Mechanical and High-temperature Dielectric Properties of SiC_f/SiC Composites with SiO₂ Filler

The mechanical and high-temperature dielectric properties of SiCf/SiC composites with nano-SiO2 filler were investigated in the present work for the development of high-temperature structural microwave absorbing materials. The results reveal that the flexural strength of SiCf/SiC composites is increased firstly and then is degraded with the filler content increased from 3% to 15%, and the maximum strength can be up to 275 MPa, meanwhile all of which show favourable fracture toughness. Owing to the high specific surface area and low permittivity of SiO2 filler, the complex permittivity of the composites decreases and the room-temperature reflection loss (RL) is promoted with the increase of filler content. When the composites possess 15% SiO2 filler, the room-temperature RL values can be reached to –8 dB in the whole X band with the thickness of 3.2-4.0 mm. The complex permittivity of the composites increases with the rising temperatures, while the specific values and increasing range of the high-temperature complex permittivity can be significantly reduced by introducing the SiO2 filler, and the composites can obtain excellent microwave absorbing property at 700 ℃ with the thickness range of 2.7-3.0 mm