A systematic molecular dynamics study was made of the diffusion mechanisms of He atoms in grain boundaries in α-Fe. Two grain boundaries, Σ11 <110>{323} and Σ3 <110>{112}, were used. The low-temperature (about 0K) equilibrium structures of these grain boundaries were determined using standard molecular dynamics relaxation techniques, with a flexible border condition. The migration of He atoms were followed for 1–14ns, at 600 to 1200K. The diffusion coefficient of He atoms using the mean square displacements of He atoms, and the effective migration energies were determined. It was found that He atoms diffused rapidly in the Σ11 grain boundary, where the binding energy of a He atom to the boundary was high. He migration was largely 1-dimensional along specific directions, but a few directional changes were observed at higher temperatures. In the Σ3 grain boundary, where the He binding energy was low, He atoms migrated 1-dimensionally at low temperature, 2-dimensionally at intermediate temperature and 3-dimensionally at higher temperatures. The different activation energies and diffusion mechanisms in these two representative grain boundaries suggested that the atomic structures of the grain boundaries played an important role in the diffusivity of He.

Diffusion of He Interstitials in Grain Boundaries in α-Fe. F.Gao, H.Heinisch, R.J.Kurtz: Journal of Nuclear Materials, 2006, 351[1-3], 133-40