Effect of rare earth element Y content on microstructure, magnetic properties, and electrochemical properties of the as-annealed FeCoNiAl0.2Yx high-entropy alloys

Abstract

FeCoNi high-entropy alloy (HEA) is widely used in the aerospace and chemical industry. However, the strength and corrosion resistance of the alloy still need to be improved. In this paper, FeCoNiAl0.2Yx (x = 0, 0.05, 0.1, 0.2, and 0.3 in mole ratio) high entropy alloys with different contents of rare earth (RE) element yttrium (Y) were prepared by the vacuum arc melting method, and then the alloys were subjected to annealing treatment at 800 °C/2h. The microstructure, hardness, magnetism, and corrosion performance of FeCoNiAl0.2Yx HEAs in the annealed state with different contents of element Y were analyzed. The results show that the annealed FeCoNiAl0.2Yx HEAs without the addition of element Y and after the addition of element Y both were composed of a face-centered cubic phase. The alloy showed a dendritic structure inside. The element Y was solidly dissolved in the alloys to refine the microstructure of the alloys, and the dendrites were gradually refined with the addition of Y. The Y element caused the phenomenon of lattice distortion inside the alloys, which led to the increase in the alloys’ hardness. The alloy with x = 0.2 showed the greatest exchange of magnetic atoms and the alloy with x = 0.05 showed the lowest coercivity. The alloy with x = 0.1 showed the lowest self-corrosion current density, the broadest passivation zone, the densest dendrites, the smallest grain spacing, and the weakest tendency for intergranular corrosion. The present study shows that the introduction of element Y improves the microstructural morphology, hardness, magnetism, and corrosion properties of FeCoNiAl0.2Yx HEAs in the annealed state.