Alloying and corrosion characteristics of FeNiMnCu-based high entropy alloys

FeNiMnCuX high entropy alloys (HEAs) (X: Co, Cr, Mo, Ti, W) were effectively synthesized in this study using mechanical alloying (MA) and spark plasma sintering (SPS), and their corrosion behavior was investigated in 1 M NaCl and 1 M H2SO4 solutions. Base (B) and Co-containing (BCo) alloys underwent SPS transformations into FCC structures; Cr-containing (BCr) alloy underwent a change into a mixture of FCC and BCC structures; and other alloys produced an intermetallic compound and a combination of FCC/BCC structure. Potentiodynamic polarization test results indicated conflicting effects of corrosion environment on corrosion behavior. In 1 M NaCl solution, Mo- (BMo) and W-containing (BW) alloys exhibited higher corrosion rates, but in 1 M H2SO4 they showed the lowest corrosion current densities. While BMo and BW alloys corroded faster in 1 M NaCl solution, they exhibited excellent resistance to pitting corrosion due to the larger passivation potential range. The electrochemical impedance spectroscopy of all alloys exposed to 1 M NaCl solution revealed two distinct time constants, which indicates a pseudo-passivation layer is formed. In agreement with the polarization test results, the alloys BMo and BW had the highest oxide film resistance, indicating their protective layers had fewer pores and flaws.