Investigation of\nTitanium Nitride as an Effective\nInterphase for Carbon-Fiber-Reinforced Silicon Carbide Ceramic Matrix\nComposites

Ceramic matrix composites (CMCs) have played a significant\nrole\nin increasing the efficiency of gas turbine engines. CMCs combine\nthe high temperature resistance of ceramics with the high mechanical\nstrength of ceramic fibers into a single unit. Interphase layers are\na crucial component in CMCs, as they prevent ceramic fibers from oxidation\nand introduce strengthening mechanisms into the composite. Hexagonal\nboron nitride and pyrolytic carbon are the most commonly used interphase\nlayers in the aerospace industry. Other than that, very few materials\nhave been evaluated as interphase layers. In this study, we explore\nthe possibilities of using titanium nitride as an interphase layer\nin single-tow CMCs (mini composite) representative of a unidirectional\ncomposite at a smaller scale. T-300 carbon fibers were coated with\nTiN by atmospheric pressure chemical vapor infiltration using TiCl<sub>4</sub>, N<sub>2</sub>, and H<sub>2</sub>. The deposition temperature,\nprecursor flow rate ratio, total precursor flow rate, and deposition\ntime were optimized to obtain high-quality coatings. The best coating\nwas produced at 800 °C, 4:1 H<sub>2</sub> [TiCl<sub>4</sub>]/N<sub>2</sub> ratio, 125 standard cubic centimeters per minute (N<sub>2</sub> + H<sub>2</sub> [TiCl<sub>4</sub>]) total flow precursor flow rate,\nand 2 h of deposition time. At these conditions, the coatings displayed\ngood fiber coverage, good fiber adhesion, minimum fiber linkage, and\nminimum surface roughness. There was minimum fiber degradation after\nTiN coating, with a retention of 95% of the initial Young’s\nmodulus and 26% of the ultimate tensile strength of the carbon fiber.\nAdding the TiN interphase coating to the Cf/SiC CMC increased the\nultimate tensile strength of the composite by 1122% and Young’s\nmodulus by 150%.