Creep deformation of whisker-reinforced alumina

Abstract

Abstract The creep behavior of alumina reinforced with SiC whiskers was studied under different loading geometries and test ambients. Deformed microstructures were examined and characterized to ascertain mechanisms of deformation and damage, and to understand better the causes of the measured creep response. The composites undergo creep by grain boundary sliding that is generally accomodated by diffusion, although high stresses and temperatures lead to increasing degrees of creep damage in the form of cavitation at interfaces and grain boundaries. Creep rates decrease with increasing whisker volume fraction as whiskers increasingly inhibit grain boundary sliding. In aerobic test atmospheres, the composites undergo a thermal oxidation reaction that generates glassy films at internal boundaries and carbon monoxide gas, both of which facilitate cavitational damage. Systematic study of the thermal oxidation reaction in the absence of stress shows that oxidation occurs at interfaces, generating silica glass and graphitic carbon via a “carbon-condensed” oxidation displacement reaction.