Coercivity enhancement of hot-deformed Nd-Fe-B magnets by the eutectic grain boundary diffusion process

Lihua Liu; H. Sepehri-Amin; T. Ohkubo; M. Yano; A. Kato; T. Shoji; K. Hono

doi:10.1016/j.jallcom.2015.12.227

Coercivity enhancement of hot-deformed Nd-Fe-B magnets by the eutectic grain boundary diffusion process

Lihua Liu, H. Sepehri-Amin, T. Ohkubo, M. Yano, A. Kato, T. Shoji, K. Hono

Research output: Contribution to journal › Article

43 Citations (Scopus)

Abstract

Nd-M (M = Al, Cu, Ga, Zn, Mn) alloys with compositions close to eutectic points were investigated as diffusion sources for the grain boundary diffusion process to hot-deformed Nd-Fe-B magnets. Coercivity enhancement was observed for most of the alloys. Among them, the sample processed with Nd₉₀Al₁₀ exhibited the highest coercivity of 2.5 T at room temperature. However, the sample processed with Nd₇₀Cu₃₀ exhibited the highest coercivity of 0.7 T at 200 ^°C. Microstructural observations using scanning transmission electron microscope (STEM) showed that nonferromagnetic Nd-rich intergranular phase envelops the Nd₂Fe₁₄B grains after the diffusion process. Abnormal grain growth and the dissolution of Al into the Nd₂Fe₁₄B grains were observed in the sample processed with Nd₉₀Al₁₀, which explains its inferior thermal stability of coercivity compared to the sample processed with Nd₇₀Cu₃₀. The coercivity enhancement and poor thermal stability of the coercivity of the Nd₉₀Al₁₀ diffusion-processed sample are discussed based on microstructure studies by transmission electron microscopy.

Original language	English
Pages (from-to)	432-439
Number of pages	8
Journal	Journal of Alloys and Compounds
Volume	666
DOIs	https://doi.org/10.1016/j.jallcom.2015.12.227
Publication status	Published - 2016 May 5
Externally published	Yes

Keywords

Coercivity
Diffusion process
Grain boundary phase
Nd-Fe-B
Permanent magnets

ASJC Scopus subject areas

Mechanics of Materials
Mechanical Engineering
Metals and Alloys
Materials Chemistry

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Liu, L., Sepehri-Amin, H., Ohkubo, T., Yano, M., Kato, A., Shoji, T., & Hono, K. (2016). Coercivity enhancement of hot-deformed Nd-Fe-B magnets by the eutectic grain boundary diffusion process. Journal of Alloys and Compounds, 666, 432-439. https://doi.org/10.1016/j.jallcom.2015.12.227

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abstract = "Nd-M (M = Al, Cu, Ga, Zn, Mn) alloys with compositions close to eutectic points were investigated as diffusion sources for the grain boundary diffusion process to hot-deformed Nd-Fe-B magnets. Coercivity enhancement was observed for most of the alloys. Among them, the sample processed with Nd90Al10 exhibited the highest coercivity of 2.5 T at room temperature. However, the sample processed with Nd70Cu30 exhibited the highest coercivity of 0.7 T at 200 °C. Microstructural observations using scanning transmission electron microscope (STEM) showed that nonferromagnetic Nd-rich intergranular phase envelops the Nd2Fe14B grains after the diffusion process. Abnormal grain growth and the dissolution of Al into the Nd2Fe14B grains were observed in the sample processed with Nd90Al10, which explains its inferior thermal stability of coercivity compared to the sample processed with Nd70Cu30. The coercivity enhancement and poor thermal stability of the coercivity of the Nd90Al10 diffusion-processed sample are discussed based on microstructure studies by transmission electron microscopy.",

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author = "Lihua Liu and H. Sepehri-Amin and T. Ohkubo and M. Yano and A. Kato and T. Shoji and K. Hono",

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AU - Liu, Lihua

AU - Sepehri-Amin, H.

AU - Ohkubo, T.

AU - Yano, M.

AU - Kato, A.

AU - Shoji, T.

AU - Hono, K.

PY - 2016/5/5

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N2 - Nd-M (M = Al, Cu, Ga, Zn, Mn) alloys with compositions close to eutectic points were investigated as diffusion sources for the grain boundary diffusion process to hot-deformed Nd-Fe-B magnets. Coercivity enhancement was observed for most of the alloys. Among them, the sample processed with Nd90Al10 exhibited the highest coercivity of 2.5 T at room temperature. However, the sample processed with Nd70Cu30 exhibited the highest coercivity of 0.7 T at 200 °C. Microstructural observations using scanning transmission electron microscope (STEM) showed that nonferromagnetic Nd-rich intergranular phase envelops the Nd2Fe14B grains after the diffusion process. Abnormal grain growth and the dissolution of Al into the Nd2Fe14B grains were observed in the sample processed with Nd90Al10, which explains its inferior thermal stability of coercivity compared to the sample processed with Nd70Cu30. The coercivity enhancement and poor thermal stability of the coercivity of the Nd90Al10 diffusion-processed sample are discussed based on microstructure studies by transmission electron microscopy.

AB - Nd-M (M = Al, Cu, Ga, Zn, Mn) alloys with compositions close to eutectic points were investigated as diffusion sources for the grain boundary diffusion process to hot-deformed Nd-Fe-B magnets. Coercivity enhancement was observed for most of the alloys. Among them, the sample processed with Nd90Al10 exhibited the highest coercivity of 2.5 T at room temperature. However, the sample processed with Nd70Cu30 exhibited the highest coercivity of 0.7 T at 200 °C. Microstructural observations using scanning transmission electron microscope (STEM) showed that nonferromagnetic Nd-rich intergranular phase envelops the Nd2Fe14B grains after the diffusion process. Abnormal grain growth and the dissolution of Al into the Nd2Fe14B grains were observed in the sample processed with Nd90Al10, which explains its inferior thermal stability of coercivity compared to the sample processed with Nd70Cu30. The coercivity enhancement and poor thermal stability of the coercivity of the Nd90Al10 diffusion-processed sample are discussed based on microstructure studies by transmission electron microscopy.

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KW - Grain boundary phase

KW - Nd-Fe-B

KW - Permanent magnets

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