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

Abstract

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 + sigma eutectic structure. The HEA coating at 600 degrees C follows a single linear oxidation law, with k and n values of 4.15 x 10-5 mgn cm-2n min-1 and 1.118, while two steps make up the oxidation process at 700-800 degrees 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 degrees C was Cr2O3, while oxidation products at 700-800 degrees C primarily consisted of Cr2O3 with a trace quantity of (Cr,Fe)2O3. The oxide layer's flat surface at 600 degrees C shows low-speed thickening behavior, while the oxide layer at 700-800 degrees 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 degrees C, while the HEA coating still exhibits excellent oxidation resistance at 700-800 degrees C due to the continuous generation and protection of dense oxidation products with Cr2O3 as primary oxide.