Effect of coloring by anodizing on the corrosion behavior of Ti-6Al-4V alloy

Abstract

Coloring of an implant material is necessary to identify parts and type of the implant for clinical purposes. The coloring process involved anodizing, which might affect the corrosion resistance of the alloy. The effect of anodizing on the corrosion resistance of Ti-6Al-4V alloy was investigated by potentiodynamic polarization test in Ringer Lactate solution. The variation of color was obtained by varying the anodizing voltage 10, 20, and 30 V in 1 M KOH solution. The resulting color was gold, dark blue, and light blue for anodizing at 10, 20, and 30 V, respectively. Surface observation by optical microscope showed that the pore density of the anodic film increased with applied voltage. The cross-sectional FE-SEM images indicated that the film was thicker with increasing applied voltage. The film thickness was 198.6, 435.5, and 1199 nm for the film formed at 10, 20, and 30 V, respectively. The variation of interference color of the film was attributed to the alteration in pore density and film thickness. The presence of the anodic film enhanced the corrosion resistance of the alloy about an order of magnitude. The corrosion current density of the alloy decreased consecutively from 14.27 to 1.93, 0.73, and 0.43 µA/cm2 after anodized at 10, 20, 30 V, respectively. The film served as a barrier layer between the metal and the solution. Therefore, the corrosion resistance increased with film thickness. Anodizing of Ti-6Al-4V provides the dual benefit of surface coloring and corrosion protection.