Antisite-assisted diffusion in the L12 ordered structure studied by Monte Carlo simulations

Diffusion in the Ll(2) structure is investigated by means of atomistic kinetic Monte Carlo simulations on a rigid lattice. Special attention is devoted to the influence of the composition on the diffusion process in a binary alloy. We observe that two diffusion mechanisms resulting from the interactions of vacancies with antisites located on both sublattices allow for the displacement of the minority element and can enhance the diffusivity of the majority element. The respective contributions to the diffusion process of these two mechanisms strongly depend on the temperature and on the degree of departure from the stoichiometric composition. These two mechanisms can explain the minimum nickel diffusivity experimentally observed around the stoichiometic composition in Ni3Al compounds and the suspected lower activation energy for gallium than for nickel in Ni3Ga.