Bottom-up characterization of electrochemical passivity from simple binary alloys to high entropy alloys

Abstract

Multi-principal element alloys (MPEAs) are an emerging class of metallic alloys with the capability of customized unique material properties. A high corrosion resistance is an intended characteristic for structural alloys, which usually is achieved by the addition of e.g. Cr. For MPEAs the interplay of alloying elements on the corrosion resistance of the resulting material is less clear. Here we demonstrate a bottom-up systematic approach to study the electrochemical activity of a library of alloys spanning from equimolar binary alloys up to the High Entropy Alloy (HEA) NiCoCrFeMn. Using this approach we can show that chromium oxide does not form an effective passive film at potentials over +0.75 V, where Fe replaces Cr as passivation element. Further, Cr does not generally result in a stable passive film, addition of Mn can significantly weaken the passivity. This and our approach provides useful insight for developing new MPEAs with simultaneously tailored corrosion resistance and mechanical properties.