The comparison of microstructure and oxidation behaviors of (SiC-C)/PyC/SiC and C/PyCHT/SiC composites in air

Silicon carbide matrix composite reinforced by both SiC and carbon fibers [(SiC-C)/PyC/SiC] to alleviate the thermal residual stresses (TRS) between carbon fiber and SiC matrix, then reduce the microcracks in the SiC coating as well as in the matrix, was fabricated by chemical vapor infiltration (CVI) process. Compared with C/PyCHT/SiC composite in which PyC interphase was heat-treated at 1800 degrees C in argon to lower the fracture energy of the interphase, the TRS in SiC matrix and SiC coating was reduced by 69.5% and 62.2%, respectively. Coating cracks density was 50 cracks/m for (SiC-C)/PyC/SiC composite, and 1090 cracks/m for C/PyCHT/SiC composite. Carbon phases could be protected in (SiC-C)/PyC/SiC composite when the composite was subjected to temperatures ranging from 700 degrees C to 1300 degrees C in air for 10 h. The residual strength of (SiC-C)/PyC/SiC composite was higher than those of C/PyCHT/SiC composite below 1200 degrees C. The residual strength of (SiC-C)/PyC/SiC composite was lower than those of C/PyCHT/SiC composite at 1300 degrees C because of the recession of SiC fiber.