SIO2 DOPED SI3N4 CERAMICS

The mechanical properties and stability of a SiO2 doped Si3N4 ceramic were investigated up to 1600 degrees C. Specimens were prepared by the encapsulation-HIP process of SiO2 doped Si3N4 powder compacts. The hipped material showed almost constant strength around 600MPa between RT and 1600 degrees C. The steady-state creep rare at 200MPa and 1500 degrees C was 5.6X10(-6)/hr, which was equivalent to that of a typical rare earth oxide doped Si3N4 ceramic at 1400 degrees C. It showed good oxidation resistance and was stable at 1600 degrees C in air. Since transgranular fracture and elongated beta-Si3N4 grains were observed in the microstructure, it was considered that the materials showed low toughness because of the rigid grain boundaries. It was concluded that the SiO2 doped Si3N4 ceramic can be possibly used above 1400 degrees C. but the fracture toughness should be improved.