Deposition and characterization of bioactive ceramic hydroxyapatite coating on surface of Ti–15Zr–5Nb alloy

The new ternary Ti–15Zr–5Nb alloy is non-toxic and non-allergenic and possesses very good mechanical and anticorrosive properties. A ceramic hydroxyapatite (HA) coating was deposited on this new alloy surface by a chemical method. The formation of HA was proved by Raman micro-spectroscopy and X-ray photoelectron spectroscopy, which identified the main characteristic features for the crystalline HA. This ceramic coating has an optimal microstructure and morphology (from scanning electron microscopy). Also, a pronounced roughness was indicated by 2D and 3D atomic force microscopy images, showing a very proper surface for the adherence of the bone cells. The electrochemical behavior and corrosion resistance of this ceramic HA coating were studied in Ringer solutions. The main electrochemical parameters had more favorable values for the HA coated alloy due to the protective effect of the coating that thickened the native passive film on the alloy surface and together acted as a barrier against the ion diffusion. The HA coating increased the corrosion resistance of the substrate by its resistive properties to a large extent. Electrochemical impedance spectroscopy data were modeled by a two time constants electric equivalent circuit for the bare alloy and with a three time constant circuit for the HA coated alloy (formed from inner oxide layer, porous oxide layer and respectively outer HA porous layer). The HA coating thickened over time, improving its bioactivity and assuring long-term corrosion resistance. Therefore, the new Ti–15Zr–5Nb alloy coated with ceramic HA satisfies the most exigent requirements and signifies a progress in the domain of the orthopedic implant alloys.