CREEP DEFORMATION OF WHISKER-REINFORCED ALUMINA

The creep behavior of alumina reinforced with SiC whiskers was studied under different loading geometries and test ambients. Deformed micros tructures were examined and characterized to ascertain mechanisms of d eformation and damage, and to understand better the causes of the meas ured creep response. The composites undergo creep by grain boundary sl iding that is generally accommodated by diffusion, although high stres ses and temperatures lead to increasing degrees of creep damage in the form of cavitation at interfaces and grain boundaries. Creep rates de crease with increasing whisker volume fraction as whiskers increasingl y inhibit grain boundary sliding. In aerobic test atmospheres, the com posites undergo a thermal oxidation reaction that generates glassy fil ms at internal boundaries and carbon monoxide gas, both of which facil itate cavitational damage. Systematic study of the thermal oxidation r eaction in the absence of stress shows that oxidation occurs at interf aces, generating silica glass and graphitic carbon via a ''carbon-cond ensed'' oxidation displacement reaction.