Study On The Fabrication Of C/Silicide Composites By RCLD Process

Carbon materials have attracted tremendous attention due to their resistance of chemical corrosion and heat, thermal conductivity, low-electronic resistivity, anti-radiation, thermal conductivity, noise reduction and shock absorption, etc. Carbon materials are potentially useful materials on new areas of technology and research of a new material. They are widely used in different fields, such as defense industry, aerospace and other advanced fields, also used in medical equipments, transportation, machinery and other civilian industry. However, when carbon materials exposed to an oxidizing atmosphere at high temperatures, they will react with oxygen and rapidly burnt away. The rapid reaction of carbon with oxygen causes the decline of their mechanical properties. Therefore, the oxidation research of carbon materials is significant.Rapid fabrication techniques deciding composite microstructure and performance are one of the key directions for the development and application of C/Si compounds composites. Kerosene was used as carbon source and tetraethoxysilane (TEOS) was used as silicon source for preparing the C/Silicide composites. C/Si compounds composites were fabricated by Rapid Chemical Liquid Deposition (RCLD) process under different experiment conditions. A systematic study on fabrication of C/Silicide composites have been made theoretical analysis and via experiments, combined with microstructure characterization, deposition and oxidation resistance in this dissertation. The main contents and results are as follows:(1) Effects of the surface treatment of perform, perform diameter, voltage, current and holding time on the microstructure of composites were studied. After the surface treatment, a good gradient formed between the silicide coating and the substrate. When the diameter of the substrate is 7mm, the coating is well bonded to the substrate. As the increase of the voltage and current, the particles size of the coating is increased. When the voltage and current is 54V and 86A respectively, a smooth and dense coating was obtained. When the holding time is 3h, the thickness of the coating is about 120μm. The x-ray diffraction analysis shows that the coating is composed by SiC and Amorphous of SiO₂.(2) Rapid Chemical Liquid Deposition mechanism was discussed, results displayed that perform was infiltrated in Liquid procurer, the continuous temperature gradient and concentration gradient were the key in rapid densification process. At the same time, deposition process included chemical dynamic and diffusion control mechanisms converted. At the end, deposition interface area was plotted.(3) The oxidation behaviors of C/Silicide composites were characterized by mass loss. The analysis shows that the diffusion of oxygen molecules through microcracks and preparation defects are mixed types spread. With the increase of the oxidation temperature, the mass loss of the composites increases. The oxidation resistance test results indicated that after oxidation at 900℃for 10h, the mass loss of the sample is only 15.4%.(4) The oxidation behaviors, modes and mechanisms of C/Silicide composites were investigated. The oxidation behavior of C/Silicide composites was controlled by microcracks and defects./ Between 400℃and 700℃, the oxidation rate of C/Silicide composites was controlled by oxidation of C phase.; between 700℃and 900℃, the oxidation rate was controlled by diffusion of oxygen through preparation defects and microcracks.; between 900℃and 1200℃, the oxidation rate was controlled by diffusion of oxygen through coating defects; beyond 1200℃,the oxidation rate dramatically accelerated as a result of the air bubbles produced.