Corrosion Behavior of Medium Entropy CoCrNi-alloy in NH4Cl Solutions
The corrosion behavior and mechanism of medium entropy equiatomic CoCrNi alloy(MEA)in various NH4Cl solutions(i.e.,with 1％,3％and 8％NH4Cl)were systematically studied by elec-trochemical test,statistical analysis,and immersion corrosion test.The results show that with the in-crease of NH4Cl concentration,the corrosion potential(Ecorr)of the MEA shifts negatively,the passive cur-rent density(/p)increases,and the corrosion rate rises,indicating that the corrosion resistance of the al-loy decreases.When the concentrations of NH4Cl solution are 3％and 8％,the anodic polarization curve displays a clear active-passive transition zone,which means that the passivity of the MEA is reduced.In addition,as NH4Cl concentration increases,the defect density within the passivation film on the MEA in-creases significantly,the thickness of the film decreases,and its stability declines,which weakens the protection ability of the film.The combined effect between NH4+and Cl-promotes the nucleation and de-velopment of metastable pitting corrosion,while in the high concentration of NH4Cl solution,the metasta-ble pits are difficult to be re-passivated,and easy to develop into steady pits.In general,the main corro-sion form of the MEA is pitting corrosion.
MEAcorrosion behaviormetastable pitting corrosionpassive film
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