Advances in Ceramic Coatings and Ceramic Matrix Composite Fabrication

Chemical Vapor Deposition (CVD) was employed to deposit BN/Si3N4 interfacial coatings onto SiC based ceramic fibers. A series of experiments were designed in order to optimize the conditions for the deposition of BN coatings. The effects of temperature, pressure, reactant gas concentrations and BN coating thickness were examined to achieve the optimal mechanical properties once employed in a Ceramic Matrix Composite (CMC). Tensile testing of the fibers after the deposition process would determine the effects of the deposition process on the mechanical strength of the fiber. CMCs were fabricated with coated fabric from these experiments to determine the flexural strengths and to investigate the relationship between deposition conditions and mechanical properties. Silicon based pre-ceramic polymers were developed through the ammonolysis of vinyltrichlorosilane to create polyvinylsilazane (PVSZ). Preceramic polymers were developed for the production of ceramic fibers and as matrix materials for CMCs. This polymer was characterized by Fourier Transform Infrared (FT-IR) spectroscopy, 1H/13C Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), Thermogalvametric Analysis (TGA), Residual Gas Analysis, and X-ray diffraction (XRD) of the ceramic char after pyrolysis in various atmospheres. Also the ability to form free standing monoliths and ceramic fibers was also determined. Processing of non-oxide based CMC’s are typically fabricated through Polymer Impregnation Pyrolysis (PIP) and Chemical Vapor Infiltration (CVI). A new hybrid process PIP/CVI was developed to reduce production time and cost of the CMC fabrication process. The new method will employ PIP to tack the ceramic fibers together and utilize the CVI process to densify the CMC. Varying the amount of PIP cycles will determine the optimal processing conditions for the hybrid process and mechanical testing will be employed to verify the process. Oxidation studies will also be performed to compliment the mechanical testing