Copper shape-memory alloy with outer space potential

The copper-based alloy exhibits a special shape-memory effect at temperatures as low as -200°C.

This has potential for space equipment and hydrogen-related technologies.

The study was led by various Japanese institutions, namely Tohoku University, Iwate University, the Japan Aerospace Exploration Agency, the National Astronomical Observation of Japan, Tokyo City University and Kyoto University.

Shape-memory alloys can be deformed into different shapes when cold, but will revert to their original shape when heated. 

However, prevalent shape-memory alloys that use nickel and titanium cannot maintain their shape-memory ability below -20°C. While the team claims that known shape-memory alloys that can operate below -100°C are not suitable for practical implementation. 

This research has reportedly developed the first functional actuator material capable of large work output at temperatures below -100°C. Its memory foam characteristics are contributed to by 'the large entropy change in martensitic transformation even at low temperatures', says Toshihiro Omori, research lead in the Department of Materials Science at Tohoku University.

The team of researchers prototyped a mechanical heat switch using a new alloy made of copper (Cu), aluminium (Al) and manganese (Mn) as an actuator. 

Four test samples of the Cu-Al-Mn alloy were made and tested as part of the study. The Cu-Al-Mn alloys contain approximately 17at% Al and 13-14at% Mn. The one used in the actuator test was CAM#2 composed of Cu-17.24Al-13.50Mn. The optimum material was CAMN, composed of Cu-16.86Al-13.39Mn-3.12Ni at.%.

CAM#2 displayed 8.01% strain at 100MPa and 7.74% strain at 400MPa, characteristics that allowed it to work successfully in the actuator.

CAMN was not ready at the time of the actuator test but presents even better characteristics, with a strain of 6.23% at 250MPa and of 6.48% at 650MPa, with comparable strain (%) displayed in between this range.

The alloys were shown to operate effectively at -170°C, controlling heat transfer by switching between contact and non-contact states based on temperature changes. 

Furthermore, the operating temperature can be adjusted by modifying its composition.

The material is manufactured using high-frequency induction melting, hot rolling, cold rolling and cycle heat treatment between 900°C and 500°C for obtaining single crystals.

Omori says this work came about because 'our research group has been investigating superelasticity at low temperatures. Superelasticity is one of the properties exhibited in shape-memory alloys.

'During our research activities, we realised that materials exhibiting some properties in low-temperature environments are required in the field of space science.'

Omori says this development paves the way for high-performance actuators that can operate even under cryogenic conditions. Potential applications include a mechanical heat switch for cooling systems in space telescopes and for advancing hydrogen transportation and storage.