Polarisation studies of ZrVTiNbAl high entropy alloy in acidic, neutral and basic aqueous solution

The electrochemical behavior of a light weight refractory high entropy alloy (HEA) system (ZrVTiNbAl) was investigated by potentiodynamic polarization experiments and electrochemical impedance spectroscopy (EIS). Experiments were done in HNO₃ (1 M and 0.1 M), NaOH (1 M and 0.1 M) and neutral aqueous solution and the results were compared with that of SS304L in the same solution. Two compositions of ZrVTiNbAl were used in this investigation, one equiatomic (named C1) and the other non-equiatomic (35Nb25V25Ti10Al5Zr at%; named C2). Results indicated that the corrosion resistance of the equiatomic HEA (C1) having higher aluminum content (∼20 at% Al) was better than that of both C2 (∼10 at% Al) and SS304L in acidic as well as neutral solution. The higher corrosion resistance of C1 was demonstrated through the absence of trans-passive behavior, lowest passive current density and the lowest corrosion current. C2 showed very high corrosion current density and transpassive dissolution in 1 M and 0.1 M NaOH solution while SS304L showed transpassive dissolution in all the environments. Glow discharge optical emission spectroscopy and XPS analysis of the HEAs after potentiostatic polarization in 0.1 M HNO₃ at 0.5 V_(SCE) indicated the passive film formed on C1 to contain a mixture of oxides of all the alloying elements while C2 did not show the presence of Al₂O₃ in the passive film. The presence of Al₂O₃ in the passive film of C1 was identified as the key factor contributing to its superior corrosion resistance, as it promoted passivation behavior.