The role of disclinations in deformation behaviour and structure formation of nanocrystalline materials was discussed. A short overview of the properties of disclination defects was given. Then a number of disclination-based models was advanced for the explanation of nanocrystalline materials mechanical properties. The relay dislocation–disclination model of plastic shear propagation in nanocrystalline materials was developed in detail. This model was based on the switching between translation and rotation deformation modes of plastic deformation. It was argued that the translation mode in nanocrystalline materials was due to the grain boundary dislocation sliding and the rotation mode was due to the formation of wedge junction disclinations which emerge by co-operation processes of intergrain dislocation motion or co-operative grain boundary diffusion. The dependence of deforming stress on the grain size for various grain aspect ratios was demonstrated in the case of relay dislocation–disclination mechanism operation. It was shown that the transition from one mode to another might contribute to the inverse Hall–Petch relationship observed in nanocrystalline materials below a critical grain size.

Disclinations in Nanocrystalline Materials - Manifestation of the Relay Mechanism of Plastic Deformation. A.E.Romanov, A.L.Kolesnikova, I.A.Ovidko, E.C.Aifantis: Materials Science and Engineering A, 2009, 503[1-2], 62-7