacted global damage response, but converging locally requires significantly higher refinement. Fatigue interrogating FEM studies evolved hot spots in the local MSFC environment in one SVE, but not in another SVE with different crystallographic orientations, suggesting strong 3D full-field neighbor effects. The study revealed a need for slip line length considerations in crystal plasticity to better capture life limiting behavior. The findings point towards strictly limiting the ALA grain size in Ni-based superalloys to extend service life.

  13. Microstructural evolution in nickel alloy C-276 after Ar-ion irradiation at elevated temperature

    SciTech Connect

    Jin, Shuoxue; He, Xinfu; Li, Tiecheng; Ma, Shuli; Tang, Rui; Guo, Liping

    2012-10-15

    In present work, the irradiation damage in nickel-base alloy C-276 irradiated with Ar-ions was studied. Specimens of C-276 alloy were subjected to an irradiation of Ar-ions (with 120 keV) to dose levels of 6 and 10 dpa at 300 and 550 Degree-Sign C, respectively. The size distributions and densities of dislocation loops caused by irradiation were investigated with transmission electron microscopy. Irradiation hardening due to the formation of the loops was calculated using the dispersed barrier-hardening model, showing that irradiation hardening was greatest at 300 Degree-Sign C/6 dpa. The microstructure evolution induced by Ar-ion irradiation (0-10 dpa) in nickel-base alloy C-276 has been studied using a multi-scale modeling code Radieff constructed based on rate theory, and the size of dislocation loops simulated by Radieff was in good agreement with the experiment. - Highlights: Black-Right-Pointing-Pointer High density of dislocation loops appeared after Ar ions irradiation. Black-Right-Pointing-Pointer Irradiation hardening due to the formation of loops was calculated by the DBH model. Black-Right-Pointing-Pointer Size of loops simulated by Radieff was in good agreement with the experiment.

  14. Manupulation of microstructure, phase evolution and mechanical properties by devitrification of andesite for use as proppant

    NASA Astrophysics Data System (ADS)

    Koseski, Ryan P.

    Small, roughly spherical ceramic particles, approximately 1mm in size are used for a number of applications including casting sands, catalysts, and cement fillers. The oil and natural gas industry utilizes such materials in tonnage quantities yearly as extraction aids. Particles intended for this application are referred to as proppants. Proppants are composed of materials that differ by density, strength and cost, and are selected on a site by site basis. Recently, competing usage and depletion of reserves of one of the most popular category of proppant materials, sintered aluminosilicates (e.g. kaolinite, bauxite) have driven the need for alternative raw materials for proppant manufacturing. Andesite, a by-product of mining operations in the south-west United States was identified as an abundant, readily available, and low cost alternative proppant material that can be fused and net-shaped into a glass which when crystallized results in microstructures which may offer substantial toughening and fracture characteristics which may serve to their advantage for use as proppants that do not decrease the permeability ("blind") the particle bed. This study addressed the devitrification behavior and its role on the mechanical properties of andesite-based glass-ceramic spheres for use as proppants. Timetemperature- transformation studies were performed to evaluate the devitrification behavior of andesite glass. Crystalline phase evolution and microstructural development were evaluated using quantitative x-ray diffraction, scanning electron microscopy, differential thermal analysis, and spectrophotometry. The andesite glass devitrification commenced with the precipitation of iron oxides (magnetite) which served as seeds for the epitaxial growth of dendritic pyroxenes. Mechanical properties, such as diametral compressive strength, fracture toughness, hardness, and fracture morphology were correlated with crystalline phase evolution. Selected heat treatments resulting in the

  15. Deformation behavior and microstructure evolution of wrought magnesium alloys

    NASA Astrophysics Data System (ADS)

    Wang, Shouren; Song, Linghui; Kang, Sukbong; Cho, Jaehyung; Wang, Yingzi

    2013-05-01

    There are many researches on the deformation behavior of wrought magnesium alloys, such as AZ31, AZ80, AZ91, and ZK60 magnesium alloys at different temperatures and strain rates, but few of them focuses on the deformation behavior of AZ41M and ZK60M alloys, especially under the twin-roll casting (TRC) state. Meanwhile, the existing researches only focus on the grain refinement law of the magnesium alloys under deformation conditions, the deformation mechanism has not been revealed yet. The hot compression behavior of AZ41M and ZK60M magnesium alloys under the temperature and strain rate ranges of 250-400 °C and 0.001-1 s-1 are studied by thermal simulation methods using Gleeble 1500 machine and virtual simulation using finite element analysis software. Simulation results show that sine hyperbolic law is the most suitable flow stress model for wider deformation conditions. The most reasonable selected deformation conditions of ZK60M alloy is 350 °C/0.1 s-1 for TRC and 350 °C/1 s-1 for conventional casting (CC), while AZ41M alloy is 300 °C/0.01 s-1 for TRC and 350 °C/0.1 s-1 for CC. Deformation behavior and dynamic recrystallization (DRX) mechanism of them are analyzed at the same deformation conditions. The microstructures of AZ41M and ZK60M alloys are observed at different deformed conditions by optical microscopy (OM) and electron back scatter diffraction (EBSD) and it reveals the flow behavior and deformation mechanism of them. Working harden and work soften contribute to the activation of basal, non-basal slip systems which promote DRX. The proposed research reveals the deformation behavior and mechanism of the AZ41M and ZK 60M magnesium alloys and concludes their optimized deformation parameters and processes and provides a theory basis for their manufacturing and application.

  16. Effect of stress evolution on microstructural behavior in U-Mo/Al dispersion fuel

    NASA Astrophysics Data System (ADS)

    Jeong, G. Y.; Kim, Yeon Soo; Jamison, L. M.; Robinson, A. B.; Lee, K. H.; Sohn, Dong-Seong

    2017-04-01

    U-Mo/Al dispersion fuel irradiated to high burnup at high power (high fission rate) exhibited microstructural changes including deformation of the fuel particles, pore growth, and rupture of the Al matrix. The driving force for these microstructural changes was meat swelling resulting from a combination of fuel particle swelling and interaction layer (IL) growth. In some cases, pore growth in the interaction layers also contributed to meat swelling. The main objective of this work was to determine the stress distribution within the fuel meat that caused these phenomena. A mechanical equilibrium between the stress generated by fuel meat swelling and the stress relieved by fission-induced creep in the meat constituents (U-Mo particles, Al matrix, and IL) was considered. Test plates with well-recorded fabrication data and irradiation conditions were used, and their post-irradiation examination (PIE) data was obtained. ABAQUS finite element analysis (FEA) was utilized to simulate the microstructural evolution of the plates. The simulation results allowed for the determination of effective stress and hydrostatic stress exerted on the meat constituents. The effects of fabrication and irradiation parameters on the stress distribution that drives microstructural evolutions, such as pore growth in the IL and Al matrix rupture, were investigated.

  17. Effect of heavy ion irradiation on microstructural evolution in CF8 cast austenitic stainless steel

    DOE PAGES

    Chen, Wei-Ying; Li, Meimei; Kirk, Marquis A.; ...

    2015-08-21

    The microstructural evolution in ferrite and austenitic in cast austenitic stainless steel (CASS) CF8, as received or thermally aged at 400 °C for 10,000 h, was followed under TEM with in situ irradiation of 1 MeV Kr ions at 300 and 350 °C to a fluence of 1.9 × 1015 ions/cm2 (~3 dpa) at the IVEM-Tandem Facility. For the unaged CF8, the irradiation-induced dislocation loops appeared at a much lower dose in the austenite than in the ferrite. At the end dose, the austenite formed a well-developed dislocation network microstructure, while the ferrite exhibited an extended dislocation structure as linemore » segments. Compared to the unaged CF8, the aged specimen appeared to have lower rate of damage accumulation. The rate of microstructural evolution under irradiation in the ferrite was significantly lower in the aged specimen than in the unaged. Finally, we attributed this difference to the different initial microstructures in the unaged and aged specimens, which implies that thermal aging and irradiation are not independent but interconnected damage processes.« less

  18. Effect of heavy ion irradiation on microstructural evolution in CF8 cast austenitic stainless steel

    SciTech Connect

    Chen, Wei-Ying; Li, Meimei; Kirk, Marquis A.; Baldo, Peter M.; Lian, Tiangan

    2015-08-21

    The microstructural evolution in ferrite and austenitic in cast austenitic stainless steel (CASS) CF8, as received or thermally aged at 400 °C for 10,000 h, was followed under TEM with in situ irradiation of 1 MeV Kr ions at 300 and 350 °C to a fluence of 1.9 × 1015 ions/cm2 (~3 dpa) at the IVEM-Tandem Facility. For the unaged CF8, the irradiation-induced dislocation loops appeared at a much lower dose in the austenite than in the ferrite. At the end dose, the austenite formed a well-developed dislocation network microstructure, while the ferrite exhibited an extended dislocation structure as line segments. Compared to the unaged CF8, the aged specimen appeared to have lower rate of damage accumulation. The rate of microstructural evolution under irradiation in the ferrite was significantly lower in the aged specimen than in the unaged. Finally, we attributed this difference to the different initial microstructures in the unaged and aged specimens, which implies that thermal aging and irradiation are not independent but interconnected damage processes.

  19. Microstructural Evolution in Hot and Cold-Rolled Ti-Nb Alloy

    NASA Astrophysics Data System (ADS)

    Tabei, A.; Startt, J.; Hoffman, R. T.; Yavari, E.; Deo, C.; Garmestani, H.

    2016-10-01

    Phase transformations, morphology, and crystallographic texture evolution in hot and cold-rolled Ti-25.51 wt.% Nb alloys are investigated. The experimental procedure involves synthesis of the alloy by arc melting followed by cold or hot rolling with intermediate prior and postheat treatments. Composition and phase analysis of all alloys are conducted using x-ray diffraction techniques and microstructural observations are conducted using an optical microscope. These examinations reveal that the as-melted alloy possesses large millimeter size grains with no stored strain energy and a two phase β - α' microstructure. Direct cold rolling followed by a short homogenization leads to a β - α'' mixture with ω precipitates. Two hour annealing before cold rolling leads to an α' - α'' mixture with a characteristic triangular martensitic microstructure evidencing the act of shear on formation of the phase. Hot rolling followed by a water quench results in a β - α'' mixture, while annealing prior to hot rolling transforms the arc-melted material to a α' - α'' mixture. The crystallographic textures of similar microstructure mixtures in hot and cold-rolled samples are distinctively different. The analysis shows that the microstructure serves as an identifying characteristic of the processing paths and is highly dependent on the mode of processing.

  20. Microstructural Evolution in Hot and Cold-Rolled Ti-Nb Alloy

    NASA Astrophysics Data System (ADS)

    Tabei, A.; Startt, J.; Hoffman, R. T.; Yavari, E.; Deo, C.; Garmestani, H.

    2017-01-01

    Phase transformations, morphology, and crystallographic texture evolution in hot and cold-rolled Ti-25.51 wt.% Nb alloys are investigated. The experimental procedure involves synthesis of the alloy by arc melting followed by cold or hot rolling with intermediate prior and postheat treatments. Composition and phase analysis of all alloys are conducted using x-ray diffraction techniques and microstructural observations are conducted using an optical microscope. These examinations reveal that the as-melted alloy possesses large millimeter size grains with no stored strain energy and a two phase β - α' microstructure. Direct cold rolling followed by a short homogenization leads to a β - α'' mixture with ω precipitates. Two hour annealing before cold rolling leads to an α' - α'' mixture with a characteristic triangular martensitic microstructure evidencing the act of shear on formation of the phase. Hot rolling followed by a water quench results in a β - α'' mixture, while annealing prior to hot rolling transforms the arc-melted material to a α' - α'' mixture. The crystallographic textures of similar microstructure mixtures in hot and cold-rolled samples are distinctively different. The analysis shows that the microstructure serves as an identifying characteristic of the processing paths and is highly dependent on the mode of processing.

  1. Phase field modeling of microstructure evolution and concomitant effective conductivity change in solid oxide fuel cell electrodes

    NASA Astrophysics Data System (ADS)

    Lei, Yinkai; Cheng, Tian-Le; Wen, You-Hai

    2017-03-01

    Microstructure evolution plays an important role in the performance degradation of SOFC electrodes. In this work, we propose a much improved phase field model to simulate the microstructure evolution in the electrodes of solid oxide fuel cell. We demonstrate that the tunability of the interfacial energy in this model has been significantly enhanced. Parameters are set to fit for the interfacial energies of a typical Ni-YSZ anode, an LSM-YSZ cathode and an artificial reference electrode, respectively. The contact angles at various triple junctions and the microstructure evolutions in two dimensions are calibrated to verify the model. As a demonstration of the capabilities of the model, three dimensional microstructure evolutions are simulated applying the model to the three different electrodes. The time evolutions of grain size and triple phase boundary density are analyzed. In addition, a recently proposed bound charge successive approximation algorithm is employed to calculate the effective conductivity of the electrodes during microstructure evolution. The effective conductivity of all electrodes are found to decrease during the microstructure evolution, which is attributed to the increased tortuosity and the loss of percolated volume fraction of the electrode phase.

  2. Microstructural Evolution and Mechanical Properties of Au-20wt.%Sn|Ni Interconnection

    NASA Astrophysics Data System (ADS)

    Dong, H. Q.; Vuorinen, V.; Liu, X. W.; Laurila, T.; Li, J.; Paulasto-Kröckel, M.

    2016-01-01

    In this paper, the microstructural evolution and properties of Au-20wt.%Sn|Ni reaction couples were investigated from two perspectives: (1) by analyzing the microstructure of the as-soldered and aged samples, as well as (2) by measuring the mechanical properties of the intermetallic compounds formed within the reaction zone. The evolution of interfacial reaction products for both the as-soldered and aged interconnections was rationalized by using the experimental results in combination with assessed thermodynamic data from the Au-Ni-Sn system. Moreover, nanoindentation tests were implemented to measure the indentation modulus and hardness of the compounds formed at the interface. It was found that aging had a negligible influence on the elastic modulus and hardness of AuSn and Au5Sn, while the solubility of the third element significantly changed the indentation modulus and hardness of the intermetallic compounds.

  3. Hot Deformation Behavior and Microstructural Evolution of a Medium Carbon Vanadium Microalloyed Steel

    NASA Astrophysics Data System (ADS)

    Cutrim, Rialberth M.; Rodrigues, Samuel F.; Reis, Gedeon S.; Silva, Eden S.; Aranas, Clodualdo; Balancin, Oscar

    2016-11-01

    Hot forging of steel requires application of large strains, under which conditions, dynamic recrystallization (DRX) is expected to take place. In this study, torsion tests were carried out on a medium carbon vanadium microalloyed steel (38MnSiVS5) to simulate hot forging. Deformations were applied isothermally in the temperature range 900-1200 °C at strain rates of 0.1-10 s-1 in order to observe for the occurrence of DRX and to investigate for the microstructural evolution during straining. The shape of the flow curves indicated that the recrystallization takes place during deformation. This was supported by optical microscopy performed on the quenched samples which displayed considerable amounts of recrystallized grains. It was shown that the grain size depends on straining conditions such as strain rate and temperature. Finally, it was revealed that these process parameters can considerably affect the evolution of microstructure of industrial grade steels by means of DRX.

  4. Microstructure Modeling of a Ni-Fe-Based Superalloy During the Rotary Forging Process

    NASA Astrophysics Data System (ADS)

    Loyda, A.; Hernández-Muñoz, G. M.; Reyes, L. A.; Zambrano-Robledo, P.

    2016-06-01

    The microstructure evolution of Ni-Fe superalloys has a great influence on the mechanical behavior during service conditions. The rotary forging process offers an alternative to conventional bulk forming processes where the parts can be rotary forged with a fraction of the force commonly needed by conventional forging techniques. In this investigation, a numerical modeling of microstructure evolution for design and optimization of the hot forging operations has been used to manufacture a heat-resistant nickel-based superalloy. An Avrami model was implemented into finite element commercial platform DEFORM 3D to evaluate the average grain size and recrystallization during the rotary forging process. The simulations were carried out considering three initial temperatures, 980, 1000, and 1050 °C, to obtain the microstructure behavior after rotary forging. The final average grain size of one case was validated by comparing with results of previous experimental work of disk forging operation. This investigation was aimed to explore the influence of the rotary forging process on microstructure evolution in order to obtain a homogenous and refined grain size in the final component.

  5. Powder bed binder jet 3D printing of Inconel 718: Densification, microstructural evolution and challenges

    DOE PAGES

    Nandwana, Peeyush; Elliott, Amy M.; Siddel, Derek; ...

    2017-01-03

    Traditional manufacturing of Inconel 718 components from castings and thermomechanical processing routes involve extensive post processing and machining to attain the desired geometry. Additive manufacturing (AM) technologies including direct energy deposition (DED), selective laser melting (SLM), electron beam melting (EBM) and binder jet 3D printing (BJ3DP) can minimize scrap generation and reduce lead times. While there is extensive literature on the use of melting and solidification based AM technologies, there has been limited research on the use of binder jet 3D printing. In this paper, a brief review on binder jet additive manufacturing of Inconel 718 is presented. In addition,more » existing knowledge on sintering of Inconel 718 has been extended to binder jet 3D printing. We found that supersolidus liquid phase sintering (SLPS) is necessary to achieve full densification of Inconel 718. SLPS is sensitive to the feedstock chemistry that has a strong influence on the liquid volume fraction at the processing temperature. Based on these results, we discuss an empirical framework to determine the role of powder particle size and liquid volume fraction on sintering kinetics. In conclusion, the role of powder packing factor and binder saturation on microstructural evolution is discussed. The current challenges in the use of BJ3DP for fabrication of Inconel 718, as well as, extension to other metal systems, are presented.« less

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

    SciTech Connect

    Hamad, Kotiba; Chung, Bong Kwon; Ko, Young Gun

    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% 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.

  7. A process model for the heat-affected zone microstructure evolution in duplex stainless steel weldments: Part I. the model

    NASA Astrophysics Data System (ADS)

    Hemmer, H.; Grong, Ø.

    1999-11-01

    The present investigation is concerned with modeling of the microstructure evolution in duplex stainless steels under thermal conditions applicable to welding. The important reactions that have been modeled are the dissolution of austenite during heating, subsequent grain growth in the delta ferrite regime, and finally, the decomposition of the delta ferrite to austenite during cooling. As a starting point, a differential formulation of the underlying diffusion problem is presented, based on the internal-state variable approach. These solutions are later manipulated and expressed in terms of the Scheil integral in the cases where the evolution equation is separable or can be made separable by a simple change of variables. The models have then been applied to describe the heat-affected zone microstructure evolution during both thick-plate and thin-plate welding of three commercial duplex stainless steel grades: 2205, 2304, and 2507. The results may conveniently be presented in the form of novel process diagrams, which display contours of constant delta ferrite grain size along with information about dissolution and reprecipitation of austenite for different combinations of weld input energy and peak temperature. These diagrams are well suited for quantitative readings and illustrate, in a condensed manner, the competition between the different variables that lead to structural changes during welding of duplex stainless steels.

  8. 3D microstructure modeling of compressed fiber-based materials

    NASA Astrophysics Data System (ADS)

    Gaiselmann, Gerd; Tötzke, Christian; Manke, Ingo; Lehnert, Werner; Schmidt, Volker

    2014-07-01

    A novel parametrized model that describes the 3D microstructure of compressed fiber-based materials is introduced. It allows to virtually generate the microstructure of realistically compressed gas-diffusion layers (GDL). Given the input of a 3D microstructure of some fiber-based material, the model compresses the system of fibers in a uniaxial direction for arbitrary compression rates. The basic idea is to translate the fibers in the direction of compression according to a vector field which depends on the rate of compression and on the locations of fibers within the material. In order to apply the model to experimental 3D image data of fiber-based materials given for several compression states, an optimal vector field is estimated by simulated annealing. The model is applied to 3D image data of non-woven GDL in PEMFC gained by synchrotron tomography for different compression rates. The compression model is validated by comparing structural characteristics computed for experimentally compressed and virtually compressed microstructures, where two kinds of compression - using a flat stamp and a stamp with a flow-field profile - are applied. For both stamps types, a good agreement is found. Furthermore, the compression model is combined with a stochastic 3D microstructure model for uncompressed fiber-based materials. This allows to efficiently generate compressed fiber-based microstructures in arbitrary volumes.

  9. Microstructure and Property Evolution in Advanced Cladding and Duct Materials Under Long-Term and Elevated Temperature Irradiation: Modeling and Experimental Investigation

    SciTech Connect

    Wirth, Brian; Morgan, Dane; Kaoumi, Djamel; Motta, Arthur

    2013-12-01

    irradiation. This project will focus on modeling microstructural and microchemical evolution of irradiated alloys by performing detailed modeling of such microstructure evolution processes coupled with well-designed in situ experiments that can provide validation and benchmarking to the computer codes. The broad scientific and technical objectives of this proposal are to evaluate the microstructure and microchemical evolution in advanced ferritic/martensitic and oxide dispersion strengthened (ODS) alloys for cladding and duct reactor materials under long-term and elevated temperature irradiation, leading to improved ability to model structural materials performance and lifetime. Specifically, we propose four research thrusts, namely Thrust 1: Identify the formation mechanism and evolution for dislocation loops with Burgers vector of a<100> and determine whether the defect microstructure (predominately dislocation loop/dislocation density) saturates at high dose. Thrust 2: Identify whether a threshold irradiation temperature or dose exists for the nucleation of growing voids that mark the beginning of irradiation-induced swelling, and begin to probe the limits of thermal stability of the tempered Martensitic structure under irradiation. Thrust 3: Evaluate the stability of nanometer sized Y- Ti-O based oxide dispersion strengthened (ODS) particles at high fluence/temperature. Thrust 4: Evaluate the extent to which precipitates form and/or dissolve as a function of irradiation temperature and dose, and how these changes are driven by radiation induced segregation and microchemical evolutions and determined by the initial microstructure.

  10. Effect of Gold on the Microstructural Evolution and Integrity of a Sintered Silver Joint

    NASA Astrophysics Data System (ADS)

    Muralidharan, Govindarajan; Leonard, Donovan N.; Meyer, Harry M.

    2017-01-01

    There is a need for next-generation, high-performance power electronic packages and systems employing wide-bandgap devices to operate at high temperatures in automotive and electric grid applications. Sintered silver joints are currently being evaluated as an alternative to Pb-free solder joints. Of particular interest is the development of joints based on silver paste consisting of nano- or micron-scale particles that can be processed without application of external pressure. The microstructural evolution at the interface of a pressureless-sintered silver joint formed between a SiC die with Ti/Ni/Au metallization and an active metal brazed (AMB) substrate with Ag metallization at 250°C has been evaluated using scanning electron microscopy (SEM), x-ray microanalysis, and x-ray photoelectron spectroscopy (XPS). Results from focused ion beam (FIB) cross-sections show that, during sintering, pores in the sintered region near to the Au layer tend to be narrow and elongated with long axis oriented parallel to the interface. Further densification results in formation of many small, relatively equiaxed pores aligned parallel to the interface, creating a path for easy crack propagation. X-ray microanalysis results confirm interdiffusion between Au and Ag and that a region with poor mechanical strength is formed at the edge of this region of interdiffusion.

  11. Mechanical Properties and Microstructural Evolution of Simulated Heat-Affected Zones in Wrought Eglin Steel

    NASA Astrophysics Data System (ADS)

    Leister, Brett M.; DuPont, John N.; Watanabe, Masashi; Abrahams, Rachel A.

    2015-12-01

    A comprehensive study was performed to correlate the mechanical properties and microstructural evolution in the heat-affected zone of Eglin steel. A Gleeble 3500 thermo-mechanical simulator was used to simulate weld thermal cycles with different peak temperatures at a heat input of 1500 J/mm. These samples underwent mechanical testing to determine strength and toughness in the as-welded and post-weld heat-treated conditions. The inter-critical heat-affected zone (HAZ) had the lowest strength following thermal simulation, while the fine-grain and coarse-grain heat-affected zone exhibited increased strength when compared to the inter-critical HAZ. The toughness of the heat-affected zone in the as-simulated condition is lower than that of the base metal in all regions of the HAZ. Post-weld heat treatments (PWHTs) increased the toughness of the HAZ, but at the expense of strength. In addition, certain combinations of PWHTs within specific HAZ regions exhibited low toughness caused by tempered martensite embrittlement or intergranular failure. Synchrotron X-ray diffraction data have shown that Eglin steel has retained austenite in the fine-grain HAZ in the as-simulated condition. In addition, alloy carbides (M23C6, M2C, M7C3) have been observed in the diffraction spectra for the fine-grain and coarse-grain HAZ following a PWHT of 973 K (700 °C)/4 hours.

  12. Microstructural evolution of a uranium-10 wt.% molybdenum alloy for nuclear reactor fuels

    NASA Astrophysics Data System (ADS)

    Clarke, A. J.; Clarke, K. D.; McCabe, R. J.; Necker, C. T.; Papin, P. A.; Field, R. D.; Kelly, A. M.; Tucker, T. J.; Forsyth, R. T.; Dickerson, P. O.; Foley, J. C.; Swenson, H.; Aikin, R. M.; Dombrowski, D. E.

    2015-10-01

    Low-enriched uranium-10 wt.% molybdenum (LEU-10wt.%Mo) is of interest for the fabrication of monolithic fuels to replace highly-enriched uranium (HEU) dispersion fuels in high performance research and test reactors around the world. In this work, depleted uranium-10 wt.%Mo (DU-10wt.%Mo) is used to simulate the solidification and microstructural evolution of LEU-10wt.%Mo. Electron backscatter diffraction (EBSD) and complementary electron probe microanalysis (EPMA) reveal significant microsegregation present in the metastable γ-phase after solidification. Homogenization is performed at 800 and 1000 °C for times ranging from 1 to 32 h to explore the time-temperature combinations that will reduce the extent of microsegregation, as regions of higher and lower Mo content may influence local mechanical properties and provide preferred regions for γ-phase decomposition. We show for the first time that EBSD can be used to qualitatively assess microstructural evolution in DU-10wt.%Mo after homogenization treatments. Complementary EPMA is used to quantitatively confirm this finding. Homogenization at 1000 °C for 2-4 h may the regions that contain 8 wt.% Mo or lower, whereas homogenization at 1000 °C for longer than 8 h effectively saturates Mo chemical homogeneity, but results in substantial grain growth. The appropriate homogenization time will depend upon additional microstructural considerations, such as grain growth and intended subsequent processing. Higher carbon LEU-10wt.%Mo generally contains more inclusions within the grains and at grain boundaries after solidification. The effect of these inclusions on microstructural evolution (e.g. grain growth) during homogenization and as potential γ-phase decomposition nucleation sites is unclear, but likely requires additional study.

  13. Incorporating physically-based microstructures in materials modeling: Bridging phase field and crystal plasticity frameworks

    DOE PAGES

    Lim, Hojun; Abdeljawad, Fadi; Owen, Steven J.; ...

    2016-04-25

    Here, the mechanical properties of materials systems are highly influenced by various features at the microstructural level. The ability to capture these heterogeneities and incorporate them into continuum-scale frameworks of the deformation behavior is considered a key step in the development of complex non-local models of failure. In this study, we present a modeling framework that incorporates physically-based realizations of polycrystalline aggregates from a phase field (PF) model into a crystal plasticity finite element (CP-FE) framework. Simulated annealing via the PF model yields ensembles of materials microstructures with various grain sizes and shapes. With the aid of a novel FEmore » meshing technique, FE discretizations of these microstructures are generated, where several key features, such as conformity to interfaces, and triple junction angles, are preserved. The discretizations are then used in the CP-FE framework to simulate the mechanical response of polycrystalline α-iron. It is shown that the conformal discretization across interfaces reduces artificial stress localization commonly observed in non-conformal FE discretizations. The work presented herein is a first step towards incorporating physically-based microstructures in lieu of the overly simplified representations that are commonly used. In broader terms, the proposed framework provides future avenues to explore bridging models of materials processes, e.g. additive manufacturing and microstructure evolution of multi-phase multi-component systems, into continuum-scale frameworks of the mechanical properties.« less

  14. Incorporating physically-based microstructures in materials modeling: Bridging phase field and crystal plasticity frameworks

    SciTech Connect

    Lim, Hojun; Abdeljawad, Fadi; Owen, Steven J.; Hanks, Byron W.; Foulk, James W.; Battaile, Corbett C.

    2016-04-25

    Here, the mechanical properties of materials systems are highly influenced by various features at the microstructural level. The ability to capture these heterogeneities and incorporate them into continuum-scale frameworks of the deformation behavior is considered a key step in the development of complex non-local models of failure. In this study, we present a modeling framework that incorporates physically-based realizations of polycrystalline aggregates from a phase field (PF) model into a crystal plasticity finite element (CP-FE) framework. Simulated annealing via the PF model yields ensembles of materials microstructures with various grain sizes and shapes. With the aid of a novel FE meshing technique, FE discretizations of these microstructures are generated, where several key features, such as conformity to interfaces, and triple junction angles, are preserved. The discretizations are then used in the CP-FE framework to simulate the mechanical response of polycrystalline α-iron. It is shown that the conformal discretization across interfaces reduces artificial stress localization commonly observed in non-conformal FE discretizations. The work presented herein is a first step towards incorporating physically-based microstructures in lieu of the overly simplified representations that are commonly used. In broader terms, the proposed framework provides future avenues to explore bridging models of materials processes, e.g. additive manufacturing and microstructure evolution of multi-phase multi-component systems, into continuum-scale frameworks of the mechanical properties.

  15. Dielectric Characteristics of Microstructural Changes and Property Evolution in Engineered Materials

    NASA Astrophysics Data System (ADS)

    Clifford, Jallisa Janet

    Heterogeneous materials are increasingly used in a wide range of applications such as aerospace, civil infrastructure, fuel cells and many others. The ability to take properties from two or more materials to create a material with properties engineered to needs is always very attractive. Hence heterogeneous materials are evolving into more complex formulations in multiple disciplines. Design of microstructure at multiple scales control the global functional properties of these materials and their structures. However, local microstructural changes do not directly cause a proportional change to the global properties (such as strength and stiffness). Instead, local changes follow an evolution process including significant interactions. Therefore, in order to understand property evolution of engineered materials, microstructural changes need to be effectively captured. Characterizing these changes and representing them by material variables will enable us to further improve our material level understanding. In this work, we will demonstrate how microstructural features of heterogeneous materials can be described quantitatively using broadband dielectric spectroscopy (BbDS). The frequency dependent dielectric properties can capture the change in material microstructure and represent these changes in terms of material variables, such as complex permittivity. These changes in terms of material properties can then be linked to a number of different conditions, such as increasing damage due to impact or fatigue. Two different broadband dielectric spectroscopy scanning modes are presented: bulk measurements and continuous scanning to measure dielectric property change as a function of position across the specimen. In this study, we will focus on ceramic materials and fiber reinforced polymer matrix composites as test bed material systems. In the first part of the thesis, we will present how different micro-structural design of porous ceramic materials can be captured

  16. Microstructural evolution of ferritic-martensitic steels under heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Topbasi, Cem

    Ferritic-martensitic steels are primary candidate materials for fuel cladding and internal applications in the Sodium Fast Reactor, as well as first-wall and blanket materials in future fusion concepts because of their favorable mechanical properties and resistance to radiation damage. Since microstructure evolution under irradiation is amongst the key issues for these materials in these applications, developing a fundamental understanding of the irradiation-induced microstructure in these alloys is crucial in modeling and designing new alloys with improved properties. The goal of this project was to investigate the evolution of microstructure of two commercial ferritic-martensitic steels, NF616 and HCM12A, under heavy ion irradiation at a broad temperature range. An in situ heavy ion irradiation technique was used to create irradiation damage in the alloy; while it was being examined in a transmission electron microscope. Electron-transparent samples of NF616 and HCM12A were irradiated in situ at the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory with 1 MeV Kr ions to ˜10 dpa at temperatures ranging from 20 to 773 K. The microstructure evolution of NF616 and HCM12A was followed in situ by systematically recording micrographs and diffraction patterns as well as capturing videos during irradiation. In these irradiations, there was a period during which no changes are visible in the microstructure. After a threshold dose (˜0.1 dpa between 20 and 573 K, and ˜2.5 dpa at 673 K) black dots started to become visible under the ion beam. These black dots appeared suddenly (from one frame to the next) and are thought to be small defect clusters (2-5 nm in diameter), possibly small dislocation loops with Burgers vectors of either ½ or . The overall density of these defect clusters increased with dose and saturated around 6 dpa. At saturation, a steady-state is reached in which defects are eliminated and created at the same rates so that the

  17. Microstructural evolution of viscoelastic emulsions stabilised by sodium caseinate and xanthan gum.

    PubMed

    Moschakis, Thomas; Murray, Brent S; Dickinson, Eric

    2005-04-15

    The time-dependent evolution of the phase-separated microstructure of a caseinate-stabilised emulsion containing xanthan gum added before emulsification has been investigated by confocal laser scanning microscopy, image analysis and rheology. Moderately low levels of xanthan addition lead to depletion flocculation and gravity-induced phase separation. Increasing the polysaccharide concentration causes immobilisation of the microstructure due to an increase in the local viscoelasticity: that is, the emulsion structure cannot easily rearrange to expel xanthan-enriched aqueous serum phase because a weak gel-like network is generated. The effect of xanthan on the evolving microstructure of phase-separated regions, which reflects indirectly the local emulsion micro-rheology, has been estimated from image analysis of time sequences of confocal micrographs. A comparison has been made between object shape analysis using four different shape descriptors. The roundness parameter has been found to be a convenient descriptor for reliably quantifying the structural change in terms of the relaxation rate of xanthan-rich aqueous drops. The Taylor parameter has been used to link the kinetics of drop relaxation to the time-dependent small-deformation rheological behaviour. The analysis of the combined experimental data reveals the difficulty of relating the evolving microstructure to bulk rheological measurements.

  18. Microstructural evolution during ultra-rapid annealing of severely deformed low-carbon steel: strain, temperature, and heating rate effects

    NASA Astrophysics Data System (ADS)

    Mostafaei, M. A.; Kazeminezhad, M.

    2016-07-01

    An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200-1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.

  19. Microstructure evolution during helium irradiation and post-irradiation annealing in a nanostructured reduced activation steel

    NASA Astrophysics Data System (ADS)

    Liu, W. B.; Ji, Y. Z.; Tan, P. K.; Zhang, C.; He, C. H.; Yang, Z. G.

    2016-10-01

    Severe plastic deformation, intense single-beam He-ion irradiation and post-irradiation annealing were performed on a nanostructured reduced activation ferritic/martensitic (RAFM) steel to investigate the effect of grain boundaries (GBs) on its microstructure evolution during these processes. A surface layer with a depth-dependent nanocrystalline (NC) microstructure was prepared in the RAFM steel using surface mechanical attrition treatment (SMAT). Microstructure evolution after helium (He) irradiation (24.8 dpa) at room temperature and after post-irradiation annealing was investigated using Transmission Electron Microscopy (TEM). Experimental observation shows that GBs play an important role during both the irradiation and the post-irradiation annealing process. He bubbles are preferentially trapped at GBs/interfaces during irradiation and cavities with large sizes are also preferentially trapped at GBs/interfaces during post-irradiation annealing, but void denuded zones (VDZs) near GBs could not be unambiguously observed. Compared with cavities at GBs and within larger grains, cavities with smaller size and higher density are found in smaller grains. The average size of cavities increases rapidly with the increase of time during post-irradiation annealing at 823 K. Cavities with a large size are observed just after annealing for 5 min, although many of the cavities with small sizes also exist after annealing for 240 min. The potential mechanism of cavity growth behavior during post-irradiation annealing is also discussed.

  20. Microstructural evolution in Mg-Zn alloys during solidification: An experimental and simulation study

    NASA Astrophysics Data System (ADS)

    Paliwal, Manas; Jung, In-Ho

    2014-05-01

    A comprehensive microstructural evolution of Mg-1.5, 4.0 and 5.5 wt% Zn alloys with respect to the solidification parameters such as thermal gradient (G), solidification velocity (V), cooling rate (GV) and solute (Zn) content were investigated in the present study. Solidification techniques such as directional solidification and wedge casting were employed in order to obtain cooling rates between 0.05 and 250 K/s. Microstructural features such as secondary dendrite arm spacing (SDAS), primary dendrite arm spacing (PDAS), microsegregration along the secondary dendrites and secondary phase fractions were experimentally determined. A solidification model that incorporates solute back diffusion, secondary arm coarsening, dendrite tip undercooling and dynamically linked with accurate thermodynamic databases is used to explain the experimental results.

  1. Microstructural evolution of Al-Cu thin-film conducting lines during post-pattern annealing

    SciTech Connect

    Kang, S.H.; Morris, J.W. , Jr. |

    1997-07-01

    This work reports a statistical analysis of the evolution of polygranular segment lengths during high-temperature annealing of Al(Cu) thin-film interconnects with quasi-bamboo microstructures. To create samples of Al(Cu) lines that could be imaged by transmission electron microscopy without breaking or thinning, the lines were deposited on electron-transparent silicon nitride films (the {open_quotes}silicon nitride window{close_quotes} technique). The microstructures of the lines were studied as a function of annealing time and temperature. In particular, the distribution of polygranular segment lengths was measured. The results show that the longer polyglranular segments are preferentially eliminated during post-pattern annealing. As a consequence, the segment-length distribution narrows monotonically during annealing, and changes in shape. The preferential loss of the longest polygranular segments leads to a dramatic increase in resistance to electromigration failure.

  2. TRXRD observations of microstructural evolution in self-shielded flux cored arc weld deposits

    SciTech Connect

    Babu, S S; Elmer, J W; David, S A; Quintana, M

    2000-06-28

    Inclusion formation and microstructure development in self-shielded flux cored arc welds has been investigated before [1,2]. Results showed that the liquid metal reactions could promote either Al{sub 2}O{sub 3} or AlN formation depending upon the aluminum concentration in the weld metal. The residual aluminum that remained in solution was found to modify the solidification behavior of liquid to {delta}-ferrite and subsequent transformation of {delta}-ferrite to austenite during weld cooling. In this work, the microstructure evolution in the heat-affected-zone (HAZ) of self-shielded flux cored arc weld (FCAW-S) overlays were investigated using in-situ Time-Resolved X-ray Diffraction (TRXRD) with a high flux Synchrotron radiation beam [3, 4].

  3. Microstructure evolution in solution treated Ti15Mo alloy processed by high pressure torsion

    SciTech Connect

    Janeček, Miloš; Čížek, Jakub; Stráský, Josef; Václavová, Kristína; Hruška, Petr; Polyakova, Veronika; Gatina, Svetlana; Semenova, Irina

    2014-12-15

    Microstructure evolution and mechanical properties of ultra-fine grained Ti15Mo alloy processed by high pressure torsion were investigated. High pressure torsion straining resulted in strong grain refinement as-observed by transmission electron microscopy. Microhardness and light microscopy showed two distinct regions — (i) a central region with radial material flow and low microhardness (340 HV) and (ii) a peripheral region with rotational material flow and high microhardness (430 HV). Positron annihilation spectroscopy showed that the only detectable defects in the material are dislocations, whose density increases with the radial distance and the number of high pressure torsion revolutions. The local chemical environment around defects does not differ significantly from the average composition. - Highlights: • Beta-Ti alloy Ti15Mo was processed by high pressure torsion (HPT). • Lateral inhomogeneity of the microstructure and microhardness was found. • Dislocations are the only lattice defects detectable by positron annihilation. • Molybdenum is not preferentially segregated along dislocation cores.

  4. Microstructural evolution of a recycled aluminum alloy deformed by equal channel angular pressing process

    NASA Astrophysics Data System (ADS)

    Makhlouf, Thabet; Rebhi, Atef; Couzinié, Jean-Philippe; Champion, Yannick; Njah, Nabil

    2012-11-01

    The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing (ECAP) up to four passes was investigated using X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation (SPD) through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs obtained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.

  5. Linking stress-driven microstructural evolution in nanocrystalline aluminium with grain boundary doping of oxygen.

    PubMed

    He, Mo-Rigen; Samudrala, Saritha K; Kim, Gyuseok; Felfer, Peter J; Breen, Andrew J; Cairney, Julie M; Gianola, Daniel S

    2016-04-13

    The large fraction of material residing at grain boundaries in nanocrystalline metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution is still poorly understood and precludes rational alloy design. Here we combine quantitative in situ electron microscopy with three-dimensional atom-probe tomography to directly link the mechanics and kinetics of grain boundary migration in nanocrystalline Al films with the excess of O atoms at the boundaries. Site-specific nanoindentation leads to grain growth that is retarded by impurities, and enables quantification of the critical stress for the onset of grain boundary migration. Our results show that a critical excess of impurities is required to stabilize interfaces in nanocrystalline materials against mechanical driving forces, providing new insights to guide control of deformation mechanisms and tailoring of mechanical properties apart from grain size alone.

  6. Linking stress-driven microstructural evolution in nanocrystalline aluminium with grain boundary doping of oxygen

    PubMed Central

    He, Mo-Rigen; Samudrala, Saritha K.; Kim, Gyuseok; Felfer, Peter J.; Breen, Andrew J.; Cairney, Julie M.; Gianola, Daniel S.

    2016-01-01

    The large fraction of material residing at grain boundaries in nanocrystalline metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution is still poorly understood and precludes rational alloy design. Here we combine quantitative in situ electron microscopy with three-dimensional atom-probe tomography to directly link the mechanics and kinetics of grain boundary migration in nanocrystalline Al films with the excess of O atoms at the boundaries. Site-specific nanoindentation leads to grain growth that is retarded by impurities, and enables quantification of the critical stress for the onset of grain boundary migration. Our results show that a critical excess of impurities is required to stabilize interfaces in nanocrystalline materials against mechanical driving forces, providing new insights to guide control of deformation mechanisms and tailoring of mechanical properties apart from grain size alone. PMID:27071458

  7. The co-evolution of microstructure features in self-ion irradiated HT9 at very high damage levels

    NASA Astrophysics Data System (ADS)

    Getto, E.; Vancoevering, G.; Was, G. S.

    2017-02-01

    Understanding the void swelling and phase evolution of reactor structural materials at very high damage levels is essential to maintaining safety and longevity of components in Gen IV fast reactors. A combination of ion irradiation and modeling was utilized to understand the microstructure evolution of ferritic-martensitic alloy HT9 at high dpa. Self-ion irradiation experiments were performed on alloy HT9 to determine the co-evolution of voids, dislocations and precipitates up to 650 dpa at 460 °C. Modeling of microstructure evolution was conducted using the modified Radiation Induced Microstructure Evolution (RIME) model, which utilizes a mean field rate theory approach with grouped cluster dynamics. Irradiations were performed with 5 MeV raster-scanned Fe2+ ions on samples pre-implanted with 10 atom parts per million He. The swelling, dislocation and precipitate evolution at very high dpa was determined using Analytical Electron Microscopy in Scanning Transmission Electron Microscopy (STEM) mode. Experimental results were then interpreted using the RIME model. A microstructure consisting only of dislocations and voids is insufficient to account for the swelling evolution observed experimentally at high damage levels in a complicated microstructure such as irradiated alloy HT9. G phase was found to have a minimal effect on either void or dislocation evolution. M2X played two roles; a variable biased sink for defects, and as a vehicle for removal of carbon from solution, thus promoting void growth. When accounting for all microstructure interactions, swelling at high damage levels is a dynamic process that continues to respond to other changes in the microstructure as long as they occur. effect of dislocations on voids, effect of precipitates on dislocations and voids and combined effect of dislocations and precipitates on voids. The overall approach will be to examine a simple system of voids and dislocations and then incorporate the more complex treatments of

  8. Modeling the Microstructure Evolution During Additive Manufacturing of Ti6Al4V: A Comparison Between Electron Beam Melting and Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Vastola, G.; Zhang, G.; Pei, Q. X.; Zhang, Y.-W.

    2016-05-01

    Beam-based additive manufacturing (AM) is an innovative technique in which parts are built layerwise, starting from the material in powder form. As a developing manufacturing technique, achievement of excellent mechanical properties in the final part is of paramount importance for the mainstream adoption of this technique in industrial manufacturing lines. At the same time, AM offers an unprecedented opportunity to precisely control the manufacturing conditions locally within the part during build, enabling local influence on the formation of the texture and microstructure. In order to achieve the control of microstructure by tailoring the AM machine parameters, a full understanding and modeling of the heat transfer and microstructure evolution processes is needed. Here, we show the implementation of the non-equilibrium equations for phase formation and dissolution in an AM modeling framework. The model is developed for the Ti6Al4V alloy and allows us to show microstructure evolution as given by the AM process. The developed capability is applied to the cases of electron beam melting and selective laser melting AM techniques to explain the significantly different microstructures observed in the two processes.

  9. Effect of alloying on microstructure and precipitate evolution in ferritic weld metal

    NASA Astrophysics Data System (ADS)

    Narayanan, Badri Kannan

    The effect of alloying on the microstructure of ferritic weld metal produced with an self-shielded flux cored arc welding process (FCAW-S) has been studied. The welding electrode has a flux core that is intentionally alloyed with strong deoxidizers and denitriding elements such as aluminum, titanium and zirconium in addition to austenite formers such as manganese and nickel. This results in formation of microstructure consisting of carbide free bainite, retained austenite and twinned martensite. The work focuses on characterization of the microstructures and the precipitates formed during solidification and the allotropic phase transformation of the weld metal. Aluminum, manganese and nickel have significant solubility in iron while aluminum, titanium and zirconium have very strong affinity for nitrogen and oxygen. The effect of these alloying elements on the phase transformation and precipitation of oxides and nitrides have been studied with various characterization techniques. In-situ X-ray synchrotron diffraction has been used to characterize the solidification path and the effect of heating and cooling rates on microstructure evolution. Scanning Transmission Electron Microscopy (STEM) in conjunction with Energy Dispersive Spectroscopy (EDS) and Electron energy loss spectroscopy (EELS) was used to study the effect of micro-alloying additions on inclusion evolution. The formation of core-shell structure of oxide/nitride is identified as being key to improvement in toughness of the weld metal. Electron Back Scattered Diffraction (EBSD) in combination with Orientation Imaging Microscopy (OIM) and Transmission electron microscopy (TEM) has been employed to study the effect of alloying on austenite to ferrite transformation modes. The prevention of twinned martensite has been identified to be key to improving ductility for achieving high strength weld metal.

  10. Microstructural evolution from stable sliding to fast stick slip: insights from rock deformation experiments on quartz

    NASA Astrophysics Data System (ADS)

    Collettini, Cristiano; Scuderi, Marco M.; Viti, Cecilia; Marone, Chris

    2016-04-01

    Inferring microstructural evolution and associated fault slip behaviour along natural and/or experimental faults is a long-standing problem in fault mechanics. For example, does grain-size reduction and shear localization facilitate earthquake slip or vice versa? We have sheared granular layers of quartz gouge in a double direct shear configuration using a biaxial apparatus. We varied loading stiffness and applied normal stresses to produce a spectrum of slip modes from stable sliding at 10 μm/s, slow stick-slip (average slip velocity 100 μm/s) and fast stick slip (average slip velocity 4 mm/s). At the end of the experiments we collected the experimental fault rocks for microstructural investigations. Additional samples were collected from control experiments to investigate shear fabric development and microstructural features before the onset of stick-slip instabilities. We investigated the role of normal stress and stick-slip properties, including slip velocity, in determining fault zone microstructural features. Ranging from stable sliding to fast stick-slip we observe a progressive localization of deformation along fault parallel boundary shear planes. Only during fast stick-slip is the deformation localized along continuous, thin (1-2 microns wide), boundary parallel shear planes. The shear zones are composed of nanograins dispersed within a patchy matrix. We conducted TEM analyses to characterize these materials. In experiments at the same normal stress, fast stick-slip results in localized shear zones and fabric with nanograins whereas for stable sliding the microstructure does not show a significant grain size reduction and localization. Our results indicate that the fault rheological properties and fault slip behaviour, ranging from stable to unstable slip, plays a significant role in shear localization and fault zone fabric development.

  11. First direct 3D visualisation of microstructural evolutions during sintering through X-ray computed microtomography

    SciTech Connect

    Bernard, Dominique . E-mail: bernard@icmcb.u-bordeaux.fr; Gendron, Damien; Heintz, Jean-Marc; Bordere, Sylvie; Etourneau, Jean

    2005-01-03

    X-ray computed microtomography (XCMT) has been applied to ceramic samples of different materials to visualise, for the first time at this scale, real 3D microstructural evolutions during sintering. Using this technique, it has been possible to follow the whole sintering process of the same grains set. Two materials have been studied; a glass powder heat treated at 700 deg. C and a crystallised lithium borate (Li{sub 6}Gd(BO{sub 3}){sub 3}) powder heat treated at 720 deg. C. XCMT measurements have been done after different sintering times. For each material, a sub-volume was individualised and localised on the successive recordings and its 3D images numerically reconstructed. Description of the three-dimensional microstructures evolution is proposed. From the 3D experimental data, quantitative evolutions of parameters such as porosity and neck size are presented for the glass sample. Possibilities offered by this technique to study complex sintering processes, as for lithium borate, are illustrated.

  12. Investigation on microstructural evolution and hardening mechanism in dilute Zrsbnd Nb binary alloys

    NASA Astrophysics Data System (ADS)

    Yang, H. L.; Matsukawa, Y.; Kano, S.; Duan, Z. G.; Murakami, K.; Abe, H.

    2016-12-01

    In this study, the microstructural changes induced by doping of Nb in Zr were investigated by the combined utilization of electron backscatter diffraction and electron transmission microscopy techniques, followed by the correlated hardening mechanism being elucidated based on the obtained microstructural parameters. Microstructural characterization results revealed that microstructural changes caused by doping of Nb in Zr were mainly embodied via two aspects: reducing the matrix α-Zr grain size and increasing the amount of β-Nb particles. β-phase stabilizing effect, dragging effect and pinning effect introduced and enhanced by Nb addition, worked together to significantly reduce the grain size in Zr-Nb alloys. β-Nb particles were firstly observed in Zr0.5Nb specimen with the fairly low number density of ∼2.0 × 1018/m3, then this value explosively increased to ∼3.3 × 1020/m3 for Zr2Nb specimen. In addition, hardness was increased with an increase in the Nb content. The hardening contributions from solid solution hardening, grain boundary hardening and precipitation hardening were quantitatively estimated as per the obtained microstructural parameters. Results inferred that solid solution hardening contributed the majority when the Nb atoms were solid dissolved (≤0.5 wt%), whereas the precipitation hardening surpassed any other factors when the β-Nb particles were steadily precipitated (≥1 wt%).

  13. Effect of Process Parameters on Microstructural Evolution, Mechanical Properties and Corrosion Behavior of Friction Stir Processed Al 7075 Alloy

    NASA Astrophysics Data System (ADS)

    Kumar, Atul; Sharma, Sandan Kumar; Pal, Kaushik; Mula, Suhrit

    2017-02-01

    Aim of the present study is to investigate the effect of process parameters on microstructural evolution, mechanical properties and corrosion behavior of an age-hardenable Al 7075 alloy. The alloy plates (6 mm thickness) were friction stir processed (FSPed) at various traverse speed, namely 25, 45, 65, 85, 100 and 150 mm/min at 2 different rpm of 508 and 720. The optimized result in terms of defect-free processed zone with refined microstructure was obtained only at a rotational speed of 720 rpm for a traverse speed of 25, 45, 65 and 85 mm/min. The microstructural evolution was investigated using optical, scanning and transmission electron microscopy. The grain size of the nugget zone was found to decrease with increase in the traverse speed from 25 to 85 mm/min at a constant rpm of 720. The mechanical properties were evaluated by Vickers hardness measurements, tensile and wear testing. Yield strength was found to be the maximum ( 366 MPa) for the FSPed sample processed at 85 mm/min. The hardness values also followed the similar increasing trend with increase in the traverse speed. The wear volume loss decreased by 38% for the sample processed at a traverse speed of 85 mm/min as compared to that of the sample processed at 25 mm/min. The friction coefficient was found to substantiate well with the wear track morphology. The improvement in mechanical properties is ascertained to the refinement of grain size at higher traverse speed (due to less heat input). The FSPed samples showed inferior corrosion resistance in contrast to that of the base metal. This is possibly due to the coarsening of precipitates and depletion of solutes in the matrix. The morphology of the corroded samples corroborated well with the corrosion behavior of the corresponding specimen.

  14. Effect of Process Parameters on Microstructural Evolution, Mechanical Properties and Corrosion Behavior of Friction Stir Processed Al 7075 Alloy

    NASA Astrophysics Data System (ADS)

    Kumar, Atul; Sharma, Sandan Kumar; Pal, Kaushik; Mula, Suhrit

    2017-03-01

    Aim of the present study is to investigate the effect of process parameters on microstructural evolution, mechanical properties and corrosion behavior of an age-hardenable Al 7075 alloy. The alloy plates (6 mm thickness) were friction stir processed (FSPed) at various traverse speed, namely 25, 45, 65, 85, 100 and 150 mm/min at 2 different rpm of 508 and 720. The optimized result in terms of defect-free processed zone with refined microstructure was obtained only at a rotational speed of 720 rpm for a traverse speed of 25, 45, 65 and 85 mm/min. The microstructural evolution was investigated using optical, scanning and transmission electron microscopy. The grain size of the nugget zone was found to decrease with increase in the traverse speed from 25 to 85 mm/min at a constant rpm of 720. The mechanical properties were evaluated by Vickers hardness measurements, tensile and wear testing. Yield strength was found to be the maximum ( 366 MPa) for the FSPed sample processed at 85 mm/min. The hardness values also followed the similar increasing trend with increase in the traverse speed. The wear volume loss decreased by 38% for the sample processed at a traverse speed of 85 mm/min as compared to that of the sample processed at 25 mm/min. The friction coefficient was found to substantiate well with the wear track morphology. The improvement in mechanical properties is ascertained to the refinement of grain size at higher traverse speed (due to less heat input). The FSPed samples showed inferior corrosion resistance in contrast to that of the base metal. This is possibly due to the coarsening of precipitates and depletion of solutes in the matrix. The morphology of the corroded samples corroborated well with the corrosion behavior of the corresponding specimen.

  15. Microstructure evolution of hot-deformed Nd-Fe-B anisotropic magnets

    SciTech Connect

    Liu, J. Hono, K.; Sepehri-Amin, H.; Ohkubo, T.; Hioki, K.; Hattori, A.

    2014-05-07

    The microstructural evolution of hot-deformed Nd-Fe-B magnets in each stage of hot-deformation process was studied using transmission electron microscopy and three dimensional atom probe (3DAP). The anisotropic growth of initially isotropic grains in rapidly solidified alloy occurs by annealing without pressing. 3DAP analyses showed a higher concentration of rare-earth elements in the intergranular phase parallel to the flat surface of platelet shaped Nd{sub 2}Fe{sub 14}B grains compared to that in the intergranular phase at the side of platelets.

  16. Microstructure evolution of hot-deformed Nd-Fe-B anisotropic magnets

    NASA Astrophysics Data System (ADS)

    Liu, J.; Sepehri-Amin, H.; Ohkubo, T.; Hioki, K.; Hattori, A.; Hono, K.

    2014-05-01

    The microstructural evolution of hot-deformed Nd-Fe-B magnets in each stage of hot-deformation process was studied using transmission electron microscopy and three dimensional atom probe (3DAP). The anisotropic growth of initially isotropic grains in rapidly solidified alloy occurs by annealing without pressing. 3DAP analyses showed a higher concentration of rare-earth elements in the intergranular phase parallel to the flat surface of platelet shaped Nd2Fe14B grains compared to that in the intergranular phase at the side of platelets.

  17. Microstructure evolution in hot rolled 7075 Al via friction stir processing

    NASA Astrophysics Data System (ADS)

    Guo, Mei Ling; Tan, Ming Jen; Liu, Feng Chao; Song, Xu; Chua, Beng Wah

    2016-10-01

    Friction stir processed (FSP) hot rolled 7075 Al alloy with grain size of 5.2 μm was investigated in the temperature range 350 °C-500 °C and strain rates from 3x10-4 to 10-1 s-1. Maximum superplastic elongation of 776.4 % was achieved at 500 °C and strain rate 10-3 s-1. The microstructure evolution of FSP 7075 Al during superplastic deformation was studied by electron backscatter diffraction (EBSD). Further analyses of superplastic results indicated the main deformation mechanism of FSP 7075 Al was grain boundary sliding (GBS).

  18. Effects of initial microstructure and texture on microstructure, texture evolution and magnetic properties of non-oriented electrical steel

    NASA Astrophysics Data System (ADS)

    Liu, Hai-Tao; Li, Hua-Long; Wang, Hui; Liu, Yi; Gao, Fei; An, Ling-Zi; Zhao, Shi-Qi; Liu, Zhen-Yu; Wang, Guo-Dong

    2016-05-01

    An equiaxed grained as-cast strip and a columnar grained as-cast strip was produced by using twin-roll strip casting, respectively. Both as-cast strips mainly containing 0.71 wt%Si and 0.44 wt%Al were cold rolled and annealed with or without the hot rolling prior to cold rolling. Microstructure, texture evolution along the whole processing routes and the magnetic properties were investigated in detail. It was found that the equiaxed grained strip was characterized by almost random texture while the columnar grained strip was dominated by strong λ-fiber (<001>‖ND) texture. After cold rolling and annealing, all the final sheets of both the as-cast strips showed extremely weak γ-fiber (<111>‖ND) recrystallization texture. In addition, the finally annealed sheets of the equiaxed grained strip were dominated by relatively weak λ-fiber and strong Goss ({110}<001>) recrystallization texture while those of the columnar grained strip were dominated by much stronger λ-fiber and much weaker Goss recrystallization texture regardless of whether the hot rolling was adopted before cold rolling, thus the former showed much lower magnetic induction than the latter. On the other hand, even though the finally annealed sheets of the equiaxed grained strip showed a little more homogeneous recrystallization microstructure with a little bigger grain size than those of the columnar grained strip in the case of no hot rolling, a much higher iron loss was displayed. By contrast, in the case of hot rolling, the former exhibited a little lower iron loss than the latter as a result of the more significant increase in grain size and λ-fiber recrystallization texture. The introduction of the hot rolling could increase the grain size, strengthen λ-fiber texture and weaken Goss texture of the finally annealed sheets of both the as-cast strips, leading to a much improvement in both the magnetic induction and iron loss.

  19. Microstructural evolution of CANDU spacer material Inconel X-750 under in situ ion irradiation

    NASA Astrophysics Data System (ADS)

    Zhang, He Ken; Yao, Zhongwen; Judge, Colin; Griffiths, Malcolm

    2013-11-01

    Work on Inconel®Inconel® is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium-based superalloys.1 X-750 spacers removed from CANDU®CANDU® is a registered trademark of Atomic Energy of Canada Limited standing for ''CANada Deuterium Uranium''.2 reactors has shown that they become embrittled and there is development of many small cavities within the metal matrix and along grain boundaries. In order to emulate the neutron irradiation induced microstructural changes, heavy ion irradiations (1 MeV Kr2+ ions) were performed while observing the damage evolution using an intermediate voltage electron microscope (IVEM) operating at 200 kV. The irradiations were carried out at various temperatures 60-400 °C. The principal strengthening phase, γ‧, was disordered at low doses (˜0.06 dpa) during the irradiation. M23C6 carbides were found to be stable up to 5.4 dpa. Lattice defects consisted mostly of stacking fault tetrahedras (SFTs), 1/2<1 1 0> perfect loops and small 1/3<1 1 1> faulted Frank loops. The ratio of SFT number density to loop number density for each irradiation condition was found to be neither temperature nor dose dependent. Under the operation of the ion beam the SFT production was very rapid, with no evidence for further growth once formed, indicating that they probably formed as a result of cascade collapse in a single cascade. The number density of the defects was found to saturate at low dose (˜0.68 dpa). No cavities were observed regardless of the irradiation temperature between 60 °C and 400 °C for doses up to 5.4 dpa. In contrast, cavities have been observed after neutron irradiation in the same material at similar doses and temperatures indicating that helium, produce during neutron irradiation, may be essential for the nucleation and growth of cavities.

  20. The Effect of Cool Deformation on the Microstructural Evolution and Flow Strength of Microalloyed Steels

    NASA Astrophysics Data System (ADS)

    Mousavi Anijdan, Seyyed Hashem

    Cool deformation is a process in which a small amount of plastic deformation is applied at temperatures well below the end of the austenite transformation temperature. In this thesis, a systematic study was conducted to evaluate the microstructural evolution and mechanical properties of microalloyed steels processed by thermomechanical schedules incorporating cool deformation. Thermodynamic analysis was conducted to predict equilibrium phases formed by the presence of microalloying elements such as Ti, Nb, Mo and their appearance were then elaborated by means of TEM microscopy. As well, continuous cooling torsion (CCT) was employed to study the transformation behavior of steels for austenite conditioned and unconditioned. Cool deformation was incorporated into a full scale simulation of hotrolling, and the effect of prior austenite conditioning on the cool deformability of microalloyed steels was investigated. Out of these studies, a new definition of no-recystallization temperature (Tnr) was proposed based on dynamic precipitation, which was then recognized in the Nb bearing steels by using TEM analysis as well as flow curves analysis. Results show that cool deformation greatly improves the strength of microalloyed steels. Of the several mechanisms identified, such as work hardening, precipitation, grain refinement, and strain induced transformation (SIT) of retained austenite, SIT was proposed, for the first time in microalloyed steels, to be the significant mechanism of strengthening due to the deformation in ferrite. Results also show that the effect of ferrite precipitation is greatly overshadowed by SIT at room temperature. Finally, considering the interplay of SIT and precipitation for the Nb bearing steels, a rolling schedule was designed incorporating austenite conditioning, cooling rate and cool deformation that maximized the strength.

  1. Modelling multi-scale deformation of amorphous glassy polymers with experimentally motivated evolution of the microstructure

    NASA Astrophysics Data System (ADS)

    Engqvist, Jonas; Wallin, Mathias; Ristinmaa, Matti; Hall, Stephen A.; Plivelic, Tomás S.

    2016-11-01

    Novel experimental data, obtained recently using advanced multi-scale experiments, have been used to develop a micro-mechanically motivated constitutive model for amorphous glassy polymers. Taking advantage of the experiments, the model makes use of a microstructural deformation gradient to incorporate the experimentally obtained deformation of the microstructure, as well as its evolving orientation. By comparing results from the model to experimental data, it is shown that the proposed approach is able to accurately predict glassy polymer deformation over a wide range of length-scales, from the macroscopic response (mm range) down to the deformation of the microstructure (nm range). The proposed model is evaluated by comparing the numerical response to experimental results on multiple scales from an inhomogeneous cold drawing experiment of glassy polycarbonate. Besides the macroscopic force-displacement response, a qualitative comparison of the deformation field at the surface of the specimen is performed. Furthermore, the predicted evolution of the fabric orientation is compared to experimental results obtained from X-ray scattering experiments. The model shows very good agreement with the experimental data over a wide range of length scales.

  2. 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.

  3. Microstructural evolution of PET under stretching and during stretch blow moulding

    NASA Astrophysics Data System (ADS)

    Picard, Martine; Billon, Noëlle

    2007-04-01

    Strain induced crystallisation of PET designed for stretch blow molding is studied combining well-controlled tensile tests and free blowing on a stretch blow prototype. Microstructure evolution is followed by WAXS and SAXS. Observations on blown parts clearly show that the microstructure can differ along the bottle and from processing conditions to another. Difference can be observed on crystalline orientation, periodic arrangement at the level of lamellae and long period. Range of long period, 8.5 to 13 nm is in agreement with literature. In certain case lamellar organisation disappears. Despite of high level of strain and evidence for strain hardening to occur during blowing no perfect crystalline pattern is observed, except in very thick zones. Interrupted tensile tests followed by quenching demonstrates that strain hardening is not correlated to prefect crystallisation. Microstructure clearly depends on the three parameters: temperature, strain rate and strain. It is concluded that strain hardening is mainly controlled by first stages of crystallisation and that actual crystallisation occurs during a following relaxation step. This later is then highly dependent upon cooling step.

  4. Comparison of microstructural evolution in Ti-Mo-Zr-Fe and Ti-15Mo biocompatible alloys.

    PubMed

    Nag, S; Banerjee, R; Stechschulte, J; Fraser, H L

    2005-07-01

    The microstructural evolution and attendant strengthening mechanisms in two biocompatible alloy systems, the binary Ti-15Mo and the quaternary Ti-13Mo-7Zr-3Fe (TMZF), have been compared and contrasted in this paper. In the homogenized condition, while the Ti-15Mo alloy exhibited a single phase microstructure consisting of large beta grains, the TMZF alloy exhibited a microstructure consisting primarily of a beta matrix with grain boundary alpha precipitates and a low volume fraction of intra-granular alpha precipitates. On ageing the homogenized alloys at 600 degrees C for 4 h, both alloys exhibited the precipitation of refined scale secondary alpha precipitates homogeneously in the beta matrix. However, while the hardness of the TMZF alloy marginally increased, that of the Ti-15Mo alloy decreased substantially as a result of the ageing treatment. In order to understand this difference in the mechanical properties after ageing, TEM studies have been carried out on both alloys in the homogenized and homogenized plus aged conditions. The results indicate that the omega precipitates dissolve on ageing in case of the Ti-15Mo alloy, consequently leading to a substantial decrease in the hardness. In contrast, the omega precipitates do not dissolve on ageing in the TMZF alloy and the precipitation of the fine scale secondary alpha leads to increased hardness.

  5. Preparation of Ag-Ni-Cu Composite Material by Ultrasonic Arc Spray Forming and Accumulative Roll Bonding and the Evolution of Its Microstructure

    NASA Astrophysics Data System (ADS)

    Zhang, Ke; Qin, Guo-Yi; Xu, Si-Yong; Guo, Jin-Xin; Ma, Guang

    2015-02-01

    We prepared a layered composite material by subjecting a deposition billet of AgNiCu15-5 formed by ultrasonic arc spray forming (UASF) to extrusion at 773 K (500 °C), rolling at 673 K (400 °C), and accumulative roll bonding (ARB). The evolution of the microstructure of the formed AgNiCu15-5 strips was analyzed through X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectrometry. The deposition billet had a rapid solidification microstructure consisting of β-Ni particles dispersed in α-Ag matrix. ARB significantly refined the microstructure of the AgNiCu15-5 samples. There was no further decrease in the grain size after the 9th ARB cycle. Thus, UASF combined with extrusion and ARB is suitable for producing high-performance AgNiCu15-5-based electrical contact materials efficiently and economically.

  6. Nonequilibrium synthesis of NbAl3 and Nb-Al-V alloys by laser cladding. I - Microstructure evolution

    NASA Technical Reports Server (NTRS)

    Sircar, S.; Chattopadhyay, K.; Mazumder, J.

    1992-01-01

    The evolution of the microstructure in NbAl3 synthesized by a laser cladding technique (a rapid solidification process, with cooling rates up to 10 exp 6 C/sec) is investigated, and the phases are identified using convergent beam electron diffraction. Two new metastable phases were identified and characterized in detail. The effect of adding V on the final microstructure was also investigated, and the various phase chemistries and the partitioning of different elements into different phases were studied.

  7. Microstructure evolution of tin under electromigration studied bysynchrotron X-Ray micro-diffraction

    SciTech Connect

    Wu, Albert T.; Lloyd, J.R.; Tamura, N.; Tu, K.-N.

    2005-05-05

    Under constant current electromigration, white tin(?-Sn)exhibited a resistance drop of up to 10 percent. It has a body centertetragonal (BCT) structure, and the resistivity along the aand b axes is35 percent smaller than that along the c axis.Microstructure evolutionunder electromigration could be responsible for the resistance drop.Synchrotron radiation white beam x-ray microdiffraction was used to studythis evolution. Both stress and grain orientation was studied.Grain-by-grain analysis was obtained from the diffracted Laue patternsabout the changes of grain orientation during electromigration testing inex-situ and in-situ samples. We observed that high resistance grainsreorient with respect to the neighboring low resistance grains, mostlikely by grain rotation of the latter. A different mechanism ofmicrostructure evolution under electromigration from the normal graingrowth is proposed and discussed.

  8. Crystallization, Microstructure, and Viscosity Evolutions in Lithium Aluminosilicate Glass-Ceramics

    NASA Astrophysics Data System (ADS)

    Fu, Qiang; Wheaton, Bryan; Geisinger, Karen; Credle, Allen; Wang, Jie

    2016-11-01

    Lithium aluminosilicate glass-ceramics have found widespread commercial success in areas such as consumer products, telescope mirrors, fireplace windows, etc. However, there is still much to learn regarding the fundamental mechanisms of crystallization, especially related to the evolution of viscosity as a function of the crystallization (ceramming) process. In this study, the impact of phase assemblage and microstructure on the viscosity was investigated using high temperature X-ray diffraction (HTXRD), beam bending viscometry (BBV), and transmission electron microscopy (TEM). Results from this study provide a first direct observation of viscosity evolution as a function of ceramming time and temperature. Sharp viscosity increases due to phase separation, nucleation and phase transformation are noticed through BBV measurement. A near-net shape ceramming can be achieved in TiO2-containing compositions by keeping the glass at a high viscosity (> 109 Pa.s) throughout the whole thermal treatment.

  9. Microstructure evolution of metallic nanocrystalline thin-films under ion-beam irradiation

    NASA Astrophysics Data System (ADS)

    Kaoumi, Djamel

    The microstructural evolution of nanocrystalline metallic thin-films under ion irradiation, especially grain growth and second-phase precipitation, was studied with detailed in situ experiments, and a theoretical model was developed to explain the results of grain-growth. Free-standing Zr, Pt, Cu and Au, Cu-Fe, and Zr-Fe nanocrystalline thin films prepared by sputter deposition were irradiated in-situ at the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory with Ar and Kr ions to fluences in excess of 1016 ion/cm2 at temperatures ranging from 20 to 773 K. The microstructural evolution of the thin-films was followed in situ by systematically recording bright field images and diffraction patterns at successive ion-irradiation doses. Grain growth was observed as a result of irradiation in all samples at all irradiation temperatures. The results suggest the existence of three regimes with increasing irradiating temperature: a low temperature regime (below about 0.15 to 0.22 Tm) where grain-growth does not depend on the irradiation temperature, a thermally assisted regime where both the grain-growth rate and the final grain size increase with increasing irradiation temperature, and a thermal regime where thermal effects dominate ion beam effects. Similarly to thermal grain growth, the ion-irradiation induced grain growth curves could be best fitted with curves of the type: Dn-Dn0=KF with n˜3 in the low temperature regime. The effect of solute addition on grain-growth was investigated using Zr(Fe) and Cu(Fe) supersaturated solid-solutions. In the case of Zr-Fe, Zr2Fe precipitates formed during irradiation (with the dose-to-precipitation of Zr2Fe decreasing with increasing irradiation temperature), whereas Cu-Fe remained as a solid-solution. The grain-growth rate and final size decreased in both alloys with respect to the pure metallic films as a result of second-phase particle pinning (Zener drag) (Zr-Fe), and solute drag (Cu-Fe). The grain

  10. Influence of the Initial Microstructure on the Reverse Transformation Kinetics and Microstructural Evolution in Transformation-Induced Plasticity-Assisted Steel

    NASA Astrophysics Data System (ADS)

    Kim, Jeong In; Ryu, Joo Hyun; Lee, Sea Woong; Lee, Kyooyoung; Heo, Yoon-Uk; Suh, Dong-Woo

    2016-11-01

    The reverse transformation behavior upon heating to intercritical temperature was studied in Fe-0.21C-2.2Mn-1.5Si (wt pct) alloy with three initial microstructures. One is the cold-rolled (CR) structure and two others are martensite having different fractions of retained austenite. The CR structure exhibits slower reverse transformation kinetics than martensite due to the lesser population of potent nucleation sites and coarse cementite particles. The film type of retained austenite at the martensite lath boundary contributes to the earlier start of the reverse transformation, because it can proceed as the growth of pre-existing retained austenite, which makes the nucleation process less critical. Besides, the growth of interlath austenite plays an essential role in the evolution of fine lath-type reverse-transformed microstructure, which was difficult to obtain from similar initial microstructures of martensite having negligible fraction of interlath austenite.

  11. Alloying effect of Ni and Cr on irradiated microstructural evolution of type 304 stainless steels

    NASA Astrophysics Data System (ADS)

    Tan, L.; Busby, J. T.

    2013-11-01

    Life extension of the existing nuclear power plants imposes significant challenges to core structural materials that suffer increased fluences. This paper presents the microstructural evolution of a type 304 stainless steel and its variants alloyed with extra Ni and Cr under neutron irradiation at ˜320 °C for up to 10.2 dpa. Similar to the reported data of type 304 variants, a large amount of Frank loops, ultrafine G-phase/M23C6 particles, and limited amount of cavities were observed in the irradiated samples. The irradiation promoted the growth of pre-existing M23C6 at grain boundaries and resulted in some phase transformation to CrC in the alloy with both extra Ni and Cr. A new type of ultrafine precipitates, possibly (Ti,Cr)N, was observed in all the samples, and its amount was increased by the irradiation. Additionally, α-ferrite was observed in the type 304 steel but not in the Ni or Ni + Cr alloyed variants. The effect of Ni and Cr alloying on the microstructural evolution is discussed.

  12. Microstructure and Microtexture Evolution of Pure Titanium during Single Direction Torsion and Alternating Cyclic Torsion

    NASA Astrophysics Data System (ADS)

    Chen, Han; Li, Fuguo; Liu, Jie; Li, Jinghui; Ma, Xinkai; Wan, Qiong

    2017-03-01

    Systematic experimental studies of microstructure and crystallographic texture of pure titanium during the Single Direction Torsion (SDT) and Alternating Cyclic Torsion (ACT) are carried out at room temperature. The microstructure evolution indicates that the grain size can be refined during SDT, while the grain morphology can be controlled during ACT. Also, lots of {10-12} and few {11-22} twins are observed and their area percentages increase with increasing torsion angles during SDT. The microtexture evolution states that the deformation texture first approaches to the B fiber (0, 90, 0 to 60 deg), and then stays away from B fiber (0, 90, 0 to 60 deg) with increasing plastic strain during SDT. The change of deformation texture is mainly attributed to the appearance of {10-12} twin. However, the deformation texture is always close to B fiber (0, 90, 0 to 60 deg) during ACT. Finally, the effects of different dislocation movements caused by SDT and ACT are discussed. Quantities of subgrains with high density dislocation are observed during SDT while the {10-12} and {11-22} twins intersect with each other, and high density dislocations distribute the twin during ACT.

  13. Mechanics, microstructure and AMS evolution of a synthetic porphyritic calcite aggregate deformed in torsion

    NASA Astrophysics Data System (ADS)

    Marques, F. O.; Machek, M.; Roxerová, Z.; Burg, J.-P.; Almqvist, B. S. G.

    2015-08-01

    In order to investigate the mechanical, microstructural and AMS evolution of porphyritic mylonites, we made a synthetic aggregate composed of 70% fine calcite (< 50 μm) and 30% coarse calcite (200-700 μm), and deformed cylindrical specimens in torsion at 300 MPa, 727 °C, a constant strain rate of 3.0E- 4 s- 1, to shear strains γ ≈ 1 and 5. After peak stress, dynamic recrystallization of porphyroclasts resulted in grain size reduction and weakening till a mechanical steady state was reached. Microstructural, AMS and EBSD analyses show the consistent evolution of pre-torsion (cold-pressed) planar fabric from perpendicular to sample cylinder axis at γ ≈ 0, to oblique at γ ≈ 1, and finally to low angle to the shear plane at γ ≈ 5, as expected for approximate simple shear. At γ ≈ 1, stretched calcite grains > 3 mm in length defined a conspicuous foliation, and showed aligned twins. At γ ≈ 5, calcite porphyroclasts were highly stretched (aspect ratio around 20), and had rotated towards the shear plane. Between γ = 1 and 5, a composite fabric formed, one at low and the other at high angle to the shear plane, from which shear sense can be deduced. The AMS patterns were sensitive to increasing shearing, and tracked strain reasonably well, despite the reduced size and low susceptibility of specimens. From the CPO and the microstructure, we infer that a balance compatible with an optimal dissipation of the applied stress was achieved between grain growth and grain reduction processes.

  14. Microstructure Evolution and Composition Control During the Processing of Thin-Gage Metallic Foil

    NASA Astrophysics Data System (ADS)

    Semiatin, S. L.; Gross, M. E.; Matson, D. W.; Bennett, W. D.; Bonham, C. C.; Ustinov, A. I.; Ballard, D. L.

    2012-12-01

    The manufacture of thin-gage superalloy and gamma-titanium-aluminide foil products via near-conventional thermomechanical processing and two different vapor-deposition methods was investigated. Thermomechanical processing was based on hot-pack rolling of plate and sheet. Foils of the superalloy LSHR and the near-gamma titanium aluminide Ti-45.5Al-2Cr-2Nb made by this approach exhibited excellent gage control and fine two-phase microstructures. The vapor-phase techniques used magnetron sputtering (MS) of a target of the desired product composition or electron-beam physical vapor deposition (EBPVD) of separate targets of the specific alloying elements. Thin deposits of LSHR and Ti-48Al-2Cr-2Nb made by MS showed uniform thickness/composition and an ultrafine microstructure. However, systematic deviations from the specific target composition were found. During subsequent heat treatment, the microstructure of the MS samples showed various degrees of grain growth and coarsening. Foils of Ti-43Al and Ti-51Al-1V fabricated by EBPVD were fully dense. The microstructures developed during EBPVD were interpreted in terms of measured phase equilibria and the dependence of evaporant flux on temperature.

  15. Atomic scale modeling of defect production and microstructure evolution in irradiated metals

    SciTech Connect

    Diaz de la Rubia, T.; Soneda, N.; Shimomura, Y.

    1997-04-01

    Irradiation effects in materials depend in a complex way on the form of the as-produced primary damage state and its spatial and temporal evolution. Thus, while collision cascades produce defects on a time scale of tens of picosecond, diffusion occurs over much longer time scales, of the order of seconds, and microstructure evolution over even longer time scales. In this report the authors present work aimed at describing damage production and evolution in metals across all the relevant time and length scales. They discuss results of molecular dynamics simulations of displacement cascades in Fe and V. They show that interstitial clusters are produced in cascades above 5 keV, but not vacancy clusters. Next, they discuss the development of a kinetic Monte Carlo model that enables calculations of damage evolution over much longer time scales (1000`s of s) than the picosecond lifetime of the cascade. They demonstrate the applicability of the method by presenting predictions on the fraction of freely migrating defects in {alpha}Fe during irradiation at 600 K.

  16. Micro-structural Evolution in Metals Subjected to Simple Shear by a Particular Severe Plastic Deformation Method

    NASA Astrophysics Data System (ADS)

    Li, Jinghui; Li, Fuguo; Li, Pan; Ma, Zhanchao; Wang, Chengpeng; Wang, Lei

    2015-08-01

    Simple shear (SS) has been considered an optimal deformation method of severe plastic deformation (SPD). To achieve SS, a particular SPD method known as mutative channel torsion extrusion (MCTE) was designed based on the geometric equivalence of SS, and the cavity parameters of a die were calculated according to strain equivalence. To investigate the characteristics of micro-structural evolution subjected to MCTE, simulated and experimental investigations were conducted. The simulated results indicate that equivalent strain distribution on the cross section is relatively uniform, and the metallographic observations confirm the simulated phenomenon. Transmission electron microscopy investigations show that the process of grain refinement undergoes the formation of shear bands, dislocation cells, dislocation forests, large-angle grain boundaries, and recrystallization nuclei. Two types of mechanisms are proposed in view of the different effects of SS on grain refinement. Eventually, MCTE is ensured as an effective method for grain refinement.

  17. Microstructural evolution and age hardening in aluminium alloys: Atom probe field-ion microscopy and transmission electron microscopy studies

    SciTech Connect

    Ringer, S.P.; Hono, K.

    2000-02-01

    This paper examines the microstructural evolution in selected aluminum alloys based on commercial age hardenable 2000, 6000, and 7000 series alloys. Atom probe field-ion microscopy and transmission electron microscopy have been used to examine the effects of microalloying and the origins of hardening. The combined application of these techniques is particularly important in the study of nanoscale precipitation processes. It is shown that the nature and kinetics of the precipitation process depend on the solute-solute interactions that produce solute clusters. The solute clusters precede the formation of GP zones or precipitation, and have a defining role on the nature and kinetics of the subsequent precipitation processes. Moreover, interactions between solute clustering and dislocations can have a significant hardening effect, the origins of which seem to be distinctly different from the conventional notion of precipitation hardening.

  18. Microstructure and Property Evolution in Advanced Cladding and Duct Materials Under Long-Term Irradiation at Elevated Temperature: Critical Experiments

    SciTech Connect

    Was, Gary; Jiao, Zhijie; Allen, Todd; Yang, Yong

    2013-12-20

    The in-service degradation of reactor core materials is related to underlying changes in the irradiated microstructure. During reactor operation, structural components and cladding experience displacement of atoms by collisions with neutrons at temperatures at which the radiation-induced defects are mobile, leading to microstructure evolution under irradiation that can degrade material properties. At the doses and temperatures relevant to fast reactor operation, the microstructure evolves by microchemistry changes due to radiation-induced segregation, dislocation loop formation and growth, radiation induced precipitation, destabilization of the existing precipitate structure, as well as the possibility for void formation and growth. These processes do not occur independently; rather, their evolution is highly interlinked. Radiation-induced segregation of Cr and existing chromium carbide coverage in irradiated alloy T91 track each other closely. The radiation-induced precipitation of Ni-Si precipitates and RIS of Ni and Si in alloys T91 and HCM12A are likely related. Neither the evolution of these processes nor their coupling is understood under the conditions required for materials performance in fast reactors (temperature range 300-600°C and doses to 200 dpa and beyond). Further, predictive modeling is not yet possible, as models for microstructure evolution must be developed along with experiments to characterize these key processes and provide tools for extrapolation. To extend the range of operation of nuclear fuel cladding and structural materials in advanced nuclear energy and transmutation systems to that required for the fast reactor, the irradiation-induced evolution of the microstructure, microchemistry, and the associated mechanical properties at relevant temperatures and doses must be understood. This project builds upon joint work at the proposing institutions, under a NERI-C program that is scheduled to end in September, to understand the effects of

  19. Microstructural Evolution and Creep-Rupture Behavior of Fusion Welds Involving Alloys for Advanced Ultrasupercritical Power Generation

    NASA Astrophysics Data System (ADS)

    Bechetti, Daniel H., Jr.

    Projections for large increases in the global demand for electric power produced by the burning of fossil fuels, in combination with growing environmental concerns surrounding these fuel sources, have sparked initiatives in the United States, Europe, and Asia aimed at developing a new generation of coal fired power plant, termed Advanced Ultrasupercritical (A-USC). These plants are slated to operate at higher steam temperatures and pressures than current generation plants, and in so doing will offer increased process cycle efficiency and reduced greenhouse gas emissions. Several gamma' precipitation strengthened Ni-based superalloys have been identified as candidates for the hottest sections of these plants, but the microstructural instability and poor creep behavior (compared to wrought products) of fusion welds involving these alloys present significant hurdles to their implementation and a gap in knowledge that must be addressed. In this work, creep testing and in-depth microstructural characterization have been used to provide insight into the long-term performance of these alloys. First, an investigation of the weld metal microstructural evolution as it relates to creep strength reductions in A-USC alloys INCONELRTM 740, NIMONICRTM 263 (INCONEL and NIMONIC are registered trademarks of Special Metals Corporation), and HaynesRTM 282RTM (Haynes and 282 are registered trademarks of Haynes International) was performed. gamma'-precipitate free zones were identified in two of these three alloys, and their development was linked to the evolution of phases that precipitate at the expense of gamma'. Alloy 282 was shown to avoid precipitate free zone formation because the precipitates that form during long term aging in this alloy are poor in the gamma'-forming elements. Next, the microstructural evolution of INCONELRTM 740H (a compositional variant of alloy 740) during creep was investigated. Gleeble-based interrupted creep and creep-rupture testing was used to

  20. Competing effects of electronic and nuclear energy loss on microstructural evolution in ionic-covalent materials

    SciTech Connect

    Zhang, Yanwen; Varga, Tamas; Ishimaru, Dr. Manabu; Edmondson, Dr. Philip; Xue, Haizhou; Liu, Peng; Moll, Sandra; Namavar, Fereydoon; Hardiman, Chris; Shannon, Prof. Steven; Weber, William J

    2014-01-01

    Ever increasing energy needs have raised the demands for advanced fuels and cladding materials that withstand the extreme radiation environments with improved accident tolerance over a long period of time. Ceria (CeO2) is a well known ionic conductor that is isostructural with urania and plutonia-based nuclear fuels. In the context of nuclear fuels, immobilization and transmutation of actinides, CeO2 is a model system for radiation effect studies. Covalent silicon carbide (SiC) is a candidate for use as structural material in fusion, cladding material for fission reactors, and an inert matrix for the transmutation of plutonium and other radioactive actinides. Understanding microstructural change of these ionic-covalent materials to irradiation is important for advanced nuclear energy systems. While displacements from nuclear energy loss may be the primary contribution to damage accumulation in a crystalline matrix and a driving force for the grain boundary evolution in nanostructured materials, local non-equilibrium disorder and excitation through electronic energy loss may, however, produce additional damage or anneal pre-existing defect. At intermediate transit energies where electronic and nuclear energy losses are both significant, synergistic, additive or competitive processes may evolve that affect the dynamic response of materials to irradiation. The response of crystalline and nanostructured CeO2 and SiC to ion irradiation are studied under different nuclear and electronic stopping powers to describe some general material response in this transit energy regime. Although fast radiation-induced grain growth in CeO2 is evident with no phase transformation, different fluence and dose dependence on the growth rate is observed under Si and Au irradiations. While grain shrinkage and amorphization are observed in the nano-engineered 3C SiC with a high-density of stacking faults embedded in nanosize columnar grains, significantly enhanced radiation resistance is

  1. Influence of process parameters on the microstructural evolution of a rear axle tube during cross wedge rolling

    NASA Astrophysics Data System (ADS)

    Ma, Jia-wei; Yang, Cui-ping; Zheng, Zhen-hua; Zhang, Kang-sheng; Ma, Wen-yu

    2016-11-01

    In the shaping process of cross wedge rolling (CWR), metal undergoes a complex microstructural evolution, which affects the quality and mechanical properties of the product. Through secondary development of the DEFORM-3D software, we developed a rigid plastic finite element model for a CWR-processed rear axle tube, coupled with thermomechanical and microstructural aspects of workpieces. Using the developed model, we investigated the microstructural evolution of the CWR process. Also, the influence of numerous parameters, including the initial temperature of workpieces, the roll speed, the forming angle, and the spreading angle, on the grain size and the grain-size uniformity of the rolled workpieces was analyzed. The numerical simulation was verified through rolling and metallographic experiments. Good agreement was obtained between the calculated and experimental results, which demonstrated the reliability of the model constructed in this work.

  2. Evolution of microstructure and mechanical properties during Q&P processing of medium-carbon steels with different silicon levels

    NASA Astrophysics Data System (ADS)

    Jenicek, S.; Vorel, I.; Kana, J.; Opatova, K.; Rubesova, K.; Kotesovec, V.; Masek, B.

    2017-03-01

    Evolution of microstructure during heat treatment plays a fundamental role in the resulting mechanical properties of steel. Today, mechanical properties in conjunction with technological properties, such as weldability, formability, and machinability, and their optimum combinations, are widely discussed in a number of mechanical engineering disciplines. In this manner, requirements arise for developing steels which could offer high strength and good formability, and which could be used for making parts with high resistance to failure and with a long life. One present-day example of such steels involves Q&P-processed martensitic steels. Their properties are dictated by their treatment, as well as their alloying, particularly by the silicon content. Silicon fundamentally affects microstructure evolution during Q&P processing and, as a result, mechanical properties. With this way it is possible to receive microstructures consinsting of martensite and retained austenite with an ultimate tensile stress of more than 1600 MPa and a uniform elongation of more than 12 %.

  3. Microstructural Evolutions During Annealing of Plastically Deformed AISI 304 Austenitic Stainless Steel: Martensite Reversion, Grain Refinement, Recrystallization, and Grain Growth

    NASA Astrophysics Data System (ADS)

    Naghizadeh, Meysam; Mirzadeh, Hamed

    2016-08-01

    Microstructural evolutions during annealing of a plastically deformed AISI 304 stainless steel were investigated. Three distinct stages were identified for the reversion of strain-induced martensite to austenite, which were followed by the recrystallization of the retained austenite phase and overall grain growth. It was shown that the primary recrystallization of the retained austenite postpones the formation of an equiaxed microstructure, which coincides with the coarsening of the very fine reversed grains. The latter can effectively impair the usefulness of this thermomechanical treatment for grain refinement at both high and low annealing temperatures. The final grain growth stage, however, was found to be significant at high annealing temperatures, which makes it difficult to control the reversion annealing process for enhancement of mechanical properties. Conclusively, this work unravels the important microstructural evolution stages during reversion annealing and can shed light on the requirements and limitations of this efficient grain refining approach.

  4. Evolution of Microstructure and Texture During Hot Compression of a Ni-Fe-Cr Superalloy

    NASA Astrophysics Data System (ADS)

    Coryell, S. P.; Findley, K. O.; Mataya, M. C.; Brown, E.

    2012-02-01

    Superalloys are being employed in more extreme conditions requiring higher strength, which requires producers to forge products to finer grain sizes with less grain size variability. To assess grain size, crystallographic texture, and substructure as a function of forging conditions, frictionless uniaxial compression testing characteristic of hot working was performed on INCOLOY 945 (Special Metals Corporation, Huntington, WV), which is a newly developed hybrid of alloys 718 and 925, over a range of temperatures and strain rates. The microstructure and texture were investigated comprehensively using light optical microscopy, electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI), and transmission electron microscopy (TEM) to provide detailed insight into microstructure evolution mechanisms. Dynamic recrystallization, nucleated by grain/twin boundary bulging with occasional subgrain rotation, was found to be a dominant mechanism for grain refinement in INCOLOY 945. At higher strain rates, static recrystallization occurred by grain boundary migration. During deformation, duplex slip along {111} planes occurred until a stable <110> fiber compression texture was established. Recrystallization textures were mostly random but shifted toward the compression texture with subsequent deformation. An exception occurred at 1423 K (1150 °C) and 0.001 seconds-1, the condition with the largest fraction of recrystallized grains, where a <100> fiber texture developed, which may be indicative of preferential growth of specific grain orientations.

  5. Influence of tempering temperature on both the microstructural evolution and elemental distribution in AISI 4340 steels

    NASA Astrophysics Data System (ADS)

    Lim, Nam Suk; Bang, Chan Woo; Das, Sanjeev; Jin, Hyun Woo; Ayer, Raghavan; Park, Chan Gyung

    2012-02-01

    In the present study, the influence of tempering temperature on the microstructural evolution and prior austenite grain boundary segregation of AISI 4340 steels was investigated by transmission electron microscope and atom probe. The transmission electron microscopy results showed a variation in the microstructure and the morphology of carbides with a change in tempering temperature. Additionally, the chemical compositions of the prior austenite grain boundaries and carbides were quantified by atom probe tomography. An increase in the tempering temperature led to a decrease in the amount of carbon segregated at the prior austenite grain boundary from 7.9 to 1.3 at.%. It was found that a higher tempering temperature can accelerate the diffusion of carbon from the prior austenite grain boundary into carbide. However, phosphorus atoms were segregated mainly at the prior austenite grain boundary in steel tempered at 400°C (up to 0.18 at.%). It was found that formation of film-like carbide and phosphorus segregation along the prior austenite grain boundary is the main cause of embrittlement in steel tempered at 400°C.

  6. Microstructure and texture evolution of TRC A8006 alloy by homogenization

    NASA Astrophysics Data System (ADS)

    Chen, Zhong-wei; Zhao, Jing; Hao, Xiao-lei

    2013-05-01

    The microstructure and texture evolution of twin-roll cast A8006 alloy by homogenization were characterized using scanning and transmission electron microscopy, and the microhardness was tested as well. According to the relationship between dendritic arm spacing and cooling rate the cooling rate of the as-cast twin-roll cast A8006 sheet of 6 mm in thickness was estimated as 1.48×103 K·s-1. It is found that the grains and the nanostructural precipitates of the twin-roll cast sheet become coarser after homogenization at 580°C for 4 h in comparison with those after homogenization at 500°C for 8 h. The textures formed after cold rolling and became weaker during homogenization. The increase in hardness of the as-cast twin-roll cast sheets is related to the supersaturated α-Al solid solution and fine microstructure, but the decrease in hardness after homogenization can be attributed to the coarsening of grains and Al6Fe(Mn) precipitates.

  7. 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.

  8. 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.

    2017-02-01

    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.

  9. Microstructural Evolution and Fracture Behavior of Friction-Stir-Welded Al-Cu Laminated Composites

    NASA Astrophysics Data System (ADS)

    Beygi, R.; Kazeminezhad, Mohsen; Kokabi, A. H.

    2014-01-01

    In this study, we attempt to characterize the microstructural evolution during friction stir butt welding of Al-Cu-laminated composites and its effect on the fracture behavior of the joint. Emphasis is on the material flow and particle distribution in the stir zone. For this purpose, optical microscopy and scanning electron microscopy (SEM) images, energy-dispersive spectroscopy EDS and XRD analyses, hardness measurements, and tensile tests are carried out on the joints. It is shown that intermetallic compounds exist in lamellas of banding structure formed in the advancing side of the welds. In samples welded from the Cu side, the banding structure in the advancing side and the hook formation in the retreating side determine the fracture behavior of the joint. In samples welded from the Al side, a defect is formed in the advancing side of the weld, which is attributed to insufficient material flow. It is concluded that the contact surface of the laminate (Al or Cu) with the shoulder of the FSW tool influences the material flow and microstructure of welds.

  10. Evolution of microstructure in vanadium oxide bolometer film during annealing process

    NASA Astrophysics Data System (ADS)

    Su, Yu-Yu; Cheng, Xing-Wang; Li, Jing-Bo; Dou, Yan-Kun; Rehman, Fida; Su, De-Zhi; Jin, Hai-Bo

    2015-12-01

    Vanadium oxide thin films were prepared through direct current magnetron reactive sputtering and post annealing process. The evolution of composition, microstructure, and electrical properties of as-deposited amorphous films during the annealing process was clarified by X-ray diffraction, scanning electron microscopy and temperature-dependent resistance measurement. A new composition of thin film was acquired which consisted of crystalline V6O13 and amorphous phase. Sheet resistance and temperature coefficient of resistance (TCR) of the thin film are 90 kΩ/□ (measured at room temperature) and 2.52%/K, respectively. No metal-to-semiconductor transition was observed in the obtained film at temperatures ranging from room-temperature to 90 °C, suggesting the thin film is suitable for the application in microbolometer.

  11. Effect of Impact and Penetration on Microstructural Evolution of High-performance Concretes

    SciTech Connect

    Ren, Fei; Mattus, Catherine H; Wang, Jy-An John; Dipaolo, Beverly P

    2013-01-01

    Due to the increased concern of public safety in recent years, blast resistance of infrastructures has become an emerging research focus in the cement and concrete industry. Ultra High Performance Concrete (UHPC) with fiber reinforcement usually possesses compressive strengths greater than 200 MPa, which makes them promising candidates for blast-resistant building materials. In the current project, two UHPC materials, Ductal and ERDC-M, were subject to projectile penetration testing. The microstructural evolution due to projectile impact was examined via scanning electron microscopy and X-ray diffraction. Possible phase changes were observed in the impact volume, which was likely a result of the high temperature and high pressure induced by the impact.

  12. Microstructure evolution during isochronal annealing of a 42% cold rolled TRIP-TWIP steel

    NASA Astrophysics Data System (ADS)

    Pramanik, S.; Saleh, A. A.; Santos, D. B.; Pereloma, E. V.; Gazder, A. A.

    2015-08-01

    A high manganese TRIP-TWIP steel was cold rolled to 42% thickness reduction and isochronally annealed between 600 to 900 °C for 300 s. The microstructural evolution during annealing was studied by high resolution electron back-scattering diffraction. After cold rolling, the steel comprised predominant fraction of α'-martensite, a small fraction of blocky ε-martensite and a trace fraction of retained austenite (γ). During annealing, the reversion of ε and α' martensite to γ was followed by the recrystallisation of γ. While the processes of reversion to and recrystallisation of γ were completed by 700 °C, further annealing between 750 to 900 °C led to γ grain growth. A novel method to delineate the γ-γ grain boundaries was developed in order to accurately quantify γ grain size and subsequently the activation energy for γ grain growth.

  13. Intergrannular strain evolution in a zircaloy-4 alloy with Widmanstatten microstructure

    SciTech Connect

    Clausen, Bjorn; Vogel, Sven C; Garlea, Eena; Choo, Hahn; Pang, Judy W L; Kenik, Edward A

    2009-01-01

    A Zircaloy-4 alloy with Widmanstatten-Basketweave microstructure and random texture has been used to study the deformation systems responsible for the polycrystalline plasticity at the grain level. The evolution of internal strain and bulk texture is investigated using neutron diffraction and an elasto-plastic self-consistent (EPSC) modeling scheme. The macroscopic stress-strain behavior and intergranular (hkil-specific) strain development, parallel and perpendicular to the loading direction, were measured in-situ during uniaxial tensile loading. Then, the EPSC model was employed to simulate the experimental results. This modeling scheme accounts for the thermal anisotropy; elastic-plastic properties of the constituent grains; and activation, reorientation, and stress relaxation associated with twinning. The agreement between the experiment and the model will be discussed as well as the critical resolved shear stresses (CRSS) and the hardening coefficients obtained from the model.

  14. Microstructure and Texture Evolutions in AISI 1050 Steel by Flow Forming

    SciTech Connect

    Bedekar, Vikram; Pauskar, Praveen; Shivpuri, Rajiv; Howe, Jane Y

    2014-01-01

    Hot rolled and annealed AISI 1050 steel cylindrical coupons were flow formed at different levels of deformation (66% and 90% wall thickness reduction). TEM studies revealed development of ultra fine (sub) grain cell structure due to severe plastic deformation. The transverse subgrain size changed from 10 m (beginning) to 300nm (66% deformation) to 40nm (90% deformation). EBSD study revealed decreased recrystallization fraction at 90% deformation compared with 66% deformation due to orientation pinning from preferred orientation along {002} planes. No evidence of dislocation pinning or cracking was observed on any samples. The aim of the present work is to study the deformation behaviour and microstructural evolution during conventional flow forming process. The study also sheds light on the strengthening behaviour and structural changes during severe straining.

  15. Microstructural evolution of V-4Cr-4Ti during ion irradiation at 200{degrees}C

    SciTech Connect

    Gazda, J.; Meshii, M.; Loomis, B.A. Chung, H.M.

    1996-04-01

    The results of a transmission electron microscopy (TEM) investigation of the microstructural evolution of V-4Cr-4Ti (Heat no. 832665) that was irradiated with 4.5 MeV {sup 58}Ni{sup ++} ions at 200 {degrees}C are presented. Dose effects were investigated for fluences ranging from 0.5 to 5 dpa. When the irradiation dose was increased, the relative number density of black dots and dislocation loops was nearly constant and accompanied by an increase in the size of the defects. Cavity formation was not observed in any of the specimens, indicating high resistance of the alloy to void swelling at the lower temperature of the experiments.

  16. Evolution of magnetic properties and microstructure of Hf2Co11B alloys

    SciTech Connect

    McGuire, Michael A.; Rios, Orlando

    2015-02-05

    Amorphous Hf2Co11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo3B2, Hf6Co23 and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf2Co11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.

  17. Evolution of magnetic properties and microstructure of Hf2Co11B alloys

    DOE PAGES

    McGuire, Michael A.; Rios, Orlando

    2015-02-05

    Amorphous Hf2Co11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo3B2, Hf6Co23 andmore » Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf2Co11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.« less

  18. A variational treatment of material configurations with application to interface motion and microstructural evolution

    NASA Astrophysics Data System (ADS)

    Teichert, Gregory H.; Rudraraju, Shiva; Garikipati, Krishna

    2017-02-01

    We present a unified variational treatment of evolving configurations in crystalline solids with microstructure. The crux of our treatment lies in the introduction of a vector configurational field. This field lies in the material, or configurational, manifold, in contrast with the traditional displacement field, which we regard as lying in the spatial manifold. We identify two distinct cases which describe (a) problems in which the configurational field's evolution is localized to a mathematically sharp interface, and (b) those in which the configurational field's evolution can extend throughout the volume. The first case is suitable for describing incoherent phase interfaces in polycrystalline solids, and the latter is useful for describing smooth changes in crystal structure and naturally incorporates coherent (diffuse) phase interfaces. These descriptions also lead to parameterizations of the free energies for the two cases, from which variational treatments can be developed and equilibrium conditions obtained. For sharp interfaces that are out-of-equilibrium, the second law of thermodynamics furnishes restrictions on the kinetic law for the interface velocity. The class of problems in which the material undergoes configurational changes between distinct, stable crystal structures are characterized by free energy density functions that are non-convex with respect to configurational strain. For physically meaningful solutions and mathematical well-posedness, it becomes necessary to incorporate interfacial energy. This we have done by introducing a configurational strain gradient dependence in the free energy density function following ideas laid out by Toupin (1962, Elastic materials with couple-stresses. Arch. Ration. Mech. Anal., 11, 385-414). The variational treatment leads to a system of partial differential equations governing the configuration that is coupled with the traditional equations of nonlinear elasticity. The coupled system of equations governs

  19. A variational treatment of material configurations with application to interface motion and microstructural evolution

    DOE PAGES

    Teichert, Gregory H.; Rudraraju, Shiva; Garikipati, Krishna

    2016-11-20

    We present a unified variational treatment of evolving configurations in crystalline solids with microstructure. The crux of our treatment lies in the introduction of a vector configurational field. This field lies in the material, or configurational, manifold, in contrast with the traditional displacement field, which we regard as lying in the spatial manifold. We identify two distinct cases which describe (a) problems in which the configurational field's evolution is localized to a mathematically sharp interface, and (b) those in which the configurational field's evolution can extend throughout the volume. The first case is suitable for describing incoherent phase interfaces inmore » polycrystalline solids, and the latter is useful for describing smooth changes in crystal structure and naturally incorporates coherent (diffuse) phase interfaces. These descriptions also lead to parameterizations of the free energies for the two cases, from which variational treatments can be developed and equilibrium conditions obtained. For sharp interfaces that are out-of-equilibrium, the second law of thermodynamics furnishes restrictions on the kinetic law for the interface velocity. The class of problems in which the material undergoes configurational changes between distinct, stable crystal structures are characterized by free energy density functions that are non-convex with respect to configurational strain. For physically meaningful solutions and mathematical well-posedness, it becomes necessary to incorporate interfacial energy. This we have done by introducing a configurational strain gradient dependence in the free energy density function following ideas laid out by Toupin (Arch. Rat. Mech. Anal., 11, 1962, 385-414). The variational treatment leads to a system of partial differential equations governing the configuration that is coupled with the traditional equations of nonlinear elasticity. The coupled system of equations governs the configurational change in crystal

  20. A variational treatment of material configurations with application to interface motion and microstructural evolution

    SciTech Connect

    Teichert, Gregory H.; Rudraraju, Shiva; Garikipati, Krishna

    2016-11-20

    We present a unified variational treatment of evolving configurations in crystalline solids with microstructure. The crux of our treatment lies in the introduction of a vector configurational field. This field lies in the material, or configurational, manifold, in contrast with the traditional displacement field, which we regard as lying in the spatial manifold. We identify two distinct cases which describe (a) problems in which the configurational field's evolution is localized to a mathematically sharp interface, and (b) those in which the configurational field's evolution can extend throughout the volume. The first case is suitable for describing incoherent phase interfaces in polycrystalline solids, and the latter is useful for describing smooth changes in crystal structure and naturally incorporates coherent (diffuse) phase interfaces. These descriptions also lead to parameterizations of the free energies for the two cases, from which variational treatments can be developed and equilibrium conditions obtained. For sharp interfaces that are out-of-equilibrium, the second law of thermodynamics furnishes restrictions on the kinetic law for the interface velocity. The class of problems in which the material undergoes configurational changes between distinct, stable crystal structures are characterized by free energy density functions that are non-convex with respect to configurational strain. For physically meaningful solutions and mathematical well-posedness, it becomes necessary to incorporate interfacial energy. This we have done by introducing a configurational strain gradient dependence in the free energy density function following ideas laid out by Toupin (Arch. Rat. Mech. Anal., 11, 1962, 385-414). The variational treatment leads to a system of partial differential equations governing the configuration that is coupled with the traditional equations of nonlinear elasticity. The coupled system of equations governs the configurational change in crystal

  1. Evolution of magnetic properties and microstructure of Hf2Co11B alloys

    NASA Astrophysics Data System (ADS)

    McGuire, Michael A.; Rios, Orlando

    2015-02-01

    Amorphous Hf2Co11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo3B2, Hf6Co23, and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf2Co11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.

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

    SciTech Connect

    Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

    2014-10-30

    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, 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

  3. Microstructural coarsening in Sn-Ag-based solders and its effects on mechanical properties

    NASA Astrophysics Data System (ADS)

    Dutta, I.; Kumar, P.; Subbarayan, G.

    2009-06-01

    Solders based on Sn-Ag alloys are susceptible to microstructural coarsening during storage or service, resulting in evolution of joint properties, and hence reliability, over time. Coarsening can occur during static aging, and even faster during thermo-mechanical cycling (TMC). The kinetics of coarsening may also depend on the scale of the joint. These effects lead to evolution of the mechanical properties of the joint over time, as well as spatial variations of property within the joint. Therefore, accurate prediction of joint properties during service or storage requires a quantitative understanding of coarsening under both isothermal and TMC conditions, and incorporating these in constitutive laws. This paper discusses the kinetics of coarsening in Sn-Ag based solders, and presents a rationale for joint-scale dependence of coarsening. The impact of coarsening on creep and fracture properties of joints under drop conditions are also presented.

  4. Microstructure Evolution and Abrasive Wear Behavior of Ti-6Al-4V Alloy

    NASA Astrophysics Data System (ADS)

    Hadke, Shreyash; Khatirkar, Rajesh K.; Shekhawat, Satish K.; Jain, Shreyans; Sapate, Sanjay G.

    2015-10-01

    This paper investigates the effect of quenching and aging treatment on microstructure and abrasive wear of Ti-6Al-4V alloy. The as-received alloy was solution treated at 1339 K, then oil quenched, followed by aging at 823 K for 4 h (14,400 s). The microstructures of as-received and quench-aged specimens were characterized by using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and electron backscattered diffraction techniques. The as-received specimen consisted of very fine α grains (average grain size 2 μm) with β phase uniformly dispersed throughout. The microstructure of the quench-aged specimen showed α plates (formed by the decomposition of α' during aging). The β phase precipitated out of α' martensite during aging and hence was dispersed uniformly in the α matrix. Ti-6Al-4V alloy was quench-aged to achieve maximum hardness with a view that the increased hardness would lead to an improvement in abrasive wear behavior. Two-body abrasive wear tests were carried out on the as-received and quench-aged specimens using pin-on-disk apparatus with SiC as abrasive media (150-grit size). The effect of sliding distance and normal load on the abrasive wear behavior was studied. The wear resistance of the as-received specimen was greater than that of quench-aged specimen, while hardness of the as-received specimen was lower than that of quench-aged specimen. The abrasive wear behavior of Ti-6Al-4V alloy has been explained based on morphology/microstructure of the alloy and the associated wear mechanism(s).

  5. 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.

  6. Microstructural aspects of fatigue in Ni-base superalloys.

    PubMed

    Antolovich, Stephen D

    2015-03-28

    Nickel-base superalloys are primarily used as components in jet engines and land-based turbines. While compositionally complex, they are microstructurally simple, consisting of small (50-1000 nm diameter), ordered, coherent Ni(3)(Al,Ti)-type L1(2) or Ni(3)Nb-type DO(22) precipitates (called γ(') and γ(''), respectively) embedded in an FCC substitutional solid solution consisting primarily of Ni and other elements which confer desired properties depending upon the application. The grain size may vary from as small as 2 μm for powder metallurgy alloys used in discs to single crystals the actual size of the component for turbine blades. The fatigue behaviour depends upon the microstructure, deformation mode, environment and cycle time. In many cases, it can be controlled or modified through small changes in composition which may dramatically change the mechanism of damage accumulation and the fatigue life. In this paper, the fundamental microstructural, compositional, environmental and deformation mode factors which affect fatigue behaviour are critically reviewed. Connections are made across a range of studies to provide more insight. Modern approaches are pointed out in which the wealth of available microstructural, deformation and damage information is used for computerized life prediction. The paper ends with a discussion of the very important and highly practical subject of thermo-mechanical fatigue (TMF). It is shown that physics-based modelling leads to significantly improved life prediction. Suggestions are made for moving forward on the critical subject of TMF life prediction in notched components.

  7. Stress and Microstructure Development in Particle-Based Coatings

    NASA Astrophysics Data System (ADS)

    Price, Kyle Kirk-Arthur

    Particle-based coatings have a wide range of uses and applications in everyday life. Stress development during the drying process has the potential to impact the performance of the coating. Stress development can be monitored in-situ using a cantilever deflection technique with a laser-photodiode combination. Stress development in the film is directly related to the development of the coating microstructure during drying. Cryogenic scanning electron microscopy (cryoSEM) is a powerful characterization method capable of visualizing the microstructure of the coating during the intermediate stages of drying. Using this method, the coating is frozen to arrest microstructure development and solidify the sample so that it can survive the high-vacuum environment of the SEM. This thesis explores the connections between stress and microstructure development in particle-based coatings during drying. Characterization is often complicated by lateral drying, a common phenomenon in particle-based coatings. To avoid these complications, walled substrates were developed which are used to suppress lateral drying and promote drying uniformity. CryoSEM revealed that latex coatings dried on substrates (with photoresist walls) exhibit a greater degree of drying uniformity. Silicon cantilevers with poly(dimethyl siloxane) (PDMS) walls along the perimeter were used to suppress the effects of lateral drying during stress measurement. The walled cantilevers were used to characterize stress development in ceramic particle coatings and latex films. For the ceramic particle coatings, stress measurements were combined with cryoSEM revealing the origins of stress development in hard particle coatings. Stress development was correlated with the extent of drying and the degree of saturation in the coating. Stress development in latex particle coatings was influenced by the composition and morphology of the latex particles. Additionally, the influence of coalescing aids on stress development was

  8. Competing Effects Of Electronic And Nuclear Energy Loss On Microstructural Evolution In Ionic-covalent Materials

    SciTech Connect

    Zhang, Yanwen; Varga, Tamas; Ishimaru, Manabu; Edmondson, P. D.; Xue, H.; Liu, Peng; Moll, Sandra; Hardiman, Christopher M.; Shannon, Steven; Weber, William J.

    2014-05-01

    Ever increasing energy needs have raised the demands for advanced fuels and cladding materials that withstand the extreme radiation environments with improved accident tolerance over a long period of time. Ceria (CeO2) is a well known ionic conductor that is isostructural with urania and plutonia-based nuclear fuels. In the context of nuclear fuels, immobilization and transmutation of actinides, CeO2 is a model system for radiation effect studies. Covalent silicon carbide (SiC) is a candidate for use as structural material in fusion, cladding material for fission reactors, and an inert matrix for the transmutation of plutonium and other radioactive actinides. Understanding microstructural change of these ionic-covalent materials to irradiation is important for advanced nuclear energy systems. While displacements from nuclear energy loss may be the primary contribution to damage accumulation in a crystalline matrix and a driving force for the grain boundary evolution in nanostructured materials, local non-equilibrium disorder and excitation through electronic While displacements from nuclear energy loss may be the primary contribution to damage accumulation in a crystalline matrix and a driving force for the grain boundary evolution in nanostructured materials, local non-equilibrium disorder and excitation through electronic energy loss may, however, produce additional damage or anneal pre-existing defect. At intermediate transit energies where electronic and nuclear energy losses are both significant, synergistic, additive or competitive processes may evolve that affect the dynamic response of materials to irradiation. The response of crystalline and nanostructured CeO2 and SiC to ion irradiation are studied under different nuclear and electronic stopping powers to describe some general material response in this transit energy regime. Although fast radiation-induced grain growth in CeO2 is evident with no phase transformation, different fluence and dose dependence

  9. The microstructural evolution of clay-bearing carbonate faults during high-velocity friction experiments

    NASA Astrophysics Data System (ADS)

    Bullock, Rachael; De Paola, Nicola; Holdsworth, Robert

    2014-05-01

    nanoparticles and often containing bubbles as evidence for frictional heating and thermal decomposition of calcite. Initial microstructure of the wet gouges, on the other hand, is characterized by a distributed and interconnected network of wet clay surrounding calcite grains. The microstructure of the sheared wet gouges is characterized by a diffuse PSS, limited fabric development, and no PSZ; deformation is much more distributed. In addition, grain-size reduction in the wet gouges is ~1 order of magnitude less than in dry gouge equivalents. Thus, we attribute the contrasting frictional behaviour and microstructural evolution in the dry vs. wet gouges to the fact that in the wet gouges, distributed slip preferentially occurs on the pre-existing, weak clay network. This reduces the need for grain-breakage to occur before slip is able to localize, explaining the lack of a slip-hardening phase. Shear induced compaction of the wet clay-bearing gouges is also likely to generate a considerable pore-fluid overpressure within the impermeable clay network, further contributing to their weak behaviour. The lack of resistance to frictional sliding shown by the wet clay-bearing gouges contrasts with the traditional concept that phyllosilicates, due to their velocity-strengthening nature, should have a stabilizing role in upper crustal fault zones, and has significant implications for seismic hazard in the Apennines.

  10. Compositional Effects on Nickel-Base Superalloy Single Crystal Microstructures

    NASA Technical Reports Server (NTRS)

    MacKay, Rebecca A.; Gabb, Timothy P.; Garg,Anita; Rogers, Richard B.; Nathal, Michael V.

    2012-01-01

    Fourteen nickel-base superalloy single crystals containing 0 to 5 wt% chromium (Cr), 0 to 11 wt% cobalt (Co), 6 to 12 wt% molybdenum (Mo), 0 to 4 wt% rhenium (Re), and fixed amounts of aluminum (Al) and tantalum (Ta) were examined to determine the effect of bulk composition on basic microstructural parameters, including gamma' solvus, gamma' volume fraction, volume fraction of topologically close-packed (TCP) phases, phase chemistries, and gamma - gamma'. lattice mismatch. Regression models were developed to describe the influence of bulk alloy composition on the microstructural parameters and were compared to predictions by a commercially available software tool that used computational thermodynamics. Co produced the largest change in gamma' solvus over the wide compositional range used in this study, and Mo produced the largest effect on the gamma lattice parameter and the gamma - gamma' lattice mismatch over its compositional range, although Re had a very potent influence on all microstructural parameters investigated. Changing the Cr, Co, Mo, and Re contents in the bulk alloy had a significant impact on their concentrations in the gamma matrix and, to a smaller extent, in the gamma' phase. The gamma phase chemistries exhibited strong temperature dependencies that were influenced by the gamma and gamma' volume fractions. A computational thermodynamic modeling tool significantly underpredicted gamma' solvus temperatures and grossly overpredicted the amount of TCP phase at 982 C. Furthermore, the predictions by the software tool for the gamma - gamma' lattice mismatch were typically of the wrong sign and magnitude, but predictions could be improved if TCP formation was suspended within the software program. However, the statistical regression models provided excellent estimations of the microstructural parameters based on bulk alloy composition, thereby demonstrating their usefulness.

  11. The effect of urea on microstructures of Ni3S2 on nickel foam and its hydrogen evolution reaction

    NASA Astrophysics Data System (ADS)

    Jinlong, Lv; Tongxiang, Liang

    2016-11-01

    The effects of urea concentration on microstructures of Ni3S2formed on nickel foam and its hydrogen evolution reaction were investigated. The Ni3S2 nanosheets with porous structure were formed on nickel foam during hydrothermal process due to low urea concentration. While high urea concentration facilitated the forming of Ni3S2 nanotube arrays. The resulting Ni3S2 nanotube arrays exhibited higher catalytic activity than Ni3S2nanosheets for hydrogen evolution reaction. This was mainly attributed to a fact that Ni3S2 nanotube arrays facilitated diffusion of electrolyte for hydrogen evolution reaction.

  12. The microstructure evolution of hydrogenated microcrystalline germanium promoted by power gradient method

    NASA Astrophysics Data System (ADS)

    Wang, Xinyu; Ni, Jian; Li, Chang; Sun, Xiaoxiang; Li, Zhenglong; Cai, Hongkun; Li, Juan; Zhang, Jianjun

    2016-12-01

    This paper studies the microstructure evolution of hydrogenated microcrystalline germanium (μc-Ge:H) thin films deposited by plasma enhanced chemical vapor deposition (PECVD). There is an amorphous incubation layer formed in the initial deposition stage of μc-Ge:H thin film. It is demonstrated that the thickness of incubation layer can be reduced by high hydrogen dilution and high discharge power method. However, at high hydrogen dilution, the deposition rate of μc-Ge:H appears a sharply decrease. Using a high discharge power can compensate the deposition rate decrease but lead to decrease of average grain size and appearance of micro-void in the μc-Ge:H thin film. In addition, by comparing two thickness groups of μc-Ge:H thin films deposited at different discharge powers, it is noticed that the evolution process relates to the formation of crystal nucleuses. Thus, a power gradient method is proposed to understand the mechanism of nucleation and crystal growth in the initial deposition process of μc-Ge:H films. Finally, by power gradient method, the incubation layer thickness of μc-Ge:H thin films has been decreased to less than 6 nm. Moreover, Raman scattering spectra shows a 38 nm μc-Ge:H film has a crystal fraction (XC) of 62.4%. Meanwhile, the mobility of TFT devices shows the improved electrical property of μc-Ge:H film deposited by power gradient method.

  13. Microstructure evolution and degradation mechanisms of reactor internal steel irradiated with heavy ions

    NASA Astrophysics Data System (ADS)

    Borodin, O. V.; Bryk, V. V.; Kalchenko, A. S.; Parkhomenko, A. A.; Shilyaev, B. A.; Tolstolutskaya, G. D.; Voyevodin, V. N.

    2009-03-01

    Structure evolution and degradation mechanisms during irradiation of 18Cr-10Ni-Ti steel (material of VVER-1000 reactor internals are investigated). Using accelerator irradiations with Cr3+ and Ar+ ions allowed studying effects of dose rate, different initial structure state and implanted ions on features of structure evolution and main mechanisms of degradation including low temperature swelling and embrittlement of the 18Cr-10Ni-Ti steel. It is shown that differences in dose rate at most irradiation temperatures mainly exert their influence on the duration of the swelling transient regime. Calculations of possible transmutation products during irradiation of this steel in a VVER-1000 spectrum were performed. It is shown that gaseous atoms (He and H), which are generated simultaneously with radiation defects, stabilize the elements of radiation microstructure and influence the swelling. The nature of deformation under different temperatures of irradiation and of mechanical testing is investigated. It is shown that the temperature sensitivity of swelling behaviour in the investigated steel, with different initial structures can be connected with the dynamic behaviour of point defect sinks.

  14. Streambed microstructure predicts evolution of development and life history mode in the plethodontid salamander Eurycea tynerensis

    PubMed Central

    Bonett, Ronald M; Chippindale, Paul T

    2006-01-01

    Background Habitat variation strongly influences the evolution of developmentally flexible traits, and may drive speciation and diversification. The plethodontid salamander Eurycea tynerensis is endemic to the geologically diverse Ozark Plateau of south-central North America, and comprises both strictly aquatic paedomorphic populations (achieving reproductive maturity while remaining in the larval form) and more terrestrial metamorphic populations. The switch between developmental modes has occurred many times, but populations typically exhibit a single life history mode. This unique system offers an opportunity to study the specific ecological circumstances under which alternate developmental and life history modes evolve. We use phylogenetic independent contrasts to test for relationships between a key microhabitat feature (streambed sediment) and this major life history polymorphism. Results We find streambed microstructure (sediment particle size, type and degree of sorting) to be highly correlated with life-history mode. Eurycea tynerensis is paedomorphic in streams containing large chert gravel, but metamorphoses in nearby streams containing poorly sorted, clastic material such as sandstone or siltstone. Conclusion Deposits of large chert gravel create loosely associated streambeds, which provide access to subsurface water during dry summer months. Conversely, streambeds composed of more densely packed sandstone and siltstone sediments leave no subterranean refuge when surface water dries, presumably necessitating metamorphosis and use of terrestrial habitats. This represents a clear example of the relationship between microhabitat structure and evolution of a major developmental and life history trait, and has broad implications for the role of localized ecological conditions on larger-scale evolutionary processes. PMID:16512919

  15. The effects of microstructural evolution on the spall response of 1100 aluminum

    NASA Astrophysics Data System (ADS)

    Williams, Cyril Labode

    In order to develop a better understanding of the spall response of aluminum and aluminum alloys, spall plate impact experiments in conjunction with shock recovery plate impact experiments were conducted using 1100 aluminum. The objectives of this thesis are to first study the effects of peak shock stress, pulse duration, strain rate, and shock induced microstructural evolution on the spall response of 1100-O aluminum. Then the 1100-O aluminum was cold rolled to various percent reductions and shock loaded to different peak shock stresses so that the effects of cold rolling on the spall response of 1100-O aluminum can be studied. These objectives may lead to a better understanding of the substructure evolution and spall failure process of aluminum and aluminum alloys under shock loading conditions and consequently lead to improved hydrocode models and the design of superior armors. Plate impact experiments were conducted to study the effects of peak shock stress and pulse duration on the spall response of fully annealed 1100 aluminum. The spall strength was observed to decrease as the pulse duration was increased from approximately 0.58 mus to 1.17 mus. Also, an increase in tensile unloading strain rate increases the spall strength. However, our results also show an increase in spall strength with increase in peak shock stress up to approximately 8.3 GPa, followed by a decrease in spall strength for higher shock stresses. Next, shock and spall plate impact recovery experiments were conducted to probe the microstructural evolution of fully annealed 1100 aluminum. It was found that as the shock stress is increased from 4.0 to approximately 8.3 GPa, the material shock hardened due to increase in the net dislocation density. Ductile transgranular fracture was identified as the fracture mode for this shock stress range. The decrease in spall strength beyond 8.3 GPa appears to be due to grain refinement induced by dynamic recovery. Brittle intergranular fracture with

  16. Microstructure evolution and strain localization in Cu and Cu-8Al single crystals subjected to channel-die compression.

    PubMed

    Lewandowska, Małgorzata; Swiatnicki, Wiesław; Piatkowski, Andrzej; Jasienski, Zdzisław

    2006-09-01

    Single crystals of pure Cu and Cu-8%Al with two initial orientations, {112}111 and {112}110, were subjected to monotonic compression in channel-die at room temperature (293 K). The dislocation microstructure and local crystallography were investigated by transmission electron microscopy after different amounts of deformation. Various factors, such as initial single crystal orientation, chemical composition and amount of plastic deformation, were analysed in order to determine their influence on the microstructure evolution, local orientation variations and strain localization phenomena.

  17. Microstructural Evolution and Functional Properties of Fe-Mn-Al-Ni Shape Memory Alloy Processed by Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Niendorf, Thomas; Brenne, Florian; Krooß, Philipp; Vollmer, Malte; Günther, Johannes; Schwarze, Dieter; Biermann, Horst

    2016-06-01

    In the current study, a Fe-Mn-Al-Ni shape memory alloy is processed by additive manufacturing for the first time. Microstructural evolution upon processing is strongly affected by thermal gradients and solidification velocity and, thus, by processing parameters and the actual specimen geometry. By single-step solutionizing heat treatment pronounced grain growth is initiated leading to microstructures showing good reversibility. The compressive stress-strain response revealed maximum reversible pseudo-elastic strain of about 7.5 pct. Critical steps toward further optimization of additively manufactured Fe-Mn-Al-Ni shape memory alloys are discussed.

  18. Microstructure Evolution and Its Effect on the Wear Performance of HVOF-Sprayed Conventional WC-Co Coating

    NASA Astrophysics Data System (ADS)

    Fu, Dingfa; Xiong, Haoqi; Wang, Qun

    2016-10-01

    In this work, a conventional tungsten carbide 12% cobalt (WC-12Co) coating was deposited by using a liquid fuel JP-8000 high velocity oxyfuel spray system. The properties of the coating namely phase content, microstructure, hardness, porosity, and fracture toughness were examined. The microstructure evolution and its influence on the abrasive wear behavior of the coatings were evaluated in detail by in-situ scanning electron microscopy and a comprehensive model for decarburization of WC has been established using x-ray diffraction and transmission electron microscopy analyses.

  19. Microstructural Evolution and Mechanical Properties of Cold-deformed Al-5Cu Alloy Samples After Isothermal Heat Treatments

    SciTech Connect

    Saklakoglu, Nursen; Gencalp, Simge

    2011-01-17

    Abstract.In this paper, the microscopic morphology of a semi solid Al5Cu alloy by strain induced melt activated (SIMA) process were investigated, and the effects of predeformation, microstructural evolution, aging response and hardness changes were determined. The microstructural observation shows that while the grain boundaries started to appear after 620 deg. C, globular grains surrounded wet boundaries needed for SSP were obtained at 650 deg. C. The grain sizes exhibited ununiformity from the outer surface to the center of the sample because of ununiform predeformation. Although isothermal heat treatments reduced hardness, age hardening gave back the hardness loss.

  20. Microstructures induced by a stress gradient in a nickel-based superalloy

    SciTech Connect

    Ignat, M.; Buffiere, J.Y.; Chaix, J.M. )

    1993-03-01

    The evolution of the microstructure of single crystals of a nickel-based superalloy during high temperature (1,323 K, 1,050 C) creep in bending has been studied. Bending provides both tensile and compressive stress gradients, consequently the effects of varying stress conditions on the evolution of the morphology of the [gamma][prime] precipitates can be determined from a single specimen. The morphological changes were analyzed by scanning electron microscopy using image analysis techniques and by transmission electron microscopy, then described by dimensionless parameters. The authors discuss the dependence of the morphological changes in the superalloy on the stresses acting in the sample (magnitude and sign). The authors also discuss the driving mechanisms for the observed morphological changes.

  1. Evolution of Mineral Fabrics and Microstructures in Kimmeridge Shale upon Kerogen Maturation

    NASA Astrophysics Data System (ADS)

    Kanitpanyacharoen, J.; Vanorio, T.; Liu, Y.; Xiao, X.; Benmore, C.

    2013-12-01

    Shale has increasingly received attention due to its recent recognition as a potential game changer of US energy outlook. However a fundamental relationship between mineral lattice preferred orientation (LPO or fabrics), kerogen, and elastic properties of shale remains questionable. Here we present different synchrotron X-ray techniques to capture microstructural transformations in Kimmeridge Shale upon temperature-induced anhydrous maturation. At room condition, the sample is mainly composed of clays 72 vol.%, quartz (15 vol.%), pyrite (11 vol.%), and a small amount of pyrite (2 vol.%). Illite-group is the dominating clay with 50 vol.% present. Illite-mica (30 vol.%) shows the highest degree of LPO (3.33 m.r.d.), which is consistent with previous studies (Wenk et al 2008, Voltolini et al. 2009, Kanitpanyacharoen et al. 2011). However the illite-smectite group exhibits relatively weaker degree of LPO due to the disordered nature of the structure. Chlorite shows the least degree of LPO due to its total clay content, which is only 2 vol.%. Upon heating to 300 °C, the phase proportions did not change much and the degrees of all clay minerals fabrics remain fairly consistent. The high-resolution 3D imaging technique allows us to record different stages of kerogen transformation, particularly a significant gas bubble formation at 400 °C. Upon heating up to 500 °C, kerogen shrinkage (17 vol.%) and clay matrix expansion continued and appeared more pronounced after 10 hours of heating. The consistent results from both experiments confirm that no significant change of mineral fabrics and microstructural features below 300 °C observed. These findings further infer that the evolution of clay fabrics and kerogen maturation may affect elastic anisotropy consistently at the temperature below 300 °C. The reduction of kerogen greatly influences elastic anisotropy properties and the identification of the promising source in the hydrocarbon reservoir.

  2. Deformation behavior and microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Lee, Woei-Shyan; Lin, Ching-Rong

    2016-10-01

    The impact deformation behavior and associated microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures are investigated using a compressive split-Hopkinson pressure bar (SHPB) system. Cylindrical specimens are deformed at strain rates of 1 × 103 s-1, 2 × 103 s-1, 3 × 103 s-1 and 5 × 103 s-1 and temperatures of 0 °C, -100 °C and -196 °C. It is shown that the flow stress is strongly dependent on the strain rate and temperature. For a given temperature, the flow stress varies with the strain rate in accordance with a power law relation with an average exponent of 0.157 and an activation energy of 0.7 kJ/mol. Moreover, the coupled effects of the strain rate and temperature on the flow stress are adequately described by the Zener-Hollomon parameter (Z). For all test temperatures, catastrophic failure occurs only under the highest strain rate of 5 × 103 s-1, and is the result of adiabatic shear. An increasing strain rate or reducing temperature leads to a greater dislocation density and a smaller grain size. Finally, the dependence of the flow stress on the microstructural properties of the impacted 7075-T6 specimens is well described by a specific Hall-Petch constitutive model with constants of K = 108.3 MPa μm1/2 and K‧ = 16.1 MPa μm, respectively. Overall, the results presented in this study provide a useful insight into the combined effects of strain rate and temperature on the flow resistance and deformability of 7075-T6 alloy and confirm that 7075-T6 is well suited to the fabrication of fuel tanks and related structural components in the aerospace field.

  3. Evolution of Local Microstructures: Spatial and Temporal Correlation in Clusters Undergoing 2-Dimensional Diffusion

    NASA Technical Reports Server (NTRS)

    Curreri, Peter A. (Technical Monitor); Frazier, D. O.; Rogers, J. R.; Witherow, W. K.; Facemire, B. R.; Inguva, R.; Glicksman, M. E.

    2003-01-01

    Diffusion-limited, capillarity-driven, coarsening of precipitates is an important and intensively studied phenomenon. Coarsening can occur among several microstructural constituents ranging from the primary phases to widely dispersed precipitates. Moreover, coarsening of three-dimensional (3-D) phase domains, occurring via mass transport through a two-dimensional (2-D) diffusion field (called mixed-dimensional phase coarsening) is a cooperative phenomenon that is of practical importance, especially in thin film technologies and catalysis. A primary objective of our current work is to focus on the details of evolving microstructures through a study of 'island' formation in heteroepitaxial film/substrate systems. Whereas this work has been designed for space-based coarsening studies, which require long-duration quality microgravity to observe 3-D Ostwald ripening, a significant amount of work has been performed during ground-based studies to observe diffusional coarsening in a liquid-liquid two-phase system. We have performed the experiment at an isopycnic point to maximize exclusion of gravity-based system disturbance. This has allowed observations of 3-D droplets, immobilized by container wall contact, undergoing coarsening by 2-D diffusion for the required long times (approximately 4 months) using a holographic imaging technique. Although such systems may not be as reliant on long-duration microgravity processing as 3-D systems are, they are of direct relevance to so-called mixed-dimensional coarsening and to the study of heterostructures grown by thin-film technique

  4. Microstructure evolution and tensile mechanical properties of thixoformed high performance Al-Zn-Mg-Cu alloy

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Chen, Qiang; Wang, Bo; Du, Zhi-ming

    2015-09-01

    Al-Zn-Mg-Cu alloys are the strongest aluminum alloys which have been widely used for aerospace applications. They are usually machined from the wrought state usually with a high waste percentage. To reduce waste, it is important to thixoform these alloys in near net shape. In this work, the thixoformability of a commercial high performance Al-Zn-Mg-Cu alloy 7075 was studied. A novel multistep reheating regime was developed in recrystallization and partial melting (RAP) route to obtain spheroidal semi-solid microstructures. The as-extruded 7075 alloy was fully recrystallized for a short holding time using the multistep reheating regime. Semi-solid microstructures with fine and spherical solid grains with a grain size of 40-50 μm embedded in liquid matrix were obtained. The advantage of the multistep reheating regimes over those conventional routes was also discussed. Some wheel-shaped components were thixoformed from the as-received 7075 alloy. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed component based on multistep reheating regime, are 510 MPa, 446 MPa and 17.5% respectively. These values are superior to those of the products manufactured with the conventional RAP route. As the results indicated, thixoforming could be conducted based on commercial extruded Al-Zn-Mg-Cu alloys, which has important practical significance.

  5. Interfacial Microstructure Evolution and Shear Strength of Titanium Sandwich Structures Fabricated by Brazing

    NASA Astrophysics Data System (ADS)

    Wang, Wentao; Fan, Minyu; Li, Jinlong; Tao, Jie

    2016-03-01

    The corrugated sandwich structure, consisting of a CP Ti (commercially pure titanium) core between two Ti-6Al-4V face sheets, was brazed using pasty Ti-37.5Zr-15Cu-10Ni as filler alloy, at the temperature of 870°C for 5, 10, 20, and 30 min. The effect of brazing time on the microstructure and elemental distribution of the brazed joints was examined by means of SEM, EDS, and XRD analyses. It was found that various intermetallic phases were formed in the brazed joints, following a brazing time of 5 min, and their contents were decreased by the increment of brazing time, while prolonged brazing time resulted in a fine, acicular Widmanstätten microstructure throughout the entire joint. In addition, shear testing was performed in the brazed corrugated specimens in order to indirectly assess the quality of the joints. The debonding between CP Ti and Ti-6Al-4V was observed in the specimen brazed for 5 min and the fracture of the CP Ti corrugated core occurred after 30 min of brazing time. Additionally, when brazed for 10 min or 20 min, brittle intermetallic compounds in the joints and the grain growth of the base metal were controllable. Therefore, the sandwich structures failed without debonding in the joints or fracture within the base metal, demonstrating a good combination of strength and ductility.

  6. Size effects on plasticity and fatigue microstructure evolution in FCC single crystals

    NASA Astrophysics Data System (ADS)

    El-Awady, Jaafar Abbas

    In aircraft structures and engines, fatigue damage is manifest in the progressive emergence of distributed surface cracks near locations of high stress concentrations. At the present time, reliable methods for prediction of fatigue crack initiation are not available, because the phenomenon starts at the atomic scale. Initiation of fatigue cracks is associated with the formation of Persistent slip bands (PSBs), which start at certain critical conditions inside metals with specific microstructure dimensions. The main objective of this research is to develop predictive computational capabilities for plasticity and fatigue damage evolution in finite volumes. In that attempt, a dislocation dynamics model that incorporates the influence of free and internal interfaces on dislocation motion is presented. The model is based on a self-consistent formulation of 3-D Parametric Dislocation Dynamics (PDD) with the Boundary Element method (BEM) to describe dislocation motion, and hence microscopic plastic flow in finite volumes. The developed computer models are bench-marked by detailed comparisons with the experimental data, developed at the Wright-Patterson Air Force Lab (WP-AFRL), by three dimensional large scale simulations of compression loading on micro-scale samples of FCC single crystals. These simulation results provide an understanding of plastic deformation of micron-size single crystals. The plastic flow characteristics as well as the stress-strain behavior of simulated micropillars are shown to be in general agreement with experimental observations. New size scaling aspects of plastic flow and work-hardening are identified through the use of these simulations. The flow strength versus the diameter of the micropillar follows a power law with an exponent equal to -0.69. A stronger correlation is observed between the flow strength and the average length of activated dislocation sources. This relationship is again a power law, with an exponent -0.85. Simulation results

  7. Evolution of microstructure, texture and inhibitor along the processing route for grain-oriented electrical steels using strip casting

    SciTech Connect

    Liu, Hai-Tao; Yao, Sheng-Jie; Sun, Yu; Gao, Fei; Song, Hong-Yu; Liu, Guo-Huai; Li, Lei; Geng, Dian-Qiao; Liu, Zhen-Yu; Wang, Guo-Dong

    2015-08-15

    In the present work, a regular grade GO sheet was produced successively by strip casting, hot rolling, normalizing annealing, two-stage cold rolling with intermediate annealing, primary recrystallization annealing, secondary recrystallization annealing and purification. The aim of this paper was to characterize the evolution of microstructure, texture and inhibitor along the new processing route by comprehensive utilization of optical microscopy, X-ray diffraction and transmission electron microscopy. It was found that a fine microstructure with the ferrite grain size range of 7–12 μm could be obtained in the primary recrystallization annealed sheet though a very coarse microstructure was produced in the initial as-cast strip. The main finding was that the “texture memory” effect on Goss texture started on the through-thickness intermediate annealed strip after first cold rolling, which was not similar to the “texture memory” effect on Goss texture starting on the surface layers of the hot rolled strip in the conventional production route. As a result, the origin of Goss nuclei capable of secondary recrystallization lied in the grains already presented in Goss orientation in the intermediate annealed strip after first cold rolling. Another finding was that fine and dispersive inhibitors (mainly AlN) were easy to be produced in the primary recrystallization microstructure due to the initial rapid solidification during strip casting and the subsequent rapid cooling, and the very high temperature reheating usually used before hot rolling in the conventional production route could be avoided. - Highlights: • A regular grade grain-oriented electrical steel was produced. • Evolution of microstructure, texture and inhibitor was characterized. • Origin of Goss nuclei lied in the intermediate annealed strip. • A fine primary recrystallization microstructure could be produced. • Effective inhibitors were easy to be obtained in the new processing route.

  8. Evolution of the microstructure of unmodified and polymer modified asphalt binders with aging in an accelerated weathering tester.

    PubMed

    Menapace, Ilaria; Masad, Eyad

    2016-09-01

    This paper presents findings on the evolution of the surface microstructure of two asphalt binders, one unmodified and one polymer modified, directly exposed to aging agents with increasing durations. The aging is performed using an accelerated weathering tester, where ultraviolet radiation, oxygen and an increased temperature are applied to the asphalt binder surface. Ultraviolet and dark cycles, which simulated the succession of day and night, alternated during the aging process, and also the temperature varied, which corresponded to typical summer day and night temperatures registered in the state of Qatar. Direct aging of an exposed binder surface is more effective in showing microstructural modifications than previously applied protocols, which involved the heat treatment of binders previously aged with standardized methods. With the new protocol, any molecular rearrangements in the binder surface after aging induced by the heat treatment is prevented. Optical photos show the rippling and degradation of the binder surface due to aging. Microstructure images obtained by means of atomic force microscopy show gradual alteration of the surface due to aging. The original relatively flat microstructure was substituted with a profoundly different microstructure, which significantly protrudes from the surface, and is characterized by various shapes, such as rods, round structures and finally 'flower' or 'leaf' structures.

  9. Microstructure Evolution during Friction Stir Welding of Mill-Annealed Ti-6Al-4V

    NASA Astrophysics Data System (ADS)

    Pilchak, A. L.; Tang, W.; Sahiner, H.; Reynolds, A. P.; Williams, J. C.

    2011-03-01

    In this study, mill-annealed Ti-6Al-4V plates were successfully friction stir welded over a wide range of processing parameters using a tungsten-1 pct La2O3 tool. Two K-type thermocouples embedded in the tool indicated that approximately 25 pct of the heat generated during welding was transferred out of the workpiece and into the tool. The thermocouple data, combined with observations of the microstructure, indicated that the stir zone of all welds exceeded the β transus. The microstructure and texture of two representative welds made just above and high above the β transus were investigated with scanning electron microscopy and electron backscatter diffraction (EBSD). The β phase orientations were reconstructed with a fully automated technique from the as-collected α phase data through knowledge of the Burgers orientation relationship. The results suggest that the fine β grains in the stir zone are formed from the base material ahead of the advancing tool by dissolution of secondary and primary α phase, and there is no further recrystallization. These grains subsequently deform by slip and rotate toward the orientations that are most stable with respect to the shear deformation induced by the tool. In the highest temperature weld, diffusion tool wear in the form of periodically spaced bands provided an internal marker of the tool/workpiece interface during welding. The flow patterns evident within the tungsten-enriched bands suggest that flow is considerably more chaotic on the advancing side than in the central stir zone.

  10. Phase transformation and microstructural evolution of nanostructured oxides and nitrides under ion irradiations

    NASA Astrophysics Data System (ADS)

    Lu, Fengyuan

    Material design at the nanometer scale is an effective strategy for developing advanced materails with enhanced radiation tolerance for advanced nuclear energy systems as high densities of surfaces and interfaces of the nanostructured materials may behave as effective sinks for defect recovery. However, nanostructured materials may not be intrinsically radiation tolerant, and the interplay among the factors of crystal size, temperature, chemical composition, surface energy and radiation conditions may eventually determine material radiation behaviors. Therefore, it is necessary to understand the radiation effects of nanostructured materials and the underlying physics for the design of advanced nanostructured nuclear materials. The main objective of this doctoral thesis is to study the behavior of nanostructured oxides and nitrides used as fuel matrix and waste forms under extreme radiation conditions with the focus of phase transformation, microstructural evolution and damage mechanisms. Radiation experiments were performed using energetic ion beam techniques to simulate radiation damage resulting from energetic neutrons, alpha-decay events and fission fragments, and various experimental approaches were employed to characterize materials’ microstructural evolution and phase stability upon intense radiation environments including transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. Thermal annealing experiments indicated that nanostructured ZrO2 phase stability is strongly affected by the grain size. Radiation results on nanostructured ZrO2 indicated that thermodynamically unstable or metastable high temperature phases can be induced by energetic beam irradiation at room temperature. Various phase transformation among different polymorphs of monoclinic, tetragonal and amorphous states can be induced, and different mechanisms are responsible for structural transformations including oxygen vacancies accumulation upon displacive

  11. Microstructure Evolution and Mechanical Properties of 2219 Al Alloy During Aging Treatment

    NASA Astrophysics Data System (ADS)

    Wang, Huimin; Yi, Youping; Huang, Shiquan

    2017-03-01

    Hardness and tensile properties of 2219 Al alloys were tested at various temperature (150, 165, 175 °C) and subjected to T6 temper heat treatment to identify the peak aging time at various temperature. Microstructure evolution and precipitate behavior were analyzed with transmission electron microscope (TEM), differential scanning calorimetry (DSC) and x-ray diffraction (XRD). It is found that the peak aging time is 24 h at 150 °C and does not vary down to 165 °C. When the aging temperature rise to 175 °C, the peak aging time down to 12 h. Considering the strength and elongation, the optimum aging treatment is at 165 °C for 24 h after the solution treatment at 535 °C for 1.5 h. Compared with that of only water-quenched sample, after aged at 165 °C for 24 h, the tensile strength of the 2219 Al alloy increases from 324.5 to 411.8 MPa, yield strength from 168 to 310.8 MPa, respectively. The improvement in the mechanical performance is mainly attributed to the precipitation strengthening of the GP zones, θ″ and θ' phases.

  12. Synthesis and Microstructure Evolution of Nano-Titania Doped Silicon Coatings

    NASA Astrophysics Data System (ADS)

    Moroz, N. A.; Umapathy, H.; Mohanty, P.

    2010-01-01

    The Anatase phase of Titania (TiO2) in nanocrystalline form is a well known photocatalyst. Photocatalysts are commercially used to accelerate photoreactions and increase photovoltaic efficiency such as in solar cells. This study investigates the in-flight synthesis of Titania and its doping into a Silicon matrix resulting in a catalyst-dispersed coating. A liquid precursor of Titanium Isopropoxide and ethanol was coaxially fed into the plasma gun to form Titania nanoparticles, while Silicon powder was externally injected downstream. Coatings of 75-150 μm thick were deposited onto flat coupons. Further, Silicon powder was alloyed with aluminum to promote crystallization and reduce the amorphous phase in the Silicon matrix. Dense coatings containing nano-Titania particles were observed under electron microscope. X-ray diffraction showed that both the Rutile and Anatase phases of the Titania exist. The influence of process parameters and aluminum alloying on the microstructure evolution of the doped coatings is analyzed and presented.

  13. Helium effects on microstructural evolution in tempered martensitic steels: In situ helium implanter studies in HFIR

    SciTech Connect

    Yamamoto, Takuya; Odette, George R.; Miao, Pifeng; Edwards, Danny J.; Kurtz, Richard J.

    2009-04-30

    Microstructural evolutions in tempered martensitic steels (TMS) under neutron-irradiation, at fusion relevant He/dpa ratios and dpa rates, were characterized using a novel in situ He-implanter technique. F82H-mod3 was irradiated at 500 C in HFIR to a nominal 9 dpa and 190 or 380 appm He in both in the as-tempered (AT) and 20% cold-worked (CW) conditions. In all cases, a high number density of 1-2 nm He-bubbles were observed, along with fewer but larger 10 nm void-like faceted cavities. The He-bubbles form preferentially on dislocations and various interfaces. A slightly larger number of smaller He bubbles were observed in the CW condition. The lower He/dpa ratio produced slightly smaller and fewer He-bubbles. Comparisons of these observations to the results in nano-structured ferritic alloy (NFA) MA957 provide additional evidence that TMS may be susceptible to He-embrittlement as well as void swelling at fusion relevant He concentrations, while NFA are much more resistant to these degradation phenomena.

  14. Thermal evolution of microstructure in ion-irradiated GaN

    SciTech Connect

    Bae, In-Tae; Jiang, Weilin; Wang, Chong M.; Weber, William J.; Zhang, Yanwen

    2009-04-20

    The thermal evolution of the microstructure created by irradiation of a GaN single crystal with 2 MeV Au2+ ions at 150 K is characterized following annealing at 973 K using transmission electron microscopy. In the as-irradiated sample characterized at 300 K, Ga nanocrystals with the diamond structure, which is an unstable configuration for Ga, are directly observed together with nitrogen bubbles in the irradiation-induced amorphous layer. Upon thermal annealing, the thickness of the amorphous layer decreases by ~13.1 %, and nano-beam electron diffraction analysis indicates no evidence for residual Ga nanocrystals, but instead reveals a mixture of hexagonal and cubic GaN phases in the annealed sample. Nitrogen molecules, captured in the as-irradiated bubbles, appear to debond and react with the Ga nanocrystals during the thermal annealing to form crystalline GaN. In addition, electron energy loss spectroscopy measurements reveal an atomic volume change of 18.9 % for the as-irradiated amorphous layer relative to the virgin single crystal GaN. This relative swelling of the damaged layer reduces to 7.7 % after thermal annealing. Partial recrystallization and structural relaxation of the GaN amorphous state are believed responsible for the volume change.

  15. Microstructure Evolution during Roller Hemming of AZ31B Magnesium Sheet

    NASA Astrophysics Data System (ADS)

    Levinson, Amanda; Mishra, Raja K.; Doherty, Roger D.; Kalidindi, Surya R.

    2012-10-01

    The differences in the microstructure evolution during laser-roller hemming and conventional roller hemming (done at room temperature) of commercial-grade AZ31B sheet were studied using electron backscatter diffraction (EBSD). It was observed that the flanging operation, done as a precursor to roller hemming, produced a heterogeneous grain structure that remained throughout the subsequent hemming steps. Laser heating, applied during the roller passes, significantly reduced the amount of both extension and contraction twinning in the inner and outer band, respectively. More importantly, after two roller passes without laser heating, extension twinning in the inner band seemed to saturate. This forced the material in the inner band to accommodate further deformation by harder mechanisms, such as pyramidal slip and contraction twinning, during the third roller pass when failure occurred. The laser-hemmed samples exhibited much lower hardness values, especially in the inner band, which was deemed to be largely responsible for the success of the hemming operation with laser heating.

  16. Microstructural Evolution of the 55 Wt Pct Al-Zn Coating During Press Hardening

    NASA Astrophysics Data System (ADS)

    Lee, Chang Wook; De Cooman, Bruno Charles

    2014-09-01

    Press hardening is increasingly being used to produce ultra-high strength steel parts for passenger cars. Al-Si, Zn, and Zn-alloy coatings have been used to provide corrosion protection to press hardening steel grades. The use of coatings has drawbacks such as coating delamination or liquid metal-induced embrittlement. In the present work, the microstructural evolution of Al-Zn coating during press hardening was studied. The 55 wt pct Al-Zn coating can in principle provide both Al barrier protection and Zn cathodic protection to press hardened steel. During the heat treatment associated with the press hardening, the 55 wt pct Al-Zn alloy coating is converted to an intermetallic surface layer of Fe2Al5 and a FeAl intermetallic diffusion layer. The Zn is separated from both intermetallic compounds and accumulates at grain boundaries and at the surface. This Zn separation process is beneficial in terms of providing cathodic protection to Al-Zn coated press hardening steel.

  17. Microstructural and textural evolution of AZ61 magnesium alloy sheet during bidirectional cyclic bending

    SciTech Connect

    Huo, Qinghuan; Yang, Xuyue Ma, Jijun; Sun, Huan; Qin, Jia; Jiang, Yupei

    2013-05-15

    In this work, the microstructural and textural evolution in the sheets of AZ61 magnesium alloy was studied by means of bidirectional cyclic bending for 8 passes at 623 K. The bended samples were examined by optical microscopy and electron backscatter diffraction analysis. The results showed that a gradient structure with fine grains about 3 μm in the regions near two surfaces and, in contrast, coarse grains in the middle of the sheet were formed. The evident grain refinement was attributed to twin-assisted dynamic recrystallization and continuous dynamic recrystallization induced by kink bands. The texture intensity was clearly reduced, resulting in a negative gradient distribution, with the texture intensity decreases from the center of the sheet to two surfaces. The weakened texture greatly facilitated the reduction of the yield strength. A higher fracture elongation and a slightly improved ultimate tensile strength were achieved concurrently. - Highlights: • The AZ61 Mg alloy is deformed at 623 K by bidirectional cyclic bending. • A symmetric gradient distribution of fine grains along the thickness is formed. • The basal texture in the regions near two surfaces is weakened significantly.

  18. Influence of doping concentration on microstructure evolution and sintering kinetics of Er:YAG transparent ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Jing; Liu, Qiang; Li, Jiang; Ivanov, Maxim; Ba, Xuewei; Yuan, Yong; Lin, Li; Chen, Min; Liu, Wenbin; Kou, Huamin; Shi, Yun; Chen, Haohong; Pan, Yubai; Cheng, Xiaonong; Guo, Jingkun

    2014-11-01

    Erbium doped yttrium aluminum garnet (Er:YAG) transparent ceramics with different Er doping concentrations were fabricated from powder mixtures of α-Al2O3, Y2O3, and Er2O3 with tetraethoxysilane (TEOS) and MgO as sintering aids by solid-state reactive sintering. The sintering temperatures were from 1500 °C up to 1750 °C. Densification, microstructure evolution and optical transparency of Er:YAG ceramics with different doping concentrations were examined. For all the doping concentration, fully dense Er:YAG transparent ceramics with homogeneous grain size distributions around 20-23 μm were obtained by sintering at 1750 °C for 50 h, whose transmittances were all above 83% at the wavelength of 1200 nm. The grain growth kinetic of Er:YAG ceramics was also investigated as a function of erbium content. The calculated activation energies for grain growth of the 0.5, 1.0, 5.0, and 10 at%Er:YAG ceramics were 779, 855, 805, and 861 kJ/mol, respectively. The luminescence spectra were also measured and discussed.

  19. Evolutions of Microstructure and Properties During Cold Rolling of 19Cr Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ran, Qingxuan; Xu, Wanjian; Wu, Zhaoyu; Li, Jun; Xu, Yulai; Xiao, Xueshan; Hu, Jincheng; Jiang, Laizhu

    2016-10-01

    Evolutions of microstructure, mechanical, and corrosion properties of 19Cr (Fe-18.9Cr-10.1Mn-0.3Ni-0.261N-0.030C-0.5Si) duplex stainless steel have been investigated during cold rolling at room temperature. Dislocation slip dominated deformation mode of ferrite phase. However, deformation mechanism of austenite phase was different with the increasing cold-rolling reductions. Dislocation slip and strengthening effect of twin boundaries caused pile-up phenomenon at the initial deformation stage. When the amount of cold-rolling reduction attained greater than 50 pct, induced α'-martensite appeared in deformed austenite phase. Hardness of austenite phase was higher than that of the deformed ferrite because of its higher strengthening effect during cold-rolling process. Cold-rolling deformation caused deterioration of the pitting corrosion resistance in 3.5 wt pct NaCl aqueous solution. Pitting corrosion always initiated in the ferrite phase and the phase boundary in the solution-treated alloy. Additional pitting holes appeared in deformed austenite phase because of the decrease in corrosion resistance caused by dislocation accumulation and induced α'-martensite.

  20. A method for studying weld fusion boundary microstructure evolution in aluminum alloys

    SciTech Connect

    Kostrivas, A.; Lippold, J.C.

    2000-01-01

    Aluminum alloys may exhibit a variety of microstructures within the fusion zone adjacent to the fusion boundary. Under conventional weld solidification conditions, epitaxial nucleation occurs off grains in the heat-affected zone (HAZ) and solidification proceeds along preferred growth directions. In some aluminum alloys, such as those containing Li and Zr, a nondendritic equiaxed grain zone (EQZ) has been observed along the fusion boundary that does not nucleate epitaxially from the HAZ substrate. The EQZ has been the subject of considerable study because of its susceptibility to cracking during initial fabrication and repair. The motivation of this investigation was to develop a technique that would allow the nature and evolution of the fusion boundary to be studied under controlled thermal conditions. A melting technique was developed to simulate the fusion boundary of aluminum alloys using the Gleeble{reg{underscore}sign} thermal simulator. Using a steel sleeve to contain the aluminum, samples wee heated to incremental temperatures above the solidus temperature of a number of alloys. In Alloy 2195, a 4Cu-1Li alloy, an EQZ could be formed by heating in the temperature range approximately from 630--640 C. At temperatures above 640 C, solidification occurred by the normal epitaxial nucleation and growth mechanism. Fusion boundary behavior was also studied in Alloys 5454-H34, 6061-T6 and 2219-T8. Nucleation in these alloys was observed to be epitaxial. Details of the technique and its effectiveness for performing controlled melting experiments at incremental temperatures above the solidus are described.

  1. Chemomechanical evolution of pore space in carbonate microstructures upon dissolution: Linking pore geometry to bulk elasticity

    NASA Astrophysics Data System (ADS)

    Arson, C.; Vanorio, T.

    2015-10-01

    One of the challenges faced today in a variety of geophysical applications is the need to understand the changes of elastic properties due to time-variant chemomechanical processes. The objective of this work is to model carbonate rock elastic properties as functions of pore geometry changes that occur when the solid matrix is dissolved by carbon dioxide. We compared two carbonate microstructures: porous micrite ("mudstone") and grain-supported carbonate ("packstone"). We formulated a mathematical model that distinguishes the effects of microporosity and macroporosity on stiffness changes. We used measures of mechanical and chemical porosity changes recorded during injection tests to compute elastic moduli and compare them to moduli obtained from wave velocity measurements. In mudstones, both experimental and numerical results indicate that bulk moduli change by less than 5%. The evolution of elastic moduli is controlled by macropore enlargement. In packstones, model predictions underestimate changes of elastic moduli with total porosity by 10% to 80%. The total porosity variation is 60% to 75% smaller than the chemical porosity variation, which indicates that pore expansion due to dissolution is counterbalanced by pore shrinkage due to compaction. Packstone elastic properties are controlled by grain sliding. The methodology presented in this paper can be generalized to other chemomechanical processes studied in rocks, such as dislocations, glide, diffusive mass transfer, recrystallization, and precipitation.

  2. Transmitted light relaxation and microstructure evolution of ferrofluids under gradient magnetic fields

    NASA Astrophysics Data System (ADS)

    Huang, Yan; Li, Decai; Li, Feng; Zhu, Quanshui; Xie, Yu

    2015-03-01

    Using light transmission experiments and optical microscope observations with a longitudinal gradient magnetic field configuration, the relationship between the behavior of the transmitted light relaxation and the microstructure evolution of ionic ferrofluids in the central region of an axisymmetric field is investigated. Under a low-gradient magnetic field, there are two types of relaxation process. When a field is applied, the transmitted light intensity decreases to a minimum within a time on the order of 101-102 s. It is then gradually restored, approaching its initial value within a time on the order of 102 s. This is type I relaxation, which corresponds to the formation of magnetic columns. After the transmission reaches this value, it either increases or decreases slowly, stabilizing within a time on the order of 103 s, according to the direction of the field gradient. This is a type II relaxation, which results from the shadowing effect, corresponding to the motion of the magnetic columns under the application of a gradient force. Under a magnetic field with a centripetal high-gradient (magnetic materials subjected to a force pointing toward the center of the axisymmetric field), the transmitted light intensity decreases monotonously and more slowly than that under a low-gradient field. Magnetic transport and separation resulted from magnetophoresis under high-gradient fields, changing the formation dynamics of the local columns and influencing the final state of the column system.

  3. Effects of ball milling parameters on microstructural evolution and mechanical properties of W-3% Y composites

    NASA Astrophysics Data System (ADS)

    Zhao, Mingyue; Zhou, Zhangjian; Tan, Jun; Ding, Qingming; Zhong, Ming

    2015-10-01

    The W-3 Y composites were successfully prepared by spark plasma sintering of milled W-3 Y powders with different milling times (0 h, 5 h, 15 h, 30 h). X-ray diffraction (XRD), scanning electron microscope (SEM), and laser particle size analysis were used to study the microstructural evolution and morphological change during the milling process. The crystallite sizes exhibited a continuous refinement along with the increased milling time. The median particle sizes, measured by the laser diffraction method, showed a similar change tendency. Due to the existence of Y particles, the W-Y milled powders exhibited spherical-like morphology while pure tungsten milled powders exhibited lamellar morphology at the early milling stage (5-15 h). The microhardness of W-3 Y compacts showed a slight increase with the increase of milling time. The maximum bending strength of 795 MPa was obtained by sintering W-3 Y powders milled for 15 h. As the milling time was prolonged to 30 h, the increased oxygen impurity resulted in a slight decrease of density as well as the degradation of bending strength.

  4. Dislocations via incompatibilities in phase-field models of microstructure evolution

    NASA Astrophysics Data System (ADS)

    Gröger, R.; Marchand, B.; Lookman, T.

    2016-08-01

    We develop a phase-field model that describes the elastic distortion of a ferroelastic material with cubic anisotropy due to an arbitrary dislocation network and a uniform external load. The dislocation network is characterized using the Nye tensor and enters the formulation via a set of incompatibility constraints for the internal strain field. The long-range elastic response of the material is obtained by minimization of the free energy that accounts for higher-order terms of the order parameters and symmetry-adapted strain gradients. The influence of dislocations on the microstructure is studied using a static equilibrium analysis of a material without dislocations and with a random array of parallel edge dislocations. A minimal continuum dislocation dynamics is then used to investigate the simultaneous evolution of the network of geometrically necessary dislocations and the internal strain field. The model developed here is directly applicable to single-phase cubic crystals with an arbitrary degree of anisotropy as well as to ferroelastic materials undergoing temperature-driven cubic-to-tetragonal phase transitions.

  5. MICROMECHANICS AND MICROSTRUCTURE EVOLUTION: Modeling, Simulation and Experiments. Held in Madrid, Spain on 12-16 September 2005

    DTIC Science & Technology

    2006-10-30

    hardening–softening curves for ferritic X10CrAl24 steel in constant plastic strain amplitude cycling (the dotted curve separates the initial region before...stress–strain curve for ferritic X10CrAl24 steel. 3432 M. Petrenec et al. / Acta Materialia 54 (2006) 3429–3443of all specimens. Two different regimes...TITLE AND SUBTITLE MICROMECHANICS AND MICROSTRUCTURE EVOLUTION: Modeling, Simulation and Experiments 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER

  6. Micromechanics and Microstructure Evolution: Modeling, Simulation and Experiments. Conference Held in Madrid, Spain, 12-16 Sep 2005

    DTIC Science & Technology

    2006-10-30

    hardening–softening curves for ferritic X10CrAl24 steel in constant plastic strain amplitude cycling (the dotted curve separates the initial region before...stress–strain curve for ferritic X10CrAl24 steel. 3432 M. Petrenec et al. / Acta Materialia 54 (2006) 3429–3443of all specimens. Two different regimes...TITLE AND SUBTITLE MICROMECHANICS AND MICROSTRUCTURE EVOLUTION: Modeling, Simulation and Experiments 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER

  7. Crack-seal microstructure evolution in bi-mineralic quartz-chlorite veins in shales and siltstones from the RWTH-1 well, Aachen, Germany

    NASA Astrophysics Data System (ADS)

    Becker, Stephan; Hilgers, Christoph; Kukla, Peter A.; Urai, Janos L.

    2011-04-01

    In core samples from the deep geothermal well RWTH-1 we studied Variscan quartz-chlorite veins formed by crack-seal processes in siliciclastics at the brittle to ductile transition. These sheared veins are common in sections of the well, which are interpreted as Variscan thrust zones based on image logs and seismic data. Microstructures interpreted to reflect different stages in the evolution of such crack-seal veins suggest the veins started in microcracks sealed by quartz and chlorite, to veinlets crossing multiple grains, and bundles of veinlets evolving by progressive localization into low-angle extensional shear veins and high-angle dilational jog veins. In the sheared veins, chlorite and quartz ribbons show evidence for crack-seal and simultaneous ductile shearing during vein evolution, forming peculiar fin-shaped microstructures in quartz ribbons. In high-angle dilational jogs fibrous crystals of quartz and chlorite point to multiple crack-seal events with simultaneous growth of two different mineral phases. This is interpreted to be the basic microstructural process in the veins. We extend earlier models of polycrystal growth in fractures and present a series of 2D simulations of the kinematics of crystal growth in these bi-mineralic veins for both localized and non-localized cracking. Results are compared with the observed microstructures. We show that when the relative growth rates of the two mineral phases are different, serrated grain boundaries evolve. The similarities between observation and model suggest that the assumption of our model is valid, although many second order processes require a more detailed study. We propose that the principles observed here can be applied to other bi-mineralic crack-seal veins.

  8. Microstructures and oxidation behavior of some Molybdenum based alloys

    SciTech Connect

    Ray, Pratik Kumar

    2011-01-01

    The advent of Ni based superalloys revolutionized the high temperature alloy industry. These materials are capable of operating in extremely harsh environments, comprising of temperatures around 1050 C, under oxidative conditions. Demands for increased fuel efficiency, however, has highlighted the need for materials that can be used under oxidative conditions at temperatures in excess of 1200 C. The Ni based superalloys are restricted to lower temperatures due to the presence of a number of low melting phases that melt in the 1250 - 1450 C, resulting in softening of the alloys above 1000 C. Therefore, recent research directions have been skewed towards exploring and developing newer alloy systems. This thesis comprises a part of such an effort. Techniques for rapid thermodynamic assessments were developed and applied to two different systems - Mo-Si alloys with transition metal substitutions (and this forms the first part of the thesis) and Ni-Al alloys with added components for providing high temperature strength and ductility. A hierarchical approach towards alloy design indicated the Mo-Ni-Al system as a prospective candidate for high temperature applications. Investigations on microstructures and oxidation behavior, under both isothermal and cyclic conditions, of these alloys constitute the second part of this thesis. It was seen that refractory metal systems show a marked microstructure dependence of oxidation.

  9. 3D Online Submicron Scale Observation of Mixed Metal Powder's Microstructure Evolution in High Temperature and Microwave Compound Fields

    PubMed Central

    Xu, Feng; Hu, Xiao-fang; Xiao, Yu; Xiao, Ti-qiao

    2014-01-01

    In order to study the influence on the mechanical properties caused by microstructure evolution of metal powder in extreme environment, 3D real-time observation of the microstructure evolution of Al-Ti mixed powder in high temperature and microwave compound fields was realized by using synchrotron radiation computerized topography (SR-CT) technique; the spatial resolution was enhanced to 0.37 μm/pixel through the designed equipment and the introduction of excellent reconstruction method for the first time. The process of microstructure evolution during sintering was clearly distinguished from 2D and 3D reconstructed images. Typical sintering parameters such as sintering neck size, porosity, and particle size of the sample were presented for quantitative analysis of the influence on the mechanical properties and the sintering kinetics during microwave sintering. The neck size-time curve was obtained and the neck growth exponent was 7.3, which indicated that surface diffusion was the main diffusion mechanism; the reason was the eddy current loss induced by the external microwave fields providing an additional driving force for mass diffusion on the particle surface. From the reconstructed images and the curve of porosity and average particle size versus temperature, it was believed that the presence of liquid phase aluminum accelerated the densification and particle growth. PMID:24737986

  10. 3D online submicron scale observation of mixed metal powder's microstructure evolution in high temperature and microwave compound fields.

    PubMed

    Kang, Dan; Xu, Feng; Hu, Xiao-fang; Dong, Bo; Xiao, Yu; Xiao, Ti-qiao

    2014-01-01

    In order to study the influence on the mechanical properties caused by microstructure evolution of metal powder in extreme environment, 3D real-time observation of the microstructure evolution of Al-Ti mixed powder in high temperature and microwave compound fields was realized by using synchrotron radiation computerized topography (SR-CT) technique; the spatial resolution was enhanced to 0.37  μm/pixel through the designed equipment and the introduction of excellent reconstruction method for the first time. The process of microstructure evolution during sintering was clearly distinguished from 2D and 3D reconstructed images. Typical sintering parameters such as sintering neck size, porosity, and particle size of the sample were presented for quantitative analysis of the influence on the mechanical properties and the sintering kinetics during microwave sintering. The neck size-time curve was obtained and the neck growth exponent was 7.3, which indicated that surface diffusion was the main diffusion mechanism; the reason was the eddy current loss induced by the external microwave fields providing an additional driving force for mass diffusion on the particle surface. From the reconstructed images and the curve of porosity and average particle size versus temperature, it was believed that the presence of liquid phase aluminum accelerated the densification and particle growth.

  11. Microstructural evolution and mechanical properties of nanostructured aluminum and aluminum alloys

    NASA Astrophysics Data System (ADS)

    Witkin, David Barry

    Nanocrystalline materials are those with grain sizes below 100 nm. Reduction of the grain size to this scale offers great promise in improving material properties, particularly strength. Ultrafine-grained materials are considered those with grain sizes between 100 and 1000 nm, although the transition between "nanocrystalline" and "ultrafine-grained" is not well defined. A clear demarcation between the two based on grain size alone is impractical because dislocation-based deformation is active both above and below 100 nm. In this work, the processing and mechanical behavior of ultrafine-grained Al and Al-Mg alloys are discussed with particular reference to the operative deformation mechanisms and how they relate to the microstructure. The materials in question are based on nanocrystalline powders produced by cryomilling. The powders were canned and degassed, then consolidated by Hot Isostatic Pressing (HIPping), followed by extrusion. The microstructures of both as-HIPped and extruded materials were characterized in detail, and the mechanical properties were assessed at different combinations of strain rates and testing temperatures. The microstructures of both as-HIPped and extruded materials were duplex in character, with a fine-grained matrix that reflects the grain refinement due to the mechanical attrition process and a coarse-grained component that forms during consolidation in interparticle void spaces. The average grain size of the fine grained regions in the HIPped materials was between approximately 100 and 150 nm for the different billets examined, and increases to 150 to 250 nm after extrusion. Grain size distributions showed a range of grain sizes from 50 to 500 nm or more. The coarse grained regions had grain sizes on the order of 500 nm to 2 mum, and after extrusion were elongated with the extrusion direction. Yield stress and flow stress of the extruded materials was consistent with the Hall-Petch model using the average grain size. The mechanical

  12. Microstructural Evolution in Novel Suction Cast Multicomponent Ti-Fe-Co Alloys

    NASA Astrophysics Data System (ADS)

    Samal, Sumanta; Agarwal, Swapnil; Gautam, Priya; Biswas, Krishanu

    2015-02-01

    The present work is aimed at understanding the solidification pathways of the Ti-rich Ti-Fe-Co in situ composites consisting of ultrafine eutectic with micron-scale dendrites. The effect of addition of Co in the Ti-rich binary Ti-Fe alloys has been systematically investigated. The series of Ti-Fe-Co ternary alloys i.e., Ti75Fe25- x Co x ( x = 0, 5, 10, 12.5, 15, 20), (Ti70.5Fe29.5)100- x Co x ( x = 0, 2, 4, 6, 8, and 10), Ti70Fe30- x Co x ( x = 0, 5, 10, 15, 20, 25), Ti65Fe35- x Co x ( x = 0, 10, 15, 17.5, 20, 25), and Ti60Fe40- x Co x ( x = 0, 16, 18, 20, 22, 24) are synthesized by arc melting cum suction casting technique under high purity Ar atmosphere to obtain alloy cylinders having diameter ( ϕ) of 3 mm. Detailed X-ray diffraction and electron microscopic (SEM and TEM) study are carried out to identify the phases as well as to monitor the sequence of phase evolution in the ternary alloys. The present study conclusively proves that the Ti65Fe10Co25, Ti70Fe30- x Co x ( x = 10, 20, 25), and Ti75Fe15Co10 alloys show the ternary quasi-peritectic reaction of L + Ti(Co,Fe) → ( β-Ti)ss + Ti2(Co,Fe) at invariant point P (=Ti75.5±0.8Fe6.3±2.1Co18.2±2.7) which is cooperated by means of eutectic reaction of L → ( β-Ti)ss + Ti2(Co,Fe) below P and peritectic reaction L + Ti(Co,Fe) → Ti2(Co,Fe) for Ti65Fe10Co25,Ti70Fe10Co20, and Ti70Fe5Co25 alloys or eutectic reaction L → ( β-Ti)ss +Ti(Co,Fe) for Ti70Fe20Co10, and Ti75Fe15Co10 alloys above the point P. In addition, the peritectic reaction L + Ti(Co,Fe) → Ti2(Co,Fe) plays a significant role in the phase evolution. The microstructural evolution, phase equilibria and solidification pathways have been explained by generating liquidus projection of the investigated alloys. Interestingly, the Co addition leads to the formation of complex Ti2Co phase and significantly affects the compositional stability of TiFe phase. This is found to have significant influence on the microstructural development during suction

  13. Microstructurally based thermomechanical fatigue lifetime model of solder joints for electronic applications

    SciTech Connect

    Frear, D.R.; Rashid, M.M.; Burchett, S.N.

    1993-07-01

    We present a new methodology for predicting the fatigue life of solder joints for electronics applications. This approach involves integration of experimental and computational techniques. The first stage involves correlating the manufacturing and processing parameters with the starting microstructure of the solder joint. The second stage involves a series of experiments that characterize the evolution of the microstructure during thermal cycling. The third stage consists of a computer modeling and simulation effort that utilizes the starting microstructure and experimental data to produce a reliability prediction of the solder joint. This approach is an improvement over current methodologies because it incorporates the microstructure and properties of the solder directly into the model and allows these properties to evolve as the microstructure changes during fatigue.

  14. Microstructurally based thermomechanical fatigue lifetime model of solder joints for electronic applications

    NASA Astrophysics Data System (ADS)

    Frear, D. R.; Rashid, M. M.; Burchett, S. N.

    We present a new methodology for predicting the fatigue life of solder joints for electronics applications. This approach involves integration of experimental and computational techniques. The first stage involves correlating the manufacturing and processing parameters with the starting microstructure of the solder joint. The second stage involves a series of experiments that characterize the evolution of the microstructure during thermal cycling. The third stage consists of a computer modeling and simulation effort that utilizes the starting microstructure and experimental data to produce a reliability prediction of the solder joint. This approach is an improvement over current methodologies because it incorporates the microstructure and properties of the solder directly into the model and allows these properties to evolve as the microstructure changes during fatigue.

  15. Evolution of microstructure and elastic wave velocities in dehydrated gypsum samples

    NASA Astrophysics Data System (ADS)

    Milsch, H.; Priegnitz, M.

    2012-04-01

    This study aims at contributing to the experimental database of changes in rock physical properties, particularly elastic wave velocities, induced by devolatilization reactions. Cylindrical samples of natural gypsum were dehydrated in air for up to 800 h at ambient pressure and temperatures between 378 and 423 K. Subsequently, the transformation kinetics, reaction induced changes in microstructure and porosity and the concurrent evolution of the sample P and S-wave velocities were constrained. Weighing the heated samples in predefined time intervals yielded the reaction progress where the stoichiometric mass balance indicated an ultimate dehydration to anhydrite regardless of temperature. Porosity was observed to continuously increase with reaction progress from approximately 2 % for fully hydrated samples to 30 % for completely dehydrated ones, whilst the initial bulk volume was preserved. In a first set, P-wave velocity was measured at ambient conditions with ultrasonic transducers indicating a linear decrease with porosity from 5.2 km/s at 2 % to 1.0 km/s at 30 %. Results of a second set of ultrasonic measurements for both P and S-waves will be presented as well aiming at a spatially resolved wave velocity dependence on microstructure. For P-waves three different effective medium models - Voigt, Wyllie (Reuss), and Nur - were compared to the data. The linear dependence of P-wave velocity on porosity observed is best represented by the Voigt bound. The Voigt bound, however, overestimates the measured values significantly. The Wyllie-Equation (the Reuss bound) does not replicate the linear decrease in P-wave velocity with porosity and generally underestimates the data. However, at porosities above approximately 25 % the agreement with measured values is excellent. The Nur-Model yields a nonlinear dependence but replicates the data best for model-inherent critical porosities between 0.25 and 0.3. Thin section micrographs taken on selected samples reveal a sharp

  16. Effect of irradiation spectrum on the microstructural evolution in ceramic insulators

    SciTech Connect

    Zinkle, S.J.

    1995-04-01

    The objective of this study is to determine and examine the effect of variations in the ionizing and displacive radiation environments on the microstructure of oxide ceramic insulators. Cross section transmission electron microscopy has been used to investigate the microstructure of MgAl{sub 2}O{sub 4} (spinel) and Al{sub 2}O{sub 3} (alumina) following irradiation with ions of varying mass and energy at room temperature and 650{degree}C. These results clearly indicate that light ion and electron irradiations produce microstructures which are not representative of the microstructure that would form in these ceramics during fission or fusion neutron irradiation.

  17. Microstructural Evolution of the Interdiffusion Zone between U-9 Wt Pct Mo Fuel Alloy and Zr-1 Wt Pct Nb Cladding Alloy Upon Annealing

    NASA Astrophysics Data System (ADS)

    Neogy, S.; Laik, A.; Saify, M. T.; Jha, S. K.; Srivastava, D.; Dey, G. K.

    2017-03-01

    Diffusion couple formed between U-9 wt pct Mo and Zr-1 wt pct Nb alloys, proposed as fuel and clad materials, respectively, in nuclear research reactors, was annealed to investigate the microstructural evolution of the interdiffusion zone (IZ) as a function of temperature. A layered-type IZ microstructure was observed, the mechanism of development of which was elucidated. Mo2Zr phase, present as dispersoids, in the U-rich part of the as-bonded IZ evolved into a continuous layer and into a "massive" morphology upon annealing. The discontinuous precipitation reaction in the matrix adjoining the Mo2Zr phase, instigated by Mo depletion, generated lamellae of α-U phase within the γ-U(Mo,Zr) matrix. Zr-rich α-Zr(U) precipitates were observed in U-rich U-Mo-Zr matrix in the IZ next to the U-9Mo base material due to the clustering tendency of the matrix phase. The IZ next to Zr-1Nb base material comprised a "basket weave" microstructure of α-Zr laths with β-Zr(Nb,U) interlath boundaries, wherein an omega like transformation of the latter to δ-UZr2 was also noticed. The growth rates of the IZ were orders of magnitude lower when compared with the ones reported between the compositionally similar U-10 wt pct Mo alloy and the presently used Al or Al-Si cladding alloys.

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

    NASA Astrophysics Data System (ADS)

    Sabbaghian, M.; Mahmudi, R.

    2016-05-01

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

  19. Microstructure and properties of pitch-based carbon composites

    PubMed

    Blanco; Santamaria; Bermejo; Bonhomme; Menendez

    1999-11-01

    Pitches prepared in the laboratory by thermal treatment and air-blowing of a commercial coal-tar pitch were used as matrix precursors of carbon composites using granular petroleum coke, foundry coke, amorphous graphite and anthracite. Pitches were characterized by standard procedures (elemental analysis, softening point, solubility tests and carbon yield) and light microscopy (mesophase content). Pitch pyrolysis behaviour was monitored by thermogravimetric analysis and from the optical texture of cokes. Pitch wettability to the different carbons, at different temperatures, was also studied. Experimental conditions selected for the preparation of composites were based on pitch composition and properties. The main microstructural features of composites were determined by light microscopy and scanning electron microscopy. Composite properties were described in terms of their density, porosity and compressive strength, and related to composite microstructure and the characteristics of the precursors. Thermal treatment and air-blowing of pitch improved carbon composite structure and properties. The lowest porosities and best mechanical properties were observed in those composites obtained with the thermally treated pitches combined with foundry coke and anthracite.

  20. Morphological and microstructural evolution in the two-step growth of nonpolar a-plane GaN on r-plane sapphire

    NASA Astrophysics Data System (ADS)

    Sun, Qian; Kong, Bo Hyun; Yerino, Christopher D.; Ko, Tsung-Shine; Leung, Benjamin; Cho, Hyung Koun; Han, Jung

    2009-12-01

    In this paper, we report a detailed study on the evolution of surface morphology and microstructure of nonpolar a-plane GaN (a-GaN) through controlled growth interruptions. Microscopy imaging shows that the two-step a-GaN growth went through a roughening-recovery process. The first-step growth (under high V/III and high pressure) produced a rough surface with tall mesas separated by voids. The second-step growth (under low V/III and low pressure) promoted the lateral growth and filled up the voids. Striations that formed during the island coalescence persisted throughout the second-step growth, but could be relieved by an additional third-step growth. The morphological evolution was explained according to the kinetic Wulff plots. The microstructure of the a-GaN films was investigated by transmission electron microscopy (TEM) and x-ray rocking curve analysis. Most of the extended defects observed in the plan-view TEM images were I1 type basal-plane stacking faults (BSFs) and their associated partial dislocations (PDs). It is found that the bending of PDs (at the inclined/vertical growth fronts) within the basal plane toward the m-axes was responsible for the substantial reduction in threading PDs and the increase in BSF dimension. Based on a careful correlation between the morphological evolution and the microstructure development, we proposed a model explaining the possible mechanisms for the great reduction in defect density during the two-step growth process.

  1. Mechanical Properties and Microstructural Evolution in Al 2014 Alloy Processed Through Multidirectional Cryoforging

    NASA Astrophysics Data System (ADS)

    Joshi, Amit; Kumar, Nikhil; Yogesha, K. K.; Jayaganthan, R.; Nath, S. K.

    2016-07-01

    Mechanical properties and microstructure evolution of Al 2014 alloy subjected to cryoforging (MDF) to a cumulative strain of 1.2, 1.8, and 2.4 were investigated in the present work. The deformed samples after 4 cycles at a cumulative strain of 2.4 shows the formation of ultrafine grain sizes in the range of 100-450 nm with high-angle grain boundaries as observed from TEM analysis. The tensile and hardness of the deformed sample were measured by Universal Testing machine and Vickers hardness Tester, respectively. The tests were also conducted for sample deformed at room temperature to compare with cryo-forged samples. The sample deformed at cryogenic temperature up to a cumulative strain 2.4 shows an improvement of tensile strength, hardness, and apparent fracture toughness (KQ) from 318 MPa to 470 MPa, 103HV to 171 HV, and 23.93 MPa √ m to 37.7 MPa √ m, respectively, with decrease in ductility from 18% to 6% as compared with solution-treated alloy. The cryo-forged Al 2014 alloy exhibits an increment of 7% in tensile strength, 3% in yield strength, and 3% in hardness up to cumulative true strain of 2.4 as compared to the samples forged at room temperature. The improvement in tensile properties of MDFed alloy is attributed to dislocation strengthening and grain boundary strengthening effect at both temperatures. The effective suppression of cross slip and climb at liquid nitrogen temperature improves the strength of cryo-forged sample better than that of room temperature-forged alloy.

  2. Microstructural Evolution and Optical Properties of (InGa)(AsN) Nanostructures Synthesized by Ion Implantation

    NASA Astrophysics Data System (ADS)

    Weng, X.; Clarke, S.; Kumar, S.; Goldman, R. S.; Rotberg, V. H.; Krishna, S.; Bhattacharya, P. K.; Holt, J.; Sipowska, J.; Francis, A.; Daniel, A.; Clarke, R.

    2001-03-01

    Mixed anion nitride-arsenide compound semiconductor heterostructures are promising for light-emitting devices operating throughout the near infrared range. However, due to the large N-As size difference, a limited miscibility of (InGa)(AsN) on the anion sublattice is predicted. Furthermore, alloy phase separation resulting in the formation of quantum dot-like nanostructures has been reported in GaAsN/GaAs [1] and InGaAsN/GaAs [2] superlattices. We have investigated the evolution of the microstructure and optical properties of (InGa)(AsN) quantum dot-like nanostructures synthesized by N ion implantation into GaAs and InAs, using a variety of implantation and rapid thermal annealing conditions. For 50keV N ion implanted GaAs and InAs substrates, high-resolution cross-sectional transmission electron microscopy reveals ~5 nm diameter amorphous nanostructures surrounded by crystalline matrices. For 100keV N ion implanted GaAs epilayers, ~10 nm diameter crystalline nanostructures surrounded by amorphous matrices are apparent. Electron diffraction indicates that these crystallites are mostly randomly-oriented cubic phases, with lattice parameters close to that of pure GaN. Furthermore, the crystalline nanostructures exhibit significant photoluminescence in the near-infrared range. The apparent lowering of the fundamental band gap is consistent with strain-induced band gap narrowing of a GaN-rich spherical cluster [1]. We will discuss the mechanisms of formation and coarsening of these nanostructures, as well as correlations between their optical and structural properties. [1] R. S. Goldman, R. M. Feenstra, B. G. Briner, M. L. O'Steen, and R. J. Hauenstein, Appl. Phys. Lett. 69, 3698 (1996), J. Electr. Mater. 26, 1342 (1997). [2] H. P. Xin, K. L. Kavanagh, Z. Q. Zhu, and C. W. Tu, Appl. Phys. Lett. 74, 2337 (1999).

  3. A modified split Hopkinson torsional bar system for correlated study of τ-γ relations, shear localization and microstructural evolution.

    PubMed

    Yang, Rong; Zhang, Husheng; Shen, Letian; Xu, Yongbo; Bai, Yilong; Dodd, Bradley

    2014-05-13

    The conventional split Hopkinson torsional bar (SHTB) system consists of two bars, which can successfully produce the data for the construction of dynamic torsional shear stress and strain relationships. However, the system cannot provide reliable information on the progression of the deformed micro-structure during the test. The reverberation of waves in the bars and the tested specimen can spoil the microstructural pattern formed during the effective loading. This paper briefly reviews a modified version of the SHTB system consisting of four bars that has been developed. This modified system can eliminate the reverberation of waves in the specimen and provide only a single rectangular torsional stress pulse, thus it can properly freeze the microstructure formed during the effective period of loading in the specimen. By using the advantage of the modified SHTB system, together with a new design of specimen, it is possible to perform a correlated study of the dynamic stress-strain response, shear localization and the evolution of the microstructure at a fixed view-field (position) on a given specimen during the sequence of the loading time. The principles, experimental set-up and procedure, calibration and some preliminary results of the correlated study are reported in this paper.

  4. A continuum approach to the modeling of microstructural evolution in polycrystalline solids

    NASA Astrophysics Data System (ADS)

    Mourad, Hashem M.

    Interest in microstructural evolution of polycrystalline materials stems from the multiplicity of interrelated phenomena that contribute to this evolution, and from the impact that such phenomena have on the performance and reliability of these materials, especially in applications such as microelectronic devices. In this work, a continuum field formulation developed to study this type of phenomena is presented. The formulation accounts fully for the coupling between mechanical behavior, self diffusion, electric effects and interface migration. Each phenomenon being modeled is treated as a coupled initial and boundary value problem, consisting of these four component problems. Atomic-level mechanisms are taken into consideration while developing the thermodynamic basis of the formulation, from which the constitutive relations are derived. The computational framework used to solve the resulting coupled field equations is described in detail. This framework is built around a staggered solution scheme in which the finite element method is used to solve each governing differential equation individually. Additional computational techniques utilized in the implementation are also discussed. Examples of these include the level set method, a least-squares projection/smoothing technique and a modified form of the Galerkin/least-squares stabilization method. To study the problem of void nucleation in polycrystals, the stability of the atom-vacancy system is examined closely. A thermodynamic instability which could lead to spinodal decomposition of this system is identified. The amplications of this result in the context of void nucleation are explored and its relation to classical nucleation theory is realized. All quantities needed to calculate void formation rates are obtained from the coupled field calculations in a consistent mannen As expected, the results indicate that a high tensile stress can lead to void nucleation in the presence of impurities. The problem of grain

  5. Linking microstructural evolution and macro-scale friction behavior in metals [Predicting the friction behavior of metals using a microstructural evolution model

    DOE PAGES

    Argibay, N.; Chandross, M.; Cheng, S.; ...

    2016-11-21

    A correlation is established between the macro-scale friction regimes of metals and a transition between two dominant atomistic mechanisms of deformation. Metals tend to exhibit bi-stable friction behavior—low and converging or high and diverging. These general trends in behavior are shown to be largely explained using a simplified model based on grain size evolution, as a function of contact stress and temperature, and are demonstrated for self-mated pure copper and gold sliding contacts. Specifically, the low-friction regime (where µ < 0.5) is linked to the formation of ultra-nanocrystalline surface films (10–20 nm), driving toward shear accommodation by grain boundary sliding.more » Above a critical combination of stress and temperature—demonstrated to be a material property—shear accommodation transitions to dislocation dominated plasticity and high friction, with µ > 0.5. We utilize a combination of experimental and computational methods to develop and validate the proposed structure–property relationship. As a result, this quantitative framework provides a shift from phenomenological to mechanistic and predictive fundamental understanding of friction for crystalline materials, including engineering alloys.« less

  6. Linking microstructural evolution and macro-scale friction behavior in metals [Predicting the friction behavior of metals using a microstructural evolution model

    SciTech Connect

    Argibay, N.; Chandross, M.; Cheng, S.; Michael, J. R.

    2016-11-21

    A correlation is established between the macro-scale friction regimes of metals and a transition between two dominant atomistic mechanisms of deformation. Metals tend to exhibit bi-stable friction behavior—low and converging or high and diverging. These general trends in behavior are shown to be largely explained using a simplified model based on grain size evolution, as a function of contact stress and temperature, and are demonstrated for self-mated pure copper and gold sliding contacts. Specifically, the low-friction regime (where µ < 0.5) is linked to the formation of ultra-nanocrystalline surface films (10–20 nm), driving toward shear accommodation by grain boundary sliding. Above a critical combination of stress and temperature—demonstrated to be a material property—shear accommodation transitions to dislocation dominated plasticity and high friction, with µ > 0.5. We utilize a combination of experimental and computational methods to develop and validate the proposed structure–property relationship. As a result, this quantitative framework provides a shift from phenomenological to mechanistic and predictive fundamental understanding of friction for crystalline materials, including engineering alloys.

  7. The Impact of Strain Reversal on Microstructure Evolution and Orientation Relationships in Ti-6Al-4V with an Initial Alpha Colony Microstructure

    NASA Astrophysics Data System (ADS)

    Muszka, K.; Lopez-Pedrosa, M.; Raszka, K.; Thomas, M.; Rainforth, W. M.; Wynne, B. P.

    2014-12-01

    The effect of forward and reverse torsion on flow behavior and microstructure evolution, particularly dynamic and static spheroidization, on Ti-6Al-4V with an alpha lamella colony microstructure was studied. Testing was undertaken sub beta transus [1088 K (815 °C)] at strain rates of either 0.05 or 0.5 s-1. Quantitative metallography and electron back scatter diffraction has identified that a critical monotonic strain ( ɛ c) in the range of 0.3 to 0.6 is required to initiate rapid dynamic spheroidization of the alpha lamella. For material deformed to strains below ɛ c and then reversed to a zero net strain the orientation relationships between alpha colonies are close to ideal Burgers, enabling prior beta grains to be fully reconstructed. Material deformed to strains greater than ɛ c and reversed lose Burgers and no beta reconstruction is possible, suggesting ɛ c is the strain required to generate break-up of lamella. Static spheroidization is, however, sensitive to strain path around ɛ c. Annealing at 1088 K (815 °C) for 4 hours for material subjected to 0.25 forward + 0.25 forward strain produces 48 pct spheroidized grains while material with 0.25 forward + 0.25 reverse strain has 10 pct spheroidization. This is believed to be a direct consequence of different levels of the stored energy between these two strain paths.

  8. Microstructure evolution of eutectic Al-Cu strips by high-speed twin-roll strip casting process

    NASA Astrophysics Data System (ADS)

    Sahoo, Seshadev; Ghosh, Sudipto

    2015-10-01

    In the present investigation, microstructural evolutions of functionally graded eutectic Al-Cu strips prepared by high-speed twin-roll strip caster at different casting speeds and liquid melt superheats were studied. The as-cast sample was subjected to scanning electron microscope to study the evolution of microstructure of the strip at different casting speeds and liquid melt superheats. At different casting speeds, non-equilibrium eutectic structure observed on the Al-Cu eutectic strip consists of lamellar as well as wavy structure with a distinct boundary. The lamellar microstructure consists of alternating layers of well-bonded α-Al phase and θ-Al2Cu phase. The globular flowery structure within the eutectic matrix was observed on the strip at different liquid melt superheats. The microhardness of the as-cast strip was studied by Vickers hardness tester, and it was found that hardness value increases with increasing casting speed and decreases with increasing liquid melt superheat.

  9. Microstructural evolution in advanced boiler materials for ultra-supercritical coal power plants

    NASA Astrophysics Data System (ADS)

    Wu, Quanyan

    The goal of improving the efficiency of pulverized coal powerplants has been pursued for decades. The need for greater efficiency and reduced environmental impact is pushing utilities to ultra supercritical conditions (USC), i.e. steam temperatures approaching 760°C under a stress of 35 MPa. The long-term creep strength and environmental resistance requirements imposed by these conditions are clearly beyond the capacity of the currently used ferritic steels and other conventional alloys. As part of a large DOE-funded consortium, new and existing materials based on advanced austenitic stainless steels and nickel base superalloys are being evaluated for these very demanding applications. In the present work, the nickel base superalloys of Inconel 617, CCA617, Haynes 230 and Inconel 740, and austenitic alloys Super 304H and HR6W, were evaluated on their microstructural properties over elevated temperature ageing and creep rupture conditions. The materials were aged for different lengths of time at temperatures relevant to USC applications, i.e., in the range from 700 to 800°C. The precipitation behaviors, namely of the gamma', carbides and eta phase in some conditions in nickel base superalloys, carbides in Haynes 230, Cu-rich precipitates in Super 304H and Laves phase particles in HR6W, were studied in detail using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and related analytical techniques. Particular attention has been given on the structure, morphology and compositional distinctiveness of various phases (including gamma, gamma', carbides, secondary phase precipitates, and other types of particles) and their nature, dislocation structures and other types of defects. The results were presented and discussed in light of associated changes in microhardness in the cases of aged samples, and in close reference to mechanical testing (including tensile and creep rupture tests) wherever available. Several mechanical strengthening

  10. Laser direct micromilling of copper-based bioelectrode with surface microstructure array

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Ling, Wei-song; Liu, Wei; Peng, Youjian; Peng, Juehao

    2015-10-01

    The laser direct micromilling is proposed to fabricate the microstructure arrays on the surface of dry bioelectrodes using red copper material. Based on the principle of laser machining and SEM results, the forming process of microstructure arrays on the surface of copper-based bioelectrodes is discussed. When the process parameters are varied, the effect of process spacing, laser output power, scanning speed and number of scan on the morphology and geometrical dimension of microstructure array of bioelectrode is investigated. The results show that the cone surface microstructure can be fabricated when process spacing is set to 0.1 mm. Surface roughness of microstructure is greatly changed with different scanning speeds. The height of surface microstructure and recast layer is greatly increased with increasing laser output power. When smaller laser output power or less number of scan are selected, surface microstructure array is difficult to be fabricated. However, it is easy to generate the damage of surface microstructure when the larger output power or excessive scanning times are selected. Moreover, our developed copper-based bioelectrode shows a hydrophobic property when the spacings are selected in the range of 0.1-0.3 mm. Eventually, the optimized process parameters are obtained to fabricate the bioelectrode with cone microstructure array.

  11. 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.

  12. SAFOD Brittle Microstructure and Mechanics Knowledge Base (BM2KB)

    NASA Astrophysics Data System (ADS)

    Babaie, Hassan A.; Broda Cindi, M.; Hadizadeh, Jafar; Kumar, Anuj

    2013-07-01

    Scientific drilling near Parkfield, California has established the San Andreas Fault Observatory at Depth (SAFOD), which provides the solid earth community with short range geophysical and fault zone material data. The BM2KB ontology was developed in order to formalize the knowledge about brittle microstructures in the fault rocks sampled from the SAFOD cores. A knowledge base, instantiated from this domain ontology, stores and presents the observed microstructural and analytical data with respect to implications for brittle deformation and mechanics of faulting. These data can be searched on the knowledge base‧s Web interface by selecting a set of terms (classes, properties) from different drop-down lists that are dynamically populated from the ontology. In addition to this general search, a query can also be conducted to view data contributed by a specific investigator. A search by sample is done using the EarthScope SAFOD Core Viewer that allows a user to locate samples on high resolution images of core sections belonging to different runs and holes. The class hierarchy of the BM2KB ontology was initially designed using the Unified Modeling Language (UML), which was used as a visual guide to develop the ontology in OWL applying the Protégé ontology editor. Various Semantic Web technologies such as the RDF, RDFS, and OWL ontology languages, SPARQL query language, and Pellet reasoning engine, were used to develop the ontology. An interactive Web application interface was developed through Jena, a java based framework, with AJAX technology, jsp pages, and java servlets, and deployed via an Apache tomcat server. The interface allows the registered user to submit data related to their research on a sample of the SAFOD core. The submitted data, after initial review by the knowledge base administrator, are added to the extensible knowledge base and become available in subsequent queries to all types of users. The interface facilitates inference capabilities in the

  13. Microstructure and property evolutions of titanium/nano-hydroxyapatite composites in-situ prepared by selective laser melting.

    PubMed

    Han, Changjun; Wang, Qian; Song, Bo; Li, Wei; Wei, Qingsong; Wen, Shifeng; Liu, Jie; Shi, Yusheng

    2017-02-20

    Titanium (Ti)-hydroxyapatite (HA) composites have the potential for orthopedic applications due to their favorable mechanical properties, excellent biocompatibility and bioactivity. In this work, the pure Ti and nano-scale HA (Ti-nHA) composites were in-situ prepared by selective laser melting (SLM) for the first time. The phase, microstructure, surface characteristic and mechanical properties of the SLM-processed Ti-nHA composites were studied by X-ray diffraction, transmission electron microscope, atomic force microscope and tensile tests, respectively. Results show that SLM is a suitable method for fabricating the Ti-nHA composites with refined microstructure, low modulus and high strength. A novel microstructure evolution can be illustrated as: Relatively long lath-shaped grains of pure Ti evolved into short acicular-shaped and quasi-continuous circle-shaped grains with the varying contents of nHA. The elastic modulus of the Ti-nHA composites is 3.7% higher than that of pure Ti due to the effect of grain refinement. With the addition of 2% nHA, the ultimate tensile strength significantly reduces to 289MPa but still meets the application requirement of bone implants. The Ti-nHA composites exhibit a remarkable improvement of microhardness from 336.2 to 600.8 HV and nanohardness from 5.6 to 8.3GPa, compared to those of pure Ti. Moreover, the microstructure and property evolution mechanisms of the composites with the addition of HA were discussed and analyzed. It provides some new knowledge to the design and fabrication of biomedical material composites for bone implant applications.

  14. THEORETICAL INVESTIGATION OF MICROSTRUCTURE EVOLUTION AND DEFORMATION OF ZIRCONIUM UNDER CASCADE DAMAGE CONDITIONS

    SciTech Connect

    Barashev, Alexander V; Golubov, Stanislav I; Stoller, Roger E

    2012-06-01

    This work is based on our reaction-diffusion model of radiation growth of Zr-based materials proposed recently in [1]. In [1], the equations for the strain rates in unloaded pure crystal under cascade damage conditions of, e.g., neutron or heavy-ion irradiation were derived as functions of dislocation densities, which include contributions from dislocation loops, and spatial distribution of their Burgers vectors. The model takes into account the intra-cascade clustering of self-interstitial atoms and their one-dimensional diffusion; explains the growth stages, including the break-away growth of pre-annealed samples; and accounts for some striking observations, such as of negative strain in prismatic direction, and co-existence of vacancy- and interstitial-type prismatic loops. In this report, the change of dislocation densities due to accumulation of sessile dislocation loops is taken into account explicitly to investigate the dose dependence of radiation growth. The dose dependence of climb rates of dislocations is calculated, which is important for the climb-induced glide model of radiation creep. The results of fitting the model to available experimental data and some numerical calculations of the strain behavior of Zr for different initial dislocation structures are presented and discussed. The computer code RIMD-ZR.V1 (Radiation Induced Microstructure and Deformation of Zr) developed is described and attached to this report.

  15. A microstructurally based model of solder joints under conditions of thermomechanical fatigue

    SciTech Connect

    Frear, D.R.; Burchett, S.N.; Rashid, M.M.

    1994-12-31

    The thermomechanical fatigue failure of solder joints in increasingly becoming an important reliability issue. In this paper we present two computational methodologies that have been developed to predict the behavior of near eutectic Sn-Pb solder joints under fatigue conditions that are based on metallurgical tests as fundamental input for constitutive relations. The two-phase model mathematically predicts the heterogeneous coarsening behavior of near eutectic Sn-Pb solder. The finite element simulations from this model agree well with experimental thermomechanical fatigue tests. The simulations show that the presence of an initial heterogeneity in the solder microstructure could significantly degrade the fatigue lifetime. The single phase model is a computational technique that was developed to predict solder joint behavior using materials data for constitutive relation constants that could be determined through straightforward metallurgical experiments. A shear/torsion test sample was developed to impose strain in two different orientations. Materials constants were derived from these tests and the results showed an adequate fit to experimental results. The single-phase model could be very useful for conditions where microstructural evolution is not a dominant factor in fatigue.

  16. A microstructurally based model of solder joints under conditions of thermomechanical fatigue

    NASA Astrophysics Data System (ADS)

    Frear, D. R.; Burchett, S. N.; Rashid, M. M.

    The thermomechanical fatigue failure of solder joints is increasingly becoming an important reliability issue. We present two computational methodologies that have been developed to predict the behavior of near eutectic Sn-Pb solder joints under fatigue conditions that are based on metallurgical tests as fundamental input for constitutive relations. The two-phase model mathematically predicts the heterogeneous coarsening behavior of near eutectic Sn-Pb solder. The finite element simulations from this model agree well with experimental thermomechanical fatigue tests. The simulations show that the presence of an initial heterogeneity in the solder microstructure could significantly degrade the fatigue lifetime. The single phase model is a computational technique that was developed to predict solder joint behavior using materials data for constitutive relation constants that could be determined through straightforward metallurgical experiments. A shear/torsion test sample was developed to impose strain in two different orientations. Materials constants were derived from these tests and the results showed an adequate fit to experimental results. The single-phase model could be very useful for conditions where microstructural evolution is not a dominant factor in fatigue.

  17. Microstructure and Texture Evolution in Cold Rotary Forging of Spur Bevel Gears of 20CrMnTi Alloy Steel

    NASA Astrophysics Data System (ADS)

    Han, Xinghui; Dong, Liying; Hua, Lin; Zhuang, Wuhao

    2016-03-01

    The microstructure of cold rotary forged gears greatly affects their working life. Therefore, the aim of this study is to reveal the evolution of microstructure and texture that occurs during the cold rotary forging of spur bevel gears of 20CrMnTi alloy steel. The evolution of grains of the gear tooth is investigated through optical microscopy. By employing scanning electron microscopy and electron backscatter diffraction, the evolution of the cementite particles and the texture of the gear tooth is also revealed. The results indicate that the grain size distribution is non-uniform from the tooth profile to its center. The cementite particles in the tooth profile are finer and more uniformly distributed than those in the tooth center. After cold rotary forging, the tooth center has a combination of α- and γ-fibers, and the γ-fibers are more developed than the α-fibers, while most of the components in the tooth profile are assembled along the α-fibers.

  18. Dolomite microstructures between 390° and 700 °C: Indications for deformation mechanisms and grain size evolution

    NASA Astrophysics Data System (ADS)

    Berger, Alfons; Ebert, Andreas; Ramseyer, Karl; Gnos, Edwin; Decrouez, Danielle

    2016-08-01

    Dolomitic marble on the island of Naxos was deformed at variable temperatures ranging from 390 °C to >700 °C. Microstructural investigations indicate two end-member of deformation mechanisms: (1) Diffusion creep processes associated with small grain sizes and weak or no CPO (crystallographic preferred orientation), whereas (2) dislocation creep processes are related with larger grain sizes and strong CPO. The change between these mechanisms depends on grain size and temperature. Therefore, sample with dislocation and diffusion creep microstructures and CPO occur at intermediate temperatures in relative pure dolomite samples. The measured dolomite grain size ranges from 3 to 940 μm. Grain sizes at Tmax >450 °C show an Arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite. The stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same Arrhenius-type evolution. In addition, the effect of second phase particle influences the grain size evolution, comparable with calcite. Calcite/dolomite mixtures are also characterized by the same difference in grain size, but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non-temperature equilibrated Mg-content in calcite.

  19. A microstructure-based model for shape distortion during liquid phase sintering

    NASA Astrophysics Data System (ADS)

    Upadhyaya, Anish

    Tight dimensional control is a major concern in consolidation of alloys via liquid phase sintering. This research demonstrates the role of microstructure in controlling the bulk dimensional changes that occur during liquid phase sintering. The dimensional changes were measured using a coordinate measuring machine and also on a real-time basis using in situ video imaging. To quantify compact distortion, a distortion parameter is formulated which takes into consideration the compact distortion in radial as well as axial directions. The microstructural attributes considered in this study are as follows: solid content, dihedral angle, grain size, grain contiguity and connectivity, and solid-solubility. Sintering experiments were conducted with the W-Ni-Cu, W-Ni-Fe, Mo-Ni-Cu, and Fe-Cu systems. The alloy systems and the compositions were selected to give a range of microstructures during liquid phase sintering. The results show that distortion correlates with the measured microstructural attributes. Systems containing a high solid content, high grain coordination number and contiguity, and large dihedral angle have more structural rigidity. The results show that a minimum two-dimensional grain coordination number of 3.0 is necessary for shape preservation. Based on the experimental observations, a model is derived that relates the critical solid content required for maintaining structural rigidity to the dihedral angle. The critical solid content decreases with an increasing dihedral angle. Consequently, W-Cu alloys, which have a dihedral angle of about 95sp°, can be consolidated without gross distortion with as little as 20 vol.% solid. To comprehensively understand the gravitational effects in the evolution of both the microstructure and the macrostructure during liquid phase sintering, W-Ni-Fe alloys with W content varying from 78 to 93 wt.% were sintered in microgravity. Compositions that slump during ground-based sintering also distort when sintered under

  20. The Evolution of As-cast Microstructure of Ternary Mg-Al-Zn Alloys: An Experimental and Modeling Study

    NASA Astrophysics Data System (ADS)

    Paliwal, Manas; Kang, Dae Hoon; Essadiqi, Elhachmi; Jung, In-Ho

    2014-07-01

    A numerical formulation of solidification model which can predict the microsegregation and microstructural features for multicomponent alloys is presented. The model incorporates the kinetic features during solidification such as solute back diffusion, dendrite tip undercooling, and secondary arm coarsening. The model is dynamically linked to thermodynamic library for accurate input of thermodynamic data. The modeling results are tested against the directional solidification experiments for Mg-Al-Zn alloys. The experiments were conducted in the cooling rate range of 0.13 to 2.33 K/s and microstructural features such as secondary arm spacing, primary dendrite arm spacing, second phase fraction, and microsegregation were compared with the modeling results. Based on the model and the experimental data, a solidification map was built in order to provide guidelines for as-cast microstructural features of Mg-Al-Zn alloys in a wide range of solidification conditions.

  1. Impact of Materials Processing on Microstructural Evolution and Hydrogen Isotope Storage Properties of Pd-Rh Alloy Powders.

    SciTech Connect

    Yee, Joshua K

    2015-02-01

    Cryomilled Pd - 10Rh was investiga ted as potential solid - state storage material of hydrogen. Pd - 10Rh was first atomized, and then subsequently cryomilled. The cryomilled Pd - 10Rh was then examined using microstructural characterization techniques including op tical microscopy, electron microscopy, and X - ray diffraction. Pd - 10Rh particles were significantly flattened, increasing the apparent surface area. Microstructural refinement was observed in the cryomilled Pd - 10Rh, generating grains at the nanom etric scale through dislocation - based activity. Hydrogen sorption properties were also characterized, generating both capacity as well as kinetics measurements. It was found that the microstructural refinement due to cryomilling did not play a significant role on hyd rogen sorption properties until the smallest grain size (on the order of %7E25 nm) was achieved. Additionally, the increased surface area and other changes in particle morphology were associated with cryomilling changed the kinetics of hydrogen absorption.

  2. Real internal microstructure based key mechanism analysis on the micro-damage process of short fibre-reinforced composites

    NASA Astrophysics Data System (ADS)

    Hu, Xiaofang; Fang, Jian; Xu, Feng; Dong, Bo; Xiao, Yu; Wang, Luobin

    2016-10-01

    In this work, the underlying micro-damage mechanisms of randomly oriented short fibre-reinforced composites were revealed based on real internal microstructural characteristics obtained by high-resolution (0.7 μm/pixel) synchrotron radiation X-ray computed tomography (SR-CT). The special ‘pore dominant micro-damage processes’ were directly observed through SR-CT three-dimensional reconstructed images, which were different from the well-known ‘fibre breakage dominant failure mode’. The mechanisms of pore formation and pore evolution were further investigated on the basis of the microstructural parameters extracted from the SR-CT results. On one hand, the pore formation mechanism caused by shear stress concentration was proposed by combining the shear-lag model with the microstructural parameters obtained from the experiment, including the fibre length and orientation angle. On the other hand, the ‘fibre-end aggregation-induced pore connection’ mode of crack initiation was proposed through a composites model, which considered the parameters of real internal microstructure, including the critical value of the distance between neighbouring fibre ends and the number of neighbouring fibre ends. The study indicated that the shear stress concentration was significant in the region with a large number of neighbouring fibre ends, thus causing pore connection and crack initiation.

  3. Real internal microstructure based key mechanism analysis on the micro-damage process of short fibre-reinforced composites

    PubMed Central

    Hu, Xiaofang; Fang, Jian; Xu, Feng; Dong, Bo; Xiao, Yu; Wang, Luobin

    2016-01-01

    In this work, the underlying micro-damage mechanisms of randomly oriented short fibre-reinforced composites were revealed based on real internal microstructural characteristics obtained by high-resolution (0.7 μm/pixel) synchrotron radiation X-ray computed tomography (SR-CT). The special ‘pore dominant micro-damage processes’ were directly observed through SR-CT three-dimensional reconstructed images, which were different from the well-known ‘fibre breakage dominant failure mode’. The mechanisms of pore formation and pore evolution were further investigated on the basis of the microstructural parameters extracted from the SR-CT results. On one hand, the pore formation mechanism caused by shear stress concentration was proposed by combining the shear-lag model with the microstructural parameters obtained from the experiment, including the fibre length and orientation angle. On the other hand, the ‘fibre-end aggregation-induced pore connection’ mode of crack initiation was proposed through a composites model, which considered the parameters of real internal microstructure, including the critical value of the distance between neighbouring fibre ends and the number of neighbouring fibre ends. The study indicated that the shear stress concentration was significant in the region with a large number of neighbouring fibre ends, thus causing pore connection and crack initiation. PMID:27713472

  4. Microstructural evolution during transient liquid phase bonding of Inconel 738LC using AMS 4777 filler alloy

    SciTech Connect

    Jalilvand, V.; Omidvar, H.; Shakeri, H.R.; Rahimipour, M.R.

    2013-01-15

    IN-738LC nickel-based superalloy was joined by transient liquid phase diffusion bonding using AMS 4777 filler alloy. The bonding process was carried out at 1050 Degree-Sign C under vacuum atmosphere for various hold times. Microstructures of the joints were studied by optical and scanning electron microscopy. Continuous centerline eutectic phases, characterized as nickel-rich boride, chromium-rich boride and nickel-rich silicide were observed at the bonds with incomplete isothermal solidification. In addition to the centerline eutectic products, precipitation of boron-rich particles was observed in the diffusion affected zone. The results showed that, as the bonding time was increased to 75 min, the width of the eutectic zone was completely removed and the joint was isothermally solidified. Homogenization of isothermally solidified joints at 1120 Degree-Sign C for 300 min resulted in the elimination of intermetallic phases formed at the diffusion affected zone and the formation of significant {gamma} Prime precipitates in the joint region. - Highlights: Black-Right-Pointing-Pointer TLP bonding of IN-738LC superalloy was performed using AMS 4777 filler alloy. Black-Right-Pointing-Pointer Insufficient diffusion time resulted in the formation of eutectic product. Black-Right-Pointing-Pointer Precipitation of B-rich particles was observed within the DAZ. Black-Right-Pointing-Pointer The extent of isothermal solidification increased with increasing holding time. Black-Right-Pointing-Pointer Homogenizing of joints resulted in the dissolution of DAZ intermetallics.

  5. Evolution of microstructure and elastic wave velocities in dehydrated gypsum samples

    NASA Astrophysics Data System (ADS)

    Milsch, Harald; Priegnitz, Mike

    2012-12-01

    We report on changes in P and S-wave velocities and rock microstructure induced by devolatilization reactions using gypsum as a reference analog material. Cylindrical samples of natural alabaster were dehydrated in air, at ambient pressure, and temperatures between 378 and 423 K. Dehydration did not proceed homogeneously but via a reaction front moving sample inwards separating an outer highly porous rim from the remaining gypsum which, above approximately 393 (±5) K, concurrently decomposed into hemihydrate. Overall porosity was observed to continuously increase with reaction progress from approximately 2% for fully hydrated samples to 30% for completely dehydrated ones. Concurrently, P and S-wave velocities linearly decreased with porosity from 5.2 and 2.7 km/s to 1.0 and 0.7 km/s, respectively. It is concluded that a linearized empirical Raymer-type model extended by a critical porosity term and based on the respective time dependent mineral and pore volumes reasonably replicates the P and S-wave data in relation to reaction progress and porosity.

  6. Microstructural evolution in high oxygen fugacity processed bismuth strontium calcium copper oxide

    NASA Astrophysics Data System (ADS)

    Gannon, John J., Jr.

    A decomposition/reformation process that uses a high oxygen fugacity (2 MPa) heat treatment followed by low oxygen fugacity (<1 MPa) annealing was applied to silver-sheathed Bisb2Srsb2CaCusb2Osb{8±delta} (Bi-2212) tapes. The rate at which the Bi-2212 phase reforms was studied using X-ray diffractometry and image analyses. The kinetic data was fitted to an Avrami-type equation and was found to be consistent with that predicted for diffusion-controlled growth of plate-like grains. The effect of varying the oxygen fugacity during reformation annealing was also studied and the rate of Bi-2212 phase formation slowed considerably with increasing oxygen fugacity. The rate of oxygen exsolution from the core is a key parameter for the overall transformation kinetics. Two of the decomposition products produced by high-fOsb2 processing of the Bi-2212 compound are a copper-free alkaline-earth bismuthate (a Bisb9Srsb{11}Casb5Osb{x}-type) and CuO. Blended mixtures of these two compounds were used to form two-powder reaction couples used to study Bi-2212 phase formation. Samples were annealed in flowing oxygen at temperatures below the Bi-2212 solidus. The formation of apparent Bi-2212/Bi-2201 intergrowths along with some alkaline-earth cuprate phases were detected. The 14:24-type alkaline-earth cuprate phase was formed in fine CuO powder couples but not in couples containing large CuO particles. The reaction leading to Bi-2212 phase formation was confirmed to be solid-state at temperatures below 875sp°C. The development of c-axis grain alignment in high-fOsb2 decomposed Bi-2212 tapes that were reformed with low-fOsb2 annealing was studied. Such processing can produce enhanced 00l grain alignment and the evolution of this texture was examined in tapes at intermediate points in the reformation process. Some of the mechanisms associated with texture development in melt-processed tapes were found to be inadequate for describing the alignment in high-fOsb2 processed Bi-2212 grains

  7. The effect of micro alloying on the microstructure evolution of Sn-Ag-Cu lead-free solder

    NASA Astrophysics Data System (ADS)

    Werden, Jesse

    The microelectronics industry is required to obtain alternative Pb-free soldering materials due to legal, environmental, and technological factors. As a joining material, solder provides an electrical and mechanical support in electronic assemblies and therefore, the properties of the solder are crucial to the durability and reliability of the solder joint and the function of the electronic device. One major concern with new Pb-free alternatives is that the microstructure is prone to microstructural coarsening over time which leads to inconsistent properties over the device's lifetime. Power aging the solder is a common method of stabilizing the microstructure for Pb-based alloys, however, it is unclear if this will be an appropriate solution to the microstructural coarsening of Pb-free solders. The goal of this work is to develop a better understanding of the coarsening process in new solder alloys and to suggest methods of stabilizing the solder microstructure. Microalloying is one potential solution to the microstructural coarsening problem. This experiment consists of a microstructural coarsening study of SAC305 in which each sample has been alloyed with one of three different solutes, directionally solidified at 100microm/s, and then aged at three different temperatures over a total period of 20 days. There are several important conclusions from this experiment. First, the coarsening kinetics of the intermetallics in the ternary eutectic follow the Ostwald ripening model where r3 in proprotional to t for each alloying constituent. Second, the activation energy for coarsening was found to be 68.1+/-10.3 kJ/mol for the SAC305 samples, Zn had the most significant increase in the activation energy increasing it to 88.8+/-34.9 kJ/mol for the SAC+Zn samples, Mn also increased the activation energy to 83.2+/-20.8 kJ/mol for the SAC+Mn samples, and Sb decreased the activation energy to 48.0+/-3.59 kJ/mol for the SAC+Sb samples. Finally, it was found that the

  8. Microstructural Evolution of Brazed CP-Ti Using the Clad Ti-20Zr-20Cu-20Ni Foil

    NASA Astrophysics Data System (ADS)

    Yeh, Tze-Yang; Shiue, Ren-Kae; Chang, Chenchung Steve

    2013-01-01

    Microstructural evolution of the clad Ti-20Zr-20Cu-20Ni foil brazed CP-Ti alloy has been investigated. For the specimen furnace brazed below 1143 K (870 °C), the joint is dominated by coarse eutectic and fine eutectoid structures. Increasing the brazing temperature above 1163 K (890 °C) results in disappearance of coarse eutectic structure, and the joint is mainly comprised of a fine eutectoid of (Ti,Zr)2Ni, Ti2Cu, Ti2Ni, and α-Ti.

  9. Microstructural evolution in NaNbO3-based antiferroelectrics

    NASA Astrophysics Data System (ADS)

    Guo, Hanzheng; Shimizu, Hiroyuki; Randall, Clive A.

    2015-11-01

    Our recent study found that CaZrO3 doping can effectively enhance the antiferroelectric P phase in NaNbO3 ceramics, leading to a double polarization hysteresis loop characteristic of a reversible antiferroelectric ↔ ferroelectric phase transition [Shimizu et al., Dalton Trans. 44, 10763 (2015)]. Here, a thorough transmission electron microscope study was performed to illustrate the CaZrO3 doping-assisted antiferroelectricity stabilization. In parallel to the bright-field imaging and selected area electron diffraction from multiple zone axes, detailed dark-field imaging was utilized to determine the superlattice structural origins, from either oxygen octahedral tilting or antiparallel cation displacements. By analogy with Pb(Zr1-xTix)O3 and rare-earth doped BiFeO3 systems, the chemical substitutions are such as to an induced polar-to-antipolar transition that is consistent with a tolerance factor reduction. The resultant chemical pressure has a similar effect to the compressive hydrostatic pressure where the antiferroelectric state is favored over the ferroelectric state.

  10. Weldability and microstructure development in nickel-base superalloys

    SciTech Connect

    David, S.A.; Babu, S.S.; Vitek, J.M.

    1997-11-01

    The integrity of nickel-base superalloy single-crystal welds depends on the weld cracking tendency, weld metal dendrite selection process, stray crystal formation, and macro- and microstructure development. These phenomena have been investigated in commercial nickel-base superalloy single crystal welds. During electron beam and laser beam welding, transverse and longitudinal weld cracking occurred. However, the weld cracking tendency was reduced with preheating. Most of the dendritic growth pattern development in these welds can be explained by a geometric model. However, the welds also contained misoriented stray crystals, which were frequently associated with weld cracks. The formation of stray crystals was related to thermal and constitutional supercooling effects. Fine-scale elemental partitioning between {gamma} and {gamma}{prime} phase was measured with atom-probe field-ion microscopy. Marked differences in partitioning characteristics in two welds were observed and are related to differences in cooling rates. In this paper, the modeling tools available to describe the above are reviewed.

  11. Microstructure-Based Strength Distribution Across the Welds of Nickel-Based Superalloy Inconel 751 and Austenite Steel 21-4N Joined by Inertia Friction Welding

    NASA Astrophysics Data System (ADS)

    Zhu, Yuanzhi; Guo, Yingying; Yang, Libin

    2013-04-01

    Welding dissimilar metals is always a challenge for their different physical property and microstructures. In this study, the two dissimilar metals 21-4N and Inconel 751 are welded together by inertia friction welding. Microstructure observation shows that the weld can be divided into three regions in 21-4N: the chemical composition mixture zone, shear zone, and base metal. The width of the chemical composition mixture zone (CMZ) is about 80 μm, with relatively larger grains and lower dislocation density distributed in this zone. Shear banding occurs in the shear zone, and carbides are found to have precipitated strongly along these shear bands noncontinuously. The base metal contains an austenite microstructure with carbides distributed in the matrix. In Inconel 751, only two typical zones can be observed: the CMZ and the base metal. The heat-affected zone is too small to be observed in the whole weld. Finally, a strength model based on microstructural evolution is proposed. The strength distribution along the axial direction of the welds is calculated. The results are in good agreement with the measurements.

  12. The Microstructural Evolution of Inconel Alloy 740 During Solution Treatment, Aging, and Exposure at 760 °C

    SciTech Connect

    Cowen, Christopher J.; Danielson, Paul E.; Jablonski, Paul D.

    2010-08-10

    In this study, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy. During double solution heat treatment, carbon is liberated from the dissolution of MC carbides during the first solution treatment at 1150 °C, and fine MC carbides are precipitated on gamma grain boundaries during the second solution treatment at 1120 °C. Due to the concurrent decrease in carbon solubility and the increase in the contribution of grain boundary diffusion at lower temperatures, the MC carbides on the gamma grain boundaries provide a localized carbon reservoir that aids in M23C6 carbide precipitation on gamma grain boundaries during exposure at 760 °C. The γ' phase, which is the key strengthening phase in alloy 740, is incorporated into the alloy microstructure during aging at 850 °C. Finally, the main source of microstructural instability observed during exposure at 760 °C was the coarsening of the γ' phase.

  13. Evolution of Microstructure and Texture during Recrystallization of the Cold-Swaged Ti-Nb-Ta-Zr-O Alloy

    NASA Astrophysics Data System (ADS)

    Guo, W. Y.; Xing, H.; Sun, J.; Li, X. L.; Wu, J. S.; Chen, R.

    2008-03-01

    The deformed microstructure and evolution of microstructure and texture during recrystallization of the cold-swaged multifunctional Ti-23Nb-0.7Ta-2Zr-1.2O (TNTZO, at. pct) alloy were investigated by optical microscope, electron backscatter diffraction, and transmission electron microscope. This alloy has been reported, by Saito et al., to possess a specific dislocation-free plastic deformation mechanism. In this study, the results show a curly grain or swirled structure and a pronounced fibrous {left< {110} rightrangle } texture along the swaging axis in the cold-swaged TNTZO alloy. The normal to the swirled grain surface is near {left< {001} rightrangle } in the cross section of the rod. This characteristic microstructure can be considered to arise from the plane strain deformation of the grains under applied stress, which is similar to that in ordinary bcc metals after heavily drawing or swaging. It is also shown that recovery involves the redistribution and partial annihilation of dislocations within the deformation bands, and recrystallization proceeds by a typical new grain nucleation-growth mechanism during annealing of the TNTZO alloy. The fibrous {left< {110} rightrangle } deformation texture is gradually replaced by random orientations with increasing annealing time. Thus, it could be concluded that the TNTZO alloy deforms by the traditional dislocation glide on {left< {111} rightrangle }{left\\{ {110} right\\}} , {112}, or {123} slip systems, rather than the dislocation-free mechanism.

  14. Modelling of the microstructure and strength evolution in Al-Mg-Si alloys during multistage thermal processing

    SciTech Connect

    Myhr, O.R.; Grong, O. . E-mail: Oystein.Grong@sintef.no; Fjaer, H.G.; Marioara, C.D.

    2004-10-04

    A numerical solution is presented, capable of handling nucleation, growth and coarsening, and likewise dissolution, of hardening precipitates in Al-Mg-Si alloys during ageing, welding and post weld heat treatment (PWHT). By coupling this to a separate strength model for shearing and bypassing of particles by dislocations, the evolution of the macroscopic yield stress at room temperature can be calculated at each time step. Following testing of the model against reliable hardness and transmission electron microscope (TEM) data obtained from dedicated Gleeble simulation experiments, the connectivity on a micro/macro level throughout a multistage manufacturing route is illustrated by means of a numerical example. These simulations show how a past process step influences the microstructure and strength evolution in the subsequent process steps due to interactions between different groups or classes of particles that form at various temperatures.

  15. Effect of expansion temperature of expandable graphite on microstructure evolution of expanded graphite during high-energy ball-milling

    SciTech Connect

    Yue Xueqing; Li Liang; Zhang Ruijun; Zhang Fucheng

    2009-12-15

    Two expanded graphites (EG), marked as EG-1 and EG-2, were prepared by rapid heating of expandable graphite to 600 and 1000 deg. C, respectively, and ball milled in a high-energy mill (planetary-type) under air atmosphere. The microstructure evolution of the ball-milled samples was characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). XRD analysis shows that the evolution degree of the average crystallite thickness along the c-axis (L{sub c}) of EG-2 is lower than that of EG-1 during the milling process. From the HRTEM images of the samples after 100 h ball-milling, slightly curved graphene planes can be frequently observed both in the two EGs, however, EG-1 and EG-2 exhibit sharply curved graphene planes and smoothly curved graphene planes with high bending angles, respectively.

  16. Relationship between the evolutions of the microstructure and semiconductor properties of yttrium-doped barium titanate ceramics

    NASA Astrophysics Data System (ADS)

    Huang, C. M.; Lin, C. Y.; Shieh, J.

    2011-08-01

    Intricate connections among the microstructural effect, semiconducting tendency and charge compensation behaviour of yttrium (Y3+) dopants in near-stoichiometric barium titanate (BaTiO3; Ba/Ti atomic ratio = 0.999) ceramics sintered at 1460 °C in air are examined. It is found that with increasing Y3+ doping up to 2.0 mol%, the microstructure of BaTiO3 evolves from a liquid-phase-assisted dense-sintered microstructure to a highly porous microstructure characterized by connected pores and loose lattices of fused submicrometre grains. During such evolution, a transitional microstructure characterized by large distinctive pores and grains with abnormal morphology is also identified. When Y3+ doping is increased progressively from 0.02 to 0.2 mol%, the (negative) majority carrier concentration and conductivity are increased substantially by 8 orders of magnitude. This increase in n-type semiconductor characteristics is contributed not only by the increasing substitution of Y3+ for Ba2+ in host BaTiO3, but also by the formation of yttrium-rich and/or oxygen-deficient precipitates at the grain boundaries. The grain boundary phases would therefore stabilize the mechanism of free electron compensation and enable the transportation of electrons through the grain boundaries. The measured Hall effect data indicate the shift from the n-type to p-type semiconductor properties with increasing Y3+ doping. The carrier mobilities of 1.0 and 2.0 mol% Y-doped BaTiO3 are high; this is attributed to their highly porous microstructures which provide easy diffusion paths for the charge carriers. Through a combined interpretation of the diffractometry, microscopy, mass spectrometry and Hall effect data, Y3+ doping at 1.0 mol% is found to be the critical doping amount separating different site-occupying behaviours of Y3+ in the BaTiO3 cation sites, which eventually lead to different charge compensation mechanisms and semiconductor properties.

  17. 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.

  18. The effect of postprocessing on tensile property and microstructure evolution of friction stir welding aluminum alloy joint

    SciTech Connect

    Hu, Z.L.; Wang, X.S.; Pang, Q.; Huang, F.; Qin, X.P.; Hua, L.

    2015-01-15

    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 the 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.

  19. The microstructural evolution of ultrananocrystalline diamond films due to P ion implantation process—the annealing effect

    SciTech Connect

    Lin, Sheng-Chang; Yeh, Chien-Jui; Leou, Keh-Chyang; Kurian, Joji; Lin, I.-Nan; Dong, Chung-Li; Niu, Huan

    2014-11-14

    The microstructural evolution of UNCD films which are P-ion implanted and annealed at 600 °C (or 800 °C) is systematically investigated. The difference of interaction that the UNCD content undergoes along the trajectory of the incident P-ions is reflected in the alteration of the granular structure. In regions where the P-ions reside, the “interacting zone,” which is found at about 300 nm beneath the surface of the films, coalescence of diamond grains occurs inducing nano-graphitic clusters. The annealing at 600 °C (or 800 °C) heals the defects and, in some cases, forms interconnected graphitic filaments that result in the decrease in surface resistance. However, the annealing at 600 °C (800 °C) induces marked UNCD-to-Si layers interaction. This interaction due to the annealing processes hinders the electron transport across the interface and degrades the electron field emission properties of the UNCD films. These microstructural evolution processes very well account for the phenomenon elaborating that, in spite of enhanced conductivity of the UNCD films along the film's surface due to the P-ion implantation and annealing processes, the electron field emission properties for these UNCD films do not improve.

  20. The effects of quartz recrystallization and reaction on weak phase interconnection, strain localization and evolution of microstructure

    NASA Astrophysics Data System (ADS)

    Gonçalves, Cristiane C.; Gonçalves, Leonardo; Hirth, Greg

    2015-02-01

    We conducted axial compression and general shear experiments, at T = 900 °C and P = 1.5 GPa, on samples of banded iron formation (BIF) and synthetic aggregates of quartz, hematite and magnetite to investigate how dynamic recrystallization of quartz promotes strain localization, and the role of weak second phases (oxides) on the rheology and microstructural evolution of the aggregates. Experiments showed strain localization into oxide rich layers, and that the oxide content and oxide distribution are key factors for the strength of the aggregate. Only 2-10 wt.% hematite leads to pronounced weakening and increasing hematite content above ˜10% has only a minor additional effect. Where oxide grains are dispersed, the initial strength contrast with quartz induces stress concentrations at their tips, promoting high stress recrystallization-accommodated dislocation creep of quartz. Fine recrystallized quartz reacts with oxide, forming trails of fine reaction product (ferrosilite/fayalite) leading to the interconnection/percolation of a weaker matrix. The strength contrast between the quartz framework and these fine-grained trails promotes strain localization into micro-shear zones, inducing drastic strain weakening. Thus dynamic recrystallization of quartz promotes syn-deformational reactions leading to a microstructurally-controlled evolution of phase strength contrast. It results in a rheologic transition from load-bearing framework to a matrix-controlled rheology, with transition from S-C‧ to S-C fabric with increasing strain.

  1. Microstructural evolution and the variation of tensile behavior after aging heat treatment of precipitation hardened martensitic steel

    SciTech Connect

    Shin, Jong-Ho; Jeong, JaeSuk; Lee, Jong-Wook

    2015-01-15

    The effects of aging temperature on the microstructural evolution and the tensile behavior of precipitation hardened martensitic steel were investigated. Microscopic analysis using transmission electron microscope (TEM) was combined with the microstructural analysis using the synchrotron X-ray diffraction (XRD) to characterize the microstructural evolution with aging temperature. Peak hardness was obtained by precipitation of the Ni{sub 3}Al ordered phase. After aging at temperature range from 420 to 590 °C, spherical Ni{sub 3}Al precipitates and ellipsoidal M{sub 23}C{sub 6} carbides were observed within laths and at lath boundaries, respectively. Strain hardening behavior was analyzed with Ludwik equation. It is observed that the plastic strain regimes can be divided into two different stages by a rapid increase in strain hardening followed by a comparatively lower increase. At the first strain hardening stage, the aged specimen exhibited higher strain hardening exponent than the as-quenched specimen, and the exponent in the aged specimen was not changed considerably with increasing aging temperature. It is revealed that the strain hardening exponents at the first and the second stages were associated with the Ni{sub 3}Al precipitates and the domain size representing the coherent scattering area, respectively. - Highlights: • All of aged specimen exhibited higher strain hardening exponent than the as-quenched specimen at the first stage. • The value of strain hardening exponent in the aged specimen was nearly constant with aging temperature. • Ni{sub 3}Al precipitation dominantly influenced to the increase of strain hardening exponent at the first strain hardening stage. • Domain size was associated with strain hardening exponent at the second strain hardening stage.

  2. Effects of aging temperature on microstructural evolution at dissimilar metal weld interfaces

    NASA Astrophysics Data System (ADS)

    Choi, Kyoung Joon; Yoo, Seung Chang; Kim, Taeho; Bahn, Chi Bum; Kim, Ji Hyun

    2015-07-01

    From the earlier study which characterized the region of a fusion boundary between a low-alloy steel (LAS) and a Ni-based weld metal of as-welded and aged samples at 450 °C for a 30-y-equivalent time, it was observed in the microstructure that the aging treatment induced the formation and growth of Cr precipitates in the fusion boundary region because of the thermodynamic driving force. Now, this research extends the text matrix and continues the previous study by compiling all the test data, with an additional aging heat treatment conducted at 400 °C for 15- and 30-y-equivalent times (6450 and 12,911 h, respectively). The results for the extended test matrix primarily represent the common features of and disparities in the effects of thermal aging on the aged samples at two different heat-treatment temperatures (400 and 450 °C). Although no difference was expected between the samples, because the heat treatment conditions simulate thermal aging effects during the same service time of 30 y, the sample aged at 450 °C exhibited slightly more severe effects of thermal aging than the sample aged at 400 °C. Nevertheless, the trends for these effects are similar and the simulation of thermal aging effects for a light-water reactor appears to be reliable. However, according to a simulation of the same degree of thermal aging effects, it appears that the activation energy for Cr diffusion should be larger than the numerical value used in this study.

  3. Microstructural evolution of the nickel platinum-aluminide bond coat on electron-beam physical-vapor deposition thermal-barrier coatings during high-temperature service

    NASA Astrophysics Data System (ADS)

    Zhang, L. C.; Heuer, A. H.

    2005-01-01

    The microstructural evolution of a (Ni,Pt)-aluminide bond coat underneath the ZrO2-based thermal-barrier coating (TBC) topcoat system on a René N5 Ni-based superalloy turbine blade during prolonged high-temperature service has been characterized using transmission electron microscopy (TEM). The as-deposited bond coat has a spatially varying microstructure, which consists of an outer layer of single-phase β-(Ni,Pt)Al, a middle layer of a β-(Ni,Pt)Al matrix containing a high number density of μ-phase precipitates, and an inner layer containing a γ/γ' matrix and numerous μ- and σ-phase precipitates. During service, microstructural changes in the hotter sections of the blade are more extensive than those in the cooler parts, as expected. As a result of interdiffusion, the inner layer grows into the γ/γ' substrate, with the formation of some M23C6 precipitates, and the β matrix in the middle layer is transformed into a two-phase mixture of β and γ'. Corresponding changes occur in the morphologies and volume fractions of the various precipitate phases present in the bond coat. The single-phase β material in the outer layer retains its basic structure, except that the compositional changes due to diffusion between the bond coat and turbine blade cause a martensitic transformation to occur in the hottest sections during the final cooling of the blade. The distribution of various elements in the different layers has also been analyzed, as has growth of the thermally grown oxide (TGO) at the bond coat/TBC interface.

  4. Investigation of a Novel NDE Method for Monitoring Thermomechanical Damage and Microstructure Evolution in Ferritic-Martensitic Steels for Generation IV Nuclear Energy Systems

    SciTech Connect

    Nagy, Peter

    2013-09-30

    The main goal of the proposed project is the development of validated nondestructive evaluation (NDE) techniques for in situ monitoring of ferritic-martensitic steels like Grade 91 9Cr-1Mo, which are candidate materials for Generation IV nuclear energy structural components operating at temperatures up to ~650{degree}C and for steam-generator tubing for sodium-cooled fast reactors. Full assessment of thermomechanical damage requires a clear separation between thermally activated microstructural evolution and creep damage caused by simultaneous mechanical stress. Creep damage can be classified as "negligible" creep without significant plastic strain and "ordinary" creep of the primary, secondary, and tertiary kind that is accompanied by significant plastic deformation and/or cavity nucleation and growth. Under negligible creep conditions of interest in this project, minimal or no plastic strain occurs, and the accumulation of creep damage does not significantly reduce the fatigue life of a structural component so that low-temperature design rules, such as the ASME Section III, Subsection NB, can be applied with confidence. The proposed research project will utilize a multifaceted approach in which the feasibility of electrical conductivity and thermo-electric monitoring methods is researched and coupled with detailed post-thermal/creep exposure characterization of microstructural changes and damage processes using state-of-the-art electron microscopy techniques, with the aim of establishing the most effective nondestructive materials evaluation technique for particular degradation modes in high-temperature alloys that are candidates for use in the Next Generation Nuclear Plant (NGNP) as well as providing the necessary mechanism-based underpinnings for relating the two. Only techniques suitable for practical application in situ will be considered. As the project evolves and results accumulate, we will also study the use of this technique for monitoring other GEN IV

  5. Microstructural evolution of a heat-treated H23 tool steel

    NASA Astrophysics Data System (ADS)

    Nurbanasari, Meilinda; Tsakiropoulos, Panos; Palmiere, Eric J.

    2015-03-01

    The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures (1100°C and 1250°C), followed by water quenching and double-aging at 650°C, 750°C, and 800°C with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched microstructures, which consisted of a ferrite matrix, M6C, M7C3, and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M6C, M7C3, and M23C6 carbides. Secondary hardening as a consequence of secondary precipitation of fine M2C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250°C and double-aging at 650°C, which suggested that this tool steel should be used at temperatures below 650°C.

  6. Evolution and Control of 2219 Aluminum Microstructural Features Through Electron Beam Freeform Fabrication

    NASA Technical Reports Server (NTRS)

    Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

    2006-01-01

    The layer-additive nature of the electron beam freeform fabrication (EBF3) process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

  7. RETRACTED ARTICLE: Microstructural evolution of AA7449 aerospace alloy refined by intensive shearing

    NASA Astrophysics Data System (ADS)

    Haghayeghi, R.; Nastac, L.

    2012-10-01

    Many aerospace alloys are sensitive to their composition thus cannot be chemically grain refined. In addition, only 1% grain refiners can act as nuclei for refining the structure. In this paper, physical refinement by intensive shearing above liquidus as an alternative technique will be investigated for AA7449 aerospace alloy. The results can open a new gateway for aerospace industry for refining their microstructure.

  8. Phase evolution, microstructure and mechanical properties of equi-atomic substituted TiZrHfNiCu and TiZrHfNiCuM (M = Co, Nb) high-entropy alloys

    NASA Astrophysics Data System (ADS)

    Park, Hae Jin; Na, Young Sang; Hong, Sung Hwan; Kim, Jeong Tae; Kim, Young Seok; Lim, Ka Ram; Park, Jin Man; Kim, Ki Buem

    2016-07-01

    In this study, alloys with composition of equi-atomic substituted TiZrHfNiCu, TiZrHfNiCuCo, and TiZrHfNiCuNb high-entropy alloys (HEAs) were produced by suction casting method. The effects of addition elements on phase composition, microstructure and mechanical behaviors of the HEA were studied. The suction casted Ti20Zr20Hf20Ni20Cu20 HEA exhibits single C14 Laves phase (MgZn2-type) with fine homogeneous microstructure. When Co or Nb elements are added, morphologies are slightly modulated toward well-developed dendritic microstructure, phase constitutions are significantly changed from single Laves phase to mixed multi-phases as well as mechanical properties are also altered with increased plasticity and high strength. It is believed that modulated mechanical properties are mainly ascribed to the change of phase constitution and crystalline structure, together with the microstructural characteristics. This clearly reveals that the selection and addition of supplementary elements based on the formation rule for HEAs play an important role on the evolution of phase, microstructural morphology and mechanical properties of Ti20Zr20Hf20Ni20Cu20 HEA.

  9. Evolution of microstructure and residual stress in sputtered chromium and chromium(x) nitrogen(y) thin films

    NASA Astrophysics Data System (ADS)

    Zhao, Zhibo

    This dissertation examines several fundamental aspects of sputtered films, including chemistry, structure, texture, residual stress and growth morphology. The systems considered are Cr films, CxNy films and Ta films. In the first system, the studies focus on some of the unique microstructural features of Cr films. These films develop well-organized anisotropic microstructures and in-plane texture. A texture turnover with thickness has been revealed. The out-of-plane preferred orientation changes from [110] to [111], and conformally, the in-plane preferred orientations vary as well. A new methodology has been developed, in which an anisotropic in-plane stress distribution in a thin film can be determined. This approach has been applied to the Cr films. The anisotropic stresses in these films are related to the evolution of anisotropic microstructure and in-plane texture. The studies of reactively sputtered CrxNy thin films concentrate on phase formation, microstructure, texture, residual stress and growth morphology. It has been shown that these characteristics are predominantly affected by nitrogen flows. The phases identified in the films include Cr, hexagonal Cr2N, and cubic CrxNy, depending on deposition conditions. The composition of the cubic phase exhibits a wide homogeneity span as indicated by large variations of its lattice parameter. At certain nitrogen flow, a nano-crystalline, N-deficient CrxN y film can be obtained. The CrxNy films deposited at high nitrogen flows develop both out-of-plane texture and in-plane texture. In these films, the elongated grains align crystallographically, forming well-defined microstructures. A new experimental apparatus, which utilizes white beam transmission Laue topography and concomitant radiography, has been developed and applied to study cracking/delamination of thin films. Using the systems, the sputtered Ta and CrN films have been studied, and their failures are related to different types of stress development

  10. Evolution of microstructure in mixed niobia-hybrid silica thin films from sol-gel precursors.

    PubMed

    Besselink, Rogier; Stawski, Tomasz M; Castricum, Hessel L; ten Elshof, Johan E

    2013-08-15

    The evolution of structure in sol-gel derived mixed bridged silsesquioxane-niobium alkoxide sols and drying thin films was monitored in situ by small-angle X-ray scattering. Since sol-gel condensation of metal alkoxides proceeds much faster than that of silicon alkoxides, the incorporation of d-block metal dopants into silica typically leads to formation of densely packed nano-sized metal oxide clusters that we refer as metal oxide building blocks in a silica-based matrix. SAXS was used to study the process of niobia building block formation while drying the sol as a thin film at 40-80°C. The SAXS curves of mixed niobia-hybrid silica sols were dominated by the electron density contrast between sol particles and surrounding solvent. As the solvent evaporated and the sol particles approached each other, a correlation peak emerged. Since TEM microscopy revealed the absence of mesopores, the correlation peak was caused by a heterogeneous system of electron-rich regions and electron poor regions. The regions were assigned to small clusters that are rich in niobium and which are dispersed in a matrix that mainly consisted of hybrid silica. The correlation peak was associated with the typical distances between the electron dense clusters and corresponded with distances in real space of 1-3 nm. A relationship between the prehydrolysis time of the silica precursor and the size of the niobia building blocks was observed. When 1,2-bis(triethoxysilyl)ethane was first hydrolyzed for 30 min before adding niobium penta-ethoxide, the niobia building blocks reached a radius of 0.4 nm. Simultaneous hydrolysis of the two precursors resulted in somewhat larger average building block radii of 0.5-0.6 nm. This study shows that acid-catalyzed sol-gel polymerization of mixed hybrid silica niobium alkoxides can be rationalized and optimized by monitoring the structural evolution using time-resolved SAXS.

  11. Modeling the microstructural evolution of metallic polycrystalline materials under localization conditions

    NASA Astrophysics Data System (ADS)

    Bronkhorst, C. A.; Hansen, B. L.; Cerreta, E. K.; Bingert, J. F.

    2007-11-01

    In general, the shear localization process involves initiation and growth. Initiation is expected to be a stochastic process in material space where anisotropy in the elastic-plastic behavior of single crystals and inter-crystalline interactions serve to form natural perturbations to the material's local stability. A hat-shaped sample geometry was used to study shear localization growth. It is an axi-symmetric sample with an upper "hat" portion and a lower "brim" portion with the shear zone located between the hat and brim. The shear zone length was 870-890 μm with deformation imposed through a Split-Hopkinson Pressure Bar system at maximum top-to-bottom velocity in the range of 8-25 m/s. The deformation behavior of tantalum tophat samples is modeled through direct polycrystal simulations. An embedded Voronoï-tessellated two-dimensional microstructure is used to represent the material within the shear zone of the sample. A thermo-mechanically coupled elasto-viscoplastic single crystal model is presented and used to represent the response of the grains within the aggregate shear zone. In the shoulder regions away from the shear zone where strain levels remain on the order of 0.05, the material is represented by an isotropic J2 flow theory based upon the elasto-viscoplastic Mechanical Threshold Stress (MTS) model for flow strength. The top surface stress versus displacement results were compared to those of the experiments and over-all the simulated stress magnitude is over-predicted. It is believed that the reason for this is that the simulations are two-dimensional. A region within the numerical shear zone was isolated for statistical examination. The vonMises stress state within this isolated shear zone region suggests an approximate normal distribution with a factor of two difference between the minimum and maximum points in the distribution. The equivalent plastic strain distribution within this same region has values ranging between 0.4 and 1.5 and is not

  12. Microstructural studies of carbides in MAR-M247 nickel-based superalloy

    NASA Astrophysics Data System (ADS)

    Szczotok, A.; Rodak, K.

    2012-05-01

    Carbides play an important role in the strengthening of microstructures of nickel-based superalloys. Grain boundary carbides prevent or retard grain-boundary sliding and make the grain boundary stronger. Carbides can also tie up certain elements that would otherwise promote phase instability during service. Various types of carbides are possible in the microstructure of nickel-based superalloys, depending on the superalloy composition and processing. In this paper, scanning electron and scanning transmission electron microscopy studies of carbides occurring in the microstructure of polycrystalline MAR-M247 nickel-based superalloy were carried out. In the present work, MC and M23C6 carbides in the MAR-M247 microstructure were examined.

  13. In situ field measurements of the temporal evolution of low-frequency sea-ice dielectric properties in relation to temperature, salinity, and microstructure

    NASA Astrophysics Data System (ADS)

    O'Sadnick, Megan; Ingham, Malcolm; Eicken, Hajo; Pettit, Erin

    2016-11-01

    The seasonal evolution of sea-ice microstructure controls key ice properties, including those governing ocean-atmosphere heat and gas exchange, remote-sensing signatures, and the role of the ice cover as a habitat. Non-destructive in situ monitoring of sea-ice microstructure is of value for sea-ice research and operations but remains elusive to date. We examine the potential for the electric properties of sea ice, which is highly sensitive to the brine distribution within the ice, to serve as a proxy for microstructure and, hence, other ice transport properties. Throughout spring of 2013 and 2014, we measured complex dielectric permittivity in the range of 10 to 95 kHz in landfast ice off the coast of Barrow (Utqiaġvik), Alaska. Temperature and salinity measurements and ice samples provide data to characterize ice microstructure in relation to these permittivity measurements. The results reveal a significant correlation between complex dielectric permittivity, brine volume fraction, and microstructural characteristics including pore volume and connectivity, derived from X-ray microtomography of core samples. The influence of temperature and salinity variations as well as the relationships between ice properties, microstructural characteristics, and dielectric behavior emerge from multivariate analysis of the combined data set. Our findings suggest some promise for low-frequency permittivity measurements to track seasonal evolution of a combination of mean pore volume, fractional connectivity, and pore surface area-to-volume ratio, which in turn may serve as proxies for key sea-ice transport properties.

  14. Microstructure and Texture Evolution During the Alternate Extrusion of an AZ31 Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Li, Feng; Jiang, Hong Wei; Liu, Yang

    2017-01-01

    In this study, a new extrusion process, alternate extrusion (AE), is proposed. We evaluated the reliability and superiority of this process in practical applications by conducting a simulation using the finite element method, which confirmed the experimental results. The microstructure characteristics of an AZ31 magnesium alloy produced by conventional extrusion (CE) and AE were investigated by electron backscattered diffraction and optical microscopy, and the effects of the microstructures on the mechanical properties were studied across the extruded specimens. The main advantage of AE is that the load is reduced to less than half that in the CE process; this results from the reduced cross-section of the split punches. Additionally, the grain size with AE is more refined than with CE because of the additional shear force, which improves the mechanical properties of the alloys. Furthermore, AE can also weaken the intensity of the basal plane texture.

  15. Microstructure evolution and mechanical properties of biomedical Mg-Zn-Gd alloy wires

    NASA Astrophysics Data System (ADS)

    Chunlei, Gan; Xiaohui, Li; Deng, Nong; Xiang, Zhang; Kaihong, Zheng; Zhenghua, Huang

    2017-03-01

    In order to manufacture the Mg-Zn-Gd alloy fine wires for the development of new biomedical Mg alloy implant devices, a hot extrusion and cold drawing process which is used to develop the Mg-Zn-Gd alloy fine wires were investigated. The results demonstrate that the Mg-Zn-Gd alloy has good formability. The microstructure and properties of the Mg-Zn-Gd alloy wires were studied by the observations of optical microscopy and scanning electron microscopy. The results show that the process is successfully developed to manufacture the high-quality wires with 3.00 mm diameter. The achievement of the high-quality Mg-Zn-Gd alloy wires is ascribed to the refined microstructure due to dynamic recrystallization during hot extrusion. Additionally, the grain morphology can play an important role in affecting the subsequent cold drawing performance.

  16. Analysis of Microstructure Evolution in Quenching and Partitioning Automotive Sheet Steel

    NASA Astrophysics Data System (ADS)

    Speer, John G.; de Moor, E.; Findley, K. O.; Matlock, D. K.; de Cooman, B. C.; Edmonds, D. V.

    2011-12-01

    Extensive research efforts are underway globally to develop new steel microstructure concepts for high-strength sheet products, driven largely by the need for lightweight automotive structures in support of designs to enhance occupant safety and energy efficiency. One promising approach, involving the quenching and partitioning (Q&P) process, was introduced in the predecessor to this paper series, Austenite Formation and Decomposition, 2003.[1] Development of the Q&P process has continued through to the present, and the current status is highlighted in this article, along with some alternative approaches that are also receiving attention. Special emphasis is placed on the synthesis and interpretation of the fundamental phase transformation responses, perspectives related to alloying and processing, and the resulting microstructure and properties. Key mechanistic issues are discussed, including carbide formation and suppression, migration of the martensite/austenite interface, carbon partitioning, and partitioning kinetics.

  17. Microstructural evolution during tension-compression in-plane deformation of a pure aluminum sheet

    NASA Astrophysics Data System (ADS)

    Härtel, M.; Bohne, B.; F-X Wagner, M.

    2017-03-01

    Classically, the Bauschinger effect refers to a reduction of yield strength after a load path change. In this contribution, we present results of an experimental and microstructural investigation on Bauschinger effects in an AA1050 sheet metal (with 1 mm thickness) subjected to in-plane uniaxial loading. We performed tension-compression tests with different values of maximum tensile strains in a novel tool that was specifically designed to avoid buckling under compressive loading. Our experimental results show that the sheet material exhibits distinct Bauschinger effects. At different stages of deformation, we interrupted the tests and prepared samples for transmission electron microscopy. Our microstructural observations allow rationalizing the occurrence and magnitude of the observed Bauschinger effects.

  18. Evolution of Microstructure and Mechanical Properties of Thermomechanically Processed Ultrahigh-Strength Steel

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, P. S.; Ghosh, S. K.; Kundu, S.; Chatterjee, S.

    2011-09-01

    In the present study, low carbon microalloyed ultrahigh-strength steel was manufactured on a pilot scale. Transformation of the aforesaid steel during continuous cooling was assessed. The steel sample was thermomechanically processed followed by air cooling and water quenching. Variation in microstructure and mechanical properties at different finish rolling temperatures (FRTs) was studied. A mixture of granular bainite and bainitic ferrite along with interlath and intralath precipitation of (Ti, Nb)CN particles is the characteristic microstructural feature of air-cooled steel. On the other hand, lath martensitic structure along with a similar type of microalloying precipitates of air-cooled steels is obtained in the case of water-quenched steel also. The best combination of strength (1440 to 1538 MPa) and ductility (11 to 16 pct) was achieved for the selected range of FRTs of water-quenched steel.

  19. Effects of titanium additions to austenitic ternary alloys on microstructural evolution and void swelling

    SciTech Connect

    Okita, T; Wolfer, W G; Garner, F A; Sekimura, N

    2003-12-01

    Ternary austenitic model alloys were modified with 0.25 wt.% titanium and irradiated in FFTF reactor at dose rates ranging over more than two orders in magnitude. While lowering of dose rate strongly increases swelling by shortening the incubation dose, the steady state swelling rate is not affected by dose rate. Although titanium addition strongly alters the void microstructure, swelling at {approx} 420 C does not change with titanium additions, but the sensitivity to dose rate is preserved.

  20. Evolution and Control of 2219 Aluminum Microstructural Features through Electron Beam Freeform Fabrication

    NASA Technical Reports Server (NTRS)

    Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

    2006-01-01

    Electron beam freeform fabrication (EBF3) is a new layer-additive process that has been developed for near-net shape fabrication of complex structures. EBF3 uses an electron beam to create a molten pool on the surface of a substrate. Wire is fed into the molten pool and the part translated with respect to the beam to build up a 3-dimensional structure one layer at a time. Unlike many other freeform fabrication processes, the energy coupling of the electron beam is extremely well suited to processing of aluminum alloys. The layer-additive nature of the EBF3 process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

  1. 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.

  2. Evolution of Globular Microstructure and Rheological Properties of Stellite™ 21 Alloy after Heating to Semisolid State

    NASA Astrophysics Data System (ADS)

    Sołek, Krzysztof Piotr; Rogal, Łukasz; Kapranos, Platon

    2017-01-01

    Metal alloys can be successfully thixoformed in the partially liquid state if they display non-dendritic near-globular microstructures. The article presents the development of feedstock with such non-dendritic microstructure produced through the solid-state route of strain-induced melt-activated (SIMA) method, for a Stellite ™ 21 alloy. Stellite ™ alloys are a range of cobalt-chromium alloys designed for wear and corrosion resistance, currently shaped by casting, powder metallurgy or forging processes, but semisolid-state processing offers the possibility of a near-net-shaping method for these alloys. In this work, sprayformed followed by extrusion samples were heated to the temperature range at which the liquid and solid phases coexist in the material and spheroidal shape solid particles in a liquid matrix were obtained as required for semisolid processing. Microstructural investigations were carried out using scanning electron microscopy (SEM) in combination with energy-dispersive spectroscopy (EDS), with a further objective of analyzing the rheological properties of Stellite ™ 21 alloy in the semisolid state, providing results to be used for identification of a processing window of temperature and viscosity ranges for thixoforming this alloy.

  3. Microstructural Evolution in Friction Stir Welding of Ti-6Al-4V

    NASA Technical Reports Server (NTRS)

    Rubisoff, H.; Querin, J.; Magee, D.; Schneider, J.

    2008-01-01

    Friction stir welding (FSW) is a thermo-mechanical process that utilizes a nonconsumable rotating pin tool to consolidate a weld joint. In the conventional FSW process, the pin tool is responsible for generating both the heat required to soften the material and the forces necessary to deform and combine the weld seam. As such, the geometry of the pin tool is important to the quality of the weld and the process parameters required to produce the weld. Because the geometry of the pin tool is limitless, a reduced set of pin tools was formed to systematically study their effect on the weldment with respect to mechanical properties and resultant microstructure. In this study 0deg, 15deg, 30deg, 45deg, and 60deg tapered, microwave sintered, tungsten carbide (WC) pin tools were used to FSW Ti-6Al-4V. Transverse sections of the weld were used to test for mechanical properties and to document the microstructure using optical microscopy. X-ray diffraction (XRD) was also used to characterize the microstructure in the welds. FSW results for the 45deg and 60deg pin tools are reported in this paper.

  4. Evolution of Globular Microstructure and Rheological Properties of Stellite™ 21 Alloy after Heating to Semisolid State

    NASA Astrophysics Data System (ADS)

    Sołek, Krzysztof Piotr; Rogal, Łukasz; Kapranos, Platon

    2016-11-01

    Metal alloys can be successfully thixoformed in the partially liquid state if they display non-dendritic near-globular microstructures. The article presents the development of feedstock with such non-dendritic microstructure produced through the solid-state route of strain-induced melt-activated (SIMA) method, for a Stellite™ 21 alloy. Stellite™ alloys are a range of cobalt-chromium alloys designed for wear and corrosion resistance, currently shaped by casting, powder metallurgy or forging processes, but semisolid-state processing offers the possibility of a near-net-shaping method for these alloys. In this work, sprayformed followed by extrusion samples were heated to the temperature range at which the liquid and solid phases coexist in the material and spheroidal shape solid particles in a liquid matrix were obtained as required for semisolid processing. Microstructural investigations were carried out using scanning electron microscopy (SEM) in combination with energy-dispersive spectroscopy (EDS), with a further objective of analyzing the rheological properties of Stellite™ 21 alloy in the semisolid state, providing results to be used for identification of a processing window of temperature and viscosity ranges for thixoforming this alloy.

  5. Comparative Evaluation of Cast Aluminum Alloys for Automotive Cylinder Heads: Part I—Microstructure Evolution

    NASA Astrophysics Data System (ADS)

    Roy, Shibayan; Allard, Lawrence F.; Rodriguez, Andres; Watkins, Thomas R.; Shyam, Amit

    2017-03-01

    The present study stages a comparative evaluation of microstructure and associated mechanical and thermal response for common cast aluminum alloys that are used for manufacturing automotive cylinder heads. The systems considered are Al-Cu (206-T6), Al-Si-Cu (319-T7), and Al-Si (356-T6, A356-T6, and A356 + 0.5Cu-T6). The focus of the present manuscript is on the evaluation of microstructure at various length scales after aging, while the second manuscript will deal with the mechanical and thermal response of these alloys due to short-term (aging) and long-term (pre-conditioning) heat treatments. At the grain-scale, the Al-Cu alloy possessed an equiaxed microstructure as opposed to the dendritic structure for the Al-Si-Cu or Al-Si alloys which is related to the individual solidification conditions for these alloy systems. The composition and morphology of intermetallic precipitates within the grain and at the grain/dendritic boundary are dictated by the alloy chemistry, solidification, and heat treatment conditions. At the nanoscale, these alloys contain various metastable strengthening precipitates (GPI and θ^'' in Al-Cu alloy, θ^' in Al-Si-Cu alloy, and β^' in Al-Si alloys) with varying size, morphology, coherency, and thermal stability.

  6. Effect of simultaneous helium implantation on the microstructure evolution of Inconel X-750 superalloy during dual-beam irradiation

    NASA Astrophysics Data System (ADS)

    Changizian, P.; Zhang, H. K.; Yao, Z.

    2015-12-01

    This study focuses on investigation into the effect of helium implantation on microstructure evolution in Inconel X-750 superalloy during dual-beam (Ni+/He+) irradiation. The 1 MeV Ni+ ions with the damage rate of 10-3 dpa/s as well as 15 keV He+ ions using rate of 200 appm/dpa were simultaneously employed to irradiate specimens at 400 °C to different doses. Microstructure characterization has been conducted using high-resolution analytical transmission electron microscopy (TEM). The TEM results show that simultaneous helium injection has significant influence on irradiation-induced microstructural changes. The disordering of γ‧ (Ni3 (Al, Ti)) precipitates shows noticeable delay in dose level compared to mono heavy ion irradiation, which is attributed to the effect of helium on promoting the dynamic reordering process. In contrast to previous studies on single-beam ion irradiation, in which no cavities were reported even at high doses, very small (2-5 nm) cavities were detected after irradiation to 5 dpa, which proved that helium plays crucial role in cavity formation. TEM characterization also indicates that the helium implantation affects the development of dislocation loops during irradiation. Large 1/3 <1 1 1> Frank loops in the size of 10-20 nm developed during irradiation at 400 °C, whereas similar big loops detected at higher irradiation temperature (500 °C) during sole ion irradiation. This implies that the effect of helium on trapping the vacancies can help to develop the interstitial Frank loops at lower irradiation temperatures.

  7. 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

  8. Influence of coarsened and rafted microstructures on the thermomechanical fatigue of a Ni-base superalloy

    SciTech Connect

    Kirka, M. M.; Brindley, K. A.; Neu, R. W.; Antolovich, S. D.; Shinde, S. R.; Gravett, P. W.

    2015-08-17

    The aging of the microstructure of Ni-base superalloys during service is mainly characterized by coarsening and rafting of the γ' precipitates. The influence of these different aged microstructures on thermomechanical fatigue (TMF) under either continuously cycled (CC) and creep-fatigue (CF) was investigated. Three different aged microstructures, generated through accelerated aging and pre-creep treatments, were studied: stress-free coarsened γ', rafted with orientation perpendicular to loading direction (N-raft), and rafted with orientation parallel to loading direction (P-raft). Under most conditions, the aged microstructures were less resistant to TMF than the virgin microstructure; however, there were exceptions. Both stress-free coarsened and N-raft microstructures resulted in a reduction in TMF life under both CC and CF conditions in comparison to the virgin material. P-raft microstructure also resulted in reduction in TMF life under CC conditions; however, an increase in life over that of the virgin material was observed under CF conditions. Finally, these differences are discussed and hypothesized to be related to the interactions of the dislocations in the γ channels with γ' precipitates.

  9. Nanostructured aluminium titanate (Al{sub 2}TiO{sub 5}) particles and nanofibers: Synthesis and mechanism of microstructural evolution

    SciTech Connect

    Azarniya, Abolfazl; Azarniya, Amir; Hosseini, Hamid Reza Madaah; Simchi, Abdolreza

    2015-05-15

    In this study, aluminium titanate (AT) particles and nanofibers were synthesized through citrate sol gel and sol gel-assisted electrospinning methods in both nanostructured powder and nanofiber forms. The results of X-ray diffraction analysis, field-emission scanning electron microscopy and differential thermal analysis showed that the synthetic products benefit a nanostructured nature with a grain size less than 70 nm. The optimal values for time and temperature at which a roughly pure AT is attained were determined as 2 h and 900 °C, respectively. It was found that the sol gel precursor bears an amorphous structure till 700 °C and begins to be crystallized to alumina, anatase and AT at higher temperatures. Moreover, AT tends to decompose into rutile and alumina at temperatures higher than 900 °C and its degradation rate reaches a maximum at temperatures near to 1100 °C. In this synthesis, citric acid was used as a chelating agent for Al{sup 3} {sup +} and Ti{sup 4} {sup +} ions and it was shown that a low citric acid-to-metal cation ratio leads to larger numbers of nuclei during crystallization and smaller grain size. Finally, a model was suggested to describe the microstructural evolution of AT compound based on a nucleation and growth regime. - Graphical abstract: Display Omitted - Highlights: • We synthesized aluminium titanate ceramic in both powder and nanofiber forms. • The methods in use were citrate sol gel and sol gel-assisted electrospinning. • Powders and nanofibers bear a nanostructured nature with a grain size less than 70 nm. • A model is suggested to describe microstructural evolution of synthetic products.

  10. Physical Simulation of Deformation and Microstructure Evolution During Friction Stir Processing of Ti-6Al-4V Alloy

    NASA Astrophysics Data System (ADS)

    Babu, S. S.; Livingston, J.; Lippold, J. C.

    2013-08-01

    The feasibility of using high-strain rate (1.475 to 3.942 s-1) hot-torsion testing with a Gleeble® thermomechanical simulator was demonstrated for simulating microstructures consistent with friction stir processing (FSP) of Ti-6Al-4V. The tests were performed on α/β-processed base material at temperatures both above and below the β-transus. Various phenomena including the refinement of α- and β-grains, deformation-induced heating, and deformation instabilities were observed. These tests reproduced the range of microstructures that are observed under FSP processing conditions. The testing methodology can be used for generating constitutive material property equations relevant to computational FSP/friction stir welding models.

  11. Texture and microstructure evolution in single-phase Ti{sub x}Ta{sub 1-x}N alloys of rocksalt structure

    SciTech Connect

    Koutsokeras, L. E.; Abadias, G.; Patsalas, P.

    2011-08-15

    The mechanisms controlling the structural and morphological features (texture and microstructure) of ternary transition metal nitride thin films of the Ti{sub x}Ta{sub 1-x}N system, grown by various physical vapor deposition techniques, are reported. Films deposited by pulsed laser deposition, dual cathode magnetron sputtering, and dual ion beam sputtering have been investigated by means of x-ray diffraction in various geometries and scanning electron microscopy. We studied the effects of composition, energetic, and kinetics in the evolution of the microstructure and texture of the films. We obtain films with single and mixed texture as well as films with columnar ''zone-T'' and globular type morphology. The results have shown that the texture evolution of ternary transition metal nitrides as well as the microstructural features of such films can be well understood in the framework of the kinetic mechanisms proposed for their binary counterparts, thus giving these mechanisms a global application.

  12. Microstructure and Texture Evolution in a Yttrium-Containing ZM31 Alloy: Effect of Pre- and Post-deformation Annealing

    NASA Astrophysics Data System (ADS)

    Tahreen, N.; Zhang, D. F.; Pan, F. S.; Jiang, X. Q.; Li, D. Y.; Chen, D. L.

    2016-12-01

    Microstructure and texture evolution of as-extruded ZM31 magnesium alloys with different amounts of yttrium (Y) during pre- and post-deformation annealing were examined with special attention given to the effect of Y on recrystallization. It was observed that the extruded ZM31 alloys exhibited a basal texture with the basal planes parallel to the extrusion direction (ED). The compression of the extruded alloys in the ED to a strain amount of 10 pct resulted in c-axes of hcp unit cells rotating toward the anti-compression direction due to the occurrence of extension twinning. Annealing of the extruded alloys altered the microstructure and texture, and the subsequent compression after annealing showed a relatively weak texture and a lower degree of twinning. A reverse procedure of pre-compression and subsequent annealing was found to further weaken the texture with a more scattered distribution of orientations and to lead to the vanishing of the original basal texture. With increasing Y content, both the extent of extension twinning during compression and the fraction of recrystallization during annealing decreased due to the role of Y present in the substitutional solid solution and in the second-phase particles, leading to a significant increase in the compressive yield strength.

  13. Evolution of the microstructure and mechanical properties during fabrication of mini-tubes from a biomedical β-titanium alloy.

    PubMed

    Zhang, Yaowu; Kent, Damon; Wang, Gui; St John, David; Dargusch, Matthew

    2015-02-01

    The processing of Ti-25Nb-3Mo-3Zr-2Sn tubes with outside diameters of 5.6-8.0 mm and wall-thicknesses of 0.7-1.0 mm were investigated in order to study the evolution of microstructure and mechanical properties and their impact on the processing of the tubes. The annealed small tubes with single β phase microstructures exhibit double yielding during tensile tests. The onset of martensitic phase transformation was observed to occur after the lowest point of the strain hardening. Cold rolling also activates the formation of the stress induced martensitic α″ phase. Its volume fraction increased with increasing ε. The rate of strain hardening and the modulus of the tubes are related to the stress induced transformation of the β phase to the α″ phase. The stress induced α″ slightly improves the yield strength of the tubes at low levels of strain. However, larger strains result in grain growth during annealing, which diminishes the mechanical properties.

  14. 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

    2017-03-01

    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.

  15. Microstructural Evolution and Mechanical Properties of Simulated Heat-Affected Zones in Cast Precipitation-Hardened Stainless Steels 17-4 and 13-8+Mo

    NASA Astrophysics Data System (ADS)

    Hamlin, Robert J.; DuPont, John N.

    2017-01-01

    Cast precipitation-hardened (PH) stainless steels 17-4 and 13-8+Mo are used in applications that require a combination of high strength and moderate corrosion resistance. Many such applications require fabrication and/or casting repair by fusion welding. The purpose of this work is to develop an understanding of microstructural evolution and resultant mechanical properties of these materials when subjected to weld thermal cycles. Samples of each material were subjected to heat-affected zone (HAZ) thermal cycles in the solution-treated and aged condition (S-A-W condition) and solution-treated condition with a postweld thermal cycle age (S-W-A condition). Dilatometry was used to establish the onset of various phase transformation temperatures. Light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were used to characterize the microstructures, and comparisons were made to gas metal arc welds that were heat treated in the same conditions. Tensile testing was also performed. MatCalc thermodynamic and kinetic modeling software was used to predict the evolution of copper (Cu)-rich body center cubic precipitates in 17-4 and β-NiAl precipitates in 13-8+Mo. The yield strength was lower in the simulated HAZ samples of both materials prepared in the S-A-W condition when compared to their respective base metals. Samples prepared in the S-W-A condition had higher and more uniform yield strengths for both materials. Significant changes were observed in the matrix microstructure of various HAZ regions depending on the peak temperature, and these microstructural changes were interpreted with the aid of dilatometry results, LOM, SEM, and EDS. Despite these significant changes to the matrix microstructure, the changes in mechanical properties appear to be governed primarily by the precipitation behavior. The decrease in strength in the HAZ samples prepared in the S-A-W condition was attributed to the dissolution of precipitates

  16. Linking microstructural evolution and macro-scale friction behavior in metals

    NASA Astrophysics Data System (ADS)

    Argibay, N.; Chandross, M.; Cheng, S.; Michael, J. R.

    2017-03-01

    A correlation is established between the macro-scale friction regimes of metals and a transition between two dominant atomistic mechanisms of deformation. Metals tend to exhibit bi-stable friction behavior -- low and converging or high and diverging. These general trends in behavior are shown to be largely explained using a simplified model based on grain size evolution, as a function of contact stress and temperature, and are demonstrated for pure copper and gold. Specifically, the low friction regime is linked to the formation of ultra-nanocrystalline surface films (10 to 20 nm), driving toward shear accommodation by grain boundary sliding. Above a critical combination of stress and temperature -- demonstrated to be a material property -- shear accommodation transitions to dislocation dominated plasticity and high friction. We utilize a combination of experimental and computational methods to develop and validate the proposed structure-property relationship. This quantitative framework provides a shift from phenomenological to mechanistic and predictive fundamental understanding of friction for crystalline materials, including engineering alloys.

  17. Microstructure evolution and thixoforming behavior of 7075 aluminum alloy in the semi-solid state prepared by RAP method

    NASA Astrophysics Data System (ADS)

    Fu, Jin-long; Wang, Kai-kun; Li, Xiao-wei; Zhang, Hai-kuan

    2016-12-01

    The effects of isothermal treatments on the microstructural evolution and coarsening rate of semi-solid 7075 aluminum alloy produced via the recrystallization and partial remelting (RAP) process were investigated. Samples of 7075 aluminum alloy were subjected to cold extrusion, and semi-solid treatment was carried out for 5-30 min at temperatures ranging from 580 to 605°C. A backward-extrusion experiment was conducted to investigate liquid segregation during the thixoforming process. The results revealed that obvious grain coarsening and spheroidization occurred during prolonged isothermal treatments. In addition, higher soaking temperatures promoted the spheroidization and coarsening process because of the increased liquid fraction and the melting of second phases. Segregation of the liquid phase caused by the difference in fluidity between the liquid and the solid phases was observed in different regions of the thixoformed specimens.

  18. Microstructural evolution of NF709 (20Cr-25Ni-1.5MoNbTiN) under neutron irradiation

    NASA Astrophysics Data System (ADS)

    Kim, B. K.; Tan, L.; Xu, C.; Yang, Y.; Zhang, X.; Li, M.

    2016-03-01

    Because of its superior creep and corrosion resistance as compared with general austenitic stainless steels, NF709 has emerged as a candidate structural material for advanced nuclear reactors. To obtain fundamental information about the radiation resistance of this material, this study examined the microstructural evolution of NF709 subjected to neutron irradiation to 3 displacements per atom at 500 °C. Transmission electron microscopy, scanning electron microscopy, and high-energy x-ray diffraction were employed to characterize radiation-induced segregation, Frank loops, voids, as well as the formation and reduction of precipitates. Radiation hardening of ∼76% was estimated by nanoindentation, approximately consistent with the calculation according to the dispersed barrier-hardening model, suggesting Frank loops as the primary hardening source.

  19. Time-Resolved SAXS/WAXS Study of the Phase Behavior and Microstructural Evolution of Drug/PEG Solid Dispersions

    SciTech Connect

    Zhu, Qing; Harris, Michael T.; Taylor, Lynne S.

    2013-03-07

    Simultaneous small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) was employed to elucidate the physical state and location of various small molecule drugs blended with polyethylene glycol (PEG), as well as the time dependent microstructural evolution of the systems. Samples were prepared by comelting physical mixtures of the drug and PEG, followed by solidification at 25 C. The model drugs selected encompassed a wide variety of physicochemical properties in terms of crystallization tendency and potential for interaction with PEG. It was observed that compounds which crystallized rapidly and had weak interactions with PEG tended to be excluded from the interlamellar region of the PEG matrix. In contrast, drugs which had favorable interactions with PEG were incorporated into the interlamellar regions of the polymer up until the point at which the drug crystallized whereby phase separation occurred. These factors are likely to impact the effectiveness of drug/PEG systems as drug delivery systems.

  20. Microstructural evolution of NF709 (20Cr–25Ni–1.5MoNbTiN) under neutron irradiation

    SciTech Connect

    Kim, Byoungkoo; Tan, Lizhen; Xu, C.; Yang, Yong; Zhang, Xuan; Li, Meimei

    2015-12-30

    In this study, because of its superior creep and corrosion resistance as compared with general austenitic stainless steels, NF709 has emerged as a candidate structural material for advanced nuclear reactors. To obtain fundamental information about the radiation resistance of this material, this study examined the microstructural evolution of NF709 subjected to neutron irradiation to 3 displacements per atom at 500 °C. Transmission electron microscopy, scanning electron microscopy, and high-energy x-ray diffraction were employed to characterize radiation-induced segregation, Frank loops, voids, as well as the formation and reduction of precipitates. Radiation hardening of ~76% was estimated by nanoindentation, approximately consistent with the calculation according to the dispersed barrier-hardening model, suggesting Frank loops as the primary hardening source.

  1. Microstructural evolution of NF709 (20Cr–25Ni–1.5MoNbTiN) under neutron irradiation

    DOE PAGES

    Kim, Byoungkoo; Tan, Lizhen; Xu, C.; ...

    2015-12-30

    In this study, because of its superior creep and corrosion resistance as compared with general austenitic stainless steels, NF709 has emerged as a candidate structural material for advanced nuclear reactors. To obtain fundamental information about the radiation resistance of this material, this study examined the microstructural evolution of NF709 subjected to neutron irradiation to 3 displacements per atom at 500 °C. Transmission electron microscopy, scanning electron microscopy, and high-energy x-ray diffraction were employed to characterize radiation-induced segregation, Frank loops, voids, as well as the formation and reduction of precipitates. Radiation hardening of ~76% was estimated by nanoindentation, approximately consistent withmore » the calculation according to the dispersed barrier-hardening model, suggesting Frank loops as the primary hardening source.« less

  2. Correlation of Impact Conditions, Interface Reactions, Microstructural Evolution, and Mechanical Properties in Kinetic Spraying of Metals: A Review

    NASA Astrophysics Data System (ADS)

    Kim, Jaeick; Lee, Changhee

    2016-12-01

    In the past, most studies into kinetic spraying technology focused on basic research, but a large portion of current research is devoted to industrial applications of the technology. To advance, however, studies about industrial applications of kinetic spraying require profound understanding of the scientific foundations of the kinetic spray process. Nevertheless, no one has yet provided a well-organized summary of the correlations among impact conditions, interface reactions, microstructural evolution, and mechanical properties across the whole field of kinetic spraying technology. This paper provides such an overview of these correlations for kinetic spraying of metals. For each correlation, the interactions between the given conditions and the material properties of the metal feedstock powder are the most influential. These interactions are so complicated that it is difficult to systematically classify all cases into certain types. Nonetheless, we try to explain and summarize the critical factors and their roles in each relationship.

  3. Microstructural Evolution of Inconel 625 and Inconel 686CPT Weld Metal for Clad Carbon Steel Linepipe Joints: A Comparator Study

    NASA Astrophysics Data System (ADS)

    Maltin, Charles A.; Galloway, Alexander M.; Mweemba, Martin

    2014-07-01

    Microstructural evolution of Inconel 625 and Inconel 686CPT filler metals, used for the fusion welding of clad carbon steel linepipe, has been investigated and compared. The effects of iron dilution from the linepipe parent material on the elemental segregation potential of the filler metal chemistry have been considered. The results obtained provide significant evidence to support the view that, in Inconel 686CPT weld metal, the segregation of tungsten is a function of the level of iron dilution from the parent material. The data presented indicate that the incoherent phase precipitated in the Inconel 686CPT weld metal has a morphology that is dependent on tungsten enrichment and, therefore, iron dilution. Furthermore, in the same weld metal, a continuous network of finer precipitates was observed. The Charpy impact toughness of each filler metal was evaluated, and the results highlighted the superior impact toughness of the Inconel 625 weld metal over that of Inconel 686CPT.

  4. Microstructures and Mechanical Properties of High-Mn TRIP Steel Based on Warm Deformation of Martensite

    NASA Astrophysics Data System (ADS)

    Guo, Zhikai; Li, Longfei; Yang, Wangyue; Sun, Zuqing

    2015-04-01

    High-Mn TRIP steel with about 5 wt pct Mn was prepared by a thermo-mechanical treatment based on warm deformation of martensite and subsequent short-time annealing in the intercritical region. The microstructural evolution and the mechanical properties of the used steel during such treatment were investigated. The results indicate that during warm deformation of martensite in the intercritical region, the decomposition of martensite was accelerated by warm deformation and the occurrence of dynamic recrystallization of ferrite led to the formation of equiaxed ferrite grains. Meanwhile, the reverse transformation of austenite was accelerated by warm deformation to some extent. During subsequent annealing in the intercritical region, static recrystallization of ferrite led to the increase in the fraction of equiaxed ferrite grains, and the formation of the reversed austenite was accelerated by the addition of the deformation-stored energy, while the stability of the reversed austenite was improved by the accelerated diffusions of C atoms and Mn atoms. As a whole, the mechanical properties of the used steel by the thermo-mechanical treatment based on warm deformation of martensite and subsequent short-time annealing in the intercritical region were comparable to the steels with similar compositions subjected to intercritical annealing for hours after cold rolling of martensite.

  5. On the origin of residual strain in shape memory alloys: experimental investigation on evolutions in the microstructure of CuAlBe during complex thermomechanical loadings

    NASA Astrophysics Data System (ADS)

    Barati, M.; Arbab Chirani, S.; Kadkhodaei, M.; Saint-Sulpice, L.; Calloch, S.

    2017-02-01

    The behaviors of shape memory alloys (SMAs) strongly depend on the presence of different phases: austenite, thermally-induced martensite and stress-induced martensite. Consequently, it is important to know the phase volume fraction of each phases and their evolution during thermomechanical loadings. In this work, a three-phase proportioning method based on electric resistivity variation of a CuAlBe SMA is proposed. Simple thermomechanical loadings (i. e. pseudoplasticity and pseudoelasticity), one-way shape memory effect, recovery stress, assisted two-way memory effect at different level of stress and cyclic pseudoelasticity tests are investigated. Based on the electric resistivity results, during each loading path, evolution of the microstructure is determined. The origin of residual strain observed during the considered thermomechanical loadings is discussed. A special attention is paid to two-way shape memory effect generated after considered cyclic loadings and its relation with the developed residual strain. These results permit to identify and to validate the macroscopic models of SMAs behaviors.

  6. Evolution of magnetic properties and microstructure of Hf{sub 2}Co{sub 11}B alloys

    SciTech Connect

    McGuire, Michael A. Rios, Orlando

    2015-02-07

    Amorphous Hf{sub 2}Co{sub 11}B alloys produced by melt-spinning have been crystallized by annealing at 500–800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo{sub 7}, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo{sub 7} phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °C contains HfCo{sub 3}B{sub 2}, Hf{sub 6}Co{sub 23}, and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf{sub 2}Co{sub 11}B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo{sub 7} and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.

  7. Micro-structural evolution and biomineralization behavior of carbon nanofiber/bioactive glass composites induced by precursor aging time.

    PubMed

    Jia, Xiaolong; Tang, Tianhong; Cheng, Dan; Zhang, Cuihua; Zhang, Ran; Cai, Qing; Yang, Xiaoping

    2015-12-01

    Bioactive glass (BG)-containing carbon nanofibers (CNFs) are promising orthopaedic biomaterials. Herein, CNF composites were produced from electrospinning of polyacrylonitrile (PAN)/BG sol-gel precursor solution, followed by carbonization. Choosing 58S-type BG (mol%: 58.0% SiO2-26.3% CaO-15.7% P2O5) as the model, micro-structural evolution of CNF/BG composites was systematically evaluated in relating to aging times of BG precursor solution. With aging time prolonging, BG precursors underwent morphological changes from small sol clusters with loosely and randomly branched structure to highly crosslinked Si-network structure, showing continuous increase in solution viscosity. BG precursor solution with low viscosity could mix well with PAN solution, resulting in CNF composite with homogeneously distributed BG component. Whereas, BG precursor gel with densely crosslinked Si-network structure led to uneven distribution of BG component along final CNFs due to its significant phase separation from PAN component. Meanwhile, BG nanoparticles in CNFs demonstrated micro-structural evolution that they transited from weak to strong crystal state along with longer aging time. Biomineralization in simulated body fluid and in vitro osteoblasts proliferation were then applied to determine the bioactivity of CNF/BG composites. CNF/BG composites prepared from shorter aging time could induce both faster apatite deposition and cell proliferation rate. It was suggested weakly crystallized BG nanoparticles along CNFs dissolved fast and was able to provide numerous nucleation sites for apatite deposition, which also favored the proliferation of osteoblasts cells. Aging time could thus be a useful tool to regulate the biological features of CNF/BG composites.

  8. Microstructural evolution and macroscopic shrinkage in the presence of density gradients and agglomeration

    NASA Astrophysics Data System (ADS)

    Lu, Peizhen

    X-ray computed tomography (CT) can characterize internal density gradients. An in-situ laser dilatometry has been constructed to track dimensional change at different positions of a sample during binder removal and sintering. This combination of tools not only allows us to better understand how microscopic change affects macroscopic dimensions, but also provides guidance for a variety of ceramic processes. Non-uniform agglomerate packing and deformation provide density gradients which drive binder migration during binder removal. Simultaneously, density undergoes a slight decrease accompanied by a 1.0% loss in dimensional tolerance. This and CT difference images suggest that capillary forces generated during binder melting can change the density distribution. During sintering, nonuniformities present in the green state persist into the fired state and become exaggerated. Regions of different initial density can occupy different stages sintering. At ˜88% sintered density, CT clearly showed that open porosity follows the distribution of low density areas. Mercury porosimetry detected three distinct levels of porosity. Microstructural examination correlated the porosity level with the coordination of (i) two to three or (ii) multiple grains around pores. Microstructural packing controls both the observed macroscopic expansion at T ≤ 1000°C and the onset of shrinkage. Neck formation initiates during expansion and not exclusively during shrinkage. Inter- and intra-agglomerate expansion/shrinkage proceed simultaneously but the effective 'transmission' of particle-level behavior to the macroscopic level appears to be controlled by the initial agglomerate bonding and internal agglomerate densities. Discrete element modeling provides corroborating evidence regarding the importance of compact continuity. Following the expansion-shrinkage transition, the higher the zone density the faster the initial shrinkage. The 25% RH sample shrank more rapidly than the same zone in

  9. On the microstructural evolution of cold-rolled Al+5at.% Mg

    SciTech Connect

    Dirras, G.F.; Biget, M.P.; Rey, C.

    1995-09-01

    The present study shows that the deformation microstructures of cold-rolled Al+5at.%Mg evolve according to the grain subdivision principles as reported elsewhere. The saturation of microband is a basic phenomenon and is clearly evidenced here. It results in: (1) The triggering of S-type MBs because of continuous accommodation requirements. These MBs are found to incorporate an intense localized shear on {l_brace}111{r_brace} slip planes. (2) The bending of saturated MBs when the surrounding matrix exhibits a non-negligible gradient of deformation.

  10. Study on micro-structure and morphological evolution of Fe/Pt nano-magnetic film.

    PubMed

    Ishiguro, S; Ju, D Y; Ogatsu, R; Nakano, T

    2011-10-01

    One of the vertical magnetic recordings medium materials of the hard disk drive (HDD) is a Fe/Pt thin film. The development of ultra-high density magnetic recording medium in next generation is expected the magnetic disks such as HDD with capacity enlargement of the data. In order to study effectiveness of the proposed sputtering method, we evaluated micro structure, magnetic and the mechanical properties of a Fe/Pt thin film by some sputtering process conditions. From research results, effect sputtering conditions on micro-structure and mechanical properties of Fe/Pt nano film are verified.

  11. Development of the Microstructure Based Stochastic Life Prediction Model

    DTIC Science & Technology

    1993-08-01

    the formulation of preliminary life prediction models[l]. In the microstruc - 3 tural characterization part of the program we have concentrated on the...microstructural models may be needed to describe behavior during different stages of fatigue life3 and intend to integrate them using Markov chain approach. -- B...precipitate phases present in the studied alloy the obtained diffraction patterns were compared with those found in the literature on 7075 and 7050 alloys. The

  12. Microstructure and Fatigue Behavior of Three Nickel Base Eutectic Composites.

    DTIC Science & Technology

    1982-11-30

    744. (a) AG-170 ............. ...... . 39 Fig. 9 Well-aligned, longitudinal microstructures. (a) Nitac 14B. 41 - (b) Cotac 744. (c) AG-170...25*C. (a) Surface initiation and Stage I cracking. (b) Crystallographic cracking ... ...... 90 Fig. 41 View of the crack wall of a longitudinal, cell...Al down to 5 w/o Al and a y-a eutectic at lower Al contents. 2.2 Tensile Strength 41 Directionally solidified eutectics are noted for their high

  13. Microstructures and Mechanical Properties of Two-Phase Alloys Based on NbCr(2)

    SciTech Connect

    Cady, C.M.; Chen, K.C.; Kotula, P.G.; Mauro, M.E.; Thoma, D.J.

    1998-12-07

    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 upon temperature and microstructure.

  14. Microthermoforming of flexible, not-buried hollow microstructures for chip-based life sciences applications.

    PubMed

    Truckenmüller, R; Giselbrecht, S

    2004-08-01

    A new method is presented for the manufacturing of flexible, not buried and thin-walled hollow microstructures from polymer films. This low-cost method seems to be especially suited for the fabrication of plastic microstructures for fluidic one-way applications in the field of life sciences. It is based on a thermoforming process adapted to microstructure technology and is called 'microthermoforming'. Inside a hot embossing press, a heated thin thermoplastic film is formed into the evacuated microcavities of a plate-shaped metal mould using a compressed gas. The film may be heat-sealed on to a thicker plastic film substrate inside the same press without demoulding the thermoformed film. To demonstrate the performance of the new manufacturing method, flexible capillary electrophoresis and cell culture chips from polystyrene, polycarbonate and a cyclo-olefin polymer with 16 and 625 parallel microstructures each, respectively, have been fabricated.

  15. Effects of neutron irradiation on microstructural evolution in candidate low activation ferritic steels

    NASA Astrophysics Data System (ADS)

    Kohno, Yutaka; Kohyama, Akira; Yoshino, Masahiko; Asakura, Kentaro

    1994-09-01

    Fe-(2.25-12)Cr-2W-V, Ta low activation ferritic steels (JLF series steels) were developed in the fusion materials development program of Japanese universities. Microstructural observations, including precipitation response, were performed after neutron irradiation in the FFTF/MOTA. The preirradiation microstructure was stable after irradiation at low temperature (< 683 K). Recovery of martensitic lath structure and coarsening of precipitates took place above 733 K. Precipitates observed after irradiation were the same as those in unirradiated materials in 7-9Cr steels, and no irradiation induced phase was identified. The irradiation induced shift in DBTT in the 9Cr-2W steel proved to be very small which is a reflection of stable precipitation response in these steels. A high density of fine α' precipitates was observed in the 12Cr steel which might be responsible for the large irradiation hardening found in the 12Cr steel. Void formation was observed in 7-9Cr steels irradiated at 683 K, but the amount of void swelling was very small.

  16. Probing microstructure evolution during the hardening of gypsum by proton NMR relaxometry.

    PubMed

    Jaffel, Hamouda; Korb, Jean-Pierre; Ndobo-Epoy, Jean-Philippe; Morin, Vincent; Guicquero, Jean-Pierre

    2006-04-13

    We report a comprehensive proton NMR relaxation study of the water confined in the evolving porous structure of hardened gypsum prepared with different water-to-plaster ratios (w/p) and increasing additions of crushed gypsum. This study gives some new information on the microstructure, the water distribution, and the hydration kinetics without any drying or perturbing preparation. The bi-exponential transverse magnetization decay reveals the existence of two water populations in slow exchange. However, the different behaviors of these populations during saturation and desaturation experiments show evidence of a fast exchange of each population with the surface. Two modes of organization of the microstructure of this material are identified through an original model of exchange as a function of the water-to-plaster ratio (0.4 < or = w/p < or = 0.6 and 0.7 < or = w/p < or = 1). A clear gap is shown in the exchange rate value above w/p = 0.6 that could be representative of a percolation threshold. Both the method and the theory presented can be applied more widely to other porous media with reactive surface areas.

  17. Microstructural evolution of nuclear grade graphite induced by ion irradiation at high temperature environment

    NASA Astrophysics Data System (ADS)

    Tsai, Shuo-Cheng; Huang, E.-Wen; Kai, Ji-Jung; Chen, Fu-Rong

    2013-03-01

    This study simulates the Wigner Effect of nuclear-grade graphite in a High Temperature Gas-cooled Reactor (HTGR). The graphite was artificially irradiated with 3 MeV C2+ ions to mimic the fast neutron-radiation damage of the HTGR core environment. The irradiation temperatures were controlled between the range of 500-800 °C in a high vacuum environment of 10-7 torr. This high-dosage radiation creates enormous amounts of Frenkel pairs, which induce lattice swelling. These Frenkel vacancies and interstitials generate new strain fields and, hence, store energy in the distorted crystalline structure. The structural integrity of nuclear grade graphite was quantified using high-resolution transmission electron microscopy (HRTEM). The microstructure was estimated by the fast Fourier transform of HRTEM images. Within the samples irradiated with 10 dpa at 600 °C, the d-spacing of {0 0 0 2} expanded from 0.336 nm to 0.396 nm accompanying with the greatest distorted graphite microstructure. The c-axis of graphite swelled approximately 18% and the disorder coefficient was 1.10 ± 0.17 (1/nm). The synchrotron X-ray experimental results, gauged from 500 μm3 volume, suggesting that the ion-implanted graphite only deformed locally and epitaxially. This study also presents possible mechanisms.

  18. Microstructure evolution and lubricant wear performance of laser alloyed layers on automobile engine chains

    NASA Astrophysics Data System (ADS)

    Sun, G. F.; Zhou, R.; Zhang, Y. K.; Yuan, G. D.; Wang, K.; Ren, X. D.; Wen, D. P.

    2014-10-01

    Wear resistant layers on nodular cast iron chains with C-B-W-Cr powders were fabricated by laser surface alloying (LSA). Microstructure, phases and lattice parameters, were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffractometry. Micro-, nano-hardness and elastic modulus were measured with a Vickers microhardness tester and a nano-indendation tester. Lubricant sliding wear performance was performed on a ball-on-disk apparatus in ambient air using the straight line reciprocating wear form. Results indicate that microstructure of the alloyed layers changes from hyper-eutectic to hypo-eutectic, varing with laser specific energy. Nano-grain size and micro-hardness decrease while martensite lattice parameters increase with laser specific energy. Existence of graphite in the substrate increases the carbon content in the retained austenite to 1.59 wt%. Nano-hardness and elastic modulus of the alloyed layers are close. Friction and wear properties of the layers are improved by LSA compared with the substrate. Wear mechanism of them is illustrated.

  19. Rapid sintering and microstructure evolution of composite TiC cermet

    NASA Astrophysics Data System (ADS)

    Ding, L.; Liu, X. G.; Pan, Y. L.; Wang, Y. W.; Xiang, D. P.

    2017-01-01

    Ti, Ni, activated carbon, and Mo powders were used as raw materials to prepare a composite TiC cermet in this study. The powders were mixed and prepared through high-energy ball milling and then sintered in a spark plasma sintering (SPS) system. Results revealed that ball milling time affected the raw materials. After ball milling was performed for 10 h, Ti and C particles reacted and generated TiC, meanwhile, the solid Mo solutionized in TiC and formed (Ti,Mo)C lumps. XRD results showed that the product of (Ti,Mo)C cermet with high hardness can be prepared at a low sintering temperature of 1150 °C. The microstructure of composite TiC cermet was different from the traditional core-ring structure. In particular, the developed microstructure comprises a (Ti,Mo)C-Ni dark-gray phase at the center surrounded by (Ti,Mo)C light-gray phase and dispersed Mo white phase.

  20. Temperature-Dependent Flow Behavior and Microstructural Evolution During Compression of As-Cast Mg-7.7Al-0.4Zn

    NASA Astrophysics Data System (ADS)

    Kulkarni, Rahul R.; Prabhu, Nityanand; Hodgson, Peter D.; Kashyap, Bhagwati P.

    2016-10-01

    The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439°C and at strain rates of 5 × 10-2, 10-2, 5 × 10-4 and 10-4 s-1. The stress exponent ( n) and activation energy ( Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg17Al12 particles with concurrent grain growth of α-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.

  1. Microstructure Modeling of Third Generation Disk Alloys

    NASA Technical Reports Server (NTRS)

    Jou, Herng-Jeng

    2010-01-01

    The objective of this program was to model, validate, and predict the precipitation microstructure evolution, using PrecipiCalc (QuesTek Innovations LLC) software, for 3rd generation Ni-based gas turbine disc superalloys during processing and service, with a set of logical and consistent experiments and characterizations. Furthermore, within this program, the originally research-oriented microstructure simulation tool was to be further improved and implemented to be a useful and user-friendly engineering tool. In this report, the key accomplishments achieved during the third year (2009) of the program are summarized. The activities of this year included: Further development of multistep precipitation simulation framework for gamma prime microstructure evolution during heat treatment; Calibration and validation of gamma prime microstructure modeling with supersolvus heat treated LSHR; Modeling of the microstructure evolution of the minor phases, particularly carbides, during isothermal aging, representing the long term microstructure stability during thermal exposure; and the implementation of software tools. During the research and development efforts to extend the precipitation microstructure modeling and prediction capability in this 3-year program, we identified a hurdle, related to slow gamma prime coarsening rate, with no satisfactory scientific explanation currently available. It is desirable to raise this issue to the Ni-based superalloys research community, with hope that in future there will be a mechanistic understanding and physics-based treatment to overcome the hurdle. In the mean time, an empirical correction factor was developed in this modeling effort to capture the experimental observations.

  2. Mechanical and Microstructural Behavior of Cold-Sprayed Titanium- and Nickel-Based Coatings

    NASA Astrophysics Data System (ADS)

    Cavaliere, P.; Silvello, A.

    2015-12-01

    Cold spraying is a coating technology that can deposit materials with unique properties. The coating forms through intensive plastic deformation of particles impacting on a substrate at temperature well below the melting point of the sprayed material. Recently, various studies have been published regarding the microstructural and mechanical evolution of metal-matrix composite coatings produced by cold spraying. Herein, we describe the principal results of the available literature in the field of cold-sprayed composites. It is shown that more research is required to solve various questions in this field, for example, the different deformation modes of the material exhibited for various processing conditions, the reinforcing percentage of different material combinations, and the mechanical properties resulting from these complex systems. In the present study, this issue is approached and described for cold-sprayed Ni- and Ti-based composites. Materials were produced with varying ceramic phase (BN and TiAl3) fraction. The variation of the grain size, adhesion strength, porosity, and hardness of the deposits as a function of the ceramic phase fraction and processing parameters (impacting particle speed) is described. The interaction mechanisms between the cold-sprayed particles and the metal matrix during the coating process are presented and described. The results demonstrate a beneficial effect on grain size and porosity with increasing reinforcing phase percentage, as well as narrow processing parameter ranges to achieve the optimal properties with respect to the pure parent materials.

  3. Microstructure based optical modeling of ZnO- porous silicon permeated nanocomposites

    NASA Astrophysics Data System (ADS)

    Gallach, D.; Le Brizoual, L.; Gautier, N.; Ynsa, M. D.; Torres Costa, V.; Ceccone, G.; Landesman, J. P.; Manso Silván, M.

    2015-07-01

    ZnO composites with porous silicon (PSi) are increasingly used in advanced optical and electronic structures. ZnO/PSi nanocomposites have been prepared by permeating anodized PSi with ZnO sols based on zinc acetate. Upon thermal annealing the ZnO sols form surface wurzite nanocrystals, as indicated by XRD from annealing temperatures of 400 °C. By increasing the annealing up to 800 °C, electron microscopies evidence that ZnO diffuses through the columnar PSi, while void ZnO crystallites decorate the surface. Angular dependent x-ray photoelectron spectra agree with the partial coverage of the PSi surface by disperse ZnO nanocrystals. In depth composition, analyzed using C-resonant backscattering spectroscopy confirms an activation of ZnO diffusion and PSi oxidation at high temperatures. This microstructural information was used to analyse the optical properties through models adapted to critical processing temperatures. A uniaxial anisotropic layer, included to consider columnar PSi, and an evolution of optical coefficients in agreement with thermally induced effects (namely PSi oxidation and ZnO diffusion-transformation) allows to satisfactorily simulate ellipsometric spectra. The results are relevant for the optimization of bifunctional electronic-antireflective ZnO/PSi structures.

  4. Microstructure and Sn crystal orientation evolution in Sn-3.5Ag lead-free solders in high temperature packaging applications

    SciTech Connect

    Zhou, Bite; Muralidharan, Govindarajan; Kurumaddali, Nalini Kanth; Parish, Chad M; Leslie, Dr Scott; Bieler, T. R.

    2014-01-01

    Understanding the reliability of eutectic Sn-3.5Ag lead-free solders in high temperature packaging applications is of significant interest in power electronics for the next generation electric grid. Large area (2.5mm 2.5mm) Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates were thermally cycled between 5 C and 200 C. Sn crystal orientation and microstructure evolution during thermal cycling were characterized by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Comparisons are made between observed initial texture and microstructure and its evolution during thermal cycling. Gradual lattice rotation and grain boundary misorientation evolution suggested the continuous recrystallization mechanism. Recrystallization behavior was correlated with dislocation slip activities.

  5. Interface Propagation and Microstructure Evolution in Phase Field Models of Stress-Induced Martensitic Phase Transformations

    DTIC Science & Technology

    2010-01-01

    simulation, the initial conditions are g1 ¼ g2 ¼ 0:1 in a circle of radius 2 nm (an embryo ) at the center of the sample and zero elsewhere. The boundary...in narrow bands around the interfaces if the driving force is less than a critical value, K: Fig. 10. Evolution of an embryo , gi ¼ 0:1, in a circle...concentration curve does not exhibit a hysteresis loop and energy dissipation. 4. In Fig. 22 we display the evolution of an embryo with gi ¼ 0:1 as in

  6. Design of an expert system based on neuro-fuzzy inference analyzer for on-line microstructural characterization using magnetic NDT method

    NASA Astrophysics Data System (ADS)

    Ghanei, S.; Vafaeenezhad, H.; Kashefi, M.; Eivani, A. R.; Mazinani, M.

    2015-04-01

    Tracing microstructural evolution has a significant importance and priority in manufacturing lines of dual-phase steels. In this paper, an artificial intelligence method is presented for on-line microstructural characterization of dual-phase steels. A new method for microstructure characterization based on the theory of magnetic Barkhausen noise nondestructive testing method is introduced using adaptive neuro-fuzzy inference system (ANFIS). In order to predict the accurate martensite volume fraction of dual-phase steels while eliminating the effect and interference of frequency on the magnetic Barkhausen noise outputs, the magnetic responses were fed into the ANFIS structure in terms of position, height and width of the Barkhausen profiles. The results showed that ANFIS approach has the potential to detect and characterize microstructural evolution while the considerable effect of the frequency on magnetic outputs is overlooked. In fact implementing multiple outputs simultaneously enables ANFIS to approach to the accurate results using only height, position and width of the magnetic Barkhausen noise peaks without knowing the value of the used frequency.

  7. Microstructural evolution in H ion induced splitting of freestanding GaN

    NASA Astrophysics Data System (ADS)

    Moutanabbir, O.; Scholz, R.; Senz, S.; Gösele, U.; Chicoine, M.; Schiettekatte, F.; Süßkraut, F.; Krause-Rehberg, R.

    2008-07-01

    We investigated the microstructural transformations during hydrogen ion-induced splitting of GaN thin layers. Cross-sectional transmission electron microscopy and positron annihilation spectroscopy data show that the implanted region is decorated with a high density of 1-2nm bubbles resulting from vacancy clustering during implantation. These nanobubbles persist up to 450°C. Ion channeling data show a strong dechanneling enhancement in this temperature range tentatively attributed to strain-induced lattice distortion. The dechanneling level decreases following the formation of plateletlike structures at 475°C. Extended internal surfaces develop around 550°C leading to the exfoliation of GaN thin layer.

  8. Microstructure evolution during annealing of an SPD- processed supersaturated Cu - 3 at.% Ag alloy

    NASA Astrophysics Data System (ADS)

    Gubicza, J.; Hegedüs, Z.; Lábár, J. L.; Subramanya Sarma, V.; Kauffmann, A.; Freudenberger, J.

    2014-08-01

    Supersaturated Cu - 3 at.% Ag alloy was processed by rolling at liquid nitrogen temperature and subsequent annealing at 623 K up to 20 min. It was found that after annealing, an inhomogeneous solute atom distribution developed, since the Ag particles with small size and/or large specific interfacial energy were dissolved due to the Gibbs-Thomson effect. In the region where the solute concentration increased, a high dislocation density was retained in the Cu matrix even after annealing, while in the region where the Ag solute content did not increase, the dislocation density decreased by more than one order of magnitude. Therefore, in the cryorolled and annealed samples, heterogeneous microstructures were developed where both the dislocation density and the solute concentration varied considerably.

  9. Heat Treatment of AZ91D Mg-Al-Zn Alloy: Microstructural Evolution and Dynamic Response

    NASA Astrophysics Data System (ADS)

    Luong, Dung D.; Shunmugasamy, Vasanth Chakravarthy; Cox, James; Gupta, Nikhil; Rohatgi, Pradeep K.

    2013-11-01

    Magnesium alloys are attracting great interest from the automotive industry because of the potential for weight reduction. An AZ91D cast alloy was studied in the current work to understand the effect of heat treatment on the microstructure and dynamic compressive properties. The selected heat treatments include solution treatment (T4) and solution treatment followed by aging (T6). The as-cast alloy microstructure consists of intermetallic β-phase (Mg17Al12) precipitates surrounded by α + β lamellar eutectic in α-Mg solid solution. The AZ91D-T4 specimens showed small β-phase precipitates along the grain boundaries and regions of eutectic mixture. The T6 heat treatment causes the β-phase platelets in the α + β eutectic to grow and develop into β-precipitates. The difference in the phase morphology reflects into the mechanical properties. The Vickers hardness of the T6 heat-treated specimens was 3.6% higher than the as-cast alloy. The compressive yield strengths of T4 and T6 treated specimens were 1.3% and 43.1% higher than those of as-cast specimens. The high strain rate compression testing resulted in increase in the strength with strain rate for the T4 and T6 specimens. A maximum increase of 42% was observed in T6 specimen tested at a strain rate of 4,000/s in comparison to the quasi-static compression. Under high strain rate compression testing, the T6 heat-treated specimens showed failure of the β-precipitates resulting in increased energy absorption in comparison to the quasi-static compression.

  10. Influence of coarsened and rafted microstructures on the thermomechanical fatigue of a Ni-base superalloy

    DOE PAGES

    Kirka, M. M.; Brindley, K. A.; Neu, R. W.; ...

    2015-08-17

    The aging of the microstructure of Ni-base superalloys during service is mainly characterized by coarsening and rafting of the γ' precipitates. The influence of these different aged microstructures on thermomechanical fatigue (TMF) under either continuously cycled (CC) and creep-fatigue (CF) was investigated. Three different aged microstructures, generated through accelerated aging and pre-creep treatments, were studied: stress-free coarsened γ', rafted with orientation perpendicular to loading direction (N-raft), and rafted with orientation parallel to loading direction (P-raft). Under most conditions, the aged microstructures were less resistant to TMF than the virgin microstructure; however, there were exceptions. Both stress-free coarsened and N-raft microstructuresmore » resulted in a reduction in TMF life under both CC and CF conditions in comparison to the virgin material. P-raft microstructure also resulted in reduction in TMF life under CC conditions; however, an increase in life over that of the virgin material was observed under CF conditions. Finally, these differences are discussed and hypothesized to be related to the interactions of the dislocations in the γ channels with γ' precipitates.« less

  11. What lies beneath? Diffusion EAP-based study of brain tissue microstructure.

    PubMed

    Zucchelli, Mauro; Brusini, Lorenza; Andrés Méndez, C; Daducci, Alessandro; Granziera, Cristina; Menegaz, Gloria

    2016-08-01

    Diffusion weighted magnetic resonance signals convey information about tissue microstructure and cytoarchitecture. In the last years, many models have been proposed for recovering the diffusion signal and extracting information to constitute new families of numerical indices. Two main categories of reconstruction models can be identified in diffusion magnetic resonance imaging (DMRI): ensemble average propagator (EAP) models and compartmental models. From both, descriptors can be derived for elucidating the underlying microstructural architecture. While compartmental models indices directly quantify the fraction of different cell compartments in each voxel, EAP-derived indices are only a derivative measure and the effect of the different microstructural configurations on the indices is still unclear. In this paper, we analyze three EAP indices calculated using the 3D Simple Harmonic Oscillator based Reconstruction and Estimation (3D-SHORE) model and estimate their changes with respect to the principal microstructural configurations. We take advantage of the state of the art simulations to quantify the variations of the indices with the simulation parameters. Analysis of in-vivo data correlates the EAP indices with the microstructural parameters obtained from the Neurite Orientation Dispersion and Density Imaging (NODDI) model as a pseudo ground truth for brain data. Results show that the EAP derived indices convey information on the tissue microstructure and that their combined values directly reflect the configuration of the different compartments in each voxel.

  12. Hydraulic tuning of vein cell microstructure in the evolution of angiosperm venation networks.

    PubMed

    Feild, Taylor S; Brodribb, Timothy J

    2013-08-01

    High vein density (D(V)) evolution in angiosperms represented a key functional transition. Yet, a mechanistic account on how this hydraulic transformation evolved remains lacking. We demonstrate that a consequence of producing high D(V is that veins must become very small to fit inside the leaf, and that angiosperms are the only clade that evolved the specific type of vessel required to yield sufficiently conductive miniature leaf veins. From 111 species spanning key divergences in vascular plant evolution, we show, using analyses of vein conduit evolution in relation to vein packing, that a key xylem innovation associated with high D(V) evolution is a strong reduction in vein thickness and simplification of the perforation plates of primary xylem vessels. Simple perforation plates in the leaf xylem occurred only in derived angiosperm clades exhibiting high D(V) (> 12 mm mm(-2)). Perforation plates in the vessels of other species, including extant basal angiosperms, consisted of resistive scalariform types that were associated with thicker veins and much lower D(V). We conclude that a reduction in within-vein conduit resistance allowed vein size to decrease. We suggest that this adaptation may have been a critical evolutionary step that enabled dramatic D(V) elaboration in angiosperms.

  13. A versatile platform for manipulating photonic spin and orbital states based on liquid crystal microstructures (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lu, Yan-Qing; Hu, Wei; Ming, Yang

    2016-09-01

    Utilizing the spin degree of freedom breaks new ground for designing photonic devices. Seeking out a suitable platform for flexible steering of photonic spin states is a critical task. In this work, we demonstrate a versatile Liquid crystal (LC) based platform for manipulating photonic spin and orbital states. Owing to the photoalignment technique, the local and fine tuning of the LC medium is effectively implemented to form various anisotropic microstructures. The light-matter interaction in the corresponding medium is tailored to control the evolution of photonic spin states. The physical mechanism of such a system is investigated, and the corresponding dynamical equation is obtained. The high flexibility endows the LC-based photonic system with great value to be used for Hamiltonian engineering. As an illustration, the optical analogue of intrinsic spin Hall effect (SHE) in electronic systems is presented. The pseudospins of photons are driven to split by the anisotropic effective magnetic field arising from the inhomogeneous spin-orbit interaction (SOI) in the twisting microstructures. In virtue of the designability of the LC-based platform, the form of the interaction Hamiltonian is regulated to present diverse PSHE phenomena, which is hard to be realized in the solid electronic systems. Some representative samples are prepared for experimental observation, and the results are in good agreement with theoretical predictions. We believe the tunable LC system may shed new light on future photonic quantum applications.

  14. Study of Alloy Microstructure Based on TiNi After High-Temperature Treatment

    NASA Astrophysics Data System (ADS)

    Senkevich, K. S.; Gusev, D. E.

    2016-09-01

    Features of microstructure formation for alloy based on titanium nickelide after high-temperature treatment at 1050 - 1250°C are studied. Heat treatment conditions are stipulated diffusion welding and sintering regimes developed previously for alloys based on TiNi.

  15. Microstructural evolution and irreversibility in the viscoelastic response of mesoscopic dusty-plasma liquids.

    PubMed

    Chan, Chia-Ling; I, Lin

    2007-03-09

    We experimentally demonstrate the viscoelastic response and construct a microscopic dynamical picture using a quasi-2D dusty-plasma liquid confined in a mesoscopic gap and sheared periodically. The correlation between microdisplacement and structural evolution at the discrete kinetic level is explored. Through hopping, the structural rearrangement associated with shear enhanced stretching, kinking, breaking, and reconnection of local lattice lines generates irreversible plastic deformation. The strain energy accumulation in the twisted regions without topological rearrangement is the source for local rebound.

  16. Microstructure Evolution During Spray Rolling and Heat Treatment of 2124 Al

    SciTech Connect

    K.M. McHugh; Y. Lin; Y. Zhou; S.B. Johnson; J.P. Delplanque; E.J. Lavernia

    2006-09-01

    Spray rolling is a strip casting technology that combines elements of spray forming and twin-roll casting. It consists of atomizing molten metal with a high velocity inert gas, quenching the resultant droplets in flight, and directing the spray between mill rolls. In-flight convection heat transfer from atomized droplets and conduction heat transfer at the rolls rapidly move an alloy’s latent heat. Hot deformation of the semi-solid material in the rolls results in fully consolidated, rapidly-solidified product. While similar in many ways to twin-roll casting, spray rolling is able to process a broader range of alloys and operates at a higher production rate. A laboratory-scale strip caster has been constructed at INL and used to evaluate the interplay of processing parameters and strip quality while producing strips up to 200 mm wide and 1.6 – 6.4 mm thick. Plans are underway to scale to 600 mm width and demonstrate steady-state operation. As-spray-rolled strip is characterized by a flat, uniformly thick profile with minimal porosity or segregation. This paper examines how processing parameters influence the microstructure transformations that take place during spray rolling and post-deposition heat treatment of 2124 Al.

  17. Effect of He implantation on fracture behavior and microstructural evolution in F82H

    NASA Astrophysics Data System (ADS)

    Yabuuchi, Kiyohiro; Sato, Kiminori; Nogami, Shuhei; Hasegawa, Akira; Ando, Masami; Tanigawa, Hiroyasu

    2014-12-01

    Reduced-activation ferritic/martensitic steels (RAFMs) are the primary candidate structural materials for fusion reactor blanket components. He bubbles, which formed under 14 MeV neutron irradiation, is considered to cause some mechanical property changes. In a previous study, Hasegawa et al. investigated the fracture behavior using Charpy impact test of He implanted F82H by 50 MeV α-particles with cyclotron accelerator, and the ductile brittle transition temperature (DBTT) was increased and intergranular fracture (IGF) was observed. However, the cause of the IGF was not shown in the previous study. To clarify the cause of the IGF of the He implanted F82H by 50 MeV α-particles with cyclotron accelerator, the microstructure of the He implanted F82H was investigated. After Charpy impact test at 233 K, the brittle fracture surface of the He implanted specimen was observed by SEM and TEM. By SEM observation, grain boundary surface was clearly observed from the bottom of the notch to a depth of about 400 μm. This area correspond to the He implanted region. On the other hand, at unimplanted region, river pattern was observed and transgranular fracture occurred. TEM observation revealed the He bubbles agglomeration at dislocations, lath boundaries, and grain boundaries, and the coarsening of precipitates on grain boundaries. IGF of the He implanted F82H was caused by both He bubbles and coarsening precipitates.

  18. Microstructural evolution during aging of an Al-Cu-Li-Ag-Mg-Zr alloy

    NASA Technical Reports Server (NTRS)

    Kumar, K. S.; Brown, S. A.; Pickens, Joseph R.

    1991-01-01

    Alloys in the Al-Cu-Li Ag-Mg subsystem were developed that exhibit desirable combinations of strength and ductility. These Weldalite (trademark) alloys, are unique for Al-Cu-Li alloys in that with or without a prior cold stretching operation, they obtain excellent strength-ductility combinations upon natural and artificial aging. This is significant because it enables complex, near-net shape products such as forgings and super plastically formed parts to be heat treated to ultra-high strengths. On the other hand, commercial extrusions, rolled plates and sheets of other Al-Cu-Li alloys are typically subjected to a cold stretching operation before artificial aging to the highest strength tempers to introduce dislocations that provide low-energy nucleation sites for strengthening precipitates such as the T(sub 1) phase. The variation in yield strength (YS) with Li content in the near-peak aged condition for these Weldalite (trademark) alloys and the associated microstructures were examined, and the results are discussed.

  19. Microstructural evolution and some mechanical properties of nanosized yttrium oxide dispersion strengthened 13Cr steel

    NASA Astrophysics Data System (ADS)

    Tich Nguyen, Van; Phuong Doan, Dinh; BaoTrung Tran, Tran; Duong Luong, Van; Nguyen, Van An; Phan, Anh Tu

    2010-09-01

    Oxide dispersion strengthened (ODS) steels, manufactured by a mechanical alloying method, during the past few years, appear to be promising candidates for structural applications in nuclear power plants. The purpose of this work is to elaborate the manufacturing processes of ODS 13Cr steel with the addition of 1.0 wt% yttrium oxide through the powder metallurgy route using the high energy ball mill. Microstructural analysis by scanning electron microscopy (SEM), x-ray diffraction (XRD) and hardness testing have been used to optimize the technological parameters of milling, hot isostatic pressing and heat-treatment processes. The steel hardness increases with decreasing particle size of 13Cr ODS steel. The best hardness was obtained from more than 70 h of milling in the two tanks planetary ball mill or 30 h of milling in the one tank planetary ball mill and hot isostatic pressing at 1150 °C . The particle size of the steel is less than 100 nm, and the density and hardness are about 7.3 g cm-3 and 490 HB, respectively. Report submitted to the 5th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN, Hanoi, 9-12 November 2010.

  20. Microstructure and oxygen evolution of Fe-Ce mixed oxides by redox treatment

    NASA Astrophysics Data System (ADS)

    Li, Kongzhai; Haneda, Masaaki; Ning, Peihong; Wang, Hua; Ozawa, Masakuni

    2014-01-01

    The relationship between structure and reduction/redox properties of Fe-Ce mixed oxides with a Fe content of 5, 10, 20 or 30 mol%, prepared by a coprecipitation method, were investigated by XRD, Raman, TEM, TPR and TPO techniques. It is found that all the iron ions can be incorporated into the ceria lattice to form a solid solution for the FeCe 5 (Fe 5%) sample, but amorphous or crystal Fe2O3 particles were found to be present on the Fe-Ce oxide samples with higher the iron content. The reducibility of single solid solution was much better than the pure CeO2, and the appearance of dispersed Fe2O3 particles improved the surface reducibility of materials. The iron ions incorporated into the CeO2 lattice accelerated the oxygen release from bulk to surface, and surface Fe2O3 particles in close contact to CeO2 acted as a catalyst for the reaction between solid solution and hydrogen. The microstructure of exposed Fe2O3 with Ce-Fe-O solid solution allows the Fe-Ce mixed oxides to own good reducibility and high OSC, which also counteracts the deactivation of the reducibility resulting from the sintering of materials in the redox cycling.

  1. Microstructural evolution in WC-Co cermet reinforced - A17075 metal matrix composites by stir casting

    NASA Astrophysics Data System (ADS)

    Gopal Krishna, U. B.; Ranganatha, P.; Auradi, V.; Mahendra Kumar, S.; Vasudeva, B.

    2016-09-01

    Aluminium metal matrix composites (AMMCs) are preferred because of their enhanced properties like high strength to weight ratio, stiffness and wear resistance. In the present work, an attempt is made to develop cermet (WC-Co) reinforced with Al7075 metal matrix composite by stir casting technique. WC-Co cermet is reduced to an average size of 10μm through ball milling using Alumina as grinding media. Ball milled WC-Co Cermet in an amount of 6 wt. % is used as reinforcement in Al7075 matrix. Microstructural characterization of the prepared composites is carried out using SEM/EDX and XRD studies. X-ray diffraction studies have revealed the peaks corresponding to α-Al, WC, Co and minor Al5W phases. SEM/EDX characterization revealed the uniform distribution of cermet in Al matrix. Further studies also revealed that, addition of WC-Co cermet to Al7075 matrix has resulted in improvement in hardness and Densities of Al7075 matrix.

  2. Microstructural evolution in multiseeded YBCO bulk samples grown by the TSMG process

    NASA Astrophysics Data System (ADS)

    Goodfellow, A.; Shi, Y.-H.; Durrell, J. H.; Dennis, A. R.; Cardwell, D. A.; Grovenor, C. R. M.; Speller, S. C.

    2016-11-01

    Superconducting single-grain YBCO bulk samples with the ability to trap high magnetic fields can be grown using the top-seeded melt-growth process. Multiseeding techniques have the potential to enable larger diameter bulks to be grown, but the performance of these materials is not yet comparable to the single-seeded bulks. Here we carry out detailed three-dimensional microstructural characterisation on a multiseeded sample grown with the seeds aligned in the 0°-0° geometry using high resolution microanalysis techniques. Chemical and structural variations have been correlated with the trapped field distribution in three separate slices of the sample. The top slice of the sample shows four peaks in trapped field, indicating that the current flows in four separate loops rather than in one large loop within the sample. This has been explained by the build-up in insulating Y-211 particles where the growth fronts from the two seeds meet, forming a barrier to current flow, as well as the low Y-211 content (and hence low J c) of the large c-axis growth sector.

  3. The effect of ageing and heat treatment on microstructure evolution of a commercial cement paste

    NASA Astrophysics Data System (ADS)

    Sabeur, Hassen; Platret, Gérard; Vincent, Julien

    2017-03-01

    This paper reports the microstructural changes on a 2 year-old cement paste, unprotected from contact with air, heated to various temperature regimes up to 1000 °C in steps of 100 °C for a constant period of 6 h. This work has been carried out using a thermal analysis technique and XRD. The parameter involved in this study is the state of the samples: powdered samples and blocks of paste. As a result, it is possible to monitor the major features of the experiments, i.e. the phase's existence domains and their growing of hydrated calcium silicate, portlandite, calcite as well as their decaying: alite, belite and lime. The result shows higher amounts of portlandite and carbonate calcium for the aged cement paste compared to fresh OPC. The carbonation is more marked for the blocks of paste while the crystallinity degree is higher for the powdered cement paste samples. The new portlandite formed during cooling continues to exist until the 1000 °C temperature plateau. Nevertheless, this portlandite is less crystalline than the original one, and its temperature of thermal decomposition gets lower. An increase in the total weight loss and in the crystallinity at 900 and 1000 °C, compared to 800 °C is also noted. The CSH dehydration to β-C2S and C3S become significant above 600 °C and the corresponding rate increases with increasing temperature.

  4. Study on sapphire microstructure processing technology based on wet etching

    NASA Astrophysics Data System (ADS)

    Shang, Ying-Qi; Qi, Hong; Ma, Yun-Long; Wu, Ya-Lin; Zhang, Yan; Chen, Jing

    2017-03-01

    Aiming at the problem that sapphire surface roughness is quite large after wet etching in sapphire microstructure processing technology, we optimize the wet etching process parameters, study on the influences of concentration and temperature of etching solution and etching time on the sapphire surface roughness and etching rate, choose different process parameters for the experiment and test and analyze the sapphire results after wet etching. Aiming at test results, we also optimize the process parameters and do experiment. Experimental results show that, after optimizing the parameters of etching solution, surface roughness of etched sapphire is 0.39 nm, effectively with reduced surface roughness, improved light extraction efficiency and meeting the production requirements of high-precision optical pressure sensor.

  5. Surface microstructure profilometry based on laser confocal feedback

    NASA Astrophysics Data System (ADS)

    Wang, Weiping; Zhang, Shulian; Li, Yan

    2015-10-01

    We demonstrate a surface microstructure profile measurement method, which utilizes the positioning ability of confocal technology and the high sensitivity of frequency-shift feedback of a microchip laser. The surface profile is measured by combination of the amplitude and phase information of the feedback light reflected by the sample. The amplitude information is used for coarse measurement and to determine the integral number of half lasing wavelengths contained in the sample profile variation. The phase information is used for fine measurement and to determine the fractional number. The measurement realizes both a large axial measuring range of tens of microns and a high axial resolution of ˜2 nm. Meanwhile, a heterodyne phase measurement approach is introduced to compensate for environmental disturbance and to realize high axial resolution measurement under common room conditions. The surface profile of a grating is measured and proves the feasibility of the method.

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

    NASA Astrophysics Data System (ADS)

    Yalavarthy, Harshavardhan

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

  7. Effects of Two-Stage Cold Rolling Schedule on Microstructure and Texture Evolution of Strip Casting Grain-Oriented Silicon Steel with Extra-Low Carbon

    NASA Astrophysics Data System (ADS)

    Song, Hong-Yu; Liu, Hai-Tao; Liu, Wen-Qiang; Wang, Yin-Ping; Liu, Zhen-Yu; Wang, Guo-Dong

    2016-04-01

    A 0.27 mm-thick grain-oriented silicon steel sheet with extra-low carbon was successfully produced by a novel processing route including strip casting, normalizing, two-stage cold rolling with an intermediate annealing, primary annealing, and secondary recrystallization annealing. The evolutions of microstructure and texture along the whole processing route were investigated with a special emphasis on the effects of two-stage cold rolling schedule. It was found that Goss orientation originated in the first cold rolling due to shear banding and relatively strong Goss texture evolved through the whole thickness after intermediate annealing. This is significantly different from the results in conventional process in which the origin of Goss texture is in the hot rolling stage and Goss texture only develops below the sheet surface. Besides, it was found that cold rolling schedule had significant influences on microstructure homogeneity, evolution of λ-fiber texture in primary annealed state and, thus, on secondary recrystallization. In case of appropriate cold rolling schedule, a homogeneous microstructure with Goss texture, relatively strong γ-fiber texture and medium α-fiber texture was observed in the primary annealed strip. Although Goss texture in primary annealed state was much weaker than that in two-stage route in conventional process, a perfect secondary recrystallization microstructure was produced and the magnetic induction B8 was as high as 1.85 T. By contrast, when the cold rolling schedule was inappropriate, the primary annealed strips exhibited inhomogeneous microstructure, together with weak γ-fiber texture, medium α-fiber and λ-fiber texture. Finally, the sheets showed incomplete secondary recrystallization microstructure in which a large number of fine grains still existed.

  8. High-resolution non-invasive 3D imaging of paint microstructure by synchrotron-based X-ray laminography

    NASA Astrophysics Data System (ADS)

    Reischig, Péter; Helfen, Lukas; Wallert, Arie; Baumbach, Tilo; Dik, Joris

    2013-06-01

    The characterisation of the microstructure and micromechanical behaviour of paint is key to a range of problems related to the conservation or technical art history of paintings. Synchrotron-based X-ray laminography is demonstrated in this paper to image the local sub-surface microstructure in paintings in a non-invasive and non-destructive way. Based on absorption and phase contrast, the method can provide high-resolution 3D maps of the paint stratigraphy, including the substrate, and visualise small features, such as pigment particles, voids, cracks, wood cells, canvas fibres etc. Reconstructions may be indicative of local density or chemical composition due to increased attenuation of X-rays by elements of higher atomic number. The paint layers and their interfaces can be distinguished via variations in morphology or composition. Results of feasibility tests on a painting mockup (oak panel, chalk ground, vermilion and lead white paint) are shown, where lateral and depth resolution of up to a few micrometres is demonstrated. The method is well adapted to study the temporal evolution of the stratigraphy in test specimens and offers an alternative to destructive sampling of original works of art.

  9. Microstructure evolution of fault rocks at the "brittle-to-plastic" transition

    NASA Astrophysics Data System (ADS)

    Heilbronner, R.; Pec, M.; Stunitz, H.

    2011-12-01

    In the continental crust, large earthquakes tend to nucleate at the "brittle-to-plastic" transition at depths of ~ 10 - 20 km indicating stress release by rupture at elevated PT. Experimental studies, field observations, and models predict peak strength of the lithosphere at depths where rocks deform by "semi-brittle" flow. Thus, the deformation processes taking place at these conditions are important aspects of the seismic cycle and fault rheology in general. We performed a series of experiments with crushed Verzasca gneiss powder (d ≤ 200 μm), "pre-dried" and 0.2 wt% H2O added, placed between alumina forcing blocks (45° pre-cut) and weld-sealed in Pt jackets. The experiments were performed at Pc = 500, 1000 and 1500 MPa, T = 300°C and 500°C. and shear strain rates of ~10-3 s-1 to ~10-5 s-1 in a solid medium deformation apparatus (Griggs rig). Samples deformed at Pc = 500 MPa attain peak strength (~ 1100-1400 MPa) at γ ~ 2, they weaken by ~20 MPa (300°C) to ~140 MPa (500°C) and reach a steady state. The 300°C experiments are systematically stronger by ~ 330 - 370 MPa than the 500°C experiments, and flow stress increases with increasing strain rate. At Pc = 1000 and 1500 MPa, peak strength (~1300-1600 MPa) is reached at γ = 1 to 1.5 followed by weakening of ~60 (300°C) and ~150 MPa (500°C). The strength difference between 300°C and 500°C samples is 270-330 MPa and does not increase with increasing confining pressure. The peak strength increase with confining pressure is modest (50-150 MPa), indicating that the rocks reach their maximal compressive strength. The microstructure develops as an S-C-C' fabric with dominant C' slip zones. At low strains, the gouge zone is pervasively cut by closely spaced C' shears containing fine-grained material (d < 100 nm). At peak strength, deformation localizes into less densely spaced, ~10 μm thick C'-C slip zones which develop predominantly in feldspars. In TEM, they show no porosity and consist of amorphous

  10. Use of High Magnetic Field to Control Microstructural Evolution in Metallic and Magnetic Materials

    SciTech Connect

    Ludtka, G.M.; Mackiewicz- Ludtka, G.; Wilgen, J.B.; Kisner, R.A.

    2010-06-27

    The Amendment 1, referred to as Phase 2, to the original CRADA NFE-06-00414 added tasks 3 through 7 to the original statement of work that had two main tasks that were successfully accomplished in Phase 1 of this project. In this Phase 2 CRADA extension, extensive research and development activities were conducted using high magnetic field processing effects for the purpose of manipulating microstructure in the SAE 5160 steel to refine grain size isothermally and to develop nanocrystalline spacing pearlite during continuous cooling, and to enhance the formability/forgability of the non-ferrous precipitation hardening magnesium alloy AZ90 by applying a high magnetic field during deformation processing to investigate potential magnetoplasticity in this material. Significant experimental issues (especially non-isothermal conditions evolving upon insertion of an isothermal sample in the high magnetic field) were encountered in the isothermal phase transformation reversal experiments (Task 4) that later were determined to be due to various condensed matter physics phenomenon such as the magnetocaloric (MCE) effect that occurs in the vicinity of a materials Curie temperature. Similarly the experimental deformation rig had components for monitoring deformation/strain (Task 3) that were susceptible to the high magnetic field of the ORNL Thermomagnetic Processing facility 9-T superconducting magnet that caused electronic components to fail or record erroneous (very noisy) signals. Limited experiments on developing nanocrystalline spacing pearlite were not sufficient to elucidate the impact of high magnetic field processing on the final pearlite spacing since significant statistical evaluation of many pearlite colonies would need to be done to be conclusive. Since extensive effort was devoted to resolving issues for Tasks 3 and 7, only results for these focused activities are included in this final CRADA report along with those for Task 7 (described in the Objectives Section

  11. Shape memory properties and microstructural evolution of rapidly solidified CuAlBe alloys

    SciTech Connect

    Ergen, Semra; Uzun, Orhan; Yilmaz, Fikret; Kiliçaslan, M. Fatih

    2013-06-15

    In this work, the effects of Be addition on the microstructure and phase transformation temperatures of Cu–12Al–xBe (x = 0.4, 0.5 and 0.6 wt.%) shape memory alloys fabricated by using the arc-melting and melt-spinning techniques have been investigated. X-ray diffraction analysis revealed that the arc-melted alloys consisted of austenitic β{sub 1}, martensitic β{sub 1}′ and γ{sub 2} precipitate phases, whereas melt-spun ribbons were composed of a fully martensitic phase. The average grain size of martensitic phases in melt-spun ribbons was determined by electron microscopy images, showing a decrease with increasing Beryllium (Be) amount. Moreover, it was found that the Be addition in the arc-melted alloys had a distinct effect on the morphology of the γ{sub 2} precipitate phase. Transmission electron microscopy analysis showed that the thickness of martensitic plates in the melt-spun ribbons reduced with increasing Be addition. In a differential scanning calorimeter analysis, no martensitic transformation (M{sub s}) peak was observed in arc-melted alloys, but it was clearly detected in melt-spun ribbons, in which M{sub s} decreased dramatically with increasing Be addition. The improvement in the shape memory ability of melt-spun ribbons was explained in terms of the refinement in grain size and martensitic plates. - Highlights: • The CuAlBe SMAs were produced by means of arc-melter and melt-spinner techniques. • MT was directly obtained in melt-spuns without any intermediate process. • The transformation temperatures decreased with increasing Be amount. • The thickness of martensitic plates in the ribbons reduced with increasing Be. • SMP of CuAl was improved by the addition of Be together with rapid solidification.

  12. Cranial base evolution within the hominin clade

    PubMed Central

    Nevell, L; Wood, B

    2008-01-01

    The base of the cranium (i.e. the basioccipital, the sphenoid and the temporal bones) is of particular interest because it undergoes significant morphological change within the hominin clade, and because basicranial morphology features in several hominin species diagnoses. We use a parsimony analysis of published cranial and dental data to predict the cranial base morphology expected in the hypothetical last common ancestor of the Pan–Homo clade. We also predict the primitive condition of the cranial base for the hominin clade, and document the evolution of the cranial base within the major subclades within the hominin clade. This analysis suggests that cranial base morphology has continued to evolve in the hominin clade, both before and after the emergence of the genus Homo. PMID:18380865

  13. Microstructure and mechanical properties of hip-consolidated Rene 95 powders. [hot-isostatic pressed nickel-based powder metal

    NASA Technical Reports Server (NTRS)

    Shimanuki, Y.; Nishino, Y.; Masui, M.; Doi, H.

    1980-01-01

    The effects of heat-treatments on the microstructure of P/M Rene 95 (a nickel-based powder metal), consolidated by the hot-isostatic pressing (HIP), were examined. The microstructure of as-HIP'd specimen was characterized by highly serrated grain boundaries. Mechanical tests and microstructural observations reveal that the serrated grain boundaries improved ductility at both room and elevated temperatures by retarding crack propagation along grain boundaries.

  14. Effects of Isothermal Aging on Microstructure Evolution, Hardness and Wear Properties of Wrought Co-Cr-Mo Alloy

    NASA Astrophysics Data System (ADS)

    Khaimanee, P.; Choungthong, P.; Uthaisangsuk, V.

    2017-03-01

    In this work, effects of isothermal aging on phase transformation, microstructure evolution, hardness and wear resistance of the wrought Co-Cr-Mo alloy with low carbon content were investigated. Initially, temperature range of FCC to HCP phase transformation of the alloy was determined by a dilatometer test. Then, aging at the temperature of 850 °C for different holding times with subsequent water quenching was carried out. Metallography examination, x-ray diffraction analysis, microhardness test and wear test were performed for Co-Cr-Mo alloy specimens after the isothermal aging. It was found that the FCC to HCP phase transformation occurred in the temperature range between 700 and 970 °C. During the aging treatment, phase fraction of the HCP martensite increased with longer aging time. The FCC to HCP phase transformation was completed after 12 h, because very fine lamellae in different orientations thoroughly dispersed within FCC grains were observed. These lamella structures could be well correlated with formation of the HCP martensite. Small amounts of carbides were found at grain boundaries and grain intersections in the samples aged for 6 and 12 h. In addition, by longer aging time, the average grain size of the aged alloy became a little bit larger, while the hardness noticeably increased. For the examined Co-Cr-Mo alloy, higher amount of the emerged HCP martensitic phase led to the increased hardness value, but reduced friction coefficient and wear rate.

  15. Microstructure evolution and magnetic properties of FeB/Pt multilayers and FeBPt composite films

    SciTech Connect

    Su, Hao; Schwarm, Samuel C.; Gupta, Subhadra; Martens, Richard L.

    2014-05-07

    Comparisons of microstructural evolution and magnetic properties were made of a FeB12/Pt10/[FeB1.2/Pt1]{sub 15}/Ta5 nm multilayered structure with a FeB12/Pt10/FeBPt33/Ta5 nm co-deposited structure. The Ta capping layer was used to protect the films from oxidation. Both these samples were sputtered in the same planetary deposition system onto thermally oxidized silicon substrates. They both represent layer-by-layer deposition, with the second type of deposition having atomically fine layers, more than an order of magnitude finer than the first type. The samples were annealed at a range of times, temperatures, and vacuum conditions. X-ray diffraction (XRD), transmission electron microscopy, and alternating gradient magnetometry were employed to characterize the structural and magnetic properties, respectively. Significant differences were observed between the two types of structures. A maximum coercivity of 8.9 kOe was seen for the atomically fine multilayer, about 10% more than that for the coarse multilayer. XRD analysis confirmed that both the coarse and fine multilayers were in the L1{sub 0} phase after annealing. Our results indicate that the co-deposited film, which is really composed of atomically fine multilayers, is superior to the coarse multilayered FeB/Pt for the formation of L1{sub 0}-phase FePt.

  16. Effects of Dynamic Multi-directional Loading on the Microstructural Evolution and Thermal Stability of Pure Aluminum

    NASA Astrophysics Data System (ADS)

    Yang, Yang; Zhang, Hua; Chen, Yadong

    2016-09-01

    Microstructural evolution and thermal stability of 1050 commercial pure aluminum processed by means of split Hopkinson pressure bar and Instron-3369 mechanical testing machine to an accumulated strain of 3.6 were investigated. The nominal strain rates reached up to 3.0 × 103 and 1 × 10-3/s, respectively. Samples in the deformed state and annealed in the temperature interval 423-523 K for 1 h were characterized by transmission electron microscopy (TEM). TEM observations reveal that the initial coarse grains are refined significantly, and the deformed structures mainly consist of equiaxed subgrains and dislocation cells with a high density of interior dislocation. In addition, the average subgrain/cell sizes of these two kinds of deformed samples are nearly the same. As to recovery behavior, recovered subgrains are observed at 473 (dynamic) versus 523 K (quasi-static), that is to say, recovery is fairly slow in the quasi-static deformed samples. It is therefore to be expected that thermal stability of this dynamic deformed aluminum is weaker than that of the quasi-static compressed one, which is due to the higher density of dislocation and nonequilibrium dislocation configurations produced during dynamic loading.

  17. In situ Scanning electron microscope study and microstructural evolution of nano silicon anode for high energy Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Hovington, P.; Dontigny, M.; Guerfi, A.; Trottier, J.; Lagacé, M.; Mauger, A.; Julien, C. M.; Zaghib, K.

    2014-02-01

    In situ and ex situ scanning electron microscopy of nano Si and SiO anode particles was carried out during the first cycles, and at various stages of charge. The particle size effects were explored in the range 0.1-20 μm, providing a new insight into the micro-structural evolution of the particles as a function of their size, and into the 'mechanical' resistance upon important volume change upon phase transformation of these anodes. For small particles, the failure of the battery comes from an electrochemical sintering that compacts the whole electrode, which results in its cracking. The particles keep their integrity when the discharge is stopped at a voltage 0.1 V, which corresponds to the chemical composition Li12Si7, while the particles are known to crack at deeper discharge up to Li22Si5. Replacing the Si particles by SiO particles in an attempt to avoid these structural effects did not help, because of the different chemical reactions during cycling, with the loss of oxygen.

  18. Molecular dynamics study of radiation damage and microstructure evolution of zigzag single-walled carbon nanotubes under carbon ion incidence

    NASA Astrophysics Data System (ADS)

    Li, Huan; Tang, Xiaobin; Chen, Feida; Huang, Hai; Liu, Jian; Chen, Da

    2016-07-01

    The radiation damage and microstructure evolution of different zigzag single-walled carbon nanotubes (SWCNTs) were investigated under incident carbon ion by molecular dynamics (MD) simulations. The radiation damage of SWCNTs under incident carbon ion with energy ranging from 25 eV to 1 keV at 300 K showed many differences at different incident sites, and the defect production increased to the maximum value with the increase in incident ion energy, and slightly decreased but stayed fairly stable within the majority of the energy range. The maximum damage of SWCNTs appeared when the incident ion energy reached 200 eV and the level of damage was directly proportional to incident ion fluence. The radiation damage was also studied at 100 K and 700 K and the defect production decreased distinctly with rising temperature because radiation-induced defects would anneal and recombine by saturating dangling bonds and reconstructing carbon network at the higher temperature. Furthermore, the stability of a large-diameter tube surpassed that of a thin one under the same radiation environments.

  19. EBSD Investigation of Cu-Sn IMC Microstructural Evolution in Cu/Sn-Ag/Cu Microbumps During Isothermal Annealing

    NASA Astrophysics Data System (ADS)

    Wang, S. J.; Hsu, L. H.; Wang, N. K.; Ho, C. E.

    2014-01-01

    The microstructural evolution of Cu/Sn-Ag (~5 μm)/Cu Cu-bump-on-line (CuBOL) joints during isothermal annealing at 180°C was examined using a field-emission scanning electron microscope equipped with an electron backscatter diffraction (EBSD) system. Cu6Sn5 and Cu3Sn were the two key intermetallic compound (IMC) species that appeared in the CuBOL joints. After annealing for 24 h (= t), the solder had completely converted to Cu-Sn IMCs, forming an "IMC" joint with Cu/Cu3Sn/Cu6Sn5/Cu3Sn/Cu structure. EBSD analyses indicated that the preferred orientation of the hexagonal Cu6Sn5 (η) was , while the preferred orientation was (100) for the monoclinic Cu6Sn5 structure (η'). Upon increasing t to 72 h, Cu6Sn5 entirely transformed into Cu3Sn, and the IMC joint became Cu/Cu3Sn/Cu accordingly. Interestingly, the grain size and crystallographic orientation of Cu3Sn displayed location dependence. Detailed EBSD analyses in combination with transmission electron microscopy on Cu3Sn were performed in the present study. This research offers better understanding of crystallographic details, including crystal structure, grain size, and orientation, for Cu6Sn5 and Cu3Sn in CuBOL joints after various annealing times.

  20. Optical parameters as a tool to study the microstructural evolution of carbonized anthracites during high-temperature treatment

    SciTech Connect

    Isabel Surez-Ruiz; Ana B. Garcia

    2007-09-15

    The graphitization process of two different carbonized anthracites in the temperature interval of 2000-2800 C was studied by using the optical properties of the materials prepared. These optical properties are defined by the main axes and parameters of the reflectance-indicating surface (RIS) and the anisotropy indexes (BW and oil bireflectance ratio). Two temperature segments, with the second one being a plateau, were found to occur in the evolution of the structural organization (textural anisotropy) of the materials. The variation with the temperature of the structural order of the materials as determined from X-ray diffraction and Raman crystalline parameters followed a similar tendency, thus confirming the validity of the optical properties as another indicator of the textural and structural changes occurring during anthracite high-temperature treatment. Moreover, as shown by the optical microscopic observation of the materials, crystalline aggregates, microspheres, and flake microstructures, which were previously detected in natural graphites, were developed from the dense and massive particles, with their proportion being higher in those materials with a larger degree of textural anisotropy and/or structural order. 29 refs., 4 figs., 3 tabs.

  1. Exploring 3D microstructural evolution in Li-Sulfur battery electrodes using in-situ X-ray tomography

    NASA Astrophysics Data System (ADS)

    Yermukhambetova, Assiya; Tan, Chun; Daemi, Sohrab R.; Bakenov, Zhumabay; Darr, Jawwad A.; Brett, Daniel J. L.; Shearing, Paul R.

    2016-10-01

    Lithium sulfur (Li-S) batteries offer higher theoretical specific capacity, lower cost and enhanced safety compared to current Li-ion battery technology. However, the multiple reactions and phase changes in the sulfur conversion cathode result in highly complex phenomena that significantly impact cycling life. For the first time to the authors’ knowledge, a multi-scale 3D in-situ tomography approach is used to characterize morphological parameters and track microstructural evolution of the sulfur cathode across multiple charge cycles. Here we show the uneven distribution of the sulfur phase fraction within the electrode thickness as a function of charge cycles, suggesting significant mass transport limitations within thick-film sulfur cathodes. Furthermore, we report a shift towards larger particle sizes and a decrease in volume specific surface area with cycling, suggesting sulfur agglomeration. Finally, we demonstrate the nano-scopic length-scale required for the features of the carbon binder domain to become discernible, confirming the need for future work on in-situ nano-tomography. We anticipate that X-ray tomography will be a powerful tool for optimization of electrode structures for Li-S batteries.

  2. Exploring 3D microstructural evolution in Li-Sulfur battery electrodes using in-situ X-ray tomography

    PubMed Central

    Yermukhambetova, Assiya; Tan, Chun; Daemi, Sohrab R.; Bakenov, Zhumabay; Darr, Jawwad A.; Brett, Daniel J. L.; Shearing, Paul R.

    2016-01-01

    Lithium sulfur (Li-S) batteries offer higher theoretical specific capacity, lower cost and enhanced safety compared to current Li-ion battery technology. However, the multiple reactions and phase changes in the sulfur conversion cathode result in highly complex phenomena that significantly impact cycling life. For the first time to the authors’ knowledge, a multi-scale 3D in-situ tomography approach is used to characterize morphological parameters and track microstructural evolution of the sulfur cathode across multiple charge cycles. Here we show the uneven distribution of the sulfur phase fraction within the electrode thickness as a function of charge cycles, suggesting significant mass transport limitations within thick-film sulfur cathodes. Furthermore, we report a shift towards larger particle sizes and a decrease in volume specific surface area with cycling, suggesting sulfur agglomeration. Finally, we demonstrate the nano-scopic length-scale required for the features of the carbon binder domain to become discernible, confirming the need for future work on in-situ nano-tomography. We anticipate that X-ray tomography will be a powerful tool for optimization of electrode structures for Li-S batteries. PMID:27748437

  3. Effects of Isothermal Aging on Microstructure Evolution, Hardness and Wear Properties of Wrought Co-Cr-Mo Alloy

    NASA Astrophysics Data System (ADS)

    Khaimanee, P.; Choungthong, P.; Uthaisangsuk, V.

    2017-02-01

    In this work, effects of isothermal aging on phase transformation, microstructure evolution, hardness and wear resistance of the wrought Co-Cr-Mo alloy with low carbon content were investigated. Initially, temperature range of FCC to HCP phase transformation of the alloy was determined by a dilatometer test. Then, aging at the temperature of 850 °C for different holding times with subsequent water quenching was carried out. Metallography examination, x-ray diffraction analysis, microhardness test and wear test were performed for Co-Cr-Mo alloy specimens after the isothermal aging. It was found that the FCC to HCP phase transformation occurred in the temperature range between 700 and 970 °C. During the aging treatment, phase fraction of the HCP martensite increased with longer aging time. The FCC to HCP phase transformation was completed after 12 h, because very fine lamellae in different orientations thoroughly dispersed within FCC grains were observed. These lamella structures could be well correlated with formation of the HCP martensite. Small amounts of carbides were found at grain boundaries and grain intersections in the samples aged for 6 and 12 h. In addition, by longer aging time, the average grain size of the aged alloy became a little bit larger, while the hardness noticeably increased. For the examined Co-Cr-Mo alloy, higher amount of the emerged HCP martensitic phase led to the increased hardness value, but reduced friction coefficient and wear rate.

  4. Evolution of permeability and microstructure of experimentally-created shear zones in Neogene siliceous mudstones from Horonobe, Japan

    NASA Astrophysics Data System (ADS)

    Uehara, Shin-ichi; Takahashi, Miki

    2014-03-01

    We report experimental measurements of bulk permeability changes due to a shear zone that is induced in siliceous mudstones collected from the Koetoi and Wakkanai Formations, northern Hokkaido, which are known to show different relationships between fault/fracture distribution and groundwater flow. We evaluate distributions of volumetric deformation in the induced shear zones by using micro-focus X-ray computed tomography. Measured permeability evolution while achieving the peak axial stress for specimens differed for the samples of the two formations. Permeability did not change obviously during shear for the Koetoi Fm. specimens, but in the Wakkanai Fm. specimens, the bulk permeability increased by a factor of 2.5 after reaching the peak stress. The difference in permeability change in these experiments can explain the differences in relationships between in situ groundwater flow and fracture distribution for the two formations. Analyses of the X-ray images reveal that this difference should reflect the differences of the volumetric deformation in the induced shear zones. Pore collapse occurred in the shear zone in the Koetoi Fm. specimen, which leads to porosity reduction, whereas fracture damages developed in the Wakkanai Fm. specimen, increasing porosity. These differences in the microstructure may reflect differences in yielding criteria for these host rocks.

  5. Effects of chemical composition and dose on microstructure evolution and hardening of neutron-irradiated reactor pressure vessel steels

    NASA Astrophysics Data System (ADS)

    Takeuchi, T.; Kuramoto, A.; Kameda, J.; Toyama, T.; Nagai, Y.; Hasegawa, M.; Ohkubo, T.; Yoshiie, T.; Nishiyama, Y.; Onizawa, K.

    2010-07-01

    The correlation of microstructure evolution and hardening was studied in two kinds of A533B-1 steel with high and low levels of Cu irradiated in a range of dose from 0.32 to 9.9 × 10 19 n cm -2 ( E > 1 MeV) under a high flux of about 1.7 × 10 13 n cm -2 s -1 using three-dimensional local electrode atom probe (3DAP), positron annihilation (PA) techniques, and Vickers microhardness. The early rapid hardening was found to be caused by mainly matrix defects such as mono- or di-vacancies ( V1 - V2) and/or dislocations indicated by the PA analysis. The 3DAP analysis showed that dense dispersion of dilute Cu rich clusters and lean distribution of Mn-Ni-Si rich clusters, which were identified to possess the same dislocation-pinning effect by applying a Russell and Brown model, were responsible for large and small hardening in high- and low-Cu steels irradiated above 0.59 × 10 19 n cm 2, respectively.

  6. An atomistic study of growth mode and microstructure evolution of amorphous carbon films by different incident carbon atoms

    NASA Astrophysics Data System (ADS)

    Xue, Chen; Zhou, Jianqiu

    2014-09-01

    In this paper, molecular dynamics (MD) simulation has been performed to describe the growth and interfacial microstructure of amorphous carbon films. We focus on the film growth mode and surface morphology for diverse deposition process parameters mainly including incident energy and incident angle. To explore the relationship between the motion of deposition atoms and amorphous films growth, a series of snapshots for each deposition process has been taken for comparison. The snapshots show that the films growth modes are diverse at different incident parameters. In the next step, surface morphology, atom distribution along film growth direction and internal structure including vacancy defects evolution during deposition process are analyzed. The results reveal that incident energy on the horizontal plane dominates the surface roughness, and incident energy on the vertical plane dominates the compactness of the film. We conclude that a suitable incident parameter is not only beneficial to prepare amorphous films with compact and smooth or bump-like surface which will meet different needs, but also can avoid formation of defects during deposition. The simulation results are expected to provide useful guidance for improving amorphous carbon films quality.

  7. Microstructural and chemical evolution near anode triple phase boundary in Ni/YSZ solid oxide fuel cells

    SciTech Connect

    Chen, Yun; Chen, Song; Hacket, Gregory; Finklea, Harry; Song, Zueyan; Gerdes, Kirk

    2011-12-01

    In this study, we report the microstructural and chemical evolution of anode grain boundaries and triple phase boundary (TPB) junctions of Ni/YSZ anode supported solid oxide fuel cells. A NiO phase was found to develop along the Ni/YSZ interfaces extending to TPBs in the operated cells. The thickness of the NiO ribbon phase remains constant at ~5 nm in hydrogen for operating durations up to 540 h. When operating on synthesis gas, an increase in interphase thickness was observed from ~11 nm for 24 h of operation to ~51 nm for 550 h of operation. YSZ phases are observed to be stable in H2 over 540 h of operation. However, for the cell operated in syngas for 550 h, a 5–10 nm tetragonal YSZ (t-YSZ) interfacial layer was identified that originated from the Ni/YSZ interfaces. Yttrium species seem to segregate to the interfaces during operation, leading to the formation of t-YSZ in the Y-depleted regions.

  8. Microstructural and chemical evolution near anode triple phase boundary in Ni/YSZ solid oxide fuel cells

    SciTech Connect

    Chen, Yun; Chen, Song; Hackett, Gregory; Finklea, Harry; Song, Xueyan; Gerdes, Kirk

    2011-12-12

    In this study, we report the micro-structural and chemical evolution of anode grain boundaries and triple phase boundary (TPB) junctions of Ni/YSZ anode supported solid oxide fuel cells. A NiO phase was found to develop along the Ni/YSZ interfaces extending to TPBs in the operated cells. The thickness of the NiO ribbon phase remains constant at ~ 5 nm in hydrogen for operating durations up to 540 h. When operating on synthesis gas, an increase in interphase thickness was observed from ~ 11 nm for 24 h of operation to ~ 51 nm for 550 h of operation. YSZ phases are observed to be stable in H{sub 2} over 540 h of operation. However, for the cell operated in syngas for 550 h, a 5–10 nm tetragonal YSZ (t-YSZ) interfacial layer was identified that originated from the Ni/YSZ interfaces. Yttrium species seem to segregate to the interfaces during operation, leading to the formation of t-YSZ in the Y-depleted regions.

  9. Microstructural and Mechanical Property Changes in the Ta-base T-111 Alloy with Aging

    SciTech Connect

    Leonard, Keith J; Busby, Jeremy T; Zinkle, Steven J

    2007-01-01

    The microstructural changes occurring in the Ta-base T-111 (Ta-8W-2Hf) alloy following 1100 h of aging at 1098, 1248 and 1398 K under inert atmosphere and its influence on the mechanical properties are reported. Microstructural evaluations were performed by optical, scanning electron microscopy and, for the first time, transmission electron microscopy. Electrical resistivity, hardness and tensile properties are compared between the as-annealed and aged samples. An increase in the amount of grain boundary precipitation with increasing aging temperature was found to decrease the electrical resistivity and material strength, leading to the eventual embrittlement of the alloy following aging at 1398 K.

  10. Microstructure-based description of the deformation of metals: Theory and application

    NASA Astrophysics Data System (ADS)

    Helm, Dirk; Butz, Alexander; Raabe, Dierk; Gumbsch, Peter

    2011-04-01

    Aiming for an integrated approach to computational materials engineering in an industrial context poses big challenges in the development of suitable materials descriptions for the different steps along the processing chain. The first key component is to correctly describe the microstructural changes during the thermal and mechanical processing of the base material into a semi-finished product. Explicit representations of the microstructure are most suitable there. The final processing steps and particularly component assessment then has to describe the entire component which requires homogenized continuum mechanical representations. A key challenge is the step in between, the determination of the (macroscopic) materials descriptions from microscopic structures. This article describes methods to include microstructure into descriptions of the deformation of metal, and demonstrates the central steps of the simulation along the processing chain of an automotive component manufactured from a dual phase steel.

  11. Periodical Microstructures Based on Novel Piezoelectric Material for Biomedical Applications

    PubMed Central

    Janusas, Giedrius; Ponelyte, Sigita; Brunius, Alfredas; Guobiene, Asta; Prosycevas, Igoris; Vilkauskas, Andrius; Palevicius, Arvydas

    2015-01-01

    A novel cantilever type piezoelectric sensing element was developed. Cost-effective and simple fabrication design allows the use of this element for various applications in the areas of biomedicine, pharmacy, environmental analysis and biosensing. This paper proposes a novel piezoelectric composite material whose basic element is PZT and a sensing platform where this material was integrated. Results showed that a designed novel cantilever-type element is able to generate a voltage of up to 80 µV at 50 Hz frequency. To use this element for sensing purposes, a four micron periodical microstructure was imprinted. Silver nanoparticles were precipitated on the grating to increase the sensitivity of the designed element, i.e., Surface Plasmon Resonance (SPR) effect appears in the element. To tackle some issues (a lack of sensitivity, signal delays) the element must have certain electronic and optical properties. One possible solution, proposed in this paper, is a combination of piezoelectricity and SPR in a single element. PMID:26694398

  12. Oxygen gas optrode based on microstructured polymer optical fiber segment

    NASA Astrophysics Data System (ADS)

    Yang, Xinghua; Peng, Lirong; Yuan, Libo; Teng, Pingping; Tian, Fengjun; Li, Le; Luo, Shenzi

    2011-06-01

    In this article, we first propose a novel type of oxygen gas optrode by forming fluorophore doped sensing film in the array microholes with the characteristics of microstructured optical fiber (MOF) segment. Comparing with the conventional O 2 detecting method, this slender shaped optrode shows potential in trace amount of O 2 sensing and online O 2 monitoring. Organical silicate gel or plastified cellulose acetate are chosen as sensing films and tris (4,7-diphenyl-1,10-phenathroline) ruthenium(II) dichloride ([Ru(dpp) 3]Cl 2) or meso-tetraphenylporphyin (TPP) as quenching fluorophores. From the experimental results, we find [Ru(dpp) 3] 2+-Gel-MOF optrode has favorable sensing characteristics, and the Stern-Volmer plots are linear in the full concentration range of O 2 (0-100% v/v). The ratio of I 0/I 100, where I 0 and I 100 respectively represents the fluorescence intensities of the optrode exposed to 100% N 2 and 100% O 2, as a sensitivity of the optrode is 10.8. Simultaneously, the optrode can make a quick response within 50 ms.

  13. Deformation Microstructures and Creep Mechanisms in Advanced ZR-Based Cladding Under Biazal Loading

    SciTech Connect

    K. Linga Murty

    2008-08-11

    Investigate creep behavior of Zr-based cladding tubes with attention to basic creep mechanisms and transitions in them at low stresses and/or temperatures and study the dislocation microstructures of deformed samples for correlation with the underlying micromechanism of creep

  14. The evolution of interface microstructure in a ZrO[sub 2]/Ag-Cu-Al-Ti system

    SciTech Connect

    Lee, Youngmin; Yu, Jin )

    1993-08-01

    Among ceramic/metal (C/M) joining technologies, the active filler metal method has been studied extensively due to the simple brazing process and excellent joint strength. Active metal elements, typically Ti, are intentionally added to braze alloys to enhance the formation of reaction products between the ceramic and the braze metal at the C/M interface. In the brazing of Al[sub 2]O[sub 3] with the Ag-Cu-Ti filler metal, reaction products such as [gamma]-TiO, Cu[sub 2](Ti, Al)[sub 4]O, Ti[sub 3](Cu[sub 0.76]Al[sub 0.18]Sn[sub 0.06])[sub 3]O were found, while products such as Ti[sub 5]Si[sub 3] and TiN formed in the brazing of Si[sub 3]N[sub 4]. The presence of reaction layers at the C/M interface influences the interface strength in a complex way. In Cu/Al[sub 2]O[sub 3], Co/Al[sub 2]O[sub 3], Ni/Al[sub 2]O[sub 3], and Cu/diamond systems, maxima of joint strength were observed at some intermediate Ti addition, while the flexural strength decreased substantially with the thickening of the TiO layer in a ZrO[sub 2]/Ag-Cu-Sn-Ti system. Thus, composition of the braze alloy (particularly, the content of the active metal), process conditions such as brazing temperature and time, microstructure and mechanical properties of reaction products at the C/M interfaces, interfacial chemistry, and residual stress are primary factors to be studied in order to understand the strengths of the C/M interfaces systematically. In the present and the following papers, evolutions of interfacial microstructures at various brazing conditions, and corresponding interface strengths are reported, respectively, for a ZrO[sub 2]/Ag-Cu-Al-Ti system.

  15. Microstructure evolution of the phase change material TiSbTe

    NASA Astrophysics Data System (ADS)

    Chen, Yongjin; Zhang, Bin; Ding, Qingqing; Deng, Qingsong; Cheng, Yan; Song, Zhitang; Li, Jixue; Zhang, Ze; Han, Xiaodong

    2016-10-01

    The crystallization process and crystal structure of the phase change material TiSbTe alloy have been successfully established, which is essential for applying this alloy in phase change memory. Specifically, transmission electron microscopy (TEM) analyses of the film annealed in situ were used in combination with selected-area electron diffraction (SAED) and radial distribution function (RDF) analyses to investigate the structural evolution from the amorphous phase to the polycrystalline phase. Moreover, the presence of structures with medium-range order in amorphous TST, which is beneficial to high-speed crystallization, was indicated by the structure factors S(Q)s. The crystallization temperature was determined to be approximately 170°C, and the grain size varied from several to dozens of nanometers. As the temperature increased, particularly above 200°C, the first single peak of the rG(r) curves transformed into double shoulder peaks due to the increasing impact of the Ti-Te bonds. In general, the majority of Ti atoms enter the SbTe lattice, whereas the remainder of the Ti atoms aggregate, leading to the appearance of TiTe2 phase separation, as confirmed by the SAED patterns, high-angle annular dark field scanning transmission electron microscopy (HAADFSTEM) images and the corresponding energy-dispersive X-ray (EDX) mappings.

  16. Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation

    PubMed Central

    He, Jie; Kaban, Ivan; Mattern, Norbert; Song, Kaikai; Sun, Baoan; Zhao, Jiuzhou; Kim, Do Hyang; Eckert, Jürgen; Greer, A. Lindsay

    2016-01-01

    At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands. PMID:27181922

  17. Microstructural Evolution and Mechanical Properties in (AuSn)eut-Cu Interconnections

    NASA Astrophysics Data System (ADS)

    Dong, Hongqun; Vuorinen, Vesa; Laurila, Tomi; Paulasto-Kröckel, Mervi

    2016-10-01

    The interfacial reactions between the widely employed solder Au-20wt.%Sn and the common contact metallizations (e.g. Ni, Cu and Pt) are normally complex and not well determined. In order to identify the proper contactor for Au-20wt.%Sn solder, the present study focuses on (1) rationalizing the interfacial reaction mechanisms of Au-20wt.%Sn|Cu as well as (2) measuring the mechanical properties of individual intermetallics formed at the interface. The evolution of interfacial reaction products were rationalized by using the experimental results in combination with the calculated Au-Cu-Sn phase diagram information. It was found that the growth of the AuCu interfacial intermetallic layer was diffusion-controlled. The diffusion path of Au-20wt.%Sn|Cu at 150°C was proposed. The hardness and indentation modulus of the interfacial reaction products were measured using nanoindentation tests. The results revealed a significant influence of the Cu solubility on the mechanical properties of (Au,Cu)Sn and (Au,Cu)5Sn, i.e. their hardness and contact modulus increased with the increase in the amount of Cu. Furthermore, results obtained here for the Au-20wt.%Sn|Cu joints were compared to those from Au-20wt.%Sn|Ni in order to assess the similarities and differences between these widely used interconnection metallization systems.

  18. Role of annealing temperatures on the evolution of microstructure and properties of Cr2O3 films

    NASA Astrophysics Data System (ADS)

    He, Nairu; Ji, Li; Liu, Xiaohong; Li, Hongxuan; Zhou, Huidi; Chen, Jianmin

    2015-12-01

    Cr2O3 films were deposited on Ni-based high-temperature alloy substrates by using a cathodic arc ion plating system and then annealed in air at different temperatures. The effects of different annealing temperatures on the microstructure, mechanical and tribological properties of the films were examined. Results showed that the as-deposited Cr2O3 films were primarily amorphous with crystallization and vaporization temperatures of 360 °C and 940 °C, respectively. Annealing above the crystallization temperature improved the hardness, adhesion, and wear life of the Cr2O3 films. A mesh-like heave structure comprising Cr2O3 and Cr2Ti7O17 phases formed on the film surface after annealing above the vaporization temperature. The mesh-like heave structure endued the film with excellent tribological properties in a wide temperature range from room temperature (RT) to 1000 °C.

  19. Biochemical evolution II: origin of life in tubular microstructures on weathered feldspar surfaces.

    PubMed

    Parsons, I; Lee, M R; Smith, J V

    1998-12-22

    Mineral surfaces were important during the emergence of life on Earth because the assembly of the necessary complex biomolecules by random collisions in dilute aqueous solutions is implausible. Most silicate mineral surfaces are hydrophilic and organophobic and unsuitable for catalytic reactions, but some silica-rich surfaces of partly dealuminated feldspars and zeolites are organophilic and potentially catalytic. Weathered alkali feldspar crystals from granitic rocks at Shap, north west England, contain abundant tubular etch pits, typically 0.4-0.6 microm wide, forming an orthogonal honeycomb network in a surface zone 50 microm thick, with 2-3 x 10(6) intersections per mm2 of crystal surface. Surviving metamorphic rocks demonstrate that granites and acidic surface water were present on the Earth's surface by approximately 3.8 Ga. By analogy with Shap granite, honeycombed feldspar has considerable potential as a natural catalytic surface for the start of biochemical evolution. Biomolecules should have become available by catalysis of amino acids, etc. The honeycomb would have provided access to various mineral inclusions in the feldspar, particularly apatite and oxides, which contain phosphorus and transition metals necessary for energetic life. The organized environment would have protected complex molecules from dispersion into dilute solutions, from hydrolysis, and from UV radiation. Sub-micrometer tubes in the honeycomb might have acted as rudimentary cell walls for proto-organisms, which ultimately evolved a lipid lid giving further shelter from the hostile outside environment. A lid would finally have become a complete cell wall permitting detachment and flotation in primordial "soup." Etch features on weathered alkali feldspar from Shap match the shape of overlying soil bacteria.

  20. Plastic-flow and microstructure evolution during hot deformation of a gamma titanium aluminide alloy

    SciTech Connect

    Seetharaman, V.; Semiatin, S.L.

    1997-11-01

    The hot workability of a near gamma titanium aluminide alloy, Ti-49.5Al-2.5Nb-1.1Mn, was assessed in both the cast and the wrought conditions through a series of tension tests conducted over a wide range of strain rates (10{sup {minus}4} to 10{sup 0} s{sup {minus}1}) and temperatures (850 C to 1,377 C). Tensile flow curves for both materials exhibited sharp peaks at low strain levels followed by pronounced necking and flow localization at high strain levels. A phenomenological analysis of the strain rate and temperature dependence of the peak stress data yielded an average value of the strain rate sensitivity equal to 0.21 and an apparent activation energy of {approximately}411 kJ/mol. At low strain rates, the tensile ductility displayed a maximum at {approximately}1,050 C to 1,150 C, whereas at high strain rates, a sharp transition from a brittle behavior at low temperatures to a ductile behavior at high temperatures was noticed. Dynamic recrystallization of the gamma phase was the major softening mechanism controlling the growth and coalescence of cavities and wedge cracks in specimens deformed at strain rates of 10{sup {minus}4} to 10{sup {minus}2} s{sup {minus}1} and temperatures varying from 950 C to 1,250 C. The dynamically recrystallized grain size followed a power-law relationship with the Zener-Hollomon parameter. Deformation at temperatures higher than 1,270 C led to the formation of randomly oriented alpha laths within the gamma grains at low strain levels followed by their reorientation and evolution into fibrous structures containing {gamma} + {alpha} phases, resulting in excellent ductility even at high strain rates.

  1. Pore- and micro-structural characterization of a novel structural binder based on iron carbonation

    SciTech Connect

    Das, Sumanta; Stone, David; Convey, Diana; Neithalath, Narayanan

    2014-12-15

    The pore- and micro-structural features of a novel binding material based on the carbonation of waste metallic iron powder are reported in this paper. The binder contains metallic iron powder as the major ingredient, followed by additives containing silica and alumina to facilitate favorable reaction product formation. Compressive strengths sufficient for a majority of concrete applications are attained. The material pore structure is investigated primarily through mercury intrusion porosimetry whereas electron microscopy is used for microstructural characterization. Reduction in the overall porosity and the average pore size with an increase in carbonation duration from 1 day to 4 days is noticed. The pore structure features are used in predictive models for gas and moisture transport (water vapor diffusivity and moisture permeability) through the porous medium which dictates its long-term durability when used in structural applications. Comparisons of the pore structure with those of a Portland cement paste are also provided. The morphology of the reaction products in the iron-based binder, and the distribution of constituent elements in the microstructure are also reported. - Highlights: • Carbonation of iron produces a dense microstructure. • Pore volume in iron carbonate lower, critical size higher than those in OPC pastes • Reaction product contains iron, carbon, silicon, aluminum and calcium. • Power-law for porosity-moisture permeability relationship was established.

  2. Evolution of pore microstructures during healing of grain boundaries in synthetic calcite rocks

    NASA Astrophysics Data System (ADS)

    Olgaard, David L.; Fitz Gerald, John D.

    1993-11-01

    The morphologies of calcite grain boundaries were analyzed to provide insight into the evolution of pore networks in unfractured rock. Two synthetic calcite rocks were fabricated by hot isostatically pressing (HIP-ing) dried analytical-grade powders of pure CaCO3 and CaCO3 plus 5% Al2O3 at 600° C and 200 MPa confining pressure for 3 hours (HIP-1). Some samples were HIPed a second time at different temperatures and pressures to investigate the stability of the structures (HIP-2a-c). SEM and TEM were used to image both grain faces and grain boundary cross-sections. Structures on grain faces vary from open shallow basins with peripheral rims, to labyrinths of irregular ridges and channels, to isolated circular depressions. All of these structures are mirrored across the plane between grain faces. The grain size in both the single and two-phase samples increased markedly during HIP-1. Migrating boundaries either dragged pores along or broke away leaving grain interiors dotted with small voids. The structures present after HIP-1 were not stable but evolved considerably in a way dependent on the conditions of the HIP-2. Confining pressure had the most pronounced effect. With low confining pressure, the grain-boundary porosity evolved into isolated circular depressions but the total pore volume did not noticeably decrease. With high confining pressure, the pore volume virtually disappeared. The structures present after HIP-1 are strikingly similar to those that develop in intragranular cracks during healing. We infer that grain boundaries and intragranular cracks heal by similar processes. Decomposition, localized melting, impurities, and anisotropic surface energies played no evident role in forming the grain-boundary structures. The timing of the formation of the porosity and of the subsequent healing processes is more difficult to ascertain. Some structures appear to have evolved gradually throughout the constant, high temperature stage of HIPing. The most obvious

  3. Neuron-based heredity and human evolution.

    PubMed

    Gash, Don M; Deane, Andrew S

    2015-01-01

    It is widely recognized that human evolution has been driven by two systems of heredity: one DNA-based and the other based on the transmission of behaviorally acquired information via nervous system functions. The genetic system is ancient, going back to the appearance of life on Earth. It is responsible for the evolutionary processes described by Darwin. By comparison, the nervous system is relatively newly minted and in its highest form, responsible for ideation and mind-to-mind transmission of information. Here the informational capabilities and functions of the two systems are compared. While employing quite different mechanisms for encoding, storing and transmission of information, both systems perform these generic hereditary functions. Three additional features of neuron-based heredity in humans are identified: the ability to transfer hereditary information to other members of their population, not just progeny; a selection process for the information being transferred; and a profoundly shorter time span for creation and dissemination of survival-enhancing information in a population. The mechanisms underlying neuron-based heredity involve hippocampal neurogenesis and memory and learning processes modifying and creating new neural assemblages changing brain structure and functions. A fundamental process in rewiring brain circuitry is through increased neural activity (use) strengthening and increasing the number of synaptic connections. Decreased activity in circuitry (disuse) leads to loss of synapses. Use and disuse modifying an organ to bring about new modes of living, habits and functions are processes in line with Neolamarckian concepts of evolution (Packard, 1901). Evidence is presented of bipartite evolutionary processes-Darwinian and Neolamarckian-driving human descent from a common ancestor shared with the great apes.

  4. Neuron-based heredity and human evolution

    PubMed Central

    Gash, Don M.; Deane, Andrew S.

    2015-01-01

    It is widely recognized that human evolution has been driven by two systems of heredity: one DNA-based and the other based on the transmission of behaviorally acquired information via nervous system functions. The genetic system is ancient, going back to the appearance of life on Earth. It is responsible for the evolutionary processes described by Darwin. By comparison, the nervous system is relatively newly minted and in its highest form, responsible for ideation and mind-to-mind transmission of information. Here the informational capabilities and functions of the two systems are compared. While employing quite different mechanisms for encoding, storing and transmission of information, both systems perform these generic hereditary functions. Three additional features of neuron-based heredity in humans are identified: the ability to transfer hereditary information to other members of their population, not just progeny; a selection process for the information being transferred; and a profoundly shorter time span for creation and dissemination of survival-enhancing information in a population. The mechanisms underlying neuron-based heredity involve hippocampal neurogenesis and memory and learning processes modifying and creating new neural assemblages changing brain structure and functions. A fundamental process in rewiring brain circuitry is through increased neural activity (use) strengthening and increasing the number of synaptic connections. Decreased activity in circuitry (disuse) leads to loss of synapses. Use and disuse modifying an organ to bring about new modes of living, habits and functions are processes in line with Neolamarckian concepts of evolution (Packard, 1901). Evidence is presented of bipartite evolutionary processes—Darwinian and Neolamarckian—driving human descent from a common ancestor shared with the great apes. PMID:26136649

  5. Numerical Simulations of One-dimensional Microstructure Dynamics

    SciTech Connect

    Berezovski, M.; Berezovski, A.; Engelbrecht, J.

    2010-05-21

    Results of numerical simulations of one-dimensional wave propagation in microstructured solids are presented and compared with the corresponding results of wave propagation in given layered media. A linear microstructure model based on Mindlin theory is adopted and represented in the framework of the internal variable theory. Fully coupled systems of equations for macro-motion and microstructure evolution are rewritten in the form of conservation laws. A modification of wave propagation algorithm is used for numerical calculations. It is shown how the initial microstructure model can be improved in order to match the results obtained by both approaches.

  6. Microstructural evolution of delta ferrite in SAVE12 steel under heat treatment and short-term creep

    SciTech Connect

    Li, Shengzhi; Eliniyaz, Zumrat; Zhang, Lanting; Sun, Feng; Shen, Yinzhong; Shan, Aidang

    2012-11-15

    This research focused on the formation and microstructural evolution of delta ferrite phase in SAVE12 steel. The formation of delta ferrite was due to the high content of ferrite forming alloy elements such as Cr, W, and Ta. This was interpreted through either JMatPro-4.1 computer program or Cr{sub eq} calculations. Delta ferrite was found in bamboo-like shape and contained large amount of MX phase. It was surrounded by Laves phases before creep or aging treatment. Annealing treatments were performed under temperatures from 1050 Degree-Sign C to 1100 Degree-Sign C and various time periods to study its dissolution kinetics. The result showed that most of the delta ferrite can be dissolved by annealing in single phase austenitic region. Dissolution process of delta ferrite may largely depend on dissolution kinetic factors, rather than on thermodynamic factors. Precipitation behavior during short-term (1100 h) creep was investigated at temperature of 600 Degree-Sign C under a stress of 180 MPa. The results demonstrated that delta ferrite became preferential nucleation sites for Laves phase at the early stage of creep. Laves phase on the boundary around delta ferrite showed relatively slower growth and coarsening rate than that inside delta ferrite. - Highlights: Black-Right-Pointing-Pointer Delta ferrite is systematically studied under heat treatment and short-term creep. Black-Right-Pointing-Pointer Delta ferrite contains large number of MX phase and is surrounded by Laves phases before creep or aging treatment. Black-Right-Pointing-Pointer Formation of delta ferrite is interpreted by theoretical and empirical methods. Black-Right-Pointing-Pointer Most of the delta ferrite is dissolved by annealing in single phase austenitic region. Black-Right-Pointing-Pointer Delta ferrite becomes preferential nucleation sites for Laves phase at the early stage of creep.

  7. Effect of Interfacial Microstructure Evolution on Mechanical Properties and Fracture Behavior of Friction Stir-Welded Al-Cu Joints

    NASA Astrophysics Data System (ADS)

    Xue, P.; Xiao, B. L.; Ma, Z. Y.

    2015-07-01

    The interfacial microstructure evolution of Al-Cu joints during friction stir welding and post-welding annealing and its influence on the tensile strength and the fracture behavior were investigated in detail. An obvious interface including three sub-layers of α-Al, Al2Cu, and Al4Cu9 intermetallic compound (IMC) layers is generated in the as-FSW joint. With the development of annealing process, the α-Al layer disappeared and a new IMC layer of AlCu formed between initial two IMC layers of Al2Cu and Al4Cu9. The growth rate of IMC layers was diffusion controlled before the formation of Kirkendall voids, with activation energy of 117 kJ/mol. When the total thickness of IMC layers was less than the critical value of 2.5 μm, the FSW joints fractured at the heat-affected zone of Al side with a high ultimate tensile strength (UTS) of ~100 MPa. When the thickness of IMC layers exceeded 2.5 μm, the joints fractured at the interface. For relatively thin IMC layer, the joints exhibited a slightly decreased UTS of ~90 MPa and an inter-granular fracture mode with crack propagating mainly between the Al2Cu and AlCu IMC layers. However, when the IMC layer was very thick, crack propagated in the whole IMC layers and the fracture exhibited trans-granular mode with a greatly decreased UTS of 50-60 MPa.

  8. Interfacial reactions and microstructural evolution of periodic Ni nanodot arrays on N2+-implanted amorphous Si substrates

    NASA Astrophysics Data System (ADS)

    Cheng, S. L.; Lai, R. H.; Huang, Y. D.; Lin, H. C.

    2017-03-01

    We report here on the results of a systematic investigation of the interfacial reactions and microstructural evolution of nanoscale Ni metal dots on N2+-implanted amorphous Si (a-Si) substrates under different annealing conditions. During annealing, Ni2Si was the first phase to form, followed by NiSi and NiSi2. The three Ni-silicide phases formed were polycrystalline and the average sizes of the annealed nanodots were observed to increase with the annealing temperature, up to 500 °C. After a further increase of the annealing temperature and/or time, it is interesting to note that the NiSi2 grains gradually migrated outward from their original nanodot positions to the a-Si regions, which resulted in the formation of a remarkable NiSi2 nanoring structure. The inner regions of the NiSi2 nanorings were found to be comprised of a single crystalline Si phase, indicating mediation of the epitaxial crystallization of N2+-implanted a-Si by the lateral migration of the NiSi2 nanodots. Furthermore, the annealing temperature required for complete recrystallization of the a-Si layer in the Ni nanodot/N2+-implanted a-Si sample could be significantly reduced to 550 °C, 200 °C lower than that which was required the blank N2+-implanted a-Si sample. It is suggested that the formation of these remarkable NiSi2 nanoring structures and the enhancement of N2+-implanted a-Si recrystallization in the presence of NiSi2 nanodots were due to the silicide-induced crystallization mechanism.

  9. 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.

  10. Microstructure and texture evolution of ultra-thin grain-oriented silicon steel sheet fabricated using strip casting and three-stage cold rolling method

    NASA Astrophysics Data System (ADS)

    Song, Hong-Yu; Liu, Hai-Tao; Wang, Yin-Ping; Wang, Guo-Dong

    2017-03-01

    A 0.1 mm-thick grain-oriented silicon steel sheet was successfully produced using strip casting and three-stage cold rolling method. The microstructure, texture and inhibitor evolution during the processing was briefly analyzed. It was found that Goss texture was absent in the hot rolled sheet because of the lack of shear deformation. After normalizing, a large number of dispersed MnS precipitates with the size range of 15-90 nm were produced. During first cold rolling, dense shear bands were generated in the deformed ferrite grains, resulting in the intense Goss texture after first intermediate annealing. The microstructure was further refined and homogenized during the subsequent cold rolling and annealing processes. After primary recrystallization annealing, a homogeneous microstructure consisting of fine and equiaxed grains was produced while the associated texture was characterized by a strong γ-fiber texture. Finally, a complete secondary recrystallization microstructure consisting of entirely large Goss grains was produced. The magnetic induction B8 and iron loss P10/400 was 1.79 T and 6.9 W/kg, respectively.

  11. Microstructural Evolution in Laser Deposited Nickel-Titanium-Carbon in Situ Metal-Matrix Composites (Preprint)

    DTIC Science & Technology

    2010-01-01

    including aerospace applications, due to their higher specific stiffness and strength, and, promising high temperature mechanical properties such as...or nickel-base matrix is very promising as a hybrid material for high temperature structural applications. There have been some previous studies on...densification behavior of the TiCx- 50 wt% Ni composites processed via self- propagating high temperature synthesis (SHS). They reported that the densities

  12. Mechanical properties and microstructural evolution of modified 9Cr-1Mo steel after long-term aging for 50,000 h

    NASA Astrophysics Data System (ADS)

    Baek, Jong-Hyuk; Kim, Sung-Ho; Lee, Chan-Bock; Hahn, Do-Hee

    2009-08-01

    The mechanical properties and microstructural evolution of modified 9Cr-1Mo steel have been studied to investigate steel property changes after long-term isothermal aging at 600 °C for 50,000 h. The microhardness and strength were maintained constantly after aging but the impact energy was dramatically reduced by 62 % during the aging period. From the viewpoint of microstructural evolution after the aging process, Cr-enrichment and Fe-depletion took place within the M23C6-type precipitates in the as-aged steel and V-depletion also happened within the VX-type precipitates after aging. In addition, the precipitates of the M2Mo-type Laves phase and the segregation of the impurity atoms would be formed during the long-term aging period. It was considered that the sharp reduction of the impact energy could be related to the formation of the Laves phases and the impurity segregation after aging at 600 °C. The phase stability was also verified by the specific heat results up to 950 °C from a DSC test. It was concluded from this study that the modified 9Cr-1Mo steel would keep its microstructural stability at 600 °C during the long-term aging period of 50,000 h, which was equivalent to the in-service life of the SFR fuel cladding.

  13. Microstructural evolution in NF616 (P92) and Fe-9Cr-0.1C-model alloy under heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Topbasi, Cem; Kaoumi, Djamel; Motta, Arthur T.; Kirk, Mark A.

    2015-11-01

    In this comparative study, in situ investigations of the microstructure evolution in a Fe-9Cr ferritic-martensitic steel, NF616, and a Fe-9Cr-0.1C-model alloy with a similar ferritic-martensitic microstructure have been performed. NF616 and Fe-9Cr-0.1C-model alloy were irradiated to high doses (up to ∼10 dpa) with 1 MeV Kr ions between 50 and 673 K. Defect cluster density increased with dose and saturated in both alloys. The average size of defect clusters in NF616 was constant between 50 and 573 K, on the other hand average defect size increased with dose in Fe-9Cr-0.1C-model alloy around ∼1 dpa. At low temperatures (50-298 K), alignment of small defect clusters resulted in the formation of extensive defects in Fe-9Cr-0.1C-model alloy around ∼2-3 dpa, while similar large defects in NF616 started to form at a high temperature of 673 K around ∼5 dpa. Interaction of defect clusters with the lath boundaries were found to be much more noticeable in Fe-9Cr-0.1C-model alloy. Differences in the microstructural evolution of NF616 and Fe-9Cr-0.1C-model alloy are explained by means of the defect cluster trapping by solute atoms which depends on the solute atom concentrations in the alloys.

  14. The comparison of microstructure and nanocluster evolution in proton and neutron irradiated Fe-9%Cr ODS steel to 3 dpa at 500 °C

    NASA Astrophysics Data System (ADS)

    Swenson, M. J.; Wharry, J. P.

    2015-12-01

    A model Fe-9%Cr oxide dispersion strengthened (ODS) steel was irradiated with protons or neutrons to a dose of 3 displacements per atom (dpa) at a temperature of 500 °C, enabling a direct comparison of ion to neutron irradiation effects at otherwise fixed irradiation conditions. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography including cluster analysis. Both proton and neutron irradiations produced a comparable void and dislocation loop microstructure. However, the irradiation response of the Ti-Y-O oxide nanoclusters varied. Oxides remained stable under proton irradiation, but exhibited dissolution and an increase in Y:Ti composition ratio under neutron irradiation. Both proton and neutron irradiation also induced varying extents of Si, Ni, and Mn clustering at existing oxide nanoclusters. Protons are able to reproduce the void and loop microstructure of neutron irradiation carried out to the same dose and temperature. However, since nanocluster evolution is controlled by both diffusion and ballistic impacts, protons are rendered unable to reproduce the nanocluster evolution of neutron irradiation at the same dose and temperature.

  15. Microstructural evolution in NF616 (P92) and Fe–9Cr–0.1C-model alloy under heavy ion irradiation

    SciTech Connect

    Topbasi, Cem; Kaoumi, Djamel; Motta, Arthur T.; Kirk, Mark A.

    2015-11-01

    In this comparative study, in situ investigations of the microstructure evolution in a Fee9Cr ferritic emartensitic steel, NF616, and a Fee9Cre0.1C-model alloy with a similar ferriticemartensitic microstructure have been performed. NF616 and Fee9Cre0.1C-model alloy were irradiated to high doses (up to ~10 dpa) with 1 MeV Kr ions between 50 and 673 K. Defect cluster density increased with dose and saturated in both alloys. The average size of defect clusters in NF616 was constant between 50 and 573 K, on the other hand average defect size increased with dose in Fee9Cre0.1C-model alloy around ~1 dpa. At low temperatures (50e298 K), alignment of small defect clusters resulted in the formation of extensive defects in Fee9Cre0.1C-model alloy around ~2e3 dpa, while similar large defects in NF616 started to form at a high temperature of 673 K around ~5 dpa. Interaction of defect clusters with the lath boundaries were found to be much more noticeable in Fee9Cre0.1C-model alloy. Differences in the microstructural evolution of NF616 and Fee9Cre0.1C-model alloy are explained by means of the defect cluster trapping by solute atoms which depends on the solute atom concentrations in the alloys.

  16. Microstructured optical fiber-based micro-cavity sensor for chemical detection

    NASA Astrophysics Data System (ADS)

    Kim, Bongkyun; Ahn, Jin-Chul; Chung, Phil-Sang; Chung, Youngjoo

    2014-02-01

    The studies on microstructured optical fibers (MOF) have drawn considerable interest and played an important role in many applications. MOFs provide unique optical properties and controllable modal properties because of their flexibilities on manipulation of the transmission spectrum and the waveguide dispersion properties. MOFs are especially useful for optical sensing applications because the micro-structured air channels in MOF can host various types of analytes such as liquids, gases, and chemical molecules. Recently, many studies have focused on the development of MOF-based optical sensors for various gases and chemical molecules. We propose a compact, and highly sensitive optical micro-cavity chemical sensor using microstructured fiber. The sensor probe is composed of a hollow optical fiber and end cleaved microstructured fiber with a solid core. The interference spectrum resulting from the reflected light at the silica and air interfaces changes when the micro-cavity is infiltrated with external chemical molecules. This structure enables the direct detection of chemical molecules such as volatile organic compounds (VOCs) without the introduction of any permeable material.

  17. Effect of the content of B4C on microstructural evolution and wear behaviors of the laser-clad coatings fabricated on Ti6Al4V

    NASA Astrophysics Data System (ADS)

    Bai, L. L.; Li, J.; Chen, J. L.; Song, R.; Shao, J. Z.; Qu, C. C.

    2016-01-01

    TiNi/Ti2Ni-based composite coatings reinforced by TiC and TiB2 were produced on Ti6Al4V by laser cladding the mixture of a Ni-based alloy and different contents of B4C (0 wt%, 5 wt%, 15 wt%, and 25 wt%). The macromorphologies and microstructures of the coatings were examined through optical microscopy, X-ray diffractometry, scanning electron microscopy, and energy dispersive spectrometry. The microhardness, fracture toughness, and wear behaviors of the coatings were also investigated by using a microhardness tester and an ultra-functional wear testing machine. Results showed that the coatings were mainly composed of TiNi/Ti2Ni and TiC/TiB2 as the matrix and reinforcement particles, respectively. The phase constituents of the coatings were not influenced by addition of different contents of B4C. The microstructure of the reinforcements in the coatings presented the following evolution: hypereutectic consisting of blocky (TiC+TiB2)e eutectic and primary TiCp cellular dendrites (0 wt% B4C), mixture of hypereutectic and willow-shaped (TiB2+TiC)p pseudoeutectic (5 wt% B4C), and pseudoeutectic (15 and 25 wt% B4C). With increasing B4C content, the volume fraction and size of the pseudoeutectic structures as well as the average microhardness of the coatings (850, 889, 969, and 1002 HV0.2) were increased. By contrast, the average fracture toughness of the coatings was gradually decreased (4.47, 4.21, 4.06, and 3.85 Mpa m1/2) along with their wear volumes (0 wt%, 5 wt%, and 15 wt% B4C). The increase in B4C content to 25 wt% did not further reduce wear loss. The wear mechanism transformed from micro-cutting (0 wt% B4C) into a combination of micro-cutting and brittle debonding (5 wt% B4C) and finally led to brittle debonding (15 wt% and 25 wt% B4C). Coatings with suitable contents of B4C (less than 15 wt%) showed excellent comprehensive mechanical properties.

  18. An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced elasticity in conducting polymer film

    NASA Astrophysics Data System (ADS)

    Pan, Lijia; Chortos, Alex; Yu, Guihua; Wang, Yaqun; Isaacson, Scott; Allen, Ranulfo; Shi, Yi; Dauskardt, Reinhold; Bao, Zhenan

    2014-01-01

    Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1 Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.

  19. Dual Microstructure Heat Treatment of a Nickel-Base Disk Alloy Assessed

    NASA Technical Reports Server (NTRS)

    Gayda, John

    2002-01-01

    Gas turbine engines for future subsonic aircraft will require nickel-base disk alloys that can be used at temperatures in excess of 1300 F. Smaller turbine engines, with higher rotational speeds, also require disk alloys with high strength. To address these challenges, NASA funded a series of disk programs in the 1990's. Under these initiatives, Honeywell and Allison focused their attention on Alloy 10, a high-strength, nickel-base disk alloy developed by Honeywell for application in the small turbine engines used in regional jet aircraft. Since tensile, creep, and fatigue properties are strongly influenced by alloy grain size, the effect of heat treatment on grain size and the attendant properties were studied in detail. It was observed that a fine grain microstructure offered the best tensile and fatigue properties, whereas a coarse grain microstructure offered the best creep resistance at high temperatures. Therefore, a disk with a dual microstructure, consisting of a fine-grained bore and a coarse-grained rim, should have a high potential for optimal performance. Under NASA's Ultra-Safe Propulsion Project and Ultra-Efficient Engine Technology (UEET) Program, a disk program was initiated at the NASA Glenn Research Center to assess the feasibility of using Alloy 10 to produce a dual-microstructure disk. The objectives of this program were twofold. First, existing dual-microstructure heat treatment (DMHT) technology would be applied and refined as necessary for Alloy 10 to yield the desired grain structure in full-scale forgings appropriate for use in regional gas turbine engines. Second, key mechanical properties from the bore and rim of a DMHT Alloy 10 disk would be measured and compared with conventional heat treatments to assess the benefits of DMHT technology. At Wyman Gordon and Honeywell, an active-cooling DMHT process was used to convert four full-scale Alloy 10 disks to a dual-grain microstructure. The resulting microstructures are illustrated in the

  20. Disparity pattern-based autostereoscopic 3D metrology system for in situ measurement of microstructured surfaces.

    PubMed

    Li, Da; Cheung, Chi Fai; Ren, MingJun; Whitehouse, David; Zhao, Xing

    2015-11-15

    This paper presents a disparity pattern-based autostereoscopic (DPA) 3D metrology system that makes use of a microlens array to capture raw 3D information of the measured surface in a single snapshot through a CCD camera. Hence, a 3D digital model of the target surface with the measuring data is generated through a system-associated direct extraction of disparity information (DEDI) method. The DEDI method is highly efficient for performing the direct 3D mapping of the target surface based on tomography-like operation upon every depth plane with the defocused information excluded. Precise measurement results are provided through an error-elimination process based on statistical analysis. Experimental results show that the proposed DPA 3D metrology system is capable of measuring 3D microstructured surfaces with submicrometer measuring repeatability for high precision and in situ measurement of microstructured surfaces.

  1. Understanding the Role of Hot Isostatic Pressing Parameters on the Microstructural Evolution of Ti-6Al-4V and Inconel 718 Fabricated by Electron Beam Melting

    SciTech Connect

    Peter, William H.; Nandwana, Peeyush; Kirka, Michael M.; Dehoff, Ryan R.; Sames, William; Erdman, III, Donald L.; Eklund, Anders; Howard, Ron

    2015-04-01

    In this project, Avure and ORNL evaluated the influence of hot isostatic pressing (HIP) and thermal cycling as standalone post processing techniques on the microstructure of electron beam powder bed deposited Ti-6Al-4V and Inconel 718 alloys. Electron beam powder bed deposition is an effective technology for fabricating complex net shape components that cannot be manufactured with conventional processes. However, material deposited by this technology results in columnar grain growth which is detrimental for many applications. For Ti-6Al-4V, it has been found that thermal cycling alone is not sufficient to breakdown the columnar microstructure that is typical of electron beam powder bed technology. HIP, on the other hand, has the potential to be an effective technique to break down the columnar microstructure of Ti-6Al-4V into a more equiaxed and refined β grain structure, and provide a more homogeneous microstructure compared to the thermally cycled samples. Overall, the project showed that hot isostatic pressing reduced/eliminated porosity in both Ti-6Al-4V and Inconel 718 However, based on the unique thermal cycle and the application of pressure in the HIP vessel, Ti-6Al-4V e-beam deposited microstructures were modified from columnar grain growth to equiaxed microstructures; a significant outcome to this collaboration. Inconel 718, on the other hand, shows no change in the macrostructure as a result of the current HIP cycle based on the thermal history, and would require further investigation. Though the results of HIP cycle were very good at changing the microstructure, further development in optimizing the post heat treatments and HIP cycles is required to improve mechanical properties.

  2. Microstructure evolution of Al/Mg butt joints welded by gas tungsten arc with Zn filler metal

    SciTech Connect

    Liu Fei; Zhang Zhaodong; Liu Liming

    2012-07-15

    Based on the idea of alloying welding seam, Gas tungsten arc welding method with pure Zn filler metal was chosen to join Mg alloy and Al alloy. The microstructures, phases, element distribution and fracture morphology of welding seams were examined. The results indicate that there was a transitional zone in the width of 80-100 {mu}m between the Mg alloy substrate and fusion zone. The fusion zone was mainly composed of MgZn{sub 2}, Zn-based solid solution and Al-based solid solution. The welding seam presented distinct morphology in different location owning to the quite high cooling rate of the molten pool. The addition of Zn metal could prevent the formation of Mg-Al intermetallics and form the alloyed welding seam during welding. Therefore, the tensile strengths of joints have been significantly improved compared with those of gas tungsten arc welded joints without Zn metal added. Highlights: Black-Right-Pointing-Pointer Mg alloy AZ31B and Al alloy 6061 are welded successfully. Black-Right-Pointing-Pointer Zinc wire is employed as a filler metal to form the alloyed welding seam. Black-Right-Pointing-Pointer An alloyed welding seam is benefit for improving of the joint tensile strength.

  3. Black hole thermodynamics based on unitary evolutions

    NASA Astrophysics Data System (ADS)

    Feng, Yu-Lei; Chen, Yi-Xin

    2015-10-01

    In this paper, we try to construct black hole thermodynamics based on the fact that the formation and evaporation of a black hole can be described by quantum unitary evolutions. First, we show that the Bekenstein-Hawking entropy SBH may not be a Boltzmann or thermal entropy. To confirm this statement, we show that the original black hole's ‘first law’ may not simply be treated as the first law of thermodynamics formally, due to some missing metric perturbations caused by matter. Then, by including those (quantum) metric perturbations, we show that the black hole formation and evaporation can be described effectively in a unitary manner, through a quantum channel between the exterior and interior of the event horizon. In this way, the paradoxes of information loss and firewall can be resolved effectively. Finally, we show that black hole thermodynamics can be constructed in an ordinary way, by constructing statistical mechanics.

  4. Modeling microstructure evolution of binary systems subjected to irradiation and mechanical loading

    NASA Astrophysics Data System (ADS)

    Kharchenko, Dmitrii O.; Shchokotova, Olga M.; Lysenko, Irina O.; Kharchenko, Vasyl O.

    2015-07-01

    We study a change in mechanical properties of binary systems subjected to irradiation influence described by ballistic flux of atomic mixing having regular and stochastic contributions. By using numerical modeling based on the phase field approach we study dynamics of deformation fields in a previously irradiated system and in the binary system deformed during irradiation. An influence of both deterministic and stochastic components of ballistic flux onto both yield strength and ultimate strength is studied. We have found that degradation of mechanical properties relates to the formation of percolating clusters of shear bands. Considering a hardening coefficient we analyze stages of plastic deformation of both initially irradiated alloy and alloy subjected to sustained irradiation. Stability of binary alloy under mechanical loading in the form of shear strain with a constant rate and cyclic deformation is discussed.

  5. Analysis of Microstructure and Damage Evolution in Ultra-Thin Wires of the Magnesium Alloy MgCa0.8 at Multipass Drawing

    NASA Astrophysics Data System (ADS)

    Milenin, Andrij; Kustra, Piotr; Byrska-Wójcik, Dorota; Grydin, Olexandr; Schaper, Mirko; Mentlein, Thorben; Gerstein, Gregory; Nürnberger, Florian

    2016-12-01

    A combined multipass hot and cold drawing process was implemented to manufacture ultra-thin wires of the magnesium alloy MgCa0.8 with a final diameter of 0.05 mm. Numerical simulations were applied to design the drawing process of 40 passes regarding the microstructure evolution. To parametrize the model, in situ tensile tests were performed. Analysis of the MgCa0.8 wires featuring diameters below 0.1 mm revealed no intergranular crack initiation. The grain size of the ultra-thin wires is within the range of 30-500 nm with grains elongated in the drawing direction. The fine-grained microstructure provides high mechanical strength properties.

  6. Microstructure Evolution and Mechanical Properties of Rheo-Squeeze Cast Mg-9Al-1Zn Alloy by Experiments and Thermodynamic Calculation

    NASA Astrophysics Data System (ADS)

    Guo, Hong-Min; Zhang, Shu-Guo; Yang, Xiang-Jie; Liu, Xu-Bo; Jin, Hua-Lan

    2015-05-01

    Microstructure evolution and mechanical properties of Mg-9Al-1Zn alloy produced by rheo-squeeze casting (R-SQC) were investigated. It was revealed that R-SQC has produced high integrity castings with fine and uniform microstructure, diminished defects, and improved mechanical properties. The solid content in semi-solid slurry determined the grain size of α-Mg phase, the volume content, and distribution of β-Mg17Al12 phase, and predominantly controlled the mechanical properties. A two-stage thermodynamic calculation procedure to analyze R-SQC has been developed, and the solidification path and phase formation of Mg-9Al-1Zn alloy in R-SQC were discussed deeply.

  7. Microstructural evolution at the bonding interface during the early-stage infrared active brazing of alumina

    NASA Astrophysics Data System (ADS)

    Shiue, R. K.; Wu, S. K.; O, J. M.; Wang, J. Y.

    2000-10-01

    Infrared brazing of Al2O3 and alloy 42 using a silver-base active braze alloy was investigated at 900 °C for 0 to 300 seconds, with a heating rate of 3000 °C/min. Experimental results show that Ti3(Cu, Al)3O intermetallic with various amounts of Al is observed in the reaction layer and plays an important role in the early stage of reactive wetting. A two-layer structure is observed at the reaction interface brazed at 900 °C for 5 seconds. The reaction layer close to the alumina contains large amounts of Al, so the mass balance of the system is maintained. The growth of the reaction layer is not rate controlled by diffusion within the first 120 seconds. After 120 seconds, the rate controlling mechanism of the reaction layer becomes the diffusion control, satisfying the parabolic law. Dynamic wetting angle measurements using a traditional vacuum furnace at the heating rate of 10 °C/min demonstrate that the wetting angle rapidly decreases within the first 150 seconds, especially 0 to 80 seconds, and eventually stabilizes after 600 seconds.

  8. Microstructural evolution and mechanical properties of high strength magneisum alloys fabricated by deformation processing

    NASA Astrophysics Data System (ADS)

    Mansoor, Bilal

    The goal of this research was to develop high strength Mg by thermo-mechanical processing. Several novel techniques were developed to impart large plastic strains on Mg alloys and Mg based composites. The main emphasis of this work was on investigating the effect of different processing schemes on grain-refinement and texture modification of processed material. The room-temperature and elevated-temperature mechanical behavior of processed-Mg was studied in detail. Biaxial corrugated pressing, also known as alternate biaxial reverse corrugation processing was applied to twin-roll cast AZ31 Mg and warm-extruded ZK60 Mg. Friction stir processing to partial depths was applied to thixomolded AM60 Mg and warm-extruded ZK60 Mg. A new process called "bending reverse-bending", was developed and applied to hot rolled AZ31-H24 Mg. A Mg/Al laminated composite was developed by hot pressing and rolling. In processed condition, Mg alloys exhibit enhancement in room-temperature strength and ductility, as well as elevated temperature formability. It was concluded that improvement in mechanical properties of processed-Mg is strongly influenced by grain size and precipitates; while ductility largely depends on resulting deformation textures.

  9. Improved microstructure of cement-based composites through the addition of rock wool particles

    SciTech Connect

    Lin, Wei-Ting; Cheng, An; Huang, Ran; Zou, Si-Yu

    2013-10-15

    Rock wool is an inorganic fibrous substance produced by steam blasting and cooling molten glass. As with other industrial by-products, rock wool particles can be used as cementitious materials or ultra fine fillers in cement-based composites. This study investigated the microstructure of mortar specimens produced with cement-based composites that include various forms of rock wool particles. It conducted compressive strength testing, rapid chloride penetration tests, X-ray diffraction analysis, thermo-gravimetric analysis, and scanning electronic microscopy to evaluate the macro- and micro-properties of the cement-based composites. Test results indicate that inclusion of rock wool particles in composites improved compressive strength and reduced chloride ion penetration at the age of 91 days due to the reduction of calcium hydroxide content. Microscopic analysis confirms that the use of rock wool particles contributed to the formation of a denser, more compact microstructure within the hardened paste. In addition, X-ray diffraction analysis shows few changes in formation of pozzolanic reaction products and no new hydrations are formed with incorporating rock wool particles. - Highlights: • We report the microstructural characterization of cement-based composites. • Different mixes produced with various rock wool particles have been tested. • The influence of different mixes on macro and micro properties has been discussed. • The macro properties are included compressive strength and permeability. • XRD and SEM observations confirm the pozzolanic reaction in the resulting pastes.

  10. Managing BHJ microstructural evolution for long-term photoconversion efficiency (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Martinez Hardigree, Josue; Morse, Graham E.; Tiwana, Priti; Mazzotta, Giulio; Ramirez, Ivan R.; Nicklin, Christopher L.; Lozman, Owen R.; Riede, Moritz K.

    2016-09-01

    In this presentation we evaluate the thermal and light-soaking stability of polymer:fullerene bulk heterojunctions (BHJs) based on a donor polymer recently developed by Merck Chemicals. Blade-coated thin films of pure polymer and BHJs incorporating either PC61BM or PC71BM were investigated using atomic force microscopy (AFM), grazing-incidence x-ray diffraction (GIXD), neutron reflectivity (NR), and UV-Visible spectroscopy. The addition of fullerene to the polymer at device-relevant concentrations (25-50% by weight) results in a 7-fold reduction in surface roughness relative to pure polymer films, attributed to a reduction in the pure polymer domain size with increasingly homogeneous polymer:fullerene mixing. Films subjected to accelerated stressing relevant to scalable OPV fabrication—thermal stressing at 120 °C for 1 hour or light-soaking under AM1.5 light for 8 hours—indicate robust stability to stressing, with thin films showing marginal but monotonic increases in roughness with increasing fullerene concentration. Wide-angle GIXD measurements indicate a contraction of 1-4% in features attributed to polymer crystalline domains upon annealing. Comparison of pre-and post-annealed films reveals increased correlation between polymer scattering features in the latter, consistent with improved ordering of the polymer backbone and sidechains. These findings, together with GIXD measurements of full device stacks and accelerated aging measurements of operational cells, support recent reports on the high photoconversion efficiency stability of this polymer BHJ system for highly scalable, long-lifetime OPVs.

  11. A surface intrinsic feature based method (SIFBM) for the characterization of optical microstructure

    NASA Astrophysics Data System (ADS)

    Cheung, C. F.; Kong, L. B.; Lee, W. B.; To, S.

    2008-12-01

    Optical microstructures are small scale topologies which are generally classified as grooves, pyramids, microlens arrays, lenticulations, echells, etc. They are widely used in advanced optics applications. Currently, there is lack of methods for the characterization of surface quality for optical microstructures with sub-micromenter form accuracy and surface finish in the nanometer range. This paper presents a Surface Intrinsic Feature Based Method (SIFBM) which makes use of surface intrinsic properties such as curvatures, normal vectors, torsion, intrinsic frames, etc. They are mapped as special images and image processing techniques are then employed to conduct image registration or correspondences searching by some algorithms such as correlation functions. The surface matching is optimized by corresponding vectors deviations. In the present study, a prototype surface characterization system has been built based on the SIFBM. Primary experimental work has been conducted to validate the proposed method. The results demonstrate that the SIFBM has potential advantages over existing methods.

  12. Microstructure-strength relationships of heavily deformed Cu-based composites

    SciTech Connect

    Trybus, C.L.

    1988-01-01

    Heavily deformed Cu-based composites attain anomalous increases in strength upon mechanical deformation. The unique filamentary microstructures that evolve during processing (cold rolling, wire drawing or swaging) are the source of the strengthening. Composite strength is correlated to microstructural characteristics for arc-melted Cu-20 vol.% Nb cold rolled up to a true strain of 6.9. During rolling Nb elongates and becomes ribbon-like while the Cu matrix undergoes a cycle of deformation-dynamic recovery-recrystallization which allows for the further reduction of the Nb. Longitudinal and transverse specimens have equivalent mechanical properties. The ultimate tensile strength of the sheet showed a weak dependence on Nb filament spacing and its strength is controlled by a dislocation propagation mechanism. The feasibility of producing heavily deformed Cu-based composites via powder metallurgical processing techniques is explored because of the wider range of composite compositions which can be produced in contrast with ingot metallurgy.

  13. Microstructure and abrasive wear of cobalt-based laser coatings

    SciTech Connect

    de Mol van Otterloo, J.L.; De Hosson, J.T.M.

    1997-01-15

    Cobalt-based alloys are used as wear-resistant materials for hardfacing cheap steel substrates. A substantial enhancement in mechanical properties of cobalt-based superalloys is attributed to the martensitic fcc {yields} hcp phase transformation. Alloying elements can be classified as phase modifiers (Ni and Fe stabilize fcc whereas W and Cr stabilize hcp), solid-solution strengtheners (W and Mo), which affect only the matrix, and elements that form carbides (Cr-rich M{sub 7}C{sub 3} and M{sub 23}C{sub 6}, M = metal). Of the different depositing techniques such as plasma spray, tungsten inert gas, oxyacetylene flame and laser cladding, the latter delivers coatings with a low dilution with the substrate material and no pores. Moreover, the laser cladding process has the advantage of being well controllable. This paper reports on the deposition of five different cobalt-based Stellite alloys on steel substrates by laser cladding.

  14. Microstructure, texture evolution and magnetic properties of strip-casting non-oriented 6.5 wt.% Si electrical steel doped with cerium

    SciTech Connect

    Li, Hao-Ze Liu, Hai-Tao; Liu, Zhen-Yu Wang, Guo-Dong

    2015-05-15

    A 0.3 mm thick non-oriented 6.5 wt.% Si electrical steel sheet doped with cerium is produced by twin-roll strip casting, hot rolling, warm rolling and annealing. A detailed study of the cerium precipitates in the as-cast strip, microstructure and texture evolution at different processing stages is carried out by electron probe micro-analysis, optical microscopy, X-ray diffraction and electron backscattered diffraction analysis. Grain interior distributing precipitates identified as Ce-oxides, Ce-oxysulfides and Ce-phosphides, and boundary distributing Ce-oxides and Ce-phosphides are observed in the as-cast strip. The initial as-cast strip is characterized by a much finer solidification microstructure and dominated by obvious < 001 >//ND texture through the strip thickness. After hot and warm rolling, inhomogeneous microstructure containing large amounts of in-grain shear bands is characterized by mixed < 110 >//RD and < 111 >//ND textures. The texture of the annealed sheet with a relatively large average grain size is far more optimized by the domination of the beneficial cube, rotated cube, (001)< 120 > to (001)< 130 > and Goss texture components, and the elimination of the detrimental γ-fiber texture, leading to a superior magnetic induction and improved iron loss. - Highlights: • An Fe–6.5 wt.% Si as-cast strip doped with cerium was produced. • A thin warm rolled sheet with limited edge cracks was obtained. • Microstructure and texture evolution at each stage were investigated. • Strong λ-fiber and Goss recrystallization textures were formed. • The magnetic properties of the annealed sheet were significantly improved.

  15. Microstructural development and segregation effects in directionally solidified nickel-based superalloy PWA 1484

    NASA Astrophysics Data System (ADS)

    Li, Lichun

    2002-09-01

    These studies were performed to investigate the effects of thermal gradient (G) and growth velocity (V) on the microstructure development and solidification behavior of directionally solidified nickel-based superalloy PWA 1484. Directional solidification (DS) experiments were conducted using a Bridgman crystal growth facility. The solidification velocity ranged from 0.00005 to 0.01 cm/sec and thermal gradients ranged from 12 to 108°C/cm. The as-cast microstructures of DS samples were characterized by using conventional metallography; chemical composition and segregation of directionally solidified samples were analyzed with energy dispersive spectroscopy in SEM. A range of aligned solidification microstructures is exhibited by the alloy when examined as-cast at room temperature: dendrites, flanged cells, cells. The microstructure transitions from cellular to dendritic as the growth velocity increases. The experimental data for PWA1484 exhibits excellent agreement with the well-known exponential equation (lambda1 ∝ G -1/2V-1/4). However, the constant of proportionality is different depending upon the solidification microstructure: (1) dendritic growth with secondary arms leads to a marked dependence of lambda1 on G-1/2 V-1/4; (2) flanged cellular growth with no secondary arms leads to much lower dependence of lambda 1 on G-1/2V -1/4. The primary dendritic arm spacing results were also compared to recent theoretical models. The model of Hunt and Lu and the model of Ma and Sahm provided excellent agreement at medium to high thermal gradients and a wide range of solidification velocities. The anomalous behavior of lambda 1 with high growth velocity V at low G is analyzed based on the samples' microstructures. Off-axis heat flows were shown to cause radial non-uniformity in the dendrite arm spacing data for low thermal gradients and large withdrawal velocities. Various precipitates including gamma', (gamma ' + gamma) eutectic pool or divorced eutectic gamma ', and

  16. Effect of Processing Scheme on Precipitation Mechanisms and Evolution of Microstructures and Properties of CuAgZr alloy

    NASA Astrophysics Data System (ADS)

    Piyawit, Waraporn

    CuAgZr alloy is a variant of the CuAg alloy that is developed for high strength and high conductivity applications. With Zr addition, the discontinuous precipitation at the grain boundaries is decreased due to slower Ag diffusion rate. Mechanical and electrical properties of copper alloys can be influenced by many factors including alloying elements, mechanical processing, heat treatment and their microstructures. For high strength and high conductivity applications, Cu-Ag alloys are one of the good candidate materials for these used because of their excellent combinations of high strength and high electrical conductivity. The primary strengthening mechanism is precipitation hardening due to the formation of Ag precipitates during the heat treatment process. Its strengthening is accomplished mainly by the precipitation of Ag precipitates, which tend to align on the {111} planes in the Cu matrix. The evolutions of hardness and electrical conductivity of the aged samples showed that the Ag particles precipitated out from the Cu matrix in the early stage of aging. The hardness of the aged samples is significantly increased from 95 HV0.1 to the maximum at 193 HV0.1 after 2 hours of aging. The density of Ag precipitates is increased with increased aging time. Ag precipitation occurs in particular Cu matrix planes due to the minimization of elastic energy. The Ag precipitates were formed by clustering of Ag atoms while maintaining the fcc crystal structure of the matrix. They have faceted {111} interfaces with the matrix. The thickening of the precipitates appears to be by the ledge growth mechanism, which is promoted by misfit dislocation networks on the interface. The ledge movement and growth were compensated with the existence of interfacial misfit dislocations. During diffusional growth, misfit dislocation arrays along the precipitate/matrix interface accommodated the lattice mismatch. Therefore, precipitate growth involves the formation and migration of ledges

  17. Melanin-based color of plumage: role of condition and of feathers' microstructure

    USGS Publications Warehouse

    D'Alba, Liliana; Van Hemert, Caroline R.; Spencer, Karen A.; Heidinger, Britt J.; Gill, Lisa; Evans, Neil P.; Monaghan, Pat; Handel, Colleen M.; Shawkey, Matthew D.

    2014-01-01

    Whether melanin-based colors honestly signal a bird's condition during the growth of feathers is controversial, and it is unclear if or how the physiological processes underlying melanogenesis or color-imparting structural feather microstructure may be adversely affected by condition. Here we report results from two experiments designed to measure the effect of condition on expression of eumelanic and pheomelanic coloration in black-capped chickadees (Poecile atricapillus) and zebra finches (Taeniopygia guttata), respectively. In chickadees, we compared feathers of birds affected and unaffected by avian keratin disorder, while in zebra finches we compared feathers of controls with feathers of those subjected to an unpredictable food supply during development. In both cases we found that control birds had brighter feathers (higher total reflectance) and more barbules, but similar densities of melanosomes. In addition, the microstructure of the feathers explained variation in color more strongly than did melanosome density. Together, these results suggest that melanin-based coloration may in part be condition-dependent, but that this may be driven by changes in keratin and feather development, rather than melanogenesis itself. Researchers should be cautious when assigning variation in melanin-based color to melanin alone and microstructure of the feather should be taken into account.

  18. Melanin-based color of plumage: role of condition and of feathers' microstructure.

    PubMed

    D'Alba, Liliana; Van Hemert, Caroline; Spencer, Karen A; Heidinger, Britt J; Gill, Lisa; Evans, Neil P; Monaghan, Pat; Handel, Colleen M; Shawkey, Matthew D

    2014-10-01

    Whether melanin-based colors honestly signal a bird's condition during the growth of feathers is controversial, and it is unclear if, or how, the physiological processes underlying melanogenesis or the role of the microstructure of feathers in imparting structural color to feathers may be adversely affected by condition. Here, we report results from two experiments designed to measure the effect of condition on expression of eumelanic and pheomelanic coloration in black-capped chickadees (Poecile atricapillus) and zebra finches (Taeniopygia guttata), respectively. In chickadees, we compared feathers of birds affected and unaffected by avian keratin disorder, whereas in zebra finches we compared feathers of controls with feathers of those subjected to an unpredictable food supply during development. In both cases, we found that control birds had brighter feathers (higher total reflectance) and more barbules, but similar densities of melanosomes. In addition, the microstructure of the feathers explained variation in color more strongly than did melanosome density. Together, these results suggest that melanin-based coloration may in part be condition-dependent, but that this may be driven by changes in keratin and feather development, rather than melanogenesis itself. Researchers should be cautious when assigning variation in melanin-based color to melanin alone and microstructure of the feather should be taken into account.

  19. Simulated evolution of the vertebral body based on basic multicellular unit activities.

    PubMed

    Wang, Chao; Zhang, Chunqiu; Han, Jingyun; Wu, Han; Fan, Yubo

    2011-07-01

    A numerical model based on the theory of bone remodeling is proposed to predict the evolution of trabecular bone architecture within the vertebral body and to investigate the process of degeneration in vertebral bone. In this study, particular attention is paid on the description of microstructure changes during the aging process. To take into account the effect of basic multicellular units (BMUs), a set of computational algorithms has been developed. It is assumed that BMU activation probability depends on the state of damaged bone tissue (damage accumulation, ω), which is evaluated according to previous research concerning bone fatigue damage. Combining these algorithms with the finite-element method (FEM), the microstructure of vertebral bone has been predicted for up to 8 simulated years. Moreover, biomechanical material properties have been monitored to investigate the changes of vertebral bone with age. This study shows that the simulation based on BMU activities has the potential to define and predict the morphological evolution of the vertebral body. It can be concluded that the novel algorithms incorporating the coupled effects of both adaptive remodeling and microdamage remodeling could be utilized to gain greater insight into the mechanism of bone loss in the elderly population.

  20. Evolution-Based Functional Decomposition of Proteins.

    PubMed

    Rivoire, Olivier; Reynolds, Kimberly A; Ranganathan, Rama

    2016-06-01

    The essential biological properties of proteins-folding, biochemical activities, and the capacity to adapt-arise from the global pattern of interactions between amino acid residues. The statistical coupling analysis (SCA) is an approach to defining this pattern that involves the study of amino acid coevolution in an ensemble of sequences comprising a protein family. This approach indicates a functional architecture within proteins in which the basic units are coupled networks of amino acids termed sectors. This evolution-based decomposition has potential for new understandings of the structural basis for protein function. To facilitate its usage, we present here the principles and practice of the SCA and introduce new methods for sector analysis in a python-based software package (pySCA). We show that the pattern of amino acid interactions within sectors is linked to the divergence of functional lineages in a multiple sequence alignment-a model for how sector properties might be differentially tuned in members of a protein family. This work provides new tools for studying proteins and for generally testing the concept of sectors as the principal units of function and adaptive variation.