Regulation of precipitation and its influence on the performances of multicomponent β-Ti-based shape memory alloy through annealing treatment

In the present study, the evolution of precipitate with the annealing temperature and its influence on the martensitic transformation and mechanical/functional properties of the multicomponent Ti–V–Al–Zr–Sn shape memory alloy were investigated. The results revealed that Ti–V–Al–Zr–Sn shape memory alloy annealed at 700 °C mainly consisted of α″ martensite and rodlike α precipitates, while annealing at 800 °C resulted in the appearance of β phase and C14-type Laves phase. Moreover, the configuration of α precipitates evolved from rodlike to striplike. Upon the annealing temperature increased to 900 °C, α precipitates and α″ martensite completely diminished, whereas the β phases expanded. Furthermore, the grain size of Ti–V–Al–Zr–Sn shape memory alloy consistently increased with the annealing temperature. Of all the annealed Ti–V–Al–Zr–Sn shape memory alloys, only α″ → β reverse martensitic transformation was observed. The martensite transformation temperature was continuously reduced due to the comprehensive effect of variation of chemical composition caused by precipitation of precipitates, grain size, and defect evolution. Additionally, the multicomponent Ti–V–Al–Zr–Sn shape memory alloy annealed at 800 °C possessed superior mechanical properties including the moderate tensile strength (797 MPa) and elongation (23.4%), highest microhardness (395 HV), and the excellent fully recoverable strain of 6%, which can be ascribed to the precipitation strengthening, grain refinement, and solution strengthening.