Effect of Cr content on the structure and corrosion properties of (FeCoNi)0.75Cu0.25-xCrx high entropy alloys in 1 M H2SO4

The present paper studies the influence of Cr addition on the structure, microstructure, and corrosion properties of (FeCoNi) 0.75 Cu 0.25-x Cr x (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) high entropy alloys fabricated by vacuum arc melting. The structure and microstructure have been evaluated utilizing X-ray diffraction and field emission scanning electron microscopy coupled with energy dispersive spectroscopy. The corrosion behavior has been analyzed by potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott–Schottky analysis. The data reveal that Cr considerably enhances both uniform and pitting corrosion resistance. The passivation current density and passivation potential range significantly increased with the incorporation of Cr, reaching 0.7 μA/cm 2 and 1156 mV, respectively, at a Cr concentration of 25 at% in 1 M H 2 SO 4 . This improvement is attributed to the development of a uniform microstructure and the elimination of microsegregation in the FCC matrix, which facilitates the formation of a protective chromium oxide/hydroxide layer. The thickness and donor density of the passive film in the alloy containing 25 at% Cr are calculated to be 0.41 nm and 5.7 × 10 21 cm −3 , respectively, which are comparable to the values reported for the passive film in high entropy alloys.