Understanding the physical metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study

TLDR

High‑entropy alloys attract interest, but their physical metallurgical mechanisms remain unclear, limiting industrial use and driving high costs. The study aims to elucidate the metallurgical origins of sluggish diffusion and cryogenic micro‑twinning in the equiatomic CoCrFeMnNi alloy and assess how individual elements influence solid‑solution hardening. Atomistic simulations—including Monte Carlo, molecular dynamics, and molecular statics—were employed to investigate these phenomena. Simulations revealed that numerous stable vacancies with high migration barriers cause sluggish diffusion, that the hcp structure is energetically favored over fcc at 0 K explaining cryogenic twinning, and that the predicted critical resolved shear stress accurately guides the design of stronger non‑equiatomic fcc HEAs, a design validated experimentally and demonstrating the method’s utility for advanced HEA development.

Abstract

Abstract 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.