A theoretical model was suggested which describes cooperative action of grain boundary sliding and rotational deformation in mechanically loaded nanocrystalline materials. Focuses were placed on the crossover from grain boundary sliding to rotational deformation occurring at triple junctions of grain boundaries. In the framework of the model, gliding grain boundary dislocations at triple junctions of grain boundaries split into dislocations that climb along the adjacent boundaries. The splitting processes repeatedly occurring at triple junctions give rise to climb of grain boundary dislocation walls that carry rotational deformation accompanied by crystal lattice rotation in grains of nanocrystalline materials. The role of grain boundary sliding, rotational deformation and conventional dislocation slip in high-strain-rate superplastic flow in nanocrystalline materials was discussed.

Crossover from Grain Boundary Sliding to Rotational Deformation in Nanocrystalline Materials. M.Y.Gutkin, I.A.Ovidko, N.V.Skiba: Acta Materialia, 2003, 51[14], 4059-71