Effect of melt superheating treatment on corrosion resistance of Al2CoCrCuFeNi high entropy alloy in 0.5 M HNO3 solution

Abstract

Al2CoCrCuFeNi high-entropy alloy (HEA) was heated by vacuum arc furnace at different powers (5.26kW, 6.15 kW, 7.28 kW, 8.26 kW) to different temperatures above the liquidus point (labeled as T1, T2, T3 and T4). The structure and corrosion resistance were investigated by means of X-ray diffraction, scanning electron microscopy with spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and electrochemical workstation. It was found that the HEAs with different superheating temperatures were all simple face-centered cubic (FCC) and body-centered cubic (BCC) solid solutions without complex phases. As the superheating temperature increased, the structure of HEAs became dense, the segregation decreased, and some fine-scale precipitations were formed at T4. When the heating temperature reached T3 or higher, the corrosion current density of the alloy decreased by more than 1/2, and the range of the passivation zone also became wider, indicating that the corrosion resistance was significantly improved. It was found that the pitting potential Eb ranked: T1<T2<T4<T3, indicating that the alloys labeled as T3 and T4 had better pitting resistance than those labeled as T1 and T2. The potential range of the stable passivation region △E ranked: T1<T2<T3<T4, which proved that the passivation film on the surface of HEA became more and more stable as the superheating temperature increased.