Abstract
TiB2-6%TaB2-1%CoB-2%TiC ceramics have a bending strength of 1000MPa and a porosity of 0.1vol%, but fracture toughness KIC of 3-3.5MPam1/2. Therefore, our desire is to improve the fracture toughness Klc of these ceramics. TiB2-6%TaB2-1%CoB-2%TiC-30%m-ZrO2 and TiB2 6%TaB2-1%CoB-2%TiC-40%t-ZrO2 ceramics in which t-ZrO2 contains 12mol%CeO2 have KIC of 7.5 and 12MPam1/2, respectively. It is thought that the high KIC of the ceramics containing m-ZrO2 and t-ZrO2 stabilized by CeO2 are mainly caused from the following reasons. The fracture cracks are stopped and diffracted by the micro-cracks between ZrO2 grain and other chemical composition grain which are caused by the difference of thermal expansion and which are occured by influence of the fracture cracks.
