The Experts below are selected from a list of 1470 Experts worldwide ranked by ideXlab platform
L Malerba - One of the best experts on this subject based on the ideXlab platform.
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effect of cr atoms on the formation of double kinks in screw dislocations in fe and its correlation with Solute Hardening and softening in fe cr alloys
2008Co-Authors: D A Terentyev, L MalerbaAbstract:Abstract In this work, we employed atomistic simulations to study the formation of a double kink (DK) on a screw dislocation in bcc Fe and to investigate how the presence of Cr affects it, using one of the most recent and reliable interatomic potentials for Fe and Fe–Cr systems (i.e. from Refs. [G.J. Ackland, M.I. Mendelev, D.J. Srolovitz, S. Han, A.V. Barashev, J. Phys.: Condens. Mat. 16 (2004) 1, P. Olsson, J. Wallenius, C. Domain, K. Nordlund, L. Malerba, Phys. Rev. B 72 (2005) 214119]). The formation energy of a DK of different lengths and structures, as well as the formation energies of each single kink and the interaction energies between them, have been obtained by performing large scale atomistic simulations and compared with the results obtained from elasticity theory. We show that the presence of Cr atoms, particularly Cr–Cr pairs, affects, sometimes significantly, the formation energy of DKs. The obtained results suggest a strong dependence of the effect of Solute Cr atoms on dislocation motion in Fe–Cr alloys, depending on the actual Cr distribution, which in turn depends strongly on concentration and temperature. A possible framework to understand Solute softening and Hardening experimentally observed in Fe–Cr alloys is accordingly discussed.
E P George - One of the best experts on this subject based on the ideXlab platform.
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recovery recrystallization grain growth and phase stability of a family of fcc structured multi component equiatomic solid solution alloys
2014Co-Authors: Hongbin Bei, F Otto, G M Pharr, E P GeorgeAbstract:Abstract The equiatomic high-entropy alloy FeNiCoCrMn is known to crystallize as a single phase with the face-centered cubic (FCC) crystal structure. To better understand this quinary solid solution alloy, we investigate various binary, ternary and quaternary alloys made from its constituent elements. Our goals are twofold: ( i ) to investigate which of these lower order systems also form solid solution alloys consisting of a single FCC phase, and ( ii ) to characterize their phase stability and recovery, recrystallization, and grain growth behaviors. X-ray diffraction (XRD) and scanning electron microscopy with backscattered electron images showed that three of the five possible quaternaries (FeNiCoCr, FeNiCoMn and NiCoCrMn), five of the ten possible ternaries (FeNiCo, FeNiCr, FeNiMn, NiCoCr, and NiCoMn), and two of the ten possible binaries (FeNi and NiCo) were single-phase FCC solid solutions in the cast and homogenized condition, whereas the others either had different crystal structures or were multi-phase. The single-phase FCC quaternary, FeNiCoCr, along with its equiatomic ternary and binary subsidiaries, were selected for further investigations of phase stability and the thermomechanical processing needed to obtain equiaxed grain structures. Only four of these subsidiary alloys—two binaries (FeNi and NiCo) and two ternaries (FeNiCo and NiCoCr)—were found to be single-phase FCC after rolling at room temperature followed by annealing for 1 h at temperatures of 300–1100 °C. Pure Ni, which is FCC and one of the constituents of the quinary high-entropy alloy (FeNiCoCrMn), was also investigated for comparison with the higher order alloys. Among the materials investigated after thermomechanical processing (FeNiCoCr, FeNiCo, NiCoCr, FeNi, NiCo, and Ni), FeNiCo and Ni showed abnormal grain growth at relatively low annealing temperatures, while the other four showed normal grain growth behavior. The grain growth exponents for all five of the equiatomic alloys were found to be ∼0.25 (compared to ∼0.5 for unalloyed Ni), suggesting that Solute drag may control grain growth in the alloys. For all five alloys, as well as for pure Ni, microhardness increases as the grain size decreases in a Hall-Petch type way. The ternary alloy NiCoCr was the hardest of the alloys investigated in this study, even when compared to the quaternary FeNiCoCr alloy. This suggests that Solute Hardening in equiatomic alloys depends not just on the number of alloying elements but also their type.
D A Terentyev - One of the best experts on this subject based on the ideXlab platform.
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effect of cr atoms on the formation of double kinks in screw dislocations in fe and its correlation with Solute Hardening and softening in fe cr alloys
2008Co-Authors: D A Terentyev, L MalerbaAbstract:Abstract In this work, we employed atomistic simulations to study the formation of a double kink (DK) on a screw dislocation in bcc Fe and to investigate how the presence of Cr affects it, using one of the most recent and reliable interatomic potentials for Fe and Fe–Cr systems (i.e. from Refs. [G.J. Ackland, M.I. Mendelev, D.J. Srolovitz, S. Han, A.V. Barashev, J. Phys.: Condens. Mat. 16 (2004) 1, P. Olsson, J. Wallenius, C. Domain, K. Nordlund, L. Malerba, Phys. Rev. B 72 (2005) 214119]). The formation energy of a DK of different lengths and structures, as well as the formation energies of each single kink and the interaction energies between them, have been obtained by performing large scale atomistic simulations and compared with the results obtained from elasticity theory. We show that the presence of Cr atoms, particularly Cr–Cr pairs, affects, sometimes significantly, the formation energy of DKs. The obtained results suggest a strong dependence of the effect of Solute Cr atoms on dislocation motion in Fe–Cr alloys, depending on the actual Cr distribution, which in turn depends strongly on concentration and temperature. A possible framework to understand Solute softening and Hardening experimentally observed in Fe–Cr alloys is accordingly discussed.
Michael L Falk - One of the best experts on this subject based on the ideXlab platform.
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atomistic simulation of solid solution Hardening in mg al alloys examination of composition scaling and thermo mechanical relationships
2016Co-Authors: Peng Yi, R C Cammarata, Michael L FalkAbstract:Abstract Dislocation mobility in a solid solution was studied using atomistic simulations of an Mg/Al system. The critical resolved shear stress (CRSS) for the dislocations on the basal plane was calculated at temperatures from 0 K to 500 K with Solute concentrations from 0 to 7 at%, and with four different strain rates. Solute Hardening of the CRSS is decomposed into two contributions: one scales with c2/3, where c is the Solute concentration, and the other scales with c1. The former was consistent with the Labusch model for local Solute obstacles, and the latter was related to the athermal plateau stress due to the long range Solute effect. A thermo-mechanical model was then used to analyze the temperature and strain rate dependences of the CRSS, and it yielded self-consistent and realistic results. The scaling laws were confirmed and the thermo-mechanical model was successfully parameterized using experimental measurements of the CRSS for Mg/Al alloys under quasi-static conditions. The predicted strain rate sensitivity from the experimental measurements of the CRSS is in reasonable agreement with separate mechanical tests. The concentration scaling and the thermo-mechanical relationships provide a potential tool to analytically relate the structural and thermodynamic parameters on the microscopic level with the macroscopic mechanical properties arising from dislocation mediated deformation.
G M Pharr - One of the best experts on this subject based on the ideXlab platform.
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recovery recrystallization grain growth and phase stability of a family of fcc structured multi component equiatomic solid solution alloys
2014Co-Authors: Hongbin Bei, F Otto, G M Pharr, E P GeorgeAbstract:Abstract The equiatomic high-entropy alloy FeNiCoCrMn is known to crystallize as a single phase with the face-centered cubic (FCC) crystal structure. To better understand this quinary solid solution alloy, we investigate various binary, ternary and quaternary alloys made from its constituent elements. Our goals are twofold: ( i ) to investigate which of these lower order systems also form solid solution alloys consisting of a single FCC phase, and ( ii ) to characterize their phase stability and recovery, recrystallization, and grain growth behaviors. X-ray diffraction (XRD) and scanning electron microscopy with backscattered electron images showed that three of the five possible quaternaries (FeNiCoCr, FeNiCoMn and NiCoCrMn), five of the ten possible ternaries (FeNiCo, FeNiCr, FeNiMn, NiCoCr, and NiCoMn), and two of the ten possible binaries (FeNi and NiCo) were single-phase FCC solid solutions in the cast and homogenized condition, whereas the others either had different crystal structures or were multi-phase. The single-phase FCC quaternary, FeNiCoCr, along with its equiatomic ternary and binary subsidiaries, were selected for further investigations of phase stability and the thermomechanical processing needed to obtain equiaxed grain structures. Only four of these subsidiary alloys—two binaries (FeNi and NiCo) and two ternaries (FeNiCo and NiCoCr)—were found to be single-phase FCC after rolling at room temperature followed by annealing for 1 h at temperatures of 300–1100 °C. Pure Ni, which is FCC and one of the constituents of the quinary high-entropy alloy (FeNiCoCrMn), was also investigated for comparison with the higher order alloys. Among the materials investigated after thermomechanical processing (FeNiCoCr, FeNiCo, NiCoCr, FeNi, NiCo, and Ni), FeNiCo and Ni showed abnormal grain growth at relatively low annealing temperatures, while the other four showed normal grain growth behavior. The grain growth exponents for all five of the equiatomic alloys were found to be ∼0.25 (compared to ∼0.5 for unalloyed Ni), suggesting that Solute drag may control grain growth in the alloys. For all five alloys, as well as for pure Ni, microhardness increases as the grain size decreases in a Hall-Petch type way. The ternary alloy NiCoCr was the hardest of the alloys investigated in this study, even when compared to the quaternary FeNiCoCr alloy. This suggests that Solute Hardening in equiatomic alloys depends not just on the number of alloying elements but also their type.