Oxidation microstructure studies of reinforced carbon/carbon

Laboratory oxidation studies of reinforced carbon/carbon (RCC) are discussed with particular emphasis on the resulting microstructures. This study involves laboratory furnace (500-1500 degrees C) and arc-jct exposures (1538 degrees C) on various forms of RCC. RCC without oxidation protection oxidized at 800 and 1100 degrees C exhibits pointed and reduced diameter fibers, due to preferential attack along the fiber edges. The 800 degrees C sample showed uniform attack, suggesting reaction control of the oxidation process; whereas the 1100 degrees C sample showed attack at the edges, suggesting diffusion control of the oxidation process. RCC with a SiC conversion coating exhibits limited attack of the carbon substrate at 500, 700 and 1500 degrees C. However samples oxidized at 900, 1100, and 1300 degrees C show small oxidation cavities at the SiC/carbon interface below through-thickness cracks in the SiC coating. These cavities at the outer edges suggest diffusion control. The cavities have rough edges with denuded fibers and can be easily distinguished from cavities created in processing. Arc-jet tests at 1538 degrees C show limited oxidation attack when the SiC coating and glass sealants are intact. When the SiC/sealant protection system is damaged, attack is extensive and proceeds through cracks, creating denuded fibers in and along the cracks. Even at 1538 degrees C, where diffusion control dominates, attack is non-uniform with fiber edges oxidizing preferentially. (c) 2005 Elsevier Ltd. All rights reserved.