FRACTOGRAPHY AS WELL AS FATIGUE AND FRACTURE OF 25-WT-PERCENT SILICON-CARBIDE WHISKER-REINFORCED ALUMINA CERAMIC COMPOSITE

Fatigue cracked and fast fractured regions in four-point bend specimens prepared from 25 wt% silicon carbide whisker reinforced alumina composite were examined by scanning electron microscopy. This composite was found to be susceptible to a fatigue crack growth phenomenon similar to that in the case of metallic materials, but with a higher crack growth exponent. In the fatigue region, the alumina matrix failed mainly in a transgranular mode and the whiskers mainly failed with a flat fracture surface but without their pullout. On the other hand, in the fast fracture 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 mode. 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 have to be increased by improving the uniformity in distribution of beta-SiC whiskers during hot pressing.