JPH05315120A - Rare earth sintered magnet and its manufacture - Google Patents

Abstract

PURPOSE:To get high magnetic property, especially, high coercive force by having R6Fe13Cu phase being a tetragonal antiferromagnetic compound as the constituent phase, with R, Fe, B, and Cu as the basic ingredients of a material. CONSTITUTION:A rare earth permanent magnet has R (but, a rare earth element having Pr and Nd for its main ingredients), Fe, B, and Cu as the basic ingredients of the material. The alloy powder consisting of these basic ingredients is heat-treated in the temperature range not less than 400 deg.C and not more than the peritectic temperature of R6Fe13Cu phase after molding and sintering. Hereby, it can have R6Fe13Cu phase being a tetragonal antiferromagnetic compound as the constituent phase. Accordingly, favorable coercive force can be gotten stably.

Description

Detailed Description of the Invention

[0001]

The present invention relates to R (where R is Pr,
The present invention relates to a rare earth sintered magnet containing Nd as a main component, Fe, B, and Cu as raw material basic components, and a method for manufacturing the same.

[0002]

2. Description of the Related Art R-Fe-B system permanent magnets have been much researched and developed since the announcement in 1983 as permanent magnets having extremely high coercive force and energy product.

Examples of the method for producing the R-Fe-B anisotropic permanent magnet include a sintering method by a powder metallurgical means, a die upset method of pressing a quenched ribbon and mechanically orienting it. There is a casting / hot working method in which a cast ingot is directly hot worked and oriented, and the industrially established method is the sintering method.

Representative documents concerning the R-Fe-B system sintered magnet are M. Sagawa, S. Fujimura, N. Togawa, H. Yamam.
oto and Y. Matsuura; J. Appl. Phys. Vol.55 (6), 15 Ma
rch1984, p2083 and the like. As a patent, JP 59
-46008 publication and the like, 8% to 30% R in atomic percentage
(Where R is at least one rare earth element including Y),
It is disclosed that a permanent magnet, which is a magnetic anisotropic sintered body composed of 2 to 28% B and the balance Fe, is manufactured by sintering based on a powder metallurgy method.

In this sintering method, an alloy ingot is produced by melting and casting and crushed to obtain a magnetic powder having an appropriate particle size (several μm). The magnetic powder is kneaded with a binder, which is a molding aid, and press-molded in a magnetic field to form a molded body. The compact is sintered in argon at a temperature of about 1100 ° C. for about 1 to 5 hours and then rapidly cooled to room temperature. 600 ° C after sintering
The permanent magnet further improves the coercive force by heat treatment at the temperature around. Regarding the heat treatment of this sintered magnet, the effects of multi-stage heat treatment are disclosed in JP-A-61-217540 and JP-A-62-165305.

As a means for improving the coercive force, the effects of various additive elements were also searched for. The most effective of these was the addition of the heavy rare earth element Dy. The addition of Dy increases the magnetic anisotropy constant of the R ₂ Fe ₁₄ B phase, which is the main phase, and a high coercive force can be obtained in the resulting magnet. Due to such an effect of adding Dy, the R—Fe—B system sintered magnet is being used for a wide range of applications.

Further, Japanese Patent Application Laid-Open No. 61-295355 discloses R-Fe-B based sintered magnets containing various boride phases. This is because the boride phase has the effect of suppressing the grain growth of the main phase crystal grains, and therefore the coercive force is improved.

[0008]

As described above, R-
The addition of Dy is a very effective means of increasing the coercive force in the Fe-B system sintered magnet. However, D, which is a heavy rare earth element
Since y is a rare element which has a very small amount of production and reserves, its use causes a significant cost increase. In addition, considering the resource balance of rare earth elements, D
It is not preferable to use a large amount of y.

Further, the improvement of the coercive force due to the grain growth suppressing effect of the main phase crystal grains by adding the boride is slight. Also in the manufacturing method, there is a drawback that the addition of the boride deteriorates the sinterability and the R ₂ Fe ₁₇ phase which is a soft magnetic phase is generated to deteriorate the magnetic properties.

The present invention solves the above-mentioned drawbacks of the prior art, and an object of the present invention is to use a rare earth sintered magnet having a high characteristic, particularly a high coercive force, by using an element supplied in a large amount, and an industrial method. It provides a manufacturing method that is easy to produce.

[0011]

In order to solve the above-mentioned problems, the present inventors focused their attention on Cu as an additional element, and obtained the R-Fe-B-Cu-based sintered magnet structure and magnetism. A detailed study was conducted on the correlation of properties. As a result, in the structure of the finally obtained magnet, R is contained in the grain boundary phase.
_It has been clarified that good coercive force can be stably obtained when the compound phase of ₆ Fe ₁₃ Cu is present. From the results as described later, this compound was also found to be a tetragonal compound showing antiferromagnetism at room temperature. See also R ₆
It was also clarified that appropriate heat treatment conditions had to be selected in order for the Fe ₁₃ Cu phase to appear in the final magnet structure.

That is, the rare earth sintered magnet of the present invention is R (provided that the rare earth element is Pr, Nd as a main component), Fe, B,
It is characterized by having Cu as a raw material basic component and having a R ₆ Fe ₁₃ Cu phase which is a tetragonal antiferromagnetic compound as a constituent phase. After binding, the temperature is 400 ° C or higher and R ₆ Fe ₁₃
It is characterized in that the heat treatment is carried out in a temperature range below the peritectic temperature of the Cu phase.

The structure of the present invention will be described in detail below.

First, the process of identifying the R ₆ Fe ₁₃ Cu phase that forms the basis of the present invention will be described. The presence or absence of this phase in the sample can be easily determined by observing the structure with a polarization optical microscope. Sample of Table 1 below
Regarding No. 1, the composition analysis by EPMA of the phase confirmed by the polarization optical microscope was performed. As a result, it was found that this phase had a composition of approximately 30 at% Pr, 66 at% Fe, 6 at% Cu, and other trace elements, and the atomic ratio of Pr: Fe: Cu was approximately 6: 13: 1. Based on this result, research on similar compounds was conducted. As a result, R ₆ Fe for M = Si, Sn, Ga, In, Al, Tl
_14-x M _x phase (when M = Si, Sn, In, Tl, x = 1,
There was a report regarding x = 3) when M = Ga and Al. The following can be cited as references.

J. Allemand et al; J. Less-Common Me
t. 166 (1990) 73 KG Knoch et al; IEEE Trans. Mag. MAG-25 (198
9), No.5,3426 J. Fidler; 6th International Symposium on Magnet
ic Anisotropy and Coercivity in RE-TM Alloys Paper
No. S2.7 B. Grieb et al; IEEE Trans. Mag. MAG-26 (1990) 136
7 P. Schrey et al; J. Mag. Magn. Mat. 101 (1991) 417 F. Weitzer et al; J. Less-Common Met. 167 (1990) 1
In the 35 reference, the crystal structure of Nd ₆ Fe ₁₃ Si is proposed based on the X-ray diffraction results. But C
No report has been made yet regarding the same type of compound containing u as a constituent element. The present inventors have adopted E as described above.
X-ray diffraction was performed on the compound phase consisting of Pr, Fe and Cu confirmed by PMA. As a result, the obtained diffraction peak was in good agreement with that of a tetragonal crystal belonging to the space group I4 / mcm. The lattice constants were measured as a = b = 0.81 nm and c = 2.31 nm. FIG. 1 shows the X-ray diffraction result and the identification result of each peak. From the above X-ray diffraction and EPMA analysis,
It was revealed that this phase was a tetragonal compound Pr ₆ Fe ₁₃ Cu phase.

The inventors of the present invention also evaluated the magnetism of Pr ₆ Fe ₁₃ Cu. The magnetization curve is shown in FIG.
As can be seen from the figure, the curve obtained does not draw a hysteresis loop but shows a paramagnetic change in which the magnetization is almost proportional to the magnetic field. Fig. 3 shows the temperature dependence of magnetization (MT curve). The obtained magnetization is very small, 118 ° C.
A peak of magnetization was seen in the vicinity. FIG. 4 shows a spectrum diagram obtained as a result of Moessbauer spectroscopy. From this result, it was found that the internal magnetic field of iron atoms occupying each site in the crystal structure has a relatively large value of about 200 kOe at each site. From the above results, although Pr ₆ Fe ₁₃ Cu does not show ferromagnetism, the iron atom in the crystal has a considerably large magnetic moment, and it can be judged that it is an antiferromagnetic compound. 118 ℃ in the MT curve mentioned above
The peak temperature is considered to be the Neel point. Regarding Nd, it was confirmed that a similar Nd ₆ Fe ₁₃ Cu phase was present.

When the R ₆ Fe ₁₃ Cu phase as described above is uniformly dispersed in the grain boundaries of the R ₂ Fe ₁₄ B compound or the triple points of the grain boundaries, which is the main phase, good magnetic properties, particularly High coercive force can be obtained.

In order to make the R ₆ Fe ₁₃ Cu phase appear in the finally obtained magnet structure, it is first necessary to properly select the alloy composition of the ingot. Basically, it is necessary that all the iron atoms are not consumed as the main phase but exist in an appropriate amount also in the grain boundary phase, and R ₂ which is the soft magnetic phase.
It is necessary not to allow the Fe ₁₇ phase to appear. Specifically, when the alloy composition is expressed as R _x Fe _y B _z Cu _(100-xyz) , it is necessary that y-14z> 0 and z ≧ 4.

Further, even if the alloy composition is appropriately determined, the R ₆ Fe ₁₃ Cu phase is not always obtained as the final magnet structure, and the heat treatment conditions must be appropriately selected. This is because the R ₆ Fe ₁₃ Cu phase stably exists only in a certain temperature range. For example, the Pr ₆ Fe ₁₃ Cu phase is formed by a peritectic reaction of Pr ₂ Fe ₁₇ +1 (liquid phase) → Pr ₆ Fe ₁₃ Cu, and the peritectic temperature is estimated to be around 650 ° C. from the results of thermal analysis. .. The peritectic temperature changes depending on the type of R and other impurity elements, but basically, the R ₆ Fe ₁₃ Cu phase does not appear unless the heat treatment below this peritectic temperature is finally performed. The coercive force remains low. On the contrary, if the heat treatment temperature is too low, the heat treatment time becomes very long, which impairs mass productivity.
Therefore, it is desirable to perform heat treatment at a temperature of 400 ° C or higher. More preferably, the heat treatment is performed at a temperature at or above at which 1 (liquid phase) in the peritectic reaction formula appears. In such a temperature range, the diffusion of atoms is facilitated and the reaction is promoted, so that the heat treatment time can be shortened. For example, in the case of R = Pr, it is desirable to perform the heat treatment at the eutectic reaction temperature (about 470 ° C.) or higher of the Pr phase and the PrCu phase.
However, such temperature changes depending on the type of R and the impurity element.

There are no problems if the molding and sintering conditions prior to the heat treatment are carried out under the conditions already known from patents and the like.

[0021]

Function As described above, R-Fe having the R ₆ Fe ₁₃ Cu phase
In the -B-Cu system sintered magnet, good magnetic properties, especially high coercive force can be obtained. It is considered that the improvement of the magnetic characteristics according to the present invention is due to the following effects.

The first effect is that the ferromagnetic phase disappears in the grain boundary phase portion. In the conventional R-Fe-B-Cu based magnet, α-Fe or R ₂ Fe ₁₇ is contained in the grain boundary phase portion.
Scattering of ferromagnetic phase with small coercive force was observed. Such a ferromagnetic phase becomes the nucleus of the magnetization reversal, so that the coercive force is drastically reduced. However, when the R ₆ Fe ₁₃ Cu phase is formed, such a ferromagnetic phase disappears. R ₆ Fe ₁₃
Since the Cu phase is an antiferromagnetic phase, it rarely exerts a magnetic influence on the main phase like a nucleus of magnetization reversal, and it is considered that good coercive force can be obtained for this reason.

The second effect is to promote the separation of the main phase crystal grains from each other and to suppress the grain growth of the main phase crystal grains. As can be seen in the examples described below, R ₆ Fe ₁₃ C is formed at the grain boundaries.
When the u phase does not exist, there are many areas where the main phase grains are in contact with each other. In such a portion, the magnetization reversal becomes easy and the coercive force is lowered. On the other hand, R ₆ Fe _{1
3 When the} Cu phase is uniformly dispersed in the grain boundary phase portion, this phase is successful in magnetically isolating the main phases from each other, which makes it difficult for magnetization reversal to occur, resulting in a high coercive force. It is thought that can be realized. Judging from the structure photograph, the final magnet structure is R ₆ Fe ₁₃ Cu.
When a phase is present, the crystal grain size of the main phase is R ₆ Fe ₁₃
It is smaller than when the Cu phase is not present. R ₆
It is not known whether the Fe ₁₃ Cu phase directly contributes to the refinement of the main phase crystal grain size, but as a result, fine main phase grains are obtained and a high coercive force is realized.

The third effect is that the main phase crystal grain interface is cleaned by the appearance of the R ₆ Fe ₁₃ Cu phase. Judging from the photomicrograph, the main phase and the R ₆ Fe ₁₃ Cu phase often exist in contact with each other, but the interface is fairly linear and has few irregularities. In the above reference, Schrey et al. Stated that the interface between the main phase and the Nd ₆ Fe ₁₃ Sn phase was observed by TEM, and as a result, the interface was very clean, which contributes to the improvement of the coercive force. It is considered that the same phenomenon occurs in the case of the magnet of the present invention, and a high coercive force is realized.

Next, examples of the present invention will be described.

[0026]

【Example】

(Example 1) An alloy having the composition shown in Table 1 was melted in an argon atmosphere using a high frequency induction heating melting furnace, and then cast in a mold. 99.9% as raw material for rare earth, iron and copper
Of the above-mentioned purity, and a ferroboron alloy was used as boron. The obtained ingot was crushed into 35 mesh through with a stamp mill, and then finely crushed with a jet mill using nitrogen gas to obtain a powder having an average particle size of about 3 μm. The powder thus obtained was kneaded with zinc stearate as a molding aid and then molded under a magnetic field of 10 kOe at a pressure of 1.5 t / cm ² . The green compact obtained was sintered at 1050 ° C. in an argon atmosphere for 3 hours.

Then, at 600 ° C. in an argon atmosphere, 1
Heat treatment was performed for 0 hours.

When the structure at this time was observed by an optical microscope with polarized light, R ₆ Fe ₁₃ C was observed as a grain boundary phase other than the main phase.
Both the presence and absence of the u phase were observed.
Here, a schematic view of the representative results of the structure observation of both is shown in FIG. 5 and FIG. In FIG. 5, the R ₆ Fe ₁₃ Cu phase is present as a grain boundary phase, the separation of the main phases is promoted, and the grain size is small. FIG. 6 shows R ₆ Fe ₁₃ C as a grain boundary phase.
This is a structure in which the u phase does not exist, the main phases are not well isolated from each other, and the main phase grain size is coarse.

Table 2 shows the magnetic characteristics of the sintered magnets having the alloy compositions shown in Table 1 and the presence / absence of the R ₆ Fe ₁₃ Cu phase judged from the result of observation with an optical microscope. The magnetic characteristics in this case were measured by a BH tracer with a maximum applied magnetic field of 25 kOe after the sample was magnetized with a pulsed magnetic field of 40 kOe.

[0030]

[Table 1]

[0031]

[Table 2]

As described above, R ₆ Fe ₁₃ Cu is used as the constituent phase.
R-Fe-B-Cu based sintered magnets with phases have high magnetic characteristics,
In particular, a high coercive force can be realized.

(Example 2) The ingot having the alloy composition shown in No. 1 of Table 1 was subjected to the same molding and sintering conditions as in Example 1, and then heat-treated for 10 hours at each temperature of 200 to 800 ° C. gave. The magnetic characteristics of the rolled magnet thus obtained were measured. FIG. 7 shows the relationship between the heat treatment temperature and the magnetic characteristics.

As is apparent from the figure, the heat treatment temperature is 400 to 6
It was found that high magnetic properties were obtained in the range of 50 ° C.
Further, when the structure of these magnet samples was observed with an optical microscope, it was found that only those heat-treated at a temperature of 400 to 650 ° C. at which high characteristics were obtained were R ₆ Fe ₁₃ Cu.
The existence of phases was confirmed.

[0035]

According to the present invention, as described above, R, Fe,
The rare earth permanent magnet having a R ₆ Fe ₁₃ Cu phase, which is a tetragonal antiferromagnetic compound as a constituent phase, is manufactured by subjecting B and Cu to the raw material basic components and performing a heat treatment after sintering, and particularly, has a high magnetic property. High coercive force can be obtained. By adding Cu, which is an additional element that is supplied in a large amount, a low-cost high-performance rare earth sintered magnet can be obtained without using expensive Dy.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction result diagram of R ₆ Fe ₁₃ Cu.

FIG. 2 is a magnetization curve diagram of R ₆ Fe ₁₃ Cu.

FIG. 3 is a relational diagram of magnetization and temperature of R ₆ Fe ₁₃ Cu.

FIG. 4 is a Moessbauer spectrum diagram of R ₆ Fe ₁₃ Cu.

FIG. 5 is a schematic diagram of a sintered magnet structure in which an R ₆ Fe ₁₃ Cu phase exists.

FIG. 6 is a schematic diagram of a sintered magnet structure in which no R ₆ Fe ₁₃ Cu phase is present.

FIG. 7 is a diagram showing the relationship between heat treatment temperature and magnetic properties.

[Explanation of symbols]

1 R ₂ Fe ₁₄ B phase 2 R-rich phase 3 R ₆ Fe ₁₃ Cu phase

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01F 41/02 G 8019-5E (72) Inventor Seiji Ihara 3-3-5 Yamato, Suwa City, Nagano Prefecture No. Seiko Epson Corporation (72) Inventor Koji Akioka 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (72) Inventor Takateru Umeda 7-3-1 Hongo, Bunkyo-ku, Tokyo University of Tokyo Engineering Department of Metal Engineering (72) Inventor Katsuhisa Nagayama 7-3-1 Hongo, Bunkyo-ku, Tokyo University of Tokyo Department of Metal Engineering (72) Inventor Toshiyuki Kajiya 7-3-1 Hongo, Bunkyo-ku, Tokyo Metal Department of Engineering, Tokyo University Department of Engineering

Claims (2)

[Claims] 1. R (where R is a rare earth element containing Pr and Nd as main components), Fe, B and Cu as raw material basic components,
R ₆ Fe ₁₃ which is a tetragonal antiferromagnetic compound as a constituent phase
A rare earth sintered magnet having a Cu phase. 2. An alloy powder containing R, Fe, B, and Cu as raw material basic components is molded and sintered, and then 400 ° C. to R ₆ Fe ₁₃
The method for producing a rare earth sintered magnet according to claim 1, wherein the heat treatment is performed within a temperature range of peritectic reaction temperature of the Cu phase.