Stability of helium clusters during displacement cascades

The interactions of displacement cascades with helium-vacancy clusters in α-Fe are investigated using molecular dynamics simulations. Initial He-vacancy clusters consist of 20 vacancies with a helium-to-vacancy ratio ranged from 0.2 to 3 and primary knock-on atom (PKA) energy, Ep, varies from 2 keV to 10 keV. The results show that the effect of displacement cascades on a helium-vacancy cluster strongly depends on the helium-to-vacancy ratio and PKA energy. For the same PKA energy, the size of helium-vacancy clusters increases with the He/V ratio, but for the same ratio, the cluster size changes more significantly with increasing PKA energy. It has been observed that the He-vacancy clusters (He-V) can be dissolved for the He/V ratio less than 1, but they are able to renucleate during the thermal spike phase, forming small He-V nuclei. For the He/V ratio larger than 1, the He-V clusters are very stable for the energies considered and they can absorb a number of vacancies produced by displacement cascades, forming larger He-V clusters.