Phase transformation and magnetic anisotropy of an iron-palladium ferromagnetic shape-memory alloy

J. Cui, Thomas W Shield, R. D. James

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Abstract

Martensitic phase transformations in an Fe7Pd3 alloy were studied using various experimental techniques: Visual observation, differential scanning calorimeter (DSC) measurements and X-ray diffraction. Magnetic measurements on this alloy were made using a vibrating sample magnetometer (VSM) and a Susceptibility Kappa bridge. The VSM measurements were made with the sample in a compression fixture to bias the martensite phase to a single variant. Both X-ray and DSC measurements show that the FCC-FCT transformation is a weak first-order thermoelastic transition. The average lattice parameters are a = 3.822±0.001 Å and c = 3.630±0. 001 Å for the FCT martensite, and a0 = 3.756±0.001 Å for the FCC austenite. The latent heat of the FCC-FCT transformation is 10.79±0.01 J/cm3. A Susceptibility Kappa bridge measurement determined the Curie temperature to be 450 °C. The saturation magnetization from VSM data is ms = 1220±10 emu/cm3 at -20 °C for the martensite and ms = 1080±10 emu/cm3 at 60 °C for the austenite. The easy axes of a single variant of FCT martensite are the [100] and [010] directions (the a-axes of the FCT lattice) and the [001] direction (FCT c-axis) is the hard direction. The cubic magnetic anisotropy constant K1 is -5±2×103 erg/cm3 for the austenite at 60 °C, and the tetragonal anisotropy constant K1+K2 is 3.41±0.02×105 erg/cm3 for the martensite at a temperature of -20 °C and under 8 MPa of compressive stress in the [001] direction.

Original languageEnglish (US)
Pages (from-to)35-47
Number of pages13
JournalActa Materialia
Volume52
Issue number1
DOIs
StatePublished - Jan 5 2004
Externally publishedYes

Bibliographical note

Funding Information:
We would like to thank the Department of Defense through the Office of Navy Research [Grant Nos. N00014-91-J-4034, N00014-01-1-0761 (MURI program), and N00014-99-1-0635 (DURIP program)] and the National Science Foundation (Grant No. NSF-0074043) for supporting this research.

Keywords

  • Ferromagnetic
  • Magnetic anisotropy
  • Martensitic phase transformation
  • Shape-memory alloys
  • X-ray diffraction

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