Exploring the Compositional Space of High-Entropy Alloys for Cost-Effective High-Temperature Applications

Abstract

High-entropy alloys (HEAs) are nearly equimolar multi-principal element alloys, exhibiting exceptional thermal and mechanical properties at extreme conditions such as high-temperatures and stresses. Since the first discovery and early conceptualization of conventional HEAs nearly two decades ago, HEAs with far-from-equimolar compositions have attracted substantial interest to provide a broader range of material properties and to adjust price fluctuations and availability of commodities. Here, we present a first-principles investigation of non-equimolar chromium-manganese-iron-cobalt-nickel (CrMnFeCoNi) HEAs and effects of molybdenum (Mo) and niobium (Nb) substitutions on cost, phase stability and solubility, and mechanical and thermal performance up to 1000 K operational temperature. Virtual-crystal approximation is used to expediently approximate random solid solutions at the disordered mean-field limit. Using multi-objective metaheuristics built on a first-principles database, golden compositions are predicted for thermally well-insulated components and effective heat sinks. Replacing Co with Fe lowers commodity costs without hindering phase stability and solubility. Lower Ni concentration leads to lower thermal conductivity, indicating better thermal insulation, while reducing Mn concentration significantly increases the thermal conductivity, indicating better performing heat sinks. Moving away from equimolar ratios commonly increases the thermal expansion coefficient, which could generate higher thermal stresses. Nb and Mo substitution always lead to substantially higher commodity cost and density but with an increment in the mechanical performance due to solid-solution hardening. However, alloying with Mo and Nb is the only compositional space that reduces the thermal conductivity and thermal expansion coefficient.

Electronic effects on the radiation damage in high-entropy alloys

“…3, the Gibbs free energy differences (∆G) of the RSS compared to the CoCrFeNi are illustrated up to 1000 K. Reducing Cr or Fe leads to thermally less stable compositions by increasing G while reducing Ni has an opposite effect. Reducing the molarfraction of Co has a less significant effect on the thermal stability, and this is consistent with previous studies carried out in five PE alloys [21]. At room temperature (300 K), a reduction up to 20% of Cr or Fe, or a reduction of Co only leads to ∆G in the order of 1 meV, which is in the order of the accuracy of the practical DFT simulations.…”

“…HEAs have been shown to exhibit exceptional thermal stability [4], hardness and strength [5][6][7][8][9][10], wear resistance [11,12], and oxidation resistance [11,13]. In particular, the equimolar chromium-cobalt-iron-nickel HEA (CrFeCoNi) has attracted considerable interest as it can serve as a base template to exploring non-equimolar compositions, or adding other elements such as manganese (Mn), copper (Cu), aluminum (Al), titanium (Ti), niobium (Nb), molybdenum (Mo) and many more to achieve exceptional materials properties [1,[14][15][16][17][18][19]21].…”