Effect of porous pre-coating on the phase composition and oxidation protective performance of SiC coating by gaseous silicon infiltration

Though gaseous silicon infiltration (GSI), as a mild and efficient method for preparing silicon-based ceramic coatings on carbon/carbon (C/C) composites, has stirred up worldwide interest, it is still a big challenge to control the phase composition and microstructure of the coatings. Herein, by adjusting the pore structure of the pre-coating via using four kinds of resin (phenolic resin (PF), boron-modified phenolic resin (BPF), cashew shell oil-modified phenolic resin (PCF), epoxy-modified phenolic resin (EPN)), the permeability and reaction degree between gas-phase Si and resin carbon were controlled effectively. A pre-coating with higher porosity and more residual carbon can provide a larger specific surface area and sufficient carbon source, which is conducive to the permeation and reaction of Si. The results show that the lower the residual carbon content in the pre-coating, the larger its specific surface area, resulting in a deeper penetration of Si. Once the residual carbon content is too low, it will lead to insufficient carbon sources and excessive free Si in the GSI coating, which has a negative effect on the oxidation performance of the coatings. The coating prepared with EPN resin, which has 53 % residual carbon content, exhibits the best oxidation protection performance for C/C. Compared to conventional PCF-GSI coating, EPN-GSI coating has a 40 % reduction in mass loss after oxidation at 1500 °C for 110 h. This study, for the first time, demonstrates the strategy for improving the oxidation protective performance of SiC coating by controlling porous pre-coating, which opens up a novel avenue for regulating the GSI process.