Vacancy jumps in a bicrystal model of a (36.9°) [001] tilt boundary in body-centered cubic Fe were simulated at 1300, 1400 and 1500K by molecular dynamics with the use of the empirical Johnson potential. The results confirmed the dominance of a vacancy mechanism in grain-boundary diffusion. An activation energy of 0.51eV for vacancy migration was obtained along with a reasonable value of the jump-attempt frequency. Analysis of the jump directions showed a preferential bias along the tilt axis. The relationship between diffusivity and atomic mean-square displacement was examined. It was suggested that the structure dependence of grain-boundary diffusion could be expressed through a matrix of transition probability for vacancy jumps among the various discrete sites.

Molecular-Dynamics Studies of Grain-Boundary Diffusion. II. Vacancy Migration, Diffusion Mechanism, and Kinetics. Kwok, T., Ho, P.S., Yip, S.: Physical Review B, 1984, 29[10], 5363-71