PNNL

Abstract

A systematic molecular dynamics study of the diffusion mechanisms of He interstitial and their small clusters at two representive interfaces has been carried out in a-Fe. The diffusion coefficient of a He interstitial and the effective migration energies were determined. The He atom diffuses rapidly along the sigma11 grain boundary one-dimensionally along specific directions, while it migrates one-dimensionally at low temperature, two-dimensionally at intermediate temperature and three-dimensionally at higher temperature, in the sigma3 grain boundary. The di-He interstitial cluster can migrate rapidly along the sigma3 interface at low temperatures, but not at the sigma11 interface. It has been observed that a di-He interstitial cluster can kick out a self interstitial atom (SIA) at high temperatures, forming a He2V complex. The SIA migrates rapidly near interfaces, whereas the He2V complex is immobile at the temperatures considered. This small cluster may serve as a smallest nucleation for the formation of helium bubbles at interfaces.