Interstitial diffusion along twist grain boundaries in Cu

Interstitial diffusion along twist grain boundaries was studied using the Embedded Atom Method (EAM). Six (100) twist grain boundaries (8.79°-43.6°) in copper were investigated. Interstitial formation energies were found to be much lower (0.26-0.78 eV) than in the bulk, and migration energies were found to be comparable (0.01 eV-0.24 eV) to the bulk values (0.09 eV). The vacancy mechanism is favored for low angle boundaries, and the interstitial mechanism is favored for high angle boundaries. The trends in formation energy versus twist angle were partly explained in terms of the volume expansion of the grain boundary. The total diffusion rate due to both mechanisms was calculated, and agreed reasonably well with experimental data for Cu in polycrystalline Cu. The calculated diffusion rate for specific twist boundaries also agreed well with experimental measurements for Zn/Al.