MOLECULAR-DYNAMICS STUDY OF DISPLACEMENT CASCADES IN NI3AL .1. GENERAL FEATURES AND DEFECT PRODUCTION EFFICIENCY

The damage produced by displacement cascades in the L1(2) alloy Ni3Al at 100 K has been investigated by molecular dynamics using many-body interatomic potentials. 76 cascades ranging in energy from 0.15 to 5 keV have been simulated in order to study the effects of the energy and species of the primary recoil atom. Computer-generated colour plots have been used to visualize the nature and arrangement of the point defects produced in the cascade events. There is a change in cascade morphology at the end of the collisional phase for cascade energies in the range 1-2 keV, and separate subcascade regions can be seen in some cascades at 5 keV. Individual replacement sequences do not make a significant contribution to the final damage state. The efficiency of production of Frenkel pairs declines with increasing cascade energy in a similar fashion to that found recently for pure metals. Approximately 90% of the interstitials created in cascades are Ni-Ni dumbbell atoms, and the tendency of interstitials to form clusters is weaker than that observed in pure metals. The antisite defects are much more numerous than the Frenkel pairs, and their production efficiency increases with increasing cascade energy. The results of this study are in general agreement with those from modelling of 5 keV cascades by Diaz de la Rubia et al. in 1992 and Diaz de la Rubia, Caro and Spaczer in 1993, except with regard to the number of antisite defects found. Finally, the simulations of the displacement threshold at 0 K by Gao and Bacon in 1993 have been extended to 100 K in order to investigate the influence of temperature on the displacement threshold energy under conditions consistent with the cascade modelling.