Oxidation-Resistant Coatings for Carbon-Carbon Composites

Carbon-Carbon (C-C) composites are candidate materials for hypersonic and aerospace applications due to their high fracture toughness coupled with extremely low density and high temperature strength. However, they easily degrade in an oxidizing environment even at temperatures as low as 450¿C. Consequently, the development of high-temperature oxidation-resistant coatings for these materials is of prime importance to the aerospace industry. A major factor that will be instrumental in the exploitation of C-C is the ability to develop oxidation resistant surfaces in order to protect the surface from high altitude or low orbit oxygen available for deterioration of the skin of an avionic or astronautic vehicle travelling at greater than Mach 1. In this Phase I effort, we will demonstrate a novel technique that can achieve oxidation resistant surfaces to 2D carbon-carbon. This process entails the application of tin with the addition of very particular transition metals (in minor but controlled amounts) which as such a mixture can form compounds on the carbon when fired in Co atmospheres and thus result in a direct metallurgical bond to the carbon-carbon workpiece. The tin rich layer can be skimmed off of the resultant metallization layer by reflowing the bulk of the metallization. This can be done while leaving the remaining transition metal rich interfacial zone that can serve as a oxidation resistant layer. We will also perform plating of a thin layer of electrolytic chromium on top of this interfacial reaction zone as a separate experiment. Finally as a control we shall compare these two sets of test specimens to chrome plated but no pretreated carbon-carbon. Coordination has also been initiated with B.F.Goodrich, a major manufacturer of C-C, so that components can be evaluated during the Phase II effort. Direct implementation in production line processes will be feasible in Phase III.