Processing and Properties of in Situ-Reinforced α-SiAlONs Stabilized with Y2O3 and Lu2O3

α-SiAlONs with equiaxed and elongated microstructures stabilized with Y₂O₃ and Lu₂O₃ were produced by hot pressing, and the phase structure and room- and high-temperature mechanical properties were assessed. Additional liquid added to the starting composition in the form of 5 wt% rare-earth monosilicate resulted in the formation of elongated microstructures and improvements in room-temperature strength and fracture toughness. The elongated grain growth was promoted by the additional liquid phase, which crystallized to form a secondary grain-boundary phase thought to be J ' (Re₄Si_{2– x} Al _x O_{7+ x} N_{2– x} ). For the equiaxed and the elongated samples, those sintered with Lu₂O₃ showed higher hardness than the comparable Y₂O₃-sintered materials, and, at elevated temperature, the strength retention of the elongated Lu₂O₃ SiAlON was much higher than that of the Y₂O₃ sample, which was attributed to properties of the residual grain-boundary phase associated with the difference in the cationic radius of the stabilizing cation.