Novel, Thermal Shock -resistant, HfC-based Coating Systems for up to 5000 F Propulsion Applications

Solid rocket propellants put stringent requirements on materials selection due very high temperature, high pressure and highly corrosive environment. Monolithic ceramics such as hafnium carbide suffer from very poor fracture toughness, putting huge design constraints on their use in solid motor propulsion systems. Refractory ceramics coated carbon-carbon (C-C) composites can offer a potential solution to this problem but the intrinsic thermal expansion (CTE) mismatch between the very low CTE C-C substrate and fairly high CTE of the refractory coating needs to be resolved preventing premature coating spallation. A unique approach, which utilizes a functionally graded (FGM) interface, was successfully employed in the X-43A flight, which reached Mach 10 under a severe thermal envelope. The X-43A flight proven coating on P-30X type C-C substrate will be extended to a low cost 3-D C-C composite substrate well suited for propulsion application and will be tested for 3200 F, long duration applications. In addition, a highly novel FGM HfC coating system applied onto a low cost 3-D C-C substrate will be tested to demonstrate virtually no erosion at 5000 F. The intrinsic properties of the CVD HfC, such as 100% density not achievable by Physical Vapor Deposition (PVD) methods such as plasma based coatings, offers a very high erosion resistance at a very high temperature.