Hydrothermal treatment of the silver-incorporated MAO coated Ti6Al7Nb alloy

Abstract

In this study, Ti6Al7Nb titanium alloy has been subjected to micro-arc oxidation (MAO) process and hydrothermal (HT) treatment sequentially. MAO process was conducted in calcium acetate hydrate (Ca(CH3COO)2.H2O) and disodium hydrogen phosphate anhydrous (Na2HPO4) containing reference electrolyte with and without the addition of silver acetate (AgC2H3O2) to provide antibacterial efficiency along with good bioactivity. Subsequently, HT treatment was employed to MAO’ed samples in an alkaline solution (pH = 11) at 230°C. HT treatment induced the covering of the titanium oxide (TiO2)-based MAO coatings with 1–2 µm thick exterior layer composed of nano-rods of titanium oxide and hexagonal columns of hydroxyapatite (HA). The presence of silver (Ag) in the MAO coating refined the structure of the HT treatment-induced exterior layer. As the primary indication of enhancement of the bioactivity, HT treatment accelerated apatite formation in the SBF solution irrespective of the silver presence, which delayed the apatite formation on the untreated MAO coatings. Moreover, HT treatment reduced the release of silver from the coatings into the SBF solution.