Improvement of mechanical properties of SiC/SiC composites by various surface treatments of fibers

In order to make an interfacial shear strength control layer (ISSCL), such as pyrolytic C layer, effective and improve SiC/SiC compositesʹ mechanical properties, heat treatment at 1500°C under Ar flow in quite low O2 partial pressure or a CVI SiC coating were applied to Hi-Nicalon™ SiC fibers. Interfacial microstructures between fiber and matrix were examined by SEM and TEM. Interfacial shear properties were evaluated by single-fiber push-out tests and compared with the results of three-point bend tests and tensile tests. Fracture surfaces after mechanical tests were examined by SEM with EDS and optical interferometric profilometry. Active oxidation of the fibers decreased fiber mechanical properties and made the composites brittle, although it was successful in making the ISSCL rough. SiC fiber coating induced strong bonding between fiber and ISSCL and turned the crack path from between the fiber and the ISSCL to the inside of the ISSCL. Interfacial frictional stress was increased and the mechanical properties of tensile tests were improved.