Effect of mass of the primary knock-on atom on displacement cascade debris in α-iron

Results are presented from molecular dynamics (MD) simulations of displacement cascades created in alpha-iron (Fe) by primary knock-on atoms (PKAs) with energy from 5 to 20 keV and mass chosen to represent C, Fe and Bi. The PKA-Fe interaction potential at short range has been varied, and damage by molecular Bi-(2) has been simulated using two Bi PKAs. Four effects are reported. First, the PKA mass has a major effect on the damage produced in individual cascades while the PKA-Fe potential has little influence. Second, the total number of point defects produced in a cascade decreases with increasing PKA mass. This fact is not accounted for in models Used conventionally for estimating damage. Third, interstitial loops of 1/2 < 111 > type and both vacancy and interstitial loops of < 100 > type are formed, the latter being observed in MD simulation for the first time. The probability of (100) loop appearance increases with increasing PKA mass as well as energy. Finally, there is a correlation between production of large vacancy and interstitial clusters in the same cascade.