Influence of Zr content on phase formation, transition and mechanical behavior of Ni-Ti-Hf-Zr high temperature shape memory alloys

Abstract

Quaternary Ni-Ti-Hf-Zr high temperature shape memory alloys containing different Zr content (0-15 at.%) were prepared by arc melting and suction casting. The addition of Zr led to change in lattice parameters and monoclinic angle of B19' martensite phase. The phase transformation temperature as well as yield strength of the alloys gradually increased with increasing the Zr content. Moreover, the alloys exhibited significant changes in phase transition and deformation behaviors. With the addition of Zr up to 7 at.%, the alloys exhibited double yielding and two-step phase transition behaviors. In contrast, alloys containing 10 and 15 at.% Zr revealed single yielding and one-step phase transition behaviors. These distinctions on phase transition and yielding behaviors of the alloys were mainly related to the structural evolution related to twinning mode in martensite phase of as-cast alloys originated from the change of lattice distortion during martensitic transformation by increasing of Zr content. Through detailed investigations on the microstructural features, thermal characteristics, mechanical properties and structural evolution on deformation of the alloys, the influence of Zr content on phase formation, phase transition and deformation behavior of Ni-Ti-Hf-Zr high temperature shape memory alloys was elucidated. (C) 2016 Elsevier B.V. All rights reserved.