Effects of pyrochemical treatment for producing interfacial carbon layer on tensile properties of polymer-derived-matrix-based SiC/SiC composites

A carbon layer can be produced on the surfaces of the SiC fibers used in SiC-fiber-reinforced SiC matrix (SiC/SiC) composites via high-temperature heat treatment in a reductive atmosphere. This layer acts as an interfacial sliding layer and helps tailor the mechanical characteristics of the composites. The pyrochemical technique is more efficient and cost-effective than the more commonly used chemical vapor infiltration (CVI) for producing the aforementioned carbon layer. In this study, the effects of the pyrochemical technique on the tensile properties of polymer-derived-matrix-based SiC/SiC composites were evaluated and compared with those obtained via CVI. Although the SiC fibers tested were not weakened by the pyrochemical treatment, the composite formed using the pyrochemically treated fibers showed a lower tensile strength than that of the composite with CVI-treated fibers. This strength reduction was probably caused by a decrease in the Young’s modulus of the fibers after the pyrochemical treatment. The matrix in the former case experienced multiple fractures, leading to the decline of its load-transferring capability at lower applied stresses. This deterioration can be redeemed by increasing the fiber volume fraction (Vf), and therefore needs to be considered when designing components for composites.