Abstract: The effects of sizes and phases contents of the starting materials Si₃N₄ and AlN, YAG additive and preheating conditions on the gas-pressure sintering
behavior, phase compositions and properties of Y-α/β-sialon composites were investigated. Three stages of sintering (1700℃ for
1h, 1800℃ for 1h and 1950℃ for 1.5h) are necessary for the densification of Y-α/β-sialon composites as the reaction between Si₃N₄ and liquid phases at high temperature is minimized.
Fine AlN powder is beneficial for the densification with proper sintering schedule and embedding powder. Amount of α-sialon phase in the product
is decreased when very fine Si₃N₄ (0.3μm) is used because of increased oxygen content in the powder. No α-sialon phase was found
in the product when pure β-Si₃N₄ was used as raw material in our experiment. By adjusting the Al₂O₃ amount such as from 3.7mol% to
5.1mol%, the morphologies of the samples varies greatly. The amount of elongated grains increases obviously in the sample with YAG instead of
Y₂O₃ and Al₂O₃ as additive. Phase development study at the temperatures between 1300℃ to 1900℃ shows that YAG additive postpones the formation of α-sialon.

Key words: α/β-sialon, gas-pressure sintering, phase compositions, microstructure, mechanical properties