Shape memory effect in thin films of a Cu-Al-Ni alloy

Thin films of Cu-26.9 at.% Al-5.5 at.% Ni were grown by dc magnetron sputtering from the alloy target previously melted in an induction furnace. The films were grown either on glass or (1 0 0)Si substrates at room temperature. The films, of approximately 3 μm thickness, were peeled off from the substrate for further studies. The structures and microstructures of the as grown films were analysed by transmission electron microscopy. A nanometric mixture of BCC and 2H phases was found irrespective of the substrate. The shape memory effect was not observed for this structural state. After an annealing at 1023 K for 3600 s in He or Ar flux, followed by quenching to room temperature, the films were found to be in a martensitic state. Mainly the 18R structure was observed. At this stage the films were mechanically deformed at room temperature and then heated up to 373 K. A good shape recovery was observed to take place in a temperature range between 334 and 360 K.