INFLUENCE OF Bi-ADDITIONS ON THE MAGNETIC AND MICROSTRUCTURAL PROPERTIES OF (Nd, Dy)-Fe-Al-B MAGNETS

1993 ◽  
Vol 07 (01n03) ◽  
pp. 725-728
Author(s):  
P. SCHREY ◽  
M. VELICESCU

Powder metallurgical additions of Bi enhance the temperature stability of (Nd, Dy)-Fe-B permanent magnets. Bi is not solved in the hardmagnetic RE2Fe14B phase, thus does not influence the intrinsic magnetic properties, Only the microstructure of the sintered magnets is changed. Addition of a few wt.% of Bi leads to the formation of a new ternary intergranular phase with the composition Nd6Fe13Bi. This phase substitutes partially the intergranular Nd-rich phase providing the magnetic insulation of hardmagnetic grains. An enhancement of HCJ by about 40% was reached at 150 ºC for a Nd15.5Dy1.5Fe74AlB8 magnet containing 2.5 wt.% Bi compared to the Bi-free material.

1987 ◽  
Vol 96 ◽  
Author(s):  
J. K. Chen ◽  
G. Thomas

ABSTRACTA microstructural and microanalytical study of aluminum substituted Nd-Fe-B sintered permanent magnets were carried out to determine the effect, if any, of aluminum on structure, composition, and magnetic properties, particularly on the observed increase in coercivity. It was found that Al enrichment occurred in the Nd-rich phase at the grain boundaries. The possible role(s) of this enrichment on the observed coercivity increase are discussed.


2008 ◽  
Vol 591-593 ◽  
pp. 96-101
Author(s):  
J.D. Angelo ◽  
C.C. Motta ◽  
Luzinete Pereira Barbosa ◽  
Hidetoshi Takiishi ◽  
Isolda Costa ◽  
...  

The hydrogenation decrepitation process was employed to produce sintered magnets using a mixture of two alloys. The effect of niobium and boron content on the magnetic properties of Pr14FebalCo16BxNby-type sintered magnets was studied. Niobium and boron have a significant effect on the magnetic behavior of these permanent magnets. The optimum amount of boron was 6 at% and niobium should be kept below to 0.50 at%. The squareness factor (0.90) has been improved considerably and good overall magnetic properties (Br=1320 mT, iHc=700 kAm-1 and (BH)max=315 kJm-3) have been achieved for the sintered magnets prepared from the Pr14Fe63.85Co16B6Nb0.15 alloy.


1999 ◽  
Vol 577 ◽  
Author(s):  
S. Hirosawa ◽  
H. Kanekiyo ◽  
Y. Shigemoto

ABSTRACTRecent progresses of materials development and their utilization of Cr-and-Co-doped Fe3B/Nd2Fe14B-type nanocomposite permanent magnets are reported. A practical balance between enhanced intrinsic coercivity and temperature stability of magnetic properties has been realized by simultaneous additions of Cr and Co. This type of magnets are less susceptible to oxidation because of the less rare-earth content. Consequently, even fine powders (e. g., under 38 micrometer sieve) are physically and chemically stable in contrast to the conventional Nd2Fe14B-type melt-spun materials. The stability in terms of the structural losses is also superior to that of the Nd2Fe14B-type melt-spun materials. Utilization of the Cr-and-Co-doped Fe3B/Nd2Fe14B nanocomposite permanent magnets as a hard magnetic component of injection-molded resin-bonded magnets seems promising because of the excellent stability of the magnetic properties of fine powders. Direct quenching of a melt into the nanocomposite structure has become possible recently in addition to the conventional processing route of crystallization of an amorphous precursor, opening up the possibility of less-expensive production of the material.


2008 ◽  
Vol 591-593 ◽  
pp. 885-890 ◽  
Author(s):  
Eliner Affonso Ferreira ◽  
S.C. Silva ◽  
E.A. Périgo ◽  
Rubens Nunes de Faria Jr. ◽  
Hidetoshi Takiishi

Sintered magnets have been produced with powder obtained using the hydrogenation, disproportionation, desorption and recombination process (HDDR). The new processing procedure for the production of the sintered magnets has been adopted in an attempt to reduce the milling time. Commercial cast ingot alloys based on the compositions Pr14Fe75.9Co4B6Nb0.1 and Pr20.5FebalB5Cu2.0 have been employed in this investigation. The HDDR powder was used to produce sintered magnets using a mixture of these alloys, in very distinct proportions. Only a small amount (20 wt. %) of the copper-containing alloy has been added as a sintering aid. Standard hydrogen decrepitation (HD) magnets have also been included in this work for a comparison. The effect of a reduced milling time on the magnetic properties of the HDDR sintered magnets has been investigated. Sintering temperature and time of were kept constant for all magnets (1050°C for 60 minutes). The microstructures of the permanent magnets have been investigated by scanning electron microscopy and energy dispersive X-ray analysis.


1997 ◽  
Vol 12 (10) ◽  
pp. 2715-2718 ◽  
Author(s):  
W. Kaszuwara ◽  
M. Leonowicz ◽  
H. A. Davies

The magnetic properties and crystallographic alignment for Fe–Nd–B–Al magnets having different Nd contents were studied. It was found that higher Nd concentration (above 18 at. %) resulted in deterioration of the alignment. Also, extended ball milling of the powder particles resulted in poorer alignment of the grains in the final sintered magnet. This behavior was attributed to the cold welding of the small particles of the Fe14Nd2B phase by a mechanically soft Nd-rich phase in the course of ball milling.


1989 ◽  
Vol 4 (4) ◽  
pp. 806-814 ◽  
Author(s):  
J. Fidler ◽  
K. G. Knoch ◽  
H. Kronmüller ◽  
G. Schneider

The microstructure and the coercivity of sintered Nd20Fe(73.5-x)B6.5Alx (x = 0, 2.5) permanent magnets are influenced by the Al concentration. In Al-containing magnets we found a homogeneous distribution of Al in the hard magnetic phase and the occurrence of an intergranular Nd(Fe, Al)2, phase between the hard magnetic grains. Our analytical TEM study revealed that in “Al2O3-doped” magnets the crystal structure of the Nd-rich intergranular phase partly changes from fcc (a = 0.52 nm) to hep (a = 0.39 nm, c = 0.61 nm), whereas the content of iron simultaneously decreases from 5–10 at.% to 1.5–4 at.%. A platelet-shaped phase, embedded in the Nd-rich intergranular phase, was determined as a Nd5Fe2 (B, O)x, phase. The influence of the microstructure on the coercivity in Al-doped magnets is discussed.


1993 ◽  
Vol 07 (01n03) ◽  
pp. 721-724
Author(s):  
W. RODEWALD ◽  
P. SCHREY ◽  
B. WALL

Simultaneous additions of Co and Mo or V, respectively, to Nd-Dy-Fe-Al-B alloys improve the temperature stability of sintered magnets. The intrinsic coercivity at 150 ºC amounts to 9 kA/cm for magnets with a Dy-content of 3 at.%. Hence magnets with a load line, B/μoH=−2, may be operated at temperatures up to 200 ºC. The additions of Mo or of V result in the precipitation of a tetragonal Mo2FeB2 compound, a=0.58 nm, c=0.32 nm, or of a tetragonal V3–xFexB2 compound, x=0.2...1.2, within the (Nd, Dy)2(Fe, Co, A1)14B grains. The dimensions of the precipitates range from 10 to 600 nm. Besides Mo2FeB2- or V3–xFex+B2-grains, respectively, with dimensions up to 10 μm were observed within the Nd-rich constituents. The intrinsic coercivity, however, is determined by nucleation of reversed domains. The addition of Co results in a partial replacement of the Nd-Fe solid solution by the Nd3Co compound. Corrosion tests revealed, that the corrosion behaviour is not improved significantly and depends much more on the surface treatment.


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