Abstract: The failure of transition metal carbide high-entropy ceramics in high-temperature oxidative environments severely limits their application as wear-resistant materials. Incorporating secondary phases to modify them represents an effective strategy to address this issue. In this study, different mass fractions (0, 2.5%, 5%, 10%) of Si were added to (Ti_0.2Zr_0.2Hf_0.2Ta_0.2Mo_0.2)C (HEC) high-entropy ceramics, and SiC and MoSi₂ secondary phases were generated in-situ via spark plasma sintering. The effects of Si content on the isothermal oxidation behavior of HEC ceramics at 1500 ℃ and its underlying mechanism were systematically investigated. The results indicate that the oxidation scale of Si-free HEC ceramic is loose and porous, exhibiting mass loss due to the release of MoO₃ (g) and CO (g). Upon Si addition, all composite ceramics exhibited a slight mass gain. Among them, the HEC ceramic with 5%Si addition exhibited the best oxidation resistance, characterized by a flat and relatively dense oxide scale surface, along with a four-layered oxide scale structure extending from the outermost layer to the substrate. Both the outermost Ti-rich oxide layer and the subouter (Zr,Hf)₆Ta₂O₁₇ layer are relatively dense, which effectively suppresses inward oxygen diffusion and the formation of volatile MoO₃ (g). However, excessive Si addition (10%) led to the formation of an excessive SiO₂ liquid phase, generating numerous interconnected pores within the oxide scale and thereby weakened the protective effect. These findings provide experimental evidence for the design of oxidation-resistant high-entropy carbide ceramics.

Key words: high-entropy carbide, silicon carbide, molybdenum disilicide, isothermal oxidation, oxidation resistance