Metallurgical and Materials Transactions A

, Volume 46, Issue 11, pp 5002–5010 | Cite as

Determination of Pressure Effects on the αγ Phase Transition and Size of Fe in Nd-Fe-B Spring Exchange Magnets

  • Manuel Abuin
  • Zafer Turgut
  • Natan Aronhime
  • Vladimir Keylin
  • Alex Leary
  • Vincent DeGeorge
  • John Horwath
  • S. Lee Semiatin
  • David E. Laughlin
  • Michael E. McHenry
Article

Abstract

Pressure effects in RE-lean Nd2Fe14B-based nanocomposite systems developed from nanocrystalline precursors are studied in this work. In particular, the pressure dependence of the α → γ phase transformation in the Fe phase is examined along with the suppression of coarsening (growth) in both phases at higher pressures. By synchrotron X-ray diffraction we determined that the α → γ-phase transformations occur at temperatures of 1120 K (847 °C) at 1 GPa and 960 K (687 °C) at 5 GPa. A composition rich in Fe appears to have an ~373 K (100 °C) range of temperature over which the α, γ-phases coexist for atmospheric pressure. We compare our experimental data with other reported observations for Fe and with equations of state (EOS) determined from first principle calculations. From this study we observe an important feature: the phase transition begins at a higher temperature in flake samples than in powder samples. We consider the magnetic contribution to the heat capacity in the EOS for Fe and describe the implications of dipole moments on the slope of the Clapeyron equation for the PT phase diagram in Fe. Additionally, the phase transition occurs at temperatures where growth by diffusional coarsening is also operative. This is significant since the size of soft Fe nanostructures is important to spring exchange. Suppression of the phase transition and Fe coarsening at higher pressures suggest that there may be interesting mechanical processing routes to be investigated to optimize spring exchange effects in Nd-Fe-B permanent magnets.

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2015

Authors and Affiliations

  • Manuel Abuin
    • 1
    • 2
  • Zafer Turgut
    • 3
  • Natan Aronhime
    • 1
  • Vladimir Keylin
    • 1
  • Alex Leary
    • 1
  • Vincent DeGeorge
    • 1
  • John Horwath
    • 3
  • S. Lee Semiatin
    • 3
  • David E. Laughlin
    • 1
  • Michael E. McHenry
    • 1
  1. 1.Department of Materials Science and EngineeringCarnegie Mellon UniversityPittsburghUSA
  2. 2.CEI Campus Moncloa, UCM-UPMMadridSpain
  3. 3.Air Force Research LaboratoryWright Patterson Air Force BaseUSA

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