PNNL

Abstract

The accumulation of He atoms in materials will significantly degrade the mechanical properties of materials; therefore, understanding the properties of He interstitials and their clusters in materials is of fundamental importance within a fusion reactor environment. The diffusion properties of single He interstitials and He clusters in the bulk and grain boundaries of a-Fe are being studied using molecular dynamics with a new Fe-He potential. It is found that the migration barrier for a single He interstitial in the bulk is very low, which is consistent with the result obtained using ab initio methods. Large He clusters can cause Fe self-interstitial atoms (SIA) to be formed, which can be trapped by the resulting vacancy, forming a He-vacancy complex. It is found that for He interstitials in grain boundaries (GBs), the He migration is one-dimensional in a S11 GB, while it is two-dimensional in a S3 GB at 600 K and three-dimensional at higher temperatures.