General properties of trijunctions were examined by considering highly symmetrical cubic microstructures in which there were only 3 grain orientations that were rotated 30 from each other about a common <001> axis. It was found that there were 2 families of trijunctions along the common <001>. In one family, there were 2 structures with 2-dimensional projected point symmetry 3m; one with point symmetry, 3, two with point symmetry, m, and one with point symmetry, 1. In the other family, there were 2 with m and one with 1. Also, when the trijunction did not lie along the common <001> axis, 2 types of trijunction with symmetry, m, and a trijunction with symmetry, 1, could occur. In microstructures with trijunctions lying along the common <001> axis, adjacent trijunctions had to belong to different families. This placed restrictions on microstructural topology and grain growth, and was expected to be of particular significance for problems of epitaxy. Application of the principles of symmetry-imposed extrema suggested that the family of less symmetrical trijunctions would often deviate from the common <001> axis, and also revealed that the usual conditions for dihedral angles were insufficient for full equilibrium.

J.W.Cahn, G.Kalonji: Journal of the Physics and Chemistry of Solids, 1994, 55[10], 1017-22