Gas-pressure Sintering of Y-α/β-sialon Composites

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 AIN 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.