Anodic Oxidation and Corrosion Resistance of Ta-Containing High Entropy Alloys

Abstract

Stainless steels are corrosion resistant, but pitting corrosion sometimes occurs in chloride solutions. Anodic oxidation is one of the effective methods to increase the pitting corrosion resistance. However, unlike valve metals, stainless steels are difficult to improve pitting corrosion resistance by anodic oxidation. In this study, Fe-based alloys containing valve metals were fabricated to investigate anodic oxidation and corrosion resistance.Equimolar CrFeNbNiTa and (CrFeTa)30(NbNi)5 alloys were fabricated by arc melting, and pure metals of Cr, Fe, Nb, Ni, and Ta were used as raw materials. After casting, the ingots were heat-treated at 1200 ℃ for 2 h (furnace-cooling) and cut into 2 mm thick sheets. After that, the specimen surfaces were polished up to 1 μm with a diamond paste. The microstructures were observed using an optical microscope and a scanning electron microscope. The chemical compositions and elemental distributions of the specimens were analyzed by energy dispersive X-ray spectroscopy. Potentiodynamic polarization was performed in 1 M H2SO4. As a reference, Type 304 stainless steel was used.The equimolar CrFeNbNiTa alloy was composed of two phases. One was Cr- and Fe-rich and the other was Nb- and Ni-rich. The (CrFeTa)30(NbNi)5 alloy was a single phase. In the potentiodynamic polarization measurements, the current densities of oxygen evolution reaction of equimolar CrFeTaNbNi and (CrFeTa)30(NbNi)5 alloys were lower than that of Type 304 stainless steel. Moreover, the passive current densities of equimolar CrFeTaNbNi and (CrFeTa)30(NbNi)5 alloys were higher than that of Type 304 stainless steel.