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Title: Improvements to the Powder Processing of near-Final Shape alnico Magnets

Abstract

Alnico permanent magnets (PMs), a recent PM system of interest as an attractive rare earth-free PM alternative, have advantageous high operating temperature and magnetic saturation with the potential for utilization in electric machines, e.g. interior-PM motors found in electric vehicles, if current directional solidification methods can be replaced by a true mass production approach. Recently, two unique alnico compositions, termed Full-Co and Co-lean, with improved coercivity, were gas atomized, compression molded, and vacuum sintered (4h at 1240°C) to high densities of 97.8% and 99.3%, respectively. However, the Co-lean remained fine grained isotropic magnets and the Full-Co grains were not textured, lowering magnetic strength in spite of attempts to grow large textured grains by a stress-biased solid state grain alignment method to convert them to high energy anisotropic magnets. It was hypothesized that oxidation during de-binding in air left many prior particle boundary oxides within the sintered microstructure that hindered grain growth and texturing during the stress-biased texturing procedure and prevented the desired abnormal grain growth (AGG). Here we explored a vacuum de-binding step that was linked (in-place) to vacuum sintering and found that the Co-lean exhibited faster uniform grain growth that doubled the average grain size (40 μm to 80more » μm). Linked vacuum de-binding and sintering of Full-Co produced some AGG after only 1 h of 1240°C sintering. A new direction for promoting AGG (and stress-biased texturing) in alnico is being explored that utilizes a fundamental analysis of systems with second phase particles that either inhibit or boost grain growth. This effort explores the influence of vacuum de-binding linked to a series of lower sintering temperatures at a fixed time (4h) to see if oxide particle size and volume fraction can be changed to promote AGG conditions in alnico. Surprising qualitative results indicate that AGG may be promoted for vacuum sintering at less than 1200°C.« less

Authors:
 [1];  [2];  [3]
  1. Iowa State Univ., Ames, IA (United States)
  2. Ames Lab., and Iowa State Univ., Ames, IA (United States)
  3. Ames Lab., and Iowa State Univ., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
Publication Date:
Research Org.:
Kansas City Nuclear Security Campus (KCNSC), Kansas City, MO (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1812862
Report Number(s):
NSC-614-3700
DOE Contract Number:  
DE-NA0002839
Resource Type:
Conference
Resource Relation:
Conference: PowderMet 2021
Country of Publication:
United States
Language:
English

Citation Formats

Rinko, Emily, Deaton, Eric, and Anderson, Iver. Improvements to the Powder Processing of near-Final Shape alnico Magnets. United States: N. p., 2021. Web.
Rinko, Emily, Deaton, Eric, & Anderson, Iver. Improvements to the Powder Processing of near-Final Shape alnico Magnets. United States.
Rinko, Emily, Deaton, Eric, and Anderson, Iver. 2021. "Improvements to the Powder Processing of near-Final Shape alnico Magnets". United States. https://www.osti.gov/servlets/purl/1812862.
@article{osti_1812862,
title = {Improvements to the Powder Processing of near-Final Shape alnico Magnets},
author = {Rinko, Emily and Deaton, Eric and Anderson, Iver},
abstractNote = {Alnico permanent magnets (PMs), a recent PM system of interest as an attractive rare earth-free PM alternative, have advantageous high operating temperature and magnetic saturation with the potential for utilization in electric machines, e.g. interior-PM motors found in electric vehicles, if current directional solidification methods can be replaced by a true mass production approach. Recently, two unique alnico compositions, termed Full-Co and Co-lean, with improved coercivity, were gas atomized, compression molded, and vacuum sintered (4h at 1240°C) to high densities of 97.8% and 99.3%, respectively. However, the Co-lean remained fine grained isotropic magnets and the Full-Co grains were not textured, lowering magnetic strength in spite of attempts to grow large textured grains by a stress-biased solid state grain alignment method to convert them to high energy anisotropic magnets. It was hypothesized that oxidation during de-binding in air left many prior particle boundary oxides within the sintered microstructure that hindered grain growth and texturing during the stress-biased texturing procedure and prevented the desired abnormal grain growth (AGG). Here we explored a vacuum de-binding step that was linked (in-place) to vacuum sintering and found that the Co-lean exhibited faster uniform grain growth that doubled the average grain size (40 μm to 80 μm). Linked vacuum de-binding and sintering of Full-Co produced some AGG after only 1 h of 1240°C sintering. A new direction for promoting AGG (and stress-biased texturing) in alnico is being explored that utilizes a fundamental analysis of systems with second phase particles that either inhibit or boost grain growth. This effort explores the influence of vacuum de-binding linked to a series of lower sintering temperatures at a fixed time (4h) to see if oxide particle size and volume fraction can be changed to promote AGG conditions in alnico. Surprising qualitative results indicate that AGG may be promoted for vacuum sintering at less than 1200°C.},
doi = {},
url = {https://www.osti.gov/biblio/1812862}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2021},
month = {10}
}

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