Thermo-Mechanical Behaviour of Cu-Al-Ni High-Temperature Shape Memory AlloysThursday (17.05.2018) 09:45 - 10:10 Part of:
Along the last decade the demand of high-temperature shape memory alloys (HT-SMA), working in the temperature range between 100ºC and 200ºC, has undergone a noticeable increase driven by the potential applications in automotive, aeronautic, aerospace, and robotic industrial sectors. Among the different candidates, Cu-Al-Ni family offers good thermo-mechanical properties in this temperature range, which is not accessible for the more worldwide spread Ti-Ni SMA limited to below 100ºC. However, polycrystalline Cu-Al-Ni SMA are very brittle due to its high elastic anisotropy, and most of previous works explored the high concentration Al range, for which the alloys transform to γ’ martensite at rather low temperatures. Consequently these alloys have been usually disregarded in the literature as potential candidates for HT-SMA.
In the present work, the progress done with another different approach along the last decade is presented. The attention was focused on single crystals of Cu-Al-Ni SMA with low Al concentration and transforming at high temperature to β’ martensite, according preliminary works . Then, the production of alloys and single crystals of Cu-Al-Ni, by several methods, was systematically developed and a complete series of Cu-Al-Ni single crystalline SMA with transformation temperature Ms between 100ºC and 170ºC was produced and fully characterized. Three experimental methods have been used to perform a complete characterization of the thermal and mechanical behaviour of such alloys: Thermal transformation by DSC, thermal transformation under load in a specific equipment and stress-induced transformation by mechanical tests. The Clausius-Clapeyron line has been determined for all the alloys and the dependence of several parameters (transformation temperatures, enthalpies, hysteresis and C-C slope) on Al concentration has been established. In parallel, the kind of transforming martensite has been analysed by EBSD. Finally, the shape memory behaviour under load has been tested along thousand cycles.
From this complete work, it can be concluded that the developed Cu-Al-Ni single crystal SMA family constitutes a reliable solution for HT-SMA applications in the range of 100ºC to 200ºC.
 V. Recarte, R.B. Pérez-Sáez, E.H. Bocanegra, M.L. Nó, J. San Juan, Metall. Mater. Trans. 33A (2002) 2581-2591.