IMPROVED FLAW TOLERANCE IN ALUMINA CONTAINING 1-VOL-PERCENT ANORTHITE VIA CRYSTALLIZATION OF THE INTERGRANULAR GLASS

The intergranular phase in an alumina containing 1 vol% anorthite glass was crystallized in order to enhance internal residual stresses within the microstructure. The influence of crystallization on the mechanical behavior was investigated by the indentation-strength method. Such crystallization was found to result in a marked improvement in the flaw tolerance of this alumina, indicative of strong R- or T-curve behavior. These results are discussed in the light of a theoretical model which assumes grain-localized crack bridging to be the predominant toughening mechanism. Particular reference is made to the influence of residual stresses and interfacial properties on grain pullout across the crack walls in the wake of the crack tip.