Superelasticity by reversible variant reorientation in a Ni-Mn-Ga microwire with bamboo grains
- Northwestern Univ., Evanston, IL (United States); Beijing Inst. of Technology, Beijing (China)
- Northwestern Univ., Evanston, IL (United States)
- Beijing Inst. of Technology, Beijing (China)
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Univ. of Science and Technology, Beijing (China)
- Boise State Univ., ID (United States)
The link between microstructure and mechanical properties is investigated for a superelastic Ni–Mn–Ga microwire with 226 μm diameter, created by solidification via the Taylor method. The wire, which consists of bamboo grains with tetragonal martensite matrix and coarse γ precipitates, exhibits fully reversible superelastic behavior up to 4% tensile strain. Upon multiple tensile load–unload cycles, reproducible stress fluctuations of ~3 MPa are measured on the loading superelastic stress plateau of ~50 MPa. During cycles at various temperatures spanning -70 to 55 °C, the plateau stress decreases from 58 to 48 MPa near linearly with increasing temperature. Based on in situ synchrotron X-ray diffraction measurements, we conclude that this superelastic behavior is due to reversible martensite variants reorientation (i.e., reversible twinning) with lattice rotation of ~13°. The reproducible stress plateau fluctuations are assigned to reversible twinning at well-defined locations along the wire. The strain recovery during unloading is attributed to reverse twinning, driven by the internal stress generated on loading between the elastic γ precipitates and the twinning martensite matrix. Lastly, the temperature dependence of the twining stress on loading is related to the change in tetragonality of the martensite, as measured by X-ray diffraction.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- National Science Foundation (NSF); National Key Basic Research Program of China; USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1245144
- Alternate ID(s):
- OSTI ID: 1251455
- Journal Information:
- Acta Materialia, Vol. 99; ISSN 1359-6454
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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