Effect of ammonium ion on the corrosion behavior of Ni2FeCrMo0.2 high-entropy alloy in simulated haze solution

Various constituents of PM 2.5 in haze can accelerate metal corrosion, but traditional carbon steel and stainless steel perform poorly in such complex corrosive environments, and thus developing new corrosion-resistant materials are of great importance for mitigating haze-induced corrosion. The corrosion behavior of Ni 2 FeCrMo 0.2 alloy in haze-simulating aqueous solutions containing various constituents of PM 2.5 in haze is investigated. By the coupling analysis of electrochemical experiments, corrosion morphology, and corrosion product film, the influence of NH+ 4 concentration on the corrosion mechanism related to multi-principal metal elements is revealed. The results show that the Ni 2 FeCrMo 0.2 alloy exhibits superior corrosion resistance compared with 2205 duplex stainless steel. As the NH+ 4 concentration increases, the corrosion rate increases initially but then decreases at higher NH+ 4 concentrations, and the corrosion morphology also confirms this changing trend. The corrosion prompt is primarily due to the lower solution pH caused by the hydrolysis reaction of NH+ 4. In contrast, the corrosion inhibition at higher NH+ 4concentration is attributed to the passive film on the alloy surface, which is composed of Cr, Fe, Mo, Ni, and their oxides, with the presence of Mo elements forming a unique structure that improved the density and stability of the film, thereby inhibiting the growth of corrosion pits. The changing trend of corrosion film resistance and corrosion product film thickness agrees well with this change in corrosion rate. This study provides an insightful understanding of the corrosion behavior of multi-principal alloy materials in haze environments, which is crucial for the corrosion protection design of metal equipment materials.