Fabrication and characterization of microarc oxidation films on Ti-39Nb-6Zr alloy at different voltages in KOH electrolyte

Abstract

The TiO2/Nb2O5/ZrO2 ceramic films were successfully prepared on Ti-39Nb-6Zr alloy by microarc oxidation (MAO) at different voltages in KOH electrolyte. Their morphology, phase structure and composition were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Their conducting properties were analyzed by impedance spectroscopy and Mott–Schottky test. Meanwhile, their corrosion behaviors were evaluated by electrochemical impedance spectroscopy (EIS). The MAO films as n-type materials were 8 μm–15.8 μm thick with fine micropores on the surface. These films consisted of anatase TiO2, rutile TiO2, Nb2O5, monoclinic ZrO2 (m-ZrO2) and ZrTiO4 phases. Their conductivity gradually increased with the frequency from 4.07 × 10−15 S cm−1 at 0.01 Hz to 1.61 × 10−6 S cm−1 at 107 Hz. Their flat band potential was in the range of 0.34 V–0.77 V, and doping density varied between 3.50 × 1017 cm−3 and 5.25 × 1018 cm−3 which decreased with increasing positive voltage of MAO process. The Ti-39Nb-6Zr alloy coated at +400 V/−60 V had good corrosion resistance with lower corrosion current density and higher impedance.