先驱体浸渍裂解C/SiCN复合材料的拉伸行为与基体开裂机制

Significant matrix cracks and residual pores may form within ceramic matrix composite which was pre¬pared by polymer infiltration and pyrolysis (PIP) method. Explore the matrix cracking mechanism and the crack evo¬lution behavior would benefit the design and performance optimization of the composite. A spinning PIP process in vacuum was adopted to prepare mini C/SiCN composite without weak interphase. The tensile properties and the matrix crack evolution phenomena were analyzed. The influences of PIP cycles and heat-treatment temperatures were dis¬cussed. Results showed that the compositions are essentially the same for the samples heat-treated at 1000-1400 ℃. While the heat-treatment temperature rises to 1600 ℃, the precursor-derived SiCN matrix decomposes, with the car¬bon content decreased and SiC content increased significantly. As PIP cycles increased from 1 to 4, the average tensile strength of the composite increased by 14.19%, 38.83%, and 63.47%, respectively. The matrix crack spacing and crack opening distance gradually decreased, and the bonding between matrix and fiber was enhanced, leading to little fiber pull-out. When the heat-treatment temperature increased from 1000 ℃ to 1400 ℃, the tensile strength of the composite changed slightly. In contrast, when heat-treatment temperature roses to 1600 ℃, the SiCN matrix was transformed from amorphous SiC_xN_4-x tetrahedron structural units to SiC crystals. Then the matrix and the fiber debonded, resulting in their bonding strength weakened. As a result, the tensile strength of the C/SiCN composite decreased by 30.0%, due to a combined effect of interfacial debonding and fiber damage.