The sintered structures of amorphous Si3N4-BN composite powder were investigated with sintering aids from the Y2O3-Al2O3 and Y2O3-TiO2-AlN systems. In the Y2O3-Al2O3 system, b-Si3N4 and h-BN crystallized during sintering. TiN additionally appeared in the Y2O3-TiO2-AlN system. The microstructure of the Si3N4-BN composite was observed by SEM. Flaky BN particles with a length of about 1.0~1.5 mm were observed in the Si3N4 matrix. The Si3N4 matrix had a fine-grained microstructure in the Y2O3-Al2O3 system, whereas rod-like Si3N4 grains with a length of 3~10 mm were observed in the Y2O3- TiO2-AlN system. The morphology of the TiN particles was observed by TEM. Small TiN particles of about 0.1 mm in diameter were included in large Si3N4 grains, but these fine TiN inclusions were a rare case. Large TiN particles of about 1 mm in diameter were located at grain boundaries throughout the sintered body. The thermal shock resistance of Si3N4 was improved by the BN inclusions in the Y2O3-Al2O3 system. With the Y2O3-TiO2-AlN system, the TiN inclusions increased the fracture toughness of the Si3N4-BN composite but the thermal shock resistance was reduced.

Keywords: silicon nitride, boron nitride, titanium nitride, composite powder, nanocomposite