Atomic-scale computer simulations, both molecular dynamics and molecular statics, were used to study self-diffusion processes in Ni3Al of stoichiometric composition at reduced temperatures of 0.85 to 0.94Tm (figure 7). A wide set of diffusional characteristics, including the self-diffusion coefficient, jump frequency, correlation factor and activation energy, was obtained by molecular dynamics for each material. Self-diffusion in pure metals occurred via the random walk of vacancies and the tracer correlation factor obtained from molecular dynamics was in a good agreement with that estimated from the theory. In the ordered alloy, the diffusion mechanism was more complicated. Thus, Ni diffused mainly via Ni sites, whereas the diffusion of Al atoms included the formation and annihilation of antisite defects. Once a Ni antisite was formed, Al diffusion occurred via the intra sub-lattice mechanism. At high temperatures, the antistructural bridge mechanism was also observed. The conclusions of the molecular dynamics study were supported by the molecular statics simulation, in which the activation energy was obtained along paths corresponding to possible diffusion mechanisms, namely the six-jump cycle, intra sub-lattice and antistructural bridge mechanisms. It was found that the intra sub-lattice and antistructural bridge mechanisms were much more favourable for Al diffusion than was the six-jump cycle one.

Atomistic Study of Self-Diffusion in Ni, Al and Ni3Al. Duan, J., Osetsky, Y.N., Bacon, D.J.: Defect and Diffusion Forum, 2001, 194-199[1], 423-8