Effects of Cr and Sn additives on the martensitic transformation and deformation behavior of Ti-Cr-Sn biomedical shape memory alloys

Abstract

The effects of Cr and Sn additives on the phase constitution, lattice deformation strain, transformation temperature, and deformation behavior of Ti-Cr-Sn alloys were systematically investigated to inform the development of a superelastic alloy with high lattice deformation strain. The addition of Cr and Sn changes the reverse martensitic transformation temperature by −190 K/mol% Cr and −141 K/mol% Sn, respectively. The lattice deformation strains (η1, η2, and η3) were evaluated in terms of the lattice parameters of the parent β phase to the martensite α″ phases. In addition, the composition range of the alloys that are expected to exhibit superelasticity and high deformation strain near the human body temperature was established based on the composition dependence of lattice deformation strain and transformation temperature. The deformation behavior of Ti-Cr-Sn alloys at room temperature changes from the shape memory effect to superelasticity with increasing Cr and Sn contents. In particular, Ti-2.5Cr-8.5Sn, Ti-3.0Cr-7.5Sn, Ti-3.0Cr-8.0Sn, Ti-3.5Cr-7.0Sn, and Ti-4.0Cr-6.5Sn alloys exhibit superelasticity at room temperature and a high lattice deformation strain (η2) that exceeds 6.32%. It is concluded that Cr and Sn are more effective than other β-stabilizing elements at lowering the martensitic transformation temperature of β-Ti shape memory alloys without reducing the lattice deformation strain.