Isothermal-oxidation behavior of vacuum-clad CrNiFeMoCo high-entropy alloy coating at 600–800 °C

The high-temperature oxidation behavior of vacuum cladding CrNiFeMoCo high-entropy alloy (HEA) coatings was investigated. The HEA coating has a strong metallurgical bonding with the substrate and an FCC + σ eutectic structure. The HEA coating at 600 °C follows a single linear oxidation law, with k and n values of 4.15 × 10−5 mgn cm−2n min−1 and 1.118, while two steps make up the oxidation process at 700–800 °C: the initial stage of rapid oxidation and the steady-state stage of slow oxidation with lower k and higher n values. The oxidation product at 600 °C was Cr2O3, while oxidation products at 700–800 °C primarily consisted of Cr2O3 with a trace quantity of (Cr,Fe)2O3. The oxide layer's flat surface at 600 °C shows low-speed thickening behavior, while the oxide layer at 700–800 °C exhibits a two-stage thickening behavior: rapid thickening and densification during initial oxidation, and a low thickening rate during stable oxidation. The main oxidation mechanism is the prolonged interaction of O2 permeation, low oxide formation rate, and metal diffusion coefficient at 600 °C, while the HEA coating still exhibits excellent oxidation resistance at 700–800 °C due to the continuous generation and protection of dense oxidation products with Cr2O3 as primary oxide.