Microstructure of the BNf/Si3N4 Composites Prepared by LPCVD

The BNf/Si3N4 composites were prepared by LPCVD using SiCl4-NH3-H-2-Ar as precursor at 950 degrees C. The microstructure of the BNf/Si3N4 composites was examined by scanning electron microscopy. The phase identification of the nanometer Si3N4 was confirmed by X-ray diffraction. The morphology and growth mechanism of the Si3N4 matrix were investigated using chemical reaction kinetics and supersaturation-condensation-fusion mechanism. Because of the mismatching of the coefficient of the thermal expansion and the poor wettability between the coating and the substrate, the coatings could be easily flaked away. The internal surface of the Si3N4 shell was very smooth, which proved the poor wettability. The external surface of the Si3N4 shell was composed of the amorphous spheroid particles, which proved the S-K growth model.