Preparation And Oxidation Resistance Of SiC/γ-Y₂Si₂O₇ Double-layer Coating On C/C Composites

Due to their excellent properties at high temperature, carbon/carbon(C/C) composites are considered as the most promising candidate materials for high temperature applications in the aviation and space flight fields. However, C/C composites are easy to oxidize at high temperature, which limits their applications as high-temperature structural materials. Application of oxidation resistant coatings is considered to be an effective method for preventing C/C composites from oxidation at high temperature. SiC has been proved to be the best bonding layer material for C/C composites due to its good physical and chemical compatibility with C/C composites. And because of high melting point, low-temperature oxygen permeability, low thermal expansion coefficient, low temperature evaporation rate, low heat conductivity, good chemical stability yttrium silicates such as Y2Si2O7 has great potential to be applied as thermal barrier/oxidation resistant outer layers. By far, the yttrium silicates coatings haven't been reported.In this paper, a double-layer coating with SiC bonding layer andγ-Y2Si2O7 outer layer was prepared. These two layer of SiC andγ-Y2Si2O7 were produced by pack cementation technique and slurry methord respectively. The morphology, component, and microstructure of the coating were characterized by SEM, XRD and EDS. The results showed that the bonding layer prepared at 1600℃for 3 h was dense and continuous, and was composed of singleβ-SiC. This bonding layer with homogeneous thickness was staggerly and serratly combined with the matrix material. It was found that a great numember of nano-SiC whiskers formed on the top surface of the bonding layer, which enhanced the integration between SiC grains. The outer layer of the double-layer coating was pureγ-Y2Si2O7.The results indicated that the initial oxidation temperature of C/C composites coated with SiC/γ-Y2Si2O7 had improved from 380℃to 700℃. During the isothermal oxidation and cyclic oxidation tests at 1100℃, compared to C/C composites, the rate of weight loss of coated composites decreased remarkably. The SiC/γ-Y2Si2O7 coating could protect C/C composites from oxidation. The as-prepared coating presented good thermal shock resistance and thermal stability. The results of high temperature ablation texts revealed thatγ-Y2Si2O7 was benefit to the improvement of oxidation resistance of C/C composites due to its sealing effect.