Generation of pits on CoCrFeMnNi high entropy alloy: an electrochemical impedance study of a single event

Abstract

In this study, a single pit was successfully generated on the surface of a CoCrFeMnNi alloy using a home-made device consisting of an electrochemical work station coupled with a microflow-cell. The three-dimensional morphology of the single pit was observed by optical microscopy, revealing that the pit radius increased with the polarization of the material, while at the same time the pit depth remained constant. Additionally, the various stages of pit evolution, including pit initiation, pit propagation, and pit repassivation were investigated as a function of the alloy polarization using electrochemical methods, in particular, electrochemical impedance spectroscopy (EIS). The incubation and initiation rates of a single pit increased with the anodic polarization of the electrode, which was attributed to an increase in the dissolution kinetics. The mechanism during the propagation phase was shown to be independent of the polarization potential. Interestingly, it was also shown that the repassivation step occurred in distinct stages, potentially due to a limited ion diffusion, which warrants further investigation.