Annealing effects on the crystallization and shape memory effect of Ti50Ni25Cu25 melt-spun ribbons

As-spun Ti50Ni25Cu25 ribbon is fully amorphous with a lower wavenumber Qp than the amorphous Ti–Ni alloys owing to its high Cu content. Both crystallization activation energy Ea and onset temperature Tx for Ti50Ni25Cu25 ribbon are lower than those for Ti50Ni50 ribbon, indicating that the former has lower thermal stability. When Ti50Ni25Cu25 ribbon is annealed at 500 °C for 3 min, the initial as-crystallized grains contain a low Cu content and perform a prominent shape memory effect. Through prolonging the annealing time, more grains are crystallized in the ribbon but it becomes more fragile and its recoverable strain decreases. This is due to the increasing Cu content in the crystallized grains. Crystallized Ti50Ni25Cu25 ribbon can exhibit a good shape memory effect only under appropriate annealing conditions.