Weakening Effects of Aluminum on the Microstructure, Mechanical Properties, and Corrosion Resistance of High‐Velocity Arc‐Sprayed FeCrNiCoAl _x High‐Entropy Alloy Coatings

Current high‐entropy alloy (HEA) coating design strategies often rely on the assumption that the beneficial effects of aluminum (Al) addition—well‐documented for enhancing the wear and corrosion resistance of bulk HEAs—are directly transferable to coating systems. However, this study reveals that within the specific processing context of high‐velocity arc spraying (HVAS), Al conversely degrades the overall performance of HEA coatings. In this work, a series of FeCrNiCoAl _x ( x = 0, 0.5, 1) HEA coatings were successfully fabricated on 45 steel substrates using the HVAS technique. The weakening mechanism of Al on the microstructure, mechanical properties, and corrosion resistance of these coatings was systematically investigated. The results revealed that the Al‐free coating exhibited superior wear and corrosion resistance under all tested conditions. This enhanced performance is attributed to its minimal porosity and single FCC phase structure, which mitigates the formation of multiphase galvanic couples. With increasing Al content, the coatings demonstrated a transition to more severe abrasive and oxidative wear mechanisms. The corrosion process was likewise exacerbated, driven by the increased porosity and the poor stability of the Al‐rich passive film in chloride‐rich environments. This demonstrates that the “Al‐strengthening” design principle is ill‐suited for the HVAS fabrication process.