Mechanical properties and interfacial microstructure of SiC whisker-reinforced ZrO₂Y₂O₃ composites

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.