Nanotube oxide coating on Ti-29Nb-13Ta-4.6Zr alloy prepared by self-organizing anodization

The present paper reports on the formation of self-organized nanotube oxide layers on β-type Ti-29Nb-13Ta-4.6Zr alloy in (NH₄)₂SO₄ containing a small amount of NH₄F. Highly ordered nanotube layers can be formed on the alloy under a wide range of applied potentials. Initiation and self-organization of pores is a potential and time dependent process. Layers removed from the electrolyte in an early growth state consist of two different morphologies-an outer nanoporous structure and an underneath ordered nanotube layer. For extended anodization, the outer nanoporous layer is completely dissolved. Within subsequent growth stages multi-scale ordering of the nanotube arrays with two discrete geometries can be observed. The different stages and morphologies depend significantly on the anodizing potentials. Clearly - compared with anodic tubes on pure Ti - a much broader range of nanotube geometries i.e. "structural flexibility" can be achieved with the Ti-29Nb-13Ta-4.6Zr alloy.