Oxidation microstructure studies of reinforced carbon/carbon

Abstract

Laboratory oxidation studies of reinforced carbon/carbon (RCC) are discussed with particular emphasis on the resulting microstructures. This study involves laboratory furnace (500–1500 °C) and arc-jet exposures (1538 °C) on various forms of RCC. RCC without oxidation protection oxidized at 800 and 1100 °C exhibits pointed and reduced diameter fibers, due to preferential attack along the fiber edges. The 800 °C sample showed uniform attack, suggesting reaction control of the oxidation process; whereas the 1100 °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 °C. However samples oxidized at 900, 1100, and 1300 °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 °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 °C, where diffusion control dominates, attack is non-uniform with fiber edges oxidizing preferentially.