Transformation toughening of Al₂O₃/ZrO₂ laminated ceramics with residual compressive stress

With the help of scanning electronic microscopy and X-ray diffraction, the relationships of microstructure characteristics, phase assemblage, and fracture micrograph of Al₂O₃/ZrO₂ laminated ceramics were studied. Compared with monolithic Al₂O₃/ZrO₂ ceramics, the existence of surface compressive stresses greatly restrained the growth of ZrO₂ and Al₂O₃ grains at high sinter temperature, fined the grain size, and increased the content of metastable t-ZrO₂, which made the fracture transformation energy quantity 70% higher than that of the monolithic ceramics. The trans-granular and inter-granular fracture features were observed in the surface and center layers, which further verified that transformation toughening is the main mechanism, whereas, micro-crack toughening is helpful for enhancing fracture toughness.