Electrochemical synthesis of porous Ti-Nb alloys for biomedical applications

Porous titanium-niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by electro-deoxidation of sintered oxide discs of mixed TiO2 and Nb2O5 powders in molten CaCl2 at 1173 K, and characterised by XRD, SEM, EDX and residual oxygen analysis. At the lower Nb content a dual-phase alpha/beta-alloy was formed consisting of hexagonal close-packed and body-centred cubic Ti-Nb, whereas at the higher Nb contents a single-phase beta-alloy was formed of body-centred cubic Ti-Nb. The corrosion behaviour of the alloys prepared was assessed in Hanks' simulated body fluid solution at 310 K over extended periods of time. Potentiodynamic polarisation studies confirmed that the alloys exhibited passivation behaviour, and impedance studies revealed that the passive films formed on the surface of the alloys comprised a bi-layered structure. XPS analysis further proved that this contained hydroxyapatite at the top and native metal oxide underneath. The mechanical properties of the alloys were evaluated, and the elastic moduli and the Vickers hardness were both found to be in the range of that of bone. Overall, Ti-35Nb is proposed to be the best-suited candidate of the materials studied in regard to biomedical applications.