Preparation Of HA Containing Coatings On Titanium By Microarc Oxidation Technique

The biological properties of titanium implant depend on its surface oxide film. But the natural oxide film is bioinert. In order to enhance the bioactivity of titanium, the bioactivity coating with hydroxylapatite is planed to form on the surface of titanium substrate in this paper.Micro-arc oxidation (MAO) was performed in many electrolyte systems by using the pulse power. The electrolyte containing CA and NaH2PO4·2H2O was mainly used in the experiment to fabricate oxide coatings. The surface morphology, the phase composition and the distribution of elements were explored by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrum (EDS). The evaluation of the bonding strength and the corrosion resistance of coatings were studied by the shear test method and electrochemical method.The MAO film contained hydroxylapatite (HA) was able to fabricate by controlling the experiment parameter. The crystal phases of the MAO film were rutile TiO2, anatase TiO2 and hydroxylapatite. The hydroxylapatite phase increased not only with the increase of electrolyte concentration, MAO time and anodic current density but also with the decrease of frequency and cathodic current density. Hydroxylapatite phase was found when the electrolyte concentration was above 0.4mol/L CA and 0.2mol/L NaH2PO4·2H2O, oxidation time was more than 20min, anodic current density was above 15A/dm2, the pulse frequency was below 100 Hz and the ja/jc was below 1/0.5. But such increase was limited. With the increase of those parameters which mentioned above, the number of micro-pore on the surface of MAO coatings decreased, but pore size and the roughness of surface increased and the coatings would be ablated if the increasing was over limited. And with the increasing of pulse frequency and the cathodic current density, the number of micro-pore on the surface of coatings increased, the pore size decreased and the coating was smoother. The chemical composition of the MAO films was Ti, O, Ca and P, which came from substrate and electrolyte. In direction of substrate to coating surface, the content of O was stable, Ca, P were increasing and Ti was decreasing. Those elements distribution depended on the involving mechanism of the elements into the coatings in MAO process. The results showed that the shearing strength of the coatings with HA phase and TiO2 phase was above 25MPa. The results of SEM showed that HA particles filled in the micropore. There was no obvious interface between HA layer and TiO2 layer, so the coatings were quite compact. And the corrosive resistance performance of the MAO coatings was better than that of the substrate material.The oxide coating with HA phase which had good adhesion to the sunstrate and corrosion resistance can be formed by Micro-arc oxidation.