The toughening behavior of whisker-reinforced ceramics is analyzed in terms of a whisker bridging zone immediately behind the crack tip. This approach is consistent with microscopy observations which reveal that intact bridging whiskers exist behind the crack tip as a result of debonding of the whisker-matrix interface. The theoretical results based on both the stress intensity and the energy change introduced by bridging whiskers reveal the dependence of toughening upon the composition and matrix, interface, and whisker properties. Furthermore, the analytical models of whisker bridging accompanied by very limited pullout accurately describe experimental observations of the toughening behavior in several Sic-whisker-reinforced ceramics. Such analytical descriptions also indicate that increases in whisker size and strength and modification of interface properties will result in further increases in toughness by whisker reinforcement.

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The microstructure and chemistry of grain-boundary phases in silicate-doped YZO3-ZrO2 ceramics were evaluated by analytical electron microscopy. Two different silicate compositions were used: one an aluminosilicate and the other a horosilicate glass. These grain-boundary phases had a significant impact on the grain morphology, the chemical composition of the grains, and the crystallization of second phases. These results indicate that controlled additions of specific glass phases may provide a means for tailoring the microstructure and physical properties of zirconia ceramics. [