Rotational Plastic Deformation in Nanocrystalline Materials

The key features of NCMs (i.e., high density of grain boundaries and triple junctions with their generic defects like grain boundary dislocations and disclinations) which mainly determine their mechanical properties, may stimulate, under special conditions, the generation and development of a rotational mode of plastic flow. This mainly concerns NCMs fabricated under highly non-equilibrium conditions like ball milling and severe plastic deformation. In the present chapter, we consider different models of rotational plastic deformation in nano- and polycrystalline materials, when this deformation is realized by conservative motion of partial disclination dipoles capturing or issuing lattice dislocations or by the formation of multipole configurations of partial grain boundary disclinations leading to rotation of grains.