Long-term oxidation behaviors and strength retention properties of self-healing SiCf/SiC-SiBCN composites

The self-healing SiCf/SiC-SiBCN composites with various boron contents in SiBCN were prepared, and their long-term oxidation behaviors and strength retention properties were investigated. The 100 h oxidation at 1200-1350 degrees C leads to parabolic mass gain of the obtained composites. With the oxidation temperature increased from 1200 degrees C to 1350 degrees C, the oxidation rate constants increase from 5.91 x 10-8 mg2/(mm4 h) to 9.31 x 10-7 mg2/(mm4 h) for the boron-lean (3.14%) composites, and from 2.57 x 10-7 mg2/(mm4 h) to 6.04 x 10-7 mg2/ (mm4 h) for the boron-rich (7.18 wt%) composites. Correspondingly, the oxidation activation energy decreases from 363 kJ/mol to 112 kJ/mol due to the low initial oxidation temperature of boron-rich SiBCN. All the composites exhibit the higher strength retention rates after 1350 degrees C oxidation due to the enhanced self-healing performance. The boron-rich composites show a high strength retention rate of up to 104% due to the good self-healing capacity of the boron-rich SiBCN as well as the high CVI-SiC content.