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Levente Vitos - One of the best experts on this subject based on the ideXlab platform.
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can experiment determine the stacking Fault Energy of metastable alloys
Materials & Design, 2021Co-Authors: Hualei Zhang, Levente Vitos, Xun Sun, Ruiwen Xie, Tianlong Zhang, Chuanxin Liang, Xiangdong Ding, Yunzhi WangAbstract:Abstract Stacking Fault Energy (SFE) plays an important role in deformation mechanisms and mechanical properties of face-centered cubic (fcc) metals and alloys. In many concentrated fcc alloys, the SFEs determined from density functional theory (DFT) calculations and experimental methods are found having opposite signs. Here, we show that the negative SFE by DFT reflects the thermodynamic instability of the fcc phase relative to the hexagonal close-packed one; while the experimentally determined SFEs are restricted to be positive by the models behind the indirect measurements. We argue that the common models underlying the experimental measurements of SFE fail in metastable alloys. In various concentrated solid solutions, we demonstrate that the SFEs obtained by DFT calculations correlate well with the primary deformation mechanisms observed experimentally, showing a better resolution than the experimentally measured SFEs. Furthermore, we believe that the negative SFE is important for understanding the abnormal behaviors of partial dislocations in metastable alloys under deformation. The present work advances the fundamental understanding of SFE and its relation to plastic deformations, and sheds light on future alloy design by physical metallurgy.
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effect of temperature on the stacking Fault Energy and deformation behaviour in 316l austenitic stainless steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019Co-Authors: Xun Sun, David Molnar, Goran Engberg, Levente VitosAbstract:The stacking Fault Energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial disloc ...
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Stacking Fault Energy of C-alloyed steels: The effect of magnetism
Acta Materialia, 2017Co-Authors: Song Lu, Ruihuan Li, Kalevi Kokko, Staffan Hertzman, Krisztina Kádas, Yanzhong Tian, Hualei Zhang, Qing-miao Hu, Se Kyun Kwon, Levente VitosAbstract:First-principles calculations have been performed to study the effect of C on the stacking Fault Energy (SFE) of paramagnetic γ-Fe and Fe[sbnd]Cr[sbnd]Ni austenitic steel. In these systems, the local magnetic structure is very sensitive to the volume in both fcc and hcp structures, which emphasizes the importance of the magnetovolume coupling effect on the SFE. The presence of C atom suppresses the local magnetic moments of Fe atoms in the first coordination shell of C. Compared to the hypothetical nonmagnetic case, paramagnetism significantly reduces the effect of C on the SFE. In the scenario of C being depleted from the stacking Fault structure or twin boundaries, e.g., due to elevated temperature, where the chemical effect of C is dissipated, we calculate the C-induced volume expansion effect on the SFE. The volume induced change in the SFE corresponds to more than ∼ 50% of the total C effect on the SFE obtained assuming uniform C distribution.
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stacking Fault Energy of face centered cubic metals thermodynamic and ab initio approaches
Journal of Physics: Condensed Matter, 2016Co-Authors: Dongyoo Kim, Stephan Schonecker, Levente Vitos, Jijun Zhao, S K KwonAbstract:The formation Energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking Fault Energy (SFE) of fcc metals a ...
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Generalized stacking Fault Energy of γ-Fe
Philosophical Magazine, 2016Co-Authors: Wei Li, Jan Y. Johnsson, Mikael Grehk, Song Lu, Qing-miao Hu, Se Kyun Kwon, Borje Johansson, Levente VitosAbstract:© 2016 Taylor and Francis.We investigate the generalized stacking Fault Energy (-surface) of paramagnetic-Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking Fault Energy (ISF). However, the unstable stacking Fault Energy (USF), representing the Energy barrier along the-surface connecting the ideal fcc and the intrinsic stacking Fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking Fault formation regime (K) towards maximum twinning (K) and finally to a dominating full-slip regime (K). Our predictions are discussed in connection with the available experimental observations.
Terence G Langdon - One of the best experts on this subject based on the ideXlab platform.
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effect of stacking Fault Energy on steady state creep rate of face centred cubic metals
Journal of Applied Science and Technology, 2014Co-Authors: A Ayensu, Terence G Langdon, A Owusu, K AkuffokumiAbstract:Continuum elastic theory was used to establish the relationships between the force of interaction required to constrict dislocation partials, Energy of constriction and climb velocity of the constricted thermal jogs, in order to examine the effect of stacking Fault Energy (SFE) on steady state creep rate of face centered cubic (FCC) metals. Values of the SFE exponent calculated for FCC metals ranged between 3.1 and 3.8; with a mean of 3.4, which was close to the accepted semi-empirical SFE exponent of 3.0; thereby confirming the suitability of the theory. The corresponding stress exponent obtained from the analysis was 5.0, which satisfied the condition that the stress exponent must be greater than 4.5 for pure FCC metals.
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Microstructure of low stacking Fault Energy silver processed by different routes of severe plastic deformation
Journal of Alloys and Compounds, 2012Co-Authors: Zoltán Hegedűs, Zsolt Fogarassy, Jenő Gubicza, Nguyen Quoc Chinh, Megumi Kawasaki, Terence G LangdonAbstract:Abstract Samples of 4 N purity Ag were processed at room temperature (RT) by equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) up to 8 passes and 20 revolutions, respectively. It was found that the minimum grain size was around 200 nm for both ECAP and HPT. However, the dislocation density and the twin boundary frequency were about three times larger in HPT due to the very high applied hydrostatic pressure. The maximum dislocation density (about 1.5 × 10 16 m −2 ) and twin boundary frequency (about 2%) achieved by HPT at RT are extremely high among pure fcc metals and this can be explained by the difficult annihilation of the highly dissociated dislocations due to the very low stacking Fault Energy in Ag.
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The effect of impurity level on ultrafine-grained microstructures and their stability in low stacking Fault Energy silver
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Zoltán Hegedűs, Zsolt Fogarassy, Jenő Gubicza, Nguyen Quoc Chinh, Megumi Kawasaki, Terence G LangdonAbstract:Abstract The effect of impurity content on the evolution of microstructure in low stacking Fault Energy silver processed by severe plastic deformation (SPD) was studied. The SPD-processing was carried out on 4N5 and 4N purity Ag samples by equal-channel angular pressing (ECAP) up to 16 passes. It was found that, although the minimum grain size and the maximum dislocation density were not affected by the different impurity atom content, there is a lower degree of twinning in the less pure material for high number of passes. The small increase of impurity level from 4N5 to 4N in Ag resulted in a significantly better thermal stability at room temperature for the ultrafine-grained microstructures obtained by ECAP.
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effect of stacking Fault Energy on strength and ductility of nanostructured alloys an evaluation with minimum solution hardening
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: P L Sun, Yonghao Zhao, Terence G Langdon, Zenji Horita, E J Lavernia, J C Cooley, M E Kassner, Y T ZhuAbstract:The effect of stacking Fault Energy (SFE) on the mechanical properties was investigated in Ni–Co alloys which have minimum solution hardening effects. Cobalt reduces the SFE in nickel and this promotes grain refinement during processing and increases the dislocation and twin densities. A reduction in SFE increases strength and tensile ductility. The higher strength is due to grain refinement and higher dislocation and pre-existing twin densities whereas the higher ductility is attributed to a higher work hardening rate.
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influence of stacking Fault Energy on deformation mechanism and dislocation storage capacity in ultrafine grained materials
Scripta Materialia, 2009Co-Authors: Zhiwei Wang, Yonghao Zhao, X Z Liao, Y T Zhu, Zenji Horita, Y B Wang, E J Lavernia, Terence G LangdonAbstract:Partial dislocation emission from grain boundaries in metals with medium-to-high stacking Fault energies is observed primarily in the grain size range of a few tens of nanometers. Here we report that a reduction in the stacking Fault Energy permits the emission of partial dislocations from grain boundaries in ultrafine-grained materials with grain sizes significantly larger than 100 nm and this produces twinning. Such twins are effective in increasing the dislocation storage capacity, which may be used to improve the ductility.
Y T Zhu - One of the best experts on this subject based on the ideXlab platform.
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Role of stacking Fault Energy in strengthening due to cryo-deformation of FCC metals
Materials Science and Engineering A, 2010Co-Authors: V. Subramanya Sarma, W W Jian, Jens Freudenberger, Alexander Kauffmann, J. Wang, H. Conrad, Y T ZhuAbstract:The effectiveness of the cryogenic (CT) rolling vis-à-vis room temperature (RT) rolling on strengthening is significantly affected by stacking Fault Energy (SFE) and there is an optimum SFE at which CT rolling is most effective. Studies on Al, Al alloy AA6061, Cu, Cu-4.6Al, Cu-9Al and Cu-15Al (in at.%) alloys revealed that in metals with very high and very low SFEs, the strength difference between CT and RT rolled samples is
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effect of stacking Fault Energy on strength and ductility of nanostructured alloys an evaluation with minimum solution hardening
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: P L Sun, Yonghao Zhao, Terence G Langdon, Zenji Horita, E J Lavernia, J C Cooley, M E Kassner, Y T ZhuAbstract:The effect of stacking Fault Energy (SFE) on the mechanical properties was investigated in Ni–Co alloys which have minimum solution hardening effects. Cobalt reduces the SFE in nickel and this promotes grain refinement during processing and increases the dislocation and twin densities. A reduction in SFE increases strength and tensile ductility. The higher strength is due to grain refinement and higher dislocation and pre-existing twin densities whereas the higher ductility is attributed to a higher work hardening rate.
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influence of stacking Fault Energy on deformation mechanism and dislocation storage capacity in ultrafine grained materials
Scripta Materialia, 2009Co-Authors: Zhiwei Wang, Yonghao Zhao, X Z Liao, Y T Zhu, Zenji Horita, Y B Wang, E J Lavernia, Terence G LangdonAbstract:Partial dislocation emission from grain boundaries in metals with medium-to-high stacking Fault energies is observed primarily in the grain size range of a few tens of nanometers. Here we report that a reduction in the stacking Fault Energy permits the emission of partial dislocations from grain boundaries in ultrafine-grained materials with grain sizes significantly larger than 100 nm and this produces twinning. Such twins are effective in increasing the dislocation storage capacity, which may be used to improve the ductility.
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determining the optimal stacking Fault Energy for achieving high ductility in ultrafine grained cu zn alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Yonghao Zhao, X Z Liao, Terence G Langdon, Zenji Horita, Y T ZhuAbstract:Bulk ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) often have low ductility. A previous study demonstrated the possibility of lowering the stacking Fault Energy to simultaneously increase the strength and ductility. This paper demonstrates, there exists an optimal stacking Fault Energy for the best ductility in UFG Cu–Zn alloys processed by the same SPD processing. When the stacking Fault Energy is too low, the grain size lies below 15 nm after SPD processing and the stacking Faults are saturated so that it is difficult to accumulate dislocations and deformation twins during the subsequent tensile testing. These results provide significant guidance for the future design of UFG and nanocrystalline alloys for achieving high ductilities.
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influence of stacking Fault Energy on microstructural characteristics of ultrafine grain copper and copper zinc alloys
Acta Materialia, 2008Co-Authors: Levente Balogh, Yonghao Zhao, Y T Zhu, Terence G Langdon, Zenji Horita, Tamas UngarAbstract:Experiments were conducted on samples of pure Cu and two Cu–Zn alloys to evaluate the influence of the stacking-Fault Energy (SFE) on microstructural development when processing using high-pressure torsion (HPT). Transmission electron microscopy, X-ray diffraction and hardness measurements were used for microstructural evaluation and the results show consistency between these techniques. Grain sizes in the nanometer range were formed at the edges of the HPT disks, larger submicrometer grains were formed in the disk centers and the measured grain sizes decreased with decreasing SFE. There was negligible twinning in pure Cu but the densities of dislocations and twins increased with increasing Zn content and thus with decreasing SFE. The values of the Vickers microhardness were lower in the centers of the disks for the two Cu–Zn alloy and this is consistent with the low SFE and slow rates of recovery.
Irene J. Beyerlein - One of the best experts on this subject based on the ideXlab platform.
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Density functional theory calculations of generalized stacking Fault Energy surfaces for eight face-centered cubic transition metals
Journal of Applied Physics, 2019Co-Authors: Irene J. BeyerleinAbstract:In this work, we use density functional theory to calculate the entire generalized stacking Fault Energy (GSFE) surface for eight transition metals with a face-centered cubic structure: Ag, Au, Cu,...
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density functional theory calculations of generalized stacking Fault Energy surfaces for eight face centered cubic transition metals
Journal of Applied Physics, 2019Co-Authors: Irene J. BeyerleinAbstract:In this work, we use density functional theory to calculate the entire generalized stacking Fault Energy (GSFE) surface for eight transition metals with a face-centered cubic structure: Ag, Au, Cu, Ir, Ni, Pd, Pt, and Rh. Analysis of the ⟨ 112 ⟩ GSFE curves finds that the displacements corresponding to the unstable stacking Fault Energy are larger than the ideal value for all eight metals except Ag and Cu. Over the entire surface, Pt is found to not possess well-defined local maxima or minima, suggesting spreading in favor of dissociation of the dislocation core, unlike the other seven metals. Our calculations also reveal that at a large ⟨ 112 ⟩ displacement, where atoms on two {111} adjacent planes are aligned, an anomalous local minimum occurs for Ir and Rh. The oddity is explained by relatively large, localized atomic displacements that take place in the two metals to accommodate the alignment that do not occur in the other six metals. In addition to the fully calculated surfaces, we characterize a continuous 11-term Fourier-series function, which provides a particularly excellent representation of the GSFE surfaces for Ag, Au, Cu, Ni, and Pd.
Yonghao Zhao - One of the best experts on this subject based on the ideXlab platform.
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effect of stacking Fault Energy on strength and ductility of nanostructured alloys an evaluation with minimum solution hardening
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: P L Sun, Yonghao Zhao, Terence G Langdon, Zenji Horita, E J Lavernia, J C Cooley, M E Kassner, Y T ZhuAbstract:The effect of stacking Fault Energy (SFE) on the mechanical properties was investigated in Ni–Co alloys which have minimum solution hardening effects. Cobalt reduces the SFE in nickel and this promotes grain refinement during processing and increases the dislocation and twin densities. A reduction in SFE increases strength and tensile ductility. The higher strength is due to grain refinement and higher dislocation and pre-existing twin densities whereas the higher ductility is attributed to a higher work hardening rate.
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influence of stacking Fault Energy on deformation mechanism and dislocation storage capacity in ultrafine grained materials
Scripta Materialia, 2009Co-Authors: Zhiwei Wang, Yonghao Zhao, X Z Liao, Y T Zhu, Zenji Horita, Y B Wang, E J Lavernia, Terence G LangdonAbstract:Partial dislocation emission from grain boundaries in metals with medium-to-high stacking Fault energies is observed primarily in the grain size range of a few tens of nanometers. Here we report that a reduction in the stacking Fault Energy permits the emission of partial dislocations from grain boundaries in ultrafine-grained materials with grain sizes significantly larger than 100 nm and this produces twinning. Such twins are effective in increasing the dislocation storage capacity, which may be used to improve the ductility.
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determining the optimal stacking Fault Energy for achieving high ductility in ultrafine grained cu zn alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Yonghao Zhao, X Z Liao, Terence G Langdon, Zenji Horita, Y T ZhuAbstract:Bulk ultrafine-grained (UFG) materials produced by severe plastic deformation (SPD) often have low ductility. A previous study demonstrated the possibility of lowering the stacking Fault Energy to simultaneously increase the strength and ductility. This paper demonstrates, there exists an optimal stacking Fault Energy for the best ductility in UFG Cu–Zn alloys processed by the same SPD processing. When the stacking Fault Energy is too low, the grain size lies below 15 nm after SPD processing and the stacking Faults are saturated so that it is difficult to accumulate dislocations and deformation twins during the subsequent tensile testing. These results provide significant guidance for the future design of UFG and nanocrystalline alloys for achieving high ductilities.
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influence of stacking Fault Energy on microstructural characteristics of ultrafine grain copper and copper zinc alloys
Acta Materialia, 2008Co-Authors: Levente Balogh, Yonghao Zhao, Y T Zhu, Terence G Langdon, Zenji Horita, Tamas UngarAbstract:Experiments were conducted on samples of pure Cu and two Cu–Zn alloys to evaluate the influence of the stacking-Fault Energy (SFE) on microstructural development when processing using high-pressure torsion (HPT). Transmission electron microscopy, X-ray diffraction and hardness measurements were used for microstructural evaluation and the results show consistency between these techniques. Grain sizes in the nanometer range were formed at the edges of the HPT disks, larger submicrometer grains were formed in the disk centers and the measured grain sizes decreased with decreasing SFE. There was negligible twinning in pure Cu but the densities of dislocations and twins increased with increasing Zn content and thus with decreasing SFE. The values of the Vickers microhardness were lower in the centers of the disks for the two Cu–Zn alloy and this is consistent with the low SFE and slow rates of recovery.
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influence of stacking Fault Energy on the minimum grain size achieved in severe plastic deformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: Yonghao Zhao, X Z Liao, Terence G LangdonAbstract:Abstract Samples of pure Cu and a Cu–10% Zn alloy were processed by high-pressure torsion and by high-pressure torsion followed by cold-rolling to a reduction of ∼75%. The grain sizes in these two conditions were measured by transmission electron microscopy and by X-ray diffraction. The experimental results show the average grain size and the width of the grain size distribution are both smaller in the Cu–10% Zn alloy by comparison with pure Cu. This difference is due to the lower stacking Fault Energy of the Cu–10% Zn alloy. An analysis shows all of the experimental results are consistent with a theoretical model predicting the minimum grain size produced by milling.
