Effect of Different Rare-Earth on Microstructure and Properties of α-Sialon Ceramics

Densified Yb-, Y-, Dy-, Sm- and Nd-alpha-Sialon ceramics were prepared by two-step hot sintering. The variation of microstructure and properties with different rare-earth was investigated. The ceramics doped with smaller cations (Yb3+, Y3+ and Dy3+) are fully composed of alpha-Sialon, while in the larger cations (SM3+ and Nd3+) doped ceramics also exist a few intergranular phase M' (Re2Si3-xAlxO3+xN4-x) in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated a-Sialon grains form instead of the equiaxed grains in Yb-alpha-Sialon, and the aspect ratio of grains increases. All the ceramics possess high hardness, and the value of 21 GPa is achieved for Yb- and Y-alpha-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-a-Sialon possesses the highest toughness with the value of 5.4 MPa.m(1/2).