| The microsturcture, phase constitution, mechanical properties, corrosion resistance, and biocompatilbity of the three series of Ti-Nb, Ti-Nb-Zr, and Ti-Nb-Hf alloys are systematically investigated. The influence of the alloying elements and the heat treatment on these properties is revealed by optical microsope, XRD, TEM, tensile test, bending test, wear test, electrochemical measurments and biocompatibility evaluations.The results show that the addition of Nb, Zr, and Hf can stablize theβphase, suppress the precipitations ofα'' martentsit phase andωphase during quenching process, and retard theβdecompsotion during aging process. In addition, the Hf can provide a strongerβ-stablized effect compared with Zr.The results of TEM indicate that the morphology of martensite in solution-treated Ti-16Nb alloy is parallel lath shape, and variants of martentsite exhibit self-accommodation with sub-structure of martensite being (111) type I twin. Ti-25Nb alloy and Ti-26.5Nb alloy have a singleβphase microstructures at room temperature. The solution-treated Ti-22Nb-(2~6)Zr/Hf alloys are also only composed of singleβphase. However, the as-annealed Ti-22Nb-(2~6)Zr/Hf alloys are composed ofα'' phase andβphase. At the same time, the martensite lath with a sub-structure of twin are also found in Ti-22Nb-(2~6)Zr/Hf alloys during TEM observation.A better balance of strength and elongation of the titanium alloys can be obtained by the addtion of alloying elements and using suibtable heat treatment. The titanium alloys with a potential biomedical application are listed as such: Ti-25Nb (solution-treated), Ti-22Nb-2Zr and Ti-22Nb-4Zr (400 ?C/1 h), Ti-22Nb-2Hf (500 ?C/12 h), and Ti-22Nb-4Hf (400 ?C/1 h or 500 ?C/0.5 h). The shape memory effect of as-annealed Ti-22Nb, Ti-22Nb-(2~6)Zr/Hf alloys is tested by bending test. The recovery ratio decreases with increase in pre-strain and deformation temperures. The 2% completely recoverable strain is obtained for the as-annealed Ti-22Nb alloy. However, The 3% completely recoverable strain is obtained for the as-annealed Ti-22Nb-(2~6)Zr/Hf alloys. The wear results indicate that the wear resistance of solution-treated Ti-22Nb-2Zr/Hf has a larger improvement compared with Ti-22Nb alloy. In addition, aging process can further improve the wear resistance of the Ti-Nb based alloys.The results of electrochemcial experiments show that the corrosion resistance of Ti-Nb alloys decrease slightly with the increase in Nb content. In addition, the EIS results indicate that the film formed ont the surface of Ti-35Nb alloy is a double-layer structure, the porous outer layer of which is helpful for the osseointegration between implant and human bone. The films formed on the surfaces of the other Ti-Nb alloys are only a single-layer structure. The types of the simulated body fluids and the change in pH value have influence on the corrosion behaviour of Ti-Nb alloys. The corrosion resistance of the alloys decreases with decrease in pH value. The corrosion resistance of the alloys are reinforced because of polarization and the prolonged immersion time in fluids. All these observations suggest a nobler electrochemical behavior of the titanium alloys with the addition of Zr or Hf elements.The cytotoxicity of the Ti-Nb based alloys are evaluated using L929 cell derived from mice. The results of the evaluations by MTT method show that the Ti-Nb based alloys are highly biocompatible. Hf element is one of the non-toxicity elements that can be used as alloying element to stabilizeβphase. Hemolysis rate of the Ti-Nb base alloys is less than 5%, so it can not arise acute hemolysis. Compared with CP Ti, the platelet morphology and activation ratio on the surface of Ti-Nb based alloys is almost same, except for the Ti-22Nb-6Hf alloy, which shows a lower activation ratio of platelet. The rough surface can activate more platelet than the smooth surface.
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