New Cu-based shape memory alloy family transforming at ultra-low temperatures for cryogenic applications

New hydrogen-based energy sources, high-power nuclear fusion and the emerging quantum computing technologies, as well as the classical superconducting ones, require low-temperature working environments. All of them need the use of sensors and actuators at cryogenic temperatures. However, at present there are not shape memory alloys (SMA) offering the possibility of operating as actuators, as valves for instance, at so low temperatures, below liquid nitrogen.

In the present talk, the design, production and characterization of a new quaternary Cu-Al-Ni-Be SMA system (patent pending) will be presented. These alloys are designed to offer transformation temperatures continuously controlled between 400 K down to 20 K or even lower. After the alloy production by inductive melting and centrifugal casting under moderate vacuum with argon atmosphere, [001] oriented single crystals were grown by Bridgman method, and further treated to exhibit the martensitic transformation. Their thermoelastic martensitic transformation involves the β’ martensite with a low thermal hysteresis. These alloys show an outstanding superelastic behavior above 8% strain, fully recoverable, as well as a good shape memory. Several representative tests of the thermal and stress-induced transformation at different temperatures, even below 78 K, will be presented and discussed.

This Cu-Al-Ni-Be SMA family opens the door for the development of new applications in many industrial sectors, which require sensors and actuators operating at cryogenic temperatures.