Microstructure and oxidation resistance of C/C-SiC composites prepared by reactive melt infiltration

In this study, two different densities of carbon/carbon (C/C) composites modified by SiC were prepared using reactive melt infiltration method (RMI). The phase composition, microstructure and element distribution of the as-prepared composites were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The oxidation resistance and thermal shock resistance of C/C-SiC composites were investigated, and the morphology changes of the C/C-SiC composites after oxidation test and thermal shock test were observed by SEM. The results show that the sizes of pores determined the infiltrating depth of the molten Si during RMI. The C/C_1.0-SiC composites had a low initial density with large sizes (10~100 μm), which was beneficial to infiltration of the molten melts and improvement of the final density. The oxidation behavior and thermal shock of C/C-SiC composites were measured at 1500 ℃ in statics air. It indicated that C/C_1.7-SiC composites had a poor oxidation resistance and thermal shock resistance due to the coefficient of thermal expansion mismatch of SiC coating and C/C substrate. The mismatch would result in cracking or peeling and even failure of the coating. Nevertheless, C/C_1.0-SiC composites had a good oxidation resistance and thermal shock resistance because of the existence of multilayer interface between SiC matrix and C/C substrate, which effectively relieved the coefficient of thermal expansion mismatch of SiC matrix and C/C substrate. Therefore, the oxidation resistance and thermal shock resistance of C/C_1.0-SiC composites were improved significantly.