Abstract: C/Si₃N₄ composites were prepared by chemical vapor infiltration methods (CVI) from SiCl₄-NH₃-H₂ system. The element and phases of the as-processed sample were characterized by EDS and XRD. The phase of the as-processed sample is an amorphous silicon nitride. The phase of the sample heat treated at 1350℃ is also an amorphous silicon nitride. The XRD indicates that the formation of α-Si₃N₄ and β-Si₃N₄ occurs after heat treatment at 1450℃. The influences of temperature, time and gas flux on densification, weight and microstructure were investigated. The results show that the gases infiltrate and react in preforms equably, the carbon preforms can be infiltrated uniformly and the uniform C/Si₃N₄ composites were prepared when the process parameters are as follows: temperatrure 900℃, SiCl₄ flow 30mL/min, H₂ flow 100mL/min, NH₃ flow 80mL/min, time 120h and total pressure 1000Pa.

Key words: chemical vapor infiltration （CVI）, C/Si₃N₄ composites, microstructure, process parameters