Influence of dual carbon distributions on the microstructure and oxidation resistance of the gaseous silicon infiltrated ZrB₂–SiC–Si-SiCw coating

Understanding the physicochemical processes in a Si–C-ceramics system is crucial for anti-oxidation coatings prepared by the slurry method and gaseous silicon infiltration (GSI). This paper investigated the effect of dual distributions of carbon in the pre-coatings, including the carbon black distributed between ceramic particles and the pyrolytic carbon (PyC) shell covering the SiC whisker (SiCw), on the microstructures of the ZrB₂–SiC–Si-SiCw coatings treated by the GSI and their oxidation performances at 1973 K. The addition of 8.1 wt% carbon black facilitates the morphological retention of SiCw after the GSI. Furthermore, the deposition duration of the PyC shell affects microstructures and phase distributions of the coatings. Notably, the heat released from the C–Si reaction promotes the condensation of gaseous silicon, and the detection of ZrSi₂ provides evidence for the mass transfer of element Zr assisted by silicon melt. For the PyC deposition duration of 2 h, the obtained ZrB₂–SiC–Si-SiCw coating shows an optimal oxidation protection ability at 1973 K, protecting the C/C composites for 37 h with a mass gain of 0.27%. The stable oxide layer is attributed to the reinforcement of SiCw, and uniformly distributed ZrB₂ within the GSI-treated coating, which turns to ZrO₂ skeleton pinning SiO₂ during oxidation.