EFFECT OF DILUTE SOLUTE ADDITIONS ON LOOP FORMATION FROM HEAVY-ION PRODUCED DISPLACEMENT CASCADES IN NI

Transmission electron microscopy has been employed to study the format ion of vacancy dislocation loops from defect cascades produced by 50 k eV Kr+ ion irradiations of Ni and its dilute alloys with Si and Al. An unusual and reproducible dependence of loop collapse, probabilities a nd loop size distributions on solute content was found. The temperatur e dependence at 30 and 300 K and ion dose dependence of these loop col lapse probabilities were measured. The results are explained by impuri ty-caused changes in both the collisional phase and thermal spike (mol ten zone) phase of the defect cascade. Specific mechanisms include dis ruption of focusons by impurities to change the energy density profile within the collison cascade, disruption of replacement collision sequ ences to place the self-interstitials closer to the molten zone, and i nterstitial trapping to reduce recombination during the thermal spike phase.