A theoretical model was proposed which described the strengthening of nanocrystalline materials due to the effects of grain-boundary triple-junctions as obstacles to grain-boundary sliding. A dependence of the yield stress, which characterized grain-boundary sliding, upon grain size and triple-junction angle was revealed by the model. Using this dependence, it was found that the yield stress of as-fabricated nanocrystalline materials, depended upon a competition between conventional dislocation slip and grain-boundary sliding. The yield-stress dependence upon grain size in heat-treated nanocrystalline materials was instead described as that caused by a competition between conventional dislocation slip and Coble creep. Grain-size and triple-junction angle distributions were incorporated into the analysis in order to account for the distributions of grain size and triple-junction angles that occurred in real specimens. The predictions of the model were in good agreement when compared with experimental data on as-fabricated and heat-treated nanocrystalline materials.

Yield Stress of Nanocrystalline Materials - Role of Grain-Boundary Dislocations, Triple Junctions and Coble Creep. M.Y.Gutkin, I.A.Ovidko, C.S.Pande: Philosophical Magazine, 2004, 84[9], 847-63