Nb-content-dependent passivation behavior of Ti–Nb alloys for biomedical applications

Ti–Nb alloys have the advantages of non-toxicity, low elastic modulus, high strength, and good biocompatibility. However, the effect of Nb content on its passivation behavior in Hank's solution still needs to be investigated. This work investigated the microstructure, hardness, and corrosion behavior of Ti-xNb (x = 5, 15, 25 wt%) alloys. The β phase gradually increases associated with the increasing Nb content in Ti–Nb alloys, resulting in the dispersion strengthening of alloys. Moreover, with the increased Nb content, the samples show higher open circuit potential, lower passivation current density, and higher charge transfer resistance in Hank's solution at 37 °C. When the passive films of Ti–Nb alloys are formed under the high potentials of 1 V and 2 V, the passive films gradually dissolve after the withdrawal of applied potential, representing the decrease in the total impedance of the passive film. The reason for this phenomenon is the addition of Nb substantially decreases the oxygen vacancies in the passive film formed on the samples. Therefore, the impedance of the passive film is increased.