Metal treatment – Stock – Magnetic
Reexamination Certificate
2001-07-10
2003-03-04
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C148S302000, C148S101000
Reexamination Certificate
active
06527874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rare earth magnet and a method for manufacturing the same.
2. Discussion of Related Art
Conventionally, in the manufacture of R—Fe—B rare earth sintered magnets, it has been proposed to add Niobium (Nb) to an alloy material for the purpose of obtaining finer crystal grains in the sintered bodies and improving the heat resistance of the magnets. Nb is known to suppress crystal grains from becoming coarse during sintering and to improve the magnetization properties of the magnet.
Japanese Laid-Open Patent Publication No. 7-94311 discloses a technique for improving the magnetic properties and the heat resistance of Nd—Fe—Co—B sintered magnets by adding 0.1 to 2.0 wt % of Nb.
Japanese Patent Publication for Opposition No. 6-69003 discloses that the magnetic properties such as coercive force can be improved by adding 1 to 10 atom % (atomic percentage) of a metal element, for example Ti, Zr, Hf, Nb, in the production of rare earth magnet alloys by a quenching method.
The above conventional techniques have the following problems. In the technique disclosed in Japanese Laid-Open Patent Publication No. 7-94311, the alloy is produced by ingot casting. Therefore, the cooling rate of the alloy melt is low. At such a low cooling rate, a nonmagnetic boride such as NbFeB
2
tends to be produced in a coarse grain state. If such coarse nonmagnetic boride is produced, the resultant rare earth magnet is hardened after sintering. This greatly deteriorates the efficiency of subsequent machining of the magnet, such as by cutting and surface polishing.
In the technique disclosed in Japanese Patent Publication for Opposition No. 6-69003, a large amount of the Nb metal, is added which also results in a nonmagnetic boride, such as NbFeB
2
, being produced. As a result, the remanence or residual flux density B
r
of the rare earth magnet decreases after sintering, and the processing efficiency of the magnet deteriorates.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide a rare earth magnet superior in terms of both permanent magnetic properties and processability, and to provide a method for manufacturing such a rare earth magnet.
The rapidly solidified alloy of the present invention has a general formula represented by (Fe
1-m
T
m
)
100-x-y-z
Q
x
R
y
M
z
where T denotes at least one element selected from the group consisting of Co and Ni, Q denotes at least one element selected from the group consisting of B and C, R denotes at least one rare earth element, and M denotes at least one kind of element selected from the group consisting of Nb and Mo, and the mole fractions x, y, z, and m respectively satisfy 2≦x≦28 (atom %), 8≦y≦30 (atom %), 0.1≦z<1.0 (atom %), and 0≦m≦0.5 (atom %).
Preferably, the cooling rate at which the alloy material melt is quenched is in the range of 10
2
K/sec to 10
4
K/sec in order to rapidly solidify the alloy.
In a preferred embodiment, Niobium is present as an essential element.
In another preferred embodiment, the alloy includes an R
2
F
14
B compound in which the crystal grains have a minor-axis size in a range between 0.1 &mgr;m and 100 &mgr;m, a major-axis size in a range between 5 &mgr;m and 500 &mgr;m; and an R-rich phase dispersed at the grain boundaries of the crystal grains, the alloy has a thickness in a range between 0.03 mm and 10 mm.
The rare earth magnet of the present invention is then manufactured from any of the rapidly solidified alloys described above.
Additionally, the rare earth magnet of the present invention is manufactured from a rapidly solidified alloy to which Nb and/or Mo have been added in an amount in a range between 0.1 atom % and 1.0 atom %.
The method for manufacturing a rare earth magnet of the present invention includes the steps of:
producing a rapidly solidified alloy by quenching and solidifying a melt of an alloy having a general formula represented by (Fe
1-m
T
m
)
100-x-y-z
Q
x
R
y
M
z
where T denotes at least one kind of element selected from the group consisting of Co and Ni, Q denotes at least one kind of element selected from the group consisting of B and C, R denotes at least one kind of rare earth element, and M denotes at least one kind of element selected from the group consisting of Nb and Mo, and the mole fractions x, y, z, and the mole fractions x, y, z, and m respectively satisfy 2≦x≦28 (atom %), 8≦y≦30 (atom %), 0.1≦z<1.0 (atom %), and 0≦m≦0.5 (atom %); and
manufacturing a permanent magnet from the rapidly solidified alloy.
Preferably, in the step of producing a rapidly solidified alloy, the cooling rate is in a range between 10
2
K/sec to 10
4
K/sec.
In another preferred embodiment, the step of producing a rapidly solidified alloy is performed by strip casting a melt of the alloy.
In still another preferred embodiment, the method further includes the step of embrittling the rapidly solidified alloy by allowing the rapidly solidified alloy to occlude hydrogen and then release the hydrogen.
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Hamano et al. “Magnetic Properties of Amorphous-Phase Remaining alphaFe/NdFeB Nanocomposite”, Rare Earth Magnets and Their Applications, vol. 1, Proceedings of the Fifteenth International Rare Earth magnets and Their Applications, Aug. 30-Sep. 3, 1998, pp. 199-204.
Nixon & Peabody LLP
Sheehan John
Sumitomo Special Metals Co. Ltd.
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