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.

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Acknowledgements

This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO), projects MAT2009-12492, MAT2012-36421 and CONSOLIDER-INGENIO 2010 CSD2009-00013, as well as by the Consolidated Research Group IT-10-310 and the ETORTEK-ACTIMAT project from the Education and Industry Departments of the Basque Government and Junta de Andalucía (INNANOMAT PAI research group TEP-946). J.F.G.-C. thanks MINECO for a PhD grant. This work made use of the FIB facilities of SGIKER from the UPV/EHU and of IMEYMAT-UCA. Co-funding from FEDER-EU and REACT projects from H-2020, grant 640241, are also acknowledged.

Author information

Affiliations

  1. Departamento Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apdo 644, 48080 Bilbao, Spain

    • Jose F. Gómez-Cortés
    • , Iñaki López-Ferreño
    •  & Jose M. San Juan
  2. Departamento Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apdo 644, 48080 Bilbao, Spain

    • Maria L. Nó
  3. Departamento de Ciencia de los Materiales e I.M. y Q.I, Facultad de Ciencias, IMEYMAT, Universidad de Cádiz, Campus Río San Pedro, 11510 Puerto Real, Cádiz, Spain

    • Jesús Hernández-Saz
    •  & Sergio I. Molina
  4. CIC nanoGUNE, Tolosa Hiribidea 76, 20018 Donostia-San Sebastian, Spain

    • Andrey Chuvilin
  5. IKERBASQUE, Basque Foundation for Science, María Díaz de Haro 3, 48013 Bilbao, Spain

    • Andrey Chuvilin

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Contributions

J.M.S.J. and M.L.N. designed the experiments, developed the model and wrote the initial manuscript with input from all the authors. I.L.-F. and J.M.S.J. produced the alloys. J.F.G.-C., J.H.-S., S.I.M., A.C., M.L.N. and J.M.S.J. performed the milling of the pillars by FIB and took the SEM micrographs. J.F.G.-C. and J.M.S.J. performed the nanocompression tests. All the authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jose M. San Juan.

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DOI

https://doi.org/10.1038/nnano.2017.91

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