Manufacture of high-purity CoCrFeNi based high entropy alloy by separating impurity elements and controlling non-metallic inclusions: A review

High-entropy alloys (HEAs) have attracted considerable attention because of their exceptional mechanical, corrosion, and oxidation resistance. However, their reliance on high-purity elemental metals results in high raw-material costs, substantial energy consumption, and considerable environmental burdens, which restrict their large-scale industrial application. In this context, low-cost feedstocks offer promising alternatives for developing more sustainable HEA manufacturing routes. Nevertheless, the use of these feedstocks inevitably introduces impurity elements together with pre-existing non-metallic inclusions. These impurities can alter inclusion formation and evolution, promote segregation and secondary-phase formation, and ultimately deteriorate the mechanical and functional properties of HEAs. This review systematically summarizes recent progress in the green and low-cost production of HEAs, with particular emphasis on the impurity evolution, non-metallic inclusion formation and removal, and refining strategies. The advantages and limitations of various manufacturing methods are critically discussed. Vacuum induction melting provides an effective basis for reducing gaseous impurities and homogenizing recycled feedstocks, whereas slag refining can facilitate the removal of oxygen-, sulfur-, and nitrogen-related impurities and non-metallic inclusions. Oxidative gas treatment, such as CO ₂ -containing gas blowing, provides a complementary approach for removing metallic impurities, particularly Al, Si, and P, which are difficult to eliminate under conventional vacuum conditions. The combination of vacuum melting, slag refining, suitable refractory selection, and controlled oxidative treatment therefore represents a promising strategy for achieving comprehensive impurity control. Furthermore, the review highlights that the cleanliness of recycled-material-derived HEAs is governed by the coupled effects of feedstock chemistry, thermodynamics, reaction kinetics, inclusion characteristics, melt properties, slag–metal interactions, refractory materials, and solidification behavior. Future research should focus on establishing quantitative impurity tolerance limits and optimizing integrated refining processes, which are essential for establishing scalable, cost-effective, and environmentally sustainable pathways toward the industrial production of high-cleanliness HEAs.