Enhancing the coercivity of Nd-Fe-B sintered magnets by consecutive heat treatment–induced formation of Tb-diffused microstructures

Sumin Kim, Dong Su Ko, Hyun Sook Lee, Donghwan Kim, Jong Wook Roh, Wooyoung Lee

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Herein, we probed the microstructure of Tb-diffused Nd-Fe-B magnets to investigate the relationship between Tb-diffused area and coercivity enhancement, employing prolonged stepwise heat treatment to ensure sufficient diffusion of Tb in relatively large-size magnets and revealing that this stepwise annealing generated core-shell structures. Quantitative compositional changes pertaining to individual phases of the multiphase system in each heat treatment process were analyzed by constructing ternary diagrams based on electron probe microanalysis compositional maps. During the grain boundary diffusion process, coercivity increased from 15.28 to 24.86 kOe, while only negligible remanence and energy product decreases were concomitantly observed. Microstructure analysis suggested that coercivity was closely related to the concentration and distribution of Tb; more precisely, the abovementioned core-shell structures successfully suppressed the nucleation of reverse domains at Nd-rich phase/main phase interfaces and therefore enhanced magnet coercivity without decreasing remanence and energy product.

Original languageEnglish
Pages (from-to)574-580
Number of pages7
JournalJournal of Alloys and Compounds
Volume780
DOIs
Publication statusPublished - 2019 Apr 5

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Coercive force
Magnets
Microstructure
Remanence
Heat treatment
Phase interfaces
Electron probe microanalysis
Grain boundaries
Nucleation
Annealing
Hot Temperature

All Science Journal Classification (ASJC) codes

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

Cite this

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title = "Enhancing the coercivity of Nd-Fe-B sintered magnets by consecutive heat treatment–induced formation of Tb-diffused microstructures",
abstract = "Herein, we probed the microstructure of Tb-diffused Nd-Fe-B magnets to investigate the relationship between Tb-diffused area and coercivity enhancement, employing prolonged stepwise heat treatment to ensure sufficient diffusion of Tb in relatively large-size magnets and revealing that this stepwise annealing generated core-shell structures. Quantitative compositional changes pertaining to individual phases of the multiphase system in each heat treatment process were analyzed by constructing ternary diagrams based on electron probe microanalysis compositional maps. During the grain boundary diffusion process, coercivity increased from 15.28 to 24.86 kOe, while only negligible remanence and energy product decreases were concomitantly observed. Microstructure analysis suggested that coercivity was closely related to the concentration and distribution of Tb; more precisely, the abovementioned core-shell structures successfully suppressed the nucleation of reverse domains at Nd-rich phase/main phase interfaces and therefore enhanced magnet coercivity without decreasing remanence and energy product.",
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Enhancing the coercivity of Nd-Fe-B sintered magnets by consecutive heat treatment–induced formation of Tb-diffused microstructures. / Kim, Sumin; Ko, Dong Su; Lee, Hyun Sook; Kim, Donghwan; Roh, Jong Wook; Lee, Wooyoung.

In: Journal of Alloys and Compounds, Vol. 780, 05.04.2019, p. 574-580.

Research output: Contribution to journalArticle

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AU - Kim, Sumin

AU - Ko, Dong Su

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AU - Roh, Jong Wook

AU - Lee, Wooyoung

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AB - Herein, we probed the microstructure of Tb-diffused Nd-Fe-B magnets to investigate the relationship between Tb-diffused area and coercivity enhancement, employing prolonged stepwise heat treatment to ensure sufficient diffusion of Tb in relatively large-size magnets and revealing that this stepwise annealing generated core-shell structures. Quantitative compositional changes pertaining to individual phases of the multiphase system in each heat treatment process were analyzed by constructing ternary diagrams based on electron probe microanalysis compositional maps. During the grain boundary diffusion process, coercivity increased from 15.28 to 24.86 kOe, while only negligible remanence and energy product decreases were concomitantly observed. Microstructure analysis suggested that coercivity was closely related to the concentration and distribution of Tb; more precisely, the abovementioned core-shell structures successfully suppressed the nucleation of reverse domains at Nd-rich phase/main phase interfaces and therefore enhanced magnet coercivity without decreasing remanence and energy product.

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