A comparison study of passive characterization of CoCrNi medium-entropy alloy and CoCrFeNi high-entropy alloy in Na2CO3/NaHCO3 solution

Abstract

A comparison of passive characterization of CoCrNi medium-entropy alloy (MEA) and CoCrFeNi high-entropy alloy (HEA) was investigated by a series of corrosion tests in Na2CO3/NaHCO3 solution. Both the two alloys exhibit secondary passivation characteristics. The MEA shows a lower passive current density (ip) in the primary passive region and a higher ip in the secondary passive zone, compared to the HEA. Moreover, the anti-corrosion property of the two alloys at higher passive potential is weakened, as revealed by low film resistance and high carrier densities. The increase in potential is unfavourable for the formation of a stable and thick passive film, which reduces the protection of the film. Compared with the HEA, the protective performance of passive film grown on the MEA is superior in the primary passive region but inferior in the secondary passive region