Suppression of twinning mechanism on nanoscale: size effect in Cu–Ni–Al shape memory alloy
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In Cu–Ni–Al shape memory alloy, we observed a significant size effect on the twinning stress, i.e. the dependency of compression stress needed for twin-variant reorientation on sample size using in situ loading of micro- and nanoscale pillars in scanning and transmission electron microscopes. With decreasing dimensions of pillars, the twinning stress sharply increases following scaling power law with an exponent approximately n = − 2/3. For very small nanopillars, the projected twinning stress is so high that the nanopillars are deformed by plastic deformation instead of twinning. Our results shed light on some of the fundamental aspects of nanoscale behaviour of shape memory alloys which is important for applications in microelectromechanical systems.
This work has been financially supported by the Czech Science Foundation (Grant Number 14-36566G) (AdMat) and furthermore by the Project LM2015087 of the Czech Ministry of Education, Youth and Sports. MV. would like to acknowledge financial support by the Grant SGS16/249/OHK4/3T/14. MK would like to acknowledge financial support of the ERDF in the frame of the Project No. CZ.02.1.01/0.0/0.0/15_003/0000485.
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Conflict of interest
The authors declare that they have no conflicts of interest to this work.
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