Phase composition and morphology of TaC coating on carbon fibers by chemical vapor infiltration

Chemical vapor infiltration was applied to deposit TaC thin film on carbon fibers using TaCl5–Ar–C3H6–H2 source. The influence of temperature, pressure and addition of H2 on phase composition and morphology of the coating had been studied. The results showed that the composition of the coating changes with temperature. The films are mainly composed of TaC and C when deposited at 800–900 °C and C phase disappears at 950 °C and 1000 °C. TaC grains are very small at 800 °C and get bigger at 900 °C; while at 1000 °C, a dense coating has developed. The influence of pressure on coating composition is much weaker when deposited at 850 °C and the films are consisted of TaC and C phases at 0.6–8.0 kPa; TaC grains formed at 0.6 kPa are smaller and more homogeneous than those obtained at 8.0 kPa. With 100 ml/min H2 flow, the coating composition changes and turns into a mixture of TaC and Ta2C with fine and homogeneous grains at 850 °C and coarse grains at 950 °C.