Enhanced mechanical properties and thermal shock resistance of C_sf/SiC-BN composites with polyborosilazane as a sintering aid

This study presents the fabrication and performance of BN-coated short carbon fiber (C_sf) reinforced SiC-BN ceramic matrix composites via in-situ synthesis reaction sintering method. The incorporation of 10 wt% polyborosilazane (PBSZ) effectively mitigates fiber degradation during high-temperature sintering and promotes matrix densification, resulting in an increase in composite density from 2.17 g/cm³to 2.25 g/cm³. Significant improvements in mechanical properties are observed, with flexural strength increasing from 39.7 MPa to 75.8 MPa, and fracture toughness rising from 1.18 MPa m^1/2to 2.14 MPa m^1/2. Fiber pull-out and debonding are prominently observed during fracture. Additionally, the inclusion of PBSZ reduces the average coefficient of thermal expansion (CTE) from 4.33 × 10⁻⁶/K to 3.79 × 10⁻⁶/K, significantly enhancing thermal shock resistance. The composites maintain excellent residual strength after thermal shock testing in air at temperatures ranging from 800 °C to 1200 °C, with a remarkable 87.1 % strength retention at a temperature gradient of 800 °C. This work offers a promising strategy for optimizing the interface design and thermal-mechanical performance of high-temperature ceramic composites.