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′ (Re4Si2–xAlxO7+xN2–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.
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