Minimum-energy structures for the symmetrical (11•1) and (11•2) twin grain boundaries, as well as for 2 asymmetrical grain boundaries that exhibited dislocations, were obtained for the hexagonal close-packed structure by means of computer modelling. Central-force potentials, constructed using the embedded-atom method, were used to represent atomic interactions. The vacancy formation energies and entropies for various 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 twin grain boundaries. Higher diffusivity values than those for the lattice were obtained, in qualitative agreement with experiment. Correlation effects, which were taken into account by using the matrix method, governed the main features of grain-boundary diffusion which 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, 32[3A], 791-6