Effect of Al₂O₃ addition on preparation and properties of AlN-Al₂O₃ multiphase ceramics

AlN-Al₂O₃ composites were prepared by hot-pressing sintering method at 1650°C under nitrogen atmosphere using AlN, Al₂O₃ as raw materials and Y₂O₃ as sintering additive. The phase composition and microstructure of AlN-Al₂O₃ were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The effect of Al₂O₃ addition on bending strength, thermal conductivity and dielectric properties of the materials were investigated. The results show that Al₂O₃ addition promotes the sintering densification and inhibits the grain growth of AlN matrix. The dense AlN-Al₂O₃ composites can be prepared when Al₂O₃ addition is 20 wt% and 30 wt%. Al₂O₃ particles play an obvious enhancement function on AlN matrix by its high strength and dispersion strengthening mechanism. As the Al₂O₃ addition increasing, the bending strength of the materials increases significantly, meanwhile thermal conductivity and dielectric properties are also improved. Typically, for the composites with 30 wt% Al₂O₃ addition, bending strength and thermal conductivity reach the maximum of 457 MPa and 57 W/(m · K), whereas dielectric constant and dielectric loss reach the minimum of 9.32 and 2.6 × 10^-4, respectively. When Al₂O₃ addition reaches 40 wt%, the reaction between AlN and Al₂O₃ leads to the formation of AlON, which results in that the bending strength, thermal conductivity and dielectric properties of the composites decrease significantly.