Effect of Precipitation on Martensitic Transformation and Shape Memory Behaviour in Rapidly Solidified Ni

The effects of precipitation of Ni5Al3 in rapidly solidified Ni66Al34 were studied using DSC, X-ray diffraction and TEM. Precipitation in the martensite during heating at 10°C/min commenced at about 250°C and subsequently degraded the shape memory behaviour by inhibiting reversibility of transformation. On the other hand, precipitation in the β phase during aging at 550°C after rapid heating, had no influence on reversible martensitic transformation during subsequent cycling. Clearly, precipitation in the martensite interfered with reverse transformation, whereas precipitation in the parent phase had no such effect. Therefore, it is concluded that, to sustain reversibility of the martensitic transformation and consequential shape memory behaviour, precipitation of Ni5Al3 in the martensite must be avoided