Corrosion behavior of anodic film formed in calcium hydroxide on Ti-6Al-4V alloy

Surface coloring by anodization of various biomedical implants material is used for clinical application. The resulting anodic oxide layer may affect the corrosion behavior, long-term degradation, and surface inertness of the material. This work investigated the effect of anodization on the corrosion behavior of Ti-6Al-4V alloy. Anodization was performed in KOH–Ca(OH)2 electrolyte for 20 s. The anodic film gave interference colors of yellow, dark blue, and light blue for anodization at 10, 20, and 30 V, respectively. The corrosion potentials measured by open circuit potential and potentiodynamic polarization modes became nobler with increasing formation voltage, indicating an enhancement in corrosion resistance. The bode phase of electrochemical impedance spectroscopy (EIS) spectra revealed that the film developed at 20 V was more compact than that formed at other voltages, which is in line with the observation by the optical microscope. Furthermore, the long-term immersion of 31 days in modified Ringer’s solution showed that the specimen anodized at 20 V remained intact while film detachment occurred in the other specimens. The anodized surface remained inert similar to the bare substrate after the immersion test, as indicated by no new phase formation detected in the XRD pattern of the specimens.