Influence of dip-coated MgO interphase on the mechanical and dielectric properties of 2D-SiCf/SiC composites

This work focused on the use of the dip-coating process to prepare magnesium oxide (MgO) coatings on silicon carbide fibers (SiCf) as an interfacial system for SiCf/SiC composites. The MgO coatings were prepared on KD-I SiCf using thermal decomposition of magnesium acetate tetrahydrate (C4H6MgO4·4H2O) in a vacuum furnace. The effect of the amount of C4H6MgO4·4H2O on the coating's microstructure and morphology, mechanical and dielectric properties of SiCf/SiC composites were investigated. The Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction results show that the coating's surface is relatively smooth and uniform as the content of C4H6MgO4·4H2O reaches 3 wt%. The SiCf/SiC composites containing an 0.18 μm thick MgO interphase show improved mechanical properties in terms of flexural strength and failure displacement. Also the complex permittivity for composites with an MgO interphase is a little lower than the as-received composites because of the low electric conductivity of MgO. The effective microwave absorbing bandwidth (below −10 dB) for composites is in the range 8.8–11.5 GHz, and the minimal reflection loss reached −12.56 dB.