JP2002025813A - Anisotropic rare earth magnet powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anisotropic rare earth magnet powder which has a high anisotropy rate and a high coercive force and is obtained through industrial production. SOLUTION: This anisotropic rare earth magnet powder is obtained, in a manner in which the hydride of an R-Fe-B alloy containing 11 to 15 at.% R, 5.5 to 8.0 at.% B, unavoidable impurities, and the residual at.% Fe is subjected to a high-temperature hydrogenation treatment and successively undergoes a dehydrogenation treatment, where an anisotropic rate Br/Bs (Bs is uniformly set at 16kG) is set at 0.8 or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to anisotropic rare earth magnet powder.

[0002]

2. Description of the Related Art A rare-earth magnet made of an RFeB-based alloy containing a rare-earth element (hereinafter abbreviated as R), boron (B) and iron (Fe) as main components has a residual magnetic flux density (Br) and a coercive force (R). Because of its excellent magnetic properties such as iHc), it has been widely used.

[0003] Rare earth magnet powders having excellent magnetic properties are obtained by releasing the occluded hydrogen after a high temperature hydrogen treatment step of causing a normal structure transformation in which the rare earth magnet raw material absorbs hydrogen while being heated to 750 to 950 ° C. And subjecting it to a dehydrogenation step to cause reverse structural transformation.

The magnetic properties are evaluated by Br and iHc, and the maximum energy product ((BH) max) proportional to the product of both. iHc mainly depends on the crystal grain size,
It becomes larger as the crystal grains are refined. In addition, Br depends on the crystal orientation. By aligning the crystal orientation, the crystal orientation can be aligned in a predetermined direction, thereby increasing anisotropy and increasing Br. As a result, a high (BH) max is obtained.

Here, the anisotropy can be numerically defined as follows. That is, the anisotropy is determined by the anisotropic ratio Br / Bs.
(Bs is uniformly set to 16 kG), and Br /
When the value of Bs is 1.0, it means complete anisotropy, and 0.5
When it is 0, it means ideal isotropy. Furthermore, Br / B
Depending on the value of s, Br / Bs ≧ 0.8: anisotropic magnet powder region 0.6 ≦ Br / Bs <0.8: region with insufficient anisotropy 0.5 ≦ Br / Bs <0.6: It is classified into the isotropic magnet powder area.

Further, iHc is desired to be 9 kOe or more as a general practical magnet.

The following techniques are disclosed for a method of producing a rare earth magnet powder for the purpose of improving magnetic properties.

In the production method described in Japanese Patent Publication No. 7-110965, an RFeB-based alloy is first produced by melting and then pulverized, and a green compact and a sintered body are produced using the obtained alloy powder. Subsequently, after absorbing hydrogen into the sintered body, the sintered body is heated to 600 ° C to 1000 ° C. During this heating and heating, the stored hydrogen and NdFeB react and decompose into three phases (normal structure transformation). This is a production method in which dehydrogenation proceeds at the same time and finally a recombined tissue is obtained.

However, the production method of Japanese Patent Publication No. Hei 7-110965 can only obtain a fine NdFeB structure which is recombined after three-phase decomposition only partially, so that it is mixed with the coarse NdFeB structure of the base material. A non-uniform organization. The coercive force was reduced due to the non-uniform structure, and was insufficient as a magnet powder. Furthermore, the anisotropic ratio is 0.75
And the anisotropy was insufficient.

[0010] The production method of Japanese Patent Publication No. 7-68161 is a high-temperature hydrogen treatment for producing an RFeB-based alloy and then holding the alloy at 500 to 1000 ° C. in a hydrogen gas atmosphere of 10 torr or more to cause forward structure transformation. Is performed in a vacuum atmosphere of 1 × 10 ^-1 torr or less.
This is a production method in which dehydrogenation treatment is performed in which hydrogen is removed by maintaining the temperature at 000 ° C. to generate a reverse transformed structure.

The production method of Japanese Patent Publication No. 7-68161 is a production method in which a raw material alloy is subjected to forward structure transformation and reverse structure transformation to obtain a fine recrystallized structure and obtain a high coercive force. However, this manufacturing method could only obtain an isotropic magnet powder having an extremely low anisotropic ratio of 0.67. This indicates that simply applying the forward transformation and the reverse transformation to the raw material alloy does not make it possible to obtain a high anisotropic ratio with a uniform crystal orientation.

[0012] With the aim of improving the anisotropic ratio, attempts have been made to improve the alloy composition and production method of the rare earth magnet powder.

JP-A-3-129703 and JP-A-4-133407 disclose an alloy having a composition in which Co is added to an RFeB-based alloy and a trace element such as Ga, Zr, Ti, or V is added. It is disclosed that the anisotropic ratio becomes 0.75 at the maximum by performing the hydrogen treatment. However, these methods have a problem that the cost becomes high because a large amount of expensive Co is added.

JP-A-3-129702 and JP-A-4-133406 disclose that anisotropy is improved by subjecting an RFeB-based alloy to an alloy having a composition in which Co is not added to hydrogen treatment. Have been. However, the anisotropic ratio was insufficient at a maximum of 0.68.

JP-A-3-146608 and JP-A-Hei-4
No. -17604, RFeB-based and RFeCoB-based alloys are put into a reaction chamber together with a heat storage material to generate heat during a hydrogen reaction.
A hydrogen treatment method for preventing a decrease in anisotropic ratio due to an endothermic problem is disclosed. However, even with these treatment methods, the anisotropic ratio was insufficient at a maximum of 0.69.

Japanese Patent Application Laid-Open No. 5-163509 discloses RFeB
A hydrogen treatment method is disclosed in which an ingot obtained by homogenizing a system and an RFeCoB-based alloy is pulverized to a uniform particle size, thereby preventing a decrease in anisotropic ratio due to a heat generation and endothermic problem during a hydrogen reaction. However, even when this treatment method was used, the anisotropic ratio was insufficient at 0.74 at the maximum.

Japanese Patent Application Laid-Open No. 5-163510 discloses RFeB
A hydrogen treatment method is disclosed in which a system and an RFeCoB-based alloy are inserted into a vacuum tube furnace to perform a hydrogen treatment, thereby preventing a decrease in anisotropic ratio due to heat generation and heat absorption during a hydrogen reaction. However, even when this treatment method was used, the anisotropic ratio was insufficient at 0.74 at the maximum.

JP-A-6-302412 discloses RFeB
A hydrogen treatment method is disclosed in which the pressure of hydrogen in a hydrogen atmosphere is changed up and down during the reaction of a hydrogen gas with an RFeCoB-based alloy and an RFeCoB-based alloy to prevent a decrease in anisotropic ratio due to heat generation and heat absorption. I have. However, even with this treatment method, the anisotropic ratio was insufficient at 0.76 at the maximum.

JP-A-8-288113 discloses RFeB
Alloy material cooled after performing hydrogen treatment on the RFeCoB-based alloy and the RFeCoB-based alloy is heated to a temperature of less than 500 ° C. and a hydrogen pressure of 1-760 t
In a hydrogen atmosphere of orr, a "low-temperature hydrogen storage process" is performed, followed by a dehydrogenation process (final dehydrogenation process) at a temperature in the range of 500 to 1000 [deg.] C. to crush the precipitated phases such as the R-rich phase and the B-rich phase. There is disclosed a hydrogen treatment method which facilitates the treatment and suppresses intragranular fracture and distortion of the Nd ₂ Fe ₁₄ B phase. It is disclosed that an anisotropic ratio of at most 0.84 can be obtained by this processing method. However, in this treatment method, since low-temperature hydrogen absorption and final dehydrogenation are performed again after the hydrogen treatment, it takes more time per batch than the conventional hydrogen treatment method, and it has been difficult to produce on an industrial scale.

Japanese Patent Laid-Open No. 10-041113 discloses RFe
Switching to an Ar atmosphere during the first hydrogen storage using a CoB-based alloy, rapidly cooling, heating again in a hydrogen atmosphere and a vacuum atmosphere (rapid cooling and reheating treatment), performing hydrogen storage after hydrogen introduction, and performing dehydrogenation. Thus, a hydrotreating method is disclosed that allows the formation of the R (FeCoM) ₂ phase. However, in this method, the anisotropic ratio was 0.69 at the maximum, which was insufficient.

Japanese Patent Application Laid-Open No. 10-259559 discloses the structure of an RFeCo (Ni) B-based alloy as a raw material alloy, particularly the influence of a grain boundary precipitation phase and the effect of a cooling rate after hydrogen treatment. It is disclosed that the anisotropic ratio becomes 0.8 at the maximum by this method. However, this method is difficult with a normal melting technique because it requires complicated control of the structure of the raw material alloy used.

Japanese Patent Application Laid-Open No. Hei 10-256014 discloses RFe
It is disclosed that the magnetic anisotropy is improved by performing a hydrogen treatment on a composition obtained by adding a trace amount of Mg to a B-based and RFeCoB-based alloy, and an anisotropic ratio of 0.85 is obtained at the maximum. . However, since Mg has a very low melting point of 650 ° C. and a boiling point of 1120 ° C., it is very difficult to control it to 0.1 at% or less.

JP-A-6-128610, JP-A-7-5
No. 4003, JP-A-7-76708, JP-A-7-76
754, JP-A-7-278615, JP-A-9-16
No. 5601, RFeB-based and RFeCoB-based alloy coarsely pulverized powder is heated to a temperature of 750 ° C. or more in a vacuum, and then a hydrogen gas of 10 Pa to 1000 kPa is introduced into the reaction furnace, and 750 to 900 ° C. Untransformed Nd ₂ as a nucleus that determines the three-phase decomposition structure and the crystal orientation during recrystallization by heating and holding
A treatment method is disclosed in which after the Fe ₁₄ B phase is left, dehydrogenation is performed at 700 to 900 ° C. under a partial pressure of H ₂ , an inert gas atmosphere, or vacuum evacuation. In this way, a maximum anisotropic ratio of 0.83 has been obtained. However, since this hydrotreating method utilizes a transient phenomenon for leaving an appropriate amount of untransformed Nd ₂ Fe ₁₄ B, industrial production is very difficult.
In fact, mass production by these methods has not been achieved.

These studies for improving the anisotropy rate are collectively described in the Journal of Alloys and Com.
pounds 231 (1995) 51 papers. There, HDDR (hydrogen treatment method: h
hydrogenation-decomposition
n-desorption-recombination
The n) method is as follows: 1) A fine recombined structure of R ₂ Fe ₁₄ B is obtained.

2) An isotropic magnet powder can be obtained with an RFeB ternary composition.

3) Although the anisotropic mechanism is unknown,
In order to obtain anisotropic magnet powder, the addition of Co as an alloy composition is essential. It is summarized as follows. This view has become the norm in the field.

The biggest problem is that a large amount of expensive Co must be added in order to obtain anisotropy.

[0028]

The present invention has been made in view of the above situation. That is, an object of the present invention is to provide a method for industrially producing an anisotropic rare earth magnet powder having a high anisotropic ratio and a coercive force without necessarily adding expensive Co.

[0029]

Means for Solving the Problems In order to solve the above problems, the present inventors have proposed a method for producing an anisotropic rare earth magnet powder, in which the anisotropy ratio of the recombined RFeB structure is improved and the crystal grains of the structure are refined. As a result of repeated examinations on the method of performing the above, an RFeB-based raw material alloy was held in a hydrogen gas atmosphere as a starting raw material in the high-temperature hydrogen treatment step, and the raw material alloy and hydrogen were heated at 600 ° C.
Hydrogen compound (R ₂ Fe ₁₄ BH _x ) by reacting at the following temperature
Low-temperature hydrogenation step, in which hydrogen necessary for the three-phase decomposition reaction is incorporated, and then the obtained hydrogen compound is microstructured under a hydrogen gas atmosphere lower than the hydrogen gas pressure in the low-temperature hydrogenation step. By heating to the transformation temperature, the normal structure transformation reaction proceeds gently, and the three-phase decomposition structure (RH ₂ phase, Fe phase, F phase
At the same time as obtaining the e ₂ B phase, the crystal orientation of the R ₂ Fe ₁₄ B phase of the master alloy is transferred to the Fe ₂ B phase (FIG. 1 schematically shows the transfer of the crystal orientation. Crystal orientation (arrow) and the crystal orientation (arrow) of the Fe ₂ B phase (tetragonal) decomposed by the three-phase decomposition by forward transformation become the same direction). The accompanying internal hydrogen is supplemented by external low-pressure hydrogen, and the reaction can proceed slowly, resulting in a three-phase decomposition reaction while maintaining the crystal orientation. After that, dehydrogenation and recombination reaction proceed,
At this time, the reaction proceeds at a hydrogen pressure as high as possible so that the reverse structure transformation reaction proceeds gently, and the crystal orientation of the finely recombined R ₂ Fe ₁₄ BH _x phase is aligned with the crystal orientation of the Fe ₂ B phase as a nucleus. First evacuation step (FIG. 1 shows the transfer of the crystal orientation.
Crystal orientation of the crystal orientation and recombined Nd ₂ Fe ₁₄ BH _x phase ₂ B phase are oriented in the same direction. ) And a hydrogen treatment method having a dehydrogenation step including a second evacuation step of forcibly exhausting hydrogen of R ₂ Fe ₁₄ BH _x was found to be able to solve the above-mentioned problem by applying to a RFeB-based alloy.

As a result, the crystal orientation of the recombination structure is the same as that of the master alloy, and a high anisotropic ratio can be obtained. Further, since the coarse crystal grains of the RFeB raw material are refined and made uniform with the structural transformation, a high coercive force is obtained.

The production method of the present invention does not require the addition of Co in particular for anisotropy, and the untransformed R ₂ Fe ₁₄ B
This method is suitable for industrial production because it does not utilize the transient phenomenon of remaining phases.

In the present invention, for the first time, N is added without adding Co.
The manner of reaction between the raw material and hydrogen was clarified in the dFeB-based alloy composition.

The anisotropic rare-earth magnet powder produced by the method for producing anisotropic rare-earth magnet powder of the present invention has excellent magnetic properties, so that it is particularly effective to use it for an anisotropic bonded magnet. is there.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing anisotropic rare earth magnet powder of the present invention has a low-temperature hydrogenation step, a high-temperature hydrogenation step, and a dehydrogenation step.

The RFeB-based alloy is an alloy containing R, Fe, and B as main components and containing unavoidable impurity elements. R represents yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (N
d), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),
One or more selected from lutetium (Lu) can be used. Among them, it is particularly preferable to use Nd.

The RFeB alloy is 0.01 to 1.0 at.
% Of gallium (Ga) and 0.01 to 0.6 at% of niobium (Nb). By containing Ga, the coercive force of the anisotropic rare earth magnet powder is improved. Here, the content of Ga is 0.01 at.
%, The effect of improving the coercive force cannot be obtained.
%, The coercive force is reduced. By containing Nb, it becomes possible to easily control the reaction rates of the forward structure transformation and the reverse structure transformation. Here, if the Nb content is less than 0.01 at%, it is difficult to control the reaction rate, and if it exceeds 0.6 at%, the coercive force is reduced.

In particular, the co-addition of Ga and Nb within the above contents can improve both the coercive force and the anisotropic property as compared with the case where they are added alone, and as a result, (BH) max
Increase.

Al, Si, Ti, V,
Cr, Mn, Ni, Cu, Ge, Zr, Mo, In, S
It is preferable to add one or more of n, Hf, Ta, W, and Pb in a total amount of 0.001 to 5.0 at%. By adding these atoms, the coercive force and the squareness ratio of the obtained magnet can be improved. If the addition amount is less than 0.001 at%, the effect of improving the magnetic properties will not be exhibited, and if it exceeds 5.0 at%, a precipitated phase or the like will precipitate and the coercive force will decrease.

0.001-20 Co in RFeB alloy
It is preferable to add at%. By adding Co, the Curie temperature of the RFeB-based alloy can be increased, and the temperature characteristics are improved. Here, when the amount of Co added is less than 0.001 at%, the effect of Co addition is not seen,
If it exceeds 20 at%, the residual magnetic flux density will decrease, and the magnetic properties will decrease.

The RFeB-based alloy is an alloy having an R ₂ Fe ₁₄ B phase which is an intermetallic compound composed of R, Fe and B as a main phase.

The RFeB-based alloy has an R of 11 to 15 at%.
And 5.5 to 8.0 at% of B and inevitable impurities, and the balance is preferably made of Fe. R is 11a
If it is less than t%, the αFe phase precipitates and the magnetic properties deteriorate, and
It exceeds 5at% R ₂ Fe _{1 4} B phase decreases and the magnetic properties lowers. If B is less than 5.5 at%, a soft magnetic R ₂ Fe ₁₇ phase is precipitated to lower the magnetic properties, and the B content is 8.0 at%.
%, The R ₂ Fe ₁₄ B phase decreases and the magnetic properties deteriorate.

The method of preparing the RFeB-based alloy is not particularly limited. As a general method, a high-purity alloy material is used, each is prepared so as to have a predetermined composition, and after mixing these, high-frequency melting is performed. It is melted by a method, a melting furnace, or the like, and is cast to produce an alloy ingot, and this raw material ingot can be used as a raw material alloy. Further, the raw material ingot may be pulverized into a coarse powder form to be used as a raw material alloy. Furthermore, an alloy obtained by subjecting a raw material ingot to a homogenization treatment to reduce the bias in the composition distribution can be used as the raw material alloy. In addition, the homogenized ingot may be pulverized into a coarse powder to be used as a raw material alloy.

In the low-temperature hydrogenation step, an RFeB-based alloy as a raw material of the anisotropic rare earth magnet powder is held in a hydrogen gas atmosphere, and the raw material alloy and hydrogen are reacted at a temperature of 600 ° C. or less to form a hydrogen compound (R ₂ Fe ₁₄ BH _x ).

[0044] The low-temperature hydrogenation process, by incorporating a hydrogen RFeB-based alloy as R ₂ Fe ₁₄ BH _x, it is possible to control the reaction rate of the forward structural transformation in the subsequent high-temperature hydrogenation process. Here, x represents the amount of hydrogen.
Note that x increases as the hydrogen pressure increases. further,
x reaches a saturation value as the reaction time between the RFeB-based alloy and hydrogen increases.

As a specific method of the low-temperature hydrogenation step,
It is preferable that the RFeB-based alloy be kept in a hydrogen gas atmosphere of 0.3 atm or more for about 1 to 3 hours. Here, when the hydrogen gas atmosphere is less than 0.3 atm, the hydride conversion of the RFeB-based alloy does not sufficiently proceed and it takes time. RFe
Since the hydrogenation of the B-based alloy proceeds sufficiently in a hydrogen gas atmosphere of 1.0 atm or less, the B-based alloy becomes 0.3 to 1.0 atm.
Is preferably maintained in a hydrogen gas atmosphere. However, this does not preclude the occurrence of hydride formation by holding the RFeB-based alloy in a hydrogen gas atmosphere of 1.0 atm or more. Here, the hydrogen gas atmosphere may be not only an atmosphere of only hydrogen gas but also a mixed gas atmosphere of hydrogen gas and an inert gas. In the case of such a mixed gas atmosphere, the hydrogen gas pressure indicates a hydrogen gas partial pressure. When the reaction temperature is 600 ° C. or higher, a forward structural transformation occurs partially and the structure becomes non-uniform, which is not preferable.

In the low-temperature hydrogenation step, the crystal orientation (for example, the C-axis direction) of the R ₂ Fe ₁₄ B compound of the mother alloy is preserved as it is in the R ₂ Fe ₁₄ BH _x compound when the compound is hydrogenated. Is done.

In the high-temperature hydrogenation step, the obtained hydrogen compound is heated to a structure transformation temperature of 600 ° C. or higher, which causes a normal structure transformation of the hydrogen compound to produce a three-phase decomposition structure.
This is a step of giving anisotropy.

In the high-temperature hydrogenation step, since a hydrogen compound containing hydrogen is used as a starting material, it is only necessary to supplement the internal hydrogen consumed by the three-phase decomposition with external hydrogen. Can be suppressed, so that the forward tissue transformation reaction can be performed gently. As a result, the reaction rate of the normal transformation structure can be controlled, and the crystal orientation (for example, C-axis direction) of the hydrogen compound can be preserved in the crystal orientation (for example, C-axis direction) of the Fe ₂ B phase of the three-phase decomposition structure. A forward structure transformation having a uniform three-phase decomposition structure occurs. Here, the forward structure transformation refers to a hydrogen compound R ₂ Fe ₁₄ BH _x
System alloy reacts with hydrogen, and the structure becomes RH ₂ phase, αFe
And Fe ₂ B phase.

The high-temperature hydrogenation step can also be carried out by charging a hydrogen compound into a reactor which has been heated to a structural transformation temperature in advance. The hydrogen gas pressure in the high-temperature hydrogenation step is preferably in the range of 0.2 to 0.6 atm, and the structure transformation temperature is preferably 760 to 860 ° C. By setting the hydrogen gas pressure to 0.2 to 0.6 atm, the reaction between the hydrogen compound and the hydrogen gas can proceed gently. If the hydrogen gas pressure is less than 0.2 atm, the hydrogen gas pressure is too low, the reaction rate becomes extremely slow, and an untransformed structure remains to cause a significant decrease in coercive force. On the other hand, when the hydrogen gas pressure is 0.
If it exceeds 6 atm, the reaction between the hydrogen compound and the hydrogen gas proceeds rapidly, the C-axis preservation of the crystal orientation is disturbed, and the anisotropic ratio is greatly reduced. If the structural transformation temperature is lower than 760 ° C., normal structural transformation occurs, but the three-phase decomposition structure becomes non-uniform, resulting in a decrease in coercive force. Further, at a temperature exceeding 860 ° C., crystal grains grow and the coercive force decreases.

Since the forward structure transformation reaction is an exothermic reaction, the temperature of the material rapidly increases with the progress of the forward structure transformation. Furthermore, the hydrogen compound stores the hydrogen, so that the hydrogen gas pressure greatly fluctuates, and the hydrogen gas pressure around the compound is greatly reduced. Therefore, in order to control the reaction rate of the normally transformed structure, strict temperature control and hydrogen gas pressure control must be performed using a reaction furnace such as the furnace disclosed in JP-A-9-251912. desirable.

The reaction rate of the normally transformed structure is mutually dependent on the structure transformation temperature and the hydrogen gas pressure. Therefore, in order to obtain a high anisotropy ratio, it is preferable to combine the hydrogen gas pressure and the temperature so that the relative reaction rate of the normal structure transformation is 0.05 to 0.80. In general, the reaction rate V between the alloy and hydrogen is

[0052]

V = V ₀ · ((P _H2 / P ₀ ) ^1/2 -1) · exp
(−Ea / RT). V ₀ : frequency factor, P _H2 : hydrogen gas pressure (Pa), P ₀ : dissociation pressure, Ea: activation energy (J / molK), T: temperature (K).

Since the reaction rate is considered to be proportional to the transformation rate of the structure, the transformation rate of the structure can be evaluated based on the reaction rate.

That is, the reaction rate V of the forward transformation reaction of the tissue
Is a reaction temperature of 830 ° C. and a hydrogen gas pressure of 0.1 MPa.
The reaction speed Vb at (1 atm) is defined as a reference reaction speed with Vb = 1, and is defined as a relative reaction speed Vr based on the reference reaction speed. Therefore, the relative reaction speed _Vr is _expressed by the following equation.

[0055]

[Number 2] _{V r = (1 / 0.576)} · (((PH 2) 1/2
−0.39) /0.61) · exp (−Ea / RT) ×
^10-9 Here, the relative reaction rate when less than 0.05 coercivity remain untransformed tissue is greatly reduced. On the other hand, 0.
If it is larger than 80, the crystal orientation is not uniform, and the anisotropic ratio is greatly reduced.

The dehydrogenation step is performed at 0.1 to 0.001 at.
m hydrogen atmosphere_TwoWhile maintaining the crystal orientation of the B phase
R_TwoFe₁₄BH_xFirst exhaust with controlled reaction rate to obtain
Qi process and then 10^-2alloy until it is below torr
To remove hydrogen from R _TwoFe₁₄The second to get B
It consists of two exhaust processes.

In the first exhaust step, the three-phase decomposition structure is reduced to 0.1 to
By maintaining the atmosphere under a hydrogen atmosphere of 0.001 atm, the reverse structure transformation reaction proceeds gently. At this time, the C-axis crystal orientation of Fe ₂ B having a uniform crystal orientation is changed to the recombination R ₂ Fe ₁₄ B
It is transferred to the C-axis crystal orientation of H _x. Subsequently, in the second exhaust step, the remaining hydrogen in the hydride is removed and RF
Recovers eB alloy. Thus, the anisotropy of the rare earth magnet powder is prevented from lowering and the crystal grains are refined.

In the dehydrogenation step, the first exhaust stroke includes:
When the retained hydrogen atmosphere is 0.1 atm or more, hydrogen is not easily separated from the RH ₂ phase of the three-phase decomposition structure,
If the pressure is less than 01 atm, hydrogen is rapidly released from the RH ₂ phase of the three-phase decomposition structure, so that the reaction rate is increased and the anisotropic ratio of the rare earth magnet powder after dehydrogenation is reduced. Here, the holding time during which the three-phase decomposition structure is maintained in a controlled hydrogen atmosphere is preferably 10 to 120 minutes. If the holding time is short, a three-phase decomposition structure remains partially, the transfer of the crystal orientation of the structure is not complete, and the anisotropic ratio of the obtained magnet powder decreases. When the holding time is long, the transfer of the orientation is sufficiently performed, but conversely, abnormal grain growth of crystal grains occurs partially, leading to a decrease in coercive force.

In the subsequent second evacuation step, the hydrogen gas pressure of the atmosphere from which hydrogen was removed was 10 ⁻² to
When it is larger than rr, hydrogen remains in the hydrogen compound, so that the coercive force of the rare earth magnet powder after hydrogen removal is reduced.

Since the reverse structure transformation reaction is an endothermic reaction, the temperature of the material rapidly decreases with the progress of the reverse structure transformation.
Furthermore, it is necessary to control to a low hydrogen pressure by the first exhaust process. Therefore, in order to be able to control the reaction rate of the reverse transformed structure, strict temperature control and hydrogen gas pressure control using a furnace disclosed in JP-A-9-251912 are required.

The reaction rate of the inversely transformed structure is mutually dependent on the structure transformation temperature and the hydrogen gas pressure. Therefore, in order to obtain a high anisotropic ratio, it is preferable to combine the hydrogen gas pressure and the temperature so that the relative reaction rate of the reverse structural transformation is 0.1 to 0.95. The reaction rate of the reverse transformation tissue reaction can be defined similarly to the reaction rate of the forward transformation tissue reaction. Ie

[0062]

V = V ₀ · (1− (P _H2 / P ₀ ) ^1/2 ) · exp
(−Ea / RT) Here, the hydrogen pressure becomes a driving force for the reverse transformation reaction. However, the reaction rate of the reverse transformation reaction of the structure is such that the reaction temperature is 830.
° C, hydrogen gas pressure is 0.0001 atm (10 ^-1 torr)
The reaction rate Vb at the time of r) was set as a reference reaction rate where Vb = 1. Therefore

[0063]

[Number 4] _{V r = (1 / 0.576)} · (0.39- (P
^{_{H 2) 1/2 /0.38) · exp}} (-Ea / RT) × 10
^{If the -9} relative reaction rate is less than 0.1, the reaction rate is low and hydrogen is not easily removed. On the other hand, the relative reaction rate is 0.
When it is larger than 95, the reaction rate is high and the crystal orientation is not uniform, and the anisotropic ratio is greatly reduced.

The anisotropic rare earth magnet powder produced by the production method of the present invention can be used for an anisotropic bonded magnet, or used for an anisotropic bulk magnet by sintering or hot pressing. Can be.

[0065]

The present invention will be described below with reference to examples.

As an example, an anisotropic rare earth magnet powder made of an NdFeB-based alloy using Nd as the main component of R was produced.

(First Example) (Production of Anisotropic Rare Earth Magnet Powder) An anisotropic rare earth magnet powder is prepared by preparing a raw material alloy for forming a magnet powder and preparing a hydrogen compound as a starting material in a high-temperature hydrogen treatment step. After forming
The hydrogen compound is produced by causing forward structure transformation and reverse structure transformation.

More specifically, first, alloy elements shown in Table 1 were weighed to a predetermined amount, and 100 kg to 300 kg of an alloy ingot having the composition shown in Table 1 was obtained by using a high frequency melting method.
/ Molded in batch. Thereafter, the alloy ingot was subjected to a heat treatment of maintaining the alloy ingot at 1140 to 1150 ° C. for 40 hours in an argon gas atmosphere to perform a homogenization treatment of the alloy ingot structure. In Table 1, the contents of the respective elements are shown in atomic percentage, the total alloy is set to 100 at%, and Fe is the rest.

[0069]

[Table 1] The homogenized alloy ingot was pulverized by a jaw crusher into coarse pulverized products having an average particle size of 10 mm or less.

Thereafter, the coarsely pulverized product was introduced into the insertion chamber of the hydrogen treatment furnace shown in FIG. In addition,
The insertion chamber into which the coarsely pulverized material is charged is sealed, and is formed so that the hydrogen gas atmosphere inside the chamber can be changed. That is, as means for changing the hydrogen gas atmosphere, a hydrogen gas supply unit for supplying hydrogen gas into the insertion chamber and an exhaust unit for exhausting the insertion chamber are provided. Here, a hydrogen compound serving as a raw material for the high-temperature hydrogenation step is produced.

The coarsely pulverized product (about 10 kg) in the insertion chamber was kept at room temperature for 0.5 to 3 hours under a hydrogen gas atmosphere shown in the low-temperature hydrogen treatment conditions in Table 2. By keeping the coarsely pulverized product in a hydrogen gas atmosphere, the hydrogen gas in the atmosphere reacts with the coarsely pulverized product to form a hydrogen compound. Specifically, the processing time was 3 hours. Here, the formation of the hydrogen compound was performed by confirming the presence or absence of hydrogen absorption. In addition, the sample No. shown in Table 2 was used. Indicates that compositions a to i correspond to samples 1 to 9, such that sample 1 has composition a and sample 2 has composition b.

Subsequently, the hydrogen compound is transferred from the insertion chamber to the reaction chamber without contacting the atmosphere. This reaction chamber is formed so as to be connected to the insertion chamber. Furthermore, it is formed so that the hydrogen gas atmosphere and temperature in the reaction chamber can be adjusted. That is, as means for changing the hydrogen gas atmosphere, a hydrogen gas supply unit for supplying hydrogen gas into the insertion chamber and an exhaust unit (first exhaust system and second exhaust system) for exhausting the insertion chamber are provided. . As means for adjusting the temperature in the reaction chamber, a heater for heating the reaction chamber and a heat balance function for exhibiting a heat compensation function in the reaction chamber are provided. The heat balance function is used, for example, to control the material temperature to a constant value and to control the reaction rate by causing the reaction heat generated by the forward heat transformation reaction, which is an exothermic reaction, to the reverse reaction, that is, by causing an endothermic reaction. Have been. In the case of an endothermic reaction, the reverse is performed.

The high-temperature hydrogen treatment conditions in Table 2 are set in the reaction chamber, and the hydrogen compound absorbs hydrogen gas in the reaction chamber and undergoes normal structure transformation (three-phase decomposition structure of αFe, NdH ₂ , and Fe ₂ B). Nd ₂ F which is the original material alloy
The crystal orientation of e ₁₄ B can be transferred to Fe ₂ B. Here, the relative reaction rate of this forward structural transformation is also shown in Table 2. After the normal structure transformation, each temperature was maintained for 3 hours or more.

Thereafter, in the dehydrogenation step, the crystallographic orientation of the Fe ₂ B phase is transferred to the crystal orientation of the recombined structure Nd ₂ Fe ₁₄ BH _x while simultaneously causing reverse structural transformation using the first exhaust system. Hydrogen was removed using a forced evacuation system to remove residual hydrogen gas in Nd ₂ Fe ₁₄ BH _x . Specifically, in the first exhaust step, the hydrogen gas pressure is adjusted to 0.05 to 0.0 using a flow control valve or a mass flow meter.
Control was performed between 01 atm for 40 minutes. The method of the first evacuation step is not limited to the above method, and can be controlled by using, for example, a low-pressure sensor and a normal valve. The control pressure is shown in Table 2. After completion of the first evacuation step, evacuation was performed using the second evacuation step in FIG. 1 until the final degree of vacuum in the reaction chamber became 10 ⁻⁴ torr or less.

[0075]

[Table 2] After the second evacuation process, the recombined NdFeB-based alloy was moved to a cooling chamber and cooled to room temperature in an Ar atmosphere or a vacuum atmosphere. After cooling, an anisotropic rare earth magnet powder is obtained.

Further, 3 wt% of an epoxy solid resin of the magnet powder is mixed with the obtained anisotropic rare earth magnet powder,
An anisotropic bonded magnet was manufactured by performing mold forming by pressing in a warm magnetic field. The magnetic field in the press in the warm magnetic field was 20 kOe. Comparative Example As a comparative example, the composition b shown in Table 1 was used.
Magnet powder samples 50 to 55 made of the above alloys were produced. Here, the samples 50 to 55 were manufactured in the same manner as the sample 2 except for the conditions shown in Table 2. In addition, samples 50 to
An anisotropic bonded magnet using 55 magnet powders was also produced. This anisotropic bonded magnet was manufactured in the same manner as the anisotropic bonded magnet of Sample 2.

Here, the sample 50 is a magnet powder that has not been subjected to the low-temperature hydrogen treatment, and the sample 51 is a magnet powder whose hydrogen gas pressure in the low-temperature hydrogen treatment is lower than that in the high-temperature hydrogen treatment.
For the sample 52, a hydrogen gas atmosphere of low-temperature hydrogen treatment was set to 10 ⁻² to
It is a magnet powder in a vacuum of rr or less, and samples 53 to 55
Was a magnet powder having a high hydrogen gas pressure in the high-temperature hydrogen treatment, and the relative reaction rate was high.

(Evaluation) The evaluation of the examples was carried out by measuring the magnetic properties of the rare earth magnet powder and the anisotropic bonded magnet using this magnet powder.

That is, (B) of the anisotropic rare earth magnet powder
H) max, Br, iHc and anisotropic ratio, and (BH) max and Br of anisotropic bonded magnets are VS
The measurement was performed using an M or BH tracer and evaluated. The measured particle size of the magnet powder was 212 μm or less.
Table 2 shows the measured magnetic properties of the magnet powder and the anisotropic bonded magnet.

As shown in Table 2, the sample No. The magnet powders Nos. 1 to 9 have a high anisotropic ratio of 0.8 or more and a high Br value of 13.0 kG or more, resulting in a high (BH) max. The sample No. 1
Also in the anisotropic bonded magnet using the magnet powders of Nos. 9 to 9,
(BH) max and Br are both high.

On the other hand, the magnet powders of Samples 50 and 51 of the comparative examples have high anisotropy of 0.82 and 0.83, respectively, although their anisotropy rates are 0.82 and 0.83, respectively. Magnetic force is decreasing. The anisotropic ratios of the magnet powders of Samples 52 and 53 are reduced to 0.77 and 0.74, respectively. Further, the magnet powder of the samples 54 and 55 is an isotropic magnet powder.

Subsequently, the magnet powder of Sample 2, the magnet powder of Sample 7, and the magnet powder of Samples 53 and 54 were oriented in a magnetic field of 10 kOe, and then subjected to X-ray diffraction. FIG. 3 shows the measurement results of X-ray diffraction. The four types of magnet powder samples subjected to X-ray diffraction have smaller anisotropy in the order of samples 2, 7, 53, and 54. From FIG. 3, as the anisotropy ratio of the magnet powder increases, (00) of 2θ = 44.4 degrees is obtained.
6) The ratio of the intensity of the plane to the intensity of the (410) plane at 2θ = 42.3 degrees is large. This can be interpreted as follows. Nd ₂ Fe ₁₄ B has a tetragonal structure,
The axis is the axis of easy magnetization. Therefore, when the orientation of all the crystal grains of the anisotropic magnet powder is aligned in one direction, a high anisotropic ratio can be obtained. When this state is analyzed by X-ray diffraction, the peak of the (006) plane, which is a plane perpendicular to the c-axis, increases, and the peak of the (410) plane, which is parallel to the c-axis, decreases. As a result, the (006) plane and (4)
10) The strength ratio of the surface increases. Conversely, when the anisotropy ratio is low, the (006) plane decreases because the orientation is random, and conversely, the (410) plane increases and the intensity ratio between the (006) plane and the (410) plane decreases. Become. It can be seen that the larger the intensity ratio, the more anisotropic. FIG. 4 shows the relationship between the strength ratio and the anisotropic ratio. FIG. 4 shows that the anisotropic ratio higher than that of the prior art region (insufficient anisotropic region) can be obtained according to the manufacturing method of the present invention.

(Second Example) An anisotropic rare earth magnet powder was produced using an alloy having a composition b shown in Table 1 as a raw material alloy. The production of the anisotropic rare earth magnet powder of the second example was carried out in the same manner as the production method of sample 2 of the first example, except that the reaction conditions for the reverse structure transformation reaction were changed. The reaction conditions for the reverse structure transformation reaction were as shown in Table 3 under the control pressure, control time, and dehydrogenation conditions under which the final degree of vacuum was obtained. Here, the relative reaction rates of the reverse structural transformation are shown in Table 3. ○ × of the first exhaust stroke pressure adjustment shown in Table 3 is:
The presence or absence of the first exhaust step is shown. Further, an anisotropic bonded magnet was produced in the same manner as in the first example, using the produced anisotropic rare earth magnet powder.

[0084]

[Table 3] (Comparative Example) As comparative examples, similarly to Samples 9 to 15, magnet powder samples 56 to 5 made of the alloy having composition b in Table 1
9 was produced. Here, the production of the samples 56 to 59 is shown in Table 3
The procedure was performed in the same manner as in the second example, except for the conditions shown in (2). In addition, anisotropic bonded magnets using the magnet powders of Samples 56 to 59 were also manufactured. This anisotropic bonded magnet was manufactured in the same manner as the anisotropic bonded magnet manufactured in the second embodiment. Here, the sample 56 is a magnet powder which has not been subjected to the first evacuation step at the time of dehydrogenation, the sample 57 is a magnet powder having a high control pressure in the first evacuation step, and the sample 58 is a control pressure control. The sample 59 is a magnet powder having a long control time and a low control pressure.

(Evaluation) As an evaluation of the second embodiment, the magnetic properties of the magnet powder and the anisotropic bonded magnet produced using this magnet powder were measured as in the first embodiment.
The measurement results are shown in Table 3.

As shown in Table 3, the magnet powders of Samples 10 to 16 were
The anisotropy ratio is as high as 0.80 or more and the value of Br is as high as 13.0 kG or more. As a result, (BH)
max is high. Also, in the anisotropic bonded magnet using the magnet powder of Samples 10 to 16, (BH) m
Both ax and Br are high.

On the other hand, in the sample 56 of the comparative example, the coercive force is obtained when the first exhaust step is not performed, but the anisotropic ratio is greatly reduced. On the other hand, in the case of the magnet powders 57 and 59, when the relative reaction rate of the reverse structure transformation in the first evacuation step is out of the optimum range, the anisotropic ratio is also reduced in this case. Sample 5
The magnet powder of No. 8 has a relative reaction rate of reverse structural transformation of 3.16 which is within the optimum range, but a high anisotropic ratio of 0.82 can be obtained because the first evacuation step time is longer than usual. However, a sharp decrease in coercive force occurs due to grain growth.

(Third Example) Next, anisotropic rare earth magnet powders were prepared by using alloys having the alloy compositions: j to ee shown in Table 1 as raw material alloys. In the method of manufacturing the anisotropic rare earth magnet powder of the third embodiment, first, a predetermined amount of the alloy elements shown in Table 1 is weighed, and 10 kg of an alloy ingot having the composition of Table 1 is weighed using a high frequency melting furnace. It was melted. Thereafter, a homogenization treatment of the alloy ingot structure was performed in the same manner as in the first embodiment. The homogenized alloy ingot was pulverized by a jaw crusher into coarse pulverized products having an average particle diameter of 10 mm or less, and a low-temperature hydrogenation step, a high-temperature hydrogenation step, and a dehydrogenation step were performed as in the first embodiment. Further, a bonded magnet was produced in the same manner as in the first example using the produced anisotropic rare earth magnet powder. Measure the magnetic properties of the anisotropic rare earth magnet powder and the bonded magnet obtained in this example,
Table 4 shows the measurement results.

[0089]

[Table 4] From Table 4, it can be seen that Al, Si, Ti, V, C
r, Mn, Co, Ni, Cu, Ge, Zr, Mo, I
By adding one or more of n, Sn, Hf, Ta, W, and Pb, the coercive force and the squareness ratio (Hk / iH
It can be seen that c) is improved. Here, Hk indicates a magnetic field when the magnetization is demagnetized by 10%.

[0090]

The method for producing anisotropic rare earth magnet powder of the present invention provides an anisotropic rare earth magnet powder having a high anisotropic ratio and a coercive force. This production method has a low-temperature hydrogenation step of preliminarily incorporating hydrogen as a raw material alloy as a hydrogen compound. The hydrogen compound as a starting material of the high temperature hydrogen treatment step, a high temperature hydrogen treatment of the crystal orientation of the R ₂ Fe ₁₄ B of the three-phase decomposition at the same time as master alloy by proceeding gently reaction rate of the forward structural transformation steps Fe ₂ B can be transferred to the crystal orientation. Furthermore, the dehydrogenation process consists first evacuation step and the second evacuation step, the first exhaust Fe ₂ by proceeding gently reaction rate of the reverse structural transformation
The crystal orientation of B can be transferred to the crystal orientation of recrystallized R ₂ Fe ₁₄ BH _x . Further, the remaining hydrogen is removed from the recombination R ₂ Fe ₁₄ BH _x by the second evacuation step. As a result, the recrystallized grains can be made finer and more uniform, and a high anisotropic ratio and a high coercive force can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state of transfer of crystal orientation during a hydrogen storage reaction.

FIG. 2 is a diagram schematically showing a hydrogen processing furnace capable of controlling a reaction rate.

FIG. 3 shows X-ray diffraction of various magnet powders.

FIG. 4 shows Br and (006) and (41) of magnet powder.
FIG. 4 is a diagram showing a relationship with a ratio of the intensity of the 0) plane.

Claims (1)

[Claims] An R of 11 to 15 at% and 5.5 to 8.
0 at% B and unavoidable impurities, and the remainder is Fe
, A hydrogen compound of an R-Fe-B-based alloy comprising high-temperature hydrogenation, followed by dehydrogenation, anisotropic ratio Br / Bs
(Bs is uniformly 16 kG) is 0.8 or more, the anisotropic rare earth magnet powder.