FRACTOGRAPHY OF FATIGUED AND FRACTURED REGIONS IN A SILICON-CARBIDE WHISKER-REINFORCED ALUMINA COMPOSITE

Fatigue cracked and fast fractured regions in four point bend specimens prepared from 25 wt% silicon carbide whisker reinforced alumina composites were examined by Scanning Electron Microscopy. In the fatigue cracked region, the alumina matrix failed mainly in a transgranular mode and the whiskers failed mainly with a flat fracture surface but without pullout. On the other hand, in the fast fractured region, the whiskers failed predominantly by pullout and the alumina matrix failed in a mixed mode with about half in transgranular and the other half in intergranular fracture. Thus, to improve the fracture toughness of the material, the grain boundary strength of alumina and the matrix whisker interfacial bonding should be improved. To increase the resistance to fatigue, the fracture strength of the alumina grains should be improved by using finer alpha-alumina particles and the fatigue strength of the whisker has to be increased by improving the uniformity in distribution of beta-SiC whiskers during hot pressing.