Sintered-reaction Bonded silicon nitride densified by a gas pressure sintering process - Effects of rare earth oxide sintering additives

Abstract

Reaction-bonded silicon nitrides containing rare-earth oxide sintering additives were densified by gas pressure sintering. The sintering behavior, microstructure and mechanical properties of the resultant specimens were analyzed. For that purpose, Lu 2O 3-SiO 2 (US), La 2O 3-MgO (AM) and Y 2O 3-Al 2O 3 (YA) additive systems were selected. Among the tested compositions, densification of silicon nitride occurred at the lowest temperature when using the La 2O 3-MgO system. Since the Lu 2O 3-SiO 2 system has the highest melting temperature, full densification could not be achieved after sintering at 1950°C. However, the system had a reasonably high bending strength of 527 MPa at 1200°C in air and a high fracture toughness of 9.2 MPa m 1/2. The Y 2O 3-Al 2O 3 system had the highest room temperature bending strength of 1.2 GPa.