Enhancement of the shape memory effect by the introductions of Cr and Sn into the β–Ti alloy towards the biomedical applications

Abstract

The effects of the Cr and Sn addition concentrations on the cold–workability, phase constituents, mechanical properties, shape memory effect (SME), and superelasticity were investigated. A systematic screening of the β–Ti alloy, which was slight–alloyed by Cr and Sn, was executed in this work. Cold–workability of the Ti–Cr–Sn alloys was greatly promoted along with the increasing concentration of Cr and Sn. The parent β–phase was successfully stabilized at room temperature merely by the slight introduction of Cr and Sn β–stabilizers. Perfect SME of 100% recovery rate was realized in the Ti–5.5Cr–3Sn alloy and the shape recovery rate performed a good inclination with the overall Cr + Sn addition concentration in the bending tests. Obvious two–stage yielding, which inferred the stress–induced martensitic transformation (SIMT) and/or martensite variant reorientation (MVR) before yielding, was observed in the tensile tests. The two–stage yielding also explained the SME well. The excellent elongation of 40% and 45%, which were found in the Ti–6.0Cr–3Sn and the Ti–6.0Cr–2Sn alloys, was explained by the {332} <113> mechanical twinning. Slight pseudoelasticity was also found in most of the specimens. Functional mappings of the Ti–Cr–Sn alloys, which could be powerful tools for future investigations, have been constructed in this study. The Ti–6.0Cr–3Sn alloy, which possessed high ultimate tensile strength, excellent ductility of 40%, outstanding SME of 91.0%, and good shape recovery after removing the external stress, could be a promising material for the applications in biomedical materials.