WO2019039235A1 - Method for producing rare earth magnet, and rare earth magnet - Google Patents

Abstract

A method for producing a rare earth magnet, which comprises: a step for preparing a hydrogenated powder which contains a plurality of hydrogenated particles that contain Nd, Fe, Al and B, and which has been subjected to a hydrogenation treatment that is performed in an atmosphere containing hydrogen at a temperature that is not less than the disproportionation temperature; a step for producing a powder molded body by press molding the hydrogenated powder; a step for producing a dehydrogenated product, which has a main phase of an Nd2Fe14B compound and a grain boundary phase that is formed at the grain boundary of the main phase, while containing Nd and Al and having a lower melting point than the main phase, by subjecting the powder molded body to a dehydrogenation treatment in an inert atmosphere or in a reduced pressure atmosphere at a temperature that is not less than the recombination temperature; and a step for covering the main phase by melting the grain boundary phase.

Description

Method of manufacturing rare earth magnet and rare earth magnet

The present disclosure relates to a rare earth magnet manufacturing method and a rare earth magnet. This application claims the priority based on Japanese Patent Application No. 2017-159227 filed on August 22, 2017, and incorporates all the contents described in the Japanese Patent Application.

As a rare earth magnet, the rare earth-iron-boron alloy material of Patent Document 1 is known. In this patent document 1, a rare earth-iron-boron alloy material is manufactured through the following preparation process → hydrogenation process → forming process → dehydrogenation process, and this alloy material is used as a material of a rare earth magnet.
Preparation process: Prepare powder of Nd-Fe-B alloy.
Hydrogenation step: Nd-Fe-B alloy powder is subjected to a hydrogenation (HD) -hydrogenation-disproportionation process at a disproportionation temperature or higher.
Forming step: The hydrotreated Nd--Fe--B alloy powder is pressure-formed.
Dehydrogenation step: The molded powder compact is dehydrogenated (DR: Recombination) above the recombination temperature.

JP, 2011-236498, A

A method of manufacturing a rare earth magnet according to the present disclosure is
Preparing a hydrogenated powder having a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere containing Nd, Fe, Al, and B; And forming a powder compact, dehydrogenating the powder compact in an inert atmosphere or in a reduced pressure atmosphere at a temperature higher than the recombination temperature to obtain a main phase of the Nd ₂ Fe ₁₄ B compound, and Forming a dehydrogenation body formed at grain boundaries of the phase, containing Nd and Al and having a grain boundary phase having a melting point lower than that of the main phase, melting the grain boundary phase to cover the main phase And a process.
The rare earth magnet according to the present disclosure is
A plurality of main phases composed of Nd ₂ Fe ₁₄ B compounds, and a grain boundary phase containing Nd and Al coated with the plurality of main phases at a coverage of 54% or more, and having a coercive force of 1050 kA / m or more is there.

FIG. 1 is a schematic view showing the cross-sectional structure of the rare earth magnet according to the embodiment.

<< Description of an Embodiment of the Present Disclosure >>
The inventors examined the alloy composition in order to manufacture a rare earth magnet having a good balance of coercivity and squareness ratio. As a result, it was found that the coercivity can be increased by including the specific additive element as compared with the case where the specific additive element is not included, but the squareness ratio is reduced. The present inventors diligently studied a method of increasing the coercivity while suppressing the decrease in squareness ratio while containing a specific additive element. As a result, the grain boundary phase melts when a specific heat treatment is performed on the dehydrogenated substance after the dehydrogenation treatment, whereby the coverage can be enhanced as compared with the case where the specific heat treatment is not performed. It was found that it is easy to suppress the decrease in squareness ratio and the coercivity can be increased by increasing the rate. The present disclosure is based on these findings. First, embodiments of the present disclosure will be listed and described.

(1) A method of manufacturing a rare earth magnet according to the present disclosure,
Preparing a hydrogenated powder having a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere containing Nd, Fe, Al, and B; And forming a powder compact, dehydrogenating the powder compact in an inert atmosphere or in a reduced pressure atmosphere at a temperature higher than the recombination temperature to obtain a main phase of the Nd ₂ Fe ₁₄ B compound, and Forming a dehydrogenation body formed at grain boundaries of the phase, containing Nd and Al and having a grain boundary phase having a melting point lower than that of the main phase, melting the grain boundary phase to cover the main phase And a process.

According to the above configuration, it is possible to manufacture a rare earth magnet having a good balance of coercivity and squareness. By including Al, the coercivity can be increased as compared to the case where Al is not included. Furthermore, after the dehydrogenation step, which is a step of preparing a dehydrogenation body, the grain boundary phase is melted to provide a melting step, which is a step of covering the main phase, thereby providing grains in the main phase along with containing Al. Since the coverage of the boundary phase (the ratio of the contact length of the main phase with the grain boundary phase to the perimeter of the main phase) can be increased, it is easy to suppress the decrease in the squareness ratio.

(2) As one form of the manufacturing method of the said rare earth magnet, it is mentioned that content of Al in a hydrogenation particle is 0.05 mass% or more and 0.5 mass% or less.

If the content of Al is 0.05% by mass or more, it is easy to form a grain boundary phase containing Al after the dehydrogenation step. Therefore, it is easy to melt the grain boundary phase in the melting step. If the content of Al is 0.5% by mass or less, the viscosity of the grain boundary phase formed in the dehydrogenation step does not become too high because the content of Al is not excessively high. Therefore, it is easy to melt the grain boundary phase in the melting step, to easily increase the coverage, and to easily suppress the decrease in the squareness ratio. The content of Al in the hydrogenated particles is equal to the content of Al in the rare earth magnet. That is, when the content of Al in the hydrogenated particles is 0.05% by mass or more and 0.5% by mass or less, the content of Al in the rare earth magnet is 0.05% by mass or more and 0.5% by mass or less.

<< Details of Embodiments of the Present Disclosure >>
The detail of the manufacturing method of the rare earth magnet which concerns on this indication is demonstrated.

[Method of manufacturing rare earth magnet]
The method for producing a rare earth magnet according to the embodiment includes a preparing step which is a step of preparing a hydrogenated powder, a forming step which is a step of press-forming the hydrogenated powder to produce a powder compact, and a powder compact. And a dehydrogenation step which is a step of producing a dehydrogenated product by dehydrogenation treatment. One of the features of the method of producing a rare earth magnet according to the present disclosure is that the hydrogenated powder contains a specific additive element, and that a specific heat treatment (melting step) is performed on the dehydrogenated substance after the dehydrogenation step. And there. The details of each step will be described below.

(Preparation process)
In the preparation step, a hydrogenated powder having a plurality of hydrogenated particles is prepared. The preparation of the hydrogenated powder can be carried out by the hydrogenated powder preparation step including the raw material alloy preparation step, the grinding step and the hydrogenation step.
The order of the grinding process and the hydrogenation process after the raw material alloy preparation process does not matter. That is, the hydrogenated powder may be prepared by hydrogenating a powder obtained by crushing a raw material alloy, or may be prepared by hydrogenation of a raw material alloy and crushing. In this example, the case where the raw material alloy is crushed after being crushed and hydrogenated is described as an example.

Hydrogenated powder preparation process
Raw Material Alloy Preparation Step In the raw material alloy preparation step, an Nd—Fe—B—Al-based alloy (raw material alloy) containing an Nd ₂ Fe ₁₄ B compound as a main phase and Al as an additive element is prepared. By containing Al, it is easy to form a grain boundary phase having a lower melting point after the dehydrogenation step than in the case where it does not contain Al. Part of this Fe may be substituted with one or more elements selected from Co and Ni. In particular, when Co is contained, further improvement in coercivity and improvement in corrosion resistance can be expected. This raw material alloy allows the inclusion of unavoidable impurities.

The content of Nd is preferably 25% by mass to 35% by mass, and more preferably 29% by mass to 33% by mass. The content of Fe is more than 50% by mass. The content of B is 0.1% by mass or more and 5.0% by mass or less, and further 0.5% by mass or more and 1.5% by mass or less. The content of Al is preferably 0.05% by mass or more and 0.5% by mass or less. When the content of Al is 0.05% by mass or more, a grain boundary phase containing Al is easily formed after the dehydrogenation step. When the content of Al is 0.5% by mass or less, the viscosity of the intergranular phase formed in the dehydrogenation step does not become too high because the content of Al is not excessively high. Furthermore, the wettability to the main phase of the grain boundary phase does not become too low. Therefore, it is easy to melt the grain boundary phase in the melting step and coat the main phase, and the coverage of the grain boundary phase in the main phase (the contact with the grain boundary phase of the main phase to the perimeter of the main phase is described in detail later) It is easy to increase the ratio of the length and to suppress the decrease of the squareness ratio. The content of Al is more preferably 0.1% by mass or more and 0.3% by mass or less, and particularly preferably 0.1% by mass or more and 0.2% by mass or less. When at least one element of Co and Ni is included, the content (total content when both are included) is preferably 0.1% by mass or more and 5.0% by mass or less, and further 1.0% by mass or more 3.0 mass% or less is preferable. These contents are all values based on 100% by mass of the raw material alloy, and are also maintained in the hydrogenated powder that has been subjected to the below-mentioned hydrogenation step.

The maximum length of the raw material alloy before grinding is preferably 100 μm or more and 50 mm or less. When the maximum length is 100 μm or more, it is easy to pulverize in the crushing step in the subsequent step, and it is easy to produce a hydrogenated powder of a size (maximum length of 106 μm to 355 μm) particularly suitable for pressure forming. When the maximum length is 50 mm or less, the time required for the grinding process in the subsequent process can be shortened. The shape of the raw material alloy is not particularly limited, and may be, for example, various shapes such as a spherical shape, a rod shape, and a flaky shape. The "maximum length" is the length of the longest portion of the raw material alloy when one raw material alloy is viewed in plan from all directions.

There are no particular limitations on the method of producing the raw material alloy, and for example, it can be produced by a melt casting method, a rapid solidification method, a gas atomization method, or the like. In particular, when the raw material alloy is manufactured by a strip casting method which is a kind of rapid solidification method, a flaky raw material alloy is obtained, and the raw material alloy of the above-mentioned size is easily manufactured, which is preferable.

Grinding Step In the grinding step, the raw material alloy is mechanically crushed to produce a raw material alloy powder having a plurality of raw material alloy particles. In the pulverizing step, the raw material alloy is crushed to a predetermined size, and the size of the raw material alloy particles is controlled to a target size.

The maximum length of the raw material alloy particles after grinding may be, for example, 50 μm to 500 μm. The raw material alloy particles have high flowability and apparent density, and are particularly excellent in formability because they are in a state suitable for pressure forming. Furthermore, it is easy to suppress oxidation. By setting the maximum length of the raw material alloy particles to 500 μm or less, it is easy to produce a rare earth magnet having a high relative density. The maximum length of the raw material alloy particles is more preferably 75 μm or more and 400 μm or less, and particularly preferably 106 μm or more and 355 μm or less.

The apparatus for grinding the raw material alloy includes, for example, a grinding-type grinder or a collision-type grinder. The grinding type crusher typically includes a brown mill and the like, and the collision type crusher typically includes a pin mill and the like. These devices are suitable for grinding the raw material alloy to the above particle size, and the particle size can be easily controlled.

Hydrogenation Step In the hydrogenation step, raw material alloy particles are heat-treated at a temperature equal to or higher than the disproportionation temperature in an atmosphere containing hydrogen to produce a hydrogenated powder having a plurality of hydrogenated particles that have been subjected to a hydrogenation treatment.

The hydrogenated particle has a structure in which the main phase (Nd ₂ Fe ₁₄ B compound) is decomposed into three phases of NdH ₂ phase, Fe phase and Fe ₂ B phase. This hydrogenated particle has an iron-containing material phase (Fe phase or Fe ₂ B phase) which is a soft phase softer than the main phase before phase decomposition or NdH ₂ phase, and therefore, when pressed and formed It is easy to deform and improve formability.

Existence form of NdH ₂ phase and the iron-containing phase is or layered form and NdH ₂ phase and the iron-containing phase is in the laminated structure, there NdH ₂ phase granular in the iron-containing phase is dispersed Dispersion forms. The form in which these are present depends on the heat treatment conditions (mainly temperature) in the hydrogenation treatment described later. In the dispersed form, the iron-containing material phase uniformly exists around the NdH ₂ phase, so that the formability can be more easily improved than the layered form. Therefore, it is easy to obtain powder compacts (dehydrogenated bodies) of various shapes such as arcs, cylinders, cylinders and the like. Moreover, it is easy to obtain a high-density powder compact having a high relative density.

The hydrogenated particles preferably have a structure comprising 10% by volume or more and less than 40% by volume of the NdH ₂ phase and the balance of the iron-containing material phase. If the balance excluding the NdH ₂ phase is substantially the iron-containing material phase and the iron-containing material phase is the main component (60% by volume or more and 90% by volume or less), the formability of the hydrogenated powder can be enhanced.

The NdH ₂ phase and the iron-containing material phase are adjacent to each other, and the distance between adjacent NdH ₂ phases through the iron-containing material phase is preferably 3 μm or less. The structure in which the iron-containing material phase is present between the NdH ₂ phases and both phases are present at the above-mentioned specific intervals is a structure in which both phases are uniformly present, so it deforms uniformly when pressed. . When the above interval is 3 μm or less, excessive energy is not input when the NdH ₂ phase and the iron-containing material phase recombine with the original Nd ₂ Fe ₁₄ B compound by dehydrogenation treatment in a later step. Furthermore, it is possible to suppress the deterioration of the characteristics due to the coarsening of the crystal grains of the Nd ₂ Fe ₁₄ B compound. In order for the iron-containing material phase to be sufficiently present between the NdH ₂ phases, the above-mentioned interval is preferably 0.5 μm or more, and more preferably 1 μm or more. The above-mentioned interval can be controlled, for example, by adjusting the composition of the Nd--Fe--B--Al alloy used for the raw material, or by adjusting the conditions of the hydrogenation treatment, particularly the heat treatment temperature. For example, if the ratio (atomic ratio) of iron is increased in the Nd-Fe-B-Al alloy or the heat treatment temperature is increased in the above temperature range, the above-mentioned interval tends to be increased.

The interval refers to distance between centers of NdH ₂ phase adjacent. The measurement of the distance can be performed, for example, by observing the cross section with a SEM (scanning electron microscope) and analyzing the composition with EDX (energy dispersive X-ray analyzer).

The atmosphere at the time of the hydrogenation treatment may be an H ₂ gas atmosphere or a mixed gas atmosphere of an H ₂ gas and an inert gas. The inert gas may, for example, be Ar gas or N ₂ gas.

The hydrotreating temperature may be equal to or higher than the hydrogen disproportionation temperature of the prepared alloy. Although depending on the material, the hydrogenation treatment temperature is, for example, 600 ° C. or more and 1100 ° C. or less, and further, 650 ° C. or more and 950 ° C. or less, particularly 700 ° C. or more and 900 ° C. or less. When the temperature of heat treatment is set near the disproportionation temperature, the existence form of the NdH ₂ phase becomes the above-mentioned layered form, and when the temperature of heat treatment is set as high as disproportionation temperature + 100 ° C. or more, the existence form of both phases is It becomes the said dispersion form.

The hydrogenation time (holding time) can be appropriately selected, and for example, 30 minutes or more and 300 minutes or less can be mentioned, and further 60 minutes or more and 150 minutes or less can be mentioned.

(Molding process)
In the forming step, the hydrogenated powder is pressure-formed to produce a powder compact. For molding, it is preferable to use a mold from which a powder compact having a desired shape can be obtained.

The relative density of the powder compact can be 85% by volume or more, further 87% by volume or more, particularly 90% by volume or more. The upper limit of the relative density of the powder compact is, for example, 95% or less. The term "relative density" as used herein means the actual density (the percentage of [measured density of molded body / true density of molded body)] with respect to the true density. The true density is a density derived by calculation from the true density of each of the hydrogenated phases (NdH ₂ , Fe, Fe ₂ B) of the Nd--Fe--B--Al alloy as the starting material and the volume ratio of each.

The molding pressure is preferably 490 MPa or more. By setting the molding pressure to 490 MPa or more, the relative density of the powder compact can be increased. The molding pressure is, for example, 1960 MPa or less. By setting the compacting pressure to 1960 MPa or less, the relative density of the powder compact does not become too high. Therefore, it is easy to release hydrogen by dehydrogenation treatment. The molding pressure is preferably 600 MPa or more and 1,500 MPa or less, and particularly preferably 700 MPa or more and 1,400 MPa or less.

(Dehydrogenation process)
In the dehydrogenation step, the powder compact is heat-treated at a temperature higher than the recombination temperature in an inert atmosphere or a reduced pressure atmosphere to perform dehydrogenation treatment to produce a dehydrogenated product.

The main phase of the hydrogenated powder constituting the powder compact is in a state of phase decomposition into an NdH ₂ phase and an iron-containing material phase by hydrogenation treatment, and is recombined by dehydrogenation treatment. As a result, a plurality of main phases consisting of nano-sized and fine Nd ₂ Fe ₁₄ B compounds and grain boundaries of the main phases are formed, containing Nd and Al and having Nd-rich and low melting point particles than the main phases. A dehydrogenation body is formed which comprises a polycrystalline structure having a phase boundary. This tissue can be grasped by observing the cross section with a SEM-EDX apparatus, and the composition can be measured by analyzing with EDX.

Examples of the inert atmosphere include Ar gas atmosphere and N ₂ gas atmosphere. The reduced pressure atmosphere may be, for example, a vacuum atmosphere having a pressure lower than the standard atmospheric pressure. The degree of vacuum of the vacuum atmosphere is 100 Pa or less, further 10 Pa or less, particularly 1 Pa or less. If a reduced pressure atmosphere is used, it is easy to promote the recombination reaction and the NdH ₂ phase hardly remains.

With the temperature more than the said recombination temperature, 600 degreeC or more and 1000 degrees C or less are mentioned, for example, Furthermore, 650 degreeC or more and 800 degrees C or less are preferable. By setting the temperature above, the growth of crystals of the recombination alloy is suppressed, and a fine polycrystalline structure can be obtained.

The holding time at a temperature higher than the recombination temperature is preferably 10 minutes to 300 minutes. If the holding time is 10 minutes or more, hydrogen can be easily released from the inside of the hydrogenated particles constituting the powder compact. Furthermore, it is easy to form a grain boundary phase. If the retention time is set to 300 minutes or less, the dehydrogenation time does not become excessively long. Therefore, it is difficult to reduce the coercive force due to the crystal grain growth of the main phase, and it is easy to suppress the concentration of the grain boundary phase in the region (triple point) surrounded by three or more adjacent main phases. Therefore, it is easy to melt the grain boundary phase in the melting step to coat the main phase.

After holding for the predetermined time above the recombination temperature, the temperature is cooled to below the freezing point temperature of the grain boundary phase.
The cooling rate in this cooling process is preferably such that the time required to reach from the recombination temperature to the freezing point temperature of the grain boundary phase is 1 hour or less. Then, it is easy to form the grain boundary phase which is easy to coat the main phase in the melting process. Since the time for which the powder compact is kept in the high temperature state is not excessively long due to the fast cooling rate, it is easy to suppress the concentration of the grain boundary phase at the triple point. Therefore, it is easy to melt the grain boundary phase in the melting step and coat the main phase. The cooling rate is, for example, preferably 500 ° C./hour or more, and more preferably 1000 ° C./hour or more. In order to obtain this cooling rate, for example, the heat treatment chamber and the heater can be separated, and the heater can be separated at the time of cooling.

(Melting process)
In the melting step, the dehydrogenated substance is heat-treated to melt the grain boundary phase of the particles. The grain boundary phase coats the main phase by this melting. Thereby, the coverage of the grain boundary phase in the main phase can be easily increased, and the decrease in squareness ratio can be suppressed. The higher the coverage, the easier it is to suppress the drop in the squareness ratio. The coverage can be, for example, 50% or more, and can be 52% or more, particularly 54% or more.

The method of measuring the coverage will be described in detail later.

The melting temperature is preferably, for example, 550 ° C. or more and 650 ° C. or less, although it depends on the composition of the grain boundary phase. If the melting temperature is 550 ° C. or more, the grain boundary phase is easily melted. If the melting temperature is 650 ° C. or less, the temperature is not excessively high. Thereby, it is easy to suppress that the grain boundary phase melts too much or the component of the main phase is eluted. Therefore, it is easy to maintain the state in which the grain boundary phase covered the periphery of the main phase, and it is easy to suppress the decrease in the coverage.

The melting time can be appropriately selected under each condition because the viscosity of the melted grain boundary phase changes depending on the temperature and the amount of the additive element. The melting time is preferably, for example, 10 minutes or more and 600 minutes or less. If the melting time is 10 minutes or more, the grain boundary phase is easily melted sufficiently. If the melting time is set to 600 minutes or less, the time is not too long and the grain boundary phase is easily melted too much, so it is easy to suppress the decrease in coverage. The melting time is preferably 30 minutes to 300 minutes.

As in the dehydrogenation step, the atmosphere in the melting step may be an inert atmosphere or a reduced pressure atmosphere. Then, the oxidation of the dehydrogenated substance can be suppressed.

(Use)
The manufacturing method of the rare earth magnet which concerns on embodiment can be suitably utilized for manufacture of the rare earth magnet used for various electric appliances, such as various motors and a generator.

[Function effect]
According to the method of manufacturing a rare earth magnet according to the embodiment, it is possible to manufacture a rare earth magnet with a good balance of coercivity and squareness ratio. The coercivity can be enhanced by containing Al as an additive element of the raw material alloy, and by providing the melting step after the dehydrogenation step, the coverage of the grain boundary phase in the main phase can be easily increased with the inclusion of Al, This is because the decrease in squareness ratio can be suppressed.

Test Example 1
Samples of rare earth magnets were prepared to evaluate the magnetic properties of each sample.

[Sample No. 1-1]
Sample No. The rare earth magnet 1-1 was prepared in the procedure of preparation step → forming step → dehydrogenation step → melting step in the same manner as the above-described method of producing a rare earth magnet.

(Preparation process)
In the preparation step, the hydrogenated powder was prepared in the order of the raw material alloy preparation step, the grinding step, and the hydrogenation step.

Hydrogenated powder preparation process
-Raw material alloy preparation process As a raw material alloy, 30% by mass Nd-5% by mass Co-1.1% by mass B-0.2% by mass Al-balance has a composition of Fe and unavoidable impurities by a strip casting method A flaky raw material alloy having a thickness of 300 μm and a maximum length of 30 mm was prepared.

Pulverizing Step The raw material alloy was crushed, and the obtained powder was sieved and classified to obtain a raw material alloy powder having a maximum length of 106 μm or more and 355 μm or less. The grinding was performed using a cemented carbide mortar.

Hydrogenation step A raw material alloy powder was subjected to a hydrogenation treatment to prepare a hydrogenated powder having a plurality of hydrogenated particles. This hydrogenation treatment was performed using a vacuum heat treatment furnace (oxygen concentration of 100 ppm or less). The hydrogen treatment conditions were such that the atmosphere was in a hydrogen flow atmosphere, the temperature was 850 ° C., and the time was 120 minutes.

(Molding process)
The hydrogenated powder was filled in a mold and pressed (uniaxial press) to prepare a cylindrical powder compact of 10 mm in diameter and 10 mm in height. The molding pressure was about 1180 MPa (12 ton / cm ² ).

The relative density of the powder compact was measured. The relative density of this powder compact was 84% by volume. The relative density was taken as the actual density (the percentage of [measured density of powder compact / true density of powder compact]) to the true density. The true density was a density (here, 7.32 g / cm ³ ) derived by calculation from each true density of the hydrogenation phase (NdH ₂ , Fe, Fe ₂ B) and the volume ratio of each.

(Dehydrogenation process)
The powder compact was dehydrogenated to prepare a dehydrogenated product. In the dehydrogenation treatment, the atmosphere in the vacuum heat treatment furnace was switched from a hydrogen atmosphere to a vacuum atmosphere. The dehydrogenation conditions were such that the atmosphere was in a vacuum atmosphere, the temperature was a temperature higher than the recombination temperature (600 ° C.) (here, 800 ° C.), and the holding time was 120 minutes. The degree of vacuum of the vacuum atmosphere was set to less than 0.5 Pa. Thereafter, the powder compact was cooled to 800 ° C to 350 ° C. This cooling was performed such that the time required to reach 800 ° C. to or below the freezing point temperature (530 ° C.) of the grain boundary phase of the powder compact was 1 hour or less. Specifically, the cooling rate was 600 ° C./hour.

The cross section of the dehydrogenated substance was structurally observed and compositionally analyzed using a SEM-EDX apparatus. This dehydrogenated substance is formed at a plurality of main phases consisting of nano-sized and fine Nd ₂ Fe ₁₄ B compounds, and at grain boundaries of the main phases, and contains Nd and Al, and is Nd-rich grains than the main phases. It has a polycrystalline structure having a boundary phase.

(Melting process)
A melting process was performed to melt the grain boundary phase of the dehydrogenated substance. Melting processing conditions were such that the atmosphere was in an Ar gas atmosphere, the temperature was 600 ° C., and the time was 360 minutes. Referring to FIG. 1, a rare earth magnet 1 according to the present disclosure includes a plurality of main phases 2 made of an Nd ₂ Fe ₁₄ B compound, and a grain boundary phase 3 covering at least a portion of the plurality of main phases 2. .

[Sample No. 1-101 to No. 1-104]
Sample No. The sample No. 1-101 rare earth magnet is the same as sample No. 1 except that it does not contain Al as an additive element of the raw material alloy. It was prepared in the same manner as 1-1.
Sample No. The rare earth magnet of No. 1-102 is the same as sample No. 1 except that the melting step after the dehydrogenation step is not performed. It was prepared in the same manner as 1-1.
Sample No. Sample No. 1-103 except for the point that it does not contain Al as an additive element of the raw material alloy and the point that the melting process after the dehydrogenation process is not performed. It was prepared in the same manner as 1-1.
Sample No. The rare earth magnet of 1-104 is not Al as an additive element of the raw material alloy, but contains 0.5 mass% of Ga, and samples No. It was prepared in the same manner as 1-1.

[Measurement of coverage rate]
The coverage of the grain boundary phase in the main phase of the rare earth magnet of each sample was determined as follows. The results are shown in Table 1. In an arbitrary cross section of the rare earth magnet, an observation view including 300 or more main phases is taken. In the observation view, 30 or more main phases are arbitrarily selected. Determine the contact length of each selected main phase with the grain boundary phase, and calculate “{(contact length of main phase with grain boundary phase) / (peripheral length of main phase)} × 100 in each main phase, The average value of the calculated values of all the main phases was taken as the coverage. The contact length of the main phase with the grain boundary phase was taken as the total contact length when a plurality of grain boundary phases were intermittently contacted around the main phase. More specifically, first, in any cross section of the rare earth magnet, mirror polishing was performed by polishing with abrasive paper and a cross polisher method. Thereafter, the grain boundary phase was removed by etching using a nital solution. Next, a plurality of images were taken at a magnification of about 30,000 times using an FE-SEM (Field Emission-Scanning Electron Microscopy) apparatus. It is preferable to include 300 or more main phases in one observation field of view. Next, 30 or more main phases are arbitrarily selected in the observation field of view. The interface length where the region etched between each of the selected main phases and the adjacent main phase has a width of 10 nm or more is the contact length, 「{(contact length with main phase grain boundary phase) in each main phase / (Peripheral length of main phase)} × 100 ”was calculated, and the average value of the calculated values of all the main phases was taken as the coverage. The contact length of the main phase with the grain boundary phase was taken as the total contact length when a plurality of grain boundary phases were intermittently contacted around the main phase.
The etching is carried out, for example, using a nital solution mixed with 1 cc of nitric acid with 600 cc to 800 cc of ethanol under a condition of immersion for 30 seconds. Since the ease of etching varies depending on the element constituting the rare earth magnet, the amount of ethanol or etching time is appropriately adjusted. The etching operation is performed within 30 minutes after completion of polishing with a cross polisher.

[Evaluation of magnetic properties]
The rare earth magnet of each sample was magnetized with a pulse magnetic field of 3.5 T, and the magnetic properties of the rare earth magnet were investigated. The magnetic properties of this rare earth magnet were measured using a BH tracer (DCBH tracer manufactured by Riken Denshi Co., Ltd.) to measure the coercive force Hcj (kA / m) and the squareness ratio (%). The results are shown in Table 1. The squareness ratio (%) is the ratio (Hk / Hcj) × 100 of the magnetic field Hk and the coercivity Hcj to 90% of the residual magnetic flux density Br.

As shown in Table 1, sample nos. It is understood that the rare earth magnet 1 of 1-1 has a high coverage, and a good balance between the coercive force and the squareness ratio. The sample No. Sample No. 1-1. 1-101 to No. Compared to 1-103, the coercivity was increased while suppressing the decrease in squareness ratio. Sample No. It can be seen that 1-104 has high coercivity but low squareness ratio. A rare earth magnet 1 according to the present disclosure comprises: a plurality of main phases 2 made of a Nd ₂ Fe ₁₄ B compound; a grain boundary phase 3 containing a plurality of main phases coated with a coverage of 54% or more; The coercivity is 1050 kA / m or more. Here, the content of Al may be 0.05% by mass or more and 0.5% by mass or less.

The present invention is not limited to these exemplifications, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

1 rare earth magnet 2 main phase 3 grain boundary phase

Claims (7)

Preparing a hydrogenated powder comprising a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere, containing Nd, Fe, Al, and B;
Press forming the hydrogenated powder to produce a powder compact;
The powder compact is dehydrogenated in an inert atmosphere or in a reduced pressure atmosphere at a temperature higher than the recombination temperature to form the main phase of the Nd ₂ Fe ₁₄ B compound and the grain boundaries of the main phase, Producing a dehydrogenated product having a grain boundary phase having a melting point lower than that of the main phase, and containing Al and Al.
Melting the grain boundary phase to coat the main phase;
Method of producing a rare earth magnet comprising: The method for producing a rare earth magnet according to claim 1, wherein the content of Al in the hydrogenated particles is 0.05% by mass or more and 0.5% by mass or less. The method for producing a rare earth magnet according to claim 1 or 2, wherein in the step of melting the grain boundary phase and coating the main phase, the grain boundary phase is melted at a temperature of 550 ° C to 650 ° C. The method of manufacturing a rare earth magnet according to claim 3, wherein in the step of melting the grain boundary phase to coat the main phase, the grain boundary phase is melted in a time of 10 minutes to 600 minutes. Preparing a hydrogenated powder comprising a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere, containing Nd, Fe, Al, and B;
Press forming the hydrogenated powder to produce a powder compact;
The powder compact is dehydrogenated in an inert atmosphere or in a reduced pressure atmosphere at a temperature higher than the recombination temperature to form the main phase of the Nd ₂ Fe ₁₄ B compound and the grain boundaries of the main phase, Producing a dehydrogenated product having a grain boundary phase having a melting point lower than that of the main phase, and containing Al and Al.
A step of melting the grain boundary phase to coat the main phase by treatment at a temperature of 550 ° C. or more and 650 ° C. or less for 10 minutes or more and 600 minutes or less;
The manufacturing method of the rare earth magnet which is provided with and Al content is 0.05 mass% or more and 0.5 mass% or less. A plurality of main phases consisting of Nd ₂ Fe ₁₄ B compounds,
Coating the plurality of main phases at a coverage of 54% or more, and including a grain boundary phase containing Nd and Al,
Coercivity is 1050 kA / m or more,
Rare earth magnets. The rare earth magnet according to claim 6, wherein the content of Al is 0.05% by mass or more and 0.5% by mass or less.

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