Faceting of high-angle grain boundaries in the coincidence lattice

Faceting of high-angle grain boundaries in Σ=3 and Σ=5 coincidence lattices of the f.c.c. structure was studied using thin-film bicrystal gold specimens of controlled geometry. A number of relatively high-index boundaries in the coincidence lattices (containing relatively low planar densities of coincidence sites) was found to break up into low-energy facets corresponding to low-index planes of the confidence lattices (containing high densities of coincidence lattice sites). These results are consistent with our general expectation that the grain boundary energy decreases as the planar density of coincidence sites increases, i.e., the two-dimensional periodicity of the boundary becomes shorter, and long-range distortions are reduced.