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

Vacancy diffusion isotropy is more significantly disrupted under stress along [001] compared to the disruption under stress along [111] in pure Ni system. Furthermore, vacancy diffusion exhibits the tensile-compressive asymmetry under stress along [001]. The addition of Re and increasing temperature enhances vacancy diffusion isotropy under uniaxial stress in Ni system. • The sensitivity of vacancy diffusion to stress decrease with increasing temperature. • The hindering effect of Re on vacancy diffusion diminishes with rising concentration. • Vacancy diffusion shows tensile-compressive asymmetry under stress along [001]. • Vacancy diffusion isotropy is better under uniaxial stress along [111] than [001]. • Re generally enhances vacancy diffusion isotropy under stress in Ni-Re alloy. 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 alloy 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 barrier 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.