The influences of NO3- concentration and AC density on corrosion resistance of FeCoNi high entropy alloy in simulated saline-alkali soil solution were studied via a series of measurements. Related results imply that the anticorrosion property of the HEA is significantly improved with the increase in NO3- concentration, particularly at high concentration of 0.1 mol/L, and the passive film covering the HEA becomes dense, intact and uniform. NO3- as a protective barrier is absorbed on the film surface, significantly inhibiting the pitting corrosion of the HEA. As AC density rises, the HEA surface status evolves from passivation to activated state, presenting a serious overall corrosion feature. The AC application facilitates the damage of passivation film grown on the HEA, resulting in a rapid increase in the number of flaws, which remarkedly decreases its resistance capacity against corrosion. Furthermore, under the combined influence of the two factors, the adverse effect of AC interference is obviously larger than the positive impact of NO3- on the corrosion resistance of the HEA at i(AC) of 50 A/m(2), causing plentiful defects within the passive film and severe corrosion of FeCoNi HEA.

The relevance between microstructure and anti-corrosion performance of FeCoNi HEA prepared with different cooling methods was studied in simulated Golmud salinized soil solution. The results reveal that the corrosion rate reduces with increasing cooling rate, and the water-cooling HEA has the best anti-corrosion performance, followed by the air-cooling and furnace-cooled samples, which mainly depends on the grain size and the protectiveness of passivation film. An increase in grain size weakens the micro-galvanic corrosion effect between the grain boundary and the internal grain. Moreover, compact and uniform passive film markedly improves the anti-corrosion performance of water-cooled HEA. Combined with electrochemical tests, the water-cooling HEA exhibits the lowest sensitivity of metastable and stable pitting, as well as its surface passive film possesses excellent self-repairing ability. In addition, the HEA substrate occurs the preferential dissolution of Ni element.

The paper systematically studied the effect of AC density on corrosion resistance of FeCoNi HEA in simulated Golmud soil solution. The results imply that the applied iAC seriously decreases the anticorrosion property of the HEA. In particular, under high AC density, the active state is presented and the corrosion characteristic changes from slightly local pitting to uneven overall corrosion with massive large-sized corrosion pits. Moreover, after imposed AC of 100 A/m2, the honeycomb holes are produced within passive film, which suggests that AC severely damages the film integrity, and reduces the protection and stability of the film. This phenomenon is due to the reason that as iAC rises, more generated hydrogen ions/atoms and Cl- are absorbed on the defect regions of passive film, significantly promoting the film dissolution, and facilitating the pitting initiation and development.