A study on the Nd-rich phase evolution in the Nd-Fe-B sintered magnet and its mechanism during post-sintering annealing

Tae Hoon Kim, Seong Rae Lee, Seok Namkumg, Tae Suk Jang

Research output: Contribution to journalArticle

56 Citations (Scopus)

Abstract

We investigated the microstructural evolution and the phase transformation of the RE-rich (Nd-Dy-O) phase, the Cu-rich (Nd-Cu-Co-O) triple junction phase (TJP), the mixed TJP, and their grain boundary phase (GBP) in the sintered Nd-Fe-B base magnet as a function of the post-sintering annealing (PSA) steps. The round-shaped RE-rich phase and triangular-shaped Cu-rich TJP have an fcc-NdO (a = 0.499 nm) type structure in the as-sintered state. These phases are gradually transformed into the hexagonal Nd 2O 3 (h-Nd 2O 3, a = 0.383 and c = 0.600 nm) type structure during the 1st and 2nd PSA steps. The Cu-enriched TJP, which contains a large amount of Cu (about 40 at.%), was transformed into the cubic Nd 2O 3 (C-Nd 2O 3, a = 1.108 nm) type structure after the 2nd PSA, suggesting that Cu-enrichment could be a trigger for the formation of the meta-stable C-Nd 2O 3 phase. The h-Nd 2O 3 GBP, formed from the Cu-rich phase and the mixed TJP in the as-sintered magnet, was also transformed into Cu-enriched C-Nd 2O 3, which is embedded in the amorphous matrix, during the 2nd PSA. The formation of the C-Nd 2O 3 TJP and the GBP after the 2nd PSA is the major factor involved in enhancing the coercivity (from 21.7 to 29.7 kOe). The mechanism of the phase evolution and the coercivity enhancement is discussed based on these results.

Original languageEnglish
Pages (from-to)261-268
Number of pages8
JournalJournal of Alloys and Compounds
Volume537
DOIs
Publication statusPublished - 2012 Oct 5

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Magnets
Sintering
Annealing
Grain boundaries
Coercive force
Microstructural evolution
Phase transitions

Keywords

  • Magnetization
  • Microstructure
  • Powder metallurgy
  • Rare-earth alloys and compounds
  • Transmission electron microscopy (TEM)

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Materials Chemistry
  • Metals and Alloys

Cite this

A study on the Nd-rich phase evolution in the Nd-Fe-B sintered magnet and its mechanism during post-sintering annealing. / Kim, Tae Hoon; Lee, Seong Rae; Namkumg, Seok; Jang, Tae Suk.

In: Journal of Alloys and Compounds, Vol. 537, 05.10.2012, p. 261-268.

Research output: Contribution to journalArticle

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abstract = "We investigated the microstructural evolution and the phase transformation of the RE-rich (Nd-Dy-O) phase, the Cu-rich (Nd-Cu-Co-O) triple junction phase (TJP), the mixed TJP, and their grain boundary phase (GBP) in the sintered Nd-Fe-B base magnet as a function of the post-sintering annealing (PSA) steps. The round-shaped RE-rich phase and triangular-shaped Cu-rich TJP have an fcc-NdO (a = 0.499 nm) type structure in the as-sintered state. These phases are gradually transformed into the hexagonal Nd 2O 3 (h-Nd 2O 3, a = 0.383 and c = 0.600 nm) type structure during the 1st and 2nd PSA steps. The Cu-enriched TJP, which contains a large amount of Cu (about 40 at.{\%}), was transformed into the cubic Nd 2O 3 (C-Nd 2O 3, a = 1.108 nm) type structure after the 2nd PSA, suggesting that Cu-enrichment could be a trigger for the formation of the meta-stable C-Nd 2O 3 phase. The h-Nd 2O 3 GBP, formed from the Cu-rich phase and the mixed TJP in the as-sintered magnet, was also transformed into Cu-enriched C-Nd 2O 3, which is embedded in the amorphous matrix, during the 2nd PSA. The formation of the C-Nd 2O 3 TJP and the GBP after the 2nd PSA is the major factor involved in enhancing the coercivity (from 21.7 to 29.7 kOe). The mechanism of the phase evolution and the coercivity enhancement is discussed based on these results.",
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T1 - A study on the Nd-rich phase evolution in the Nd-Fe-B sintered magnet and its mechanism during post-sintering annealing

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AU - Lee, Seong Rae

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AU - Jang, Tae Suk

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N2 - We investigated the microstructural evolution and the phase transformation of the RE-rich (Nd-Dy-O) phase, the Cu-rich (Nd-Cu-Co-O) triple junction phase (TJP), the mixed TJP, and their grain boundary phase (GBP) in the sintered Nd-Fe-B base magnet as a function of the post-sintering annealing (PSA) steps. The round-shaped RE-rich phase and triangular-shaped Cu-rich TJP have an fcc-NdO (a = 0.499 nm) type structure in the as-sintered state. These phases are gradually transformed into the hexagonal Nd 2O 3 (h-Nd 2O 3, a = 0.383 and c = 0.600 nm) type structure during the 1st and 2nd PSA steps. The Cu-enriched TJP, which contains a large amount of Cu (about 40 at.%), was transformed into the cubic Nd 2O 3 (C-Nd 2O 3, a = 1.108 nm) type structure after the 2nd PSA, suggesting that Cu-enrichment could be a trigger for the formation of the meta-stable C-Nd 2O 3 phase. The h-Nd 2O 3 GBP, formed from the Cu-rich phase and the mixed TJP in the as-sintered magnet, was also transformed into Cu-enriched C-Nd 2O 3, which is embedded in the amorphous matrix, during the 2nd PSA. The formation of the C-Nd 2O 3 TJP and the GBP after the 2nd PSA is the major factor involved in enhancing the coercivity (from 21.7 to 29.7 kOe). The mechanism of the phase evolution and the coercivity enhancement is discussed based on these results.

AB - We investigated the microstructural evolution and the phase transformation of the RE-rich (Nd-Dy-O) phase, the Cu-rich (Nd-Cu-Co-O) triple junction phase (TJP), the mixed TJP, and their grain boundary phase (GBP) in the sintered Nd-Fe-B base magnet as a function of the post-sintering annealing (PSA) steps. The round-shaped RE-rich phase and triangular-shaped Cu-rich TJP have an fcc-NdO (a = 0.499 nm) type structure in the as-sintered state. These phases are gradually transformed into the hexagonal Nd 2O 3 (h-Nd 2O 3, a = 0.383 and c = 0.600 nm) type structure during the 1st and 2nd PSA steps. The Cu-enriched TJP, which contains a large amount of Cu (about 40 at.%), was transformed into the cubic Nd 2O 3 (C-Nd 2O 3, a = 1.108 nm) type structure after the 2nd PSA, suggesting that Cu-enrichment could be a trigger for the formation of the meta-stable C-Nd 2O 3 phase. The h-Nd 2O 3 GBP, formed from the Cu-rich phase and the mixed TJP in the as-sintered magnet, was also transformed into Cu-enriched C-Nd 2O 3, which is embedded in the amorphous matrix, during the 2nd PSA. The formation of the C-Nd 2O 3 TJP and the GBP after the 2nd PSA is the major factor involved in enhancing the coercivity (from 21.7 to 29.7 kOe). The mechanism of the phase evolution and the coercivity enhancement is discussed based on these results.

KW - Magnetization

KW - Microstructure

KW - Powder metallurgy

KW - Rare-earth alloys and compounds

KW - Transmission electron microscopy (TEM)

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