Enhanced oxidation resistance and failure mechanism of carbon/carbon composites with ZrO2/ZrSiO4-glass composite coating

Abstract

A new coating of ZrO2/ZrSiO4-composited borosilicate glass (ZO-glass) was developed to protect the carbon/carbon composites (C/C) from oxidation in the air. It was found that the oxidation resistance first increased and then decreased with the increase of ZO content, and the ZO content of 20% corresponded to the best anti-oxidation properties (the weight loss was only 0.6% at 1573 K after 650 h). The significant enhancement of oxidation resistance was probably attributed to the stabilization effect of ZO filler and self-healing effect of glass. Excessive ZO may decrease the viscosity, self-healing ability of glass, and shorten the coating’s protection time (crack failure model). On the other hand, inadequate ZO can hardly restrain the bubble growth during oxidation, resulting in premature failure of the coating (bubble control model). The growth of bubbles was due to the active reaction between SiC and oxygen from crack diffusion, and the oxygen increases the gas concentration in the coating, and then diffuses into bubbles to its expansion. Different thermal expansion coefficient (CTE) of substrate and coating results in the formation of high thermal stress at the interface, which may induce through-cracks in coating during cooling. This paper gives insight into the oxidation resistance of composite coating, and offers an effective way for durable oxidant protection of C/C.