Influence of Electrolyte Ca/P Ratio on Microstructure and Properties of Micro-arc Oxidation Titanium Alloy Coatings

HA/TiO2 composite coatings were prepared on Ti-13Nb- 13Zr alloy by micro-arc oxidation. By changing the ratio of Ca/P in the electrolyte, the phase composition and microstructure changes, as well as the effects of different Ca/P ratios on the wear resistance, corrosion resistance and in vitro biological activity of micro-arc oxidation coating were studied. The results show that the coating roughness and porosity increase with the increase of electrolyte Ca/P ratio. The coating phase is mainly composed of anatase and rutile, and the rutile phase content increases with the increase of Ca/P ratio of electrolyte. The coating thickness of CA35 prepared with 35 g/L calcium acetate electrolyte is 80.59 mu m and the surface Ca/ P ratio is 1.98, showing the best wear and corrosion resistance. Compared with the substrate, the average friction coefficient of CA35 coating is about 0.19, which decreases by 43%. The corrosion resistance of the coating was tested by Pt reference electrode and 0.9wt% NaCl test solution. The corrosion current density of CA35 coating is 4.94 mu A/cm2, and the corrosion potential is - 221.73 mV. The CA35 coating produces the fastest mineralized products in Kokubo solution. It is proved that increasing the Ca/P ratio of electrolyte can effectively promote the formation of HA and improve the wear resistance. In addition, the influence mechanism of Ca/P ratio on coating properties was discussed.