LONG-TERM OXIDATION PROTECTION OF CARBON-CARBON FLIGHT STRUCTURES

HIGH-STRENGTH CARBON-CARBON COMPOSITES ARE CANDIDATE STRUCTURAL MATERIALS FOR THE NATIONAL AERO-SPACE PLAN (NASP) IF LONG-TERM OXIDATION PROTECTION CAN BE DEVELOPED. THE SPARTA CONCEPT FOR OXIDATION PROTECTION COATINGS FOR LONG-TERM USE IN AN ULTRAHIGH TEMPERATURE FLIGHT ENVIRONMENT INVOLVES A GRADED PROPERTY, MULTILAYER COATING (GPMC). THE GPMC PERFORMS SEVERAL FUNCTIONS AND OVERCOMES THE VARIOUSFAILURE MECHANISMS WHICH HAVE BEEN OBSERVED PREVIOUSLY: (1) CARBON DIFFUSION IS CONTROLLED RESULTING IN THE STABILIZATION OF THE INTERFACE BETWEEN THE COATING AND THE CARBON-CARBON COMPOSITE, (2) OXYGEN DIFFUSION IS CONTROLLED BY THE USE OF A NEW BARRIER CONCEPT WITHIN THE MULTILAYER COATING, AND (3) COEFFICIENT OF EXPANSION MISMATCH PROBLEMS ARE OVERCOME BY GRADING THE COMPOSITION (AND THEREFORE, THE PROPERTIES) WITHIN THE VARIOUS LAYERS OF THE COATING. NEW SOL-GEL PROCESSING TECHNOLOGY BEING DEVELOPED AT SPARTA WILL BE USED TO FABRICATE COATED CARBON-CARBON COMPOSITE SPECIMENS. THIS PROGRAM IS DESIGNED TO ANALYTICALLY AND EXPERIMENTALLY DETERMINE THE FEASIBILITY OF DEVELOPING OXIDATION PROTECTION COATINGS FOR LONG-TERM USE IN ULTRAHIGH TEMPERATURE FLIGHT ENVIRONMENTS.