Effect of different rare-earth on microstructure and properties of α-Sialon ceramics

Densified Yb-, Y-, Dy-, Sm- and Nd-α-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 α-Sialon, while in the larger cations (Sm³⁺ and Nd³⁺) doped ceramics also exist a few intergranular phase M′ (Re₂Si_3-xAl_x O_3+xN_4-x) in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated α-Sialon grains form instead of the equiaxed grains in Yb-α-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-α-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-α-Sialon possesses the highest toughness with the value of 5.4 MPa-m^1/2.