Diffusion kinetics and structural order in γ'-Ni₃Al-Re/Mo/Ta: A theoretical study

Diffusion kinetics and structural order in γ'-Ni₃Al precipitate plays a dominant role in the structural stability and creep life of Ni-based superalloy. However, accurately estimating their physical mechanisms remains a challenging task through experiments. In this study, vacancy-mediated diffusion and structural order in γ'-Ni₃Al-Re/Mo/Ta systems have been systematically evaluated via incorporating first-principles and kinetic Monte Carlo (KMC) simulation. The results indicate that the decreasing effects of alloying elements on vacancy diffusion constants follow the order of Ta > Re > Mo at 1573 K. It primarily originates from the stable occupations of alloying elements on Al sublattice sites with very few jumps. These alloying atoms at Al sublattice sites further increase the intra-sublattice migration barriers of the host atoms with the order of Ta > Mo > Re and the inter-sublattice migration barriers with the order of Ta ≈ Re > Mo. Besides, each alloying element raises the equilibrium long and short order degree of the γ'-Ni₃Al system at high temperatures. The alloying atoms increase the barriers for Ni migration from Ni to Al sublattice sites, thereby decreasing the equilibrium concentration of Ni_β antisites. Further analysis suggests that the structural disorder primarily originates from fewer Ni jumps within inter-sublattice sites.