Effect of Al addition on the corrosion behavior of the VCoNi medium-entropy alloys

Abstract

The Al addition has presented promising application in tailoring the mechanical properties of VCoNi medium-entropy alloys. However, as far as its real application was concerned, the effect of Al addition on the corrosion behavior of VCoNi alloy should also be taken into account, which, however, has not been reported so far. In this paper, Al0.23VCoNi MEA was designed, and its corrosion behavior was investigated by electrochemical and immersion test in 1 M H2SO4 solution at room temperature. The results in the present work suggested that the Al addition worsens the corrosion resistance of VCoNi alloy. Detailed microstructural and Scanning Kelvin Probe Force Microscopy analysis displayed that the refined grains and Al-enriched BCC phase formed in the Al0.23VCoNi alloy, the high-density grain boundaries and the potential difference between the BCC phase and FCC phases accelerate the dissolution of Al0.23VCoNi alloy in the initial stage of corrosion. Moreover, X-ray photoelectron spectroscopy analysis indicated that the V-depleted and (Al3+, Ni2+)-enriched corroded specimen surface decreased the stability of the passive layer, and hence decreased its resistance to pitting corrosion. Therefore, the degradation of the corrosion resistance of VCoNi MEA after the addition of Al is due to the synergic effects of component segregation, increase in grain boundary and deterioration of the stability of the passive layer.