Thermo-mechanical behaviour of a Ni-Ti-Cu melt spun alloy

Abstract
The martensitic transformation of a melt spun Ti₅₀Ni₂₅Cu₂₅ alloy (cubic B2 = orthorhombic B19) has been investigated by means of thermo-mechanical cycling. The alloy was initially amorphous and it has been characterised after a controlled crystallisation process using differential scanning calorimetry, X-ray diffraction, thermal cycling tests under constant load, tensile tests and transmission electron microscopy. The recoverable elongation and the transformation temperatures have been studied as a function of the applied stress. However a new phenomena not yet completely understood has been observed during the cycling experiments under constant load. For the direct transformation, although the net shape change is an elongation, the strain-temperature ε(T) curve has a region with a local contraction (opposite to the external load). The equivalent effect is also observed in the reverse transformation curve. The "training ability" (to achieve the two way shape memory effect) shown by the melt spun studied ribbons is lower than in other Ni-Ti ribbons.