Reactive pack-cementation coating of silicon carbide on carbon-carbon composite

Abstract
Silicon carbide is used as a thermal protective coating material to prevent carbon-carbon composites from oxidation. The coating system is applied by a high temperature pack-cementation process. Gaseous silicon monoxide generated from a SiC-SiO₂ powders mixture reacts with carbon substrate by converting the outer surfaces into silicon carbide. Both single carbon fibers and actual composites are used and the fracture surfaces of the cemented substrates are observed by scanning electron microscopy. The obtained comb-like reaction interface is discussed as the consequence of the silicon carbide growth mechanism, and the leading part of the remaining open porosity of the composite is clearly evidenced. Oxidation experiments at 1600°C and under reduced pressure of oxygen are performed on cemented composites with additionnal outer protective coatings. The excellent behaviour of the samples demonstrates that such a cementation silicon carbide layer constitutes an appropriate interphase between carbon materials and an outer oxidation resistant coating.