Atomistic studies of nucleation of He clusters and bubbles in bcc iron

Atomistic simulations of the nucleation of He clusters and bubbles in bcc iron at 800K have been carried out using the newly developed Fe–Fe interatomic potential, along with Ackland potential for the Fe–Fe interactions. Microstructure changes were analyzed in detail. We found that a He cluster with four He atoms is able to push out an iron interstitial from the cluster, creating a Frenkel pair. Small He clusters and self-interstitial atom (SIA) can migrate in the matrix, but He-vacancy (He-V) clusters are immobile. Most SIAs form clusters, and only the dislocation loops with a Burgers vector of b=1/2 appear in the simulations. SIA clusters (or loops) are attached to He-V clusters for He implantation up to 1372appm, while the He-V cluster–loop complexes with more than one He-V cluster are formed at the He concentration of 2057appm and larger.