Corrosion behavior of β titanium alloys for biomedical applications

The corrosion behavior of biocompatible β titanium alloys Ti–13Mo–7Zr–3Fe (TMZF) and Ti–35Nb–7Zr–5Ta (TiOsteum) was investigated in 0.9% NaCl and 5 M HCl solutions. Extra-low-interstitial Ti–6Al–4V, which is also a candidate material for biomedical applications, was studied for comparison. The as-received TiOsteum and TMZF alloys exhibited single-phase β and α + β microstructures, respectively, so the latter was also investigated in the solutionized and quenched condition. In 0.9% NaCl solution, all three alloys exhibited spontaneous passivity and very low corrosion rates. Ti–6Al–4V and the as-received TMZF exhibited active-passive transitions in 5 M HCl whereas TiOsteum and TMZF in the metastable β condition showed spontaneous passivity. Potentiodynamic polarization tests, weight loss and immersion tests revealed that TiOsteum exhibited the best corrosion resistance in 5 M HCl. Analysis of surfaces of the corroded specimens indicated that the α/β phase boundaries were preferential sites for corrosion in Ti–6Al–4V while the β phase was preferentially attacked in the two-phase TMZF. The performance of the alloys in corrosive environment was discussed in terms of the volume fraction of the constituent phases and partitioning of alloying elements between these phases.