In vitro bioactivity and corrosion resistance enhancement of Ti-6Al-4V by highly ordered TiO2 nanotube arrays

In the present study, the structural features, corrosion behavior, and in vitro bioactivity of TiO2 nanotubular arrays coated on Ti–6Al–4V (Ti64) alloy were investigated. For this reason, Ti64 plates were anodized in an ammonium fluoride electrolyte dissolved in a 90:10 ethylene glycol and water solvent mixture at room temperature under a constant potential of 60 V for 1 h. Subsequently, the anodized specimens were annealed in an argon gas furnace at 500 and 700 °C for 1.5 h with a heating and cooling rate of 5 °C min−1. From XRD analysis and Raman spectroscopy, a highly crystalline anatase phase with tetragonal symmetry was formed from the thermally induced crystallization at 500 °C. Besides, the Ti 2p3/2 and Ti 2p1/2 binding energies showed the presence of the Ti4+ oxidation state. According to the in vitro bioassay, the modified surface proved its outstanding capability in enhancing the bioactivity, where a thick layer of bone-like apatite was formed on the annealed TiO2 nanotube surface. In addition, the corrosion measurements indicated that the corrosion protection efficiency increased remarkably and reached 87% after annealing at 500 °C.