Size-effect and scaling power-law for superelasticity in Shape Memory Alloys at the nano-scale
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Date
2017-05-29Author
Gómez Cortés, José Fernando
Nó Sánchez, María Luisa
López Ferreño, Iñaki
Hernández-Saz, Jesús
Molina, Sergio I.
Chuvilin, Andrey
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Nature Nanotechnology 12 : 790-796 (2017)
Abstract
Shape-memory alloys capable of a superelastic stress-induced phase transformation and a high displacement actuation have promise for applications in micro-electromechanical systems for wearable healthcare and flexible electronic technologies. However, some of the fundamental aspects of their nanoscale behaviour remain unclear, including the question of whether the critical stress for the stress-induced martensitic transformation exhibits a size effect similar to that observed in confined plasticity. Here we provide evidence of a strong size effect on the critical stress that induces such a transformation with a threefold increase in the trigger stress in pillars milled on [001] L21 single crystals from a Cu–Al–Ni shape-memory alloy from 2 μm to 260 nm in diameter. A power-law size dependence of n = −2 is observed for the nanoscale superelasticity. Our observation is supported by the atomic lattice shearing and an elastic model for homogeneous martensite nucleation.