Helium–self-interstitial atom interaction in α-iron

The effect of He impurities on the properties and behavior of self-interstitial atom (SIA) clusters in α-Fe has been simulated by atomistic molecular dynamics (MD) and molecular statics (MS) simulation techniques using semi-empirical interatomic potentials and compared to ab initio electronic structure calculations. The MD simulations reveal many interactions between He and SIA clusters, including a spontaneous SIA–substitutional He recombination and replacement mechanism that ejects He into interstitial positions and a strong interaction between He, in either interstitial or substitutional positions, with SIA and SIA clusters and also with other He atoms. The MS calculations reveal relatively small interaction trapping radii of about 1 nm between interstitial He and SIA cluster complexes, but strong binding energies from 1.3 to 4.4 eV, depending on cluster size and interaction geometry. The comparisons between the ab initio and semi-empirical interactions are in generally good agreement and indicate that the He–point defect interactions in bcc Fe are well represented by considering the displacement (strain) field interactions amongst the defects.