ZrB_2/SiC as a protective coating for C/SiC composites: Effect of high temperature oxidation on mechanical properties and anti-ablation property

摘要

C/SiC composites are raising great interest as a thermal shielding for aerospace applications, provided that they are protected from oxidation by suitable coatings. Conversely, ultra high temperature ceramics, and in particular ZrB_2, is among the best oxidation resistant materials as known. A new type of oxidation protective coating (ZrB_2/SiC coating) was produced on C/SiC composites. The composites were produced by precursor infiltration and pyrolysis (PIP), which is a simple and low cost method; the coating was ZrB_2 mixed with SiC, which was fabricated by painting slurry on the surface of the composite followed by chemical vapor deposition (CVD) SiC on the top. Mechanical tests were conducted before and after oxidation test. Anti-ablation property was tested under oxy-acetylene torch. Oxidation test shows that the uncoated samples are oxidized quickly and the weight loss reaches 29.2% and the reservation of original flexural strength is only 6.74%, while the weight loss of ZrB_2/SiC coated samples is only 5.19%, and the reservation of original flexural strength is 37.4%. ZrB_2/SiC coating can provide longtime protection for C/SiC composites at 1973 K. Compared with the uncoated composites, the linear and mass ablation rates of the coated composites decreased by 62.1% and 46.1%, respectively, after ablation for 30 s. The formation of zirconia and silicon dioxide from the oxidation of ZrB_2/SiC improved the ablation resistance of the composites, because of the evaporation at elevated temperature, which absorbed heat from the flame and reduced the erosive attack to carbon fibers and SiC matrix.