Minimum-energy structures for the symmetrical (11▪1) and (11▪2) twin grain boundaries, as well as for 2 non-symmetrical grain boundaries that exhibited dislocations, were obtained for the hexagonal close-packed structure by computer modeling. Central force potentials constructed within the embedded-atom method were used to represent atomic interactions. Vacancy-formation energies and entropies for different sites were calculated, and the properties of various vacancy jumps were investigated. Unstable vacancy sites, located in the grain boundary dislocation cores, were observed. The random-walk approach, combined with simulation results, was used to study tracer diffusion via a vacancy mechanism in the twin grain boundaries. Higher diffusivity values than those for

the lattice were obtained, in qualitative agreement with experiments. Correlation effects, taken into account by the matrix method, showed that the main features of grain boundary diffusion were contributed by jumps within a narrow region.

Grain-Boundary Diffusion by Vacancy Mechanism in α-Ti and α-Zr. J.R.Fernandez, A.M.Monti, R.C.Pasianot: Metallurgical and Materials Transactions A, 2002, 33[3A], 791-6