Investigation of functionally graded HA-TiO2 coating on Ti–6Al–4V substrate fabricated by sol-gel method

In this study, functionally graded hydroxyapatite-titanium dioxide coating (FGC HA-TiO2), with bottom-up composition: 100% TiO2, 50% TiO2 -50% HA, 100% HA, was produced by sol-gel method on the Ti–6Al–4V alloy substrate. The XRD, FTIR and XRF results signified heat treatment of each coating's layer at 450 °C leads to desired phase achievement. The coherence, strength and scratch resistance of FGC HA-TiO2 in comparison with control samples namely; single-layer HA and double-layer HA-TiO2 coatings, were assessed by cross-sectional SEM images and nano-scratch test. According to the results, the insertion of the TiO2 layer improves the bonding strength of the coating to the substrate and grading the coating composition plays an essential role in upgrading the integrity and coherency of the coating. The contribution of the TiO2 intermediate layer and composition gradient on developing coating strength was 22% and 36%, respectively. The immersion test in the simulated body fluid (SBF) suggested bioactivity of the Ti–6Al–4V substrate enhances by coating.