Universal Scaling Law for the Size Effect on Superelasticity at the Nanoscale Promotes the Use of Shape‐Memory Alloys in Stretchable Devices

What is it about?

Shape memory alloys are the most stretchable metallic materials thanks to their superelastic behavior associated to the stress-induced martensitic transformation, being of potential interest for flexible and wearable electronic technologies, provide that their properties would be retained at small scale. Nano-compression experiments on Cu-Al-Be shape memory alloy single crystals, demonstrate that micro and nano pillars, between 2 μm and 260 nm in diameter, exhibit a reproducible superelastic behavior fully recoverable up to 8% strain, even at the nano scale. Additionally, these micro/nano pillars exhibit a size effect on the critical stress for superelasticity, which dramatically increases for pillars smaller than ∼1 μm in diameter, scaling with a power law of exponent n = -2. The observed size-effect agrees with a theoretical model of homogeneous nucleation of martensite at small scale and the universality of this scaling power law for Cu-based shape memory alloys is proposed. These results open new directions for using shape memory alloys as stretchable conductors and actuating devices in flexible and wearable technologies.

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