Self-organized nanotubular oxide layers on Ti-6A1-7Nb and Ti-6A1-4V formed by anodization in NH4F solutions

The present work reports the fabrication of self-organized porous oxide-nanotube layers on the biomedical titanium alloys Ti-6Al-7Nb and Ti-6Al-4V by a simple electrochemical treatment. These two-phase alloys were anodized in 1M (NH4)(2)SO4 electrolytes containing 0.5 wt % of NH4F. The results show, that under specific anodization conditions self-organized porous oxide structures can be grown on the alloy surface. SEM images revealed that the porous layers consist of arrays of single nanotubes with a diameter of 1.00 nm and a spacing of 150 nm. For the V-containing alloy enhanced etching of the P phase is observed, leading to selective dissolution and an inhomogeneous pore formation. For the Nb-containing alloy,an almost ideal coverage of both phases is obtained. According to XPS measurements the tubes are a mixed oxide with an almost stoichiometric oxide composition, and can be grown to thicknesses of several hundreds of nanometers. These findings represent a simple surface treatment for Ti alloys that has high potential for biomedical applications. (c) 2005 Wiley Periodicals, Inc.