Nanotubular oxide layers and hydroxyapatite coatings on ‘Ti–13Zr–13Nb’ alloy

The presented research was aimed to determine the mechanical properties of the nanotubular oxide layer covered with hydroxyapatite coating. The Ti–13Zr–13Nb alloy was oxidised in 1M phosphoric acid with an addition of 0·5% HF for HF solution at 20 V voltage. The electrochemically assisted deposition of hydroxyapatite was performed at cyclic polarisation in NH₄H₂PO₄ and CaCl₂ solution at 80°C. The mechanical properties were determined by nanoindentation, nanocreep and nanoscratch tests. The surface examinations were made with the light, scanning electron and atomic force microscopes. The measurements showed the significant difference between an oxide layer and nanotubular oxide coated with hydroxyapatite. The observed differences may be explained by an appearance of mechanically strong oxide layer, to which the ceramic hydroxyapatite layer is not tightly bound. The obtained results suggest that the nanotubular oxide layers should be covered with nanohydroxyapatite coatings, which would come inside the nanotubes resulting in better adhesion.