Effects of BN and pyrolytic carbon interface materials on the microstructure and mechanical properties of B4C-SiCf ceramics

Abstract

The overall reinforcement in fiber-reinforced ceramics is affected by the high-temperature stability of the fiber and stress transfer across the interface material. In this study, the morphology and high-temperature thermal stability of boron nitride (BN)-coated SiC_f (SiC_f/BN) and pyrolytic carbon (PyC)-coated SiC_f (SiC_f/PyC) were investigated at temperatures ranging from 1700 °C to 1800 °C. The BN and PyC coatings mitigated the high-temperature degradation of SiC_f via preferential oxidation, resulting in no noticeable defects on the fiber surface and negligible grain growth within the fibers. The protective effect of the BN interface in B₄C-SiC_f ceramics depended on the sintering temperature because its oxidation and decomposition progressively increased with temperature. A typical fiber pull-out toughening mechanism was exhibited in B₄C–SiC_f/BN composite sintered at 1700 °C. The stress carried by the matrix was transferred to the fibers through the BN interface, which directed crack propagation and enhanced the fracture toughness of the composites. In PyC-coated SiC_f, the consumption of the PyC coating via reaction with B₂O₃ in the B₄C matrix resulted in the ineffective contribution of SiC_f to the toughening of the B₄C ceramics under the experimental conditions. The results of this study provide a valuable foundation for further research in the interface regulation of B₄C–SiC_f ceramic materials.