Enhanced corrosion resistance of gradient structured CoCrFeMnNi high entropy alloy by laser surface heat-treatment process

Abstract

The corrosion behavior of the gradient structured CoCrFeMnNi high entropy alloys (HEAs) which has excellent strength-ductility synergy is investigated in this study. Compared to the conventional fine-grained and coarse-grained structures, the gradient structured CoCrFeMnNi HEAs exhibits better corrosion resistance, which can be demonstrated by the highest corrosion potential of ∼−0.34 V, lowest corrosion current density of ∼1.07×10⁻⁷ A/cm², maximal impedance modulus of ∼4.72×10⁴ Ω·cm², maximum charge transfer resistance of ∼3.41×10⁵ Ω·cm², least serious corrosion pits, and smallest corrosion rate of ∼7.384 g·m⁻²·h⁻¹. The passive film generated on the gradient structured sample which is characterized by low density of charge carrier has relatively high content of Cr/Fe oxides and bound water, along with the low content of Mn oxide. The enhanced corrosion resistance in the gradient structured CoCrFeMnNi HEAs is mainly attributed to the interaction between soft surface severed as cathode and anode zone characterized by relatively high microhardness in middle region. That is, the cathodic soft region combined with the high-density grain boundary of central region accelerates the formation of passive film with higher Cr content on the hard center layer, while the anodic hard zone improves the anti-corrosion of soft layer due to the cathodic protection and transferred electrons. Therefore, gradient structure is a great method to simultaneously increase the strength-ductility synergy and corrosion resistance, suggesting a promising prospect for industrial applications.