Melt-spun Nd-Fe-B magnets and the Nd/sub 1+//sub epsilon/Fe/sub 4/B/sub 4/ phase

Journal Article · Tue Nov 15 00:00:00 EST 1988 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.342308· OSTI ID:6746925

Mishra, R K

The microstructure of Nd-Fe-B magnets made from melt-spun ribbons differs significantly from that of the sintered magnets. An ideal two-phase microstructure of small Nd/sub 2/Fe/sub 14/B grains surrounded by a Nd-rich intergranular phase is easily achieved in the melt-spun magnets while sintered magnets invariably contain the boron-rich Nd/sub 1.1/Fe/sub 4/B/sub 4/ phase. This phase can form in the melt-spun alloys only when the cooling rates are slow and excess Nd and B are added deliberately. In those cases, this new phase appears as randomly distributed and randomly oriented grains of the same size as the Nd/sub 2/Fe/sub 14/B grains. The Nd/sub 1.1/Fe/sub 4/B/sub 4/ grains are highly faulted in the Fe sublattice with their fault planes parallel to the (110) plane. Energy dispersive x-ray analysis and diffraction shows that this phase forms with varying Nd:Fe ratios in different grains. We have also found that the faults form in pure bulk samples of Nd/sub 1.1/Fe/sub 4/B/sub 4/ but not in pure NdCo/sub 4/B/sub 4/ samples. Possible antiphase boundaries arising from modulated Fe sublattice are seen. The faulted microstructure is believed to result from (a) sluggish kinetics of formation of this phase, (b) incommensurate crystal structure, and (c) weak bonding between the Nd chains and chains of Fe-B tetrahedra that make up the structure. Lorentz microscopy shows this phase to act as a weak barrier to domain wall motion.

• Research Organization: Physics Department, General Motors Research Laboratories, Warren, Michigan 48090-9055
• OSTI ID: 6746925
• Journal Information: J. Appl. Phys.; (United States), Vol. 64:10
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
IRON BORIDES
PHASE DIAGRAMS
SOLIDIFICATION
NEODYMIUM BORIDES
PERMANENT MAGNETS
FABRICATION
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DOMAIN STRUCTURE
GRAIN ORIENTATION
MAGNETIZATION
BORIDES
BORON COMPOUNDS
DIAGRAMS
IRON COMPOUNDS
MAGNETS
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PHASE TRANSFORMATIONS
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360202* - Ceramics
Cermets
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