SELF-DIFFUSION ALONG TWIST GRAIN-BOUNDARIES IN CU

In a previous paper we studied vacancy diffusion in two high-angle twist grain boundaries in Cu, using the EAM. In this paper, we discuss vacancy diffusion along four additional twist grain boundaries, from 8.8-43.6-degrees. Vacancy formation energies in all the possible sites were calculated (0.14-1.42 eV) and found to be directly related to the degree of coincidence with the neighboring crystal planes. The optimal migration paths were found to coincide with the screw dislocations which comprise the boundary. Vacancy migration energies were found to be low (0.02-0.52 eV). The activation energies for self-diffusion at the boundaries were found to be less than half of the bulk value, in general agreement with experiment. Calculated diffusion rates, deltaD, for medium-high angle twist grain boundaries were in reasonable agreement with experimental data for polycrystalline material. Diffusion rates were found to decrease with increasing twist angle, in contrast with two sets of conflicting experimental data.