Solute diffusion in the γ′ phase of Ni based alloys

We systematically investigate the diffusion mechanisms of 3d (Ti–Cu), 4d (Zr–Ag) and 5d (Hf–Au) transition metal solutes in γ′-Ni3Al phase using first-principles calculations. The results reveal that the diffusion of Ni-substituting solute is mainly controlled by the sublattice diffusion mechanism via Ni vacancies and the diffusion of Al-substituting solute is mostly governed by the formation of the anti-structure defects on the Ni sublattice with negligible contribution of the anti-structure bridge mechanism. The elements which occupy both the Al and Ni sites show a diffusion behavior similar to that of the Ni-substituting solutes. Our calculations show that larger atoms can move much faster than smaller atoms, which disprove the traditional view that larger atoms move slower than smaller atoms.