Influence of dilute impurities on the evolution of defect cascades in nickel

We have employed transmission electron microscopy to study the formation of vacancy-type dislocation loops from defect cascades produced by a 50 keV Kr+ ion irradiation of Ni and its dilute alloys with Si and Al. An unusual and reproducible dependence of the probability of loop formation and loop size distributions on solute content was found. The results are explained by impurity caused changes in both the collisional and thermal spike (molten zone) phase of the defect cascade. Specific mechanisms include disruption of focussons by impurities to change the energy density profile within the collision cascade, interruption of replacement collision sequences, and interstitial trapping to reduce recombination during the thermal spike phase. Applying these mechanisms to a statistical distribution of the spatial extent of cascades and to the molten zones, all the experimental observations can be explained. (orig.)