Thermal Protection and Dielectric Properties of Borosilicate Coatings for SiCf/SiC Composites Under High-Temperature Oxidation

Currently, oxidation of SiCf/SiC composites in harsh environments such as high temperatures has become a key challenge for their application in high-temperature structural wave-absorbing materials. In this study, borosilicate glass (BSZ) coatings were prepared using the thermal nitrogen–oxygen process. The evolution of mechanical and coating microwave dielectric properties of the composites with and without BSZ coatings after oxidation at 1100 °C, 1200 °C, 1300 °C and 1400 °C was investigated. The results showed that the mechanical strength of the BSZ-coated SiCf/SiC specimens remains virtually unchanged, with a remarkable strength retention rate of 94%. The exceptional oxidation resistance of these coatings can be attributed to the formation of self-healing oxides and the reinforcing “pinning” effect of ZrSiO4. With an increase in oxidation temperature, the dielectric properties of the oxidized coatings are determined by the intrinsic properties of the generators and the porosity. Overall, these features highlight the potential of borosilicate coatings in the field of electromagnetic wave-absorbing composites, and the current work establishes a correlation between the oxidized microscopic properties of the coatings and the dielectric properties.