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Title: Microstructure and coercivity in alnico 9

Abstract

Magnetic property enhancement of alnico, a rare-earth free permanent magnet, is highly dependent on both the initial microstructure and the evolution of the spinodal decomposition (SD) inside each grain during the heat treatment process. The size, shape and distribution of the magnetic FeCo-rich (α 1) phase embedded in continuous non-magnetic AlNi-rich (α 2) phase as well as a minor Cu-enriched phase residing in between are shown to be crucial in controlling coercivity. Phase and magnetic domain morphology in a commercial alnico 9 alloy was studied using a combination of structural characterization techniques, including scanning electron microscopy, electron backscatter diffraction, aberration-corrected scanning transmission electron microscopy and Lorentz microscopy. Our results showed that casting created structural nonuniformity and defects, such as porosity, TiS 2 precipitates and grain misorientation, are heterogeneously distributed, with the center section having the best crystallographic orientation and minimal defects. The optimal spinodal is a “mosaic structure”, composed of rod-shape α1 phase with {110} or {100} planar faceting and diameter of ~30–45nm. There is also a Cu-enriched phase residing at the corners of two < 110 > facets of the α1 phase. Furthermore, it was observed that grain boundary phase reverse magnetization direction at lower external magnetic field comparedmore » to the SD region inside the grain. Improving grain orientation uniformity, reducing detrimental grain boundary phase volume fraction, and the branching of the α 1 rods, as well as their diameter, are promising routes to improve energy product of alnico.« less

Authors:
 [1]; ORCiD logo [1];  [1]; ORCiD logo [2];  [3];  [4];  [1];  [1];  [1]
  1. Ames Lab., Ames, IA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  4. Arnold Magnetic Technologies Corp., Rochester, NY (United States)
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1477200
Alternate Identifier(s):
OSTI ID: 1490587; OSTI ID: 1542141
Report Number(s):
IS-J-9763; SAND-2019-7284J
Journal ID: ISSN 0304-8853; PII: S0304885318303779
Grant/Contract Number:  
AC02-07CH11358; AC05-00OR22725; AC04-94AL85000
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Magnetism and Magnetic Materials
Additional Journal Information:
Journal Volume: 471; Journal Issue: C; Journal ID: ISSN 0304-8853
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Permanent magnets; Microstructure; Spinodal decomposition; Atom-probe tomography; TEM; STEM HAADF; Lorentz microscopy

Citation Formats

Zhou, Lin, White, Emma, Ke, Liqin, Cullen, David A., Lu, Ping, Constantinides, S., McCallum, R. W., Anderson, I. E., and Kramer, Matthew J. Microstructure and coercivity in alnico 9. United States: N. p., 2018. Web. doi:10.1016/j.jmmm.2018.09.085.
Zhou, Lin, White, Emma, Ke, Liqin, Cullen, David A., Lu, Ping, Constantinides, S., McCallum, R. W., Anderson, I. E., & Kramer, Matthew J. Microstructure and coercivity in alnico 9. United States. doi:10.1016/j.jmmm.2018.09.085.
Zhou, Lin, White, Emma, Ke, Liqin, Cullen, David A., Lu, Ping, Constantinides, S., McCallum, R. W., Anderson, I. E., and Kramer, Matthew J. Mon . "Microstructure and coercivity in alnico 9". United States. doi:10.1016/j.jmmm.2018.09.085. https://www.osti.gov/servlets/purl/1477200.
@article{osti_1477200,
title = {Microstructure and coercivity in alnico 9},
author = {Zhou, Lin and White, Emma and Ke, Liqin and Cullen, David A. and Lu, Ping and Constantinides, S. and McCallum, R. W. and Anderson, I. E. and Kramer, Matthew J.},
abstractNote = {Magnetic property enhancement of alnico, a rare-earth free permanent magnet, is highly dependent on both the initial microstructure and the evolution of the spinodal decomposition (SD) inside each grain during the heat treatment process. The size, shape and distribution of the magnetic FeCo-rich (α1) phase embedded in continuous non-magnetic AlNi-rich (α2) phase as well as a minor Cu-enriched phase residing in between are shown to be crucial in controlling coercivity. Phase and magnetic domain morphology in a commercial alnico 9 alloy was studied using a combination of structural characterization techniques, including scanning electron microscopy, electron backscatter diffraction, aberration-corrected scanning transmission electron microscopy and Lorentz microscopy. Our results showed that casting created structural nonuniformity and defects, such as porosity, TiS2 precipitates and grain misorientation, are heterogeneously distributed, with the center section having the best crystallographic orientation and minimal defects. The optimal spinodal is a “mosaic structure”, composed of rod-shape α1 phase with {110} or {100} planar faceting and diameter of ~30–45nm. There is also a Cu-enriched phase residing at the corners of two < 110 > facets of the α1 phase. Furthermore, it was observed that grain boundary phase reverse magnetization direction at lower external magnetic field compared to the SD region inside the grain. Improving grain orientation uniformity, reducing detrimental grain boundary phase volume fraction, and the branching of the α1 rods, as well as their diameter, are promising routes to improve energy product of alnico.},
doi = {10.1016/j.jmmm.2018.09.085},
journal = {Journal of Magnetism and Magnetic Materials},
number = C,
volume = 471,
place = {United States},
year = {2018},
month = {9}
}

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