High temperature flexural strength, microstructure, phase evolution and anti-oxidation mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composite modified with TiB2 and B4C

Carbon fiber/phenolic resin composites (CF/Ph) have attracted great interests in the field of thermal protection materials for their characteristics of high specific strength and easy manufacturing. However, CF/Ph are inherently susceptible to oxidation failure at elevated temperatures. In this study, a novel Al-coated carbon fiber/ boron phenolic resin ceramizable composite modified with TiB2 and B4C was fabricated by an impregnating and compression molding route. Thermal stability, flexural strength, microstructure and phase evolution of the resulting ceramizable composite were studied. The residue yield at 1400 degrees C and flexural strength after treated at 1400 degrees C for 15min was 90.4% and 53.1 MPa, respectively, which was increased by 15.9% and 532.1% than that without ceramizable fillers. Surface defects generated by matrix pyrolysis were well healed, and PyC and carbon fibers were covered with dense ceramic layers while the fracture surface was covered with relatively continuous ceramic layers without visible pores. Multiphase ceramics composed of TiB2, TiO2, TiC and PyC were identified. Furthermore, oxidation failure and anti-oxidation mechanism was revealed based on the aforementioned characterizations and thermodynamic calculation results. Oxidation resistance got enhanced markedly for synergistic effects of oxygen consuming, carbon fixation, oxygen barrier and endothermic effect, which were derived from ceramization reactions between TiB2, B4C, O2, Al and PyC.