Effect of thermo-mechanical treatment on microstructural evolution and mechanical properties of a superelastic Ti-Zr-based shape memory alloy

Abstract

Achieving a combination of good superelastic performance and high strength in the bio-functional nickel-free Ti-based shape memory alloys is always required for the superelastic biomedical devices. For achieving this combination, in this paper, the thermo-mechanical treatment's influence on the microstructural development, mechanical performance and superelastic behavior of a Ti-45Zr-8Nb-2Sn (at.%) shape memory alloy was studied by using X-ray diffraction (XRD), transmission electron microscope (TEM), and tensile tests. 773 K and 823 K annealed specimens after cold rolling showed (beta+alpha) two-phase microstructure. The grain size increased from 0.11 um in 773 K annealed specimen to 125 mu m in 1173 K solution-treated specimen. A maximum recovery strain of 5.4% was achieved at room temperature in the 1073 K annealed specimen due to some extent of the favorable recrystallization texture together with reasonable grain size but the tensile strength was 830 MPa. A combination of a large recovery strain of 5.0%, a high tensile strength of 1030 MPa and good ductility with fracture strain of 13.2% was achieved at room temperature in the 823 K annealed specimen due to the fine beta grains of 0.74 mu m, which can be beneficial for biomedical applications.