Anodization growth of TiO₂ nanotubes on Ti–35Nb–7Zr–5Ta alloy: effects of anodization time, strain hardening, and crystallographic texture

Titanium and its alloys are the most suitable metallic materials available for the fabrication of medical implants. Their biocompatibility can be improved by the growth of TiO₂ nanotubes on their surface by a simple anodization process. This work involved an investigation into the anodization behavior of Ti–35Nb–7Zr–5Ta (TNZT) alloy, focusing on the effect of processing conditions (anodization time and type of electrolyte), previous strain hardening, and crystallographic texture of the substrate. Studies about the growth of TiO₂ nanotubes on β-type titanium alloys, as the TNZT alloy, are rare in the literature. The TNZT alloy proved to be an excellent substrate for the growth of TiO₂ nanotubes, resulting in threefold longer nanotubes than those obtained on a commercially pure (CP) Ti substrate. Moreover, TiO₂ nanowires grew after 6 h of anodization in an organic electrolyte, which could not be achieved using the CP-Ti substrate. Samples with different crystallographic textures displayed similar nanotube morphology and only slight differences in grain length, indicating that grain orientation played only a minor role in the growth kinetics. Lastly, the crystallization of nanotubes at 450 °C did not alter their morphology, but caused complete detachment of the TiO₂ nanotubes at 700 °C.