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

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Abstract
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)2SO4 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 100 nm and a spacing of 150 nm. For the V‐containing alloy enhanced etching of the β 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. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005