Corrosion Resistance of Al 0.5 CoCrFeNiCu x Ag y ( x = 0.25, 0.5; y = 0, 0.1) High-Entropy Alloys in 0.5M H 2 SO 4 Solution.

The electrochemical behavior of the as-cast Al 0.5 CoCrFeNiCu x Ag y ( x = 0.25, 0.5; y = 0, 0.1) high-entropy alloys (HEAs) in a 0.5M H 2 SO 4 solution was studied. Polarization measurements were carried out in a standard three-electrode electrochemical cell at room temperature using a platinum counter electrode and a saturated silver chloride reference electrode. For Al 0.5 CoCrFeNiCu 0.5 and Al 0.5 CoCrFeNiCu 0.5 Ag 0.1 , copper segregation along the grain boundaries was observed, which highly dissolved in the sulfuric acid solution and resulted in low corrosion resistance of the samples. Introducing Ag into Al 0.5 CoCrFeNiCu 0.25 HEA led to the precipitation of a copper-silver eutectic structure, in which the copper regions were selectively dissolved in the sulfuric acid solution. Al 0.5 CoCrFeNiCu 0.25 exhibited the best corrosion resistance with the corrosion current density of I corr = 3.52 ± 0.02 μA/cm 2 , significantly superior to that of the Al 0.5 CoCrFeNi sample without copper and silver ( I corr = 6.05 ± 0.05 μA/cm 2 ). Finally, the results indicated that suppressing elemental segregation by annealing or tailoring chemical composition is essential to improve the corrosion resistance of Al 0.5 CoCrFeNiCu x Ag y HEAs.