JP2002246253A - Method of manufacturing sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Nd2Fe14B-based sintered magnet that has sufficiently high coercive force in practical use even if aging treatment is not made. SOLUTION: This method is used for manufacturing the sintered magnet containing R that is at least one kind of rare earth elements, Fe, and B, and includes a formation process for forming the powder of a raw material alloy to obtain a forming body, and a sintering process for sintering the forming body to obtain a sintered body. In the sintering process, atmospheric pressure is set to 1 atmosphere or more and 10 atmospheres or less for at least a period from the time when relative density in the sintered body becomes 70% in heat-up to the time when fall in temperature is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a rare earth sintered magnet having an Nd ₂ Fe ₁₄ B-based composition.

[0002]

2. Description of the Related Art As a rare earth magnet having high performance, for example, Nd described in Japanese Patent No. 1431617 is disclosed.
₂ Fe ₁₄ B-based magnets are known.

The higher the density of the Nd ₂ Fe ₁₄ B-based magnet, the higher the residual magnetic flux density. However, if sintering is performed at high temperature or for a long time for high density, the crystal grains become coarse and high coercive force cannot be obtained. A hot isostatic press is used to increase the density while suppressing the decrease in coercive force. However, the hot isostatic press uses a high pressure of about 500 atm or more, so that the equipment cost and the maintenance and inspection cost are high, and the manufacturing time is long. Therefore, the manufacturing cost increases.

[0004] Under such circumstances, Japanese Patent Laid-Open No. 2000-23
According to Japanese Patent Publication No. 2012, sintering is performed at 1000 to 1150 ° C. in a vacuum or an inert gas atmosphere at or below atmospheric pressure until the density of the sintered body becomes 90 to 98% of the true density. A method for producing a rare earth magnet, characterized in that sintering is performed at 900 to 1150 ° C. for 0.1 to 5 hours in an atmosphere of an inert gas at atmospheric pressure.
According to the same publication, sintering in vacuum at the first stage increases the density (90-98%) to eliminate open pores, and sintering at 1-20 atm in the second stage almost increases the size of crystal grains. It is described that the density is increased without any change.

In Japanese Patent Application Laid-Open No. 7-335468, sintering is performed to a true density of 85 to 95% in a vacuum, and subsequently, the sintering is performed in an inert gas atmosphere for 50 to 500%.
A method for producing a rare earth magnet characterized by sintering at atmospheric pressure has been proposed. The operation and effect of this manufacturing method are almost the same as those of the manufacturing method described in JP-A-2000-232012.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an Nd ₂ Fe ₁₄ B sintered magnet having a high coercive force. Another object of the present invention is to provide a Nd ₂ Fe ₁₄ B-based sintered magnet having a practically sufficiently high coercive force without aging treatment.

[0007]

This and other objects are achieved by the present invention which is defined below as (1) to (3). (1) A method for producing a sintered magnet containing R (R is at least one kind of rare earth element), Fe and B, comprising a step of molding a powder of a raw alloy to obtain a molded body; A sintering step of sintering the molded body to obtain a sintered body. In the sintering step, at least from the time when the relative density of the sintered body becomes 70% at the time of raising the temperature to the start of the temperature decrease A method for producing a sintered magnet in which the atmospheric pressure is set to more than 1 atm and 10 atm or less during the period. (2) The method for producing a sintered magnet according to the above (1), wherein the sintered body obtained in the sintering step is used as a sintered magnet without performing aging treatment. (3) A method for producing a sintered magnet containing R (R is at least one kind of rare earth element), Fe and B, comprising a step of molding a powder of a raw material alloy to obtain a compact. A sintering step of sintering the molded body to obtain a sintered body. In the sintering step, at least from the time when the relative density of the sintered body becomes 70% at the time of raising the temperature to the start of the temperature decrease A method of producing a sintered magnet in which the same raw material alloy is used to obtain sintered bodies having different coercive forces and residual magnetic flux densities by controlling the atmospheric pressure within a range of 0 to 10 atm.

[0008]

According to the present invention, in the sintering step when manufacturing the Nd ₂ Fe ₁₄ B-based magnet, the relative density of the sintered body becomes 70% at the time of raising the temperature and the period from the time when the temperature is lowered is reduced. Sintering is performed in a high pressure atmosphere. Thereby, a high coercive force is obtained. It is well known that a practical coercive force cannot be obtained unless aging treatment is performed after sintering in the production of Nd ₂ Fe ₁₄ B-based magnets. If controlled, a practical coercive force can be obtained without aging treatment. Therefore, according to the present invention, the manufacturing time can be remarkably reduced, and a remarkable cost reduction effect which has not been achieved in the past can be obtained.

In the present invention, since the sintered body is sintered at a high pressure from a relatively low density stage, pores (voids) are confined in the sintered body. Therefore, the density of the sintered body is relatively low, and the weight of the magnet can be reduced. In addition, since the shrinkage ratio during sintering is low, a magnet with good dimensional accuracy can be obtained, and the burden of shape processing after sintering can be reduced.

[0010] In the present invention, the pores formed in the sintered body are mainly closed pores that do not communicate with the outside of the sintered body. In the present invention, the reason why a high coercive force is obtained despite the fact that the density of the sintered body is quite low is not that the sintered body is coarse as a whole, but that the densely sintered high coercive force region and the closed pore are formed. This is probably due to the mixed organizational structure. As a result, it is considered that a sintered body having a low density and a high coercive force can be obtained.

In the above-mentioned JP-A-2000-232012 and JP-A-7-335468, in order to eliminate open pores communicating with the outside of the sintered body, until the density of the sintered body becomes at least 85% or more. Sinter under vacuum or reduced pressure, and then sinter in a high pressure atmosphere. That is, the timing of setting the sintering atmosphere to a high pressure is significantly later than the present invention. If the timing of changing from the vacuum or low pressure to the high pressure atmosphere is late, the improvement rate of the coercive force decreases, and a practical coercive force cannot be obtained without aging treatment. Further, since the density of the sintered body increases, the weight of the magnet increases. In addition, since the shrinkage ratio during sintering increases, it is difficult to obtain a magnet with good dimensional accuracy.

Further, according to the present invention, the pressure of the sintering atmosphere is controlled during the period from when the relative density of the sintered body becomes 70% at the time of raising the temperature to when the temperature is lowered, whereby the magnetic properties of the sintered body are controlled. Further, it is possible to control the magnetic properties after the aging treatment. Specifically, by sintering at a relatively low pressure, a magnet having a high residual magnetic flux density and a high maximum energy product can be obtained. In addition, by sintering at a relatively high pressure, a magnet having a high coercive force can be obtained although the residual magnetic flux density is not so high. In other words, various magnets having different magnet properties can be obtained from the same raw material alloy by simply controlling the pressure of the sintering atmosphere and without changing other conditions such as sintering temperature, sintering time, and aging treatment conditions. Can be manufactured. Therefore, when manufacturing magnets having various characteristics, the management of the raw material alloy and the management of the manufacturing process become easy.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A sintered magnet manufactured according to the present invention contains R (where R is one or more rare earth elements including Y), Fe and B.

It is preferable that the contents of R and B satisfy 12 ≦ R ≦ 16 and 4 ≦ B ≦ 8 in atomic percentage. The balance is Fe.

As the rare earth element R, Nd, Pr, D
It is preferable to use at least one of y and Tb. In addition, in addition to these, La, Ce, Sm, Pm,
One or more of Eu, Gd, Ho, Er, Tm, Yb, Lu, and Y may be used. When two or more elements are used as R, a mixture such as misch metal can be used as a raw material. If the R content is too small, a high coercive force cannot be obtained because the crystal structure becomes a cubic structure having the same structure as α-Fe. On the other hand, if the R content is too large,
The number of R-rich non-magnetic phases increases, and the residual magnetic flux density decreases. If the Fe content is too low, the residual magnetic flux density will be low, and if it is too high, the coercive force will be low. If the B content is too small, the coherence becomes insufficient due to the rhombohedral braiding, and if it is too large, the B-rich nonmagnetic phase increases and the residual magnetic flux density decreases.

By substituting a part of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics. In this case, if the amount of Co substitution exceeds 50% of Fe, the magnetic properties deteriorate, so the amount of Co substitution is preferably set to 50% or less.

Further, by replacing a part of B with one or more of C, P and S, it is possible to improve productivity and reduce costs. In this case, the substitution amount is preferably 4 mol% or less of the whole. In addition, improvement of coercive force,
Al, Ti, V,
Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, G
e, Sn, Zr, Ni, Si, Hf, Ga, Zn, Cu
And the like may be added. In this case, the amount of addition is preferably 10 mol% or less in total.

The sintered magnet has a main phase having a substantially tetragonal crystal structure. The particle size of this main phase is 3-50 μm
It is preferred that it is about. And usually, the volume ratio is 1
15% non-magnetic phase.

Next, the manufacturing method of the present invention will be described.

First, an alloy is cast to obtain an ingot.
The obtained ingot is placed in a disc mill or the like for 10 to 1
The material is roughly pulverized to a particle size of about 00 μm, and then finely pulverized to a particle size of about 0.5 to 5 μm by a jet mill or the like.
In addition, hydrogen occlusion grinding can also be performed. In the hydrogen storage pulverization, the ingot is coarsely pulverized to about 30 mm square, and finely pulverized by performing hydrogen storage and hydrogen release at least once. The hydrogen storage pulverization and the mechanical pulverization may be used in combination. The element R becomes a hydride when the hydrogen absorbing and pulverizing is performed, but is dehydrogenated at around 800 ° C. in the temperature rising process of the sintering step.

The obtained powder is preferably molded in a magnetic field to obtain a molded product. In this case, the magnetic field strength is 800 kA / m
As described above, the molding pressure is preferably about 50 to 500 MPa. The density of the compact is the theoretical density (true density) of the sintered body
Is preferably 50 to 65%. If the density of the compact is too low, the shrinkage ratio during sintering will increase, and the dimensional accuracy of the sintered compact will decrease. On the other hand, if the density of the compact is too high, it is difficult to obtain a sufficiently high residual magnetic flux density after sintering.

Next, the compact is sintered. At this time, in the entire region from the time when the relative density of the sintered body becomes 70% at the time of raising the temperature to the time when the temperature is reduced, the atmospheric pressure exceeds 1 atm.
The sintering is performed preferably while maintaining the pressure at 1.2 atm or more, more preferably at 2 atm or more. Thus, a sintered body having a coercive force that can be used as a magnet without aging treatment is obtained. When the temperature is increased under a pressure of 1 atm or less and the pressure is increased to a pressure exceeding 1 atm for the first time after the relative density becomes, for example, about 90%, a high coercive force cannot be obtained. Also,
If the atmospheric pressure is too low during the above period, a high coercive force cannot be obtained.

On the other hand, if the atmospheric pressure is too high during the above period, the closed pores are less likely to shrink during sintering, resulting in a lower residual magnetic flux density. Further, even if the atmospheric pressure in the above period is significantly increased, the effect of improving the coercive force is not significantly improved. On the other hand, if the atmospheric pressure is too high, the high-pressure gas is trapped in the closed pores of the sintered body, and there is a risk that the sintered body may burst when subjected to aging treatment. If the pressure exceeds 10 atm, strict legal regulations must be met, and the cost will increase. Therefore, the atmospheric pressure in the above period is set to 10 atm or less, preferably 4 atm or less, more preferably 3 atm or less.

The control of the atmospheric pressure during sintering in the present invention is performed at least when the relative density of the sintered body is 7 at the time of temperature rise.
What is necessary is just to perform in the period from 0% to the start of temperature fall. That is, a high-pressure atmosphere may be used before the relative density of the sintered body reaches 70%, for example, from the beginning of the heating process. In addition, depending on the composition of the sintered body and the temperature control pattern in the sintering step, sintering may progress even in the temperature decreasing step. Therefore, it is preferable to control the above-mentioned atmospheric pressure also in the temperature decreasing step.

The atmosphere gas during sintering is preferably composed of a rare gas such as Ar or an inert gas such as nitrogen.
In particular, it is preferable to be composed of a rare gas.

The relative density of the sintered body is a value obtained by dividing the measured density of the sintered body by its theoretical density. The theoretical density of the sintered body in the present specification, "Solid Physics Vol. 21, No. 1, 37-45
(1986) "(published by Agne Technical Center), which is the density of R ₂ Fe ₁₄ B, for example, Nd ₂ Fe ₁₄
B is 7.58 Mg / m ³ and Dy ₂ Fe ₁₄ B is 8.07 Mg / m ³ . When two or more elements R are used, a linear approximation is performed according to the ratio of each element. Specifically, Nd and Dy are used as the element R, and their molar ratio is Nd: Dy =
If x: y, the theoretical density is (7.58x + 8.07y) / (x + y).

The sintering temperature (stable temperature) is 1000 to 11
The temperature is preferably set to 00 ° C. The stable temperature is a temperature in a stable temperature range between a temperature rising process and a temperature falling process. The time for maintaining the temperature at a stable temperature is preferably 0.1 to 100 hours. If the sintering temperature is too low or the sintering time is too short, sintering does not proceed sufficiently and the residual magnetic flux density tends to be low. On the other hand, if the sintering temperature is too high or the sintering time is too long, the crystal grains become coarse and the coercive force tends to decrease. The temperature at which the relative density of the sintered body becomes 70% depends on the composition of the sintered body and the pressure of the molded body, but is usually about 800 to 900 ° C.

When sintering in a high-pressure atmosphere according to the present invention, the relative density of the sintered body after completion of sintering is usually 91%.
~ 96%.

By sintering at a relatively high pressure as described above,
A sintered body that can be used as a magnet can be obtained without aging treatment, but may be subjected to aging treatment if necessary. The aging treatment is preferably performed by heating in an inert gas atmosphere at a temperature of preferably 500 ° C. or more and a sintering temperature or less, more preferably 500 to 950 ° C. for 0.1 to 100 hours. The coercive force is further improved by the aging treatment. Note that the aging treatment may be constituted by a multi-step heat treatment. For example, in the aging treatment including the two-stage heat treatment, the first-stage heat treatment is performed at a temperature of 700 ° C. or higher and lower than the sintering temperature by 0.1%.
It is preferable to perform the heat treatment in the second stage at 500 to 700 ° C. for 0.1 to 100 hours.

As described above, the present invention includes not only high-pressure sintering but also an invention in which the magnetic properties of a sintered body are controlled by controlling the atmospheric pressure. In this case, at least during the period from the time when the relative density of the sintered body becomes 70% at the time of raising the temperature to the start of the temperature drop, the atmospheric pressure is set to 0 to 10
By controlling the pressure within the range of the atmospheric pressure, sintered bodies having different coercive force and residual magnetic flux density can be obtained using the same raw material alloy.

The use of the sintered magnet produced according to the present invention is not particularly limited, and can be applied to various devices such as a motor and a speaker.

[0032]

EXAMPLES Example 1 Sintered body samples shown in Table 1 were produced by the following procedure.

An alloy powder was obtained by grinding the cast alloy ingot in a nitrogen gas atmosphere. The composition (molar percentage) of the alloy powder was as follows: composition 1: 12.78Nd-5.96B-0.06Cu-0.11Co-balance Fe, composition 2: 12.78Nd-5.96B-0.08Cu-0.11Co-balance Fe, composition 3: 12.78 Nd-5.96B-0.04Cu-0.55Co-balance Fe, composition 4: 12.78Nd-5.96B-0.04Cu-0.11Co-balance Fe, composition 5: (11.65Nd-2.38Dy) -6.08B-0.10Cu-0.56 Co-0.49A
l-0.05Sn-The balance was Fe.

Next, the alloy powder was compacted at a pressure of 50 MPa in a pulse magnetic field having a strength of 5 T to obtain a compact having a relative density of 50%. However, in the sample of composition 5, the strength was 1.2T.
Molding at a pressure of 150 MPa in a static magnetic field of
% Of a molded product was obtained.

Next, the compact was sintered in a vacuum or in an Ar atmosphere to obtain a sintered body sample. Table 1 shows the atmospheric pressure during sintering. The atmosphere pressure was kept constant throughout the sintering process. Sintering was performed under the following conditions. In the following sintering conditions, the temperature is the stable temperature, and the time is the holding time at the stable temperature.

Sintering condition 1: heat treatment at 1070 ° C. for 4 hours, sintering condition 2: heat treatment at 1050 ° C. for 4 hours, sintering condition 3: heat treatment at 1090 ° C. for 4 hours

Table 1 shows the composition, sintering conditions, relative density, coercive force (HcJ), residual magnetic flux density (Br), and maximum energy product ((BH) max) for each sample. Each sample was subjected to aging treatment in an Ar atmosphere under the following conditions. Table 1 also shows the coercive force and the maximum energy product after the aging treatment.

Aging condition 1: After heat treatment at 700 ° C. for 1 hour,
Heat treatment at 600 ° C for 10 hours, Aging condition 2: Heat treatment at 900 ° C for 1 hour, then 540 ° C for 1 hour
Time heat treatment

[0039]

[Table 1]

From Table 1, it can be seen that, according to the present invention, a sintered body having a low density and a high coercive force can be obtained by sintering in a high pressure atmosphere from the time when the density of the sintered body is low. The coercive force at this time is close to the coercive force after the aging treatment of the sample sintered in a vacuum, even though the aging treatment is not performed, and is a value that can withstand practical use. And, after the aging treatment, the coercive force is further improved. On the other hand, the sample sintered in a vacuum has only a low coercive force that is not practical before aging treatment.

The theoretical density of the samples of compositions 1 to 4 is 7.58 Mg / m ³ , and the theoretical density of the sample of composition 5 is 7.66 Mg / m ³ .

In Table 1, the coercive force of the samples of compositions 1 to 4 is not particularly high as a Nd ₂ Fe ₁₄ B-based magnet, but this is because the content of element R is considerably smaller than that of a normal composition. It is. However, since the element R was reduced and Cu was added, the coercive force was considerably higher than when the element R was reduced without adding Cu. Since a high residual magnetic flux density is obtained by reducing the amount of the element R, as a result, an extremely large maximum energy product is obtained over the sample of the composition 5 having a large amount of the element R.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Atsushi Sakamoto 1-1-13 Nihonbashi, Chuo-ku, Tokyo TDK Corporation F-term (reference) 4K018 AA27 DA22 DA31 DA35 5E040 AA04 BD01 CA01 HB03 NN12 NN13 NN17 5E062 CD04 CG02

Claims (3)

[Claims] 1. A method for producing a sintered magnet containing R (R is at least one of rare earth elements), Fe and B, comprising forming a compact by molding powder of a raw material alloy. And a sintering step of sintering the molded body to obtain a sintered body. In the sintering step, the temperature is lowered at least when the relative density of the sintered body becomes 70% at the time of temperature rise. A method for producing a sintered magnet in which the atmospheric pressure is increased from more than 1 atm to 10 atm or less in a period up to the start. 2. The method according to claim 1, wherein the sintered body obtained in the sintering step is used as a sintered magnet without performing aging treatment. 3. A method for producing a sintered magnet containing R (R is at least one of rare earth elements), Fe and B, wherein a powder of a raw material alloy is molded to obtain a molded body. And a sintering step of sintering the molded body to obtain a sintered body. In the sintering step, the temperature is lowered at least when the relative density of the sintered body becomes 70% at the time of temperature rise. A method for producing a sintered magnet in which a sintered body having a different coercive force and a different residual magnetic flux density is obtained using the same raw material alloy by controlling the atmospheric pressure within a range of 0 to 10 atm until the start.