Relaxation of metals: A model based on MD calculations

The relaxation processes of copper associated with the presence of point defects such as vacancies and interstitials, have been analysed via Molecular Dynamics (MD). The accommodation of the atoms in the lattice is due to a tension field which arises from the presence of the above mentioned defects, These tension fields are calculated and expressed in terms of the effective displacement volume associated with the corresponding defect. Two main conclusions are: First, the finiteness of the tension fields, in contradiction with usual relaxation models applied in solving problems related to atomic mixing. Second, the relaxation process may be considered on average as isotropic except for very near to the surface, where the process is markedly anisotropic due to the surface itself. These results are summarised by means of an analytical expression, applicable in studies of solid relaxation and in other related problems of ion beam modification of materials. (C) 1998 Elsevier Science B.V.