The damage which was produced by displacement cascades in the hexagonal close-packed -phase metal at 100K was investigated by using molecular dynamics methods, involving a many-body interatomic potential. This was the first simulation to be made of cascades in the hexagonal close-packed structure, and 32 cascades which ranged in energy from 0.3 to 5keV were generated. Computer-generated plots were used to visualize the nature and arrangements of the point defects which were produced in the cascade events. There was no apparent effect of the primary knock-on atom direction, and individual replacement sequences made only a small contribution to the final damage state. Views of the displaced atoms, along the basal planes, clearly showed regions with liquid-like disorder. However, they were small (even at 5keV) and did not lead to vacancy clustering when crystalline order was restored. The production efficiency of Frenkel pairs declined, with increasing cascade energy, in a similar manner to that which had been found for cubic metals. Interstitial clusters were formed during the cascade process, and self-interstitial atoms were observed to migrate preferentially along basal planes during the thermal spike. The hexagonal close-packed structure was expected to exhibit anisotropy in atomic mixing during cascade-inducing radiation, but analysis of the mean square displacement of atoms in the final state of 2 and 5keV cascades showed that mixing in the present model was essentially isotropic.

S.J.Wooding, D.J.Bacon, W.J.Phythian: Philosophical Magazine A, 1995, 72[5], 1261-79