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Deformation twinning in Ni–Mn–Ga micropillars with 10M martensite

Authors
  • Reinhold, M.1
  • Kiener, D.2
  • Knowlton, W. B.1, 3
  • Dehm, G.2, 4
  • Müllner, P.1
  • 1 Department of Materials Science and Engineering, Boise State University, Boise, Idaho 83725, USA
  • 2 Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, 8700 Leoben, Austria
  • 3 Department of Electrical and Computer Engineering, Boise State University, Boise, Idaho 83725, USA
  • 4 Department Materials Physics, Montanuniversität Leoben, 8700 Leoben, Austria
Type
Published Article
Journal
Journal of Applied Physics
Publisher
AIP Publishing
Publication Date
Sep 01, 2009
Volume
106
Issue
5
Identifiers
DOI: 10.1063/1.3211327
PMID: 19859577
PMCID: PMC2766397
Source
PubMed Central
License
Unknown

Abstract

The maximum actuation frequency of magnetic shape-memory alloys (MSMAs) significantly increases with decreasing size of the transducer making MSMAs interesting candidates for small scale actuator applications. To study the mechanical properties of Ni–Mn–Ga single crystals on small length scales, two single-domain micropillars with dimensions of 10×15×30 μm3 were fabricated from a Ni–Mn–Ga monocrystal using dual beam focused ion beam machining. The pillars were oriented such that the crystallographic c direction was perpendicular to the loading direction. The pillars were compressed to maximum stresses of 350 and 50 MPa, respectively. Atomic force microscopy and magnetic force microscopy were performed prior to fabrication of the pillars and following the deformation experiments. Both micropillars were deformed by twinning as evidenced by the stress-strain curve. For one pillar, a permanent deformation of 3.6% was observed and ac twins (10M martensite) were identified after unloading. For the other pillar, only 0.7% remained upon unloading. No twins were found in this pillar after unloading. The recovery of deformation is discussed in the light of pseudoelastic twinning and twin-substrate interaction. The twinning stress was higher than in similar macroscopic material. However, further studies are needed to substantiate a size effect.

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