JPH0696928A - Rare-earth sintered magnet and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the irreversible demagnetization of an Nd-Fe-B magnet and, at the same time, to minimize the deterioration of the maximum energy product of the magnet. CONSTITUTION:This magnet is manufactured in such a way that a first component powder composed mainly of an Nd2Fe14B (where, the Nd and B contents are respectively controlled to 11.8-20.0at.% and 5.9-20.0at.%) intermetallic compound is mixed with a second compound powder composed mainly of one or two kinds of R(Cu1-XTX) and R(Cu1-XTX)2 (where, R, T, and x respectively represent rare-earth elements containing Dy and Tb by >=30%, one kind or a mixture of two or more kinds of transition metals or metalloid (such as Fe, Co, Ni, Al, Ga, Ti, Mo, V, Sn, B, P, Si, etc., and 0.3-0.7) and the mixture is molded in a magnetic field, and then, the molded product is subjected to liquid-phase sintering. Therefore, part of the Nd near the surface of the main phase, namely, the Nd2Fe14B intermetallic compound is replaced with Dy and Tb and the occurrence of an inverse magnetic domain in the vicinity of the surface can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an R-Fe-B system (R is a rare earth element) rare earth magnet, and more particularly to a rare earth sintered magnet having a high energy product and excellent heat resistance and its production. Regarding the method.

[0002]

2. Description of the Related Art As a permanent magnet having a high energy product, S
Known are m-Co based magnets and R-Fe-B based rare earth magnets. Of these, R-F represented by Nd-Fe-B
Since the e-B rare earth magnet is mainly composed of resource-rich Nd and Fe, Sm that uses resource-poor Sm.
It is lower in cost than the -Co magnet and has a high maximum energy product of 40 MGOe at the maximum with respect to about 30 MGOe of the Sm-Co magnet. Therefore, it is widely used as a rotor or a stator of a motor. There is.

Recently, automobiles use a large number of motors as actuators for various automation devices, but it must be assumed that the motors used in various parts of the automobile are placed in a high temperature environment of 180 ° C. or higher. In general, a magnet material not only has a lower coercive force and residual magnetic flux density than normal temperature at such a high temperature, but also has a high coercive force and residual magnetic flux density even if it is returned to normal temperature once it is exposed to a high temperature history. The phenomenon of not returning (irreversible demagnetization) occurs. Therefore, it is a necessary condition for a magnet material for automobiles, etc. that is subjected to a high temperature history that the irreversible demagnetization is small. It is generally considered that the allowable value of irreversible demagnetization (the ratio of the decrease in the magnetic flux after heating to high temperature to the magnetic flux before heating to high temperature) is 3% or less.

In order to reduce the value of irreversible demagnetization, it is effective to increase the coercive force at high temperature, but Nd-
In the case of Fe-B based magnet material, (1) part of Nd is D
Methods such as substituting with y (dysprosium) or Tb (terbium), (2) adding Al, Ga, Mo, V, etc. increase coercive force at high temperature and reduce irreversible demagnetization. It is known to be effective.

[0005]

However, Nd-Fe-
Each of these measures for reducing the irreversible demagnetization of the B-based magnet material has a problem of reducing the maximum energy product. When a magnet is used in a motor, a reduction in the maximum energy product directly leads to a reduction in performance such as torque reduction. Further, since Dy and Tb are rare resources, there is a problem that their addition causes an increase in cost.

Further, in the R-Fe-B system permanent magnet, the magnetic characteristics (in particular, the intrinsic coercive force) are strongly influenced by the kind and the content of the rare earth element near the surface of the crystal grains, and the heat resistance (irreversible reduction). (Magnetism) is greatly affected,
It is important to control the composition of the surface part. As a method of controlling the rare earth composition near the surface, a method of sintering a mixture of an R—Fe—B based alloy powder and an R oxide powder has been proposed (Japanese Patent Laid-Open No. 61-253805). However, when an oxide is added, the amount of oxygen in the magnet increases and the magnetic properties, especially the residual magnetic flux density, decrease, so a sufficient maximum energy product cannot be obtained. In addition, R-Fe-
A method of sintering a mixture of a B-based alloy powder and a rare earth hydride or rare earth metal powder has also been proposed (JP-A-4-1).
However, since rare earth hydrides and rare earth metal powders have high melting points, it is difficult to form a liquid phase during sintering, and the sinterability is impaired.

The present invention has been made to solve such a problem, and reduces the irreversible demagnetization of the Nd-Fe-B system magnet, and further, minimizes the decrease of the maximum energy product. Providing a rare earth sintered magnet and further controlling the composition near the grain surface throughout the magnet without reducing the irreversible demagnetization due to high temperature history without increasing the oxygen content, which is a drawback of the conventional measures. An object of the present invention is to provide a method for producing a rare earth sintered magnet that can be used.

[0008]

The rare earth sintered magnet according to the present invention made to solve the above problems is Nd ₂ Fe.
The core of the ₁₄ B intermetallic compound phase and a part of Nd of the phase are Dy
And / or a Tb-substituted outer shell of the phase.

In order to obtain such a rare earth sintered magnet, first, a first component powder containing Nd ₂ Fe ₁₄ B intermetallic compound as a main component and R (Cu _1-X T _X ) and R (Cu _{1 -X} T _X) after mixing the second component powder based on one or two of the _2, the mixture was molded in a magnetic field, it performs liquid-phase sintering. Here, R is a rare earth element containing 30% or more of Dy + Tb (for example, Nd, Pr, Ce other than Dy and Tb).
Etc., and T is a transition metal or submetal (eg, Fe,
Co, Ni, Al, Ga, Ti, Mo, V, Sn, B,
P, Si, etc.), or a mixture of two or more thereof,
X is 0.3 to 0.7.

The first component powder containing Nd ₂ Fe ₁₄ B intermetallic compound as a main component has an atomic composition ratio of Nd: 11.8 to.
20.0 at%, B: 5.9 to 20.0 at% (balance F
e), more preferably Nd: 11.8 to
13.0 at%, B: 5.9 to 7.5 at% (remainder F
e) is preferred. In addition, this Nd ₂ Fe ₁₄ B
Nd of the intermetallic compound is 1% of other rare earth elements such as Pr, Ce and Dy in the portion where the atomic ratio is 10% or less.
May be substituted with one or two or more, or in addition to or in place thereof, 10% or less of Fe (atomic ratio) of Fe in the Nd ₂ Fe ₁₄ B intermetallic compound may be substituted with Co. Good.

[0011]

In a magnet called a nucleation type magnet such as a Nd-Fe-B system sintered magnet, a reverse magnetic domain (a reverse magnetic field magnetizes in a direction opposite to other parts) inside a magnet magnetized in a certain direction. Magnetic domain) is generated (magnetization reversal), the reverse magnetic domain region rapidly expands like a landslide thereafter, so that the coercive force is determined by the generation of the reverse magnetic domain. Therefore, in order to increase the coercive force, it is important to prevent the occurrence of the first reverse magnetic domain (magnetization reversal) as much as possible.

In a sintered magnet such as the Nd-Fe-B rare earth sintered magnet targeted by the present invention, the reverse magnetic domain is most likely to occur in the vicinity of the surface of the crystal grain which is the main phase. Therefore, in the present invention, in the surface part (outer shell) of the crystal grains of the Nd ₂ Fe ₁₄ B intermetallic compound, a phase in which a part of Nd is replaced with Dy and / or Tb is generated, and the magnetization reversal is less likely to occur. Incidentally, in terms of the effect of increasing the coercive force of the Nd ₂ Fe ₁₄ B intermetallic compound (preventing magnetization reversal), D
Both y and Tb are effective elements. On the other hand, Dy, T
The b substitution region is only the outer shell portion, and as a whole crystal grain (that is, as a whole sintered magnet), Nd ₂ F of the core is
Since the e ₁₄ B intermetallic compound phase occupies a high volume ratio and maintains a high saturation magnetic flux density, a high energy product is consequently maintained. In the Nd ₂ Fe ₁₄ B intermetallic compound phase of the core, even if it is substituted with one or more kinds of other rare earth elements such as Pr, Ce and Dy in a portion of 10% or less of Nd, Even if 10% or less of Fe is replaced by Co, the above high energy product characteristic is pure Nd ₂
It is not much different from the Fe ₁₄ B intermetallic compound. In addition, in the substitution phase portion near the surface of each crystal grain, Pr,
It may be replaced by a rare earth element such as Ce.

The replacement of part of Nd in the vicinity of the surface of each crystal grain with Dy and Tb is most suitable at the same time as liquid phase sintering. That is, Dy and Tb are included in the liquid phase, and crystal growth of the Nd ₂ Fe ₁₄ B intermetallic compound phase, which is the core, and diffusion and penetration of Dy and Tb in the liquid phase into the growth region Substitute only in the neighborhood.

However, it is difficult to pulverize (difficult to grind) only with Dy or Tb, and the melting point is relatively high, so that it is difficult to diffuse into the liquid phase as it is. Therefore, in the method for producing a rare earth sintered magnet according to the present invention, Cu is added in order to facilitate pulverization thereof and lower the melting point, and further, a part of this Cu is replaced with a transition metal or a submetal. As a result, the magnetic characteristics are improved. The use of Cu is
There is also the aim of improving the oxidation resistance during pulverization. This facilitates pulverization and liquid phase sintering, and also improves magnetic properties. By facilitating the pulverization in this way, the dispersibility with the powder of the Nd ₂ Fe ₁₄ B intermetallic compound, which is the main phase, becomes good, and the above effects of the present invention can be stably obtained. In addition, R (Cu _1-X T _X ), R (Cu
The use of _1-X T _X ) ₂ enables liquid phase sintering at low temperature and / or for a short time, so that the thickness of the outer shell (substitution phase) of crystal grains can be controlled to be small, The concentrations of Dy and Tb in the substitution phase can be increased without increasing the amounts of Dy and Tb added. Further, since Dy and Tb are present in the liquid phase, they are uniformly spread over the entire magnet, and a homogeneous magnet can be manufactured.

The content of Dy + Tb in the second component powder is set to 30% or more. Below that, the amount of Dy and / or Tb substituted in the outer shell phase after sintering becomes insufficient, so This is because the effect of preventing the magnetization reversal becomes insufficient. Further, the atomic composition ratio X of T (transition metal or submetal) is limited to 0.3 to 0.7 for the following reason. First, the lower limit is set to 0.3 because below that, Cu may be liberated after sintering and a harmful non-magnetic portion may be formed. Further, the upper limit is set to 0.7 because R (Cu _1-X T _x ) and R (Cu _1-x
A uniform phase of T _x ) ₂ cannot be formed, and the pulverizability for pulverization deteriorates. Therefore, it takes a long time to pulverize, the oxygen content increases, and the coercive force of the sintered material decreases.

As for the mixing ratio of the first component (main phase) powder and the second component powder, the weight ratio of the second component powder to the whole is 5 to 5.
It is preferably 25%. Below this, the amount of Dy and Tb substituted becomes insufficient, and the effect of improving sinterability is small. Further, if the mixing ratio is higher than this, the volume ratio of the core phase becomes too small, and it becomes difficult to obtain sufficient magnetic characteristics (especially maximum energy product). The recommended range is 5 to 16%.

The average particle size of both powders is usually 0.1.
It is preferably about 50 μm. If the average particle size is smaller than this, the surface area becomes too large and oxidation becomes a problem, and it is also disadvantageous in terms of wear and orientation of the mold during molding. On the other hand, if it is larger than this range, in the case of the first powder, the decrease of coercive force becomes a problem. For the second powder,
Dispersion during sintering becomes insufficient, and the homogeneity of the structure may be impaired. The recommended average particle size range is 0.5 to 10 μm.

The mixed powder is vacuum (or inert gas)
Inside, temperature 900 ~ 1200 ℃, pressure 0.5 ~ 5
Liquid phase sintering is performed at about t / cm ² for 0.1 to 10 hours. This sinter molding is performed in a magnetic field of 5 kOe or more. As a result, the sintered body becomes a permanent magnet having large magnetization in the direction of the applied magnetic field. Then, heat treatment is preferably performed in vacuum or in an inert gas atmosphere at 450 to 900 ° C. for 1 to 5 hours.

[0019]

EXAMPLES In order to clarify the effects of the present invention, as shown in Table 1, 12 types of test materials (invention materials) (No. 1 to 12) prepared according to the method of the present invention and Six types of test materials (comparative materials) (Nos. 13 to 18) prepared by a method that did not satisfy any of the specified conditions were prepared, and their magnetic properties were investigated. Each of the test materials was prepared by mixing the first component powder and the second component powder (in the case of the comparative material, there may be only one component) and performing liquid phase sintering. . Table 1 shows the atomic composition ratio of each component powder and the mixing ratio of each component powder (wt% of the second component powder). For both powders, the ingot is a jaw crusher,
After roughly pulverizing with a disc mill to a particle size of 10 to 100 μm, finely pulverizing with a ball mill (a jet mill may be used) to obtain a powder having an average particle size of about 3 μm. The two powders may be mixed at the stage of coarse powder or may be finely pulverized.

[0020]

Each test material was mixed with the first and second component powders shown in Table 1 and then 1.5 t in a magnetic field of 10 kOe.
Press-molded at a pressure of / cm ² and at a temperature of 1 in vacuum.
Sintering was performed at 100 ° C. for 1 hour. Then, it heat-processed at 450-900 degreeC x 1 hour in vacuum. This heat treatment temperature is set to a temperature at which the magnetic properties are most excellent according to the composition of the second component powder.

Residual magnetic flux density Br and coercive force iH of each test material
Table 2 shows the results of measurement of c, maximum energy product (BH) max and heat resistant temperature. Here, the heat resistant temperature is Pc =
The temperature at which the irreversible demagnetization is 3% in the sintered magnet having the shape of −0.5 is adopted. As is clear from Table 2, all the materials of the present invention satisfy both the maximum energy product of 30 MGOe or more and the heat resistance of 180 ° C. or more. On the other hand, the comparative material has a low maximum energy product and a low heat resistance, or one of them has a high energy product, but one of them has a low energy product.

Comparative materials Nos. 16, 17, and 18 were prepared by melting ingots so as to have the same composition as invention materials Nos. 1, 6, and 11, respectively. Comparing these,
It can be seen that the present invention has an effect of particularly improving the coercive force.

[0024]

[0025]

The main cause of the decrease in coercive force in the Nd-Fe-B system sintered magnet is the occurrence of reverse magnetic domains in the vicinity of the surface of each crystal grain. Nd ₂ Fe ₁₄ B according to the present invention
In a sintered magnet mainly composed of an intermetallic compound, Nd is formed in the vicinity of the surface (outer shell) of the crystal grain, which is a site where reverse magnetic domains are generated.
Since a part of is replaced by Dy and Tb, which have the effect of increasing the coercive force, a high coercive force is obtained even at high temperatures. For this reason, the irreversible demagnetization is suppressed to a low level, which makes the magnet particularly suitable as a vehicle mounting magnet that is subjected to a high temperature history. Further, the substitution phase of Dy and Tb is limited to the vicinity of the surface (outer shell) of the crystal grain, and Nd ₂ Fe ₁₄ B having a high saturation magnetization is mainly contained in the inside (core), so that the energy product is not lowered. D, which is kept to a minimum and is rare in terms of resources
The cost increase due to the use of y and Tb is also minimized.

Next, in a Nd-Fe-B system sintered magnet, the coercive force generally decreases as the crystal grain size increases. Therefore, in order to increase the coercive force, it is necessary to make the crushed grain size as small as possible. However, if the crushed particle size is reduced, problems such as oxidation and mold wear occur as described above. However, in the magnet according to the present invention, even if the crystal grain size becomes slightly larger, the Dy, Tb substitution region (outer shell) with respect to the entire crystal grain is thereby increased.
Is relatively decreased, and the Dy and Tb concentrations in the replacement region are increased (when the same amounts of Dy and Tb are used), so that the coercive force is increased. Therefore, there is also an advantage that it is not necessary to control the crystal grain size very strictly.

Claims (6)

[Claims] 1. A crystal grain having a core of an Nd ₂ Fe ₁₄ B intermetallic compound phase and a shell of the phase in which a part of Nd of the phase is substituted with Dy and / or Tb. Sintered rare earth magnet. 2. A first component powder containing Nd ₂ Fe ₁₄ B intermetallic compound as a main component, and R (Cu _1-X T _X ) and R (Cu
Nd formed by mixing a second component powder containing 1 or 2 of _1-X T _X ) ₂ as a main component, molding the mixture in a magnetic field, and performing liquid phase sintering. _A rare earth sintered magnet composed of crystal grains having a core of a ₂ Fe ₁₄ B intermetallic compound phase and an outer shell of a phase in which a part of Nd of the phase is substituted with Dy and / or Tb. Here, R is a rare earth element containing 30% or more of Dy + Tb, T is one kind or a mixture of two or more kinds of transition metals or submetals, and X is 0.3 to 0.
7 3. The composition of the first component powder containing Nd ₂ Fe ₁₄ B intermetallic compound as a main component is Nd: 11.8 to 20.0.
The rare earth sintered magnet according to claim 2, wherein at%, B: 5.9 to 20.0 at% and the balance Fe. 4. Nd 1 of Nd ₂ Fe ₁₄ B intermetallic compound
The rare earth sintered magnet according to claim 2 or 3, wherein 0% or less is substituted with one kind or two or more kinds of other rare earth elements, and / or 10% or less of Fe is replaced with Co. 5. R (Cu _1-X T _X ) and R (Cu _1-X T _X )
First second-component powder based on one or two of the _two rare earth according to any one of claims 2 to 4 weight ratio to the sum of the second component powder is 5-25% Sintered magnet. 6. A first component powder containing an Nd ₂ Fe ₁₄ B intermetallic compound as a main component, and R (Cu _1-X T _X ) and R (Cu
Nd ₂ Fe _{14 is} obtained by mixing the second component powder containing 1 or 2 of _1-X T _X ) ₂ as a main component, and then molding the mixture in a magnetic field and performing liquid phase sintering. A method for producing a rare earth sintered magnet comprising crystal grains having a core of a B intermetallic compound phase and an outer shell of a phase in which a part of Nd of the phase is substituted with Dy and / or Tb. Here, R is a rare earth element containing 30% or more of Dy + Tb, T is one kind or a mixture of two or more kinds of transition metals or submetals, and X is 0.3 to 0.3.
It is 0.7.