Nano-mechanical Properties, Corrosion And Wear Behavior Of Two Biomedical Titanium Alloys

With medical equipments widely used in clinical medicine, it is faced the increasing demand for biomedical materials. Titanium alloys due to its low elastic modulus, high strength, non-toxic, good corrosion resistance and excellent biocompatibility, have become outstanding biomedical metallic materials. However, years of clinical experience have shown that the applications of titanium alloys still have many problems, such as its elastic modulus is much higher than the human bones which are easy to produce "stress shielding" effect, causing osteoporosis and loosening of the implant. In order to maintain the characteristics of titanium alloys and matching elastic modulus of the human skeleton, it is an effective way to add non-toxic elements Nb, Zr, Sn, etc. in preparation of β-type titanium alloy. In addition, medical titanium alloys due to poor wear resistance implants are vulnerable to be damaged in actual working conditions, finally, resulting in implant failure. It is required not only considering a single improvement, but to improve the overall performance of the titanium alloys. To solve the above problems, the present study used a non-consumable arc melting furnace to prepare Ti-33Nb-4Sn and Ti-31Nb-3Zr-4Sn these two new medical β type titanium alloys, and tested the nano-mechanical properties, corrosion resistance, friction and wear resistance of these two kinds of β-type titanium alloys. At the same time, considering the titanium alloy in aerospace applications, its high-temperature oxidation resistance had been also investigated. The results are as follows:1. The nano-mechanical properties of new medical Ti-33Nb-4Sn and Ti-31Nb-3Zr-4Sn alloys are studied by Nanoindentation techniques. Experimental results show that contact stiffness-displacement fitting curves of Ti-33Nb-4Sn alloy and Ti-31Nb-3Zr-4Sn alloy are linear relationship, and the slope of contact stiffness fitting curve for Ti-33Nb-4Sn alloy is greater than the slope of Ti-31Nb-3Zr-4Sn alloy; The ability for resisting the applied load of Ti-31Nb-3Zr-4Sn alloy is superior to the Ti-33Nb-4Sn alloy, and the plastic deformation of Ti-31Nb-3Zr-4Sn alloy after unloading is smaller than the Ti-33Nb-4Sn alloy; The elastic modulus of Ti-33Nb-4Sn and Ti-31Nb-3Zr-4Sn two alloys is significantly lower than the elastic modulus of the Ti-6Al-4V alloy, and Ti-31Nb-3Zr-4Sn alloy has the lowest elastic modulus which match the human skeleton’s well. Ti-31Nb-3Zr-4Sn alloy has relatively high hardness, excellent resistance to external load, small plastic deformation.2. The friction tester is used to do fry friction tests for the specimens. Experimental results show that, Ti-31Nb-3Zr-4Sn alloy exhibits relatively stable friction coefficient, and the friction coefficient of Ti-33Nb-4Sn alloys has increased slowly over time; The friction coefficient of Ti-6AL-4V alloy has obvious fluctuations over time, but in the end has hasten in stabilize. The average coefficient of friction for the three alloys decreasing in order: Ti-33Nb-4Sn > Ti-31Nb-3Zr-4Sn > Ti-6AL-4V alloy. Three alloys in friction process have formatted relatively clear furrows and generated a lot of debris, which exhibit in the form of abrasive wear, oxidation wear and adhesive wear. By comparing the coefficient of friction and wear scar morphology, it is showed that wear resistance of Ti-31Nb-3Zr-4Sn alloy is the best.3. Potentiodynamic polarization curves and impedance spectroscopy curves are adopted to do the electrochemical corrosion research of Ti-33Nb-4Sn, Ti-31Nb-3Zr-4Sn alloys in simulated human body fluids, with compared to Ti-6AL-4V alloy. Experimental results show that, compared to Ti-6Al-4V alloy, the corrosion resistance of Ti-33Nb-4Sn and Ti-31Nb-3Zr-4Sn two alloys are not significantly reduced in simulated body fluids, and Ti-33Nb-4Sn and Ti-31Nb-3Zr-4Sn alloys can keep stable passivation and have a wide range of passivation area.4. High temperature oxidation resistance of Ti-33Nb-4Sn and Ti-31Nb-3Zr-4Sn two alloys are compared and analyzed. The results show that, Ti-33Nb-4Sn, Ti-31Nb-3Zr-4Sn these two alloys respectively appear rutile Ti O2 structure in 700℃ and 650℃, and there is new TixNbyO phase appeared at about 700℃; As the temperature increases, increasing the degree of oxidation, the oxidation weight gain will increase, and it continues to have new substrate oxidized. With the temperature rising, the stress of substrate between the oxide layer exceeds the critical value, so that the surface cracks, ultimately leading to the oxide films peeling.