The effect of Mn addition on corrosion behaviour of equiatomic CoCrFeNi high entropy alloys in NaCl solution

ABSTRACT

The corrosion behaviour of equiatomic CoCrFeNi and CoCrFeNiMn high entropy alloys manufactured by the vacuum arc melting were studied in 3.5 wt-% NaCl solution. And the reasons for the differences in corrosion resistance were investigated in terms of microstructure, electrochemical behaviour and oxide film. The results show that the two alloys exhibit different corrosion characteristics, with CoCrFeNi alloy displaying typical passivation characteristics and CoCrFeNiMn alloy exhibiting activation behaviour. The CoCrFeNi HEA with compact and protective passive film has lower corrosion current density, larger film resistance and polarisation resistance, meaning a lower corrosion rate and superior corrosion resistance compared with those of CoCrFeNiMn alloy. Moreover, CoCrFeNiMn alloy forms a discontinuous and loose corrosion product film with higher Mn content and lower contents of Cr, Fe and Co compared to the matrix, which decreases its protection performance. The addition of Mn changes the electrochemical behaviour, and higher Mn oxides/hydroxides within oxide film are unfavourable to forming a stable passive film.

GRAPHICAL ABSTRACT

KEYWORDS:

• HEA
• passive characterisation
• corrosion product film
• corrosion resistance

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Natural Science Foundation of Zhejiang Province, China [grant number LY18E010004]; Fundamental Research Funds of Zhejiang Sci-Tech University, China [grant number 22242293-Y]; National Natural Science Foundation of China [grant number 51871026].