Ti alloys have attracted continuing research attention as promising biomaterials due to their superior corrosion resistance and biocompatibility and excellent mechanical properties. Metastable β-type Ti alloys also provide several unique properties such as low Young's modulus, shape memory effect, and superelasticity. Such unique properties are predominantly attributed to the phase stability and reversible martensitic transformation. In this study, the effects of the Nb and Zr contents on phase constitution, transformation temperature, deformation behavior, and Young's modulus were investigated. Ti-Nb and Ti-Nb-Zr alloys over a wide composition range, i.e., Ti-(18-40)Nb, Ti-(15-40)Nb-4Zr, Ti-(16-40)Nb-8Zr, Ti-(15-40)Nb-12Zr, Ti-(12-17)Nb-18Zr, were fabricated and their properties were characterized. The phase boundary between the β phase and the α'' martensite phase was clarified. The lower limit content of Nb to suppress the martensitic transformation and to obtain a single β phase at room temperature decreased with increasing Zr content. The Ti-25Nb, Ti-22Nb-4Zr, Ti-19Nb-8Zr, Ti-17Nb-12Zr and Ti-14Nb-18Zr alloys exhibit the lowest Young's modulus among Ti-Nb-Zr alloys with Zr content of 0, 4, 8, 12, and 18 at.%, respectively. Particularly, the Ti-14Nb-18Zr alloy exhibits a very low Young's modulus less than 40 GPa. Correlation among alloy composition, phase stability, and Young's modulus was discussed.
Keywords: Ti alloys; Young’s modulus; martensitic transformation; shape memory effect; superelasticity.