Protective ceramic multilayer coatings for carbon fibers

Uniform, adherent, crack-free and non-bridging HfC and HfC/SiC coatings on carbon fibers have been synthesized by a reactive CVD (RCVD) process at low temperatures. To fabricate SiC coating on HfC-coated carbon fiber, an alternative approach using unsaturated organosilicon polymer solution was also proposed. The schemes describing the formation of carbide coatings on carbon fibers by RCVD and transformation of unsaturated organosilicon polymers into silicon carbide are discussed. The HfC and HfC/SiC coatings were studied by SEM, EDS and XPS techniques. Coatings are composed of hafnium, silicon and carbon as the main constituents and oxygen and fluorine as contaminants. As was proposed, the composition of the coatings is affected by several factors, among them a chemical attack of coated fibers by gaseous oxygen- and fluorine-containing by-products can be considered as dominant ones. The duplex HfC/SiC-coated carbon fibers exhibit more oxidation resistance at elevated temperatures than the initial and HfC-coated carbon fibers.