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Mechanical properties and fracture mechanisms of 20 vol% SiC whisker-reinforced ZrO2 (Y2O3) composites were investigated. The phase composition, fractography and the microstructure of the whisker-matrix interface were studied by XRD, SEM, TEM and HREM. The results show that flexural strength and fracture toughness of SiCw/ZrO2 (with 2 mol% Y2O3) composites increase by 453 MPa and 2.6 MPa m(1/2), respectively. However, in the composites with 6 mol% Y2O3, the increment is only 17 MPa and 1.6 MPa m(1/2), respectively. It reveals that the ZrO2 (2 mol% Y2O3) composites have a good toughening effect by incorporating SiC whiskers. HREM observations indicate that the whiskers in ZrO2 (2 mol% Y2O3) composites are directly bonded with the ZrO2 matrix, only few atom disorder zones exist at the interface. In contrast, for ZrO2 (6 mol% Y2O3) composites, there is a thin, uniform layer of amorphous phase at the interface between SiC whisker and ZrO2 matrix, indicating that high Y2O3 content promotes the formation of an interfacial layer. The study of fracture surfaces by SEM indicates that the main toughening mechanisms in SiCw/ZrO2 (with 2 mol% Y2O3) composites are crack deflection, crack bridging, whisker pull-out and dynamic t-->m transformation. Crack deflection is the main toughening mechanism in SiCw/ZrO2, (with 6 mol% Y2O3) composites.