The corrosion behavior of ultra-fine grained CoNiFeCrMn high-entropy alloys

The ultra-fine grained (UFG) CoCrFeMnNi alloy (Cantor alloy) exhibits high mechanical strength. As far as its real application is concerned, the corrosion behavior of the UFG Cantor alloy should also be taken into account, which, however, has not been reported so far. In this paper, the UFG Cantor alloy was prepared using Cryo-rolling followed by short time annealing, and its corrosion behavior was investigated by electrochemical test in 3.5 wt% NaCl aqueous solution at ambient temperature. Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) indicated that an unstable passive layer formed more easily on the surface of the UFG Cantor alloy and made it show an enhanced corrosion rate, as compared with coarse grained (CG) sample. Detailed microstructural characterization showed that after the mechanical processing, the Cr-enriched region (σ phase) formed in the UFG Cantor alloy, resulting in the galvanic corrosion between the σ phase and its nearby matrix phase. Moreover, Cr-depleted passive layer formed on the surface of corroded specimen decreased the stability of the passive layer, and hence decreased the resistance to pitting corrosion.