Effect of annealing conditions on microstructures and shape memory characteristics of Ti50–Ni30–Cu20 alloy ribbons

Ti50–Ni30–Cu20 alloy ribbons without any crystal phases have been fabricated at the wheel velocities of 55 m/s and the melt spinning temperature of 1500 °C by melt spinning process. Their microstructures and shape memory characteristics were investigated by means of optical microscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The crystallization temperature was measured to be 440 °C. The crystallized ribbon exhibited fine microstructure after annealed at 440 °C for 10 min and was deformed up to about 6.8%. During thermal cycle with the applied stress of 220 MPa, transformation hysteresis and elongation associated with a B2–B19 transformation were observed to be 4 and 3.6%. The ribbons showed a perfect superelasticity and their stress hysteresis was as small as 20 MPa which was attributed to the single pair martensite variants in small grains. This controlled microstructure was achieved by a proper heat treatment of amorphous ribbons in Ti50–Ni30–Cu20 alloy.