Microstructure evolution and oxidation behavior of SiC-HfB₂-MoSi₂ coating prepared by gaseous/liquid silicon infiltration

Targeting the issue of C/C composites easily oxidizing at elevated temperatures, SiC-HfB₂-MoSi₂ coating was prepared on C/C-SiC-HfB₂ composites. This paper presents a comparative study of the microstructure and oxidation resistance of the coating prepared by gaseous infiltration silicon (GSI) and liquid infiltration silicon (LSI), respectively. The silicon infiltration process was simulated to assist in analyzing the morphology changes of the coating. The GSI coating is denser and more uniform than the LSI coating, whose bottom coating is thin and defective. These morphological differences are mainly due to the rearrangement of the ceramics in the coating with the flow of Si. The GSI coating protected the matrix for 78 h at 1700 °C with a mass loss of only 1.67 %, demonstrating good oxidation resistance, while the LSI coating lost 3.19 % of its mass after oxidation for 34 h. The primary reason for the discrepancy is that the GSI coating has a more homogeneous, dense structure than the LSI coating, providing a better oxygen barrier. This work provided a technical reference for the stable service of C/C composites in a high-temperature aerobic environment.