Electrochemical characterization of oxidized nanostructured superelastic Ti-Nb-Zr alloy for medical implants

Metastable Ti-Nb-based shape memory and superelastic alloys are known to be strong candidates for bone implant applications. The issues of the materials' biochemical and biomechanical compatibility and its characterization are reviewed. Thermomechanical treatment is conventionally applied to these alloys in order to obtain supreme functional properties; the processing scheme comprises cold rolling and post-deformation air annealing. The structure and electrochemical characteristics of annealing-induced oxide films were studied by scanning electron microscopy, open circuit potential measurement and voltammetry. It is shown that the samples after the annealing treatment exhibit higher steady-state potential value and lower anodic dissolution current density in simulated biological solution, compared with the samples with mechanically removed oxide films. At the same time, the samples with thermal oxide films exhibited lower rate of passive layer recovery than those subjected to mechanical renewal of the oxidized surface. This fact underlies the recommendation to remove the annealing-induced oxide film from the implants operating under friction conditions.