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 composites' mechanical properties, heat treatment at 1500 degreesC under Ar flow in quite low O-2 partial pressure or a CVI SiC coating were applied to Hi-Nicalon(TM) SiC fi bers. Interfacial microstructures between fiber and matrix were examined by SEM and TEM. Interfacial shear properties were evaluated by single-fiber p ush-out tests and compared with the results of three-point bend tests and t ensile 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 britt le, although it was successful in making the ISSCL rough. SiC fiber coating induced strong bonding between fiber and ISSCL and turned the crack path f rom between the fiber and the ISSCL to the inside of the ISSCL. Interfacial frictional stress was increased and the mechanical properties of tensile t ests were improved. (C) 2001 Elsevier Science B.V. All rights reserved.