Grain boundary-dislocation interactions

Abstract

Our current understanding of the structure of grain boundaries will be described first. The structure of low angle boundaries can be rigorously described in terms of arrays of dislocations. The structure of high angle boundaries continues to defy a complete and rigorous description. A model has been developed based on coincidence site lattices. This model postulates the presence of grain boundary dislocations even at high angles of misorientation to accommodate the deviation from exact coincidence conditions. The Burgers vectors of such grain boundary dislocations can be found by the translation vectors of thedsc lattice. An interesting point is that the Burgers vectors are not lattice translations. Hence the dislocations are confined to the surface of the boundary and cannot move into the grain. Alternative descriptions of the structure of grain boundaries make appeal to the Bernal type of polyhedral voids that occur in metallic glasses. A brief discussion of the strength of this approach will be outlined. Dislocations at grain boundaries can affect both grain boundary migration and sliding. The possible mechanisms for these phenomena will be described. The importance of understanding these mechanisms to explain deformation of metals at high temperatures will be stressed.