Effect of SiC-ZrC Coating Prepared by SiZr Liquid Phase Sintering on the Oxidation Resistance of C/SiC Composites

Owing to their low density and good mechanical properties at high temperatures, C/SiC composites are increasingly used in the aerospace industry. They are also being proposed as thermal-structural materials in the hypersonic field; however, C/SiC composites are easily oxidized in high-temperature air environments. In this study, a C/SiC composite was coated with a SiC-ZrC oxidation-resistant layer by a two-step sintering method using Si-25%Zr (mass fraction) alloy, and the phase evolution of the coating was studied during the sintering. The oxidation resistance of the material was then tested at 1400 degrees C in an air environment. The microstructural changes of the coating before and after oxidation and the effect of oxidation on the bending properties of C/SiC were analyzed. After the reaction with carbon, Si and ZrSi2 disappear in the coating, leaving only pure ZrC and SiC. The ZrC phase refined the structure of the reactive SiC layer. The grain size of the sintered SiC was 2 mu m, versus 5-20 mu m for SiC sintered from pure Si. The refined grains created a dense and continuous SiO2 film during the oxidation process. As the oxidation time was increased at 1400 degrees C, the C/SiC composite with the SiC-ZrC coating began losing weight at 200 s, but began gaining weight at 500 s as a dense SiO2 film was formed. After 1000 s of oxidation, the flexural strength of the C/SiC composites was 335 MPa, only 5% lower than that of the initial C/SiC composite. According to this result, the sintered SiC-ZrC oxidation-resistant film effectively protected the mechanical properties of the C/SiC composite during the oxidation process.

Automated summary

By coating a C/SiC composite with a SiC-ZrC oxidation-resistant layer, the oxidation resistance can be improved, effectively protecting the mechanical properties during high-temperature oxidation.