Effect of CeO2 addition on densification and microstructure of Al2O3–YSZ composites

Alumina (Al2O3) and alumina–yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO2) were prepared by spark plasma sintering (SPS) at temperatures of 1350–1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al2O3 based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl11O18 grains was observed in the ceria containing composites sintered at 1400 °C. Al2O3–YSZ composites without CeO2 had higher hardness than monolithic Al2O3 sintered body and the hardness of Al2O3–YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO2 increased from 10 to 30 vol%. The fracture toughness of Al2O3 increased from 2.8 MPa m1/2 to 5.6 MPa m1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m1/2, was achieved with the addition of 30 vol% YSZ.