Microstructure, Mechanical Properties, and Electrochemical Behavior of Ti-Nb-Fe Alloys Applied as Biomaterials

New β metastable Ti alloys based on Ti-30Nb alloy with the addition of 1, 3, or 5 wt pct Fe have been developed using the bond order and the metal d-orbital energy level (\( \overline{\text{Bo}} {-} \overline{\text{Md}} \)) design theory. The samples were prepared by arc melting, hot working, and solution heat treatment above the β transus followed by water quenching (WQ) or furnace cooling (FC). The effect of the cooling rate on the microstructure of Ti-30Nb-3Fe wt pct was investigated in detail using a modified Jominy end quench test. The results show that Fe acts as a strong β-stabilizing alloying element. The addition of Fe also leads to a reduction in the ω and α phases volumetric fractions, although the ω phase was still detected in the WQ Ti-30Nb-5Fe samples, as shown by TEM, and α phase clusters were detected by SEM in the FC Ti-30Nb-3Fe samples. Among the WQ samples, the addition of 5 wt pct Fe improves the ultimate tensile strength (from 601 to 689 MPa), reduces the final elongation (from 28 to 16 pct), and impairs the electrochemical corrosion resistance, as evaluated by potentiodynamic polarization tests in Ringer’s solution. The microstructural variation arising from the addition of Fe did not change the elastic modulus (approximately 80 GPa for all experimental WQ samples). This study shows that small Fe additions can tailor the microstructure of Ti-Nb alloys, modifying α and ω phase precipitation and improving mechanical strength.