It was recalled that, due to the discrete nature of their dislocation structure, finite-length grain boundaries in polycrystalline materials exhibited discrete values of misorientation angle. For a grain boundary with a length that was not a multiple of the grain-boundary period, this led to the formation of specific disclinations at their junctions with neighboring grain boundaries. These compensated for the difference between the misorientations of finite and infinite boundaries. The origin of these compensating disclinations within grain-boundary triple-junctions was clarified here, and their strength was calculated by using the disclination structural unit model. It was shown that, for a grain boundary with a length of about 10nm, the junction disclinations could have a strength that was not more than 1°. This contrasted with previous calculations, which had indicated much larger values. The elastic energies of triple junctions, due to compensating disclinations, were calculated for equilibrium and non-equilibrium structures of a finite-length grain boundary. These differed with regard to the position of the grain-boundary dislocation network with respect to the junctions. The calculations showed that triple-junction energies were comparable to dislocation energies, and that compensating disclinations could play an important role in determining the properties of nanocrystalline metals with grain sizes of less than about 10nm.

On the Origin and Energy of Triple Junction Defects Due to the Finite Length of Grain Boundaries. A.A.Nazarov, D.V.Bachurin, O.A.Shenderova, D.W.Brenner: Interface Science, 2003, 11[4], 417-24