Permanent magnets -- New microstructural aspects

Journal Article · Thu Nov 30 23:00:00 EST 1995 · Scripta Metallurgica et Materialia

DOI:https://doi.org/10.1016/0956-716X(95)00392-9· OSTI ID:131464

Fidler, J; Bernardi, J; Schrefl, T ^[1]

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1. TU Wien (Austria). Institut fuer Angewandte und Technische Physik

The influence of the microstructure on the hard magnetic properties of rare earth-iron based magnetic materials with outstanding coercivities and energy density products is surveyed. Nd{sub 2}Fe{sub 14}B based permanent magnets exhibit a complex multiphase microstructure. The grain size of the magnets strongly depends on the processing technique. If dopant and substituent elements are added to conventional magnets, the coercivity is mostly increased and the remanence slightly decreased. Substituent elements such as Dy or Co mainly change the magnetocrystalline anisotropy and Curie temperature of the hard magnetic Nd{sub 2}Fe{sub 14}B-phase. The systematical TEM-study shows that the dopants, because of their different effect on the microstructure, can be divided into two groups independently of the processing technique, each with similar microstructural features. Secondary phases in the form of precipitates or new intergranular phases are formed after the dotation. Both types of dopants partly increase the coercivity or improve corrosion resistance. If a combination of type 1 and type 2 dopant elements of Nd-Fe-B or (Nd,Dy)-(Fe,Co)-B magnets is chosen, the coercivity and corrosion resistance is considerably improved. Magnets of the type Nd-Fe-B:(Ga,Nb), Nd-Fe-B:(Cu,Nb), Nd-(Fe,Co)-B:(Al,Mo) and (Nd,Dy)-(Fe,Co)-B:(Al,V) were systematically investigated and were found to behave according to the microstructural predictions. Secondary, soft magnetic phases, such as {alpha}-Fe, play an important role in the new, composite type hard magnetic materials. The numerical, finite element comparison of the coercivity and remanence enhancement of nanocrystalline Nd{sub 2}Fe{sub 14}B and Sm{sub 2}Fe{sub 17}N{sub 2.7} isotropic magnets show that the dipolar and exchange interactions between the hard and soft magnetic grains control the exchange hardening.

• OSTI ID: 131464
• Journal Information: Scripta Metallurgica et Materialia, Journal Name: Scripta Metallurgica et Materialia Journal Issue: 10-11 Vol. 33; ISSN SCRMEX; ISSN 0956-716X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM
ANISOTROPY
COBALT
COERCIVE FORCE
COPPER
CURIE POINT
DOPED MATERIALS
DYSPROSIUM
FINITE ELEMENT METHOD
GALLIUM
GRAIN SIZE
IRON BORIDES
IRON NITRIDES
MAGNETIC PROPERTIES
MICROSTRUCTURE
MOLYBDENUM
NEODYMIUM BORIDES
NIOBIUM
PRECIPITATION
SAMARIUM NITRIDES
TRANSMISSION ELECTRON MICROSCOPY
VANADIUM