SiC Nanoparticles Toughened-SiC/MoSi₂-SiC Multilayer Functionally Graded Oxidation Protective Coating for Carbon Materials at High Temperatures

A SiC nanoparticle toughened-SiC/MoSi₂-SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi₂, α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi₂-SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi₂-SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10⁻² g/cm³/h, respectively.