scholarly journals Visualizing temperature-dependent phase stability in high entropy alloys

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Daniel Evans ◽  
Jiadong Chen ◽  
George Bokas ◽  
Wei Chen ◽  
Geoffroy Hautier ◽  
...  
Keyword(s):  
Phase Stability ◽  
Temperature Stability ◽  
Barycentric Coordinates ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Spatial Dimensions ◽  
Thermodynamic Conditions ◽  
Inverse Hull ◽  
Multi Phase

AbstractHigh entropy alloys (HEAs) contain near equimolar amounts of five or more elements and are a compelling space for materials design. In the design of HEAs, great emphasis is placed on identifying thermodynamic conditions for single-phase and multi-phase stability regions, but this process is hindered by the difficulty of navigating stability relationships in high-component spaces. Traditional phase diagrams use barycentric coordinates to represent composition axes, which require (N – 1) spatial dimensions to represent an N-component system, meaning that HEA systems with N > 4 components cannot be readily visualized. Here, we propose forgoing barycentric composition axes in favor of two energy axes: a formation-energy axis and a ‘reaction energy’ axis. These Inverse Hull Webs offer an information-dense 2D representation that successfully captures complex phase stability relationships in N ≥ 5 component systems. We use our proposed diagrams to visualize the transition of HEA solid-solutions from high-temperature stability to metastability upon quenching, and identify important thermodynamic features that are correlated with the persistence or decomposition of metastable HEAs.

Fundamental Core Effects in Transition Metal High-Entropy Alloys: “High-Entropy” and “Sluggish Diffusion” Effects

2021 ◽  
Vol 29 ◽  
pp. 75-93
Author(s):  
Abhishek Mehta ◽  
Yong Ho Sohn
Keyword(s):  
High Temperature ◽  
Temperature Stability ◽  
High Temperature Strength ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Diffusion Effects ◽  
Initial Work ◽  
Entropy Effect ◽  
Sluggish Diffusion

High entropy alloys (HEAs) are equimolar multi-principal-element alloys (MPEAs) that are different from traditional solvent-based multicomponent alloys based on the concept of alloy design. Based on initial work by Yeh and co-workers, HEAs were postulated to exhibit four “core” effects: high entropy, sluggish diffusion, lattice distortion, and cocktail effect. Out of these four proposed core effects, “high entropy” and “sluggish diffusion” effects were most debated in the literature as these core effects directly affect the thermodynamic and kinetic understanding of HEAs. The initial work on HEAs by several researchers utilized these effects to indirectly support the experimentally observed “unique” properties, without independent investigation of these core effects. The presumed implications of these core effects resulted in justification or generalization of properties to all HEAs, e.g., all HEAs should exhibit high temperature stability based on high entropy effect, high temperature strength owing to limited grain growth, good diffusion barrier application due to sluggish diffusion kinetics, etc. However, many recent studies have challenged these core effects, and suggested that not all HEAs were observed to exhibit these core effects.

scholarly journals The formation and stability of bulk amorphous and high entropy alloys

2021 ◽  
Vol 4 (1) ◽  
pp. 51-57
Author(s):  
Attila Szabó ◽  
Krisztián Bán ◽  
József Hlinka ◽  
Judit Pásztor ◽  
Antal Lovas
Keyword(s):  
Amorphous Alloys ◽  
Configurational Entropy ◽  
Temperature Stability ◽  
High Entropy Alloy ◽  
Alloy Formation ◽  
High Entropy Alloys ◽  
High Temperature Stability ◽  
High Entropy ◽  
Phase Stabilization ◽  
Fcc Phase

Abstract Two kinds of phase stabilization mechanism are discussed and compared: the first is characteristic of the formation of bulk amorphous alloys, in which the high supercooling ability of multicomponent liquids is responsible for the glassy phase stabilization. Here the hindered nucleation of crystalline phases is the center phenomenon. The origin of this hindering is the slowing atomic mobility in the supercooling melt. In contrast the melt supercooling is negligible during the high entropy alloy formation. It is believed that stability of the crystalline single fcc phase is the consequence of the characteristic of high configurational entropy at high temperatures. However, the significance of this entropy-dominated stabilization is overestimated in several references. It has been concluded that transition metal contraction (arising from the d electron participation in the overall bonding state) does also contribute to the high temperature stability of fcc single phase in the high entropy alloys.

On phase stability of Mo-Nb-Ta-W refractory high entropy alloys

2022 ◽  
pp. 105780
Author(s):  
Enkuan Zhang ◽  
Ying Tang ◽  
Mingwen Wen ◽  
Abdulmonem Obaied ◽  
Irina Roslyakova ◽  
...  
Keyword(s):  
Phase Stability ◽  
High Entropy Alloys ◽  
High Entropy

A New Criterion for Prediction of Phase Stability in Al‐Containing High Entropy Alloys

2020 ◽  
pp. 2000470
Author(s):  
Fangjie Li ◽  
Yeyu Sha ◽  
Xin Zeng ◽  
Shidong Zhang ◽  
Tao Shi ◽  
...  
Keyword(s):  
Phase Stability ◽  
High Entropy Alloys ◽  
High Entropy ◽  
New Criterion

scholarly journals Bulk high-entropy nitrides and carbonitrides

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Olivia F. Dippo ◽  
Neda Mesgarzadeh ◽  
Tyler J. Harrington ◽  
Grant D. Schrader ◽  
Kenneth S. Vecchio
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Configurational Entropy ◽  
Temperature Stability ◽  
High Hardness ◽  
Valence Electron Concentration ◽  
High Temperature Stability ◽  
High Entropy ◽  
Rule Of Mixtures ◽  
Traditional Ceramics

AbstractHigh-entropy ceramics have potential to improve the mechanical properties and high-temperature stability over traditional ceramics, and high entropy nitrides and carbonitrides (HENs and HECNs) are particularly attractive for high temperature and high hardness applications. The synthesis of 5 bulk HENs and 4 bulk HECNs forming single-phase materials is reported herein among 11 samples prepared. The hardness of HENs and HECNs increased by an average of 22% and 39%, respectively, over the rule-of-mixtures average of their monocarbide and mononitride precursors. Similarly, elastic modulus values increased by an average of 17% in nitrides and 31% in carbonitrides over their rule-of-mixtures values. The enhancement in mechanical properties is tied to an increase in the configurational entropy and a decrease in the valence electron concentration, providing parameters for tuning mechanical properties of high-entropy ceramics.

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