Effects of sintering aids on microstructure, mechanical, and optical properties of AlON ceramics synthesized by SPS

Aluminum oxynitride (AlON) ceramics doped with different sintering aids were synthesized by spark plasma sintering process. The microstructures, mechanical, and optical properties of the ceramics were investigated. The results indicate that the optimal amount of sintering aids is 0.06 wt% La₂O₃ + 0.16 wt% Y₂O₃ + 0.30 wt% MgO. The addition of La³⁺ and Mg²⁺ decreases the rate of grain boundary migration in ceramics, promotes pore elimination, and inhibits grain growth. The addition of Y³⁺ facilitates liquid-phase sintering of AlON ceramics. Moreover, the addition of Mg²⁺ effectively promotes twin formation in the ceramics, which hinders crack propagation and dislocation motion when the ceramics are loaded. Hence, the AlON ceramic doped with 0.06 wt% La₂O₃ + 0.16 wt% Y₂O₃ + 0.30 wt% MgO exhibits a relative density of 99.95%, an average grain size of 9.42 μm, and a twin boundary content of 10.3%, which contributes to its excellent mechanical and optical properties.