Effect of the Carbon Interface on the Mechanical Behavior of Amorphous SiC Fiber/Si-Co Composites

The objective of this study was to propose a novel lightweight and affordable structural material that can withstand temperatures in the range of 500°C–1000°C. A processing technology for amorphous SiC fiber (Nicalon or Hi-Nicalon)/Si-CoSi2 matrix composites with a fiber-matrix interface of film-boiling (FB)-derived carbon (FB-C) was developed. The mechanical properties of the composites were evaluated at room temperature (25°C). The average 4-point bending strength of the Hi-Nicalon/FB-C/Si-CoSi2 composite was 511 MPa. Fiber pullout and bridging was clearly observed on the fracture surface of the composites. By contrast, the Nicalon/FB-C/Si-CoSi2 composite exhibited brittle failure, with an average 4-point bending strength of 87 MPa and no fiber pullout was observed in it. The apparent shear strength at the fiber/FB-C interface was evaluated using a fiber bundle pushout test. The test results indicated that the interfacial shear strength of the Nicalon/FB-C interface was approximately 1.7 times higher than that of the Hi-Nicalon/FB-C interface, indicating the stronger adhesion of the former compared with the latter. Thus, the carbon layer formed using the FB method may not be a suitable interface for Nicalon fiber.