Magnetic and mechanical properties of grain-refined Dy-free Nd-Fe-B sintered magnets

Journal Article · Tue Nov 10 00:00:00 EST 2020 · Journal of Magnetism and Magnetic Materials

DOI:https://doi.org/10.1016/j.jmmm.2020.167533· OSTI ID:1722887

Tang, Wei ^[1]; Ouyang, Gaoyuan ^[1]; Cui, Baozhi ^[1]; Wang, Jing ^[1]; Dennis, Kevin W. ^[1]; Kramer, Matthew J. ^[1]; Anderson, Iver E. ^[1]; Cui, Jun ^[2]

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1. Ames Lab., Ames, IA (United States)
2. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)

In this work, the effects of grain size on magnetic and mechanical properties of Dy-free Nd-Fe-B sintered magnets were studied. The grain size of the sintered magnets was varied by using different sized Dy-free Nd-Fe-B alloy feedstock powders which were ball milled to different extents. Increasing the ball milling time from 7 to 11 h caused the average particle size of the powders to decrease from 3.6 to 2.1 µm, while the average grain size of the corresponding sintered magnets decreased from 5.0 to 4.0 µm. The intrinsic coercivity Hcj and maximum energy product (BH)_max of these magnets increased from 11.6 to 13.7 kOe and 41.6 to 43.6 MGOe, respectively. The finer grain magnets exhibited better thermal stability, as indicated by a smaller temperature coefficient of H_cj (-0.71%/°C). With extending ball milling time to 15 h, the magnetic properties of the magnets deteriorate, while the flexural strengths first decrease and then increase. The flexural strength improvement is attributed to the increased Oxygen content in the magnets due to finer grains. The coercivity enhancement by reduction of grain size is a promising approach to develop Dy-free Nd-Fe-B sintered magnets with better thermal stability. It is important to control the Oxygen contents in the magnets to compromise both magnetic and mechanical properties.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Vehicle Technologies Office
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1722887
• Alternate ID(s): OSTI ID: 1809543
• Report Number(s): IS--J-10,351
• Journal Information: Journal of Magnetism and Magnetic Materials, Journal Name: Journal of Magnetism and Magnetic Materials Vol. 521; ISSN 0304-8853
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Magnetic measurement
Mechanical properties
Permanent magnet
Powder metallurgy
Rare earth alloy and compounds
Sintering