Effect of titanium dioxide intermediate layer on scratch and corrosion resistance of sol-gel-derived HA coating applied on Ti-6Al-4V substrate.

Modification of dental and orthopedic implants' surface by coating them with bioactive materials, such as hydroxyapatite (HA), diminishes the implants' fixation time. Appropriate adhesion to the substrate and stability in biological conditions are essential requirements for these coatings. In this study, sol-gel-derived HA coating was applied on the Ti-6Al-4 V substrate, which is a high-performance alloy for manufacturing bone implants. Also, titanium dioxide (TiO2) which was prepared by the sol-gel method was used as an intermediate layer between HA coating and the substrate. The nano-scratch and potentiodynamic polarization tests were employed to evaluate the effectiveness of TiO2 intermediate layer on improving the scratch resistance, as an indicator of coating adhesion strength, and the corrosion resistance of the coated samples. The quality of the coating bonded to the substrate was studied by cross-sectional SEM images. The XRD tests indicated that HA and TiO2 coatings were formed with predetermined phase compositions. The biocompatibility of sol-gel-derived HA coating was established by simulated body fluid (SBF) immersion tests. The SEM images, along with the results of electrochemical and nano-scratch tests, proved the significant effect of a TiO2 intermediate layer on improving the scratch resistance and stability of HA coating on titanium alloy substrate.