It was recalled that defect accumulation was the principal factor leading to the swelling and embrittlement of materials during irradiation. It was commonly assumed that, once defect clusters nucleated, their structure remained essentially constant while they grew in size. Here, a new mechanism which had been discovered during accelerated molecular dynamics simulations of vacancy clusters in face-centred cubic metals, was described. It involved the direct transformation of a vacancy void into a stacking fault tetrahedron via a series of 3-dimensional structures. This mechanism contrasted with collapse to give a 2-dimensional Frank loop which then transformed into a stacking-fault tetrahedron. The kinetics of this mechanism were characterized by an extremely large pre-factor which was tens of orders of magnitude larger than that typical of atomic processes in face-centred cubic metals.

Direct Transformation of Vacancy Voids to Stacking Fault Tetrahedra. B.P.Uberuaga, R.G.Hoagland, A.F.Voter, S.M.Valone: Physical Review Letters, 2007, 99[13], 135501