Microstructural relationship with fracture toughness of undoped and rare earths (Y, La) doped Al2O3–ZrO2 ceramic composites

Ceramic composites in undoped Al₂O₃–5 wt% ZrO₂ (AZ) and doped with rare earth elements Y, La separately and simultaneously were prepared by solid state sintering process. These composites were characterized for microstructural investigation and determination of phase formation to draw a possible relationship between these characterization results with the fracture toughness measured by single-edge precracked beam (SEPB) test method using three-point bend test. The fracture toughnesses of Y and Y + La doped AZ are found to be higher for samples sintered at 1700 °C for long soaking times, than that of La doped and undoped AZ composites. It is predicted from the XRD and EDS analyses that the phases of Zr_0.88Y_0.12O_1.94 and Zr_0.935Y_0.065O_1.968 are formed at or near the intergranular region and therefore the higher fracture toughness of Y and Y + La doped AZ composites compared to undoped AZ and La doped AZ composite for samples sintered at 1700 °C for long soaking times, is attributed to these intergranular phases.