Interaction between lattice dislocations and grain boundaries in F.C.C. materials

Abstract

Introduction The interaction between dislocations and grain boundaries is generally believed to be of great importance to the mechanisms of mechanical failure in metals. Especially the difference between ductile and brittle fracture might be explained by variations in the way of interaction between dislocations and grain boundaries. In this paper we concentrate on the detailed phenomena, at the atomic level, which occur when extrinsic lattice dislocations impinge on the grain boundary. One of the topics of interest is the meaning of the well known structural unit model [1] for the interaction between dislocations and grain boundaries. The mechanisms for the interaction between dislocations and grain boundaries have to do with the DSC lattice [2]. A grain boundary dislocation has a Burgers vector which is a vector of the DSC lattice associated with the grain boundary. Its core may be associated with a step in the boundary plane. In general two mechanisms for the interaction between a lattice dislocation and a grain boundary can be discriminated. The first mechanism is referred to as dislocation absorption, which can be explained by the dissociation in the grain boundary plane of the lattice dislocation into DSC dislocations. As the Burgers vectors of the DSC dislocations are relatively small, the dislocation can reduce its energy in this way. The second mechanism for the interaction is referred to as dislocation transmission. A lattice dislocation in one grain can create another lattice dislocation in the other grain, usually leaving a residue at the boundary. The residue is always a DSC dislocation. A number of experimental studies of dislocation-grain boundary interactions has been carried out in the past. See e.g. ref. [3,4].