Pitting Corrosion Resistance and Electrochemical Properties of Equimolar CoCrFeMnNi and Non-Equimolar Alcocrfeni High-entropy Alloys

Abstract

Equimolar CoCrFeMnNi high entropy alloy (HEA) exhibits excellent mechanical properties, but the corrosion resistance is relatively poor because of high Mn content. Thus, this study focused on Al addition and non-equimolar AlCoCrFeNi HEAs were fabricated. To investigate the effect of alloy composition on corrosion resistance, non-equimolar HEAs, Al8Co19Cr23Fe32Ni18 and Al25Co14Cr10Fe19Ni32, were fabricated by arc-melting. Their pitting corrosion resistance was studied by polarization in 0.1 M NaCl. Moreover, Al-containing HEAs have great potential to develop high corrosion resistant alloys by anodizing. Thus, the properties and the pitting corrosion resistance of passive oxide film formed by polarization from -0.55 to 0.5 VSCE in H2SO4 were also investigated.On the basis of the XRD results and surface images, Al8Co19Cr23Fe32Ni18 alloy was single phase alloy. On the other hand, equimolar AlCoCrFeNi and Al25Co14Cr10Fe19Ni32 alloys have multi-phase structures of Al and Ni rich phase and Cr and Fe rich phase. The pitting potential of Al8Co19Cr23Fe32Ni18 alloy was higher than that of equimolar CoCrFeMnNi alloy. After H2SO4 treatment, both alloys have apparent increase in their pitting potential. In the case of multi-phase alloy, Al25Co14Cr10Fe19Ni32 alloy has a lower pitting potential than that of equimolar AlCoCrFeNi alloy. After H2SO4 treatment, the Al and Ni rich phase was dissolved, and a Cr rich oxide layer was formed. This was likely to contribute the improvement of pitting corrosion of both AlCoCrFeNi and Al25Co14Cr10Fe19Ni32 alloys.