Abstract
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.
Highlights
Metallic materials such as Ti alloys, cobalt-chromium based alloys and stainless steels have been extensively used as structural biomaterial
One of the critical issues associated with metallic biomaterials is their high Young’s modulus because the large difference of the elastic modulus between metallic implants and adjacent bone tissues can lead to stress shielding, causing bone resorption and osteoporosis [1,2]
This study focuses on the effect of the Zr addition on the phase stability and Young’s modulus in Ti–Nb alloys because Zr has been used as a major alloying element in β-type Ti alloys for biomedical applications due to its superior biocompatibility [2,9,11,25,26,27,28,29,30,32,33]
Summary
Metallic materials such as Ti alloys, cobalt-chromium based alloys and stainless steels have been extensively used as structural biomaterial. It has been reported that the Bo-Md map for Ti alloys is useful to predict the martensitic transformation temperature and deformation mechanism [53,54,55,56,57] Despite such extensive research, much uncertainty still exists on the relations among Young’s modulus, martensitic transformation behavior, and the values of e/a, Bo, and Md, and the experimental data are still insufficient to understand the mechanisms involved. This study focuses on the effect of the Zr addition on the phase stability and Young’s modulus in Ti–Nb alloys because Zr has been used as a major alloying element in β-type Ti alloys for biomedical applications due to its superior biocompatibility [2,9,11,25,26,27,28,29,30,32,33]. A novel guideline to design β-type Ti alloys with low Young’s modulus was proposed
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