采用极化曲线分析、电化学阻抗谱(EIS)测试和浸泡实验的方法, 并结合XPS, XRD和SEM等分析手段对新型医用Ti-24Nb-4Zr-8Sn合金在37 ℃的Hanks人工模拟体液中的电化学腐蚀行为进行了研究, 并与纯Ti和Ti-6Al-4V合金进行了比较. 结果表明: 在37 ℃的Hanks溶液中, Ti-24Nb-4Zr-8Sn合金的腐蚀电流密度与纯Ti相等, 并且钝化性能优于纯Ti和Ti-6Al-4V, 这与其钝化膜中存在大量的 Nb₂O₅密切相关; EIS结果显示, Ti-24Nb-4Zr-8Sn合金表面形成内层致密而外层疏松的双层钝化膜结构, 致密层特性对材料的耐蚀性能起到决定性作用; 随着浸泡时间的延长, 致密内层的电阻大幅度提高, Ti-24Nb-4Zr-8Sn合金的耐蚀性能增强, 同时疏松外层中的微缺陷发展成为宏观裂纹, 造成疏松外层整体脱落.

Titanium and its alloy have been widely used in medical applications owing to their light weight, low elastic modulus, good corrosion resistance and biocompatibility. A new multifunctional β-type titanium alloy Ti-24Nb-4Zr-8Sn has been developed recently for intention of biomedical applications. In comparison with the previously reported alloys, it possesses better biomechanical properties of high strength and low elastic modulus. Since corrosion resistance of biomaterials in human body environment plays important role on bio-safety, it is crucial to evaluate their corrosion behavior in simulated body fluid (SBF). In this paper, the electrochemical corrosion behavior of Ti-24Nb-4Zr-8Sn alloy was investigated in Hanks solution at 37 ℃ by utilizing potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques while XPS, XRD and SEM were employed to analyze the surface morphology, composition and phase constituent. Both commercially  pure titanium (CP-Ti) and Ti-6Al-4V alloy were also investigated to make a comparison. Ti-24Nb-4Zr-8Sn alloy has equiaxed microstructure with the averaged grain size about 200 $\mu$m. In Hanks solution, it exhibits a typical active-passive characterization by the formation of a protective passive film. XPS analyses revealed the passive film mainly consisting of TiO₂, Nb₂O₅ and a little quantity of ZrO₂ and SnO₂. Since the formation of Nb⁵⁺ cations that locate in the crystal lattice of titanium oxide, can cause a decrease in the concentration of defects in the passive film and makes it more stoichiometric and stable, Ti-24Nb-4Zr-8Sn alloy presents much wider passivation region than CP-Ti and Ti-6Al-4V alloy, and its corrosion current density is only 0.049 µA/cm² which is equal to that of CP-Ti. The EIS results indicated the presence of a double layer passive film with a porous outer layer and a dense inner one on the surface of Ti-24Nb-4Zr-8Sn alloy. The resistance of the dense inner layer can reach to the order of 10⁶ Ω·cm², which is much higher than that of the porous outer layer. This indicates that the corrosion resistance of Ti-24Nb-4Zr-8Sn alloy is determined mainly by the dense inner layer. With the immersion time increasing, the inner barrier layer became thicker and its resistance increased, resulting in the improvement of corrosion resistance. The study also found that some of the micro-defects formed in the outer porous layer changed to macro cracks and caused a rapid breakaway of the porous layer due to the binding force between two layers decreasing.