FRACTURE-BEHAVIOR OF AL2O3 SIC-PLATELET COMPOSITES/

Mechanical behavior of hot-pressed SiC platelet reinforced alumina com posites has been analyzed as a function of SiC platelet content for tw o different alumina matrix powders. Fracture toughness and flexural st rength at temperatures ranging from 25 to 1200 degrees C, R-curve beha vior, and thermal shock resistance have been determined. Small differe nces in the impurity content of the starting Al2O3 powders strongly de termine the microstructure and the mechanical behavior of Al2O3/SiC-pl atelet composites. Low alkali content alumina led to composites with l arge matrix grain size which presented spontaneous microcracking. At h igh temperature, a high viscosity liquid phase is formed that shields cracks enhancing mechanical properties and R-curve behavior. A small a mount of impurities reduced Al2O3 matrix grain size and avoided sponta neous microcracking. Enhanced fracture toughness (up to 30%) at room t emperature, R-curve behavior, and thermal shock resistance were achiev ed for these materials.