Effect of CVD carbon coatings on properties of SiC fibres

Different thicknesses of smooth and uniform carbon coatings composed of disordered carbon and micro-crystallite graphite were prepared on KD-II silicon carbide (SiC) fibres by atmospheric pressure chemical vapour deposition. The effects of carbon coatings on the mechanical property and thermal stability of SiC fibres were investigated. Carbon coatings have both favourable and unfavourable influences on SiC fibres strength. The fibres with up to 0.3 µm carbon coatings showed higher strength than the uncoated fibres due to surface flaw healing effect of the thin coatings, in contrast, the 1 µm carbon-coated fibres showed lower strength than uncoated fibres owing to effect of soft nature of the thick coatings. Furthermore, the carbon coatings effectively improved the thermal stability of SiC fibres by suppressing thermal decomposition of SiC X O Y and SiC X O Y N Z phase.