Large helium-vacancy clusters coalescence during helium bubble evolution under cascade in iron with edge dislocation: A MD simulation

Abstract

The nucleation and growth of helium bubbles under the mutual effect of cascade and dislocation in bcc Fe was investigated by molecular dynamic simulations. The helium atoms along with primary knock-on atoms (PKA) were gradually added in the simulation system to imitate the real neutron irradiation condition. Several coalescence events of large helium-vacancy (He-V) clusters during the molecular dynamic simulation in bcc Fe were discovered. The detailed analysis of these coalescence events revealed that in the bulk region, if two helium-vacancy clusters are close enough, they are inclined to combine into one cluster by kicking out host atoms between the two clusters. However, two close helium-vacancy clusters near the dislocation line will not merge by this kick-out mechanism. Instead, it’s found that they could be promoted to combine together by cascade, even if the two clusters locate on the edge of the cascade thermal spike. The mutual influence of dislocation and cascade will lead to the formation of low content and large size helium-vacancy clusters around the dislocation line.