A theoretical model was proposed describing a new physical microscopic mechanism of increased fracture toughness of nanocrystalline ceramics. According to this model, when a ceramic with a microcrack was deformed, intensive grain boundary sliding occurred near the crack tip under certain conditions. This sliding was accompanied by the formation of an array of disclination dipoles (rotational defects) producing elastic stresses. These stresses partially compensate the high local stresses concentrated near the microcrack tip and thereby hamper the microcrack growth. The proposed model was used to theoretically estimate the increase in the critical microcrack length (the length above which the catastrophic growth of microcracks occurred) caused by the formation of disclination dipoles during grain boundary sliding in nanoceramics. The increase in the critical microcrack length was a quantitative characteristic of the increased fracture toughness of nanoceramics.

Influence of Grain Boundary Sliding on Fracture Toughness of Nanocrystalline Ceramics. I.A.Ovidko, N.V.Skiba, A.G.Sheinerman: Physics of the Solid State, 2008, 50[7], 1261-5