Creation of super elastic and plastic-functional titanium materials with low elastic modulus for biomedical applications by controlling nanostructure

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Titanium alloys have been getting an attention as high biocompatible material with a modulus similar to that of bone. Thus, a number of titanium alloys. have been currently developed for biomedical applications. Especially, the beta-type Ti-29Nb-13Ta-4.6Zr alloy, which has been designed by DV-Xα cluster method targeting a low Young's modulus and high workability, is a titanium alloy composed of non-toxic and allergy-free elements for biomedical applications. It has been reported that this alloy possesses excellent properties that are required for biomaterials. Recently, it has been reported that there is a high possibility for Ti-Nb-Ta-Zr system alloy to exhibit super elasticity because the behavior of stress-strain curve at tensile loading is nearly equal to that of super elastic alloys such as TiNi alloy, which has been already put into practical applications. However, the numbers of the reports on the effects of alloying elements on the various properties of the Ti-Nb-Ta-Zr system a … More lloys including the Ti-29Nb-13Ta-4.6Zr alloy are few. Therefore, the effects of conditions of fabrication and thermo-mechanical treatments, and alloying elements on the mechanical properties and tensile deformation behaviors of the Ti-Nb-Ta-Zr system alloys are investigated with relating to nano/micro-structures in this study.Young's moduli of the Ti-XNb-10Ta-5Zr alloys subjected to swaging after fabrication using power metallurgy method decrease with an increase in the Nb content. However, the Young's moduli of the Ti-XNb-10Ta-5Zr alloys with 15 mass%, 20 mass%, and 25 mass% Nb, which have co phase, exhibit a reverse trend. The Ti-25Nb-10Ta-5Zr alloy exhibits the greatest elongation among the other Ti-XNb-10Ta-5Zr alloys because multi deformation mechanisms act simultaneously. Stress-induced transformation of metastable co phase to martensite phase, and its reversion are recognized in the Ti-XNb-10Ta-5Zr alloys with 20 mass% and 25 mass% Nb at tensile loading-unloading. The shape memory effect and the super elastic property are expected to be achieved in these types of the Ti-Nb-Ta-Zr system alloys. The elastic deformation behavior of the Ti-30Nb-10Ta-5Zr alloy disobeys Hooke's law. In this case, the maximum elastic strain is around 2.9%.The Ti-29Nb-13Ta-4.6Zr alloy wires with diameters of 0.3 and 1.0 mm fabricated by thermo-mechanical processing including cold-drawing and heat treatment also show an unique elastic behavior with two gradients under tensile loading. Their maximum elastic strains are around 2.8 and 2.9%, respectively, which are around twice higher than that of the hot forged bar of the Ti-29Nb-13Ta-4.6Zr alloy subjected to a solution treatment. Therefore, it is highly expected to be applied to dental and surgical wires. From these results, in this study, an important guideline can be obtained for designing new titanium alloys for medical applications, which have the functionalities such as low Young's modulus, shape memory effect and super elasticity. Less