STRUCTURE AND PROPERTIES OF POINT DEFECTS IN GRAIN BOUNDARIES IN METALS

Abstract
The atomistic structures of a number of single vacancies and interstitials at a number of sites in the cores of a number of grain boundaries in a number of metals were calculated [1,2] by the method of molecular statics. These point defects were found to exist in all cases as bona fide point defects. In some cases binding energies to the boundaries were also determined. The thermally activated jumping of single vacancies and interstitials in a Σ=5 tilt boundary in BCC iron was also studied by means of molecular dynamics [2,3]. The vacancies executed relatively rapid jumps between a variety of sites in the boundary core to produce diffusive displacements mainly along the tilt axis. The interstitial became tightly bound to a particular site in the boundary and was unable to jump thermally amongst other sites. All of these results were considered along with other information in the literature, and it was concluded [4] that grain boundary self-diffusion in this boundary (and very likely most boundaries in metals) occurs by a vacancy exchange mechanism.