Corrosion behavior of NbxCu0.3Cr2Fe2Ni3Mn2 high-entropy alloys in HNO3 solution

NbxCu0.3Cr2Fe2Ni3Mn2 (x = 0, 0.2, and 0.4; named Nb0, Nb0.2, and Nb0.4, respectively) high-entropy alloys (HEAs) were prepared using arc melting process. The effect of Nb content on the microstructure and corrosion behavior of HEAs in HNO3 solution was studied. Nb0 and Nb0.2 alloys are composed of a single FCC phase, whereas Nb0.4 alloy is composed of FCC + Laves phase. In 10% and 30% HNO3 solutions, the immersion corrosion rate and potentiodynamic polarization corrosion rate of the HEAs showed a trend of first increasing and then decreasing with the increase in Nb content. After 30 days of immersion corrosion, Nb0.4 alloy exhibited the lowest average corrosion rate in 10% and 30% HNO3 solutions, with values of 4.6 x 10-3 and 2.8 x 10-3 mm/yr, respectively. Potentiodynamic polarization corrosion showed that Nb0.4 alloy also had the lowest corrosion current density and average corrosion rate in 10% and 30% HNO3 solutions, with values of 1.74 x 10-5, 5.56 x 10-6 A/cm2 and 0.18, 0.06 mm/yr, respectively. In addition, The Rpo of Nb0.4 alloy are 91 times and 8737 times higher than those of Nb0 alloy, respectively, and has the largest relative thickness of the passivation film. Therefore, Nb0.4 alloy exhibited the best resistance to HNO3 corrosion, mainly because adding Nb reduced the segregation of Cu, thereby weakening the corrosion effect of the primary battery. Meanwhile, Nb could play a stabilizing role in the passivation film of the alloy. The formation of corrosion-resistant Laves phase also correspondingly improved the HNO3 corrosion resistance of the alloy.