Improved tensile strength and toughness of dense C/SiC-SiBC with tailored PyC interphase

In this study, in order to improve the tensile strength and toughness of dense C/SiC-SiBC, the thickness of PyC interphase (e_PyC) was increased from 200 nm to 400 nm. C/SiC (e_PyC≈200 nm) was also fabricated as a benchmark comparison. C/SiC-SiBC (e_PyC≈200 nm) exhibited higher axial thermal residual stress (TRS) than C/SiC (e_PyC≈200 nm). Increased axial TRS resulted in increased interfacial shear strength (τ) through fiber bending, which caused lowered mechanical properties of C/SiC-SiBC (e_PyC≈200 nm). By increasing the thickness of PyC interphase from 200 nm to 400 nm, the axial TRS in C/SiC-SiBC decreased. Accordingly, the radial stress induced by fiber bending decreased, leading to a reduced τ in C/SiC-SiBC (e_PyC≈400 nm). Decreased axial TRS and τ are beneficial to the effective loading of fiber bundles and pull out of fibers. Therefore, C/SiC-SiBC (e_PyC≈400 nm) performed excellent tensile strength (250 ± 11 MPa) and fracture toughness (23.7 ± 0.5 MPa·m^1/2).