MULTILAYER COATING FOR CARBON-CARBON COMPOSITES

Because of the excellent mechanical properties at elevated temperature, carbon-fiber reinforced carbon (carbon-carbon) composites have received much attention for high-temperature structural applications. One serious drawback against actual use of carbon-carbon composites is their poor oxidation resistance in high-temperature oxidizing atmospheres. In many attempts to develop an effective oxidation-protection coating, silicon carbide coating has shown the best performance for short periods of up to 1900 K. For longer periods and higher temperature applications, a challenging coating system should be developed. There exist certain difficulties in establishing a new coating system, such as coefficients of thermal expansion (CTE) mismatch between coating layer and carbon-carbon composites, and chemical stability of the interface. This paper describes a basic idea for a new multilayer coating system, the candidate materials for each coating layer, and the characteristics of the new coating system.