JPH08279406A - R-tm-b permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide a practical T-TM-B permanent magnet having high (BH)max and iHc of 13kOe or more. CONSTITUTION: An R-TM-B permanent magnet contains 12.0 to 16.0at% of R (where R is one or more types of range of rare earth elements including Y), 5.5 to 8.0at% of B, and the residue TM (where TM is that Fe or the part of the Fe is replaced by less than 20at% of Co), and has R2TM14B phase as a main phase, the mean crystalline grain size of the main phase is 3 to 8μm and its standard deviation is 2.5μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a sintered type R-TM-B.
System permanent magnet and its manufacturing method, (BH) max,
The present invention relates to a permanent magnet having high Br and iHc and excellent magnetic properties, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A manufacturing process of an R-TM-B type permanent magnet by a powder metallurgy method is carried out in the order of melting, pulverizing, forming in a magnetic field, sintering, heat treatment and the like. The starting material is R2Fe1 which is the main phase
An ingot having a composition in which R and B are larger than 4B (R is a rare earth element) is used. A ball mill, a jet mill, or the like is used for crushing the ingot, and molding in a magnetic field is performed by using a mold to compress the raw material powder while orienting it in the magnetic field. Sintering is performed in a temperature range of 1000 to 1150 ° C. in vacuum or in an inert gas, and heat treatment is generally performed at an appropriate temperature.

(BH) m of this R-TM-B system permanent magnet
In order to improve ax and Br, the composition is the main phase R2F
It is necessary to increase the volume ratio of the main phase as close as possible to e14B. In order to increase the volume ratio of the main phase, the minimum necessary amount of Nd-rich phase and B-rich phase that contribute to the expression of iHc is secured, while the minimum amount of R-rich phase, B-rich phase, and oxide phase is minimized. Need to be kept to. Of these, the R-rich phase is very active with respect to oxygen, so that the Nd-rich phase changes to an oxide phase in proportion to the amount of oxygen mixed in during the process of sintering. Therefore, in a composition in which the amount of R is extremely reduced, it is necessary to minimize the inclusion of oxygen.

Another method for increasing (BH) max and Br is to improve the orientation. In order to improve the orientation, a method of strengthening an applied magnetic field (molding magnetic field) at the time of molding and a method of releasing magnetic agglomeration of raw material fine powder are known. On the other hand, iHc is greatly influenced by the composition, the crystal grain size distribution of the sintered body, and three factors of heat treatment. As a method for improving iHc, a method of substituting Nd with an element having large magnetic anisotropy such as Dy or adding an additional element is often used. Another method for improving iHc is to make the crystal grain size of the sintered body fine and uniform. Nd-Fe-B
The iHc of the sintered magnet is improved as the crystal grain size of the sintered body is closer to the single domain particle size of Nd2Fe14B (about 0.3 μm). Further, there is a method of heat-treating the sintered body under appropriate conditions. The heat treatment pattern generally has a temperature in one or two stages.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Proposals for an R-TM-B system permanent magnet having an increased (BH) max are disclosed in JP-B-5-61345, JP-A-63-93841, and JP-A-63-197305. And JP-A-6-13219. However, iHc is at most 1 in both cases.
It is about 0 kOe, iHc is low and not practical. i
When Hc is low, thermal demagnetization is large, and when used in a device that is heated, the magnetic force is reduced. Therefore, for industrial use, (BH) max is high, and iHc of 13 kOe or more is required. Therefore, the present invention has a high (B
It is an object of the present invention to provide a practical R-TM-B based permanent magnet having H) max and an iHc of 13 kOe or more, and a method for producing the same.

[0006]

Means for Solving the Problems As a result of intensive studies for achieving the above object, the inventors of the present invention have determined that the average crystal grain size of the R2TM14B phase is 3 to 8 μm and its standard deviation is 2.5 μm or less. Results in high (BH) max and high iHc
It was found that the R-TM-B type permanent magnet of That is, the present invention is 12.0 to 16.0 at% R (R is one or more rare earth elements including Y),
5.5-8.0 at% B, balance TM (TM is Fe or a part of Fe replaced by less than 20 at% Co)
A R-TM-B system permanent magnet having an R2TM14B phase as a main phase, wherein the main phase has an average crystal grain size of 3 to 8 μm and a standard deviation of 2.5 μm or less. It is a permanent magnet. Further, the R-TM-B system permanent magnet of the present invention has M of 4 at% or less (M is Nb, Al, Ga, Zn,
By adding at least one of Cu), iHc
Can be further improved.

[0007]

The R-TM-B system permanent magnet of the present invention is R2TM14
By controlling the average crystal grain size of the B phase to 3 to 8 μm and the standard deviation thereof to 2.5 μm or less, an R-TM-B system permanent magnet having a high (BH) max and a high iHc can be obtained. Since the crystal grain size distribution of the sintered body reflects the grain size distribution of the raw material powder, in order to make the average crystal grain size of the R2TM14B phase 3 to 8 μm and its standard deviation 2.5 μm or less, the raw material powder must be fine and the grain size is small. The distribution needs to be sharp. Considering the crystal growth during sintering, the average crystal grain size of the sintered body is 3 μm.
In order to reduce the amount to less than 3 μm, a raw material powder having an average particle size of less than 3 μm is required. Therefore, the average crystal grain size of the sintered body is 3
At least μm. When the average crystal grain size of the R2TM14B phase of the sintered body exceeds 8 μm, the coercive force decreases and the squareness of the demagnetization curve also decreases. Further, if the standard deviation of the crystal grain size of the sintered body exceeds 2.5 μm, iHc is lowered and the squareness of the demagnetization curve is lowered. In the present invention, the average crystal grain size and its standard deviation are based on the grain size distribution of the crystal grain size of the sintered body, and the grain size distribution of the crystal grain size of the sintered body is perpendicular to the magnetization orientation direction. Using an optical microscope photograph of 1000 times of the plane, for all the crystal grains in the 73 × 95 mm field of view,
This is a distribution of average values of the major axis and the minor axis of individual crystal grains.

The reasons for limiting the composition will be described below. R is 1
If it is less than 2.0 at%, the amount of R necessary for liquid phase sintering is insufficient and it becomes difficult to sinter, and if it exceeds 16.0 at%, the volume ratio of the main phase is decreased and Br is decreased. .0a
t%. As R, Nd and / or Pr is preferable, and it is more preferable to partially replace it with 3 at% or less of Dy. B is iHc at 5.5 at% or less
Decreases, and Br decreases at 8.0 at% or more.
It is set to 5.5 to 8.0 at%. TM is Fe or Fe
Is partially replaced with Co of less than 20 at%.
When Fe is replaced by Co in an amount of more than 20 at%, iHc is lowered. M is at least one element of Nb, Al, Ga, Zn and Cu, and iHc is obtained by adding 4 at% or less.
Has the effect of improving. Nb, A exceeding 4 at%
Br decreases when at least one element selected from the group consisting of 1, Ga, Zn, and Cu is added.

The R-TM-B system permanent magnet of the present invention is
0 to 16.0 at% R (R is 1 of rare earth elements including Y)
Alloy of B to 5.5 to 8.0 at%, and the balance TM (TM is Fe or a part of Fe replaced with Co of less than 20 at%) with an average grain size of 3 to 5
It is obtained by pulverizing to a size of μm, molding in a magnetic field, sintering, and three-step heat treatment in a specific temperature range. Average particle size of 3 by crushing
A pulverized powder having a particle size of up to 5 μm is obtained. By using a jet mill, such a pulverized powder can be obtained as a fine pulverized powder having a uniform fineness distribution. In addition, when the orientation is enhanced by applying a high magnetic field of 10 kOe or more during molding,
IHc with almost no decrease in (BH) max and Br
Can be increased. As for the heat treatment of the sintered body, the squareness of the iHc and the demagnetization curve can be remarkably improved by performing the heat treatment at three stages of temperature. In this three-step heat treatment pattern, it is preferable that the first heat treatment is performed at a temperature of 800 to 1000 ° C., the second heat treatment is performed at 560 to 760 ° C., and further the third heat treatment is performed at 460 to 660 ° C. IHc is improved by relaxing the strain due to cooling after sintering by the primary heat treatment, and iHc is improved by smoothing the grain boundaries by the secondary heat treatment, and iHc is improved and variation of iHc is reduced by the third heat treatment. To do. The reason why the respective heat treatment temperatures of the three-step heat treatment are limited as described above is that iHc does not sufficiently rise even if the heat treatment is performed outside the temperature range.

[0010]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. Example 1 A jet mill was used to ingot an ingot obtained by arc melting so that the composition was Nd14.1Dy0.4FebalB6.2Nb0.3Al0.2Ga0.1Cu0.1 (at%) using a raw material having a purity of 99% or more. Then, four kinds of raw material powders were prepared by finely pulverizing so as to have an average particle size of 3 to 5 μm. The obtained raw material powder was molded in a magnetic field at 0.6 ton / cm 2. The molding magnetic field strength was 1.59 MA / m (20 kOe). The obtained molded body was vacuum-sintered at 1353K (1080 ° C) for 2 hours and cooled, then subjected to a first heat treatment at 1173K (900 ° C) for 2 hours and cooled, and then at 893K (620 ° C) for 1 hour secondary. Heat treated and cooled, then 1 at 793K (520 ° C)
The third heat treatment was performed for a period of time and cooled. Here, each cooling was performed up to room temperature, and the heat treatment atmosphere was an Ar gas atmosphere. A BH tracer was used for magnetic measurement at 297K (24 ° C). The average crystal grain size of the obtained permanent magnet was 3.3 μm,
The standard deviations are 4.0 μm, 5.2 μm, and 8.0 μm, and the standard deviations are 0.9 μm, 1.3 μm, 1.6 μm, and 2.8 μm, respectively.
Met. FIG. 1 shows the dependency of the coercive force of the obtained permanent magnet on the crystal grain size of the sintered body. (B of the permanent magnet obtained in FIG.
The dependency of H) max on the crystal grain size of the sintered body is shown.

(Comparative Example 1) Heat treatment was performed at 1173K (900
The first heat treatment at ℃) for 2 hours and cooled, 793K (5
A permanent magnet was produced in the same manner as in Example 1 except that a two-step heat treatment was performed in which the secondary heat treatment was performed at 20 ° C. for 1 hour and then cooling. FIG. 1 shows the dependency of the coercive force of the obtained permanent magnet on the crystal grain size of the sintered body. From FIG. 1, iHc increases as the crystal grain size and its standard deviation decrease, and iHc increases as the crystal grain size decreases in the three-step heat treatment than in the two-step heat treatment (Comparative Example 1).
It can be seen that it is effective in improving Hc.

(Conventional Example 1) An R-TM-B system permanent magnet was prepared by the following conventional manufacturing method. An ingot obtained by arc melting using a raw material having a purity of 99% or more so as to have a composition of Nd14.1Dy0.4FebalB6.2Al0.2Ga0.1Cu0.1 (at%) has a mean particle diameter of 5.1 μm with a jet mill. Pulverize so that
It was molded at 1.6 ton / cm 2 in a magnetic field. The molding magnetic field strength was 8 kOe. The obtained molded body is 135
After vacuum sintering at 3K (1080 ° C) for 2 hours and cooling, 11
A first heat treatment of 73 K (900 ° C.) × 2 hours was performed, followed by cooling, and a second heat treatment of 793 K (520 ° C.) × 1 hour was performed. The obtained permanent magnet has an average crystal grain size of 10.2μ.
The standard deviation in m was 3.6. Further, when the magnetic characteristics were evaluated, (BH) max = 42.9MGOe, iHc =
It was 11.9 kOe.

Example 2 A molding magnetic field strength of 0.95 MA
/ M (12 kOe), the R-TM-B system permanent magnet was produced in the same manner as in Example 1. FIG. 2 shows the dependency of (BH) max of the obtained permanent magnet on the crystal grain size of the sintered body.
The average crystal grain size of the obtained sintered body is 3.3 μm, 4.0 μm
m, 5.2 μm, and 8.0 μm, and the standard deviations are 0.
It was 9 μm, 1.3 μm, 1.6 μm and 2.8 μm.

(Embodiment 3) The forming magnetic field strength is 0.24 MA.
/ M (3 kOe), the same method as in Example 1
A TM-B based permanent magnet was created. FIG. 2 shows the dependency of (BH) max of the obtained permanent magnet on the crystal grain size of the sintered body. The average crystal grain size of the obtained sintered body is 3.3 μm, 4.0 μm
m, 5.2 μm, and 8.0 μm, and the standard deviations are 0.
It was 9 μm, 1.3 μm, 1.6 μm and 2.8 μm.

From FIG. 2, when the forming magnetic field is small, the maximum energy product (BH) m increases as the crystal grain size decreases.
Although ax decreases, it can be seen that (BH) max hardly changes with respect to the crystal grain size when a molding magnetic field of at least 10 kOe or more is applied. As can be seen from Examples 1 to 3 and Comparative Example 1 and the conventional example, the crystal grain size of the sintered body is 3 to 8 μm (desirably 3 to 5 μm) and the standard deviation thereof is 2.5 μm or less (desirably 2.0 μm). The following control) is applied, and a forming magnetic field of 10 kOe or more is applied, so that (BH) max is hardly changed and iH
c can be improved. Further, iHc can be further increased by performing the heat treatment after sintering in three stages.

(Example 4) An ingot obtained by arc melting using a raw material having a purity of 99% or more so that the composition is Nd13.0Dy0.3FebalB6.2Nb0.3Al0.2Ga0.1Cu0.1 (at%). The average particle diameter is 3.7 μm with a jet mill while suppressing the mixture of oxygen.
Finely pulverized to 0.3 ton / cm in a magnetic field of 22 kOe
The sample was prepared by molding in step 2 so that the average crystal grain size was 3 to 5 μm and the standard deviation was 2.0 μm or less. The first heat treatment was performed at 1173K (900 ° C) for 2 hours, the second heat treatment was performed at 893K (620 ° C) for 1 hour, and the third heat treatment was performed at 793K (520 ° C) for 1 hour. The average grain size of the obtained sintered body was 4.0 μm, and the standard deviation was 1.3 μm.
Is. The magnetic characteristics of this sintered magnet are (BH) max =
406 kJ / m3 (51.0 MGOe), iHc = 1.
07MA / m (13.4kOe), Br = 14.44k
It was G. The density is 7.53 g / cm3,
The amount of oxygen was 2020 ppm, the amount of nitrogen was 500 ppm, and the amount of hydrogen was 5 ppm. According to the present invention, a practical sintered magnet having iHc of 13 kOe or more and a high (BH) max of 50 MGOe or more can be obtained.

[0017]

The crystal grain size of the sintered body and its standard deviation are regulated, the heat treatment method is improved, and the applied magnetic field at the time of molding is regulated.
A B-type sintered magnet can be obtained. Further, according to the method of the present invention, a practical high energy product magnet having an iHc of 13 kOe or more can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an average crystal grain size of a sintered body and iHc.

FIG. 2 is a diagram showing a relationship between an average crystal grain size of a sintered body and (BH) max.

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Claims (6)

[Claims] 1. 12.0 to 16.0 at% R (R is Y
One or more rare earth elements including)), 5.5 to
An R-TM-B-based permanent magnet having 8.0 at% B and the balance TM (TM is Fe or a part of Fe replaced by less than 20 at% Co) and having an R 2 TM 14 B phase as a main phase. , The main phase has an average crystal grain size of 3 to 8 μm and a standard deviation of 2.5 μm or less.
MB permanent magnet. 2. M of 4 at% or less (M is Nb, Al, G
at least one of a, Zn and Cu).
The R-TM-B system permanent magnet according to 1. 3. (BH) max ≧ 50 MGOe and iHc
The permanent magnet according to claim 1, wherein ≧ 13 kOe. 4. 12.0 to 16.0 at% R (R is Y
1 or 2 or more kinds of rare earth elements including, or a part of which is replaced with 3 at% or less of Dy), 5.5
~ 8.0 at% B, balance TM (TM is Fe or Fe
Alloy obtained by substituting a part of Co with less than 20 at%) for crushing, forming in a magnetic field, sintering, and heat treatment.
A method of manufacturing an MB permanent magnet, wherein the pulverized alloy powder has an average particle size of 3 to 5 μm, the heat treatment is 800 to 1000 ° C., and the primary heat treatment is 560 to 760 ° C.
R-TM-, which is a three-stage heat treatment consisting of a second heat treatment and a third heat treatment at 460 to 660 ° C.
Method for manufacturing B-based permanent magnet. 5. M of 4 at% or less (M is Nb, Al, G
at least one of a, Zn, and Cu).
The method for producing an R-TM-B system permanent magnet according to item 1. 6. The method for producing an R-TM-B system permanent magnet according to claim 4, wherein a high magnetic field of 10 kOe or more is applied during molding in a magnetic field.