Structural properties of the fiber –matrix interface in carbon-fiber/carbon-matrix composites and interfaces between carbon layers and planar substrates

Abstract

Abstract The structure of the fiber –matrix interface region of carbon-fiber/carbon-matrix (C/C)-composites, which is important for the mechanical properties of a composite, was studied by transmission electron microscopy. The pyrolytic carbon matrix was obtained by chemical vapor infiltration of carbon fiber preforms with different fiber architecture and fiber types. While the texture of the carbon matrix can be controlled by the infiltration conditions, the carbon texture at the fiber –matrix interface differs from the bulk matrix and cannot be determined by the infiltration parameters. We often observe a high-textured layer with a thickness up to 100 nm at the interface prior to the formation of the bulk matrix with a lower texture. The fiber –matrix interface properties of C/C-composites are compared with the interface of pyrolytic carbon layers deposited on planar Si-, BN- and cordierite-substrates. In contrast to BN-substrates, thin high-textured pyrolytic layers are observed at the interface of carbon on planar Si- and cordierite-substrates where strong bonding between pyrolytic carbon and the substrate is achieved by the formation of Si-C bonds. Stress-induced ordering is discussed as a mechanism for the formation of the high-textured interface layers.