A systematic molecular dynamics study was made of the diffusion mechanisms of He interstitials and di-He clusters at 2 representative interfaces in α-Fe. The diffusion coefficient of a He interstitial, and the effective migration energies, were determined. The He atoms diffused 1-dimensionally along the Σ11 grain boundary, along specific directions, while they migrated 2-dimensionally at low temperatures, and 3-dimensionally at higher temperatures, in the Σ3 grain boundary. The di-He interstitial cluster could migrate rapidly along the Σ3 interface at low temperatures, but not at the Σ11 interface. It was observed that a di-He interstitial cluster could kick-out a self-interstitial atom, at high temperatures, to form a He2V complex. The self-interstitial atom migrated rapidly near to interfaces, whereas the He2V complex was immobile at the temperatures considered. This small cluster could serve as the smallest nucleation for the formation of He bubbles at interfaces.

Diffusion of He Interstitial and Di-He Cluster at Grain Boundaries in α-Fe. F.Gao, H.L.Heinisch, R.J.Kurtz: Journal of Nuclear Materials, 2007, 367-370[1], 446-50