SiCw/SiC Coating On C/C Composite By Chemical Vapour Deposition

Silicon carbide (SiC) with excellent high temperature performance is outstanding candidate material for the high temperature anti-oxidation coating of the carbon/carbon (C/C) composites. However, the mismatch about the coefficient of thermal expansion between SiC and C/C composites, which has discount the capacity of SiC coating. This paper studied systematically about SiCw layer on surface of C/C composites material, catalytic growth of silicon carbide whisker (SiCw) and SiCw/SiC coating were prepared on the C/C composites material by the atmospheric chemical vapor deposition (CVD), the coating of microstructure, texture and mechanical properties of cross section were tested with the aid of SEM, XRD, XPS, MTC. Compared with SiC without SiCw layer, meanwhile, the preparation of coating and anti-oxidation was studied by different density matrix of C/C composites. The main contents and results are listed as follows:With dipping metal salt on C/C composites matrix, the effects of the catalyst type (Fe, Co, Ni), catalyst content, deposition temperature and α=QH2/QMTS in catalytic growth of SiCw layer were studied. The results showed that the dipping Ni salt of C/C matrix is better than Co and Fe in generated one-dimension SiC layer structure; the nickel salt improves the deposition efficiency, and the increased ratio of SiC increase with the content of nickel salt and become stable subsequently, meanwhile, the diameter of SiC decreases and the length-diameter ratio increases; At the same time, during low temperature, under dipping Nickel, the deposition rate is sped up and the deposition efficiency is increases of2-3times. When a is equal or greater than10, high length-diameter ratio of SiC nanowhiskers were abtained, meanwhile, the production rate of SiCw is the highest in a=10.With preparation SiC layer and SiCw/SiC coating in C/C composites and the deposition rate and the anti-oxidant properties were influenced by the density of C/C composites. The results show that well-rounded and fine equiaxial-like SiC particles are prompted, the crack width and orientation in the coating are changed, and the texture is adjusted for the SiCw/SiC coating; meanwhile, the hardness of inner-coating of SiC is lower than that of outer and the lower hardness and lesser elastic modulus of the coating are caused by a great number of cavities in the SiCw area. During preparation SiCw layer in Low-density matix (1.2±0.1g/cm3) by catalyst, deposition efficiency has been improved, saturated weight increase rate has been increased. Meanwhile, the growth of crack also was restrained. Therefore, the oxidation of the protection ability of SiC coating with SiCw layer was improved in the air at1200℃. In addition, compared with different density matrix, the matrix form of the porosity itself was not changed by the catalyst and the type of absorption curve was uniform. The more open pore in Low-density matrix, the more catalyst adherence, thus the inner surface was reduced futher. In additon, low-density sample contained of highly growth efficiency, larger diameter of SiCw, thicker thickness of SiCw layer, was improved effectively the adherence between the outer SiC coating and C/C composites matrix, thus its property of anti-oxidation is better in the air at1500℃.