IMPACT OF GLISSILE INTERSTITIAL LOOP PRODUCTION IN CASCADES ON DEFECT ACCUMULATION IN THE TRANSIENT

Defect interactions in displacement cascades produced during high energy particle irradiation result in the annihilation and clustering of vacancies and self-interstitial atoms (SIAs) within the cascade volume. SIA clusters produced in the form of small glissile loops may glide and reach extended sinks such as dislocations and grain boundaries. In the present paper, this process is suggested to represent an efficient driving force for void swelling, in particular in regions adjacent to grain boundaries. For describing the evolution of the point defect and defect cluster concentrations in the initial stage of irradiation a set of kinetic equations taking the escape of one-dimensionally gliding SIA loops into account is proposed. The calculation of the vacancy supersaturation as a function of dose shows that at sufficiently high dislocation densities, microvoids that are not stable in the quasi-steady-state at higher doses could be stabilized during a transient maximum of the vacancy supersaturation at lower doses. The enhanced swelling observed adjacent to grain boundaries is attributed to the escape of SIA loops to these planar sinks. The width of the swelling zone is shown to be of the order of the mean range of one-dimensionally gliding loops. From the maximum swelling rate, the fraction of SIAs produced in the form of glissile loops is estimated.