Role of grain boundary plane in grain boundary engineering

There is an increasing amount of interest in grain boundary engineering (GBE) to improve the properties of the grain boundary network. In general, research has concentrated on use of a grain boundary misorientation based approach, namely, the coincidence site lattice (CSL), to categorise 'special' boundaries. The present paper presents the case that the specialness of grain boundaries is based on having at least one low index plane at the boundary, rather than because the boundary is a CSL type. It is shown that grain boundary planes play a pivotal role in GBE, and hence, an approach which focuses on the plane is advocated. Some potential routes for 'grain boundary plane engineering' are discussed.