The Experts below are selected from a list of 2094 Experts worldwide ranked by ideXlab platform
Kris A. Darling - One of the best experts on this subject based on the ideXlab platform.
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Isothermal Annealing of a Thermally Stabilized Fe-Based Ferritic Alloy
Journal of Materials Engineering and Performance, 2015Co-Authors: Hasan Kotan, Kris A. DarlingAbstract:In this study, the stability and microstructural evolution, including grain size and hardness of nanocrystalline Fe_91Ni_8Zr_1 alloyed powders, produced by ball milling, were investigated after annealing at 900 and 1000 °C for up to 24 h. Results indicate that rapid grain growth to the micron scale occurs within the first few minutes of exposure to the elevated annealing temperatures. However, despite the loss of nanocrystallinity, an extremely stable and efficient hardening effect persists, which has been found to be equal to that predicted by Hall-Petch Strengthening even at the smallest grain sizes. The mechanical properties of the samples consolidated to bulk via equal channel angular extrusion at 900 °C were evaluated by uniaxial compression at room and elevated temperatures. Results reveal high compressive yield stress as well as the appearance and disappearance of a yield drop indicating the presence of coherent (GP zone like) precipitates within the microstructure. Such a hardening mechanism has implications for developing new Fe-Ni-based alloys exhibiting a combination of high strength and ductility for high temperature applications.
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Isothermal Annealing of a Thermally Stabilized Fe-Based Ferritic Alloy
Journal of Materials Engineering and Performance, 2015Co-Authors: Hasan Kotan, Kris A. DarlingAbstract:In this study, the stability and microstructural evolution, including grain size and hardness of nanocrystalline Fe91Ni8Zr1 alloyed powders, produced by ball milling, were investigated after annealing at 900 and 1000 °C for up to 24 h. Results indicate that rapid grain growth to the micron scale occurs within the first few minutes of exposure to the elevated annealing temperatures. However, despite the loss of nanocrystallinity, an extremely stable and efficient hardening effect persists, which has been found to be equal to that predicted by Hall-Petch Strengthening even at the smallest grain sizes. The mechanical properties of the samples consolidated to bulk via equal channel angular extrusion at 900 °C were evaluated by uniaxial compression at room and elevated temperatures. Results reveal high compressive yield stress as well as the appearance and disappearance of a yield drop indicating the presence of coherent (GP zone like) precipitates within the microstructure. Such a hardening mechanism has implications for developing new Fe-Ni-based alloys exhibiting a combination of high strength and ductility for high temperature applications.
Hasan Kotan - One of the best experts on this subject based on the ideXlab platform.
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Isothermal Annealing of a Thermally Stabilized Fe-Based Ferritic Alloy
Journal of Materials Engineering and Performance, 2015Co-Authors: Hasan Kotan, Kris A. DarlingAbstract:In this study, the stability and microstructural evolution, including grain size and hardness of nanocrystalline Fe_91Ni_8Zr_1 alloyed powders, produced by ball milling, were investigated after annealing at 900 and 1000 °C for up to 24 h. Results indicate that rapid grain growth to the micron scale occurs within the first few minutes of exposure to the elevated annealing temperatures. However, despite the loss of nanocrystallinity, an extremely stable and efficient hardening effect persists, which has been found to be equal to that predicted by Hall-Petch Strengthening even at the smallest grain sizes. The mechanical properties of the samples consolidated to bulk via equal channel angular extrusion at 900 °C were evaluated by uniaxial compression at room and elevated temperatures. Results reveal high compressive yield stress as well as the appearance and disappearance of a yield drop indicating the presence of coherent (GP zone like) precipitates within the microstructure. Such a hardening mechanism has implications for developing new Fe-Ni-based alloys exhibiting a combination of high strength and ductility for high temperature applications.
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Isothermal Annealing of a Thermally Stabilized Fe-Based Ferritic Alloy
Journal of Materials Engineering and Performance, 2015Co-Authors: Hasan Kotan, Kris A. DarlingAbstract:In this study, the stability and microstructural evolution, including grain size and hardness of nanocrystalline Fe91Ni8Zr1 alloyed powders, produced by ball milling, were investigated after annealing at 900 and 1000 °C for up to 24 h. Results indicate that rapid grain growth to the micron scale occurs within the first few minutes of exposure to the elevated annealing temperatures. However, despite the loss of nanocrystallinity, an extremely stable and efficient hardening effect persists, which has been found to be equal to that predicted by Hall-Petch Strengthening even at the smallest grain sizes. The mechanical properties of the samples consolidated to bulk via equal channel angular extrusion at 900 °C were evaluated by uniaxial compression at room and elevated temperatures. Results reveal high compressive yield stress as well as the appearance and disappearance of a yield drop indicating the presence of coherent (GP zone like) precipitates within the microstructure. Such a hardening mechanism has implications for developing new Fe-Ni-based alloys exhibiting a combination of high strength and ductility for high temperature applications.
X H Zeng - One of the best experts on this subject based on the ideXlab platform.
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a simple dislocation model of deformation resistance of ultrafine grained materials explaining hall petch Strengthening and enhanced strain rate sensitivity
Acta Materialia, 2009Co-Authors: W Blum, X H ZengAbstract:A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the deformation resistance is independent of strain, that the strain rate sensitivity of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of grain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni.
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A simple dislocation model of deformation resistance of ultrafine-grained materials explaining Hall–Petch Strengthening and enhanced strain rate sensitivity
Acta Materialia, 2009Co-Authors: W Blum, X H ZengAbstract:A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the deformation resistance is independent of strain, that the strain rate sensitivity of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of grain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni.
C. S. Pande - One of the best experts on this subject based on the ideXlab platform.
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Deformation and Coble Creep of Nanocrystalline Materials
MRS Proceedings, 2002Co-Authors: C. S. Pande, Robert A. MasumuraAbstract:ABSTRACTModeling of Strengthening by nanocrystalline materials need consideration of dislocation interactions and sliding due to Coble creep, both of which may be acting simultaneously. Such a mechanism is considered in this paper. It is shown that a model based on using Coble creep (with a threshold stress) for finer grains and conventional Hall-Petch Strengthening for larger grains, appears to be most successful in explaining experimental results provided care is taken to incorporate into the analysis the effect of grain size distribution occurring in most specimens. A generalized expression relating yield stress to grain size is also proposed.
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YIELD STRESS OF NANOCRYSTALLINE MATERIALS
2002Co-Authors: C. S. Pande, Robert A. Masumura, P M HazzledineAbstract:Modeling of Strengthening by nanocrystalline materials need consideration of both dislocation interactions and sliding due to Coble creep acting simultaneously. Such a mechanism is considered in this paper. It is shown that a model based on using Coble creep (with a threshold stress) for finer grains and conventional Hall-Petch Strengthening for larger grains, appears to be most successful in explaining experimental results provided a grain size distribution is incorporated into the analysis to account for a distribution of grain sizes occurring in most specimens. Use of an alternate formalism of Coble creep proposed recently gives a somewhat less satisfactory agreement with experiments.
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yield stress of fine grained materials
Acta Materialia, 1998Co-Authors: Robert A. Masumura, P M Hazzledine, C. S. PandeAbstract:Abstract A model is proposed for the yield stress of ultra-fine grained materials based upon Coble creep. Using Coble creep with a threshold stress for finer grains and conventional Hall–Petch Strengthening for larger grains, an analytical relation is derived for the yield stress as a function of grain size for a range from very large to very small. A grain size distribution is incorporated into the analysis to account for a distribution of grain sizes occurring in most specimens. This result is compared with experimental data from Cu and NiP and shown to be in good agreement.
W Blum - One of the best experts on this subject based on the ideXlab platform.
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Temperature dependence of the strength of fine- and ultrafine-grained materials
Acta Materialia, 2011Co-Authors: Joachim Schneibel, Martin Heilmaier, W Blum, G. Hasemann, T. ShanmugasundaramAbstract:Abstract The yield stress of oxide dispersion-strengthened (ODS) PM2000 steel and nanocluster-strengthened (NCS) 14YWT steel was measured as a function of temperature for grain sizes from 0.2 μm to ∞. In combination with data from the literature, it was found that the indirect Strengthening (i.e., the Hall–Petch Strengthening) for small grain sizes was often greater than the direct Strengthening (i.e., the Orowan Strengthening due to the dispersoids). The yield stress dropped significantly at a transition temperature near 500 °C even though the grain size remained constant. For small grain sizes, a large fraction of this drop was attributed to a decrease in grain size Strengthening. Three published models describing this effect were compared with the experimental data. The observed transition temperatures were consistent with two of them. The strength–temperature curves for PM2000 with different grain sizes tended to intersect, whereas those for 14YWT did not. Because of this feature, the description of the strength–temperature dependence of 14YWT could be narrowed down to a single model. It is concluded that ODS and NCS materials are well suited to examining the temperature dependence of grain size Strengthening.
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a simple dislocation model of deformation resistance of ultrafine grained materials explaining hall petch Strengthening and enhanced strain rate sensitivity
Acta Materialia, 2009Co-Authors: W Blum, X H ZengAbstract:A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the deformation resistance is independent of strain, that the strain rate sensitivity of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of grain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni.
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A simple dislocation model of deformation resistance of ultrafine-grained materials explaining Hall–Petch Strengthening and enhanced strain rate sensitivity
Acta Materialia, 2009Co-Authors: W Blum, X H ZengAbstract:A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the deformation resistance is independent of strain, that the strain rate sensitivity of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of grain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni.
