COMPUTER-SIMULATION OF VACANCY AND INTERSTITIAL CLUSTERS IN BCC AND FCC METALS

Interstitial clusters ill bcc-Fe and fee-Cu and vacancy clusters in fc c-Cu have been studied by computer simulation using different types of interatomic potentials such as a short-ranged empirical pair potentia l of Johnson type, short-ranged many-body potentials of Finnis-Sinclai r type and long-ranged pair potentials obtained within the generalized pseudopotential theory. The stability of a self interstitial in bcc-F e was found to be dependent on the range of potential but not on the t ype. Thus, both short-ranged potentials simulated [110] dumb-bell as a stable configuration while in the cast of the long-ranged potential t he stable configuration Is tile [111] crowdion. Nevertheless the struc ture and properties of interstitial clusters were found to be qualitat ively the same with all the potentials. Up to 50 interstitials. the mo st stable clusters were found as perfect dislocation loops with Burger s vector (b) over right arrow = 1/2[111]. The stability of interstitia l clusters in Cu also does not depend on the potential and fer the sam e sizes the most stable configurations are faulted Frank loops 1/3[111 ]{111} and edge loops in die {110} plane. The structure and stability of vacancy clusters in fcc-Cu were found to be dependent mainly on bat h the range of potential and equilibrium conditions. Thus for long-ran ged non-equilibrium pair potentials vacancy clusters in the {111} plan e collapsed and formed vacancy loops or stacking fault tetrahedra depe nding on the shape of the initial vacancy platelet. For the short-rang ed equilibrium many-body potential vacancy clusters do not collapse in to loops or tetrahedra. The process of vacancy clustering in the casca de region has been studied by molecular dynamics. This study has been done for the case of a PKA energy of about 20-25 keV. We found thar th e processes simulated with the short-ranged many-body potential and th e lone-ranged pair potential are qualitatively different. Thus for the many-body potential we have observed melting and crystallization of t he central part of the cascade region, sweeping of vacancies inside du e to the moving of the liquid-solid interface and increasing of vacanc y concentration in the centre of the cascade region: however no signif icant clustering was observed. Contrarily for the long-ranged pair pot ential we have observed a very fast diffusion in the solid crystallite and the formation of stacking fault tetrahedra. The results obtained have been discussed and compared with the experimental data. (C) 1997 Elsevier Science B.V.