Oxidation behaviors of carbon fiber reinforced multilayer SiC-Si₃N₄ matrix composites

Oxidation behaviors of carbon fiber reinforced SiC matrix composites (C/SiC) are one of the most noteworthy properties. For C/SiC, the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion (CTEs) and elastic modulus between carbon fiber and SiC matrix. In order to improve the oxidation resistance, multilayer SiC-Si₃N₄ matrices were fabricated by chemical vapor infiltration (CVI) to alleviate the above two kinds of mismatch and change the local stress distribution. For the oxidation of C/SiC with multilayer matrices, matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC-Si₃N₄ matrix to lengthen the oxygen diffusion channels, thereby improving the oxidation resistance of C/SiC, especially at 800 and 1000 ℃. The strength retention ratio was increased from 61.9% (C/SiC-SiC/SiC) to 75.7% (C/SiC-Si₃N₄/SiC/SiC) and 67.8% (C/SiC-SiC/Si₃N₄/SiC) after oxidation at 800 ℃ for 10 h.