Microstructure and oxidation property of CrSi₂-ZrSi₂-Y₂O₃/SiC coating prepared on C/C composites by supersonic atmosphere plasma spraying

Double silicon-based ceramic coatings of CrSi₂-ZrSi₂-Y₂O₃/SiC were deposited on the surface of C/C composites to improve their oxidation resistance. The SiC inner coating was prepared by pack cementation while the CrSi₂-ZrSi₂-Y₂O₃ outer coatings with different CrSi₂ contents were deposited on the surface of the SiC coating by supersonic atmosphere plasma spraying (SAPS). Microstructure feature, phase composition and oxidation resistance of the coatings were studied. The coatings prepared by the two steps had a dense microstructure with few pores and microcracks, and the interface exhibited good coherence. Oxidation experimental results showed that the CrSi₂-ZrSi₂-Y₂O₃/SiC coating with 30 wt% CrSi₂ effectively protect C/C composites from being oxidized at 1500 °C in air, the mass change of which decreased by 1.2% after the oxidation time of 288 h. Meanwhile, it could also withstand 15 times thermal shock cycles from 1500 °C to room temperature (RT). A glass layer including SiO₂ and Cr₂O₃ could effectively heal the microcracks and pores of the coating and thus reduce oxygen permeation. Meanwhile, the oxides such as ZrO₂, ZrSiO₄, Y₂Si₂O₇ and Y₂SiO₅ could inhibit the growth and propagation of the coating microcracks and improve the oxidation resistance of the specimen.