Effects of Rare-Earth Element Yttrium (Y) on the Hot Corrosion of AlCrFeNi Medium-Entropy Alloy in NaCl-KCl Molten Salt at 750°C

AlCrFeNi medium-entropy alloys (MEA) have attracted considerable attention for high-temperature applications owing to their modifiable mechanical properties and excellent corrosion resistance attributed to their protective oxide scales. A small amount of rare-earth element yttrium (Y) can further improve the resistance of alloys to oxidation/corrosion. In this study, 1 wt.% Y was added to the AlCrFeNi alloy via arc melting, and the effects of the Y addition on the microstructure, mechanical properties, and hot corrosion of the MEA in molten NaCl-KCl salt at 750°C were investigated. To better evaluate the role of Y in enhancing the hot-corrosion resistance, stainless-steel 316 (SS316) was also tested for comparison. It has been demonstrated that the Y addition markedly enhances the mechanical strength and hot-corrosion resistance of the alloy in both air and argon atmospheres. In air, Y improves oxide scale adhesion, and reduces spallation and large void formation in the oxide scale. While, in argon, Y suppresses the outward diffusion of Cr and Al, reduces the formation of volatile chlorides, and inhibits salt penetration into the substrate. This study highlights the beneficial role of Y in improving the hot-corrosion resistance of both AlCrFeNi MEAs and SS316 for applications in hot corrosive environments and at elevated temperatures.