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

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. High entropy alloys: property prediction 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.