Effect of Sn and Zr on microstructure and mechanical properties of Ti-Ta based shape memory alloys

Ti-Ta binary shape memory alloys have attracted great interest due to absence of toxic element and low Young’s modulus. However, effect of third element on the microstructure and mechanical properties of Ti-Ta based alloys has not been well understood. In the present study, the effect of Zr and Sn addition on the microstructure and mechanical properties of Ti65Ta35 (at.%) alloys has been investigated using optical microscope, X-ray diffraction and tensile test. The results show that the microstructure of the solution-treated Ti-Ta based alloys mainly consists of equiaxial grains. The addition of Zr and Sn does not significantly influence the grain size and morphology. The structure of alloys consists of β phase and α" martensite phase at room temperature, except for the Ti65Ta30Sn5 which consists only β phase. This can be attributed to the presence of Sn providing a stronger β-stabilized effect upon quenching relative to Zr addition. The lattice parameter of β phase increase with the increasing of Zr and Sn content. The addition of Zr and Sn causes obvious increase in the tensile strength, yielding strength and fracture strength. The Young’s modulus increases slightly with the increase of Zr and Sn content. The effect of alloying elements on Young’s modulus is consistent with the d-electronic theory.