A molecular dynamics study of displacement cascades in α-zirconium

Abstract

The damage produced in the hcp metal α-zirconium at 100 K by displacement cascades with energy in the range from 0.3 to 5keV has been investigated by molecular dynamics using a many-body interatomic potential. Comparisons have been made with the results of a recent study by Wooding et al. of α-titanium, a hcp metal with a much smaller atomic mass. There is no discernible effect of primary-knock-on-atom direction, and individual replacement sequences make only a minor contribution to the final damage state. In comparison with titanium, fewer atoms in zirconium are displaced temporarily to interstitial sites during the collisional phase and the cascade core size is smaller. Nevertheless, the core temperature during the thermal spike is higher. The number of Frenkel pairs, produced in the final damage state is smaller in zirconium than in titanium, and the efficiency of their production declines with increasing cascade energy in a similar fashion to that found for all other metals. Some interstitial clusters are formed in the cascade process. They have dislocation character and migrate preferentially along basal planes during and after the thermal spike. Analysis of the mean square displacement of atoms in the final state of 2 and 5 keV cascades shows that the atomic mixing in zirconium is approximately half that reported for α-titanium.