Atomic diffusion, segregation, and grain boundary migration in nickel-based alloys from molecular dynamics simulations

Grain boundary diffusion and metal mobility in alloys control material performance in many applications and yet remain poorly understood at a mechanistic level. With advances in accessible time and length scales for computational molecular simulations, and recent force field developments, we now possess tools to help unravel those mechanisms. Using large-scale molecular dynamics simulations, here we examined vacancy-mediated diffusion processes in Ni-5Cr alloy with low and high-energy grain boundaries. We show that atomic diffusion inside the grain boundary plane is about four times higher than bulk diffusion, at any temperature, and exhibits a typical Arrhenius behavior with a very small energy barrier (similar to 0.8 eV for Cr and 0.7 eV for Ni within 1300-1600 K). Additionally, the fastest diffusing species inverts; Cr diffusion was faster than Ni in the bulk but slower in the grain boundaries. This is attributed to the creation of high cohesive energy clusters of Cr at the grain boundary. Grain boundary migration was also observed to be temperature dependent and appears to be two times higher in the 5% Cr alloy than in pure Ni, highlighting the important role of the alloying element on grain boundary motion.

Automated summary

Grain boundary diffusion and metal mobility in alloys play a crucial role in material performance. Through molecular dynamics simulations, it was found that atomic diffusion within grain boundaries is much faster than in the bulk, exhibiting typical Arrhenius behavior. The diffusion of chromium is faster in the bulk but slower in grain boundaries due to the formation of high cohesive energy clusters. Additionally, the temperature-dependent grain boundary migration is significantly influenced by the alloying element.