抄録
Pressureless sintered TiO2 bodies were annealed to change their grain sizes from 10μm to 59μm. Microstructural observations of the specimens indicated that the spontaneous critical grain size of TiO2 was about 20μm, and the mean length of network of microcracks was about 1.5mm. The thermal expansion analysis indicated that the volume fraction of spontaneous microcracks was about 1.5×10-3. The grain size dependences of Young's modulus and fracture stress ensured the spontaneous microcracking. Fracture toughness KIC was measured by a chevron-notched beam method. KIC took a constant value below the critical grain size, but it was reduced to about 65% above the critical grain size. The reduction of KIC could be estimated quantitatively using the length and volume fraction of microcracks.
