Computer modeling of diffusion in Ni-richNi3Al and compositiondependence of diffusion in γ′ Ni3Al

Abstract

Atomistic simulations of diffusion in off-stoichiometric Ni-richNi3Al (Ni77Al23) at temperatures ranging from 1300 to 1550 K and comprehensiveanalysis of the composition dependence of Ni and Al diffusion inγ′ Ni3Al of threecompositions, 73, 75 and 77 at.% Ni, are presented. The interatomic forces are described by Finnis–Sinclairtype N-body potentials. The simulations reveal that Ni diffusion is dominated by Ni vacancy mechanisms;Al diffusion is via both the intrasublattice and antistructure bridge (ASB) mechanism inNi77Al23 at the temperatures investigated. The presence of an extra 2% of antisitedefects enhances diffusion of both Ni and Al at off-stoichiometric Ni-enrichedNi3Al via the vacancy–antisite interaction. The single vacancy diffusivity of Ni and Al inNi3Al of three compositions, 73, 75 and 77 at.% Ni, at the above temperatures are corrected withthermal equilibrium concentration of point defects. The corrected Ni and Al diffusion dataare in good agreement with available experimental data. The Ni diffusivity decreases withthe Ni concentration, while Al diffusivity has a minimum at the stoichiometric compositionin the simulated temperature range.