Determination of pressure effects on the alpha - gamma phase transition and size of Fe in Nd-Fe-B spring exchange magnets

Abuin Herraez, Manuel and Turgut, Zafer and Aronhime, Natan and Keylin, Vladimir and Leary, Alex and DeGeorge, Vincent and Horwath, John and Lee Semiatin, S. and Laughlin, David E. and McHenry, Michael E. (2015). Determination of pressure effects on the alpha - gamma phase transition and size of Fe in Nd-Fe-B spring exchange magnets. "Metallurgical and Materials Transactions A", v. 46 (n. 11); pp. 5002-5010. ISSN 1073-5623. https://doi.org/10.1007/s11661-015-3120-0.

Description

Title: Determination of pressure effects on the alpha - gamma phase transition and size of Fe in Nd-Fe-B spring exchange magnets
Author/s:
  • Abuin Herraez, Manuel
  • Turgut, Zafer
  • Aronhime, Natan
  • Keylin, Vladimir
  • Leary, Alex
  • DeGeorge, Vincent
  • Horwath, John
  • Lee Semiatin, S.
  • Laughlin, David E.
  • McHenry, Michael E.
Item Type: Article
Título de Revista/Publicación: Metallurgical and Materials Transactions A
Date: November 2015
ISSN: 1073-5623
Volume: 46
Subjects:
Faculty: E.T.S.I. Telecomunicación (UPM)
Department: Electrónica Física
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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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 P–T 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.

More information

Item ID: 41097
DC Identifier: http://oa.upm.es/41097/
OAI Identifier: oai:oa.upm.es:41097
DOI: 10.1007/s11661-015-3120-0
Official URL: http://link.springer.com/article/10.1007/s11661-015-3120-0
Deposited by: Memoria Investigacion
Deposited on: 03 Jul 2016 07:38
Last Modified: 01 Dec 2016 23:30
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