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 gravita-tional separation self-propagate high-temperature synthesis (SHS) process. The microstructure of the ceramics was observed by meansof SEM and EPMA. The fracture toughness of the multiphase ceramics was tested by using the Vickers indentation method. Thefracture toughness of hypoeutectic Al2O3-ZrO2 multiphase ceramics is 15.96 MPa·m1/2 and that of hypoeutectic Al2O3-ZrO2 multiphaseceramics is 15.23 MPa·m1/2. The toughening mechanisms were systematically investigated by means of SEM and XRD. The resultsshow that the bridging toughening mechanism, stress induced ZrO2 transformation toughening mechanism, and microcrack tougheningmechanism are the predominant toughening mechanism.