WO2019049691A1

WO2019049691A1 - Method for producing rare earth magnet

Info

Publication number: WO2019049691A1
Application number: PCT/JP2018/031372
Authority: WO
Inventors: 前田　徹; 一誠嶋内; 慧平井
Original assignee: 住友電気工業株式会社
Priority date: 2017-09-05
Filing date: 2018-08-24
Publication date: 2019-03-14
Also published as: JP2019047021A

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, Cu and B and are hydrogenated in an atmosphere containing hydrogen at a temperature that is not less than the disproportionation temperature; a step for producing a powder compact by press molding the hydrogenated powder; a step for producing a dehydrogenated body by dehydrogenating the powder compact in an inert atmosphere or in a reduced pressure atmosphere at a temperature that is not less than the recombination temperature, said dehydrogenated body having a main phase of an Nd2Fe14B compound and an intergranular phase that is formed at the grain boundary of the main phase and contains Nd and Cu, while having a lower melting point than the main phase; and a step for recrystallizing the intergranular phase by melting the intergranular phase so that the intergranular phase reacts with the main phase.

Description

Method of manufacturing rare earth magnet

The present disclosure relates to a method of manufacturing a rare earth magnet. This application claims the priority based on Japanese Patent Application No. 2017-170256 filed on September 5, 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 comprising a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere comprising Nd, Fe, Cu, 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 Cu and Cu;
Remelting the grain boundary phase by reacting it with the main phase.

In FIG. It is a microscope picture which shows the cross section orthogonal to the pressurization direction of the rare earth magnet of 1-1. FIG. It is a microscope picture which shows the cross section parallel to the pressurization direction of the rare earth magnet of 1-1. In FIG. It is a microscope picture which shows the cross section orthogonal to the pressurization direction of the rare earth magnet of 1-104. FIG. 4 shows sample nos. It is a microscope picture which shows the cross section parallel to the pressurization direction of the rare earth magnet of 1-104.

<< Description of an Embodiment of the Present Disclosure >>
The conventional dehydrogenated product after dehydrogenation is an aggregate of particles containing an Nd ₂ Fe ₁₄ B compound as a main component. These particles are composed of an Nd ₂ Fe ₁₄ B crystal phase and a grain boundary phase, and exhibit the properties of a permanent magnet. However, the Nd ₂ Fe ₁₄ B crystal phase in the conventional dehydrogenation body is isotropic because its crystal magnetization easy axis (typically c axis) is oriented in various directions, so the degree of crystal orientation is enhanced. hard. Therefore, it is difficult to increase the residual magnetic flux density of the dehydrogenated substance. Therefore, the present inventors diligently studied to align the easy axis of crystal magnetization of the Nd ₂ Fe ₁₄ B crystal phase in one direction. As a result, the following findings were obtained. When a specific heat treatment is performed on a dehydrogenated substance containing a specific additive element, the grain boundary phase and the main phase react to recrystallize. Along with the recrystallization, the easy axis of crystal magnetization is easily aligned in one direction, and the residual magnetic flux density can be increased. 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 an aspect of the present disclosure,
Preparing a hydrogenated powder comprising a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere comprising Nd, Fe, Cu, 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 Cu and Cu;
Remelting the grain boundary phase by reacting it with the main phase.

According to the above configuration, a rare earth magnet having a high residual magnetic flux density can be manufactured. The reason why the residual magnetic flux density can be improved is considered as follows. A dehydrogenated product having a grain boundary phase containing Cu can be produced by preparing a hydrogenated powder containing Cu, shaping and dehydrogenating treatment. By melting the grain boundary phase of this dehydrogenated substance, the grain boundary phase and the main phase react with each other to be easily recrystallized. With this recrystallization, the easy axis of crystal magnetization is easily aligned in one direction.

Further, according to the above configuration, since the crystal easy magnetization axis can be easily oriented in one direction without applying a magnetic field in a forming step or the like, equipment for applying a magnetic field is unnecessary. Therefore, the equipment cost can be reduced.

<< Details of the Embodiment of the Present Invention >>
Details of a method of manufacturing a rare earth magnet according to an embodiment of the present invention will be described.

[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. One of the features of the method for producing this rare earth magnet is that the hydrogenated powder contains a specific additive element, and the above-mentioned main heat treatment (dissolving the grain boundary phase for the dehydrogenated substance after the dehydrogenation step) And a melting step, which is a step of reacting and recrystallizing the phase. 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--Cu-based alloy (raw material alloy) containing an Nd ₂ Fe ₁₄ B compound as a main phase and Cu as an additive element is prepared. By containing Cu, 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 Cu. 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 Cu is preferably 0.05% by mass or more and 0.5% by mass or less. If the content of Cu is 0.05% by mass or more, a grain boundary phase containing Cu is easily formed after the dehydrogenation step. Therefore, it is easy to melt the grain boundary phase in the melting step and to react with the main phase. If the content of Cu is 0.5% by mass or less, the content of Cu is not excessively large, so the size of the grain boundary phase does not become too large, and the coarsening of crystal grains after recrystallization is suppressed. easy. Furthermore, 0.1 mass% or more and 0.3 mass% or less are preferable, and, as for content of Cu, 0.1 mass% or more and 0.2 mass% or less are especially preferable. 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--Cu alloy used as the raw material, or by adjusting the conditions of the hydrogenation treatment, particularly the heat treatment temperature. For example, when the ratio (atomic ratio) of iron is increased in the Nd-Fe-B-Cu 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. This molding includes general uniaxial press molding.

The relative density of the powder compact can be 80% by volume or more, further 85% by volume or more, 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 respective true densities of the hydrogenated phases (NdH ₂ , Fe, Fe ₂ B) of the Nd--Fe--B--Cu-based alloy as the starting material and the respective volume ratios.

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, and Nd and Cu containing Nd-rich and low melting point grains 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. This dehydrogenated substance is an aggregate of powder composed of the above-mentioned main phase and the above-mentioned grain boundary phase, and the powder boundary coincides with the boundary of the hydrogenated powder in the powder compact. The crystal easy magnetization axis (c axis) of the main phase is oriented in various directions, and is in an isotropic state. The (006) plane when X-ray diffraction (XRD) is performed (the diffraction angle 2θ = about 44.56 ° when a Cu tube is used as a radiation source) as the ratio in which the crystallographic easy axis is aligned in one direction is higher. There is a specific orientation in which the diffraction intensity of x is relatively large. In this dehydrogenated substance, although the diffraction intensity of the (006) plane is small when the surface (pressure surface) orthogonal to the pressure direction in the forming step is the measurement surface, the rare earth magnet is subjected to the melting step described later. The diffraction intensity of the (006) plane at the same measurement plane can be made larger.

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 hard to occur the coercive force fall by the crystal grain growth of the main phase. Furthermore, it is easy to suppress that the grain boundary phase is concentrated too much in the region (triple point) surrounded by three or more main phases adjacent to each other. Therefore, the volume ratio of the grain boundary phase which is in surface contact with the main phase in the melting step and which is susceptible to reaction can be increased.

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 be reacted with the main phase in the melting step. 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. 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. By this melting, the grain boundary phase and the main phase react to recrystallize. With recrystallization, the crystal easy magnetization axis (c axis) of the main phase tends to be aligned in one direction. Specifically, in the melt-processed body after the melting step, the diffraction intensity of the (006) plane when X-ray diffraction is performed using a plane (pressure plane) orthogonal to the pressing direction in the forming step is a dehydrogenated body Or more, or 1.5 or more times, particularly preferably 1.75 or more times.

The crystallographic easy axis of this melt processed body is particularly easy to be in the pressure direction. The reason is considered as follows. When the grain boundary phase is melted, the grain boundary phase is likely to flow in the direction perpendicular to the pressure direction in the forming step (hereinafter, the pressure perpendicular direction) in the dehydrogenated body. This is because, when the hydrogenated powder is pressurized, the Fe phase (iron-containing material phase) which is the soft phase is stretched in the pressure orthogonal direction, and the NdH ₂ particles (NdH ₂ phase) which is the hard phase which was homogeneously present It is considered that when the layer is dispersed in layers and then dehydrogenated, it becomes easy to form a thick intergranular phase in this layer portion. At this time, in the uniaxial press molding of the powder, the stacking direction of the grain boundary phase tends to coincide with the pressing direction. When the melting area of the grain boundary phase and the adjacent main phase increases during the melting process, the melting portion of the main phase and the grain boundary phase dispersed in the layer combine to form a planar melting layer, which is again It is believed that when it is crystallized, it forms flat Nd ₂ Fe ₁₄ B crystals. Here, the Nd ₂ Fe ₁₄ B crystal is characterized in that it is easy to form a flat crystal in which the c-axis is oriented in the thickness direction, and in the above flat recrystallization, the normal direction of the surface, ie, the pressing direction. It is believed that the c-axis tends to be oriented. For this reason, in the melt-processed body, when the XRD evaluation is performed with the orthogonal plane (pressure surface) in the pressing direction in the forming step as the measurement surface, the diffraction intensity of the (006) plane of the melt-processed body is compared And grow.

The structure of the melt-processed body has flat crystal grains. Flat means that the major axis of the crystal grain is 0.8 μm or more, and the aspect ratio (major axis / minor axis) of the major axis to the minor axis of the crystal grain is 1.6 or more in a cross section parallel to the pressure direction. Say to meet. The aspect ratio of the flat crystal grains is further 1.8 or more, and particularly 2.0 or more. The proportion of the number of flat crystal grains is, for example, 1% or more. The ratio of the number of flat crystal grains can be determined as follows. Using a field emission scanning electron microscope (FE-SEM), one or more observation fields including 500 or more crystal grains are taken in the cross section. The number of flat crystal grains in each observation visual field is determined, and {(the number of flat crystal grains / the number of all crystal grains present in each visual field) x 100} in each visual field is calculated. And let the average of all the visual field be the ratio of the number of flat-shaped crystal grains. The proportion of the number of flat crystal grains is further 10% or more, in particular 20% or more.

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 suppress the coarsening of crystal grains.

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 and the main phase are easily reacted sufficiently. If the melting time is set to 600 minutes or less, it is easy to suppress the reaction between the grain boundary phase and the main phase because the time is not too long and it is easy to suppress the coarsening of crystal grains. The melting time is preferably 30 minutes to 360 minutes, and more preferably 300 minutes or less.

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, a rare earth magnet having a high residual magnetic flux density can be manufactured. By preparing a hydrogenated powder containing Cu, it is possible to prepare a dehydrogenated body provided with a grain boundary phase containing Cu, and by containing Cu in the grain boundary phase of the dehydrogenated body, the grain boundary phase and the main phase are mixed in the melting step. It is because it is easy to react and recrystallize, and it is easy to align the easy axis of crystal magnetization in one direction with the recrystallization.
In addition, rare earth magnets with high coercivity can be manufactured. By containing Cu as an additive element of the raw material alloy, the coercive force can be enhanced.

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 mass% Nd-5.0 mass% Co-1.1 mass% B-0.12 mass% Cu-Remainder composition of Fe and unavoidable impurities by 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 to 355 μm. 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 press-molded (uniaxial press molding) to prepare a cylindrical powder compact having a diameter of 10 mm and a height of 10 mm. The molding pressure was about 1470 MPa (15 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 (about 500 ° 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 phase, and contains Nd and Cu, and has more Nd-rich grains than the main phase. 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.

[Sample No. 1-101 to No. 1-104]
Sample No. The rare earth magnet of No. 1-101 is the same as the sample No. 1 except that it does not contain Cu 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 the sample No. 1 except that the processing temperature in the melting step is 450.degree. It was prepared in the same manner as 1-1.
Sample No. Sample No. 1-103, except that the melting step after the dehydrogenation step is not performed, is the rare earth magnet of 1-103. It was prepared in the same manner as 1-1.
Sample No. Sample No. 1-104 except for the point that it does not contain Cu as an additive element of the raw material alloy and the point that the melting step after the dehydrogenation step is not performed. It was prepared in the same manner as 1-1.

[Measurement of grain size]
The average grain size of each sample was measured. The measurement of the average crystal grain size can be performed by acquiring an image of the cross section with FE-SEM (JSM-7600F manufactured by Nippon Denshi Co., Ltd.) and analyzing it using commercially available image analysis software. At that time, the equivalent circle diameter is taken as the crystal grain size. The circle equivalent diameter specifies the outline of a crystal grain, and is the diameter of a circle having the same area as the area S enclosed by the outline. That is, it is expressed by circle equivalent diameter = 2 × {area S / π} ^1/2 in the above contour. The results are shown in Table 1.

[Evaluation of crystal orientation]
The orientation direction of the crystal easy axis of the main phase in the rare earth magnet of each sample was analyzed. Here, a cross section perpendicular to the pressing direction of the rare earth magnet of each sample was taken, and the X-ray diffraction was performed on this cross section to measure the diffraction intensity of the (006) plane. The results are shown in Table 1. Sample No. shown in Table 1 1-1, no. 1-101 to No. The diffraction intensity of the (006) plane of No. 103 is the same as that of sample No. The ratio when the diffraction intensity of the (006) plane of 1-104 is 100 is shown.

[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 for residual magnetic flux density Br (T) and coercive force Hcj (kA / m) using a BH tracer (DCBH tracer manufactured by Riken Denshi Co., Ltd.). The results are shown in Table 1.

As shown in Table 1, sample nos. The diffraction intensity of the (006) plane of 1-1 is the same as that of sample No. 1-101 to sample nos. It can be seen that it is higher than 1-104. Sample No. The diffraction intensity of the (006) plane of 1-1 is the same as that of sample No. It is at least 1.9 times the diffraction intensity of the (006) plane of 1-104.
The sample No. The residual magnetic flux density of 1-1 is the same as that of sample no. 1-101 to sample nos. It can be seen that it is higher than 1-104. Sample No. The residual magnetic flux density of 1-1 is 0.67T. Also, for sample no. It can be seen that the coercivity of 1-1 is relatively high. Sample No. The coercive force of 1-1 is 780 kA / m.

Sample No. 1-1 and sample no. The structure of 1-104 rare earth magnets was observed. For the observation of structure, FE-SEM (JSM-7600F manufactured by JEOL Ltd.) was used as in the measurement of the average grain size. Sample No. A photomicrograph of a cross section orthogonal to the pressing direction of the 1-1 rare earth magnet is shown in FIG. 1, and a photomicrograph of a cross section parallel to the pressing direction is shown in FIG. Sample No. A photomicrograph of a cross section orthogonal to the pressing direction of the 1-104 rare earth magnet is shown in FIG. 3, and a photomicrograph of a cross section parallel to the pressing direction is shown in FIG.

Sample No. In 1-1, as shown in FIG. 1 and FIG. 2, it was found that flat crystal grains were present. Sample No. For 1-1, for example, the major axis and the minor axis of the crystal grain shown in the circled numbers “1” to “11” in FIG. 2 were measured to determine the aspect ratio (major axis / minor axis). As a result, all of these crystal grains were flat crystal grains having a major axis of 0.8 μm or more and an aspect ratio of 1.6 or more. The average value of the aspect ratios of the eleven flat crystal grains was 2.17. {(The number of flat crystal grains / the number of all grains present in the field of view) × 100} in the microphotograph of FIG. 2 was calculated. The total number of crystal grains present in the field of view was 959. The ratio of the number of flat crystal grains was found to be 1% or more, specifically 4.3%.

Sample No. As shown in FIGS. 3 and 4, it was found that 1-104 was composed of dice-shaped crystal grains substantially without flat crystal grains. Sample No. 1-104 is the sample No.1. In the same manner as 1-1, for example, the major axis and the minor axis of the crystal grain shown in the circled numbers "1" to "11" of FIG. 4 were measured to calculate the aspect ratio. As a result, all of these crystal grains had an aspect ratio of less than 1.6. The average value of the aspect ratio of the 11 crystal grains was 1.16. {(The number of flat crystal grains / the number of all grains present in the field of view) × 100} in the microphotograph of FIG. 4 was calculated. The number of all grains present in the field of view was 1192. The proportion of the number of flat-shaped grains was found to be less than 1%, specifically 0.8%.

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.

Claims

Preparing a hydrogenated powder comprising a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere comprising Nd, Fe, Cu, 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 Cu and Cu;
And D) reacting the main phase with the grain boundary phase to cause recrystallization.
2. The method of manufacturing a rare earth magnet according to claim 1, wherein the grain boundary phase is melted at a temperature of 550 ° C. or more and 650 ° C. or less in the step of reacting and recrystallizing the grain boundary phase by melting the grain boundary phase. Method.
The rare earth element according to claim 1 or 2, wherein the grain boundary phase is melted in a time of 10 minutes or more and 600 minutes or less in the step of reacting and recrystallizing the grain boundary phase by melting the grain boundary phase. Manufacturing method of magnet.
The method according to claim 3, wherein the grain boundary phase is melted in a time of 30 minutes or more and 360 minutes or less in the step of reacting and recrystallizing the grain boundary phase by melting the grain boundary phase. .
Preparing a hydrogenated powder comprising a plurality of hydrogenated particles hydrotreated at a temperature above the disproportionation temperature in a hydrogen-containing atmosphere comprising Nd, Fe, Cu, 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 Cu and Cu;
A method of manufacturing a rare earth magnet comprising the steps of: melting the grain boundary phase at a temperature of 550 ° C. to 650 ° C. for a time of 30 minutes to 360 minutes to cause a reaction with the main phase to cause recrystallization.