Nanotubular oxide layers formation on Ti-24Nb-4Zr-8Sn and Ti-13Zr-13Nb alloys in the ethylene glycol-based electrolyte: the role of alloying elements and phase composition

Abstract In this work, the self-organized mixed-oxide nanotubes (NTs) have been fabricated on a commercially pure α-phase titanium, single β-phase Ti-24Nb-4Zr-8Sn alloy and α+β-phase Ti-13Zr-13Nb alloy. Anodization process was performed in ethylene glycol-based electrolyte with fluoride ions at constant voltage of 20 V for 2 h. Morphology of obtained NTs was characterized by scanning and transmission electron microscopy and the chemical analysis was performed by Auger electron and X-ray photoelectron spectroscopy methods. Despite of applying the same process parameters in all cases, NTs obtained on three different substrates showed a different morphology: ribbed walls for titanium and smooth walls for Ti-24Nb-4Zr-8Sn and Ti-13Zr-13Nb alloys. The presence of alloying additives as well as phase composition of both Ti alloys strongly affected the uniformity and height of the obtained nanotubular layers. NTs layers formed on the surface of both Ti alloys were significantly higher but also more inhomogeneous in comparison to pure Ti. Moreover, NTs of different heights were observed on Ti-13Zr-13Nb, the higher growing on the β phase and lower on the α phase. Anodization of titanium alloys led to obtaining layers with mixture of stoichiometric oxides – TiO2, Nb2O5, ZrO2, SnO2.