Effects of free surface on primary radiation damage in α-Fe induced by different ion irradiations: A molecular dynamics study

Abstract Ion irradiation serves as a critical tool for investigating material response to radiation-induced damage. This study employs molecular dynamics simulations to systematically investigate surface damage in α-Fe under Ar, Fe, and Au ion irradiation, with cascade damage in bulk Fe included for comparative analysis. The simulation results demonstrate that the presence of a free surface significantly enhances vacancy production for all three ion species, compared to bulk cascades, with the severity of surface damage following the order of Au > Fe > Ar. This trend is primarily driven by ion-specific penetration depths. Further analysis reveals that equivalent penetration depth methods—including SRIM-predicted energies and reduced incident energies—fail to ensure consistent damage outcomes across ion species. These findings highlight that ion irradiation damage is governed by a coupled mechanism involving both energy transfer processes within the cascade and the modulating influence of the free surface, with ion species playing a pivotal role in determining the resulting microstructural evolution.