Fabrications and mechanical properties of Si-Ti-C-O fiber SiC composites with CVD-SiC layer between fiber and matrix

Si-TiC-O-F/SiC composites were fabricated by the polymer-impregnation pyrolysis (PIP) process. Before the PIP process, the fibers were coated with thin CVD-SIC or thin resin derived carbon. The composite with uncoated fibers was also prepared by the same PIP process for comparison. SEM and TEM observations and TEM-EDX analysis were performed to characterize the interfaces between fiber and matrix of three kinds of composites. The turbostratic carbon layer with a thickness of 20-200 nm was recognized between the fiber and the CVD-SiC layer in the composite with the CVDed-SiC fiber. Mechanical properties of three kinds of composites were compared by the tensile test, the 4 point bending test, and the Chevron notched beam bending test at room temperature. The composites with the surface treated fiber were much higher in strength and toughness than those with the untreated fiber. Especially for the composite with the CVD-SiC fiber, the tensile strength was 400 MPa, the flexure strength was 640 MPa, and the fracture toughness was 22 MPa.m(1/2).