The formation and migration of vacancies in (11•1) twin boundaries in the α-type phases were studied by means of computer modelling. Three empirical central force potentials were constructed within the embedded-atom method and were used to represent atomic interactions. Minimum-energy structures for the twin boundary were first found, and a vacancy was then introduced by removing an atom and permitting relaxation of the structure. The formation energies, entropies and relaxation volumes were calculated for various positions of the vacancy. Possible vacancy jumps were considered, and the corresponding migration energies and entropies were calculated in order to analyse vacancy migration, and therefore boundary self-diffusion. The most probable paths which comprised these simple jumps were then identified. It was found that the formation energy, and the migration free energy, was significantly lower than the bulk value. This emphasized the role of the grain boundary as a vacancy sink and a rapid-diffusion channel. The free energies were used to evaluate the diffusion coefficient tensor, the effective activation energies; and the pre-exponential factors when the jj-component of the tensor was assumed to obey an Arrhenius relationship.

An Atomistic Study of Formation and Migration of Vacancies in (11¯21) Twin Boundaries in Ti and Zr. J.R.Fernández, A.M.Monti, R.C.Pasianot, V.Vitek: Philosophical Magazine A, 2000, 80[6], 1349-64