JP3489741B2 - Rare earth sintered magnet and manufacturing method thereof - Google Patents

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.

An R-Fe-B system magnet to which Ce, which is one of rare earth elements, is added together with Nd and Pr is Proc. 16th I
nter. Workshop on Rare Earth Magnets and their App
lications, 2000. P99. According to this report, the residual magnetic flux density B _r monotonically decreases due to the addition of Ce.

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 not only constitute the main phase, but also exist in the grain boundary phase and play an important role of forming a liquid phase during the sintering process. However, even if Nd and Pr existing in the grain boundary phase play an important role in the sintering process, they form a non-magnetic phase in the grain boundary phase and do 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.

On the other hand, conventionally, in order to improve the heat resistance of the R-Fe-B system rare earth magnet, Co is added to the raw material alloy to form a main phase having a tetragonal R ₂ Fe ₁₄ B type crystal structure. It has been practiced to replace a part of Fe in Co 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.

In recent years, in the field of automobile motors and the like, higher performance magnets have been required, and it has been demanded to use R-Fe-B rare earth magnets having higher performance than ferrite magnets. is there. However, R-
The heat resistance of the Fe-B rare earth magnet is insufficient for use in a high temperature environment such as an automobile motor, and there is a strong demand for further improvement of the heat resistance.

It is considered preferable to add a larger amount of Co in order to further improve the heat resistance of the R-Fe-B system rare earth magnet. However, Co added to the raw alloy
Not only replaces Fe in the main phase of the sintered magnet, but also exists in the grain boundary phase, where it forms an NdCo ₂ compound (or PrCo ₂ compound). That is, part of the added Co is wasted in the grain boundary phase without being used to replace Fe. Further, since this NdCo ₂ compound is a ferromagnetic material, there is a problem that the coercive force of the sintered magnet is lowered. For this reason,
It is not possible to efficiently replace Fe in the main phase with Co by simply increasing the amount of Co added, and the coercive force of the R-Fe-B rare earth magnet is greatly reduced due to the increase of the above compound. become.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the amounts of Nd and Pr constituting a nonmagnetic phase in a grain boundary phase, and to provide excellent magnetic characteristics. To provide a rare earth sintered magnet and a method for manufacturing the same.

Another object of the present invention is to provide a rare earth sintered magnet that exhibits excellent magnetic characteristics by efficiently incorporating the added Co into the main phase, and a method for producing the same.

[0015]

The rare earth sintered magnet of the present invention has a composition formula represented by (R1 _x + R2 _y ) T _100-xyz Q _z (where R1 is La (lanthanum), Y (yttrium) and Sc). At least one element selected from the group consisting of all rare earth elements except (scandium), R2 is L
a, Y and at least one element selected from the group consisting of Sc, T is at least one element selected from the group consisting of all transition elements, Q is selected from the group consisting of B and C At least one element), Nd ₂ Fe
₁₄ A rare earth sintered magnet containing crystal grains having a B-type crystal structure as a main phase, wherein the composition ratios x, y, and z are 8 ≦ x ≦ 18 at% and 0.1 ≦ y ≦ 3.5 at, respectively.
%, And 3 ≦ z ≦ 20 at%, and the concentration of R2 is higher in the grain boundary phase than in the crystal grains.

The composition ratios x and y are 0.01≤y /
It is preferable to satisfy the relational expression of (x + y) ≦ 0.23.

It is preferable that R2 always contains Y (yttrium).

The amount of oxygen is not less than 2000 ppm by weight 8
It is preferably 000 ppm or less.

In the method for producing a rare earth sintered magnet according to the present invention, a rare earth alloy having a composition formula represented by (R1 _x + R2 _y ) T _{100- xyz} Q _z (R1 is all rare earth except La, Y, and Sc). At least one selected from the group consisting of elements
Element, R2 is at least one element selected from the group consisting of La, Y, and Sc, T is at least one element selected from the group consisting of all transition elements, and Q is from B and C. A powder of at least one element selected from the group consisting of, wherein the composition ratios x, y, and z are
8 ≦ x ≦ 18 at% and 0.1 ≦ y ≦ 3.5a, respectively
including the step of preparing an alloy powder satisfying t% and 3 ≦ z ≦ 20 at% and the step of sintering the rare earth alloy powder, wherein N in the rare earth alloy is contained before sintering.
The R2 existing in the main phase crystal grains having the d ₂ Fe ₁₄ B type crystal structure is diffused into the grain boundary phase during the sintering process, so that the concentration of R2 is higher than that in the crystal grains. Be high in at least some of the.

The amount of oxygen contained in the rare earth alloy powder is preferably 2000 ppm or more and 8000 ppm or less in weight ratio.

The sintering step functions to diffuse R1 existing in the grain boundary phase in the rare earth alloy before sintering into the main phase crystal grains during the sintering process. Further, the sintering step forms an oxide of R2 in the grain boundary phase.

The sintering step includes a first step of maintaining the temperature in the range of 650 to 1000 ° C. for 10 to 240 minutes,
It is preferable to include a second step of further advancing the sintering at a temperature higher than the holding temperature in the first step.

The powder of the rare earth alloy is preferably pulverized in a gas whose oxygen concentration is controlled.

The rare earth alloy powder has an oxygen concentration of 20.
It is preferably pulverized in a gas controlled to 000 ppm or less.

Average particle size of the rare earth alloy powder (FSS
The S particle size) is preferably 5 μm or less.

Further, it is preferable that a thin oxide layer is formed on the surface of the particles of the rare earth alloy powder.

The rare earth sintered magnet of the present invention has a composition formula (R
1 _x + R2 _y ) (T1 _p + T2 _q ) _{100- xyzr} Q _z M _r is expressed (R1 is La (lanthanum), Y (yttrium))
And at least one element selected from the group consisting of all rare earth elements except Sc (scandium), R2 is at least one element selected from the group consisting of La, Y, and Sc, and T1 is Fe and T2. Is at least one element selected from the group consisting of all transition elements except Fe, Q is at least one element selected from the group consisting of B and C, M is selected from Al, Ga, Sn, and In At least one element selected from the group consisting of: Nd ₂
A rare earth sintered magnet containing crystal grains having an Fe ₁₄ B type crystal structure as a main phase, the composition ratios of which are x, y, z, p, q,
And r are 8 ≦ x + y ≦ 18 at%, 0 <y ≦ 4 at%, 3 ≦ z ≦ 20 at%, 0 <q ≦ 20 at%, 0 ≦ q / (p + q) ≦ 0.3, and 0 ≦ r, respectively. ≦ 3 at%, and the concentration of R2 is higher in at least a part of the grain boundary phase than in the crystal grains.

It is preferable that the composition ratio y satisfies the relational expression of 0.5 ≦ y ≦ 3 at%.

It is preferable that R2 always contains Y (yttrium).

It is preferable that T2 always contains Co (cobalt).

The amount of oxygen is not less than 2000 ppm by weight 8
It is preferably 000 ppm or less.

Manufacturing method of rare earth sintered magnet according to the present invention
Has the composition formula (R1_x+ R2_y) (T1 _p+ T2_q)
_100-xyzrQ_zM_r(R1 is La (Lanta
), Y (yttrium) and Sc (scandium)
A few selected from the group consisting of all rare earth elements except
At least one element, R2 consists of La, Y, and Sc
At least one element selected from the group
e and T2 are selected from the group consisting of all transition elements except Fe.
At least one element selected, Q consisting of B and C
At least one element selected from the group M is Al,
A few selected from the group consisting of Ga, Sn, and In
At least one element), Nd₂Fe₁₄Has B type crystal structure
A rare-earth sintered magnet containing crystal grains as a main phase,
The composition ratios x, y, z, p, q, and r are respectively 8 ≦ x + y ≦ 18 at%, 0 <y ≦ 4 at%, 3 ≦ z ≦ 20 at%, 0 <q ≦ 20at%, 0 ≦ q / (p + q) ≦ 0.3, and 0 ≦ r ≦ 3 at%, And a step of preparing an alloy powder satisfying
Including the step of sintering the gold powder, and before sintering
Nd in the rare earth alloy₂Fe₁₄Has B-type crystal structure
During the sintering process, R2, which was present in the main-phase crystal grains, was changed to the grain boundary phase.
To thereby increase the concentration of R2 in the grains.
Higher in at least a part of the grain boundary phase.

The amount of oxygen contained in the powder of the rare earth alloy is preferably 2000 ppm or more and 8000 ppm or less in weight ratio.

In a preferred embodiment, the sintering step causes R1 existing in the grain boundary phase in the rare earth alloy before sintering to diffuse into the main phase crystal grains during the sintering process.

In a preferred embodiment, the sintering step forms an oxide of R2 in the grain boundary phase.

The sintering step includes a first step of holding the temperature within a range of 650 to 1000 ° C. for 10 to 240 minutes,
It is preferable to include a second step of further advancing the sintering at a temperature higher than the holding temperature in the first step.

The powder of the rare earth alloy is preferably pulverized in a gas whose oxygen concentration is controlled.

The rare earth alloy powder has an oxygen concentration of 20.
It is preferably pulverized in a gas controlled to 000 ppm or less.

Average particle size of the rare earth alloy powder (FSS
The S particle size) is preferably 5 μm or less.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) In the first embodiment of the present invention, Y, La and Sc are added in addition to Nd, and these are concentrated in the grain boundary phase so that Y and the like are added. Otherwise, it would have been consumed in the formation of the non-magnetic phase in the grain boundary phase.
d is diffused from the grain boundary phase into the main phase crystal grains, and is effectively utilized as a constituent element of the main phase (Nd ₂ Fe ₁₄ B phase) responsible for hard magnetism. The Nd ₂ Fe ₁₄ B phase referred to here is N
It is intended to include phases in which some of d is substituted with Pr, Dy, and / or Tb.

According to the rare earth magnet of the present invention, most of Nd exists in the Nd ₂ Fe ₁₄ B phase which is the main phase, and in the grain boundary phase, Y, La and Sc play the role of Nd instead of Nd. Is playing. Therefore, it is possible to reduce the amount of Nd (Pr) used without substantially reducing the magnetization.

According to the experiments by the present inventor, Y is an ingot
Stages of raw alloys such as casting alloys and strip cast alloys
On the floor, it exists mainly in the main phase and reduces the magnetization.
According to the present invention, after the powder of such a raw material alloy is formed, it is baked.
The feature is that Y in the main phase is concentrated in the grain boundary phase when binding.
Have The ingot casting method (cooling rate: 10
²If the molten alloy is cooled at a temperature of less than ℃ / sec)
Can be present in the main phase at any given time. In addition,
The cooling rate in the rapid cooling method such as the precast method is 10 ²° C / sec
That is all.

First, the features of the present invention will be described with reference to FIG.

FIG. 1 is a diagram schematically showing the main phase crystal grains and the grain boundary phases, and shows how Nd and Y diffuse and distribute from the stage of the raw material alloy through the sintering process. .

First, as shown in FIG. 1 (a), at the stage of the mother alloy, Y is incorporated in the main phase crystal grains together with Nd to form the main phase Nd ₂ Fe ₁₄ B phase. There is.
In the ingot alloy, the Y concentration in the grain boundary phase is lower than the Y concentration in the grain, and the grain boundary phase contains Nd-r.
The ich phase is formed.

In the strip cast alloy, R2 such as Y is used.
Exists also at grain boundaries, but this is due to nonequilibrium. R2 existing in the grain boundary also has the same effect as R2 existing in the main phase in the following steps.

According to the present invention, as shown in FIG. 1 (b), Y is diffused from the inside of the main phase crystal grains to the grain boundary phase in the sintering process, and the oxide of Y is generated in the grain boundary phase. At that time, Nd is diffused in the opposite direction. As a result, as shown in FIG. 1C, the Y concentration in the grain boundary phase can be made higher than the Y concentration in the main phase crystal grains, Y contained in the main phase can be decreased, and the magnetization can be increased. .

As described above, in order to realize the interdiffusion of Y and Nd, it is considered that an appropriate amount of oxygen must be present in the grain boundary phase during the sintering process. That is, in the present invention, in order to cause the diffusion, Y has a property of being more stably bonded to oxygen than Nd to form an oxide. In order to introduce such oxygen into the grain boundary phase, it is preferable to thinly oxidize the powder surface, for example, in a pulverizing step.

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

[Raw material alloy] First, the composition formula is (R1 _x + R
2 _y ) Prepare a rare earth alloy represented by T _100-xyz Q _z . Here, R1 is at least one element selected from the group consisting of all rare earth elements except Y (yttrium), La (lanthanum) and Sc (scandium), and R1
2 is at least one element selected from the group consisting of La, Y, and Sc, T is at least one element selected from the group consisting of all transition elements, and Q is selected from the group consisting of B and C At least one element
The composition ratios x, y and z are 8 ≦ x ≦ 18a, respectively.
t%, 0.1 ≦ y ≦ 3.5 at%, and 3 ≦ z ≦ 20
Satisfy at%.

To produce such an alloy, for example,
An ingot casting method or a quenching method (strip casting method, centrifugal casting method, etc.) can be used. Below, taking the case of using the strip casting method as an example,
A method for producing the raw material alloy will be described.

First, the 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 quenched alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm before the subsequent hydrogen pulverization. The method for producing the raw material alloy by the strip casting method is disclosed in, for example, US Pat. No. 5,383,978.

As described above, Y is mainly present in the main phase of Nd ₂ Fe _{1 4} B at the stage of such a raw material alloy.

[First crushing step] A plurality of raw material packs (for example, made of stainless steel) are filled with the 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. 2, for example. In the example of FIG. 2, 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 reduced pressure of about 0 to 3 Pa and carrying out dehydrogenation process III for 5.0 hours, while supplying argon gas into the furnace, cooling process IV of the raw material alloy was carried out.
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 reduced 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 hydrogen pulverization, 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 that portion, so that a large amount of Nd is exposed on the surface of the produced coarse pulverized powder, which is extremely 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 pulverized powder introduced into the pulverizer is wound up in the pulverizer by the inert gas jetted at a high speed from the internal nozzle, and swirls in the pulverizer together with the high-speed air stream. Then, the crushed objects are finely crushed by mutual collision.

The powder particles thus finely pulverized are carried 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 the present 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.

It is considered that the oxidation of the powder surface plays an important role in diffusing Y from the main phase into the grain boundary phase in the sintering step. According to the study by the present inventor, it is preferable to adjust the amount of oxygen in the powder within a range of 2000 ppm to 8000 ppm in weight ratio.

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

Further, in order to diffuse Y from the inside of the grains 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, but may be an attritor or a ball mill.

[Press molding] In the present embodiment, the magnetic powder produced by the above method is added and mixed with a lubricant, for example, 0.3 wt% in a rocking mixer, and the surface of the alloy powder particles is coated with the lubricant. To do. As the lubricant, a fatty acid ester diluted with a petroleum solvent can be used. In this embodiment, methyl caproate is used as the fatty acid ester, and isoparaffin is used as the petroleum solvent. The weight 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.

Next, the magnetic powder produced by the above-described method is molded in a magnetic field for orientation using a known press machine.

[Sintering Step] For the above powder compact,
A step of holding at a temperature in the range of 650 to 1000 ° C. for 10 to 240 minutes and a step of further advancing the sintering at a temperature higher than the above holding temperature (for example, 1000 to 1100 ° C.) may be sequentially performed. preferable. During sintering, especially when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), when Nd in the grain boundary phase begins to melt, Y and grains existing in the main phase crystal grains are often present. N that often exists in the phase
Mutual diffusion occurs with d. That is, Y receives a diffusion driving force that is proportional to the concentration gradient between the inside of the main phase crystal grains and the grain boundary phase (corresponding to the “difference in Y concentration between the main phase and the liquid phase”), and Y The Nd diffuses into the phase, and conversely, Nd diffuses from the grain boundary phase into the main phase.

Y diffused in the grain boundary phase is combined with oxygen existing in the grain boundary phase and consumed as an oxide, so that the concentration gradient of Y serving as a diffusion driving force is maintained. Compared to Nd, Y is more likely to stably form an oxide, so that the diffusion of Y from the main phase to the liquid phase progresses, while the N in the liquid phase progresses.
d diffuses into the main phase.

In order to sufficiently diffuse Y into the grain boundary phase and incorporate a large amount of Nd existing in the grain boundary phase into the main phase, as described above, the amount of oxygen in the powder is 2000 ppm by weight.
It is preferably controlled within the above range of 8000 ppm or less. This is because if the amount of oxygen is less than 2000 ppm, Y is not sufficiently diffused into the grain boundary phase, a large amount of Y remains in the main phase, and the magnetization decreases. On the other hand, if the oxygen amount exceeds 8000 ppm and becomes too large, the rare earth element is consumed for the formation of the oxide, so that the amount of the rare earth element that contributes to the liquid phase formation decreases, resulting in sintering. It is not preferable because the density is lowered and the magnet characteristics are deteriorated. As described above, the sintered magnet formed by using the powder whose oxygen concentration is controlled finally contains 2000 to 8000 ppm by weight of oxygen.

If too much hydrogen remains in the alloy after the hydrogen crushing step, the sintering step may not proceed properly, but according to the present embodiment, the temperature within the range of 650 to 1000 ° C. Since hydrogen is released from the alloy during the heat treatment step performed in step 1, a sintered magnet having excellent magnetic properties can be obtained. The hydrogen concentration contained in the final sintered magnet is 5 to 5 by weight.
It is 100 ppm.

Even when La or Sc is added, N
It is possible to provide a rare earth sintered magnet that can suppress consumption of rare earth elements such as d and Pr, which are indispensable for the main phase, in the grain boundary phase, maintain high magnetization of the main phase, and exhibit excellent magnetic characteristics. It will be possible.

(Example) Using the above-described manufacturing method of the present invention, a sintered magnet was produced from a raw material alloy in which each of Y, La, and Ce was added as a rare earth element together with Nd. However, the raw material alloy was produced by the ingot casting method (molten metal cooling rate: less than 10 ² ° C / sec).

FIG. 3 shows the relationship between the amounts of Y, La, and Ce added and the residual magnetic flux density B _r . The composition formula of each sintered magnet is represented by Nd _11.8 RE ' _2.4 Fe _79.7 B _6.1 . Here, RE ′ is Y, La, or Ce.

As can be seen from FIG. 3, Ce as RE '
When B is added, B _r monotonically decreases as the added amount increases. On the other hand, when Y or La was added as RE ′, the decrease in B _r was extremely small in the region where the addition amount was about 3.5 at% or less as compared with the case where Ce was added. In particular, when Y is added, the reduction rate of B _r is extremely small, and it is understood that Y is more preferable as an additional element than La.

The following can be estimated from the graph of FIG. That is, when the addition amount is 3.5 at% or less, Y and La are present in the grain boundary phase and hardly enter the main phase.
Although the decrease in magnetization does not occur, when the addition amount exceeds 3.5 at%, excessive Y and La cannot be diffused into the grain boundary phase, and a large amount is contained in the main phase, resulting in a clear decrease in magnetization. Will be observed in. On the other hand, in Ce, the magnetization monotonously decreased with the increase of the added amount.
It is considered that e is taken into the main phase from the beginning.

Next, sintered magnets A to C having the following compositions
About these tissues by using EPMA (electron probe
It was observed using a micro analyzer.

Sintered magnet A: Nd _11.8 Y _2.4 Fe _79.7 B _6.1 Sintered magnet B: Nd _11.8 La _2.4 Fe _79.7 B _6.1 Sintered magnet C: Nd _11.8 Ce _2.4 Fe _79.7 B _6.1

4 to 6 show a composition image photograph (backscattered electron image), an element mapping photograph (fluorescent X-ray image), and a schematic view of the structure of each magnet. 4 (a) and 5 (a)
Further, in the composition image photograph shown in FIG. 6A, the bright portion shows the grain boundary phase, and the dark portion shows the inside of the main phase crystal grains. As can be seen from the element mapping photographs of FIG. 4 (b) and FIG. 5 (b), Y and La are mostly evenly present in the grain boundary phase, and segregate and concentrate from the main phase to the grain boundary phase. confirmed. On the other hand, Ce is almost uniformly present in the sintered magnet as shown in FIG.
No phenomenon was observed in which the grains were concentrated in the grain boundary phase.

According to various experiments conducted by the present inventor,
The composition ratios x and y in the composition formula of (R1 _x + R2 _y ) T _100-xyz Q _z are 0.01 ≦ y / (x + y) ≦ 0.2.
It is preferable that the relational expression 3 is satisfied.

(Second Embodiment) The second embodiment of the present invention will be described below. In the present embodiment, Y, La, and Sc are added in addition to the rare earth element such as Nd and Pr, and these elements are concentrated in the grain boundary phase. The transition metal such as Co that would have been consumed in the generation of Co is taken into the main phase crystal grains, and Fe in the main phase (Nd ₂ Fe ₁₄ B phase) responsible for hard magnetism is effectively replaced with Co or the like. The Nd ₂ Fe ₁₄ B referred to here is
The phase includes a phase in which a part of Nd is replaced with Pr, Dy, or Tb.

In the present embodiment, when Co is added,
Most of Co is present in the Nd ₂ Fe ₁₄ B phase, which is the main phase of the sintered magnet. On the other hand, when Y, La, or Sc is not added as in the conventional case, if a large amount of Co is added, Co also exists in the grain boundary phase in a large amount, and a ferromagnetic compound is generated in the grain boundary phase. As described above, NdC is contained in the grain boundary phase.
When a large amount of a ferromagnetic compound such as o ₂ is formed, not only the amount of Co contributing to the increase of the Curie temperature in the main phase is decreased but also the coercive force of the entire magnet is decreased.

In the present embodiment, Y, La, and Sc are concentrated in the grain boundary phase, so that the Co concentration in the grain boundary phase decreases,
Nd ₃ Co is more likely to be generated than NdCo ₂ . Nd
_{Since 3} Co is a non-magnetic compound, it does not cause a decrease in coercive force of the sintered magnet.

Further, in the case of the present invention, as a result of Y, La and Sc being concentrated in the grain boundary phase, most of Nd (Pr) is efficiently taken into the main phase, so that the magnetization is hardly reduced. It is also possible to reduce the amount of Nd (Pr) used.

According to the experiments conducted by the present inventor, Y exists mainly in the main phase at the stage of a raw material alloy such as an ingot casting alloy or a quenched alloy (strip cast alloy), and reduces the magnetization. The present embodiment is characterized in that Y in the main phase is concentrated in the grain boundary phase when the powder of such a raw material alloy is formed and then sintered.

Next, the features of the magnet in this embodiment will be described with reference to FIG.

FIG. 7 is a diagram schematically showing the main phase crystal grains and the grain boundary phases, and how Nd, Y and Co diffuse and distribute through the sintering process from the stage of the raw material alloy. Is shown.

First, as shown in FIG. 7 (a), at the stage of the mother alloy, Y was incorporated in the main phase crystal grains together with Nd to form the main phase Nd ₂ Fe ₁₄ B phase. There is.
The Y concentration in the grain boundary phase is lower than the Y concentration in the grain, and the Nd-rich phase is formed in the grain boundary phase. Co exists in the main phase and the grain boundary phase.

In quenched alloys such as strip cast alloys and centrifugally cast alloys, R2 such as Y is also present in the grain boundary phase.
This is because of the non-equilibrium state. R2 existing in the grain boundary also exhibits the same effect as Y existing in the main phase in the following steps.

According to the present invention, as shown in FIG. 7B, Y is diffused from the main phase crystal grains to the grain boundary phase in the sintering process, and Y oxide is generated in the grain boundary phase. At that time, Nd is diffused in the opposite direction. As a result, as shown in FIG. 7C, the Y concentration in the grain boundary phase becomes higher than the Y concentration in the main phase crystal grains, the Y contained in the main phase decreases, and the magnetization increases. As a result of such interdiffusion of Y and Nd,
Since the grain boundary phase changes to a Y-dominant phase, Co also moves to the main phase.

As described above, in order to realize the mutual diffusion of Y and Nd (and Co), it is considered that an appropriate amount of oxygen must be present in the grain boundary phase during the sintering process. That is, in the present invention, in order to cause the diffusion, Y has a property of being more stably bonded to oxygen than Nd to form an oxide. In order to introduce such oxygen into the grain boundary phase, it is preferable to thinly oxidize the powder surface, for example, in a pulverizing step.

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

[Raw Material Alloy] First, (R1 _x + R2 _y ) (T1 _p + T2 _q ) _100-xyzr
A rare earth alloy represented by Q _z M _r is prepared. Where R
1 is La (lanthanum), Y (yttrium) and Sc
At least one element selected from the group consisting of all rare earth elements except (scandium), R2 is La, Y,
And at least one element selected from the group consisting of Sc, T1 is Fe, T2 is at least one element selected from the group consisting of all transition elements except Fe, and Q is B
And at least one element selected from the group consisting of C, M is at least one element selected from the group consisting of Al, Ga, Sn, and In, and the composition ratio x,
y, z, p, q, and r are respectively 8 ≦ x + y ≦
18 at%, 0 <y ≦ 4 at%, 3 ≦ z ≦ 20 at%,
It satisfies 0 <q ≦ 20 at%, 0 <q /(p+q)≦0.3, and 0 ≦ r ≦ 3 at%. Note that p + q = 10
0-x-y-z-r is established.

To make such an alloy, for example, an ingot casting method or a strip casting method 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, the 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 quenched alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm before the subsequent hydrogen pulverization. The method for producing the raw material alloy by the strip casting method is disclosed in, for example, US Pat. No. 5,383,978.

As described above, Y is present in the main phase of Nd ₂ Fe ₁₄ B at the stage of such a raw material alloy.

[First crushing step] A plurality of raw material packs (for example, made of stainless steel) are filled with the 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. 2, for example. In the example of FIG. 2, 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.

Subsequently, a dehydrogenation process III is performed for 5.0 hours under a reduced pressure of about 0 to 3 Pa, and then a cooling process IV of the raw material alloy is performed for 5.0 hours while supplying argon gas into the furnace. .

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 introduced into the hydrogen furnace 10. Supplying is preferable from the viewpoint of cooling efficiency. The supply amount of argon gas is 10 to 10.
It may be about 100 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 frozen and vaporized in the evacuation step, it is difficult to increase the degree of vacuum, and the time required for the evacuation step 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 pulverization, 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 hydrogen pulverization, 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.

A large amount of Nd is exposed on the surface of the coarsely pulverized powder produced by hydrogen pulverization, and it is in a state of being easily oxidized.

[Second crushing step] Next, the coarsely crushed powder produced in the first crushing step is subjected to fine crushing 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 following is a more detailed description.

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

The powder particles thus finely pulverized are carried by the ascending air current to the classification rotor and classified by the classification rotor, so that the coarse powder 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.

It is considered that the oxidation of the powder surface plays an important role in diffusing Y from the main phase into the grain boundary phase in the sintering step. According to the study by the present inventor, it is preferable to adjust the amount of oxygen in the powder within a range of 2000 ppm to 8000 ppm in weight ratio.

Further, in order to diffuse Y from the inside of the grains to the grain boundary phase, the average grain size (FSSS grain size) of the powder is preferably 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.

[Press Molding] In this embodiment, a lubricant, for example, 0.3 wt% is added to and mixed with the magnetic powder produced by the above method, and the surface of the alloy powder particles is coated with the lubricant. To do. As the lubricant, a fatty acid ester diluted with a petroleum solvent can be used. In this example, methyl caproate is used as the fatty acid ester and isoparaffin is used as the petroleum solvent. The weight ratio of methyl caproate and isoparaffin is
For example, set to 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.

Next, the magnetic powder manufactured by the above method is molded in a magnetic field for orientation using a known press machine.

[Sintering Step] For the above powder compact,
A step of holding at a temperature in the range of 650 to 1000 ° C. for 10 to 240 minutes and a step of further promoting sintering at a temperature higher than the above holding temperature (for example, 1000 to 1100 ° C.) are sequentially performed. During sintering, especially when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), when Nd in the grain boundary phase begins to melt, Y and grains existing in the main phase crystal grains are often present. Mutual diffusion occurs between Nd, which is often present in the field phase. That is, Y receives a diffusion driving force that is proportional to the concentration gradient between the inside of the main phase crystal grains and the grain boundary phase (corresponding to the “difference in Y concentration between the main phase and the liquid phase”), and Y The Nd diffuses into the phase, and conversely, Nd diffuses from the grain boundary phase into the main phase.

In this embodiment, the oxygen content is 20 by weight.
It is possible to obtain a sintered body of 00 to 8000 ppm. Further, since the hydrogen content is reduced by the heat treatment performed in the range of 650 to 1000 ° C., the hydrogen content in the final sintered body can be suppressed within the range of 5 to 100 ppm by weight.

Y diffused in the grain boundary phase is combined with oxygen existing in the grain boundary phase and consumed as an oxide, so that the concentration gradient of Y serving as a diffusion driving force is maintained. Compared to Nd, Y is more likely to stably form an oxide, so that the diffusion of Y from the main phase to the liquid phase progresses, while the N in the liquid phase progresses.
d diffuses into the main phase. At this time, since the grain boundary phase is a Y-based phase, due to the volume ratio, Co moves to the main phase and partially replaces Fe of the main phase.

In order to sufficiently diffuse Y into the grain boundary phase and to take in a large amount of Nd, Co, etc. existing in the grain boundary phase into the main phase, the amount of oxygen in the powder is in a weight ratio as described above. 20
It is preferably controlled within the range of 00 ppm or more and 8000 ppm or less. This is because if the amount of oxygen is less than 2000 ppm, Y is not sufficiently diffused into the grain boundary phase, a large amount of Y remains in the main phase, and the magnetization decreases. On the other hand, if the oxygen amount exceeds 8000 ppm and becomes too large, the rare earth element is consumed for the formation of the oxide, so that the amount of the rare earth element that contributes to the liquid phase formation decreases, resulting in sintering. It is not preferable because the density decreases and the main phase ratio decreases, which deteriorates the magnet characteristics.

Even when La or Sc is added, by concentrating these elements in the grain boundary phase, transition metal elements such as Co and rare earth elements essential to the main phase such as Nd and Pr are bound to the grain boundaries. It is possible to suppress consumption in the phase.

[Reasons for Limiting Composition] The rare earth element R1 is specifically Pr, Nd, Sm, Gd, Tb, D.
At least one element selected from y, Ho, Er, Tm, and Lu can be used. In order to obtain sufficient magnetization, it is preferable that 50 at% or more of the rare earth element R1 is occupied by Pr or Nd or both.

The total of rare earth elements (R1 + R2) is 8 at.
If it is less than%, the coercive force may decrease due to the precipitation of the α-Fe phase. When the total amount of rare earth elements (R1 + R2) exceeds 18 at%, the desired tetragonal Nd2
In addition to the Fe14B type compound, a large amount of R-rich second phase may be precipitated, and the magnetization may be reduced. Therefore, the total of the rare earth elements (R1 + R2) is preferably in the range of 8 to 18 at% of the total.

As T2, other than Co, Ni, V,
Transition metal elements such as Cr, Mn, Cu, Zr, Nb and Mo are preferably used. Of the transition metal elements (T1 + T2), T1, that is, the proportion of Fe is preferably 50 at% or more. This is because when the ratio of Fe is less than 50 at%, the saturation magnetization itself of the Nd2Fe14B type compound decreases. In the present invention, as a result of R2 gathering in the grain boundary phase, the added T2 is efficiently incorporated into the main phase. Since R2 does not form many undesired compounds in the grain boundary phase, it is possible to increase the amount of R2 added as compared with the conventional one. In the present invention, the addition amount of T2 is 20
It can be increased to at%.

Q is B and / or C and is essential for stably precipitating a tetragonal Nd2Fe14B type crystal structure. If the amount of Q added is less than 3 at%, R2T17
Since the phases are precipitated, the coercive force is lowered and the squareness of the demagnetization curve is significantly impaired. Moreover, if the amount of addition of Q exceeds 20 at%, the second phase having a small magnetization will be precipitated. Therefore, the content of Q is preferably in the range of 3 to 20 at%.

In order to enhance the magnetic anisotropy of the powder, another additive element M may be added. As the additional element M, at least one element selected from the group consisting of Al, Ga, Sn, and In is preferably used.
Such an additional element M may not be added at all. When adding, it is preferable that the addition amount be 3 at% or less. This is because if the addition amount exceeds 3 at%, not the ferromagnetic phase but the second phase precipitates and the magnetization decreases. The additional element M is not necessary to obtain magnetically isotropic magnetic powder,
You may add Al, Cu, Ga, etc. in order to raise an intrinsic coercive force.

Example An example of the second embodiment according to the present invention will be described below.

In this embodiment, first, (R1 _x + R2 _y )
In the composition formula of (T1 _p + T2 _q ) _100-xyz Q _z M _r ,
R1 is Nd and Dy, R2 is Y (yttrium), T
Raw material alloys having various compositions in which 1 is Fe, T2 is Co, Q is B (boron), and M is Cu and Al are prepared. The composition ratio of each element is such that Nd is 5 to 10 at% and Dy
Is 4 at%, Y is 0 to 5 at%, Co is 0 to 6 at%,
B at 6 at%, Cu at 0.2 at%, Al at 0.4 at%.
%, Fe was adjusted so as to be the rest.

A molten alloy was prepared by heating the above alloy to about 1400 ° C. in an Ar atmosphere, and the molten alloy was poured into a water-cooled mold. The molten alloy was cooled, and an alloy cast piece having a thickness of about 5 mm was obtained.

After hydrogen was absorbed into this alloy slab, it was embrittled by heating it to about 600 ° C. while evacuating it (hydrogen treatment). Coarse crushed powder was obtained from the alloy by this hydrogen treatment. The coarsely pulverized powder was finely pulverized with a jet mill to prepare a powder having an average particle size (FSSS particle size) of about 3.5 μm. The crushing atmosphere of the jet mill is 100 oxygen.
A nitrogen gas containing about 00 volume ppm was used.

[0135] The powder produced in this manner was treated with 100MP
Pressed with a (megapascal), 55 mm x 25 mm x
A molded body having a size of 20 mm was produced. At the time of pressing, an orientation magnetic field is applied in a direction perpendicular to the pressing direction,
The powder was oriented.

Next, this powder forming body was sintered in an Ar atmosphere. The sintering temperature was 1060 ° C. and the sintering time was about 4 hours.

The Curie point and coercive force of the thus obtained sintered magnet were evaluated.

FIG. 8 shows the case where the amount of Co added is 3 at%, and
Curie temperature (Curie point) and Y for at%
It is a graph which shows the relationship with the amount added. FIG. 9 is a graph showing the relationship between the coercive force H _cj and the Co addition amount when the Y addition amount is 0 at%, 1 at%, 3 at%, and 5 at%.

First, as can be seen from FIG. 8, the Curie temperature rises as the Y addition amount is increased from 0 at%, but it is almost saturated at a certain level. This saturation level becomes higher as the amount of Co added increases. From FIG. 8, it can be confirmed that the Curie temperature increasing effect of Co is increased by the addition of Y.

On the other hand, the following can be seen from FIG.

That is, when Y is not added, the coercive force sharply decreases as the amount of Co added increases, whereas when an appropriate amount of Y is added, the coercive force does not decrease and Co is added. The amount can be increased. In other words, the addition of Y avoids a large decrease in coercive force while maintaining C
o It is possible to increase the amount of addition and thereby to sufficiently improve the Curie temperature.

According to FIG. 9, when Y is not added at all,
When the amount of Co added exceeds about 2 at%, the decrease in coercive force becomes large. This is because if Y is not added at all, C
o NdC formed in the grain boundary phase increases with increasing addition amount
It is considered that this is because the amount of o ₂ (ferromagnetic compound) increases.

No large difference in coercive force is observed between the case where the amount of Co added is small, the case where Y is not added and the case where the amount of Y added is 1 at%. However, the amount of Co added is about 3 at
%, The coercive force without adding Y is C
While it decreases greatly as the amount of o added increases, the coercive force when Y is added maintains a substantially constant value regardless of the amount of Co added. This is because as a result of the addition of Y, the amount of NdCo ₂ (ferromagnetic compound) formed in the grain boundary phase can be suppressed low. However, Y
If the amount of addition is too large (for example, 5 at% or more), the amount of Y oxide in the grain boundary phase increases and the coercive force decreases. According to the inventor's experiment, the preferable range of the Y addition amount is 0 <y ≦ 4 at%, and the more preferable range is 0.5 <y.
≦ 3 at%. If the upper limit of the Y addition amount is further limited from the viewpoint of avoiding the decrease of the coercive force as much as possible, it becomes about 2 at%.

When the amount of Y added is optimized, Co
It becomes possible to increase the addition amount to 20 at%.
In the case of the present invention, the preferable range of Co addition amount is 0 <q ≦
20 at%, more preferable range is 0 <q ≦ 15a
t%.

Next, the structures of the ingot alloy and the sintered magnet having the composition of Nd ₁₀ Dy ₄ Y ₂ Fe ₇₁ Co ₇ B ₆ were observed using EPMA (electron probe / microanalyzer).

FIG. 10 shows a composition image photograph and an element mapping photograph of the ingot alloy, and FIG. 11 shows a composition image photograph and an element mapping photograph of the sintered magnet.

In the composition image photographs shown in FIGS. 10A and 11A, the bright portion shows the grain boundary phase and the dark portion shows the inside of the main phase crystal grains.

In FIGS. 10 and 11, (b)-
(F) shows mapping photographs of Nd, Dy, Co, Fe, and Y, respectively.

As can be seen by comparing FIGS. 10A and 10B, a large amount of Nd is present in the grain boundary phase at the stage of the ingot alloy. Further, as can be seen by comparing FIGS. 10A and 10D, Co is also present in the grain boundary phase in a large amount at this stage. On the other hand, a large amount of Y is present in the main phase, as can be seen by comparing FIGS. 10A and 10F.

At the stage of the sintered magnet, Y is as shown in FIG.
As can be seen from FIG. 11, a large amount of Co is present in the grain boundary phase (concentrated in the grain boundary phase), and a large amount of Co is incorporated in the main phase as can be seen by comparing FIGS. 11 (a) and 11 (d). .

As described above, as a result of Y being concentrated in the grain boundary phase by sintering, it was found that Co moves from the grain boundary phase into the main phase. Then, in the main phase, Co replaces Fe and contributes to the Curie temperature increase. C in the grain boundary phase as in the past
When a large amount of o exists, ferromagnetic NdCo ₂ is obtained after sintering.
However, in the present invention, the concentration of Co in the grain boundary phase is greatly reduced in the present invention, and as a result, ferromagnetic NdCo ₂ is scarcely formed in the grain boundary phase, and a decrease in coercive force is suppressed. To be done.

Note that (R1 _x + R2 _y ) (T1 _p + T2 _q ).
Composition ratios x and y in the composition formula of _100-xyz Q _z M _r
Preferably satisfies the relational expression 0.01 ≦ y / (x + y) ≦ 0.23.

Note that the R-Fe-B magnet has a problem that the rare earth element R is easily oxidized, so that the corrosion resistance is low and, as a result, the magnetic characteristics are deteriorated. R-F
The reason why the corrosion resistance of the e-B magnet is low is considered as follows. That is, Nd and Pr present at the grain boundaries in the R-Fe-B magnet react with moisture in the atmosphere to form hydroxide. Since the volume expansion occurs at the grain boundaries due to the formation of the hydroxide, a strong stress is locally generated, and the grain is shed in a part of the magnet. Oxidation and corrosion are likely to proceed from the site where such powder removal occurs.

The present inventors evaluated the corrosion resistance of the rare earth sintered magnet according to the present invention. The composition (at%) of the sample used for this corrosion resistance evaluation is as shown in Table 1 below.

[0155]

[Table 1]

For the magnets of Samples 1 to 4, 2 atm,
A corrosion resistance test was carried out by holding in an accelerated test environment of 125 ° C. and a relative humidity of 85% for 24 hours. The degree of corrosion resistance was evaluated by the amount of shedding generated by corrosion.

As a result of the test, between Samples 1 and 2,
No significant difference was observed. However, in Sample 3, the amount of shattering was about 1/2 of that of Sample 1, and in Sample 4, the amount of shattering was about 1/5 of that of Sample 1.

The Y added to the above sample has a strong bonding force with oxygen and stably exists as an oxide without forming a hydroxide. Therefore, when Y is present at the grain boundaries, it is considered that volume expansion due to the formation of hydroxide is less likely to occur and de-dusting is less likely to occur. This is a special effect due to the addition of Y, and cannot be obtained when La is added instead of Y.

[0159]

According to the present invention, by diffusing Y or the like into the grain boundary phase, rare earth elements essential to the main phase such as Nd and Pr can be efficiently used without being consumed in the grain boundary phase, It is possible to provide a rare earth sintered magnet that maintains high magnetization of the main phase and exhibits excellent magnetic characteristics.

According to another aspect of the present invention, by collecting the rare earth element R2 such as Y in the grain boundary phase, an element (Co, Ni, etc.) that contributes to the improvement of magnetic characteristics in the main phase.
Can be efficiently incorporated into the main phase without wasting in the grain boundary phase. Also, rare earth elements such as Nd and Pr, which are indispensable for the main phase, can be incorporated into the main phase. Therefore, it is possible to further improve the magnet performance such as heat resistance while efficiently utilizing these elements.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a main phase and a grain boundary phase, (a)
Shows the texture structure in the stage of the raw material alloy, (b) shows the texture structure in the sintering process, and (c) shows the texture structure of the sintered magnet.

FIG. 2 is a graph showing an example of a temperature profile in a hydrogen pulverization process that can be preferably used in the present invention.

[Fig. 3] Nd _11.8 RE ' _2.4 Fe _79.7 B _6.1 (RE' is
6 is a graph showing the relationship between the residual magnetic flux density B _r and the addition amounts of Y, La, and Ce in a sintered magnet represented by the composition formula of Y, La, or Ce).

FIG. 4 (a) is a sintered magnet A (Nd _11.8 Y _2.4 Fe _79.7).
B _6.1 ) is a composition image photograph, (b) is a Y mapping photograph of the sintered magnet A, and (c) is a diagram schematically showing the structure of the sintered magnet A.

FIG. 5 (a) is a sintered magnet B (Nd _11.8 La _2.4 Fe).
_79.7 B _6.1 ) composition image photograph, (b) shows L of sintered magnet B
A mapping photograph, (c) is a diagram schematically showing the structure of the sintered magnet B.

FIG. 6A is a sintered magnet C (Nd _11.8 Ce _2.4 Fe).
_79.7 B _6.1 ) Composition image photograph, (b) is C of sintered magnet C
e mapping photograph, (c) is a diagram schematically showing the structure of the sintered magnet C.

FIG. 7 is a diagram schematically showing a main phase and a grain boundary phase, (a)
Shows the structural structure at the stage of the raw material alloy, (b) and (c) show the structural structure in the sintering process, and (d) shows the structural structure of the sintered magnet.

FIG. 8 is a graph showing the relationship between Curie point (Curie temperature), Y addition amount, and Co addition amount. The vertical axis of the graph is the Curie temperature, and the horizontal axis is the Y addition amount.

FIG. 9 is a graph showing the relationship between coercive force H _cj , Y addition amount, and Co addition amount. The ordinate of the graph is the coercive force, and the abscissa is the amount of Co added.

FIG. 10 shows a composition image photograph and an element mapping photograph of a raw material alloy, (a) is a composition image photograph, and (b) to (f).
Are mapping pictures of Nd, Dy, Co, Fe, and Y, respectively.

FIG. 11 shows a composition image photograph and an element mapping photograph of a sintered magnet, (a) is a composition image photograph, and (b) to (f).
Are mapping pictures of Nd, Dy, Co, Fe, and Y, respectively.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01F 41/02 H01F 1/04 H (56) Reference JP-A-7-11306 (JP, A) JP-A-4-155902 ( JP, A) JP-A-8-1007034 (JP, A) JP-A-4-268048 (JP, A) JP-A-2000-82610 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) H01F 1/08 B22F 3/00 B22F 9/04 C22C 38/00 303 H01F 1/053 H01F 41/02

Claims (14)

(57) [Claims] 1. The composition formula is (R1 _x + R2 _y ) T _100-xyz.
It is represented by Q _z (R1 is La (lanthanum), at least one element selected from the group consisting of all rare earth elements except Y (yttrium) and Sc (scandium), and R2 is La, Y, and Sc). Is at least one element selected from the group consisting of Y and T is at least 1 selected from the group consisting of all transition elements.
Element, Q is at least one element selected from the group consisting of B and C), and a rare earth sintered magnet containing crystal grains having a Nd ₂ Fe ₁₄ B type crystal structure as a main phase, wherein the composition ratio is x, y, and z satisfy 8 ≦ x ≦ 18 at%, 0.1 ≦ y ≦ 3.5 at%, and 3 ≦ z ≦ 20 at%, respectively, and the oxygen content is 2000 ppm or more and 8000 ppm in weight ratio.
The rare earth sintered magnet having the following R2 concentration is higher in at least a part of the grain boundary phase than in the crystal grains. 2. The composition ratios x and y are 0.01 ≦ y /
The rare earth sintered magnet according to claim 1, which satisfies a relational expression of (x + y) ≦ 0.23. 3. The composition formula is (R1 _x + R2 _y ) T _100-xyz.
A rare earth alloy represented by Q _z (R1 is at least one element selected from the group consisting of all rare earth elements except La, Y, and Sc, and R2 is selected from the group consisting of La, Y, and Sc. At least one element,
A powder containing Y, T is at least one element selected from the group consisting of all transition elements, Q is at least one element selected from the group consisting of B and C, and the composition ratio is x, y, and z are each 8 ≦ x ≦
18 at%, 0.1 ≦ y ≦ 3.5 at%, and 3 ≦ z
A step of preparing an alloy satisfying ≦ 20 at% and a tube containing oxygen and having an oxygen concentration of 20000 ppm or less.
Including a step of producing powder of the alloy by crushing the alloy in a controlled gas, and a step of sintering powder of the rare earth alloy, wherein the sintering step is performed at 650 to 1000 ° C. It includes a first step of holding at a temperature within the range for 10 to 240 minutes, and a second step of further advancing the sintering at a temperature higher than the holding temperature in the first step. R2 existing in the main phase crystal grains having the Nd ₂ Fe ₁₄ B type crystal structure in the rare earth alloy is diffused into the grain boundary phase during the sintering process, whereby the concentration of R2 is higher than that in the crystal grains. A method for producing a rare earth sintered magnet, wherein the grain boundary phase is increased in at least a part thereof. 4. The method for producing a rare earth sintered magnet according to claim 3, wherein the amount of oxygen contained in the powder of the rare earth alloy is 2000 ppm or more and 8000 ppm or less in weight ratio. 5. The sintering step diffuses R1 existing in a grain boundary phase in the rare earth alloy before sintering into the main phase crystal grains during the sintering process. 4. The method for producing a rare earth sintered magnet according to item 4. 6. The method for producing a rare earth sintered magnet according to claim 3, wherein the sintering step forms an oxide of R 2 in the grain boundary phase. 7. The average particle diameter (FS) of the rare earth alloy powder.
The method for producing a rare earth sintered magnet according to claim 3, wherein the SS grain size) is 5 μm or less. 8. The composition formula is (R1 _x + R2 _y ) (T1 _p + T
2 _q ) _100-xyzr Q _z M _r (R1 is at least one element selected from the group consisting of all rare earth elements except La (lanthanum), Y (yttrium) and Sc (scandium), R2 Is at least one element selected from the group consisting of La, Y, and Sc,
Must contain Y, T1 is Fe, T2 is at least one element selected from the group consisting of all transition elements except Fe, must contain Co, Q is selected from the group consisting of B and C At least one element, M is Al, Ga,
At least one element selected from the group consisting of Sn and In), a rare earth sintered magnet containing crystal grains having a Nd ₂ Fe ₁₄ B type crystal structure as a main phase, wherein the composition ratios x, y, z , P, q, and r are 8 ≦ x + y ≦ 18 at%, 0 <y ≦ 4 at%, 3 ≦ z ≦ 20 at%, 0 <q ≦ 20 at%, and 0 <q / (p + q) ≦ 0.3, respectively. , And 0 ≦ r ≦ 3 at%, and the oxygen content is 2000 ppm or more and 8000 ppm in weight ratio.
The rare earth sintered magnet having the following R2 concentration is higher in at least a part of the grain boundary phase than in the crystal grains. 9. The rare earth sintered magnet according to claim 8, wherein the composition ratio y satisfies the relational expression of 0.5 ≦ y ≦ 3 at%. 10. The composition formula is (R1 _x + R2 _y ) (T1 _p + T
2 _q ) _100-xyzr Q _z M _r (R1 is at least one element selected from the group consisting of all rare earth elements except La (lanthanum), Y (yttrium) and Sc (scandium), R2 Is at least one element selected from the group consisting of La, Y, and Sc,
Must contain Y, T1 is Fe, T2 is at least one element selected from the group consisting of all transition elements except Fe, must contain Co, Q is selected from the group consisting of B and C At least one element, M is Al, Ga,
At least one element selected from the group consisting of Sn and In), a method for producing a rare earth sintered magnet containing, as a main phase, crystal grains having an Nd ₂ Fe ₁₄ B type crystal structure, wherein a composition ratio x, y, z, p, q, and r are 8 ≦ x + y ≦ 18 at%, 0 <y ≦ 4 at%, 3 ≦ z ≦ 20 at%, 0 <q ≦ 20 at%, 0 <q / (p + q) ≦, respectively. A step of preparing an alloy satisfying 0.3 and 0 ≦ r ≦ 3 at%, and a tube containing oxygen and having an oxygen concentration of 20000 ppm or less.
Including a step of producing powder of the alloy by crushing the alloy in a controlled gas, and a step of sintering powder of the rare earth alloy, wherein the sintering step is performed at 650 to 1000 ° C. It includes a first step of holding at a temperature within the range for 10 to 240 minutes, and a second step of further advancing the sintering at a temperature higher than the holding temperature in the first step. R2 existing in the main phase crystal grains having the Nd ₂ Fe ₁₄ B type crystal structure in the rare earth alloy is diffused into the grain boundary phase during the sintering process, whereby the concentration of R2 is higher than that in the crystal grains. A method for producing a rare earth sintered magnet, wherein the grain boundary phase is increased in at least a part thereof. 11. The method for producing a rare earth sintered magnet according to claim 10, wherein the amount of oxygen contained in the powder of the rare earth alloy is 2000 ppm or more and 8000 ppm or less by weight. 12. The sintering process according to claim 10, wherein R1 existing in the grain boundary phase in the rare earth alloy before sintering is diffused into the main phase crystal grains during the sintering process. A method for producing the rare earth sintered magnet described. 13. The method for producing a rare earth sintered magnet according to claim 10, wherein the sintering step forms an oxide of R2 in the grain boundary phase. 14. The average particle diameter (F) of the rare earth alloy powder.
The method for producing a rare earth sintered magnet according to claim 10, wherein the SSS particle size) is 5 μm or less.