MD and KMC modeling of the growth and shrinkage mechanisms of helium–vacancy clusters in Fe

A multiscale modeling approach, which is based on atomistic simulations, was applied to investigate the growth and shrinkage mechanisms of helium–vacancy (He–V) clusters in Fe. Firstly, a molecular dynamics technique with empirical interatomic potentials was used to determine energies for the formation and dissociation of clusters as a function of their size and He density. Both the number of He atoms and vacancies in a cluster ranged from 0 to 20. The dissociation energy of clusters showed a strong dependence on the He density, rather than the cluster size, indicating that the growth and shrinkage of clusters strongly depend on the He density. Secondly, these dissociation energies were employed in a kinetic Monte-Carlo (KMC) simulation, to explore long-time cluster behavior. The KMC simulation indicated that He can stabilize He–V clusters by suppressing thermal vacancy emission and by promoting thermal self-interstitial Fe atom emission. A preliminary KMC simulation to investigate the migration behavior of He–V clusters is also presented.