JP2001068317A - Nd-Fe-B sintered magnet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Nd-Fe-B sintered magnet in which an eddy current generated inside a magnet is extremely effectively reduced, heat generation is suppressed, and sufficient magnetic properties are obtained, and its production. Provide a way. SOLUTION: A magnet layer 1 comprising a magnet main phase and a grain boundary phase.
And an insulator-containing layer 2 composed of a magnet main phase, a grain boundary phase, and an insulator phase, having a laminated structure in which the two end surfaces are alternately stacked in one direction such that the magnet layers 1 are provided. The volume content of the insulator phase in the content layer 2 is 30 to 90%,
The magnetization direction of the magnet layer 1 is parallel to the surfaces of the magnet layer 1 and the insulator-containing layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered Nd--Fe--B magnet used in an alternating magnetic field such as a magnet for a motor and a method for producing the same.

[0002]

2. Description of the Related Art Since Nd-Fe-B sintered magnets have high magnetic properties, they have been used in various fields including computer-related fields such as VCM and pickup, and medical fields such as MRI. . This Nd-Fe-B
The sintered magnet is manufactured by crushing a magnet alloy obtained by melting and casting, press-molding the magnet alloy in an applied magnetic field, and then sintering and aging. Its internal structure is composed of an Nd ₂ Fe ₁₄ B phase as a magnet main phase and an Nd-rich grain boundary phase, and often contains a B-rich compound.
The grain boundary phase has a function of expressing a coercive force and is an indispensable phase for performing liquid phase sintering. In addition, the internal structure often contains a rare-earth oxide which is an unavoidable product in production. However, if this content is high, the magnetic properties are deteriorated. The manufacturing process is devised to eliminate as much as possible.

[0003] In the Nd-Fe-B sintered magnet, a part of Nd is further substituted with another rare earth element such as Pr or Dy,
The magnetic properties can be improved as needed, such as by increasing the coercive force by adding Al, Ga, Cu, Mo, V, Nb and other additives. Therefore, Nd-F
The e-B sintered magnet can meet a wide range of needs, and is expanding its application range, for example, by replacing it with an inexpensive ferrite magnet or opening up a new application. Motors are also one of the promising markets for Nd-Fe-B sintered magnets. In order to improve efficiency in large motors as well as small motors,
The adoption of Nd-Fe-B sintered magnets is being actively studied. However, when the Nd-Fe-B sintered magnet is a metal material and has a low electric resistance, and is installed in an environment where the magnetic field fluctuates periodically like a motor, an eddy current generated inside the magnet is generated. Can no longer be ignored. That is, there is a problem in that heat generated by the eddy current causes a decrease in motor efficiency and the like.

[0004]

As a method of solving the problem of the eddy current, it is considered effective to increase the electric resistance of the magnet by some means. So N
For the purpose of increasing the electrical resistance of the d-Fe-B sintered magnet, oxide and fluoride powders are mixed with the magnet powder and press-molded, so that the oxides and fluorides are uniformly distributed in the magnet structure. A method of fine dispersion has been devised (see Japanese Patent Application Laid-Open No. 9-186010). However, when an effective amount of the powder is added to improve the electric resistance, the sinterability of the magnet itself is significantly reduced, and it is difficult to sufficiently increase the density. In addition, the presence of oxides and fluorides also lowers the magnetic properties of the magnet. Therefore, in a large motor or the like, a method of reducing the amount of generated heat by bonding several small magnet blocks is often adopted. However, in this method, a laminating step is further added, and the number of steps for processing each magnet block is increased in accordance with the number of divided magnets, so that the manufacturing cost is significantly increased. Then, the present invention, when the Nd-Fe-B sintered magnet is installed in a fluctuating magnetic field, extremely effectively reduces the eddy current generated inside the magnet, suppresses the heat generation of the magnet, It is another object of the present invention to provide an Nd—Fe—B sintered magnet having sufficient magnetic properties and a method for manufacturing the same.

[0005]

Means for Solving the Problems The present inventor has made various studies to solve the above-mentioned problems, and as a result, the structure of the Nd-Fe-B sintered magnet was changed to a laminated structure of a magnet layer and an insulator-containing layer.
In addition, it has been found that by making the magnetization direction of the magnet parallel to the plane of each of the layers, the eddy current generated inside the magnet is extremely effectively reduced, and sufficient magnetic characteristics can be obtained. . Further, the present inventor has set forth the above Nd-
As a method of manufacturing an Fe-B sintered magnet, a simple method of alternately pressing a magnet layer and an insulator-containing layer in an applied magnetic field was found, and various conditions were established to complete the present invention.
That is, the first present invention relates to a Nd—Fe—B sintered magnet in which a magnet layer composed of a magnet main phase and a grain boundary phase, and an insulator-containing layer composed of a magnet main phase, a grain boundary phase, and an insulator phase are provided. Are alternately stacked in one direction so that both end surfaces become magnet layers, the volume content of the insulator phase in the insulator-containing layer is 30 to 90%, and the magnetization of the magnet layer is Wherein the direction is parallel to the plane of each of the two layers.
It is a Fe-B sintered magnet. The second invention is an invention of a method for producing the Nd-Fe-B sintered magnet of the first invention, and in the method for producing a Nd-Fe-B sintered magnet, the pressing direction and the magnetic field direction are different. The Nd-Fe is characterized in that, in a vertical state, the Nd-Fe is characterized in that a magnet alloy powder forming the magnet layer and a mixture of the magnet alloy powder and the insulating powder forming the insulator containing layer are alternately press-formed in an applied magnetic field. This is a method for producing a -B sintered magnet.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. As described above, the Nd—Fe—B sintered magnet of the present invention includes a magnet layer composed of a magnet main phase and a grain boundary phase, and an insulator-containing layer composed of a magnet main phase, a grain boundary phase, and an insulator phase. Has a laminated structure alternately stacked in one direction so that both end faces become magnet layers, the volume content of the insulator phase in the insulator-containing layer is 30 to 90%, and the magnetization direction of the magnet layer is Are parallel to the planes of the two layers. 1 and 2 are cross-sectional views schematically showing the Nd—Fe—B sintered magnet of the present invention. FIG. 1 shows a case where the magnet layer 1 has two layers, and FIG. 2 shows a case where the magnet layer 1 has three layers. This is an example of the case. As shown in these figures, the Nd of the present invention
-The Fe-B sintered magnet has a structure in which the insulator-containing layer 2 is formed between the magnet layers 1, that is, the magnet layer 1 is formed on both end faces so that the magnet layer 1 and the insulator-containing layer 2 are combined. It has a laminated structure alternately stacked in the directions. In the same figure, the magnetization direction 3 of the magnet layer indicated by the arrow is parallel to the surfaces of the magnet layer 1 and the insulator-containing layer 2.

The insulator-containing layer 2 is manufactured so as to have a higher electric resistance than the magnet layer 1. By doing this,
Since the eddy current hardly flows between the upper and lower magnet layers 1 sandwiching the insulator-containing layer 2, when the present magnet is installed in a fluctuating magnetic field, the eddy currents of the magnet layers 1 partitioned by the insulator-containing layer 2 It will only occur internally. The eddy current loss greatly depends on the cross-sectional area perpendicular to the magnetization direction of the magnet,
The smaller the cross-sectional area, the smaller the generated Joule heat. Therefore, when the section in the magnetization direction of the magnet is divided by the insulator-containing layer 2 as in the present invention, the influence of the eddy current can be reduced according to the number of divisions.

The insulator-containing layer 2 is preferably thinner than the magnet layer 1, and the thicknesses of the magnet layer 1 and the insulator-containing layer 2 are preferably uniform. Although the effect of the insulator-containing layer 2 depends on the content of the insulator, a certain thickness is required to effectively exert the effect of the present invention. If the thickness of the insulator-containing layer 2 is too small, the conductivity between the magnet layers 1 does not decrease effectively. Conversely, if the thickness is too large, the effect on the residual magnetic flux density Br is large. Cracks are also likely to occur. Usually, the more finely divided the magnet layer 1 is, the more the eddy current is suppressed.
From the viewpoint of productivity, it is preferable to set the thickness so as to divide the whole into two to ten parts. In this range, the thickness of the insulator-containing layer 2 is preferably 1 μm to 1 mm, and particularly preferably 10 μm to 100 μm is preferred.

The internal structure of the magnet layer 1 is a conventional Nd-Fe
Same as -B magnet. That is, the magnet main phase
Nd_TwoFe₁₄B phase and generally called Nd rich phase
Particles having a composition of about Fe-3 to 20 at% Nd.
And Nd_{1 + ε}Fe_FourB_FourB B
The compound may contain a compound. Complete oxidation during the manufacturing process
Because it is difficult to control
Nd_TwoO_ThreeIs included at the same time, but from the viewpoint of magnetic properties,
Nd in the magnet layer 1_TwoO_ThreeThe abundance ratio should be as small as possible
No. Therefore, in the Nd—Fe—B magnet of the present invention, the magnet
Nd contained in layer 1_TwoO_ThreeThe amount is the weight of oxygen in the magnet layer 1
1.5% or less, especially 1% or less in terms of ratio
No. Nd_TwoO_ThreeIf the amount is set to 1.5% or less, it is contained in the magnet layer 1.
Nd _TwoO_ThreeThe volume ratio can be 15% or less,
If it is 1% or less, Nd_TwoO_ThreeReduce volume ratio to 10% or less
Can be

In order to enhance the magnetic properties of the Nd-Fe-B magnet, a part of Nd forming the magnet layer 1 is further substituted with another rare earth element containing Y, and a part of Fe is Al, Si, Ti, V, Cr, Mn, Co, Ni, C
u, Zn, Ga, Ge, Zr, Nb, Mo, In, S
n, Sb, Hf, Ta, W, Pt, Au, Hg, Pb,
It may be replaced with an element such as Bi. Further, a part of B may be replaced with C.

The internal structure of the insulator-containing layer 2 includes a dispersed granular insulator phase together with the magnet main phase and the Nd-rich grain boundary phase. This insulator phase needs to be able to stably exist together with the magnet main phase and the grain boundary phase in addition to having high electric resistance. Materials satisfying such requirements include rare earth elements (including Y), oxides, carbides or fluorides of elements selected from Mg and Ca, and boron nitride. In order to increase the electrical resistance of the insulator-containing layer 2, it is desirable that the ratio of the insulator phase is high. However, if the ratio is too high, the density will not be sufficiently increased during sintering and cracking will occur at the interface with the magnet layer. Occurs. Therefore, the insulator phase preferably contains 30 to 90% of the insulator-containing layer 2 by volume, more preferably 40 to 70%. In order to prevent cracking during sintering, the insulator phase is made of the insulator-containing layer 2.
It is preferable that the particles are uniformly dispersed as finely as possible.

In order to manufacture the Nd-Fe-B magnet of the present invention, the amount of the magnet alloy powder forming the magnet layer 1 is divided into the number of layers, and the magnet alloy powder is formed by a press forming apparatus as illustrated in FIG. The mixture of the magnet alloy powder and the insulator powder forming the insulator-containing layer 2 may be sandwiched between the presses by using a multi-stage pressing method in which press molding is performed sequentially. Thereby, the magnet layer 1
A Nd—Fe—B magnet in which the Nd—Fe—B magnet and the insulator-containing layer 2 are alternately stacked can be obtained. Also, by setting the press forming apparatus so that the magnetic field application direction 9 and the pressing direction 8 are perpendicular to each other, the magnetization direction of the magnet layer 1 is made parallel to the surfaces of the magnet layer 1 and the insulator-containing layer 2. Can be. Note that FIG.
Medium, 4 indicates an upper punch, 5 indicates a lower punch, 6 indicates a die, and 7 indicates an electromagnet.

As a method for forming the insulator-containing layer 2, various thin film forming methods such as a sputtering method, a vapor deposition method, a CVD method, a spray method, and a plating method may be used. However, in these methods, it is necessary to take out the molded body every one press and separately form an insulator-containing layer, and there is a problem that the process is complicated and lacks practicality. Therefore, in the present invention, a method of forming and pressing the magnet layer 1 and the insulator-containing layer 2 alternately is used. Since the insulator-containing layer 2 is a thin layer and has a small amount of powder filling at one time, it is difficult to form a layer having a uniform thickness by directly filling and molding. To solve this problem,
The insulator-containing layer 2 is also press-formed in a magnetic field. Since the magnet alloy powder mixed with the insulator powder is ferromagnetic, if pressed in a uniform magnetic field, these magnet alloy powders will be uniformly distributed, and this effect will also cause the insulator powder to be formed to a uniform thickness. can do. That is,
The application of a magnetic field during molding is performed for the purpose of orienting the magnet powder in the magnet layer 1 and for achieving uniformity of the layer thickness in the insulator-containing layer 2.

In order to improve the sintering resistance of the Nd—Fe—B magnet, it is effective to increase the composition ratio of the Nd-rich grain boundary phase in the insulator-containing layer 2. For that purpose, the Nd composition ratio of the magnet alloy powder mixed with the insulator powder to form the insulator containing layer 2 is made higher than the Nd composition ratio of the magnet alloy powder used to form the magnet layer 1. The composition ratio of Nd in the portion excluding the insulator phase from the insulator-containing layer 2 may be higher than the composition ratio of Nd in the magnet layer 1.

[0015]

EXAMPLES Hereinafter, embodiments of the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 12 Fe-15 at% Nd
After roughly pulverizing a magnet alloy having a composition of -7 at% B, jet
Magnet alloy powder A for forming a magnet layer by pulverizing the powder pulverized with a mill
As well as mixed with various insulator powders
Fe-30at% Co-45at% Nd-5at% B
Magnet alloy powder for forming insulator containing layer
Prepared as End B. Nd% in magnet alloy powder B is magnet
It was higher than that of the alloy powder A. Press forming in a magnetic field
Set the direction of the applied magnetic field of the device and the pressing direction to be perpendicular.
Specified. After pressing the magnet alloy powder A in a magnetic field,
Without removing from the mold, insulator powder and magnet alloy powder
The mixture of B was filled and pressed again in a magnetic field.
Press molding the magnetic alloy powder A in a magnetic field in the same manner
Thus, molded article samples (Examples 1 to 12) were obtained. The applied magnetic field is
10kOe, press pressure 400kgf / cm ^TwoAnd
After performing sintering and aging treatment on the fabricated molded body sample,
When measuring the magnetic flux density Br and the electrical resistance in the pressing direction,
In addition, the volume fraction of the insulator phase in the insulator-containing layer was determined by electron microscopy.
Estimated from the electron image. The results are shown in Table 1.
No cracks after sintering were observed in any of the examples. Ma
In addition, the electric resistance in the pressing direction is lower than that of the comparative example.
It has the effect of light.

Comparative Example 1 Only the magnet alloy powder A was pressed once under the same conditions as in the example, and no insulator-containing layer was formed. Then, the measurement was performed in the same manner as in the examples, and the results are shown in Table 1.

(Comparative Examples 2 and 3) Except that the volume ratio of the insulator phase in the insulator-containing layer was out of the range of 30 to 90%,
Samples were prepared and measured in the same manner as in the examples, and the results are shown in Table 1. In a sample in which the volume ratio of the insulator phase was less than 30% (Comparative Example 2), sufficient electric resistance was not obtained. Further, in the sample exceeding 90% (Comparative Example 3), cracks occurred after sintering. The volume fraction of the insulator phase was estimated from a reflected electron image of an electron microscope.

Comparative Example 4 Magnet powder B was used in the insulator-containing layer.
Instead, a sample was prepared and measured in the same manner as in the example except that the magnet alloy powder A was used, and the results were shown in Table 1. Cracks occurred after sintering.

[0020]

[Table 1]

[0021]

The Nd-Fe-B sintered magnet of the present invention, when installed in a fluctuating magnetic field, reduces the occurrence of eddy currents, so that the temperature rise due to heat generation of the magnet and the deterioration of the magnetic properties are reduced. Is suppressed. Therefore, it can be used for applications such as large motors and is extremely useful industrially.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the magnet of the present invention.

FIG. 2 is a sectional view showing an example of the magnet of the present invention.

FIG. 3 schematically shows a press molding apparatus used for manufacturing the magnet of the present invention.

[Explanation of symbols]

 1: Magnet layer 2: Insulator-containing layer 3: Magnetization direction of magnet layer 4: Upper punch 5: Lower punch 6: Die 7: Electromagnet 8: Press direction 9: Magnetic field application direction

Claims (8)

[Claims] In a sintered Nd—Fe—B magnet, a magnet layer composed of a magnet main phase and a grain boundary phase and an insulator-containing layer composed of a magnet main phase, a grain boundary phase and an insulator phase are formed on both end faces. Has a layered structure alternately stacked in one direction such that a volume ratio of the insulator phase in the insulator containing layer is 3
0 to 90%, and the magnetization direction of the magnet layer is parallel to the plane of each of the two layers. 2. The sintered Nd—Fe—B magnet according to claim 1, wherein the thickness of the insulator-containing layer is 1 μm to 1 mm. 3. The Nd—Fe— according to claim 1, wherein the insulator phase constituting the insulator containing layer is made of an oxide of an element selected from rare earth elements (including Y), Mg and Ca.
B sintered magnet. 4. The N phase according to claim 1, wherein the insulator phase constituting the insulator containing layer is made of a carbide or fluoride of an element selected from rare earth elements (including Y), Mg and Ca.
d-Fe-B sintered magnet. 5. The Nd—Fe—B sintered magnet according to claim 1, wherein the insulator phase constituting the insulator containing layer is made of boron nitride. 6. The Nd—Fe—B sintered magnet according to claim 1, wherein a composition ratio of Nd in a portion excluding the insulator phase from the insulator containing layer is higher than a composition ratio of Nd in the magnet layer. 7. A method for producing a sintered Nd—Fe—B magnet, wherein a magnet alloy powder for forming a magnet layer, a magnet alloy powder for forming an insulator-containing layer, and The method for producing a sintered Nd-Fe-B magnet according to any one of claims 1 to 6, wherein the mixture of the insulator powders is press-formed alternately in an applied magnetic field. 8. The Nd—Fe—B sintered magnet according to claim 7, wherein the Nd composition ratio of the magnet alloy powder forming the insulator-containing layer is higher than the Nd composition ratio of the magnet alloy powder forming the magnet layer. Manufacturing method.