Study on the Corrosion Behavior and Mechanism of CoCrNi Medium-Entropy Alloy in NaCl Solution with Various NaHSO3 Concentrations

The corrosion resistance and passivation property of CoCrNi MEA in NaCl solution containing various concentrations of NaHSO3 were systematically investigated. The results reveal that the presence of HSO3- increases defects within the passive film, thins its thickness and disrupts the stability and integrity of the film. Increasing HSO3- concentration reduces the passivity of the MEA, facilitates the nucleation of metastable pitting and increases the tendency of metastable pitting to evolve into stable pitting, as well the corrosion rate increases significantly. Moreover, the corrosion of the MEA is aggravated by the micro-galvanic corrosion cells constituted between the substrate and the oxide inclusion. In addition, the MEA suffers a significant selective dissolution.