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

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 thermomagneto-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 has also been carried out to determine the effect of temperature on the magneto-mechanical behaviour of the Ni-Mn-Ga alloys. Strong temperature dependence of the magnetic shape memory effect in a Ni47.8Mn27.5Ga24.7 alloy has been observed.

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Document Details

Document Type
Technical Report
Publication Date
Dec 01, 2004
Accession Number
ADA436253

Entities

People

  • Calvin V. Hyatt
  • Leon M. Cheng
  • Rosaura Ham-su
  • Shannon P. Farrell

Organizations

  • Defence Research and Development Canada

Tags

Communities of Interest

  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Alloys
  • Boundaries
  • Crystal Structure
  • Crystals
  • Curie Temperature
  • Heat Treatment
  • Laboratory Magnetometers
  • Magnetic Anisotropy
  • Magnetic Fields
  • Magnetic Forces
  • Magnetic Properties
  • Materials
  • Measurement
  • Mechanical Properties
  • Shape Memory Alloys
  • Single Crystals
  • Stress Strain Relations

Fields of Study

  • Materials science

Readers

  • Materials Science (Mechanical Engineering).
  • Materials Science and Engineering.