The atomic structures of symmetrical tilt grain boundaries, and their interaction with vacancies and interstitials, were studied by using molecular statics, molecular dynamics, kinetic Monte Carlo and other simulation methods. It was found that the point-defect formation energy in grain boundaries was generally lower than that in the lattice. There were large variations from site to site within the grain-boundary core. The formation energies of the vacancies and interstitials were similar; which made these defects equally important for grain-boundary diffusion. The vacancies exhibited interesting effects, such as delocalization and instability at certain grain-boundary sites. They moved, within grain boundaries, via simple vacancy-atom exchange or via so-called long jumps which involved several atoms. The interstitial atoms could occupy relatively open positions between atoms, form split dumb-bell configurations or form highly delocalized displacement zones. They diffused via direct jumps, or via an indirect mechanism which involved the collective displacement of several atoms. The diffusion coefficients in the grain boundaries were calculated by using kinetic Monte Carlo simulations, and defect jump-rates which were determined from transition state theory. The grain-boundary diffusion could be dominated by vacancies or interstitials; depending upon the grain-boundary structure. The diffusional anisotropy also depended upon the grain-boundary structure, with diffusion along the tilt axis being faster or slower than diffusion normal to the tilt axis. The activation energy for grain-boundary diffusion tended to decrease with grain-boundary energy.

Atomistic Modeling of Point Defects and Diffusion in Copper Grain Boundaries. A.Suzuki, Y.Mishin: Interface Science, 2003, 11[1], 131-48