Corrosion dynamics of Ni2FeCrMo0.2 high-entropy alloy in haze constituents: Role of oxalic acid

Water-soluble inorganic salts in haze significantly accelerate metallic corrosion, posing serious threats to both environmental safety and industrial equipment. Conventional carbon steels, stainless steels, and many engineering alloys often exhibit limited durability in environments coupled with acid and salt. In this study, the corrosion behaviour of the Ni 2 FeCrMo 0.2 high-entropy alloy was systematically investigated in haze-simulating oxalate-containing solutions. A combination of electrochemical measurements, surface morphology observations, and corrosion product analyses was employed to elucidate the effects of oxalic acid concentration and temperature on the corrosion mechanism. The results revealed that Ni 2 FeCrMo 0.2 exhibits markedly superior corrosion resistance compared with 2205 duplex stainless steel. Specifically, increasing the oxalic acid concentration initially decreases the corrosion rate due to complexation-assisted passivation. However, higher concentrations destabilize Cr and Fe based oxides in the passive film, leading to accelerated corrosion. Elevated temperatures further exacerbate corrosion by enhancing ionic mobility and facilitating the penetration of aggressive species. These findings provide mechanistic insights into the passivation behaviour and service performance of multi-principal element alloys in haze-associated corrosive environments, highlighting the potential of high-entropy alloys for applications under complex atmospheric conditions.