Corrosion behavior of CrFeCoNi high-entropy alloys through cerium addition

The corrosion behavior of CrFeCoNi high-entropy alloys (HEAs) with varying cerium (Ce) additions was systematically investigated in a 0.9 wt% NaCl solution. The microstructure, composition, and surface chemistry of the alloys were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky tests were employed to evaluate the corrosion behavior. XRD analysis confirmed that the base alloy had a single face-centered cubic (FCC) phase, whereas adding 0.5 at% cerium resulted in the formation of the secondary CeNi₃ phase. Potentiodynamic testing revealed that the 0.02 at% Ce optimally enhances corrosion resistance, reducing the current density by 40 % and improving pitting resistance through a more stable passive film with fewer defects. Mott-Schottky analysis demonstrated that the passive film of this alloy exhibited n-p heterojunction behavior and the lowest donor density. The XPS analysis revealed that this enhancement was attributable to the formation of a stable passive film. These findings prove that a minor addition of Ce can modify the properties of passive films and enhance the corrosion resistance of CrFeCoNi HEAs.