It was recalled that the well-known sigma combination rule governed the connectivity of coincidence site lattice grain boundaries at triple junctions, but was strictly applicable only to ideal coincidence site lattice boundaries. This relationship was extended here to boundaries that deviated from ideal coincidence site lattice misorientations, and a complementary rule was derived that related their angular deviations. This so-called deviation limit rule stated that the angular deviation of one boundary at a triple junction

was at most equal to the sum of the other 2 deviation angles. This analysis also provided some insight into apparent violations of the sigma combination rule, which could arise when one boundary deviated beyond the allowable limit for coincidence site lattice classification.

Combination Rule for Deviant CSL Grain Boundaries at Triple Junctions. M.Frary, C.A.Schuh: Acta Materialia, 2003, 51[13], 3731-43