MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF SIC WHISKER-REINFORCED ZRO2-Y2O3 COMPOSITES

The mechanical properties of 20 vol.-%SiC whisker reinforced ZrO2-Y2O3 composites containing 2 and 6 mol-% Y2O3 were measured at room temperature and the fracture surface was examined. The results indicate that the mechanical behaviour of the composites is strongly influenced by the Y2O3 content. The magnitude of the enhancement ofthe toughness in composites containing 2 mol.-% Y2O3 compared with unreinforced ZrO2-Y2O3 matrix is larger than that for the composites containing 6 mol-% Y2O3. Crack propagation modes were characterised by crack deflection, whisker bridging, and whisker pullout. High resolution electron microscopic observations show that in composites containing 2 mol.-% Y2O3 the whiskers are directly bonded to the matrix. However; in composites containing 6 mol.-%Y2O3 there is always a thick amorphous layer at the interface, indicating that the high Y2O3 content has promoted the formation of interfacial amorphous layers. These interfacial amorphous layers strengthen the interfacial bonding, resulting in a composite with a low fracture toughness.