Addressing challenges in high-temperature oxidation of ultra-supercritical boiler tubes via FeCoNiCrMo high-entropy alloy coatings

The engineering realm confronts formidable challenges in combating the persistent issue of high-temperature oxidation in ultra-supercritical coal-fired boiler tubes. This study is dedicated to tackling these challenges by employing high-velocity oxy-fuel spraying (HVOF) and high-frequency induction remelting techniques. Our primary objective is to establish a metallurgical bond between self-fusing FeCoNiCrMo high-entropy alloy (HEA) powder and the conventional 15CrMo boiler steel tube surfaces, all within ambient atmospheric conditions. Our investigation reveals two distinct stages of oxidation for the HEA coating when exposed to a 900 °C air environment. Initially, there is a rapid oxidation stage driven by interfacial reactions, followed by a steady-state slow oxidation stage influenced by ion diffusion. The presence of a dense Cr2O3 layer plays a pivotal role in reducing the oxidation rate significantly, thereby imparting exceptional high-temperature oxidation resistance to the FeCoNiCrMo HEA coating. Notably, during the steady-state stage, the oxidation rate is two orders of magnitude lower than observed in Ni-based superalloys. Minimal phase transformations or transitional layers at the interface underscore superb interface bonding at 900 °C. These findings provide a promising avenue for the cost-effective fabrication of highly oxidation-resistant ultra-supercritical boiler tubes. This advancement contributes significantly to the progress of engineering applications.