Effect of MoSi₂ content on the oxidation behavior and mechanism of the ZrSi₂-Y₂O₃ coating for SiC coated C/C composites

Carbon/carbon (C/C) composites are prone to oxidation above 500 °C, and a single SiC coating is likely to peel off during repeated use due to a mismatch in the coefficient of thermal expansion (CTE), making it difficult to provide long-term effective protection. For this purpose, in this paper, a ZrSi₂-Y₂O₃-MoSi₂ multiphase outer coating was prepared on the surface of the SiC coating of C/C composites by supersonic atmospheric plasma spraying (SAPS). The introduction of MoSi₂ was intended to alleviate the CET mismatch within the coating system and promote the formation of a dense protective oxide layer during high-temperature exposure. The effects of the addition amount of MoSi₂ on the phase composition, microstructure and antioxidant performance of the coating were systematically studied. The results show that the optimized components can achieve a high-density surface morphology. After oxidation at 1500 °C for 336 h, the multiphase coating with 30 wt% MoSi₂ added lost only 3.6% of its weight. The oxidation resistance did not increase monotonically with MoSi₂ content. When the MoSi₂ content was further increased to 40 wt%, the protective effect deteriorated. ZrSi₂ provides a high-temperature-stable skeleton, Y₂O₃ stabilizes the structure and forms a high-viscosity Si-O-Y network, and MoSi₂ supplements SiO₂ and regulates its fluidity to facilitate pore and microcrack sealing. The interaction among these three elements constructs an adaptive composite protective network, providing a feasible idea for the design of long-term protective coatings in the extreme thermal environment of aerospace.