Unveiling the effect of stress on vacancy diffusion isotropy at high temperature in Ni-Re Systems: Insights from atomic simulations

Abstract

Stress-affected vacancy diffusion significantly impacts the element distributions in Ni-based single-crystal (SX) superalloys, determining their precipitate coarsening and creep behaviors under service conditions consequently. Rhenium (Re), as a slow-diffusing element, exhibits nonnegligible effects on the vacancy diffusion behavior varied with its atomic concentration and position particularly. In this work, we comprehensively study the vacancy diffusion behavior in Ni-Re alloys at 1173 ∼ 1573 K under stress along [001] and [111], by using the Self-Evolving Atomistic Kinetic Monte Carlo (SEAKMC) method with interatomic potentials. The simulation results reveal that vacancy diffusion is isotropic under stress-free states. However, applying stress along [001] and [111] leads to vacancy diffusion anisotropy. External stress applied along [111] has a smaller effect on the lattice parameter than stress along [0 0 1]. This results in less change in vacancy migration distances, leading to smaller changes in chemical bonding. Consequently, the alternation in vacancy migration barriers is less significant. This ultimately results in less disruption to the vacancy diffusion isotropy. In Ni-Re systems under external stress, temperature affects the probability of the vacancy overcoming high migration barriers while the addition of Re affects solute–vacancy binding. Typically, higher temperatures and increased Re concentrations further decrease the extent of vacancy diffusion anisotropy.