Journal of Materials Science

, Volume 50, Issue 22, pp 7473–7487

Thermally induced martensitic transformations in Cu-based shape memory alloy microwires

  • Nihan Tuncer
  • Lei Qiao
  • Raul Radovitzky
  • Christopher A. Schuh
Original Paper

DOI: 10.1007/s10853-015-9306-4

Cite this article as:
Tuncer, N., Qiao, L., Radovitzky, R. et al. J Mater Sci (2015) 50: 7473. doi:10.1007/s10853-015-9306-4

Abstract

Prior studies on shape memory alloys have identified size effects on the superelastic, i.e., stress-induced, hysteresis of martensitic transformations. However, literature on thermally induced transformations and size effects upon stored elastic energy is rather limited. In this work, a complementary sample size effect on the stored elastic energy of the transformation, and its effect on variant selection, is elaborated. Shape memory alloy microwires of a CuAlMnNi alloy are drawn with diameters varying between 45 and 255 μm and processed to obtain bamboo grain structures, where the grain boundaries lay almost perpendicular to the wire axis. Calorimetric and thermomechanical analyses of the microwires establish a decreasing contribution of stored elastic energy to the free energy of martensitic transformation as the wire diameter is reduced. This in turn affects the transformation ranges and macroscopic strain generated in constrained thermal cycling. The effect is shown to be associated with a decrease in number of interacting martensite variants as well as relaxation on free surfaces. The presented results indicate that thermal actuation of lightly biased SMA wires is enhanced in finer wires.

Funding information

Funder NameGrant NumberFunding Note
U. S. Army Research Laboratory and the U.S. Army Research Office
  • W911NF-13-D-0001

Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  • Nihan Tuncer
    • 1
  • Lei Qiao
    • 2
  • Raul Radovitzky
    • 2
  • Christopher A. Schuh
    • 1
  1. 1.Department of Materials Science and EngineeringMassachusetts Institute of TechnologyCambridgeUSA
  2. 2.Department of Aeronautics and AstronauticsMassachusetts Institute of TechnologyCambridgeUSA

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