Effects of BN/SiC dual-layer interphase on mechanical and dielectric properties of SiC_f/SiC composites

BN/SiC dual-layer interphase in SiC_f/SiC composites was successfully prepared using urea-boric acid solution as precursor for dip-coating process and PCS/xylene solution for PIP process. XRD and Raman spectrum results show that both BN and SiC sub-layers have relatively low crystalline degree. The surface of as-prepared BN/SiC dual-layer interphase is smooth and homogeneous, and its thickness is about 0.42 μm. The flexural strength and failure displacement of composites with BN/SiC dual-layer interphase are improved conspicuously to 272 MPa and 0.26 mm, which are both much higher than those of composites without interphase, whose ultimate values are only 126 MPa and 0.14 mm, respectively. The composites with dual-layer interphase show better anti-oxidation capability than do the composites with BN interphase below 1000 C. ε′ and ε″ of the composites increase from 30-i22 to 45-i32 after incorporation of dual-layer interphase, which are caused by relaxation polarization and conductance losses established in the components, including fibers, matrix and interphase.