Simulated displacement cascades at 100K in this material were analyzed in order to investigate the effect of the energy, of primary knock-on atoms, upon the kinetics of defect production, the degree of disorder and on atomic mixing of the various atomic species. It was found that Ni atoms were more readily displaced during the ballistic phase, but they also returned to lattice sites at a faster rate than did Al atoms. The characteristic time for this recombination increased with increasing primary knock-on energy, and this was attributed to the development of a highly defective so-called ‘molten’ zone with a radius that was equal to about 3 times the product of the unit cell parameter and the cube root of the primary knock-on energy. The final concentration of antisite defects in this region was between 2 and 5% for most cascades. This was consistent with an integrated long-range order parameter of 0.85 to 0.9 over the same region. The value of this parameter in the cascade center fell to between 0.5 and 0.7 for all values of primary knock-on energy. The chemical short-range order was almost entirely lost at the peak number of ballistic displacements; especially in the case of high cascade energies. It finally declined with increasing primary energy. A high proportion of the atomic mixing occurred in the ballistic phase, and was larger for Ni atoms; thus implying that the phenomenon was not purely a liquid-like process. This conclusion was inconsistent with some published data. The cascade thermal diffusivity was found to be approximately independent of the primary energy. The mechanisms of radiation-induced disordering were assessed, and the importance of so-called wrong recombination in the highly defective region that was produced in the thermal spike was emphasized. It was noted that replacement collision sequences played only a small role in the disordering process.

Molecular Dynamics Study of Displacement Cascades in Ni3Al II. Kinetics, Disordering and Atomic Mixing. Gao, F., Bacon, D.J.: Philosophical Magazine A, 1995, 71[1], 65-84