Computer simulation of vacancy properties in twin boundaries in h.c.p. metals

Abstract
The influence of boundaries on vacancy properties in interfaces has been considered for the case of twin boundaries in the h.c.p. structure. Twinning is a common occurrence in the h.c.p. metals and the atomic structure of several boundaries has been well characterized by recent computer modelling. In the present work, the formation and migration energies of vacancies have been investigated in {1011}, {1012}, {1121} and {1122} boundaries in a model with nearideal c/a ratio. It is found that, even though the atomic density at these interfaces is close to perfect, the vacancy formation energy can be reduced by up to 27% and the migration energy by up to 50% from the single-crystal values. These results are discussed in terms of the crystallography of the interfaces and the hydrostatic component of internal stress at individual atomic sites, but these features provide only a partial explanation of the results found.