JP2003293008A - Rare-earth sintered magnet and manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare-earth sintered magnet in which the amount of a rare-earth element (Nd or Pr as a typical example) constituting a nonmagnetic phase in a grain-boundary phase is reduced and which has excellent magnetic properties and reliability on corrosion resistance and also to provide its manufacturing method. <P>SOLUTION: A sintered compact is produced using a first rare-earth alloy powder represented by (R1)<SB>2</SB>T<SB>14</SB>Q (wherein, R1 is at least one element selected from the group of rare-earth elements including Sc and Y; T is Fe or a mixture of Fe and at least one element among transition-metal elements excluding Fe; and Q is boron or a mixture of boron and carbon) and a second rare-earth alloy powder represented by (R2)<SB>x</SB>T<SB>100-x</SB>(wherein, R2 is at least one element which is selected from the group of rare-earth elements including Sc and Y and necessarily includes at least either of Sc and Y; T is Fe or a mixture of Fe and at least one element among transition-metal elements excluding Fe; and x (mass%) satisfies the relation of 0<X≤60. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an R—Fe—B rare earth magnet and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, Nd and / or Pr have been mainly used as the rare earth element R of R-Fe-B system rare earth magnets. The reason is that these rare earth elements bring particularly excellent magnetic properties.

Recently, the applications of R-Fe-B magnets have expanded more and more, and the consumption of Nd and Pr has been rapidly increasing.
There is a strong demand to efficiently use Nd and Pr, which are valuable resources, and to keep the material cost of the R—Fe—B magnet low.

[0004]

The simplest method of reducing the consumption of Nd and Pr is to replace Nd and Pr with a rare earth element that acts similarly to Nd and Pr. However, rare earth elements other than Nd and Pr are added to R-Fe-B.
It is known that when added to a rare earth based magnet, magnetic properties such as magnetization are deteriorated, and until now, rare earth elements other than Nd and Pr have been used in the manufacture of R—Fe—B based rare earth magnets. Almost never.

For example, when yttrium (Y), which is one of rare earth elements, is added to a raw material together with Nd and the raw material is melted and solidified to produce an R-Fe-B type alloy, Y is the main phase of the alloy. Is taken into. Main phase of R-Fe-B based alloy is originally has a R ₂ Fe _{1 4} B-type tetragonal crystal structure, the R is substituted with Nd or Pr (and their Dy
, Tb, etc.) is known to exhibit the highest magnetization. R ₂ which constitutes such a main phase
When R of the Fe ₁₄ B type crystal structure is partially or wholly replaced with a rare earth element such as Y, the magnetization is greatly reduced.

From the above, it is considered that addition of a rare earth element R other than Nd and Pr (and Dy and Tb substituting for them) which lowers the magnetization to the raw material should be avoided as much as possible. ing.

On the other hand, Nd and Pr are the main phase (R ₂ Fe ₁₄ B
Phase), it also exists in the grain boundary phase (R-rich phase) and plays an important role of forming a liquid phase during the sintering process. However, Nd and P existing in the grain boundary phase
Although r plays an important role in the sintering process, it forms a nonmagnetic phase in the grain boundary phase and does not contribute to the improvement of magnetization. In other words, the portion containing Nd and Pr charged as the raw material is always consumed for the formation of the nonmagnetic phase and does not directly contribute to the magnet characteristics.

In order to effectively utilize Nd and Pr and to effectively exhibit excellent magnetic characteristics, it is preferable to incorporate most of Nd and Pr into the R ₂ Fe ₁₄ B type crystal phase. However, conventionally, there has been no technique for realizing this.

Further, the rare earth element is easily oxidized, and a rare earth element oxide is formed in the grain boundary phase (R-rich phase) during the liquid phase sintering process, and this oxide lowers the corrosion resistance reliability of the sintered magnet. I have something to do. For example, Nd oxide (Nd ₂
O ₃ ) further reacts with water in the air, etc.
d (OH) ₃ ) is produced. Since the process of producing this hydroxide is accompanied by volume expansion (about 3 times), cracks or the like may occur in the grain boundary phase, or even grain removal may occur. Further, even if a plating film is formed on the surface of the sintered body, the film may swell or peel off.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to reduce the amount of rare earth elements (typically Nd and Pr) forming a nonmagnetic phase in a grain boundary phase. In addition, it is an object of the present invention to provide a rare earth sintered magnet excellent in magnetic characteristics and corrosion resistance and a manufacturing method thereof.

[0011]

The method for producing a rare earth sintered magnet according to the present invention comprises (R1) ₂ T ₁₄ Q (R1 is at least one element selected from the group of rare earth elements containing Sc and Y). , T is Fe, or a mixture of Fe and at least one kind of transition metal element other than Fe, and Q is boron or a mixture of boron and carbon), which is a first rare earth alloy powder having a main phase. Preparation process and (R2) _x T
_100-x (R2 is at least one element selected from the group of rare earth elements including Sc and Y, and always contains at least one element of Sc and Y, and T is Fe, or Fe and Fe other than Fe. A mixture of at least one transition metal element with x (mass%) satisfying a relation of 0 <x ≦ 60), which is a main phase of the first rare earth alloy powder. For preparing a second rare earth alloy powder having a main phase having a composition containing a large amount of at least one element of Sc and Y than the above, and for sintering containing the first rare earth alloy powder and the second rare earth alloy powder A step of preparing a powder mixture and a step of sintering the powder mixture for sintering to obtain a sintered body having a main phase having a composition represented by R ₂ T ₁₄ Q (R includes R ₁ and R ₂ ). And the step of making The above object is achieved.

The powder mixture for sintering has a content of 8 atomic% or more and 2
The total content of Sc and Y in R is 1.5 atomic% or less of R and 3 atomic% or more and 20 atomic% or less of Q, the balance is T, additional elements and unavoidable impurities.
It is preferably 0.5 atomic% or more and 25 atomic% or less. The additive elements are Al, Cu, Ga, Cr, Mo, V,
It is preferably at least one of Nb and Mn. It is preferable that the total amount of trace additives be 1% by mass or less.

In a preferred embodiment, the sintering step includes a liquid phase sintering step, and (R2) _x T _100-x forms a liquid phase in the sintering step, and in the liquid phase sintering step,
Sc or Y contained in the powder mixture for sintering is made to exist more in the grain boundary phase around the main phase than in the main phase.

In a preferred embodiment, Sc or Y oxide is formed in the grain boundary phase in the sintering step.

It is preferable that R1 does not contain Sc and / or Y or contains more than 0 atom% and 15 atom% or less, and R2 contains Sc and / or Y in an amount of 5 atom% or more and 100 atom% or less. R1 is preferably substantially free of Sc and Y, and R2 is preferably substantially free of Sc and / or Y.

In a preferred embodiment, the second rare earth alloy powder has a main phase having a composition represented by (R2) ₂ T ₁₇ .

In a preferred embodiment, the first rare earth alloy powder contains Co.

In the powder mixture for sintering, the second
The average particle size of the rare earth alloy powder is preferably smaller than the average particle size of the first rare earth alloy powder. The average particle size of the first rare earth alloy powder is 1 μm or more and 5 μm or less,
The average particle diameter of the second rare earth alloy powder is 1 μm or more and 3 μm
The following is preferable.

The content of the second rare earth alloy powder in the sintering powder mixture is preferably 1% by mass or more and 30% by mass or less.

The amount of oxygen contained in the sintering powder mixture is preferably 1000 ppm or more and 10000 ppm or less on a mass basis.

The sintering step is performed at 650 ° C. or higher and 1000 ° C.
First to maintain the temperature within the following range for 10 minutes to 240 minutes
It is preferable to include the step (1) and the second step of further promoting the sintering at a temperature higher than the holding temperature in the first step.

The rare earth sintered magnet of the present invention is characterized by being manufactured by any one of the above methods for manufacturing a rare earth sintered magnet.

The rare earth sintered magnet of the present invention is R ₂ T ₁₄ Q
(R is at least one element selected from the group of rare earth elements including Sc and Y, T is Fe, or a mixture of Fe and at least one transition metal element other than Fe,
Q has a main phase having a composition represented by boron or a mixture of boron and carbon) and a grain boundary phase containing an oxide of R, and the oxide of R is other than the oxide of Sc or Y. It contains more than the oxide of the rare earth element.

In a preferred embodiment, the main phase is S
Substantially free of c or Y, the grain boundary phase contains an oxide of Sc or Y.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION R-Fe of an embodiment according to the present invention
Method for producing -B based rare-earth sintered _{magnet, R 2 T 1 4 Q (} R
Is at least one element selected from the group of rare earth elements including Sc and Y, T is Fe, or Fe and Fe
A mixture with at least one kind of transition metal element other than Q, wherein Q is boron or a mixture of boron and carbon), and a method for producing a rare earth sintered magnet, the method comprising: ) -Step (d) are included.

Step (a): A step of preparing a first rare earth alloy powder having a main phase having a composition represented by (R1) ₂ T ₁₄ Q.

Step (b): (R2) _x T _100-x (0 mass%
Second rare earth alloy powder having a main phase represented by <x ≦ 60% by mass and having a composition containing more of at least one element of Sc and Y than the main phase of the first rare earth alloy powder. A step of preparing.

Step (c): A step of preparing a sintering powder mixture containing the first rare earth alloy powder and the second rare earth alloy powder.

Step (d): A step of producing a sintered body having a main phase having a composition represented by R ₂ T ₁₄ Q by sintering the powder mixture for sintering.

The rare earth element R1 contained in the main phase of the first rare earth alloy powder is at least one element selected from the group of rare earth elements containing Sc and Y. The rare earth element R2 contained in the main phase of the second rare earth alloy powder is selected from the group of rare earth elements containing Sc and Y, and is at least one element necessarily containing at least one element of Sc and Y.

In the manufacturing method of the embodiment of the present invention, the rare earth element constituting the main phase (also referred to as R ₂ T ₁₄ Q phase) responsible for hard magnetism in the rare earth sintered magnet is a non-magnetic grain boundary phase ( Sc and / or Y is added in order to prevent wasteful consumption by composing the oxide). The rare earth element that constitutes the R ₂ T ₁₄ Q phase is
Typically, it is a light rare earth element such as Nd or Pr, and may be used as a mixture with a heavy rare earth element such as Dy or Tb in order to improve heat resistance and the like. Sc and Y are Nd
The free energy (ΔGo) of oxide formation is smaller than that of light rare earth elements such as Cr and Pr and heavy rare earth elements such as Dy and Tb, and they are more easily oxidized than these rare earth elements, and
It produces an oxide that is more chemically and thermally stable than the above oxides of rare earth elements. For example, the free energy of oxide formation (ΔGo) at 800 ° C. is about −1590 kJ / mol for Y and Sc, and about −1500 k for Nd.
Less than about -1550 kJ / mol for J / mol and Dy. Therefore, when Sc or Y coexists with other rare earth elements, they are preferentially oxidized to produce oxides of Sc and Y. Further, when Sc or Y coexists with the oxide of the other rare earth element, it reduces the oxide of the other rare earth element to generate the oxide of Sc or Y.

Therefore, when the rare earth element constituting the main phase responsible for hard magnetism and Sc or Y are mixed and used, Sc and Y are preferentially oxidized, so that other rare earth elements are oxidized. Can be suppressed. Even when Sc or Y is mixed with other rare earth elements in the raw material alloy and a raw material alloy having a single composition is used, consumption (oxidation) of the rare earth elements forming the R ₂ T ₁₄ Q phase can be suppressed ( Japanese Patent Application 20 by the applicant
01-300511). However, as a result of further study by the present inventor, when a raw material alloy having a single composition is used,
Sc and Y may remain in the vicinity of the center of the R ₂ T ₁₄ Q phase, which may cause deterioration of magnetic properties beyond the allowable range.
For example, the Is of the Nd ₂ Fe ₁₄ B phase is 1.6T, while the Is of the Y ₂ Fe ₁₄ B phase is only 1.4T.
It is preferable to reduce the amount of Y remaining in the main phase as much as possible.

Therefore, in the manufacturing method of the embodiment of the present invention, in order to reduce the amount of Sc or Y remaining in the R ₂ T ₁₄ Q phase, the composition represented by (R1) ₂ T ₁₄ Q is used. A first rare earth alloy powder having a main phase, and (R2) _x T
_100-x (typically (R2) ₂ T ₁₇ (where 2, 17 are atomic ratios)), which is at least one of Sc and Y more than the main phase of the first rare earth alloy powder. And a second rare earth alloy powder having a main phase having a composition containing a large amount of the above element. To prevent Sc and Y from substantially remaining in the main phase of the sintered magnet, the first rare earth alloy powder should be S.
It is preferable to use a material that does not substantially contain c or Y.

Hereinafter, FIGS. 1 (a) to 1 (c) and FIG.
A mechanism capable of reducing Sc and Y contained in the main phase of the sintered magnet in the method for manufacturing a rare earth sintered magnet according to the embodiment of the present invention will be described with reference to (a) to (c). Here, for simplification, a case where the first rare earth alloy powder mainly has the Nd ₂ Fe ₁₄ B phase and the second rare earth alloy powder mainly has the Y ₂ Fe ₁₇ phase will be described as an example.

FIG. 1 is a schematic diagram for explaining a method for producing a rare earth sintered magnet described in Japanese Patent Application No. 2001-300511, and FIG. 1 (a) is a schematic view of a raw material alloy powder compact. 1B is a diagram schematically showing the interdiffusion phenomenon in the liquid phase sintering process.
(C) is a figure which shows typically the concentration profile of the rare earth element in the main phase crystal grain in the obtained sintered compact. Figure 2
FIG. 2A is a schematic diagram for explaining a method for manufacturing a rare earth sintered magnet according to an embodiment of the present invention, FIG. 2A is a diagram schematically showing a raw material alloy powder compact, and FIG. FIG. 2 is a diagram schematically showing an interdiffusion phenomenon in a liquid phase sintering process, and FIG. 2C schematically shows a concentration profile of rare earth elements in main phase crystal grains in the obtained sintered body. It is a figure.

First, referring to FIGS. 1A to 1C, (Nd, Y) ₂ Fe ₁₄ having a single composition containing Nd and Y.
A method of forming a sintered body using B powder will be described.

First, as shown in FIG. 1A, a known method (for example, ingot casting method or strip casting method) is used.
To produce (Nd, Y) ₂ Fe ₁₄ B powder. Ingot casting method (cooling rate: less than 10 ² ° C / sec)
By cooling the molten alloy with, Y can be made to exist in the main phase in a high concentration. The cooling rate in the quenching method such as the strip casting method is 10 ² ° C / sec or more.

In this raw material alloy powder, Y exists mainly in the main phase (R ₂ Fe ₁₄ B phase) together with Nd. In the ingot alloy, the Y concentration in the grain boundary phase (R rich phase) is lower than the Y concentration in the main phase, and the Nd-rich phase is formed in the grain boundary phase. On the other hand, in the strip cast alloy, Y is also present in the grain boundary phase, which is due to nonequilibrium. Note that Y existing in the grain boundary phase also has the same effect as Y existing in the main phase in the following steps.

When a compact of such a raw material alloy powder is sintered, a plurality of crystal grains grow in the liquid phase sintering process while being fused to each other, as shown in FIG. 1 (b).
Y is diffused from inside the main phase crystal grains to the grain boundary phase, and an oxide of Y is generated in the grain boundary phase. At that time, Nd is diffused in the opposite direction (toward the main phase crystal grains). As a result, the Y concentration in the grain boundary phase becomes higher than the Y concentration in the main phase crystal grains, so that Y contained in the main phase of the sintered body can be reduced and the magnetization can be increased. Such interdiffusion between Y and Nd occurs because Y has a lower oxide formation free energy than Nd.

However, only by utilizing mutual diffusion, the Y concentration near the center of the main phase remains relatively high as shown in FIG. 1 (c). That is, of the Y contained in the main phase of the raw material alloy powder, the Y existing outside the crystal grains is replaced with Nd by mutual diffusion, but the Y near the center of the crystal grains cannot be sufficiently diffused. This is because they will remain.

On the other hand, in this embodiment, as shown in FIG.
As shown in, the first rare earth alloy powder mainly containing the Nd ₂ Fe ₁₄ B phase and the second rare earth alloy powder mainly containing the Y ₂ Fe ₁₇ phase are used.

When a compact containing the first rare earth alloy powder and the second rare earth alloy powder is sintered, Y ₂ Fe is produced in the liquid phase sintering process.
Y contained in the _17th phase is preferentially oxidized, and Y ₂ O ₃ is formed in the grain boundary phase, as shown in FIG. Of course, Nd ₂
O ₃ (not shown) may be formed, but the amount is Y ₂
Less than O ₃ .

As a result, as shown in FIG. 2C, Nd
Y does not exist in the ₂ Fe ₁₄ B phase, and the Nd-rich phase and Y ₂ O
A grain boundary phase containing ₃ and ₃ is formed. Therefore, in the obtained sintered body, Y ₂ Fe ₁₄ B is hardly present in the main phase responsible for hard magnetism, and the magnetization can be increased. Further, chemically and thermally stable Y ₂ O ₃ is preferentially generated in the grain boundary phase, and the formation of Nd ₂ O ₃ , which causes deterioration in corrosion resistance reliability, is suppressed.

As described above, according to the method for manufacturing a rare earth sintered magnet of the embodiment of the present invention, the amount of Nd forming the nonmagnetic phase in the grain boundary phase is reduced, and moreover, the magnetic characteristics and the corrosion resistance are excellent. A rare earth sintered magnet is obtained.

Here, for simplicity, the first rare earth alloy powder is Nd ₂ Fe as the main phase represented by (R1) ₂ T ₁₄ Q.
_{Although the} case where the second rare earth alloy powder has the ₁₄ B phase and the Y ₂ Fe ₁₇ phase as the main phase is exemplified, the present invention is not limited to this.
Sc may be used instead of Y, or Y and Sc may be mixed and used.

The first rare earth alloy powder may contain another rare earth element (for example, Pr, Dy or Tb) as the rare earth element forming the main phase as described above, or may contain Y and / or Sc. good. Y and / or S
If the content of c is less than the content in the second rare earth alloy powder, the effect of the present invention can be obtained. When the first rare earth alloy powder contains Y and / or Sc, the interdiffusion mechanism described with reference to FIG. 1 also occurs.

The first rare earth alloy powder having the main phase represented by (R1) ₂ T ₁₄ Q does not have to be one kind.
A plurality of kinds of first rare earth alloy powders having different compositions of the rare earth alloy powders may be used. For example, depending on the composition of the main phase, the first rare earth alloy powder containing a larger amount of Q (typically B) may be further mixed, that is, the first rare earth alloy powder containing a larger amount of the R rich phase.

Further, the first rare earth alloy powder preferably contains Co. Conventionally, in order to improve the heat resistance of R-Fe-B rare earth magnet, Fe in R ₂ Fe ₁₄ B phase
Is partially replaced with Co. When a part of Fe is replaced by Co, the Curie temperature of the main phase rises, so that it becomes possible to exhibit excellent magnet characteristics even in a higher temperature environment. However, if Co is simply added to the raw material alloy, Co not only replaces Fe in the main phase, but also NdCo ₂ compound (or P
rCo ₂ compound) is formed. That is, the added Co
Is not used for the substitution of Fe and is wasted in the grain boundary phase. Since this NdCo ₂ compound is a ferromagnetic material, there is a problem that the coercive force of the sintered magnet is lowered.

According to the manufacturing method of the embodiment of the present invention, N
In addition to rare earth elements such as d and Pr, Y and Sc are added and these elements are concentrated in the grain boundary phase, so that Y and the like can be obtained in the same manner as described in Japanese Patent Application No. 2001-300511. In the grain boundary phase, transition metals such as Co, which would have been consumed in the production of ferromagnetic compounds, were incorporated into the main phase crystal grains, and Fe, which is the main phase responsible for hard magnetism, was effectively replaced with Co. Can be made.

The second rare earth alloy powder is not limited to one mainly having the (R2) ₂ T ₁₇ phase, but one having a main phase represented by (R2) _x T _100-x (where x is% by mass). If However, the total content of Sc and / or Y in the second rare earth alloy powder is set to be larger than the total content of Sc and / or Y in the first rare earth alloy powder. The (R2) _x T _100-x phase contained in the second rare earth alloy powder preferably forms a liquid phase in the liquid phase sintering process of the sintering process. Here, (R2) _x T _100-x is not limited to the one that alone forms a liquid phase, and the liquid phase may be formed by a eutectic reaction or the like. For example, a rare earth alloy powder mainly having a (R2) ₁ T ₁ phase, a (R2) ₁ T ₂ phase, a (R2) ₁ T ₄ phase, or the like can be used.

From the viewpoint of the magnetic characteristics of the sintered magnet, the sintering powder mixture (including the first rare earth alloy powder and the second rare earth alloy powder) used for forming the compact is 8 atomic% or more 2
The total content of Sc and Y in R is 1.5 atomic% or less of R and 3 atomic% or more and 20 atomic% or less of Q, the balance is T, additional elements and unavoidable impurities.
It is preferably 0.5 atomic% or more and 25 atomic% or less. The additive elements are Al, Cu, Ga, Cr, Mo, V,
It is preferably at least one of Nb and Mn. The total amount of added elements is preferably 1% by mass or less.

The average particle size of the second rare earth alloy powder is
It is preferably smaller than the average particle size of the first rare earth alloy powder. By making the average particle size of the second rare earth alloy powder smaller than the average particle size of the first rare earth alloy powder, the second rare earth alloy powder is more uniformly sintered around the first rare earth alloy powder. Therefore, it is possible to uniformly react with oxygen in the mixed powder for sintering and more reliably obtain the effect of the present invention. From the viewpoint of magnetic properties and moldability, the average particle size (FSSS particle size) of the first rare earth alloy powder is preferably 1 μm or more and 5 μm or less, and the average particle size of the second rare earth alloy powder is 1 μm or more and 3 μm or less. It is preferable.

The content of the second rare earth alloy powder in the sintering powder mixture is preferably 1% by mass or more and 30% by mass or less. If it is 1 mass% or less, the above effects may not be sufficiently exhibited, and if it exceeds 30 mass%, Sc
In some cases, Y and / or Y cannot completely react and remain in the main phase to deteriorate magnetic properties.

Further, in order to effectively utilize the property that Sc and Y are more easily oxidized than other rare earth elements, the amount of oxygen contained in the sintering powder mixture is 1000 on a mass basis.
It is preferably from ppm to 10,000 ppm. If the oxygen amount is less than 1000 ppm, Sc and Y are not sufficiently oxidized, and as a result, Sc and Y may be present in the main phase, which is not preferable. Conversely, the amount of oxygen is 1000
If the amount exceeds 0 ppm and becomes too large, rare earth elements other than Sc and Y are also consumed for oxide formation, so that the amount of rare earth elements contributing to liquid phase formation decreases, which is sufficient in the sintering step. A liquid phase is not formed, and as a result, the sintered density is lowered and the magnetic properties are deteriorated, which is not preferable. As described above, the sintered magnet formed by using the powder whose oxygen concentration is controlled contains oxygen in a final mass ratio of 1000 to 10000 ppm. It is preferable to control the final oxygen concentration to 6000 ppm or less.

The embodiments according to the present invention will be described in more detail below.

[Raw material alloy] First, (R1) ₂ T ₁₄ Q (R
1 is at least one element selected from the group of rare earth elements including Sc and Y, T is Fe, or Fe and F
a mixture with at least one transition metal element other than e, Q
Is a first rare earth alloy powder having a main phase of a composition represented by boron or a mixture of boron and carbon.

Raw material alloy of the first rare earth alloy powder (mother alloy)
Where R1, T and Q are each 8 atomic% ≦ R1 ≦
18 atomic%, 62 atomic% ≤ T ≤ 89 atomic%, 3 atomic% ≤
An alloy having a range of Q ≦ 20 atomic% is prepared. The raw material alloy for the first rare earth alloy powder is the main phase (R1) ₂
It includes many R1 and B than the stoichiometric composition of the T ₁₄ Q phase, to form an R-rich phase with the main phase. As described above, the R-rich phase plays a role of forming a liquid phase in the sintering process.

The first rare earth alloy powder having the (R1) ₂ T ₁₄ Q phase does not have to be of one type, and a plurality of types of first rare earth alloy powders having different overall compositions may be used. good. For example, R and / or Q
1) ₂ T ₁₄ first rare-earth alloy powder may be mixed and used, further containing excess than the stoichiometric composition of the Q-phase. The composition of the first rare earth alloy powder is R1, T and Q.
Are 10 atom% ≦ R1 ≦ 20 atom% and 60 atom% respectively
It is preferably in the range of ≦ T ≦ 87 atomic%, 3 atomic% ≦ Q ≦ 20 atomic%. R and Q, which are contained in excess of the stoichiometric composition of the (R1) ₂ T ₁₄ Q phase, contribute to forming a liquid phase in the sintering process, but when R and B are insufficient, the second rare earth alloy is formed. (R2) _x T mainly contained in powder
_{The 100-x} phase (for example, the above-mentioned Nd ₂ Fe ₁₇ phase) may not be sufficiently liquefied, and the (R2) _x T _{100 -x} phase may remain in the sintered body. Since the (R2) _x T _100-x phase is typically a soft magnetic phase, a large amount of the (R2) _x T _100-x phase may cause a decrease in coercive force.

The first rare earth alloy powder preferably contains substantially no Sc or Y, but if the content is more than 0 atomic% and 15 atomic% or less, and more preferably less than 5 atomic%, It is possible to obtain an effect that is substantially the same as that in the case where it is not substantially included.

To prepare the raw material alloy of the first rare earth alloy powder, for example, an ingot casting method or a quenching method (strip casting method, centrifugal casting method, etc.) can be used.
Hereinafter, the method for producing the raw material alloy will be described by taking the case of using the strip casting method as an example.

First, a raw material alloy having the above composition is melted by high frequency melting in an argon atmosphere to form a molten alloy. Next, after holding this molten alloy at 1350 ° C., the molten alloy is rapidly cooled by the single roll method to obtain a flaky alloy ingot having a thickness of, for example, about 0.3 mm. The rapid cooling conditions at this time are, for example, a roll peripheral speed of about 1 m / sec, a cooling rate of 500 ° C./sec, and supercooling of 200 ° C. The rapidly-quenched alloy slab produced in this manner is used for 1 to 10 m before the next hydrogen pulverization.
Grind into flakes of size m. The method for producing the raw material alloy by the strip casting method is disclosed in, for example, US Pat. No. 5,383,978.

[First Grinding Step] A plurality of raw material packs (for example, made of stainless steel) are filled with the above-mentioned raw material alloy slabs roughly crushed into flakes and mounted on a rack. After this,
The rack on which the raw material pack is mounted is inserted into the hydrogen furnace. Next, the lid of the hydrogen furnace is closed, and hydrogen embrittlement treatment (hereinafter,
The process may be referred to as "hydrogen pulverization process"). The hydrogen pulverization process is executed according to the temperature profile shown in FIG. 3, for example. In the example of FIG. 3, the vacuum evacuation process I is first performed for 0.5 hours, and then the hydrogen storage process II is performed for 2.5 hours. In the hydrogen storage process II, hydrogen gas is supplied into the furnace to create a hydrogen atmosphere in the furnace. The hydrogen pressure at that time is preferably about 200 to 400 kPa.

Then, after heating under a reduced pressure of about 0 to 3 Pa and carrying out the dehydrogenation process III for 5.0 hours, while supplying argon gas into the furnace, the cooling process IV of the raw material alloy was carried out at 5.
Run for 0 hours.

In the cooling step IV, when the atmospheric temperature in the furnace is relatively high (for example, when it exceeds 100 ° C.), an inert gas at room temperature is supplied to the inside of the hydrogen furnace for cooling. After that, when the raw material alloy temperature has dropped to a relatively low level (for example, 100 ° C. or lower), an inert gas cooled to a temperature lower than room temperature (for example, room temperature minus 10 ° C.) is supplied into the hydrogen furnace. It is preferable from the viewpoint of cooling efficiency. The supply amount of argon gas is 10 to 10
It may be about 0 Nm ³ / min.

When the temperature of the raw material alloy is lowered to about 20 to 25 ° C., an inert gas at about room temperature (a temperature lower than room temperature but within a range of 5 ° C. or less) is blown into the hydrogen furnace. However, it is preferable to wait until the temperature of the raw material reaches the room temperature level. By doing so, when the lid of the hydrogen furnace is opened, it is possible to avoid the situation where dew condensation occurs inside the furnace. If moisture is present inside the furnace due to condensation,
Since the water content is vaporized in the subsequent vacuuming process, it is difficult to increase the degree of vacuum, and the time required for the vacuuming process I becomes longer, which is not preferable.

When the roughly crushed alloy powder after hydrogen crushing is taken out from the hydrogen furnace, it is preferable to carry out the taking out operation in an inert atmosphere so that the roughly crushed powder does not come into contact with the atmosphere.
This is because the coarsely pulverized powder is prevented from oxidizing and generating heat, and the magnetic characteristics of the magnet are improved. Next, the roughly crushed raw material alloy is filled in a plurality of raw material packs and mounted on a rack.

By hydrogen crushing, the rare earth alloy is 0.1 m
It is crushed to a size of m to several mm, and the average particle size is 5
It becomes less than 00 μm. After pulverizing with hydrogen, it is preferable that the embrittled raw material alloy is finely crushed and cooled by a cooling device such as a rotary cooler. When the raw material is taken out in the relatively high temperature state, the cooling process time by the rotary cooler or the like may be relatively long.

According to the hydrogen pulverization, the R-rich portion of the raw material alloy occludes a large amount of hydrogen and cracks are formed from the portion, so that a large amount of Nd is exposed on the surface of the produced coarse pulverized powder, which is extremely high. It is in a state where it is easily oxidized.

[Second crushing step] Next, the coarsely crushed powder produced in the first crushing step is finely crushed using a jet mill crushing device. A cyclone classifier is connected to the jet mill grinding device used in this embodiment.

The jet mill crushing device receives the supply of the rare earth alloy (coarse crushed powder) roughly crushed in the first crushing step,
Grind in a grinder. The powder pulverized in the pulverizer is collected in the recovery tank through the cyclone classifier.

The details will be described below.

The coarsely crushed powder introduced into the crusher is wound up in the crusher by the inert gas jetted at a high speed from the internal nozzle, and swirls in the crusher together with the high-speed air stream. Then, the crushed objects are finely crushed by mutual collision.

The powder particles finely pulverized in this way are guided by the ascending air current to the classification rotor and classified by the classification rotor. The coarse powder cannot be passed through the classification rotor and is pulverized again. The powder pulverized to a predetermined particle size or less is introduced into the classifier body of the cyclone classifier. In the main body of the classifier, relatively large powder particles having a predetermined particle size or more are accumulated in a recovery tank installed in the lower part, but the ultrafine powder is discharged to the outside through an exhaust pipe together with an inert gas flow.

In this embodiment, a slight amount of oxygen (20,000 pp is added to the inert gas introduced into the jet mill pulverizer.
m or less, for example, about 10,000 ppm). As a result, the surface of the finely pulverized powder is appropriately oxidized so that sudden oxidation and heat generation do not occur when the finely pulverized powder comes into contact with the atmosphere.

In order to preferentially oxidize Y and / or Sc contained in the first rare earth alloy powder and / or the second rare earth alloy powder to form a stable oxide in the grain boundary phase, the surface of the powder should be oxidized. It seems to play an important role. According to the study by the present inventor, it is preferable to adjust the amount of oxygen in the powder within a range of 1000 ppm or more and 10000 ppm or less by mass ratio. Particularly, when Y and / or Sc is added to the first rare earth alloy powder, by controlling the oxygen concentration within the above range, the amount of R contributing to the generation of the liquid phase is not decreased and the first rare earth alloy is Sc and / or Y in the alloy powder can be sufficiently diffused in the grain boundary phase.

As described above, the surface of coarsely pulverized powder obtained by hydrogen pulverization is easily oxidized. Therefore, hydrogen pulverization has a preferable effect in diffusing Y from the main phase into the grain boundary phase in the sintering step. Bring

Further, in order to diffuse Y from inside the grain to the grain boundary phase, it is preferable that the average grain size (FSSS grain size) of the powder is 5 μm or less, more preferably 4 μm or less. This is because when the grain size becomes larger than 5 μm, the diffusion distance of Y becomes too long, so that the Y remaining in the crystal grains (main phase) remains.
This is because the amount of P increases and the magnetization decreases.

The crushing device is not limited to the jet mill and may be an attritor or a ball mill.

(R2) _x T _100-x (R2 is Sc and Y
Is at least one element selected from the group of rare earth elements including at least one element of Sc and Y, and T is Fe or at least one element of transition metal elements other than Fe and Fe. Mixture of x (mass%)
The second rare earth alloy powder having a main phase represented by 0 <x ≤ 60) can also be produced by the same method as the first rare earth alloy powder. The composition of the second rare earth alloy powder is such that R2 and T are each 5% by mass ≦ R2 ≦ 75.
It is preferable that the content is within the range of 25% by mass and 25% by mass ≦ T ≦ 95% by mass. Of course, as the second rare earth alloy powder, a plurality of types of second rare earth alloy powders having different compositions may be used.

[Preparation of Sintered Mixed Powder and Press Molding] By mixing the first rare earth alloy powder and the second rare earth alloy powder prepared as described above, the mixed powder for sintering to be subjected to press molding To make.

The step of mixing the first rare earth alloy powder and the second rare earth alloy powder may be carried out after the first pulverizing step or the second pulverizing step. However,
Generally, since the pulverizability of the first rare earth alloy and the second rare earth alloy is different, it is preferable that the first rare earth alloy and the second rare earth alloy are mixed with each other after the second pulverization step to obtain a rare earth alloy powder having a predetermined average particle diameter.

Here, the first rare earth alloy powder and the second rare earth alloy powder, each of which is adjusted to have a predetermined grain size, are mixed through the second crushing step. The total composition of the mixed powder for sintering is 8 atomic% or more and 21.5 atomic% or less R and 3
The content of Q is not less than 20 atomic% and not more than 20 atomic%, the balance is T, additional elements and inevitable impurities, and the total content of Sc and Y in R is not less than 0.5 atomic% and not more than 25 atomic%. Mix and mix so that

For example, the first rare earth alloy powder and the second rare earth alloy powder are weighed so as to have a predetermined composition and put into a rocking mixer. At this time, a lubricant such as 0.3 w is added to the mixed powder in a rocking mixer.
Add t% and mix, and coat the surface of the alloy powder particles with a lubricant.

As the lubricant, a fatty acid ester diluted with a petroleum solvent can be used. In the present embodiment, methyl caproate is used as the fatty acid ester,
Isoparaffin is used as the petroleum solvent. The mass ratio of methyl caproate and isoparaffin is, for example, 1: 9. Such a liquid lubricant coats the surface of the powder particles, exerts an antioxidant effect on the particles, and has the function of improving the orientation and powder formability during pressing (the density of the formed body becomes uniform, Exhibit cracks and other defects).

The type of lubricant is not limited to the above. As the fatty acid ester, other than methyl caproate, for example, methyl caprylate, methyl laurate, methyl laurate and the like may be used. As the solvent, a petroleum solvent represented by isoparaffin, a naphthene solvent, or the like can be used. The lubricant may be added at any timing, for example, before the fine pulverization by the jet mill pulverizer, during the fine pulverization, or after the fine pulverization. A solid (dry) lubricant such as zinc stearate may be used instead of the liquid lubricant or together with the liquid lubricant.

The lubricant may be added separately to the first rare earth alloy powder and the second rare earth alloy powder in the second pulverizing step.

Next, the mixed powder for sintering produced by the above method is molded in a magnetic field for orientation using a known press machine.
The molding pressure is, for example, 100 MPa (megapascal),
An orienting magnetic field (for example, 1.6
T) is applied.

[Sintering Step] For the above powder compact,
10 minutes to 24 at a temperature in the range of 650 ° C to 1000 ° C
It is preferable to sequentially perform the step of holding for 0 minutes and the step of further proceeding the sintering at a temperature higher than the above holding temperature (for example, 1000 ° C. to 1100 ° C.).

In the sintering step, the temperature is 650 ° C. to 10 ° C.
In the temperature range of 00 ° C., R1 (eg Nd) in the grain boundary phase of the first rare earth alloy powder and (R2) _x T _100-x phase in the second rare earth alloy powder are melted to form a liquid phase. To do. In the liquid phase sintering process, as described with reference to FIG. 2, Sc and Y combine with oxygen existing in the grain boundary phase to form a stable oxide. Further, it is preferably 650 ° C. in order to sufficiently form the liquid phase, and is preferably set to 1000 ° C. or less in order to prevent Sc and Y from diffusing into the main phase. By maintaining the temperature range of 650 ° C. to 1000 ° C. for 10 minutes to 240 minutes, oxygen in the grain boundary phase and Sc or Y can be sufficiently reacted.

In order to sufficiently react Sc and Y with oxygen in the grain boundary phase, as described above, the amount of oxygen in the mixed powder for sintering is 1000 ppm or more and 10000 or more by mass ratio.
It is preferably controlled within the range of ppm or less.

If too much hydrogen remains in the alloy after the hydrogen crushing step, the sintering step may not proceed properly, but according to this embodiment, 650 ° C. to 1000 ° C.
Since hydrogen is released from the alloy during the heat treatment step carried out at a temperature within the range, a sintered magnet having excellent magnetic properties can be obtained. The hydrogen concentration contained in the final sintered magnet is 5 in mass ratio.
ppm to 100 ppm.

(Example) The rare earth sintered magnets of Example 1 and Example 2 were produced according to the manufacturing method of the embodiment of the present invention described above. For comparison, the sintered magnets of Comparative Example 1 and Comparative Example 2 to which Y is not added and the raw material alloy powder of a single composition to which Y is added are used for Comparative Example 3 and Comparative Example 4.
The sintered magnet of was produced.

Table 1 shows the composition of each sintered magnet and the composition (atomic%) of the alloy powder used. For Comparative Examples 1 to 4, since only the raw material alloy powder having a single composition (described in the column of the first alloy powder) is used, the composition of the sintered body and the composition of the raw material alloy powder basically match. The composition of the sintered body is omitted.

[0094]

[Table 1]

The magnetic properties of the obtained sintered magnet were evaluated. As the magnetic characteristics, the residual magnetic flux density B _r (T),
BH _max (kJ / m ³ ) and coercive force H _cj were evaluated. The obtained results are shown in Tables 2 and 3. BH _max and H
_{For cj} , the values at aging temperatures of 500 ° C., 540 ° C. and 580 ° C. are shown, respectively. The aging treatment time was 1 hour for each.

[0096]

[Table 2]

As can be seen from the results of Table 2, the residual magnetic flux densities B _r of Comparative Example 3 and Comparative Example 4 using the raw material alloy powder of the single composition to which Y was added are the same as those of Comparative Example 1 in which Y is not added. And is lower than in Comparative Example 2. On the other hand, the residual magnetic flux densities B _r of Examples 1 and 2 according to the present invention are maintained at values substantially equal to those of Comparative Examples 1 and 2.

Next, the results of evaluating the corrosion resistance of the sintered magnet will be described. For the evaluation of corrosion resistance, a corrosion resistance test was carried out by holding for 24 hours in an accelerated test (PCT test) environment of 2 atm, 125 ° C. and relative humidity of 85%. The degree of corrosion resistance is
It was evaluated by the change in mass generated by corrosion (the decrease in mass due to shedding). The obtained results are shown in FIG.

As is clear from the results shown in FIG. 4, the mass reductions of Examples 1 and 2 are suppressed as compared with Comparative Examples 1 and 2 in which Y is not added. The effect of improving the corrosion resistance by adding Y is also seen in Comparative Examples 3 and 4, but even with the same composition, Example 1 and Example 2 are more effective than Comparative Example 3 and Comparative Example 4. Is high. When Co is added, it is considered preferable to add it to the first rare earth alloy powder.

Comprehensively judging the above results, it can be said that the sintered magnets of Examples 1 and 2 of the present invention are excellent in magnetic characteristics and corrosion resistance.

[0101]

According to the present invention, the amount of rare earth elements (typically Nd and Pr) constituting the nonmagnetic phase in the grain boundary phase is reduced by allowing Y and the like to be present in the grain boundary phase in a large amount. ,
Moreover, a rare earth sintered magnet excellent in magnetic characteristics and corrosion resistance and a method for manufacturing the same are provided.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a sintering process in the case of using an alloy powder having a single composition to which Y is added, (a) schematically showing a powder compact, and (b) a liquid phase. The structural structure in the sintering process is schematically shown, and (c) schematically shows the concentration profile of the rare earth element in the main phase of the sintered body.

FIG. 2 is a diagram for explaining a sintering process in the case of using an alloy powder containing a first rare earth alloy powder and a second rare earth alloy powder, (a) schematically showing a powder compact, (B)
Shows a schematic structure of the liquid phase sintering process,
(C) schematically shows the concentration profile of the rare earth element in the main phase of the sintered body.

FIG. 3 is a graph showing an example of a temperature profile in hydrogen pulverization processing that can be preferably used in the present invention.

FIG. 4 is a graph showing the results of evaluating the corrosion resistance reliability of a sintered magnet.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01F 1/053 H01F 1/08 B 1/08 1/04 H

Claims (15)

[Claims] 1. (R1) ₂ T ₁₄ Q (R1 is at least one element selected from the group of rare earth elements including Sc and Y, T is Fe, or Fe and a transition metal element other than Fe. A mixture of at least one, Q is boron or a mixture of boron and carbon), and a step of preparing a first rare earth alloy powder having a main phase having a composition represented by (R2) _x T _100-x (R2 is , Sc and Y, which is at least one element selected from the group of rare earth elements, including at least one of Sc and Y, and T is
Fe or a mixture of Fe and at least one element of transition metal elements other than Fe, x (mass%) is 0 <x ≦ 6
A second rare earth alloy having a main phase represented by satisfying a relation of 0) and having a composition containing more of at least one element of Sc and Y than the main phase of the first rare earth alloy powder. R ₂ T by preparing a powder, preparing a sintering powder mixture containing the first rare earth alloy powder and the second rare earth alloy powder, and sintering the sintering powder mixture.
_{14 A} method for producing a rare earth sintered magnet, which comprises a step of producing a sintered body having a main phase having a composition represented by Q (R includes R1 and R2). 2. The sintering powder mixture is 8 at% to 21.5 at% R and 3 at% to 20 at% R.
The following Q is included, the balance is T, an additive element and unavoidable impurities, and the total content of Sc and Y in R is 0.5 atom% or more and 25 atom% or less.
The method for producing a rare earth sintered magnet according to 1. 3. The sintering process includes a liquid phase sintering process,
(R2) _x T _100-x forms a liquid phase in the sintering step, and in the liquid phase sintering step, Sc or Y contained in the sintering powder mixture is contained in the main phase more than in the main phase. The method for producing a rare earth sintered magnet according to claim 1 or 2, wherein a larger amount is present in the peripheral grain boundary phase. 4. The S in the grain boundary phase in the sintering step
The method for producing a rare earth sintered magnet according to claim 3, wherein an oxide of c or Y is formed. 5. R1 does not contain Sc and / or Y or contains more than 0 atomic% and 15 atomic% or less, and R2 contains 5 atomic% or more and 100 atomic% or less Sc and / or Y. 5. The method for producing a rare earth sintered magnet according to any one of 1 to 4. 6. The second rare earth alloy powder is (R2) ₂
The method for producing a rare earth sintered magnet according to claim 1, which has a main phase having a composition represented by T ₁₇ . 7. The method for manufacturing a rare earth sintered magnet according to claim 1, wherein the first rare earth alloy powder contains Co. 8. The rare earth element according to claim 1, wherein in the sintering powder mixture, the average particle diameter of the second rare earth alloy powder is smaller than the average particle diameter of the first rare earth alloy powder. Manufacturing method of sintered magnet. 9. The average particle size of the first rare earth alloy powder is 1
The method for producing a rare earth sintered magnet according to claim 8, wherein the second rare earth alloy powder has an average particle diameter of 1 μm or more and 3 μm or less. 10. The rare earth sintered magnet according to claim 1, wherein the content of the second rare earth alloy powder in the sintering powder mixture is 1% by mass or more and 30% by mass or less. Production method. 11. The method for producing a rare earth sintered magnet according to claim 1, wherein the amount of oxygen contained in the sintering powder mixture is 1000 ppm or more and 10000 ppm or less on a mass basis. 12. The sintering step is performed at 650 ° C. or higher and 100
A first step of holding at a temperature in the range of 0 ° C. or lower for 10 minutes to 240 minutes, and a second step of further promoting sintering at a temperature higher than the holding temperature in the first step,
A method for manufacturing a rare earth sintered magnet according to claim 1. 13. A rare earth sintered magnet produced by the method for producing a rare earth sintered magnet according to claim 1. 14. R ₂ T ₁₄ Q (R is at least one element selected from the group of rare earth elements including Sc and Y, T is Fe, or at least one of Fe and a transition metal element other than Fe. A mixture with a seed, Q is a main phase having a composition represented by boron or a mixture of boron and carbon, and a grain boundary phase containing an oxide of R, and the oxide of R is Sc or Y. Rare earth sintered magnet containing more oxides of other rare earth elements than other oxides. 15. The rare earth sintered magnet according to claim 14, wherein the main phase does not substantially contain Sc or Y, and the grain boundary phase contains an oxide of Sc or Y.