The Fabrication Of Continuous High Performance SiC Fiber By Chemical Vapor Deposition

The engineering materials with the properties of low density, high strength, high modulus and high melting point are urgent needed as the development of aeronautic and astronautic industry. SiC is an attractive reinforcement for composite materials because of its low density, low coefficient of thermal expansion, high strength, high hardness, high modulus, high thermal stability and good oxidation resistance. Although SiC fibers manufactured by chemical vapor deposition (CVD) are available abroad, the properties of the CVD SiC fiber made in China are still very poor. Therefore, it is necessary to make a further study on the fiber.In the study, a tungsten wire was heated by a ratio frequency-heater and then SiC was deposited onto the wire by CVD. The results show that depositing temperature is an important factor that affects fiber performance. The SiC grains grow preferred at 1150℃. In addition, the performance of the SiC fiber is influenced by the flux of argon and hydrogen, the concentration of CH₃SiCl₃ and CH₃SiHCl₂, and the deposition time. The optimum depositing process was obtained in the study, that is, depositing temperature of 1150℃, driving voltage (i.e. depositing time) of 2.5V, hydrogen flux of 1.7ml/min. mole ratio of CH₃SiCl₃ and CH₃SiHCl₂ of 2:1 and argon flux of 1.25ml/min. It was found that, under the optimum condition, the SiC fiber is with excellent surface morphology and has better performance.The surface morphology, the chemical composition and the fracture surface of the SiC fibers were observed and the tensile strength was measured. The strength distribution of the fiber follows the Weibull distribution. Some impurities such as oxygen were detected and the impurities result in the increasing of defects in the fiber, which decrease the tensile strength of the SiC fiber.A thin carbon layer was deposited onto the outmost surface of the SiC fiber. The C-coating makes the surface of the fiber dense and smooth. The micro-holes and micro-cracks on surface of the SiC fiber disappear after depositing the thin carbon layer. The tensile strength of the fiber after depositing carbon is 1000MPa larger than that before depositing carbon. The distribution of the tensile strength is more concentrated...