Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2001-09-14
2004-11-16
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C075S348000, C075S355000, C148S101000, C148S302000
Reexamination Certificate
active
06818041
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth magnetic alloy powder used for producing rare earth bonded magnets, sintered magnets, and other suitable magnets that can be applied to various types of motors and actuators, and a permanent magnet manufactured by using such a magnetic alloy powder.
A Nd—Fe—B rare earth magnetic alloy is mass-produced by an ingot casting method or a strip casting method in which a material molten alloy is cooled and solidified, thereby forming a structure including a Nd
2
Fe
14
B tetragonal phase as a primary phase.
In addition to the mass-production technique described above, another technique for producing powder of a Nd—Fe—B type rare earth magnetic alloy by a gas atomize method is disclosed in Japanese Patent Publication Nos. 5-18242, 5-53853, 5-59165, 7-110966, U.S. Pat. No. 4,585,473, for example.
The gas atomize method is a method in which a molten metal alloy is atomized in an inert atmospheric gas, causing free fall of liquid drops of the molten metal alloy so as to manufacture powder particles from the liquid drops of the molten metal alloy. In the gas atomize method, the liquid drops of the molten metal alloy are solidified during the free fall thereof, so that substantially spherical powder particles are produced by this method.
However, in the above-described prior art methods, the powder particles produced by the gas atomize method are only capable of exerting an insufficient coercive force. The reason why a coercive force of the magnetic powder is too low in this method is that a quenching speed required for finely crystallizing a metal alloy of general composition could not be sufficiently attained by the conventional gas atomize method.
In order to obtain a sufficient coercive force that is practically acceptable by using a gas atomize method, it is necessary to perform a process of more finely pulverizing the powder and a sintering process after the atomizing process, or to classify and selectively filter particle sizes of the magnetic powder so as to use only specific lower level particle sizes, which causes penalties in yield. Such additional processes eliminate the advantage of the atomize method that magnetic powder for producing the magnet can be obtained without any pulverizing process, and also causes an additional problem in that the yield is significantly lowered because of the required classification.
For the above-described reasons, the gas atomize method is not practically used as a large quantity production technique of Nd—Fe—B type rare earth magnetic alloy powder. Currently, after a Nd—Fe—B type rare earth magnetic alloy is produced by a melt spinning method, the alloy is pulverized, thereby producing fine powder.
In order to eliminate the disadvantage of the gas atomize method that the quenching speed is insufficient, a secondary atomize method in which liquid drops of molten metal is sprayed on to a cooling plate, is also performed such that the cooling is further accelerated by the cooling plate, as is described in Japanese Laid-Open Patent Publication No 1-8205. According to such a gas atomize method, magnetic powder having magnetic anisotropy can be obtained, and the quenching speed is sufficiently large, so that the structure of alloy is much finer, and the coercive force is increased. In this method, however, molten metal particles which are not completely cooled are strongly sprayed on to the cooling plate, so that there exists a problem in that the shape of the magnetic powder becomes compressed. The compression of the magnetic powder degrades the powder flowability, and significantly reduces the compaction efficiency, so as to greatly decrease the production yield in a press or compacting process and an injection process.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a magnetic alloy powder for a permanent magnet in which the particle shape of powder is prevented from being compressed and maintained to be spherical and the coercive force is greatly increased to a sufficient or more than sufficient level for practical use, and a method for producing the magnetic alloy powder, and provides a permanent magnet manufactured from the magnetic alloy powder for a permanent magnet.
A preferred embodiment of the present invention provides a magnetic alloy powder for a permanent magnet containing:
R of about 20 mass percent to about 40 mass percent (R is Y, or at least one type of rare earth element);
T of about 60 mass percent to about 79 mass percent (T is a transition metal including Fe as a primary component); and
Q of about 0.5 mass percent to about 2.0 mass percent (Q is an element including B (boron) and C (carbon)), wherein
the magnetic alloy powder is formed by an atomize method, the shape of particles of the powder being spherical,
the magnetic alloy powder includes a compound phase having Nd
2
Fe
14
B tetragonal system as a primary composition phase, and
a ratio of a content of C to a total content of B and C is within a range of about 0.05 to about 0.90.
In a preferred embodiment, one or more kinds of elements selected from a group consisting of Co, Ni, Mn, Cr, and Al are preferably substituted for part of Fe included in T.
In a preferred embodiment, one or more kinds of elements selected from a group consisting of Si, P, Cu, Sn, Ti, Zr, V, Nb, Mo, and Ga is preferably added to the magnetic alloy powder.
In a preferred embodiment, an intrinsic coercive force H
cJ
is approximately 400 kA/m or more.
Another preferred embodiment of the present invention provides a production method of magnetic alloy powder for a permanent magnet, wherein a molten alloy including R of about 20 mass percent to about 40 mass percent (R is Y, or at least one type of rare earth element); T of about 60 mass percent to about 79 mass percent (T is a transition metal including Fe as a primary component); and Q of about 0.5 mass percent to about 2.0 mass percent (Q is an element including B (boron) and C (carbon)) is atomized into a non-oxidizing atmosphere, thereby forming the powder.
In a preferred embodiment, a ratio of a content of C to a total content of B and C is preferably within a range of about 0.05 to about 0.90.
Preferably, the powder is spherical.
In a preferred embodiment, heat treatment at temperatures of about 500° C. to about 800° C. may be performed for the powder.
Alternatively, the permanent magnet of the present invention is manufactured from the magnetic alloy powder for a permanent magnet according to preferred embodiments described above.
Alternatively, the method for manufacturing a permanent magnet according to another preferred embodiment of the present invention includes the steps of:
preparing magnetic alloy powder for a permanent magnet produced by the production method of magnetic alloy powder according to one of preferred embodiments described above; and
manufacturing a permanent magnet from the magnetic alloy powder for a permanent magnet.
In another preferred embodiment of the present invention, in addition to the compound phase having the Nd
2
Fe
14
B tetragonal system, a second compound phase having a diffraction peak in a position in which lattice spacing d is about 0.295 nm to about 0.300 nm is provided, and a ratio of intensity of the diffraction peak of the second compound phase to a diffraction peak (lattice spacing is about 0.214 nm) with respect to a (410) plane of the compound phase having the Nd
2
Fe
14
B tetragonal system is approximately 10% or more.
Another preferred embodiment of the present invention provides a magnetic alloy powder for a permanent magnet containing:
R of about 20 mass percent to about 40 mass percent (R is Y, or at least one type of rare earth element);
T of about 60 mass percent to about 79 mass percent (T is a transition metal including Fe as a primary component); and
Q of about 0.5 mass percent to about 2.0 mass percent (Q is an element including B (boron), C (carbon), S (sulfur), P (phosphorus), and/or Si (silicon)), wherein
the magnetic alloy powder
Kaneko Yuji
Tomizawa Hiroyuki
Keating & Bennett LLP
Mai Ngoclan
Neomax Co., Ltd
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