Study On Shape Memory Effect And Mechanical Properties Of Ti-Ta Based Alloys For Biomedical Applications

Ni-Ti alloys are widely used as biomedical materials due to their special shape memory effect(SME) and superelasticity(SE).However,it is necessary to develop Ni-free Ti-based shape memory alloys for biomedical applications to avoid the potential Ni-hypersensitivity in Ni-Ti alloys.In this paper,studies were carried out concerning the microstructures,martensitic transformation,shape memory behaviors and mechanical properties of Ti-Ta alloys,as well as the effects of Si/Zr content on the microstructures and properties of Ti-55Ta-xSi/Zr(wt.%) alloys.The results are as follows:Ta content affects greatly the microstructures and SME of Ti-(40-65)Ta(wt.%) alloys.Ti-55Ta alloys exhibits mainlyα″and a littleβphase,it appears the best shape memory effect and the shape memory strain varys obviously with the condintion of heat treatment.The maximum shape memory strain of 3.32%was obtained in Ti-55Ta alloy quenched at 1273 K followed by aging at 723 K for 10 min.Addition of a little Si element hardly affects the structures of Ti-55Ta-(0-0.3)Si alloys.(Ti,Ta)₃Si precipitation were found to formed when the Si content over 0.2 wt.%.With the increase of Si,the tensile strength increases and elongation at fracture decreases,Young's modulus decreases firstly and then increases.Shape memory recovery ratio of Ti-55Ta-xSi alloy varys with Si content,increasing firstly and then decreasing.When the residual strain is 3.2%,the maximum shape recovery ratio of 77%was obtained in Ti-55Ta-0.1Si alloy,which is apparently improved as compared with that value of 52%in Ti-55Ta alloy.Microstructures of quenched Ti-55Ta-xZr alloys depend on Zr content,and their martensitic transformation temperatures decrease with Zr content.When Zr content is less than 3 wt.%,it exhibits predominantlyα″phase,and appears shape memory effect.Metastableβand a littleα″phase were present and a good superelasticity was found in Ti-55Ta-9Zr alloy.When the Zr content increased to 12 wt.%,singleβphase was present,and a linear elastic strain up to 1.6%was obtained in Ti-55Ta-12Zr alloy.With the increase of Zr content in Ti-55Ta-xZr alloys,the elongation decrease, the tensile stress increases,but it decreases abnormally to the lowest value of 551 MPa in Ti-55Ta-9Zr alloy.With the addition of Zr,Young's modulus of Ti-55Ta-xZr alloys decreases firstly and then increases.The lowest value is 28 GPa in Ti-55Ta-9Zr alloy.Aging at 723 K for 10 to 30 min can improve greatly the superelasticity and mechanical properties of Ti-55Ta-9Zr alloy.The aged Ti-55Ta-9Zr alloy appears the maximal superelasticity strain of 2.24%,its Young's modulus is less than 40 GPa, tensile strength reaches or over 1000 MPa,and the ratio of stress-to-modulus over 27. Compared with the traditional implant alloys and other new-developed high strength low modulus titanium alloys,the aged Ti-55Ta-9Zr alloy has a good combination of high strength and low modulus,as well as good superelasticity.All these results revealed that Ti-55Ta-9Zr is promising to be developed for biomedical applications.