Shape memory characteristics of rapidly solidified Ti50Ni15Cu35 alloy ribbons

The shape memory alloy ribbons of Ti50Ni15Cu35 had been fabricated by two rapid solidification processes of melt spinner and melt overflow to achieve different rapidly solidified structures. The ribbon fabricated by the melt spinner was an amorphous and any martensitic transformations occurred in the crystallized ribbon due to the formation of an equilibrium intermetallic phase (Cu4Ti3). However, the microstructure of the ribbon prepared by the melt overflow exhibited columnar grains normal to the ribbon surface. X-ray diffraction analysis showed that one-step martensitic transformation of B2-B19 occurred in the ribbon. According to the DSC analysis, it was known that the martensitic transformation temperature of B2 → B19 was 71.2 °C. During thermal cyclic deformation with the applied stress of 120 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be 4.6 °C and 1.68%, respectively, in the Ti50Ni15Cu35 alloy. It is considered that these shape memory characteristics were ascribed to solid-solution strengthening by the supersaturation of excess Cu content.