Densification of copper oxide doped alumina toughened zirconia by conventional sintering

The effect of copper oxide doping (0.05–1 wt%) on the densification, microstructure evolution and mechanical characteristics of alumina toughened zirconia (ATZ: 80 wt% Y-TZP + 20 wt% Al₂O₃) ceramic composites was investigated. Green samples were pressureless sintered using a short hold time of 12 min at temperatures varying from 1250 °C to 1500 °C. The incorporation of up to 0.2 wt% copper oxide was beneficial in promoting densification at low sintering temperature and improving the mechanical properties of ATZ without affecting the tetragonal phase stability. It was found that 0.2 wt% copper oxide addition was most efficacious, and the samples could attain a relative density of approximately 92% at 1250 °C, approximately 97% dense at 1350 °C and above 99% dense at 1450–1500 °C. This approach was also accompanied by an improvement in the Vickers hardness (12.7 GPa) and fracture toughness (6.94 MPam^1/2) when consolidated at 1450 °C/12 min. In comparison, the undoped composite exhibited relative densities of approximately 80% at 1250 °C, 87% at 1350 °C and approximately 97%–98% at 1450 °C-1500 °C. However, the study also found that higher dopant levels (0.5 wt% and 1 wt%) was not beneficial because the tetragonal zirconia phase was disrupted upon cooling from sintering, resulting in the monoclinic phase formation. In addition, low densification and poor mechanical properties were obtained.