Self-organized nanotubular layer on Ti–4Zr–22Nb–2Sn alloys formed in organic electrolytes

Self-organized nanotubular layers are electrochemically fabricated on Ti–4Zr–22Nb–2Sn alloys in water/glycerol (volume ratio 1:1) mixtures containing 0.3 M NH₄F. Highly ordered nanotubes with two distinct diameters of ∼203 ± 5 (large size) and 113 ± 5 nm (small size) were observed at the bottom of the layer, which may be ascribed to the different microstructure and composition in this alloy. On extended anodization, the small-size tubes gradually disappeared because of the increasing H⁺. After annealing for 1 h at 500 °C, the nanotube layer on the Ti–4Zr–22Nb–2Sn alloy was transformed from the amorphous phase to anatase. The nanotubes were connected to each other by spaced rings at the sidewalls, whereas the distance between neighboring rings increased with the amplitude of applied current density.