Microstructure and properties of Cu–Al–Ni shape memory alloy strips prepared via hot densification rolling of argon atomized powder preforms

In the present work, Cu–Al–Ni SMA strips with grain size less than 100 μm were successfully prepared via a novel powder metallurgy route involving hot densification rolling of unsheathed sintered powder preforms prepared from argon atomized pre-alloyed Cu–Al–Ni powder. It has been shown that the hot rolled Cu–Al–Ni strips exhibited a very small grain growth during heat treatment at 950 °C up to 4 h. This behavior was attributed to the pinning effect of nano-sized alumina segregated on the grain boundaries. It was established that the grain size of the finished Cu–Al–Ni strips is governed by the starting powder particle size, and the mechanism of this aspect has been discussed. The finished heat-treated Cu–Al–Ni alloy strips consisted of elongated shape grains, with average grain size approximately 27 μm. The heat treated strips were fully martensitic in nature consisting of self-accommodated β ′ 1 martensite along with small amount of γ ′ 1 martensite. The heat treated strips had an extremely good combination of average fracture strength (∼626 MPa) and fracture strain (∼13.5%). The two-way shape memory strain was found approximately 0.23% after 25 training cycles at 4% applied training strain.