Optimized fabrication and characterization of TiO2–Nb2O5–Al2O3 mixed oxide nanotube arrays on Ti–6Al–7Nb

Abstract

Highly oriented arrays of TiO₂–Nb₂O₅–Al₂O₃ mixed oxide nanotubes were fabricated via physical vapor deposition (PVD) to sputter a niobium film on Ti–6Al–7Nb (Ti67) and subsequent electrochemical anodization in ethylene glycol/ammonium fluoride/ionized water (5 wt%) electrolyte. Parametric optimization for higher adhesion strength and microhardness was conducted using Taguchi experimental design methodology. The highest adhesion strength and microhardness of the as-deposited Nb film was achieved at 350 W DC power, 20 sccm argon flow rate and a 90 V bias voltage. The microstructural features were found to depend on the anodization time and subsequent thermal treatment. The anodization of Nb/Ti67 for 4 h resulted in a homogeneous ordering of the mixed oxide nanotubes. Upon annealing at a low heating and cooling rate of 1 °C at 440 °C for 30 min in an atmospheric furnace, a highly ordered nanotube array contained a mixture of TiO₂, Al₂O₃ and Nb₂O₅ phases, wherein the composition of the oxide nanotubes was strongly influenced by the chemistry of the phases present in Ti67. The results of in vitro bioactivity indicated that the crystallized mixed oxide nanotubes could induce a quick apatite formation after immersion in simulated body fluid (SBF). The above findings may contribute to the development of novel nanostructured materials for metallic orthopedic implants.