The degradation behavior of C/SiC composites in complex environment

Highlights: ► A C/SiC was exposed in O2, AO, mode A (first O2 and then AO) and mode B (first AO and then O2) oxidation. ► The O2 produced SiO2 layer on the specimens, but the AO can preferentially etch off the Si of SiC. ► The mode B oxidation can induce more serious degradation for specimen. ►The mechanisms of the coupled oxidations were proposed in this study. - Abstract: The advanced high temperature composites have been considered as structural or functional material in complex and harsh environments, which usually comprise of various oxidizing particles such as molecular oxygen (MO), atomic oxygen (AO) and molecular water. This study aimed to investigate C/SiC behaviors in single factor or combination environments. In the MO oxidation, an inert surface is formed on SiC. At the AO oxidation, the Si of SiC is preferentially etched off leaving a certain depth of C layer on the sample. Two types of coupled oxidations defined as mode A (first MO and then AO oxidation), and mode B oxidation (first AO and then MO oxidation) were investigated systematically in this study, and found that the prior oxidative effect majorly determined the corresponding coupled oxidation behavior. From microscopic observation and fractural test, the mode B oxidation induced a more serious degradation upon the material than that of the mode A, which is illustrated by the proposed erosion mechanisms for the modes A and B.