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C T Liu - One of the best experts on this subject based on the ideXlab platform.
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atomic packing and size effect on the hume rothery rule
Intermetallics, 2019Co-Authors: Zhijun Wang, C T Liu, Yunhao Huang, Jincheng WangAbstract:Abstract Atomic packing problems have been widely investigated by physicists, mathematicians, material scientists as a long-standing scientific issue. While it is widely known that the monodisperse particles are closely packed into the face-centered cubic structure, the increase of polydispersity will suppress the crystallization. It is still unsolved when and how the crystalline packing collapses as the particle-size difference increases over a critical value. On the other hand, the atomic-size factor of the solution has gone deeply into the concept of applied physicists and Physical Metallurgy scientists since the proposal of Hume-Rothery rules in 1934. Although great efforts have been devoted to understanding this simple but important empirical rule of the atomic size effect, it remains a question without a complete answer even in binary alloy systems. Here, the two outstanding issues were solved in a rigorous geometric packing instability model even in the multicomponent system. The Physical scenario presented here are helpful for understanding the close packing instability and the atomic-size effect in the Hume-Rothery rules.
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effect of minor alloying additions on glass formation in bulk metallic glasses
Intermetallics, 2005Co-Authors: C T LiuAbstract:Abstract This paper provides a comprehensive review of recent work on the effect of minor alloying additions on glass formation in bulk metallic glasses. Recently, minor alloying addition or microalloying technology has shown to have dramatic effects on the glass formation and thermal stability of many bulk metallic glasses. This technology basically involves adding small amounts of alloying additions (usually, less 2 at%) to existing bulk metallic glasses for the purpose of further improving their glass forming ability. Experimental evidences indicate that alloying additions of small atoms with atomic radius 0.16 nm (such as Y and Sc) are most effective in enhancing glass forming ability. The beneficial effects of these elements are discussed in terms of Physical Metallurgy principles.
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a new approach to understanding and measuring glass formation in bulk amorphous materials
Intermetallics, 2004Co-Authors: C T LiuAbstract:Abstract This paper summarizes our recent work on the understanding of glass formation from considering both liquid phase stability and crystallization resistance from a Physical metallurgical point of view. A comprehensive expression to predict glass-forming ability (GFA) for various glass-forming systems, γ=Tx/(Tg+Tl), was derived, where Tx is the crystallization temperature, Tg the glass transition temperature and Tl the liquidus temperature. Our Physical-Metallurgy approach is supported strongly by experimental data reported for various bulk amorphous materials. Also, some misconception commonly used for assessing the GFA in the literature will be clarified.
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Glass formation criterion for various glass-forming systems
Physical Review Letters, 2003Co-Authors: Z P Lu, C T LiuAbstract:A conceptual approach to evaluate glass-forming ability for various glass-forming systems has been proposed from a Physical Metallurgy point of view. It was found that the glass-forming ability for noncrystalline materials was related mainly to two factors, i.e., 1/(T(g)+T(l)) and Tx (wherein Tx is the onset crystallization temperature, T ( g) the glass transition temperature, and T(l) the liquidus temperature), and could be predicated by a unified parameter gamma defined as T(x)/(T(g)+T(l)). This approach was confirmed and validated by experimental data in various glass-forming systems including oxide glasses, cryoprotectants, and metallic glasses.
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ordered intermetallic alloys part i nickel and iron aluminides
JOM, 1993Co-Authors: C T Liu, K S KumarAbstract:This article summarizes recent progress in research and development on nickel and iron aluminide intermetallic alloys. Ordered intermetallics possess attractive properties for structural applications at elevated temperatures in hostile environments; however, brittle failure and poor fracture resistance limit their use as engineering materials. In recent years, efforts to understand this brittle fracture behavior have identified both intrinsic and extrinsic factors governing brittle fracture. Parallel work on alloy design using Physical Metallurgy principles has led to the development of aluminide alloys with improved mechanical and metallurgical properties for structural use.
Seok Su Sohn - One of the best experts on this subject based on the ideXlab platform.
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shear band driven precipitate dispersion for ultrastrong ductile medium entropy alloys
Nature Communications, 2021Co-Authors: Tae Jin Jang, Pyuck Pa Choi, Wonseok Choi, Dae Woong Kim, Gwanghyo Choi, Hosun Jun, Alberto Ferrari, Fritz Kormann, Seok Su SohnAbstract:Precipitation strengthening has been the basis of Physical Metallurgy since more than 100 years owing to its excellent strengthening effects. This approach generally employs coherent and nano-sized precipitates, as incoherent precipitates energetically become coarse due to their incompatibility with matrix and provide a negligible strengthening effect or even cause brittleness. Here we propose a shear band-driven dispersion of nano-sized and semicoherent precipitates, which show significant strengthening effects. We add aluminum to a model CoNiV medium-entropy alloy with a face-centered cubic structure to form the L21 Heusler phase with an ordered body-centered cubic structure, as predicted by ab initio calculations. Micro-shear bands act as heterogeneous nucleation sites and generate finely dispersed intragranular precipitates with a semicoherent interface, which leads to a remarkable strength-ductility balance. This work suggests that the structurally dissimilar precipitates, which are generally avoided in conventional alloys, can be a useful design concept in developing high-strength ductile structural materials.
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Shear band-driven precipitate dispersion for ultrastrong ductile medium-entropy alloys
'Springer Science and Business Media LLC', 2021Co-Authors: Jang, Tae Jin, Choi, Won Seok, Kim, Dae Woong, Choi Gwanghyo, Jun Hosun, Ferrari A., Körmann F.h.w., Pyuck Pa Choi, Seok Su SohnAbstract:Precipitation strengthening has been the basis of Physical Metallurgy since more than 100 years owing to its excellent strengthening effects. This approach generally employs coherent and nano-sized precipitates, as incoherent precipitates energetically become coarse due to their incompatibility with matrix and provide a negligible strengthening effect or even cause brittleness. Here we propose a shear band-driven dispersion of nano-sized and semicoherent precipitates, which show significant strengthening effects. We add aluminum to a model CoNiV medium-entropy alloy with a face-centered cubic structure to form the L21 Heusler phase with an ordered body-centered cubic structure, as predicted by ab initio calculations. Micro-shear bands act as heterogeneous nucleation sites and generate finely dispersed intragranular precipitates with a semicoherent interface, which leads to a remarkable strength-ductility balance. This work suggests that the structurally dissimilar precipitates, which are generally avoided in conventional alloys, can be a useful design concept in developing high-strength ductile structural materials.Team Marcel Sluite
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Shear band-driven precipitate dispersion for ultrastrong ductile medium-entropy alloys
'Springer Science and Business Media LLC', 2021Co-Authors: Jang, Tae Jin, Choi, Won Seok, Kim, Dae Woong, Choi Gwanghyo, Jun Hosun, Ferrari A., Körmann F.h.w., Pyuck Pa Choi, Seok Su SohnAbstract:Precipitation strengthening has been the basis of Physical Metallurgy since more than 100 years owing to its excellent strengthening effects. This approach generally employs coherent and nano-sized precipitates, as incoherent precipitates energetically become coarse due to their incompatibility with matrix and provide a negligible strengthening effect or even cause brittleness. Here we propose a shear band-driven dispersion of nano-sized and semicoherent precipitates, which show significant strengthening effects. We add aluminum to a model CoNiV medium-entropy alloy with a face-centered cubic structure to form the L21 Heusler phase with an ordered body-centered cubic structure, as predicted by ab initio calculations. Micro-shear bands act as heterogeneous nucleation sites and generate finely dispersed intragranular precipitates with a semicoherent interface, which leads to a remarkable strength-ductility balance. This work suggests that the structurally dissimilar precipitates, which are generally avoided in conventional alloys, can be a useful design concept in developing high-strength ductile structural materials.+ Author Correction https://doi.org/10.1038/s41467-021-26008-1Team Marcel Sluite
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Understanding the Physical Metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study
npj Computational Materials, 2018Co-Authors: Won-mi Choi, Yong Hee Jo, Seok Su SohnAbstract:Although high-entropy alloys (HEAs) are attracting interest, the Physical metallurgical mechanisms related to their properties have mostly not been clarified, and this limits wider industrial applications, in addition to the high alloy costs. We clarify the Physical metallurgical reasons for the materials phenomena (sluggish diffusion and micro-twining at cryogenic temperatures) and investigate the effect of individual elements on solid solution hardening for the equiatomic CoCrFeMnNi HEA based on atomistic simulations (Monte Carlo, molecular dynamics and molecular statics). A significant number of stable vacant lattice sites with high migration energy barriers exists and is thought to cause the sluggish diffusion. We predict that the hexagonal close-packed (hcp) structure is more stable than the face-centered cubic (fcc) structure at 0 K, which we propose as the fundamental reason for the micro-twinning at cryogenic temperatures. The alloying effect on the critical resolved shear stress (CRSS) is well predicted by the atomistic simulation, used for a design of non-equiatomic fcc HEAs with improved strength, and is experimentally verified. This study demonstrates the applicability of the proposed atomistic approach combined with a thermodynamic calculation technique to a computational design of advanced HEAs. Atomistic calculations elucidate crucial strengthening mechanisms in high entropy alloys and predict better performing compositions. A team led by Byeong-Joo Lee at South Korea’s Pohang University of Science and Technology used various simulations techniques to study the movement of atoms in a series of disordered high entropy alloys. They attributed sluggish diffusion in the classic CoCrFeMnNi alloy to the large number of stable vacancy sites, and at cryogenic temperatures showed that micro-twinning was due to a more stable hexagonal crystal structure. Finally, they used their simulation results to predict the effect of alloying on the critical resolved shear stress and designed a high entropy alloy with improved properties. A computational approach to the design of high entropy alloys may thus help us develop more complex alloys and tailor their properties.
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.
Fritz Kormann - One of the best experts on this subject based on the ideXlab platform.
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shear band driven precipitate dispersion for ultrastrong ductile medium entropy alloys
Nature Communications, 2021Co-Authors: Tae Jin Jang, Pyuck Pa Choi, Wonseok Choi, Dae Woong Kim, Gwanghyo Choi, Hosun Jun, Alberto Ferrari, Fritz Kormann, Seok Su SohnAbstract:Precipitation strengthening has been the basis of Physical Metallurgy since more than 100 years owing to its excellent strengthening effects. This approach generally employs coherent and nano-sized precipitates, as incoherent precipitates energetically become coarse due to their incompatibility with matrix and provide a negligible strengthening effect or even cause brittleness. Here we propose a shear band-driven dispersion of nano-sized and semicoherent precipitates, which show significant strengthening effects. We add aluminum to a model CoNiV medium-entropy alloy with a face-centered cubic structure to form the L21 Heusler phase with an ordered body-centered cubic structure, as predicted by ab initio calculations. Micro-shear bands act as heterogeneous nucleation sites and generate finely dispersed intragranular precipitates with a semicoherent interface, which leads to a remarkable strength-ductility balance. This work suggests that the structurally dissimilar precipitates, which are generally avoided in conventional alloys, can be a useful design concept in developing high-strength ductile structural materials.
Y Y Chen - One of the best experts on this subject based on the ideXlab platform.
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Physical Metallurgy of concentrated solid solutions from low entropy to high entropy alloys
Current Opinion in Solid State & Materials Science, 2017Co-Authors: Chunyang Cheng, Yachu Yang, Yizhen Zhong, Y Y ChenAbstract:Abstract The alloy world could be divided into low-entropy (LEAs), medium-entropy (MEAs) and high-entropy alloys (HEAs) based on the configurational entropy at the random solution state. In HEAs, four core effects, i.e. high entropy, sluggish diffusion, severe lattice distortion and cocktail effects, are much more significant than low-entropy alloys in affecting phase transformation, microstructure and properties. In fact, the degree of the influence from these core effects more or less increases with increased mixing entropy. The trend is gradual from low-entropy alloys to high-entropy alloys. In this article, Physical Metallurgy of HEAs is discussed with the bridge connected to that of conventional alloys. As disordered and ordered solid solutions are the main constituent phases of alloys, the understanding of solid solutions is fundamental for the understanding of alloys. In addition, as dilute solid solutions have been well treated in current Physical Metallurgy, concentrated solid solutions from low-entropy to high-entropy alloys are focused in this article. Physical properties are especially emphasized besides mechanical properties.