IMPROVEMENT OF OXIDATION RESISTANCE OF CARBON/CARBON COMPOSITES BY THE MULTILAYER CVD COATING TECHNIQUE

Carbon/carbon composites are promising material for use at ultra high temperature in gas turbines, space plane airframes and engines because of their low density and high thermal resistance. However, one of the problems with carbon/carbon composites is their low oxidation resistance. In this study, multi-layer coated carbon/carbon composites by the CVD technique were developed to improve the oxidation resistance. Four kinds of multi-layer coating with TiC and SiC were applied to carbon/carbon composites by the CVD technique and the oxidation resistance were evaluated in air at high temperatures. In multi-layer-coated carbon/carbon composites with thin TIC layer, cracks in the coating layer were far narrower than those in the single-layer-coated carbon/carbon composites. As results of oxidation tests at 1773 K and 1273 K, the multi-layer-coated carbon/carbon composites showed much better oxidation resistance than the single-layer coated carbon/carbon composites. This improvement is thought to be caused by two reasons; (1) in multi-layer coated carbon/carbon composites, the cracks of the coating-layer close at much lower temperature than in singlelayer coated carbon/carbon composites. (2) TiO2 produced by oxidation of TiC in multi-layer coating seals the cracks of the coating-layer.