The statics and dynamics of vacancies and adatoms on various surfaces of these hexagonal close-packed metals were studied by using static relaxation techniques and many-body potentials. The formation and migration energies, entropies and attempt frequencies were deduced and were used in the random walk approach in order to derive correlation factors and diffusivities. It was found that the main features of the surface diffusion were dominated by jumps on, and between, a few atomic layers. A consistent comparison between the 2 mechanisms was therefore possible. The activation energies and diffusivities for the bulk (Qb, Db), symmetrical grain boundaries (Qgb, Dgb) and surfaces (Qs, Ds) as calculated by using the same simulation technique and interatomic potentials, obeyed the expected relationships: Qs < Qgb < Qb and Ds > Dgb > Db. It was found that adatoms were usually faster surface diffusers than were vacancies.

Modeling of Surface Diffusion in HCP Zr and Ti. M.I.Pascuet, J.R.Fernández, R.C.Pasianot, A.M.Monti: Interface Science, 2003, 11[1], 121-9