Abstract
Mullite-ZrO2 and mullite-ZrO2-Al2O3 composite ceramics were prepared by in-situ reaction between alumina and synthetic zircon powders. The mechanical properties of these composites were investigated as a function of Al2O3/SiO2 weight ratio in the matrix. Three-point bending strength at room temperature and fracture toughness increased with increasing content of Al2O3 over the entire range of the Al2O3/SiO2 ratio from 70/30 to 90/10. In particular, the mean bending strength was 650MPa in the vicinity of the composition ratio of 90/10. As judged by the crystalline phases and observation of the fine structure, a strengthening mechanism which acts significantly on the mechanical properties of the composite sintered bodies was indicated by the following: (1) grain size reduction of the mullite matrix by dispersion of the Al2O3 phase, (2) nano-structure in which Al2O3 and ZrO2 particles were finely dispersed in the mullite grains and (3) dispersion-effect of the Al2O3 and ZrO2 crystalline phase with a larger thermal expansion coefficient than that of the matrix.
