The collapse of vacancy clusters: a molecular dynamics study

The method of molecular dynamics has been used to investigate the defects produced by the collapse of vacancy clusters in model f.c.c. and b.c.c. metals. The results are pertinent to the geometry of defects formed by the collapse of displacement cascades, although the nature of the problem was simplified here to the consideration of almost spherical voids containing about 40 vacancies. The collapsed structure is dependent on the form of the interatomic potential and is sometimes too disordered to be described as a conventional defect. However, in a non-equilibrium f.c.c. model representing copper, the void transformed to a stacking-fault tetrahedron, the nature of which is described in section 3. In a non-equilibrium model of a b.c.c. crystal, the void collapsed directly to a loop with Burgers vector : the relevance of this result to the crystallography of loops in b.c.c. metals is discussed in sections 4 and 5