Modeling of void nucleation under cascade damage conditions

In recent years, significant progress has been made in understanding the void growth and swelling behaviour in metals under cascade damage conditions in terms of differences in the intra-cascade clustering of self-interstitials (SIAs) and vacancies, and the thermal stability and (one-dimensional) mobility of the resulting clusters. The problem of void nucleation was, however, not treated in any detail within this ‘production bias model’. In treating void nucleation, the following experimental findings have to be considered: (1) Both nucleation and growth of voids are much more efficient under cascade damage conditions than under electron irradiation. (2) Void nucleation occurs at low dose, particularly in pure metals, and tends to saturate at higher doses. (3) There are significant differences in the void nucleation behaviour between pure metals of different crystal structure and between pure metals and alloys. In the present contribution, we discuss these findings in terms of a production bias controlled vacancy supersaturation rising in the transient to quasi-steady-state and falling during cascade damage accumulation, and thus inducing a limited void nucleation pulse, the yield of which represents the experimentally observed saturated void density.