Toughening mechanism of lined Al₂O₃-ZrO₂ multiphaseceramics in SHS composite pipes

Hypoeutectic and hypereutectic Al₂O₃-ZrO₂ multiphase ceramics-lined composite pipes were produced by using the gravitational separation self-propagate high-temperature synthesis (SHS) process. The microstructure of the ceramics was observed by means of SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. The fracture toughness of hypoeutectic Al₂O₃-ZrO₂ multiphase ceramics is 15.96 MPa·m^1/2 and that of hypoeutectic Al₂O₃-ZrO₂ multiphase ceramics is 15.23 MPa·m^1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The results show that the bridging toughening mechanism, stress induced ZrO₂ transformation toughening mechanism, and microcrack toughening mechanism are the predominant toughening mechanism.