Corrosion behavior of as-cast Al0.75CoCr1.25FeNi high entropy alloy in 0.5 mol/L sulfuric acid

This study focuses on the corrosion behaviors of an as-cast Al_0.75CoCr_1.25FeNi high entropy alloy (HEA) in 0.5 mol/L H₂SO₄ solution. The results showed that the HEA exhibited mixed column dendrite and inter-dendrite structures composed of face-centered cubic (FCC) phase, body-centered cubic (BCC) phase, and ordered BCC phase (B2). The corrosion resistance of the HEA in 0.5 mol/L H₂SO₄ solution was inferior to that of 316L stainless steel (SS); the HEA displayed an incomplete capacitive reactance arc at higher frequencies and an inductive reactance arc at lower frequencies during the electrochemical impedance spectroscopy test. The immersion experiments demonstrated an electrical potential difference between the Ni–Al-rich phase and the Fe-Co-Cr-rich phase of the HEA, resulting in micro-galvanic corrosion. This micro-galvanic corrosion prefers on the B2 (Ni–Al-rich) phase of the HEA. Moreover, the FCC phase and BCC1 phase of HEA corroded with the prolongation of immersion time. The surface of HEA has a loose and porous corrosion product film due to its relatively high percentage of Al₂O₃. Additionally, the ratio of Cr₂O₃/(Cr + Cr(OH)₃) in the corrosion product film decreased with the increase of immersion time.

Graphical Abstract

Al_0.75CoCr_1.25FeNi high entropy alloy exhibited mixed column dendrite and inter-dendrite structures composed of face-centered cubic (FCC) phase, body-centered cubic (BCC) phase, and ordered BCC phase (B2). The corrosion resistance of the high entropy alloy in 0.5 mol/L H₂SO₄ solution was inferior to that of 316L stainless steel.