Corrosion and Surface Film Characterization of TaNbHfZrTi High Entropy Alloy

TaNbHfZrTi high-entropy alloy (HEA) was prepared by arc melting alloying elements, and the formation of single phase bcc structure was confirmed. The developed HEA alloy exhibited low current density values during potentiodynamic polarization in 11.5 M HNO3 at room temperature. The corrosion rate was negligible (0.002 mm/y) in boiling 11.5 M HNO3 and the X-ray photoelectron spectroscopic (XPS) analyses confirmed that the passive film was predominantly composed of Ta2O5. In contrast, the air formed native film consisted of ZrO2 and HfO2. On the other hand, the potentiodynamic polarization studies indicated high corrosion current values for the HEA in 11.5 M HNO3 + 0.05 M NaF at ambient condition. In boiling fluorinated nitric acid, the corrosion rate is high about 2.2 mm/y, and a severely corroded morphology was obtained. XPS investigations confirmed the presence of ZrF4, ZrOF2, and HfF4 along with un-protective oxides of Ta, Nb, and Ti on the film.