Growth kinetics of dislocation loops and voids - the role of divacancies

The effect of divacancies on the growth or shrinkage of dislocation loops and voids has been investigated by using the general rate equations which include the reactions of vacancy association, divacancy dissociation, divacancy-interstitial interaction, and divacancy loss to unsaturable sinks. Simple analytic expressions have been derived, which provide an estimate for the role of divacancies for given sink strength, temperature, and vacancy supersaturation. Based on the available defect parameters for f.c.c. metals it was found that divacancies are most important in Al and Ni, moderately important in Cu and Ag, and not important in Au. Numerical calculations for Al and Ni under various irradiation conditions show that void swelling is enhanced by divacancies in the recombination-dominant regime of the growth kinetics, whereas in the sink-dominant regime void swelling is reduced due to the preferential flux of divacancies to dislocations. The effect of divacancies on the growth of interstitial loops is much more pronounced than on void swelling, and it depends sensitively upon irradiation temperature, dose rate, and dose. (author)