Vacancy defects in Fe: Comparison between simulation and experiment

The evolution of radiation damage under heavy-ion irradiation in thin foils of pure bcc Fe has been investigated by simulation and experiment. Simulations showed that vacancy loops are about as mobile as interstitial loops, and can be lost to the surface of a foil. Consistent with this, in situ real-time dynamic observations of the damage evolution showed that loops, many of which are believed to be of vacancy nature, were mobile and were often lost during irradiation. Atomistic simulations of vacancy defects in Fe showed that spherical voids, rather than vacancy loops, represent the lowest energy configurations for clusters of vacancies of any size. The simulations also indicated that the stability of loops strongly varies depending on their size. Closed loops above a critical diameter (∼2 nm) are highly metastable due to the difficulty of their transformation into voids. The greater stability of voids explains why the loop yield in Fe and other ferritic materials is very low.