JP2000286118A - Manufacture of sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide an Nd2Fe14M sintered magnet having high magnetic characteristics. SOLUTION: A method for manufacturing a sintered magnet, containing R (at least one kind of rare-earth element including Y), T (Fe or Fe and Co), and B includes a process for molding a mixture of the powder of a first alloy, a second alloy, and a third alloy and sintering the molded product. The first alloy contains 26-29 wt.% R, 0.8-1.08 wt.% B, and the balance T and the second alloy contains 28 wt.% or larger R, 1.1-1.5 wt.% B, and the balance T. The third alloy contains 30 wt.% R, 0.5 wt.% B or smaller, and T as the balance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a rare earth sintered magnet.

[0002]

2. Description of the Related Art A rare earth magnet having a high performance is an Sm-Co magnet manufactured by powder metallurgy and has an energy product of 32M.
GOe is mass-produced. In recent years, Nd ₂ Fe
R-T-B magnets (R is a rare earth element, T is Fe, or Fe and Co) such as a ₁₄ B magnet have been developed.
No. 46008 discloses a sintered magnet. R
The raw material of the -TB magnet is less expensive than that of the Sm-Co magnet. For the production of RTB based sintered magnets, conventional Sm
-A Co-based powder metallurgy process (melting → mother alloy casting → ingot coarse grinding → fine grinding → molding → sintering → magnet) can be applied.

Various reports have reported in detail that the coercive force of an Nd ₂ Fe ₁₄ B-based sintered magnet depends on the existence of an Nd-rich phase at a crystal grain boundary. Therefore, sintering so that the Nd-rich phase uniformly covers the crystal grains composed of the Nd ₂ Fe ₁₄ B phase,
It is important to uniformly disperse the Nd-rich phase in the sintered magnet. In order to uniformly disperse the Nd-rich phase in the magnet, it is preferable to use the two-alloy method. In the two-alloy method, a mixture of the main phase powder mainly composed of Nd ₂ Fe ₁₄ B and the Nd-rich grain boundary phase powder is formed,
Sintering (JP-A-63-93841, JP-A-63-93841)
-278208, JP-A-5-21219). The powder for the grain boundary phase is melted at the time of sintering, and Nd ₂ Fe ₁₄ B
It becomes a liquid phase with extremely good wettability to the main phase and flows, and coats the periphery of the main phase powder to become a grain boundary phase of the magnet,
Improve coercive force.

However, when pulverizing and pulverizing an alloy, a rare earth element or boron is scattered to easily cause a composition deviation, but the two alloy method can compensate for the composition deviation of one element. It is difficult to compensate for the deviation of the composition of the seed elements.

In the case of Nd ₂ Fe ₁₄ B-based sintered magnets,
In consideration of the weight loss due to the oxidation of d, it was general to make the composition considerably more Nd-rich side than the stoichiometric composition. Absent. Therefore, when the oxidation of Nd can be suppressed, the Nd content is reduced to, for example, 3%.
The content is preferably 1% by weight or less. In this case, a magnet having a high coercive force and a high residual magnetic flux density is realized. However, the conventional two-alloy method has not been optimized for producing a sintered magnet having a low Nd content.

[0006]

An object of the present invention is to stably provide an Nd ₂ Fe ₁₄ B-based sintered magnet having high magnetic properties.

[0007]

This and other objects are achieved by the present invention which is defined below as (1) to (4). (1) R (R is at least one of rare earth elements including Y
A method for producing a sintered magnet containing B, which is a seed), T (T is Fe or a transition element other than Fe and Fe), and B, comprising a powder of a first alloy and a powder of a second alloy. And sintering the mixture of the first alloy and the powder of the third alloy, wherein the composition of the first alloy is R: 26 to 29% by weight,
B: 0.8 to 1.08% by weight, T: the balance,
Alloy composition: R: 28% by weight or more, B: 1.1 to 1.5
% By weight, T: balance, R: 30
% Or more, B: 0.5% by weight or less, T: The balance of the manufacturing method of the sintered magnet. (2) The method for producing a sintered magnet according to (1), wherein the third alloy does not contain B. (3) The composition of the mixture is R: 28 to 31% by weight,
B: 0.9 to 1.1% by weight, T: the balance (1)
Or (2) a method for producing a sintered magnet. (4) The method for producing a sintered magnet according to the above (1) or (2), wherein the composition of the mixture is R: 28 to 29.5 wt%, B: 0.95 to 1.05 wt%, and T: balance. .

[0008]

According to the present invention, by sintering a mixture of the above three kinds of alloy powders, a sintered magnet having higher characteristics than the conventional two alloy method can be obtained.

In the present invention, the first alloy powder and the second alloy powder are mixed.
Part of the powder is the main phase R_TwoT_{1 Four}Form B crystal grains
And the remainder of the powder of the second alloy reacts with the powder of the third alloy.
To form a grain boundary phase. Therefore, the first pass
Gold powder is R_TwoT₁₄Preferably have phase B
No. The powder of the second alloy is also R_TwoT₁₄With phase B
May be. The powder of the second alloy has a high B content and the third alloy
Powder has a high R content. So both powders react
By the way, R_TwoT₁₄Grain boundary phase required for B magnet
That is, the grain boundary phase including the R-rich phase and the B-rich phase is logical.
Formed in a state close to the imagination, and as a result,
In addition, compared to the conventional two-alloy method using only R-rich powder,
It is believed that higher characteristics are realized.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, R (R is at least one kind of rare earth element including Y), T (T is F
e, or Fe and other rare earth elements) and B
In producing a sintered magnet containing, a mixture of the first alloy powder, the second alloy powder, and the third alloy powder is molded and sintered.

[0011] The composition of the first alloy first alloy, R: 26 to 29 wt%, B: 0.8
1.08% by weight, T: balance. The lower limit of the R amount is preferably 27.0% by weight, more preferably 27.8% by weight, and the upper limit of the R amount is preferably 28.5% by weight.
More preferably, it is 28.2% by weight. The lower limit of the B content is preferably 0.9% by weight, more preferably 0.9% by weight.
5% by weight, and the upper limit of the amount of B is preferably 1.05% by weight.

If the amount of R in the first alloy is too small, a large amount of the α-Fe phase precipitates when the first alloy is manufactured by casting or the like. If the first alloy containing a large amount of the α-Fe phase is used, the coercive force of the sintered magnet will be low. Meanwhile, the first
If the amount of R is too large in the alloy, high characteristics cannot be obtained even if the composition of the sintered magnet is set within a preferable range.

If the amount of B in the first alloy is too small, a large amount of the R ₂ T ₁₇ phase precipitates in the first alloy. If the first alloy containing a large amount of the R ₂ T ₁₇ phase is used, the coercive force of the sintered magnet will be low. On the other hand, when the amount of B is too large in the first alloy, a large amount of nonmagnetic B-rich phase precipitates in the first alloy.
If the first alloy containing a large amount of the B-rich phase is used, a sintered magnet having good magnetic properties cannot be obtained.

[0014] The composition of the second alloy second alloy, R: 28 wt% or more, B: 1.1 to
1.5% by weight, T: balance. The lower limit of the R amount is preferably 28.5% by weight, more preferably 28.8% by weight, and the upper limit of the R amount is preferably 31% by weight, more preferably 30.0% by weight, and further preferably 29% by weight. 0.2% by weight. Further, the lower limit of the B amount is preferably 1.15% by weight, and the upper limit of the B amount is preferably 1.4% by weight.
More preferably, it is 1.3% by weight.

If the amount of R in the second alloy is too small, a relatively large amount of the α-Fe phase precipitates when the second alloy is manufactured by casting or the like, and it becomes difficult to obtain a sintered magnet having a high coercive force. On the other hand, if the amount of R in the second alloy is too large, it is difficult to obtain high characteristics even if the composition of the sintered magnet is set within a preferable range.

If the amount of B in the second alloy is too small, high characteristics cannot be obtained even if the composition of the sintered magnet is set within a preferable range. This is considered because a sufficient B-rich phase is not formed in the grain boundary phase. On the other hand, in the second alloy, B
If the amount is too large, a large amount of nonmagnetic B-rich phase will precipitate in the second alloy. If the second alloy containing a large amount of the B-rich phase is used, a sintered magnet having good magnetic properties cannot be obtained.

[0017] The composition of the third alloy third alloy, R: 30 wt% or more, B: 0.5 wt% or less, T: the balance. The lower limit of the R amount is preferably 32% by weight, more preferably 34% by weight, and the upper limit of the R amount is preferably 60% by weight, more preferably 50% by weight, and still more preferably 40% by weight. The upper limit of the amount of B is preferably 0.2% by weight, more preferably 0.1% by weight.

If the amount of R in the third alloy is too small, a large amount of R ₂ T ₁₇ phase will precipitate in the third alloy, and the coercive force of the sintered magnet will be low. On the other hand, in the third alloy, R
If the amount is too large, it is difficult to obtain high characteristics even if the composition of the sintered magnet is set within a preferable range.

If the amount of B in the third alloy is too large, high characteristics cannot be obtained even if the composition of the sintered magnet is set within a preferable range. Note that the third alloy may not contain B.

The method of obtaining powder of the powder and the second alloy mixing first alloy and a mixture of a powder of the third alloy is not particularly limited, may be pulverized by mixing a block of each alloy, each alloy Coarse powder may be mixed and pulverized, or fine powder of each alloy may be mixed. If each alloy is mixed as a block or coarse powder, it can be flown as one lot in the subsequent pulverization process, so that it is efficient and the uniformity of mixing becomes good. On the other hand, when each alloy is mixed with fine powder, each alloy powder can be adjusted to an optimum particle size, so that a magnet with high characteristics can be easily obtained. In addition, the composition deviation of the R amount and the B amount tends to occur at the time of pulverization. However, in the present invention, since three kinds of alloys are mixed, such a composition deviation can be compensated according to the pulverization conditions. .

The ratio of each alloy powder in the mixture is
The composition of the compound is preferably R: 28 to 31% by weight, B:
0.9 to 1.1% by weight, T: remaining, more preferably
Is R: 28 to 29.5% by weight, B: 0.95 to 1.05
% By weight, T: set to be the balance. That is, the book
In the invention, the amount of R is close to the stoichiometric composition._TwoT_{1 Four}B type rare earth
It is suitable for manufacturing magnets. Low R content in the mixture
When it breaks, a phase rich in iron precipitates and high coercive force cannot be obtained.
If the R content is too high, a high residual magnetic flux density cannot be obtained.
Become. If the B content is too small, a high coercive force cannot be obtained.
If the B content is too large, a high residual magnetic flux density cannot be obtained.
Become.

The specific mixing ratio is generally 1 to 12 parts by weight of the first alloy with respect to 10 parts by weight of the second alloy and the third alloy.
0 parts by weight, and a total of 10 of the second alloy and the third alloy
The content of the second alloy may be 2 to 9.5 parts by weight in the weight part, but is not limited to this as long as the composition of the mixture is within the above range.

In the present invention, R is at least one of Nd, Pr, and Tb, particularly preferably Nd.
It is preferable to include Also, La, Ce, Gd, E
One or more of r, Ho, Eu, Pm, Tm, Yb, and Y may be included. As a raw material of the rare earth element, a mixture such as misch metal can also be used.

T is Fe or a transition element other than Fe and Fe. As a transition element other than Fe, Co is preferable. In T, the content of transition elements other than Fe is 3
The content is preferably 0% by weight or less. The transition elements other than Fe include Co, for example, Al, Cr, M
n, Mg, Si, Cu, Nb, Sn, W, V, Zr, T
i, Mo and the like.

In the production method of the present invention, since the anisotropy is caused by the magnetic field orientation in the molding step, the powder of each alloy, particularly the powder of the first alloy and the powder of the second alloy, are preferably single crystal particles. . The average particle size of each alloy powder may be determined so that the crystal particle size of the magnet after sintering has a desired value, and may be appropriately selected from, for example, about 1 to 10 μm.

The method for pulverizing the alloy is not particularly limited.
After an alloy is manufactured by casting or a liquid quenching method (for example, a single roll method), the alloy may be pulverized by a hydrogen storage method or a normal mechanical pulverization method, or an alloy powder may be manufactured by a reduction diffusion method.

Since the magnet manufactured according to the present invention has a relatively low content of rare earth elements, the margin for oxidation of rare earth elements is small. Therefore, it is preferable that each step such as pulverization, mixing, and molding is performed in a non-oxidizing atmosphere such as Ar or N ₂ .

[0028] In the molding forming process, forming a mixture of three alloy powders in a magnetic field. The molding pressure is not particularly limited, but is generally 0.1 t /
cm ² or more, preferably 1 t / cm ² or more. The magnetic field strength during molding is usually at least 10 kOe, preferably at least 15 kOe.

In the sintering and sintering step, the compact is heated and sintered to be magnetized.
The stabilization temperature in the sintering step is preferably 900 to 1100 ° C., and the stabilization time is preferably 0.5 to 24 hours. The sintering atmosphere is preferably a vacuum or an inert gas atmosphere such as Ar gas.

After sintering, aging treatment is performed as needed to improve coercive force.

The composition of the sintered magnet is a mixture of three alloys and
It is almost the same, except for unavoidable impurities or
Contains trace amounts of additives such as carbon and oxygen
Is also good. Sintered magnets have a substantially tetragonal crystal structure.
Phase, and R _TwoT₁₄Higher R ratio than B
R-rich phase and B-rich phase with high B ratio exist
You.

[0032]

EXAMPLES Sintered magnet samples shown in Tables 3 and thereafter are prepared according to the method of the present invention using three kinds of alloys, the two alloy method using two kinds of alloys, or the normal sintering method using one kind of alloy. Produced by

Powders having the compositions shown in Tables 1 and 2 were used as the raw material alloys. In each of these tables, the Nd content and the B content of each alloy powder are shown. The balance is Fe.
These alloy powders were obtained by grinding a cast alloy ingot in an Ar atmosphere.

The combinations of the alloy powders used in the production of the respective sintered magnets, the mixing ratios and the compositions after the mixing are shown in Tables 3 and thereafter. The average particle size of the alloy powder was 3.3 μm for the first alloy, 3.2 μm for the second alloy, and
The thickness was 3.0 μm in the alloy. Mixing of alloy powder is A
r performed in an atmosphere.

Next, the alloy powder was subjected to isostatic pressing in a pulse magnetic field of 10 T, sintered in vacuum at 1050 ° C. for 8 hours, and quenched. Further, in an Ar atmosphere, 5
After aging at 50 ° C. for 1 hour, a sintered magnet sample was obtained. The density, residual magnetic flux density (Br), coercive force (HcJ), and maximum energy product ((BH) max) of each sample are shown in Table 3 and subsequent tables.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

From the above tables, the effect of the present invention is clear. That is, in the method of the present invention in which three kinds of alloys are mixed, a sintered magnet having characteristics superior to those obtained by using either the normal sintering method or the two-alloy method is obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Ryo Fukuno, Inventor TDK Corporation, 1-13-1 Nihonbashi, Chuo-ku, Tokyo (72) Inventor Jun Nakagawa 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Incorporated F term (reference) 4K018 AA27 KA45 5E040 AA04 BD01 CA01 HB05 NN01

Claims (4)

[Claims] 1. A sintered magnet containing R (R is at least one kind of rare earth element including Y), T (T is Fe, or a transition element other than Fe and Fe) and B. A method of manufacturing, comprising a step of molding and sintering a mixture of a powder of a first alloy, a powder of a second alloy, and a powder of a third alloy, wherein the composition of the first alloy is R: 26 to 29% by weight, B: 0.8 to 1.08% by weight, T: balance, the composition of the second alloy is R: 28% by weight or more, B: 1.1 to 1.5% by weight, T: balance Wherein the composition of the third alloy is 30% by weight or more, R: 0.5% by weight or less, and T: the balance. 2. The method according to claim 1, wherein the third alloy does not contain B.
Of manufacturing sintered magnets. 3. The method for producing a sintered magnet according to claim 1, wherein the composition of the mixture is R: 28 to 31% by weight, B: 0.9 to 1.1% by weight, and T: balance. 4. The method for producing a sintered magnet according to claim 1, wherein the composition of the mixture is R: 28 to 29.5% by weight, B: 0.95 to 1.05% by weight, and T: balance.