Dependence of magnetic, phase-transformation and microstructural characteristics on the Cu content of Nd-Fe-B sintered magnet

Tae Hoon Kim, Seong Rae Lee, Min Woo Lee, Tae Suk Jang, Jin Woo Kim, Young Do Kim, Hyo Jun Kim

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

We have investigated the changes in the magnetic, phase-transformation and microstructural properties of Nd-Fe-B sintered magnets as a function of Cu content (0.2-0.5 at.%). The coercivity decreased (28.7 → 27.1 kOe) with increasing Cu content without changing the remanence of the magnets under the normal post-sintering annealing (PSA) conditions. Phase-transformation temperature changes of the magnet were observed as the Cu content of the magnet was increased. In the 0.2 at.% Cu magnet, the triple junction phase (TJP) and grain boundary phase (GBP), composed of the Cu-enriched C-Nd2O 3 phase, were formed. However, in the 0.5 at.% Cu magnet, the TJP and GBP were composed of the h-Nd2O3 phase. By considering the dependence of Cu content on the phase transformation, we have modified the 1st-PSA temperature to recover the coercivity. Through our newly established PSA conditions, the TJP and GBP in the 0.5 at.% Cu magnet were formed as the C-Nd2O3 phase. As a result, the coercivity of the magnet was noticeably enhanced (27.1 → 29.4 kOe). The reasons for the coercivity deterioration in the high-Cu-content magnet were clarified. The detailed mechanism of the microstructural and magnetic property improvements induced by the modified 1st-PSA condition is discussed. The critical role of Cu in the microstructural changes of Nd-rich TJP and GBP during the PSA is also analyzed based on these results.

Original languageEnglish
Pages (from-to)12-21
Number of pages10
JournalActa Materialia
Volume66
DOIs
Publication statusPublished - 2014 Mar 1

Fingerprint

Magnets
Phase transitions
Phase boundaries
Coercive force
Sintering
Annealing
Grain boundaries
Remanence
Deterioration
Magnetic properties
Temperature

Keywords

  • Cu content
  • Nd-Fe-B sintered magnets
  • Nd-rich phase
  • Phase-transformation temperature
  • Post-sintering annealing

ASJC Scopus subject areas

  • Ceramics and Composites
  • Metals and Alloys
  • Polymers and Plastics
  • Electronic, Optical and Magnetic Materials

Cite this

Dependence of magnetic, phase-transformation and microstructural characteristics on the Cu content of Nd-Fe-B sintered magnet. / Kim, Tae Hoon; Lee, Seong Rae; Lee, Min Woo; Jang, Tae Suk; Kim, Jin Woo; Kim, Young Do; Kim, Hyo Jun.

In: Acta Materialia, Vol. 66, 01.03.2014, p. 12-21.

Research output: Contribution to journalArticle

Kim, Tae Hoon ; Lee, Seong Rae ; Lee, Min Woo ; Jang, Tae Suk ; Kim, Jin Woo ; Kim, Young Do ; Kim, Hyo Jun. / Dependence of magnetic, phase-transformation and microstructural characteristics on the Cu content of Nd-Fe-B sintered magnet. In: Acta Materialia. 2014 ; Vol. 66. pp. 12-21.
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AU - Kim, Young Do

AU - Kim, Hyo Jun

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AB - We have investigated the changes in the magnetic, phase-transformation and microstructural properties of Nd-Fe-B sintered magnets as a function of Cu content (0.2-0.5 at.%). The coercivity decreased (28.7 → 27.1 kOe) with increasing Cu content without changing the remanence of the magnets under the normal post-sintering annealing (PSA) conditions. Phase-transformation temperature changes of the magnet were observed as the Cu content of the magnet was increased. In the 0.2 at.% Cu magnet, the triple junction phase (TJP) and grain boundary phase (GBP), composed of the Cu-enriched C-Nd2O 3 phase, were formed. However, in the 0.5 at.% Cu magnet, the TJP and GBP were composed of the h-Nd2O3 phase. By considering the dependence of Cu content on the phase transformation, we have modified the 1st-PSA temperature to recover the coercivity. Through our newly established PSA conditions, the TJP and GBP in the 0.5 at.% Cu magnet were formed as the C-Nd2O3 phase. As a result, the coercivity of the magnet was noticeably enhanced (27.1 → 29.4 kOe). The reasons for the coercivity deterioration in the high-Cu-content magnet were clarified. The detailed mechanism of the microstructural and magnetic property improvements induced by the modified 1st-PSA condition is discussed. The critical role of Cu in the microstructural changes of Nd-rich TJP and GBP during the PSA is also analyzed based on these results.

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