It was noted that computer simulations had shown that small clusters of self-interstitial atoms which were formed in displacement cascades consisted of crowdions and were highly mobile in the crowdion direction. Molecular dynamics were used here to investigate whether the small perfect vacancy loops which were formed in cascades in a-Fe and Cu were also mobile. Loops in Fe which contained more than about 30 vacancies were found to produce atomic displacements during annealing, due to a thermally activated movement in the direction of their Burgers vector that was qualitatively similar to the mechanism of self-interstitial atom cluster motion. Although vacancy clusters were slightly less mobile than self-interstitial atom clusters under the same conditions, their mobility was significantly higher than that of the monovacancy. The motion of vacancy loops in Cu did not occur because they transformed into sessile configurations which were similar to stacking-fault tetrahedra. The results indicated a possibly important contribution of vacancy-loop mobility to the difference in radiation damage between body-centered cubic and face-centered cubic metals, and between face-centered cubic metals with differing stacking-fault energies.

Thermally Activated Glide of Small Dislocation Loops in Metals. J.N.Osetsky, D.J.Bacon, A.Serra: Philosophical Magazine Letters, 1999, 79[5], 273-82