Synthesis and properties of Cu-Al-Ni shape memory alloy strips prepared via hot densification rolling of powder preforms

Cu-Al-Ni shape memory alloy strips were successfully prepared by a powder metallurgy route consisting of preparing powder preforms from premixed Cu, Al and Ni powders by cold compaction, stepwise sintering in the range 873-1273 K, followed by unsheathed multipass hot rolling at 1273 K in protective atmosphere. The densification behaviour of the sintered powder preforms during hot rolling has been discussed. Homogenisation of the hot rolled strips was carried out at 1173 K for 4 h. It has been shown that the finished Cu-Al-Ni alloy strip consisted of self-accommodated plates of beta' and gamma' martensites together with a small amount of nanocrystalline Cu9Al4 phase. The finished hot rolled Cu-Al-Ni strips had fracture strength of 476 MPa, coupled with 2.5% elongation. The shape memory tests showed almost 100% recovery after 10 thermomechanical cycles in the hot rolled strips at 1 and 2% applied prestrain.