Effects of ZrO₂ interphase on mechanical and microwave absorbing properties of SiC_f/SiC composites

Zirconia (ZrO₂) coatings were successfully prepared on KD-II SiC fibers by sol-gel approach in zirconyl chloride and ethanol-water solution. Subsequent heat treatment at 1000 °C was done in vacuum. Phase composition and morphological characteristics of the ZrO₂ coatings were investigated by XRD, FTIR, and SEM. The SiC_f/SiC composites with ZrO₂ coatings as interphase were fabricated by chemical vapor infiltration (CVI). The effects of ZrO₂ interphase on the mechanical and dielectric properties of composites were studied. The results show that the flexural strength of SiC_f/SiC composites with and without ZrO ₂ interphase are 261 and 103 MPa, respectively. It is demonstrated that ZrO₂ interphase can effectively adjust the interfacial bonding strength and improve the mechanical properties of SiC_f/SiC composites. In addition, both the real and imaginary parts of the complex permittivity (Ïμ′ and Ïμ″) of the SiC _f/SiC composites with ZrO₂ interphase are higher than those of without ZrO₂ interphase. The effective absorbing bandwidth (below -10 dB) of SiC_f/SiC composites with ZrO₂ interphase is 1.6 GHz and the lowest reflection loss is -11.5 dB when the sample thickness is 2.7 mm.