Damping behaviors and strain recovery characteristics of Hf-modified TiNb-based shape memory alloys

Abstract

In the present study, the electron concentration, bond order and metallic average d-electron orbital energy level of Ti-Nb-Hf shape memory alloys were controlled by adjusting the Hf content, which further determined the phase constituents and phase stability. The Ti-Nb-Hf shape memory alloys with various Hf contents were composed of the α´´ martensite phase and β phase, regardless of Hf contents. With increasing Hf content, the martensitic transformation temperature (Ap) slightly increased. Hf addition could enhance the strength and optimize the strain recovery characteristics. A higher strength and larger recoverable strain can be obtained in Ti-Nb shape memory alloy modified by 2 at.% Hf due to grain refinement, precipitation strengthening and solution strengthening. Training can achieve perfect superelasticity with a completely recoverable strain of approximately 2%. In conclusion, the perfect combination of damping capacity and strain recovery characteristics can be attained by tailoring the Hf content in Ti-Nb-Hf shape memory alloys.