Production bias driven defect accumulation in the transient regime

Consequences of the nature of the damage production in multidisplacement cascades are analyzed. Considerations of intracascade clustering of self-interstitial atoms (SIAs) and vacancies during the cooling-down phase of a cascade and of the difference between thermal stabilities of SIA and vacancy clusters give rise to the concept of production bias. Within this concept, the fraction of vacancies and SIAs escaping the cascade region is taken to be the effective rates of defect production. The fraction of vacancies in excess of SIAs has been calculated and used for determining the temporal dependence of void swelling purely in terms of production bias. It is proposed that small SIA clusters/loops may perform one-dimensional glide motion and may get transported to dislocations and grain boundaries. This is considered to be a viable mechanism for the removal of a fraction of SIA population. The resulting vacancy supersaturation would drive void nucleation, growth and void swelling. The swelling behaviour in the transient regime predicted by the production bias is found to be in reasonable agreement with the experimental results.