ANISOTROPIES AND MECHANICAL-PROPERTIES OF HOT-PRESSED AL2O3 AND SIC-WHISKER AL2O3 COMPOSITES/

The anisotropies and mechanical properties of hot-pressed Al2O3 and Si C-whisker/Al2O3 composites were investigated. The c-axis of Al2O3 crys tals in monolithic Al2O3 was oriented in the direction of hot-pressing . The same tendency was observed in Al2O3 matrices of composites, but orientation of Al2O3 crystals was smaller than that of monolithic Al2O 3. SiC-whiskers obstructed plastic deformation and mass transfer of Al 2O3 matrices. The twist mode crack deflection was remarkable on fractu red surfaces of polycrystalline Al2O3 in which the main crack propagat ed perpendicular to hot-pressing direction. This was caused by the ori entation of Al2O3 crystals. This anisotropy resulted in a small differ ence in fracture toughness; however, other mechanical properties didn' t change. The fracture mode of SiC-whisker/Al2O3 composites was obviou sly changed, depending on the direction of crack extension as compared with the changes observed in monolithic Al2O3. However, there was no difference in mechanical properties among the composites. Macroscopic fracture mode seemed to have less effect than microscopic fracture mec hanism, such as whisker bridging and pull-out.