The effect of chromium content on the corrosion behavior of ultrafine-grained CrxMnFeCoNi high-entropy alloys in sulfuric acid solution

Chromium (Cr) plays a critical role in the corrosion resistance of conventional alloys via the formation of a dense Cr oxide-based passive film. However, the exact role of Cr in the corrosion of high-entropy alloys (HEAs) remains unclear. The effect of Cr content on the corrosion behavior of the ultrafine-grained CrxMnFeCoNi (x = 0, 0.6, 1, and 1.5) HEAs in the sulfuric acid solution (0.5 M H2SO4) was investigated. These HEAs were fabricated using a combination of mechanical alloying and spark plasma sintering. The electrochemical tests show that the passive film was more compact and thicker at higher Cr concentration, but the corrosion rate first increased and then decreased, due to the presence of the nanocrystalline-amorphous phase boundaries in the passive film. Long-time immersion tests show that the corrosion rate increased exponentially with the Cr content, due to the gradual accumulation of the galvanic corrosion.