Abstract
Transmission electron microscopy has been employed to study the formation of vacancy dislocation loops from defect cascades produced by 50 ke V Kr+ ion irradiations of Ni and its dilute alloys with Si and Al. An unusual and reproducible dependence of loop collapse probabilities and loop size distributions on solute content was found. The temperature dependence at 30 and 300 K and ion dose dependence of these loop collapse probabilities were measured. The results are explained by impurity-caused changes in both the collisional phase and thermal spike (molten zone) phase of the defect cascade. Specific mechanisms include disruption of focusons by impurities to change the energy density profile within the collison cascade, disruption of replacement collision sequences to place the self-interstitials closer to the molten zone, and interstitial trapping to reduce recombination during the thermal spike phase.
