Corrosion resistance and passive film characteristics of Sc-added Al_1.2CoCrFeNi high-entropy alloys in sulfuric acid solution

Abstract

This study investigates the effects of varying Sc content on phase composition, corrosion resistance and passive film characteristic of Al_1.2CoCrFeNiSc_x (x=0, 0.1, 0.2, 0.3) high-entropy alloys in 0.5 mol/L H₂SO₄ solution. The addition of Sc causes the alloys to form a Laves phase which is a (Ni, Co)₂Sc intermetallic compound with face centred cubic (FCC) structure and lattice parameter of 0.695 nm. During the potentiodynamic polarization process, Laves phase is severely corroded due to its large grain orientation spread value and high electrochemical activity. Sc deteriorates the corrosion resistance of the alloy primarily by significantly accelerating the corrosion rate rather than altering the corrosion tendency. Al_1.2CoCrFeNiSc_x alloys exhibit poorer corrosion resistance in 0.5 mol/L H₂SO₄ than in 3.5 wt.% NaCl solution, with severe intergranular corrosion observed on the alloy surface. The passive films on Sc-free alloys primarily composed of Al₂O₃ and Cr₂O₃, while for Sc-containing alloys, the film mainly contains Al₂O₃, Cr₂O₃ and Sc₂O₃. In addition, the passive films on Sc-free alloys behave as an n-type semiconductor, while the passive films on Sc-containing alloys surface exhibit the electronic characteristics of p-n junctions. As the Sc content rises, the defect density in passive film increases from 10²¹ cm⁻³ to 10²³ cm⁻³, which leads to a less compact and less protective passive film, ultimately decreasing the alloy’s corrosion resistance. This work holds significant guiding significance for the engineering application of high-entropy alloys in acidic environments and is conducive to the development of highperformance corrosion-resistant alloys.

Keywords

AlCoCrFeNi-based high-entropy alloy / corrosion resistance / passive film / sulfuric acid solution

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