Study on Densification of Gd2Zr2O7-Based Ceramic Target for EB-PVD Application and Its Effect on Fracture Toughness

In this study, the Gd2Zr2O7-based ceramic target was densified via pressureless sintering which follows well with Kingery’s three-stage sintering theory. Sintering temperature is the key factor affecting the densification of targets. In the initial stage, when the sintering temperature is in the range of 1200–1450 °C, the porosity decreases with the density of targets slowly increasing to 64.71%. Grain boundary diffusion controls the densification process. In the middle stage, at 1450–1500 °C, the density ratio of the target rapidly rises to 77.6%. The competition between grain boundary migration rate and pore shrinkage rate leads to the maximum isolated porosity. In the final stage, when the sintering temperature is above 1500 °C, the density ratio of the target significantly increases to 97.28% at the temperature of 1600 °C. Even when the holding time is extended to 7 h at 1500 °C, the density ratio of the target only reaches 85.72%. With the increase in sintering temperature and prolongation of holding time, the fracture toughness of the ceramic targets exhibited a trend of initial increase followed by a decrease. Density ratio and grain size were identified as key factors influencing fracture toughness. When the density ratio reached approximately 80%, the fracture toughness achieved its maximum value of 2.245 MPa·m0.5. When the sintering temperature exceeds 1450 °C, both the Young’s modulus and hardness of the targets increase rapidly, which significantly enhances their fracture toughness. However, with the increase in sintering temperature or holding time, the grain grows rapidly. This excessive grain growth reduces grain boundary.