Mechanical properties and microstructures of new Ti–Fe–Ta and Ti–Fe–Ta–Zr system alloys

β-type titanium alloys consisting of non-toxic elements, Ti–8Fe–8Ta, Ti–8Fe–8Ta–4Zr, and Ti–10Fe–10Ta–4Zr, were newly designed and developed for biomedical applications. Changes in the mechanical properties of the designed alloys with various heat treatments were discussed on the basis of the resultant microstructures. In addition, the corrosion resistance of the designed alloys was evaluated by polarization testing in Hank's solution. Conventional biomedical titanium (cp-Ti) and the titanium alloy Ti–6Al–4V ELI were also polarized for comparison. The structural phase of the designed alloys, after cold rolling and solution treatment, was only the β phase. Ultimate tensile strength and elongation to fracture of Ti–8Fe–8Ta, Ti–8Fe–8Ta–4Zr, and Ti–10Fe–10Ta–4Zr after solution treatment were 1066 MPa and 10%, 1051 MPa and 10%, and 1092 MPa and 6%, respectively. Ti–8Fe–8Ta and Ti–8Fe–8Ta–4Zr have higher strength than those of conventional biomedical titanium alloys such as Ti–6Al–4V ELI, Ti–6Al–7Nb, and Ti–13Nb–13Zr. In particular, the elongations at failure of Ti–8Fe–8Ta and Ti–8Fe–8Ta–4Zr were equal to those of Ti–6Al–4V ELI and Ti–6Al–7Nb. The designed alloys and conventional biomedical titanium alloys were spontaneously passivated in Hank's solution. The current density of cp-Ti and Ti–6Al–4V ELI was increased at a potential above 2.5 V. On the other hand, the current density of the designed alloys abruptly increased at a potential above 3.5 V. The designed alloys have the advantage over cp-Ti and Ti–6Al–4V ELI in their high resistance to pitting corrosion in biological environments. Therefore, new β-type titanium alloys designed in this study, Ti–8Fe–8Ta and Ti–8Fe–8Ta–4Zr, are expected to have good properties as biomaterials.