Corrosion resistance improvement of Ti-6Al-4V alloy by anodization in the presence of inhibitor ions

Colorful thin oxide films were synthesized by galvanostatic anodization on Ti-6Al-4V alloy. Three different aqueous solutions containing corrosion inorganic inhibitors (Na₂MoO₄, NaH₂PO₄ and NH₄VO₃) were employed for the anodization treatment. The effect of inhibitor anions on the corrosion behavior of the alloy in Ringer solution was studied. Open circuit potential (OCP), Tafel polarization, linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to evaluate the corrosion performance of the treated electrodes. The incorporation of the inhibitor ions was detected by the release of Mo, V and P through ICP-AES technique. The formed oxides were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that compact, amorphous oxides without pores or cracks were obtained independently of the solution used. The sample anodized in Na₂MoO₄ solution registered the lowest corrosion current density (0.11 μA/cm²), and it was able to protect the alloy even after 168 h of immersion in Ringer solution. No cracks or corrosion products were detected. The XPS analysis reveals the incorporation of molybdenum to the oxide film in the form of Mo⁶⁺ and Mo⁴⁺.