Thermal and stress impacts on vacancy diffusion through atomistic simulations

Abstract

Vacancy diffusion is involved in a variety of destructive failure processes in metals, whose impact becomes more magnificent in real engineering applications with external thermal and/or mechanical loadings. Here we examined the vacancy diffusion in nickel under a wide range of pressure and temperature with the aid of collective variable-driven hyperdynamics (CVHD), which is challenging for traditional molecular dynamics (MD) due to its intrinsic femtosecond time step. In line with previous studies, the vacancy diffusivity in nickel decreases when the hydrostatic pressure increases. Interestingly, the total diffusion rate increases when the uniaxial stress is applied, and the diffusion becomes anisotropic. Additionally, vacancy diffusivity becomes less dependent on either hydrostatic pressure or uniaxial stress when the temperature increases. This work provides in-depth atomistic insights into the diffusion phenomenon in nickel, which could be beneficial for unveiling the damage mechanisms and the design of next-generation Ni-based high-temperature alloys.