MOLECULAR-DYNAMICS STUDY OF THE RELAXATION PROCESSES INDUCED BY DEFECTS IN METALS

The aim of this work is to study the relaxation processes associated w ith the most common defects generated in solids by ion bombardment. Va cancies, self-interstitials, di-vacancies, di-self-interstitials and s mall clusters of vacancies and/or self-interstitials were generated in a microcrystal of copper, allowing the system defect+crystal to evolv e dynamically. Elastic deformation and effective volumes were some of the physical magnitudes determined in this study. The depth dependence of the above-mentioned magnitudes was also investigated. The crystals had 13 x 13 x 13 cubic unit cells containing 9842 atoms. Prior to the generation of any defect, relaxation of the whole crystal at T=0 K wa s performed in order to isolate the relaxation processes being studied from relaxation processes such as surface relaxation or the displacem ent of the atoms to accommodate themselves exactly at the minima of th e potential energy of the lattice. The tension fields generated in the solid by a single point defect (one interstitial or one vacancy) were calculated. Their corresponding effective volumes were also determine d, showing a strong dependence on the distance to the point at which t he defects were generated. Both vacancy and interstitial effective vol umes tend to zero for large distances from the defect. For the vacancy , distances greater than 9 Angstrom are enough for the defect to produ ce a negligible deformation. The interstitial, however, requires dista nces of the order of 15 Angstrom to be absorbed by the lattice without significant displacement of the lattice atoms.