Evaluation of effects of crack deflection and grain bridging on toughening of nanocrystalline SiO2 stishovite

Nanocrystalline SiO2 stishovite has a fracture toughness higher than 10 MPa m1/2 due to the toughening mechanism by fracture-induced amorphization. In order to identify other toughening mechanisms which may operate simultaneously, we evaluated effect of crack deflection on fracture toughness. The median deflection angle of nanocrystalline stishovite was lower than polycrystalline ceramics such as silicon nitride and Y-TZP. While the crack deflection can contribute to fracture toughness to some extent, it cannot be the major origin of high fracture toughness of nanocrystalline stishovite. We discussed also the role of grain bridging from the relation between the fracture toughness and grain size.