Boundary structure modification and magnetic properties enhancement of Nd–Fe–B sintered magnets by diffusing (PrDy)–Cu alloy

doi:10.1016/j.scriptamat.2016.02.019

Scripta Materialia

Volume 117, May 2016, Pages 60-63

https://doi.org/10.1016/j.scriptamat.2016.02.019 Get rights and content

Abstract

The grain boundary diffusion process was applied to the commercial sintered Nd–Fe–B magnets using Pr₆₈Cu₃₂, Dy₇₀Cu₃₀ and Pr₃₅Dy₃₅Cu₃₀ ribbons as direct diffusion source. The coercivities increased from 1114.4 kA/m for the original magnet to 1642.8 kA/m for the processed magnet by Pr₆₈Cu₃₂, higher than 1402.7 kA/m by Dy₇₀Cu₃₀. Microstructural investigations showed that the evident coercivity enhancement for the sample by Pr₆₈Cu₃₂ was mainly attributed to continuous intergranular layers isolating Nd₂Fe₁₄B grains. Nevertheless, the coercivity enhancement of the sample by Dy₇₀Cu₃₀ was mainly resulted from the magnetic strengthening of the extensive layers in Nd₂Fe₁₄B grains.

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Acknowledgment

This work was supported by National Natural Science Foundation of China (No. 51401021).

References (18)

H. Sepehri-Amin et al.
Acta Mater.
(2013)
Tae-Hoon Kim et al.
Acta Mater.
(2015)
W.Q. Liu et al.
J. Rare Earths
(January 2013)
C. Sun et al.
J. Mater. Sci. Technol.
(October 2012)
J.J. Ni et al.
J. Alloys Compd.
(2010)
N. Oono et al.
J. Magn. Magn. Mater.
(2011)
L.P. Liang et al.
J. Magn. Magn. Mater.
(2014)
H. Sepehri-Amin et al.
Scr. Mater.
(2010)
H. Sepehri-Amin et al.
Acta Mater.
(2013)

There are more references available in the full text version of this article.

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Boundary structure modification and magnetic properties enhancement of Nd–Fe–B sintered magnets by diffusing (PrDy)–Cu alloy

Abstract

Section snippets

Acknowledgment

Acta Mater.

Acta Mater.

J. Rare Earths

J. Mater. Sci. Technol.

J. Alloys Compd.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

Scr. Mater.

Acta Mater.