Temperature effects on defect production and disordering by displacement cascades in Ni3Al

Molecular dynamics simulations are used to obtain detailed information on d efect production and disordering produced in the primary cascade state of r adiation damage in Ni3Al as a function of irradiation temperature T-irr. Al though the number of Frenkel pairs decreases with increasing T-irr, the siz e of interstitial clusters and the interstitial clustering fraction increas e with temperature. Temperature has a strong effect in enhancing the produc tion of antisite defects, for the number per cascade increases by about 20% as T-irr increases from 100 K to 600 K, and then by about 90% as it increa ses further to 900 K. These effects are believed to be due to the increase in the intensity and lifetime of the thermal spike. The average size of dis ordered zones at different temperatures in the simulations is compared with experimental transmission electron microscopy data and the results are in reasonable agreement. The long range order parameter in the cascade region is found to be consistent with values obtained experimentally on Ni3Al irra diated by ions to a similar damage dose. The chemical short range order par ameter is about 0.6 over the whole range of T-irr considered, suggesting th at the cascade core retains some short range order at high temperature due to local reordering.