Tuning the electrochemical properties of [FeNi]69Cr15Mn10Nb6 high-entropy alloy by severe cold rolling process with dual-phase ultrafine-grained architecture

The purpose of this research is to investigate the effect of grain size and ultrafine lamellar microstructures on the electrochemical behavior of [FeNi]69Cr15Mn10Nb6 high-entropy alloys (HEAs) in a 0.5 M H2SO4 solution. The as-homogenized specimen exhibits a two-phase microstructure with [FeNiNb]-rich dendrites distributed in a nearly homogenous face-centered cubic (FCC) matrix of HEAs. The [FeNiNb]-rich dendrites were elongated, broken down, and stretched along the rolling direction during the severe cold rolling (SCR) process with a 50 % and 90 % thickness reduction. After 90 % cold rolling, the grain size entered the nanostructured range, with sizes smaller than 220 nm. The microhardness tests showed that by implementing the SCR, the values of microhardness improved with increasing rolling deformation (reduction in thickness). At a thickness reduction of 90 %, the microhardness was measured at 420 HV, which is 1.53 times greater than that in the as-homogenized state (275 HV). Additionally, the potentiodynamic polarization (PDP) plots and electrochemical impedance spectroscopy (EIS) measurements confirmed that the electrochemical behavior of the HEAs was improved by increasing strain via thickness reduction, due to the improved surface conditions promoting the formation of oxide films through higher homogeneity.