Effect of alkali treatments on apatite formation of microarc-oxidized coating on titanium alloy surface

Alkali treatments with three concentrations were used to modify a microarc-oxidized (MAO) coating on titanium alloy surface in order to further improve its surface bioactivity. Morphology, chemical compositions and phase constitues, roughness, contact angle and apatite induction of the alkali-treated coatings were studied and compared. Scanning electron microscope (SEM) was applied to observe the morphologies, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to detect the phase constitutes and chemical compositions, a surface topography profilometer was used to analyze the surface roughness, and contact angle was measured by liquid drop method. Alkali treatements result in the formation of Na2Ti6O13 and Na2Ti3O7 phase on the MAO coating, which leads to the increase of surface roughness and the decrease of contact angle. Experimental results showed that the apatite induction of the alkali-treated coatings was dependent on the applied alkali concentrations during treatments, and Na+ concentration can promote the formation of apatite phase.