Effects of La_2O_3 addition on microstructure development and physical properties of harder ZTA-CeO_2 composites with sustainable high fracture toughness

The influence of La₂O₃ inclusion (0–3 wt%) on the microstructure, phase formation and mechanical properties of zirconia toughed alumina (ZTA) added with 5.0 wt% CeO₂ was investigated. ZTA CeO₂ composites were sintered at 1600 °C for 4 h. The microstructure, phase formation, density, fracture toughness and hardness properties were characterised through FESEM, Microscopy Image Analysis Software and XRD diffractometer, Archimedes principle and Vickers indentation technique, respectively. The XRD, image processing and FESEM reveal the existence of LaAl₁₁O₁₈. The addition of La₂O₃ incites the sintering, microstructure refinement, densification of ZTA-CeO₂ matrix and phase transformation. Hence, the hardness of ZTA-CeO₂ ceramics is increased rapidly based on refinement of Al₂O₃ grains, densification of ZTA-CeO₂ composites and porosity reduction. It is observed that the fracture toughness is enhanced through in situ formation of elongated LaAl₁₁O₁₈ grains. The addition of 0.7 wt% La₂O₃ culminated in the achievement of the optimum findings for density (4.41 g/cm³), porosity (0.46%), hardness (1792 HV) and fracture toughness (8.8 MPa·m^1/2). Nevertheless, excess La₂O₃ is proven to be detrimental as it displays poor mechanical properties due to the poor compactness of numerous LaAl₁₁O₁₈ grains, coarsening of Al₂O₃ grains and decline in density.