HYBRID FIBER CARBON-CARBON COMPOSITES FOR IMPROVED COMPATIBILITY WITH OXIDATION RESISTANT COATINGS

CARBON-CARBON COMPOSITES ARE USEFUL HIGH TEMPERATURE STRUCTURAL MATERIALS OPPORTUNITIES EXIST FOR THEIR USE IN HOT, OXIDIZING ENVIRONMENTS, BUT PROTECTION SYSTEMS HAVE TO BE DEVELOPED TO PREVENT OXIDATION WHICH POSES A SERIOUS PROBLEM ABOVE 400 DEGREE C. CONVENTIONAL OXIDATION RESISTANT COATING SYSTEMS EMPLOYING THIN LAYERS OF EITHER SIC OR SI N CRACK WHILE UNDERGOING LARGE TEMPERATURE CHANGES DUE TO THE DIFFERENCE BETWEEN THEIR COEFFICIENTS OF THERMAL EXPANSION (CTE) AND THAT OF CARBON-CARBON. THE PURPOSE OF THE PROPOSED PROGRAM IS TO DETERMINE THE FEASIBILITY OF USING HYBIRD FIBER CARBON-CARBON COMPOSITES TO REDUCE THE CTE MISMATCH BETWEEN THE SUBSTRATE SURFACE AND OXIDATION RESISTANT COATING. 3D TAPES WILL BE CONSTRUCTED IN WHICH HIGH CTE FIBERS WILL BE PLACED IN WEAVE LOCATIONS THAT CONTROL THE CTE OF SURFACE PORTIONS OF THE SUBSTRATE. HIGH STRENGTH T-300 PERFORM LOCATIONS. BOTH CVD SIC AND SI3N4 WILL BE APPLIED TO THE DESIFIED COMPOSITES IN ORDER TO DETERMINE HOW THEIR DIFFERENT CTES AND ELASTIC MODULI WILL AFFECT THEIR PERRFORMANCE AS PROTECTIVE COATINGS. COATED SPECIMENS WILL BE EVALUATED IN STATIC AIR OXIDATION TESTS, AND SUCCESSFUL SUBSTRATE-COATING COMBINATIONS WILL UNDERGO MECHANICAL TEST AS WELL.