Functionally graded HA–TiO2 nanostructured composite coating on Ti–6Al–4V substrate via electrophoretic deposition

• Fabrication of functionally graded HA–TiO2 coatings via EPD
• Lower porosities in microstructure by addition of TiO2 and using graded structure
• Highest bonding strength of 27.8 MPa for FG sample
• Higher total corrosion resistance of FG sample after in-vitro tests
• Accelerated apatite formation and higher wettability for FG sample

In the present study, electrophoretic deposition was carried out in the ethanol-based suspensions at the voltage of 20 V for 3 min to form functionally graded coatings of HA/TiO2 nanoparticles and HA–TiO2 nanocomposite coatings with 0, 10 and 20 wt.% of TiO2 on Ti–6Al–4V substrate. The gradual addition of HA suspension into the deposition cell containing TiO2 nanoparticles caused the functionally graded structure of HA–TiO2 coatings. The microstructure of coatings showed the lower porosities by the addition of TiO2 and using graded structure. The pull-off test results showed the highest bonding strength for the graded coating. The electrochemical impedance spectroscopic studies after in vitro tests, revealed that the total corrosion resistance of graded coating is higher than that of HA and HA–TiO2 samples. The accelerated apatite formation on functionally graded coating corresponding to inductively coupled plasma spectroscopy was attributed to the higher wettability of its surface.