Effect of interface type on the static and dynamic mechanical properties of 3D braided SiCf/SiC composites

The static and dynamic mechanical properties of three dimensional (3D) braided SiCf/SiC composites with pycrocarbon (PyC) and SiC and without an interphase layer prepared by polymer infiltration and pyrolysis (PIP), were investigated using static and dynamic bending tests as well as microstructural characterization. Test results indicated that the interfacial shear stress, flexural strength, elastic modulus, and storage modulus of 3D braided SiCf/SiC composites with an interphase layer were superior to those the composites without an interlayer; the former also showed a lower internal friction than the latter. Results from Weibull statistical analysis also indicated that the scale parameter σ0 (337.1 MPa and 630.6 MPa, respectively) and Weibull modulus m (16.85 and 19.91, respectively) of 3D braided SiCf/SiC composites with SiC and PyC interphase were higher than those of composites without an interphase (103.2 MPa, 14.02). The composite with the PyC interphase presented the highest flexural strength and the most ductile fractures because it featured relatively ideal interfacial bonding and a layered interphase structure, leading to effective energy-dissipation mechanisms, such as fiber pull-out. The composite with the SiC interphase exhibited highest elastic and dynamic moduli because of strong interfacial bonding and a non-layered rough interphase structure, which enhanced its ability to resist strain. The ideal interface improves load transfer and did not contribute to damping. The occurrence of interfacial damping in the 3D braided SiCf/SiC caused the internal friction to become more sensitive to temperature, frequency and amplitude. The static and dynamic mechanical properties, including internal friction and storage modulus, as well as failure behavior of the 3D braided composites were remarkably affected by the interface type.