Magneto-Mechanical Response in Ni-Mn-Ga Magnetic Shape Memory Alloys

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Authors
  1. Chen, L.M.
  2. Ham-Su, R.
  3. Farrell, S.P.
  4. Hyatt, C.
Corporate Authors
Defence R&D Canada - Atlantic, Dartmouth NS (CAN)
Abstract
It is generally accepted that the large reversible, magnetic-field-induced strain observed in ferromagnetic shape memory alloys is due to the rearrangement of twin variants in the martensite by an applied magnetic field leading to an overall change of shape. The main thermodynamic driving force for twin boundary motion in the presence of a magnetic field is the high magnetocrystalline anisotropy of the low symmetry martensitic phase. Low twin boundary energy, high magnetocrystalline anisotropy energy and saturation magnetization are some of the key factors for large magnetic field induced strain. In order to achieve optimum performance, thermomechanical and magnetic treatments are necessary. In this investigation, a systematic investigation is being carried out on single crystals of Ni-Mn-Ga alloys to determine the combined effects of composition and thermo-magneto-mechanical treatments on the crystal structure of the martensitic phases and the magnetomechanical properties of the Ni-Mn-Ga alloys. Repeated mechanical and magnetic forces have been applied to the samples. The results demonstrate that prior history has strong influence on the twinning start stress and twinning strain. In addition, heat treatment of the materials seems to increase the amount of strain that can be obtained (e.g. increased from 3% to 6%). Moreover, there is indication that prior heat treatment may also affect the martensite crystal structure that is formed during cooling. A systematic investigation

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Keywords
Ni-Mn-Ga;magneto-mechanical;temperature dependence;Shape memory materials;Magnetic shape memory alloys
Report Number
DRDC-ATLANTIC-TM-2004-267 — Technical Memorandum
Date of publication
01 Dec 2004
Number of Pages
44
DSTKIM No
CA025890
CANDIS No
523654
Format(s):
CD ROM

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