Molecular dynamics studies of sluggish grain boundary diffusion in equiatomic FeNiCrCoCu high-entropy alloy

Molecular dynamics simulations are conducted to study the self-diffusion process along a < 100 > Sigma 5(210) symmetric tilt grain boundary in a model equiatomic FeNiCrCoCu high-entropy alloy (HEA), for the directions both perpendicular and parallel to the tilt axis. For comparison, the grain boundary diffusion process is also quantified for each of the pure components of the HEA. Most importantly, the results are compared with the diffusion along the same grain boundary using the corresponding "average atom" potential that has similar average bulk properties but no compositional randomness as in the HEA. These comparisons show that the self-diffusion in the HEA grain boundary is slower than in the average atom material as well as the average of pure components, suggesting that a "sluggish" diffusion effect exists for this special grain boundary in the HEA. This effect is significant at low temperatures but diminishes at higher temperatures, indicating that the grain boundary sluggish diffusion is likely temperature dependent. Interestingly, the grain boundary sluggish diffusion behavior is different from the bulk diffusion that was studied previously using the same methods and interatomic potentials, in which no significant sluggish diffusion effect was observed. Our further analysis suggests that the combination of the "trapping effect" by compositional complexity in the HEA and the confined 2-D diffusion paths at this special grain boundary is responsible for the observed grain boundary sluggish diffusion. [GRAPHICS] .