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| ELECTROCHEMICAL CORROSION BEHAVIOR OF A NEW BIOMEDICAL Ti-24Nb-4Zr-8Sn ALLOY IN HANKS SOLUTION |
| BAI Yun1, 2), LI Shujun1), HAO Yulin1), YANG Rui1) |
1) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016
2) Chemistry Department, Anshan Normal University, Anshan 114005 |
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Cite this article:
BAI Yun LI Shujun HAO Yulin YANG Rui. ELECTROCHEMICAL CORROSION BEHAVIOR OF A NEW BIOMEDICAL Ti-24Nb-4Zr-8Sn ALLOY IN HANKS SOLUTION. Acta Metall Sin, 2012, 48(1): 76-84.
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Abstract 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.
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Received: 19 August 2011
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| Fund: Supported by National Basic Research Program of China (Nos.2012CB619103 and 2012CB933901), High Technology Research and Development Program of China (No.2011AA030106), National Natural Science Foundation of China (Nos.51071152 and 50901080) and Natural Science Foundation of Liaoning Province (No.20092075) |
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