Particle-aided chemical vapor deposition (PACVD) of silicon carbide composites

Abstract

Silicon carbide (SiC) is a hard, oxidation-resistant material which has been used extensively in electronic and structural applications. It has exceptional erosion resistance and hardness, but its brittle nature limits its application as a high-temperature engineering material. Several composites of SiC have been produced in an attempt to further improve its properties. This paper deals with the production of SiC and several of its composites by a technique called particle-aided chemical vapor deposition (PACVD). This technique makes use of the deposition of fine particles of a chosen material onto the substrate in addition to normal CVD from the vapor phase. Previous studies have shown that a significant increase in overall growth rate can be achieved by particle and chemical codeposition. In this study PACVD was successfully applied for the production of SiC TiB 2, SiC Si 3N 4, and SiC B 4C composites. Hardness and fracture toughness of these films proved better than those of normal CVD-SiC films. The study also deals with theoretical aspects of PACVD. The reactor environment is modeled and the gas flow and temperature distribution determined for different reactor conditions. The movement of fine particles in these nonisothermal flow fields is followed and their deposition onto the substrate is predicted. A random sphere model of simultaneous particle and vapor deposition (RASSPVDN) is used to predict the enhancement in overall growth rate possible under different conditions. It was found that a dramatic enhancement in growth rate is possible, but that this can lead to undesirable levels of porosity in the resulting deposits.