Microstructure and mechanical properties of in-situ toughened re-α-sialon ceramics

The α-sialon ceramics were prepared using single or dual rare-earth oxides as stabilizer. The effects of type of rare-earth element (RE) on the phase assemblages, grain morphology, microstructure and properties were investigated. The results reveal that ceramic doped with a smaller cation (Yb³⁺) is fully composed of equiaxial α-sialon while the morphology with elongated grains can be obtained by partially substituting Yb with Y as a modifying cation, accompanied by a few intergranular phases in triple-point pockets and continuous thin glassy film between the α-sialon grains. In the larger cation-doped ceramics (Sm³⁺ and Nd³⁺) there are a few block-like M′(RE₂Si_3-x Al_xO_3+xN_4-x) phases and even β-sialon in the Nd-α-sialon ceramic, which causes the hardness to decrease slightly. Yb- and Dy-α-sialons have relatively lower toughness due to the normal distribution in grain size, whereas Y-, Sm-, Nd-′ and Yb/Y-α-sialons with bimodal distribution of grains size possess higher toughness.