Correlation of PyC/SiC interphase to the mechanical properties of 3D HTA C/SiC composites fabricated by polymer infiltration and pyrolysis

3D braided carbon fiber preforms were used to fabricate C/SiC composites using polymer infiltration and pyrolysis (PIP). Before the PIP, the preforms were coated by isothermal chemical vapor infiltration with methane to produce pyrocarbon (PyC) and then with hexamethyldisilazane to form SiC and produce the PyC/SiC interphase. The correlation of the PyC/SiC interphase to the microstructure and the mechanical properties of the fabricated composites was investigated. The flexural properties of the composites were measured using the three-point-bend test, and the fracture surfaces observed by SEM. The bend strengths were 247 MPa and 46 MPa, with and without the PyC/SiC interphase respectively. Long fiber pullout dominated the fracture surface for the composite with the PyC/SiC interphase, while for the one without the interphase, almost no fiber pullout was observed.