Preparation and Characterization of Si3N4(P)/Si3N4 Composites by Chemical Vapor Infiltration

Silicon nitride particle reinforced silicon nitride composites (Si3N4(P)/Si3N4 composite) were prepared by chemical vapor infiltration (CVI) process from SiCl4-NH3-H-2-Ar system. X-ray fluorescence (XRF) results show that the main elements in the composites were Si, N, and O. X-ray diffraction (XRD) results show that the composite is composed of alpha-Si3N4, amorphous Si3N4 and amorphous SiO2. Also there are small amounts of beta-Si3N4 and free Si. The amorphous Si3N4 would transform into crystal phase Si3N4 after heat treatment at 1600 degrees C for 2h. The scanning electron microscope (SEM) results show that the composites are compact especially at the interface of conglomerations. The morphology of CVI Si3N4 is similar to cauliflower, which can be associated with little-liquid-drop growth mechanism. Micro-cracks exist due to the thermal expansion mismatch between the silicon nitride particles and CVI Si3N4. The density of the preform is 1.63g.cm(-3), and the pore ratio is 47.18%. After CVI process, the density of the preform is 2.30g.cm(-3), and the pore ratio is 12.03%.