Design Of Ti-based Shape Memeory Alloys For Medical Application And Their Microstructure And Properties

Shape memory alloys (SMA) have a wide medical application due to their shape memory effect (SME) and their super elasticity (SE). Among many shape memory alloys, only Ti-Ni shape memory alloys have been widely applied for biomedical uses to date. However, it has been pointed out that pure Ni is a toxic element,and excessive nickel results in allergic, inflammation and even carcinogenicity. Therefore, developing new generation of Ti-based SMA with the combination of good biocompatibility and good SME is a hot research topic in the field of Ti alloys for the medical usage.Alloying elements Mo, Nb, Ta, Zr and Sn were proved excellent additives with superior biocompatibility. The alloys containing Ta, Mo, Nb, Zr and Sn can enhance strength and improve the plasticity and the hot working properties of alloys. What's more, the shape memory effect and superelastic behavior have been reported in Ti-Nb and Ti-Mo alloys by adjusting Mo and Nb content. In this thesis, using the d-electrons concept and the experimental results, two Ti-based alloys with the shape memory effect were developed by adding the biocompatible elements of Nb, Mo and Sn. The influence of the Mo content and the heat treatment on the microstructure and the shape memory behavior of the two alloys were discussed based on the experimental measurement results of X-ray diffraction (XRD), optical microstructures and tensile tests.The results indicated that the Mo concentration had a significant influence on the microstructure of Ti-7.5Nb-1Sn-xMo (at.%, x=1-6) alloys, and with the increase of the Mo concentration from 1 to 6 at.%, the microstructure of the alloys changed in the sequence ofα",α"+βandβ. Mo content has also a strong influence on the properties of the alloys. The 5at.% Mo alloy exhibited a low Yang's modulus, relatively high strength and good ductility. While 3at.% and 4at.% Mo alloys exhibited the shape memory effect, which was sensitive to the Mo content. 4at.% Mo alloy had better SME than that of 3at.% Mo alloy, but the later showed a good super elasticity. Annealing had a significant impact on the SME of 4at.% alloy. The alloy after annealing at 600℃showed an improved SME, while after annealing at 500℃, the SME of the alloy became worse.