Corrosion Properties of Ti-Nb-Sn Alloys Prepared by Mechanical Alloying

Recent efforts to develop materials for biomedical applications, such as rigid implants, have focused on improving biocompatibility, and obtaining equivalent microstructure and mechanical properties. However, due to the complex biological environment of the human body, materials often fail in one or more of their required properties. In this study, we examined the mechanical and electrochemical behavior of Ti base alloys combined with Nb and Sn. Titanium-niobium-tin alloys of composition Ti<bold>-</bold>30Nb, Ti<bold>-</bold>30Nb<bold>-</bold>6Sn, Ti<bold>-</bold>30Nb<bold>-</bold>9Sn and Ti<bold>-</bold>30Nb<bold>-</bold>12Sn were synthesized by mechanical alloy of powders and thermally sintered. The alloys were characterized microstructurally and mechanically. Subsequently, the corrosion of alloys in Hank's solution by electrochemical techniques was assessed. The characterization results showed that the alloy microstructure is composed by a major beta<bold>-</bold>Ti phase rich in Nb and Sn, and minor alpha<bold>-</bold>Ti phase containing less Nb and Sn. The microstructural porosity observed was similar between the alloys, except for the Ti<bold>-</bold>30Nb<bold>-</bold>6Sn alloy, which presented less porosity. Electrochemical results showed polarization associated with the microstructural characteristics of alloys, particularly their porosity and density. Consequently, the Ti<bold>-</bold>30Nb<bold>-</bold>6Sn alloy presented the lowest corrosion current density (i(corr)) due to having the lowest exposed surface area. However, the higher porosity present in the other alloys promoted of increase in their i(corr) values. Ti<bold>-</bold>Nb based alloys showed either passive or limited current density behaviour, due to the formation of TiO2, Nb2O5 and SnO2. According to the EIS results, the corrosion mechanisms in Hank<acute accent>s solution, were controlled by resistive-capacitive impedance and by diffusion through the oxide layer. Optical microscopy, scanning electron microscopy and x-ray diffraction characterizations, were used to complement the results.