MD Investigation of Thermal Spike Effects on Defect Production and Disordering by Displacement Cascades in Ni₃Al

Abstract

Molecular dynamics (MD) simulations are used to obtain detailed information on defect production and disordering produced in the primary cascade state of radiation damage in Ni₃AI as a function of irradiation temperature, T_irr Although the number of Frenkel pairs decreases with increasing T_irr, the size of interstitial clusters and the interstitial clustering fraction increase with T_irr. The number of antisites defects per cascade increases by about 20% as Tir increases from 100 to 600K, and then by about 90% from 600 to 900K due to the increase in the intensity and lifetime of the thermal spike. The average size of disordered zones at different Tir, 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 Ni₃A1 irradiated by ions to a similar dose. The chemical short-range order parameter is about 0.6 over the whole range of T_irr, considered, suggesting that the cascade core retains some short-range order at high temperature due to local reordering.