o′-β′ sialon ceramics

Abstract

Powders of Si₃N₄, Al₂O₃ and SiO₂ were mixed with Y₂O₃ as sintering aid and hot-pressed to form o′-β′ sialon. During sintering, the o′ phase preferentially precipitated in the temperature region of 1550 to 1600 °C, and the β′ phase precipitated at temperatures of 1700 °C and above. The resultant microstructure consisted of dual phases of o′ and β′. The mechanical properties of o′-β′ sialon were improved with increasing amount of the β′ phase. When SiO₂ required for the formation of the o′ phase was all included in the grain boundary phase, o′-β′ sialon exhibited a three-point bending strength as much as 1400 MPa. The oxidation resistance of o′-β′ sialon is expected to improve due to the presence of the o′ phase, but actually was not so good due to the presence of the grain-boundary glassy phase and impurities.