INFLUENCE OF DILUTE IMPURITIES ON THE EVOLUTION OF DEFECT CASCADES INNICKEL

We have employed transmission electron microscopy to study the formati on 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 A l. An unusual and reproducible dependence of the probability of loop f ormation and loop size distributions on solute content was found. The results Are explained by impurity caused changes in both the collision al and thermal spike (molten zone) phase of the defect cascade. Specif ic 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 reduc e recombination during the thermal spike phase. Applying these mechani sms to a statistical distribution of the spatial extent of cascades an d to the molten zones, all the experimental observations can be explai ned.