A kinetic Monte Carlo study of vacancy diffusion in non-dilute Ni-Re alloys

The beneficial effect of Re on the creep strengthening properties in single crystal Ni-based superalloys is well known, albeit understanding the underlying mechanism is still an ongoing area of investigation. The microstructure in these alloys comprises of cuboids of the hard precipitate phase embedded in a softer matrix phase. At high temperatures, the glide of creep dislocations is restricted to the matrix only, and dislocation climb is required to get around a precipitate. Vacancy diffusion is an essential component of dislocation climb and elements like Re which are slow-diffusing in Ni are expected to affect this phenomenon. In the present work, we aim to study this by calculating the effect of Re composition on the rate of vacancy diffusion in Ni using kinetic Monte Carlo simulations. First principles electronic structure calculations based on density functional theory have been used to calculate the thermodynamic and kinetic parameters in both dilute as well as non-dilute alloys. Results suggest appreciable modification of the vacancy diffusion coefficients, indicating that the beneficial role of Re in Ni-based superalloys can be largely explained by its effect on vacancy diffusion.