Fracture behavior of Al₂O₃/SiC-platelet composites

Mechanical behavior of hot-pressed SiC platelet reinforced alumina composites has been analyzed as a function of SiC platelet content for two different alumina matrix powders. Fracture toughness and flexural strength at temperatures ranging from 25 to 1200 °C, R-curve behavior, and thermal shock resistance have been determined. Small differences in the impurity content of the starting Al₂O₃ powders strongly determine the microstructure and the mechanical behavior of Al₂O3/SiC-platelet composites. Low alkali content alumina led to composites with large matrix grain size which presented spontaneous microcracking. At high temperature, a high viscosity liquid phase is formed that shields cracks enhancing mechanical properties and R-curve behavior. A small amount of impurities reduced Al₂O₃ matrix grain size and avoided spontaneous microcracking. Enhanced fracture toughness (up to 30%) at room temperature, R-curve behavior, and thermal shock resistance were achieved for these materials.