Microstructural development and corrosion behavior of self-organized TiO2 nanotubes coated on Ti–6Al–7Nb

In this study, the microstructural features and corrosion behavior of self-organized TiO2 nanotubular arrays on Ti–6Al–7Nb (Ti67) produced from different electrolytes, namely glycerol (G) and ethylene glycol (EG) were investigated. From the XRD data, the TiO2 characteristic peaks were absent after the anodization, but TiO2 crystallization occurred during annealing at 600 °C for 2 h, and consequently, led to the formation of highly crystalline TiO2 (anatase). The corrosion resistance of the anodized samples was higher than the substrate after 30 min of immersion in phosphate buffer saline (PBS) solution. In fact, the surface modification of Ti67 with a nanotubular TiO2 layer was effective in enhancing the passive layer resistance and reducing the corrosion current density (Icorr) compared to the substrate. Due to the decrease in Icorr, the corrosion rate decreased and reached a minimum of 6.38×10−2 mm y−1 for the nanotubes (anodized sample in G) annealed at 600 °C for 2 h. These results show that the corrosion behavior of the nanotubular structure was affected by the type of electrolyte and subsequent thermal treatment.