MULTILAYER COATINGS ON CFC COMPOSITES FOR HIGH-TEMPERATURE APPLICATIONS

The interest in carbon-fiber-reinforced carbon (CFC) composites has in creased recently because of their excellent performance at high temper atures. However, a protective coating is necessary to avoid the oxidat ion of carbon. Multilayer coatings on CFC composites consist of pyroly tic carbon (PyC), hafnium carbide (HfC) and silicon carbide (SIC) as a ground layer, diffusion barrier and oxidation protection, respectivel y. The HfC coating was deposited by a thermally induced chemical vapor deposition (CVD) technique using a gas mixture of hafnium tetrachlori de, methane and hydrogen as precursor. The SIC was deposited from meth yltrichlorosilane (MTS) and hydrogen. The coatings were characterised by transmission electron microscopy (TEM), scanning electron microscop y (SEM), auger electron spectroscopy (AES), and X-ray diffraction (XRD ). The quality of the adhesion of the coatings was measured by ultraso nics. (C) 1998 Elsevier Science S.A.