Investigation on the mechanism and properties of HA/TiO₂ composite coatings with selecting Ca/P contents by plasma electrolytic oxidation

In the current study, a HA/TiO₂ composite coating is effectively fabricated on a Ti-13Nb-13Zr alloy using the plasma electrolytic oxidation (PEO) technique. Electrolytes with different Ca/P contents are selected to study the evolution of phase composition and microstructure of PEO coating. The relationship between Ca/P contents and the wear resistance and corrosion resistance of the coatings are evaluated. The Ca/P-30 g coating exhibits the best performance with Ca/P≈1.66. The average thickness and roughness of the coating manufactured by this system are about 159 µm and 1.591 µm. The HA/TiO₂ coatings akin to honeycomb have analogous pore size and uniform distribution, and the phase composition is mainly anatase. Compared with the substrate, the corrosion current density decreases by 19.65% and the corrosion potential increases by 0.805 V. The findings suggest that suitable Ca/P can promote the formation of HA, which is associated with the nucleation and growth rate of HA crystal. Furthermore, the formation mechanism of HA is simulated and the effect of Ca/P on the growth of HA is discussed. The process aims to reduce the allergic and toxic reactions caused by Ti-13Nb-13Zr implants, which is of great significance for increasing the service life of titanium alloy implants and reducing the implant failure.