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 800 K 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 <111> clusters, and only the dislocation loops with a Burgers vector of b = 1/2 <111> appear in the simulations. SIA clusters (or loops) are attached to He-V clusters for He implantation up to 1372 appm, while the He-V cluster-loop complexes with more than one He-V cluster are formed at the He concentration of 2057 appm and larger.