JP2015142119A - Method for manufacturing rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a rare earth magnet high in relative density and superior in magnetic property.SOLUTION: A method for manufacturing a rare earth magnet comprises: a preparation step for preparing Sm-Fe based alloy powder having a main phase of a Sm-Fe based compound including Sm and Fe; a coating step for coating surfaces of particles of the Sm-Fe based alloy powder with a non-magnetic metal material; a thermal treatment step for performing a thermal treatment on the Sm-Fe based alloy powder coated with the metal material to form a surface layer including a metal element of the metal material for a surface layer of each of particles of the powder; a nitration step for obtaining Sm-Fe-N based alloy powder having a main phase of a Sm-Fe-N based compound by performing a nitriding treatment on the Sm-Fe based alloy powder with the surface layer formed thereon in a magnetic field to nitride the Sm-Fe based compound of the main phase; and a molding step for molding the Sm-Fe-N based alloy powder in a compression manner in a magnetic field to obtain a Sm-Fe-N based magnet.

Description

  The present invention relates to a method for producing a rare earth magnet. In particular, the present invention relates to a method for producing a rare earth magnet which is an Sm—Fe—N based magnet and has a high relative density and excellent magnetic properties.

For applications such as motors and generators, rare earth magnets using rare earth-iron alloys mainly containing a rare earth-iron compound containing rare earth elements and Fe are widely used. A typical rare earth magnet is an Nd—Fe—B based magnet (neodymium magnet) using an Nd—Fe—B based alloy having a Nd—Fe—B based compound (eg, Nd ₂ Fe ₁₄ B) as a main phase. It is. Except neodymium magnets, Sm-Fe-based compound _(e.g., Sm 2 _{Fe 17)} and Sm-Fe-based alloy as a main phase as a raw material, which Sm-Fe-N-based compound nitride _(eg, Sm 2 _{Fe 17} Sm—Fe—N magnets (samarium iron nitrogen magnets) using Sm—Fe—N alloys having N ₃ ) as the main phase have been put into practical use.

  Sm-Fe-N magnets have magnetic properties next to Nd-Fe-B magnets, and have better heat resistance than Nd-Fe-B magnets, so they can be used in high-temperature environments. . However, since the Sm—Fe—N alloy (Sm—Fe—N compound) decomposes at a high temperature exceeding 550 ° C. and loses its magnetic properties, the Sm—Fe—N alloy powder can be sintered. Have difficulty. Therefore, in general, Sm-Fe-N-based magnets are used as bonded magnets in which Sm-Fe-N-based alloy powder is mixed with a binder such as a resin or a low-melting-point metal, and this is compression-molded and solidified. .

Patent Document 1 proposes a method of manufacturing an Sm—Fe—N magnet as shown below. First, an Sm—Fe—N alloy magnet powder obtained by nitriding an Sm—Fe alloy (Sm ₂ Fe ₁₇ ), at least one metal oxide powder selected from Zn, Sn, Pb, and Bi, Granular Ca is mixed at a predetermined ratio. Next, after heating the mixture at a temperature of 300 ° C. to 1200 ° C. in an inert gas atmosphere, the reaction product is treated with water or a weak acid aqueous solution, so that the particle surface is coated with the metal powder. Get. And after compressing and molding the obtained magnet powder in a magnetic field, Sm-Fe-N type magnet is obtained by sintering on the conditions of 500 degreeC x 2 hours.

JP-A-5-326229

  Further improvement of the magnetic properties of rare earth magnets is desired. In particular, from the viewpoint of realizing high heat resistance and high magnetic force, improvements in coercive force iHc and residual magnetization Br, which are performance indicators of magnets, are required.

  The bond magnet has a low ratio (volume ratio) of the Sm—Fe—N alloy (Sm—Fe—N compound), which is a hard magnetic phase, as much as the binder is required, and has low magnetic properties such as residual magnetization. Therefore, it is desired to develop a technique for solidifying Sm—Fe—N alloy powder with high density in Sm—Fe—N magnets.

  In the method for producing an Sm—Fe—N magnet described in Patent Document 1, the above metal oxide and Ca are mixed and heated in a nitrided Sm—Fe—N alloy powder, and then the reaction product is produced. Is treated with water and a weak acid to coat the particle surface of the powder with the metal. As described above, since the Sm—Fe—N alloy is decomposed at a high temperature, in the manufacturing method described in Patent Document 1, the heating temperature is limited when the powder of the Sm—Fe—N alloy is heated. Moreover, the manufacturing method described in Patent Document 1 needs to mix Ca in order to reduce the oxide, or to treat the reaction product with a weak acid in order to separate the alloy powder and the Ca-containing component. Therefore, the manufacturing process is complicated and the cost is increased.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to provide a method for producing a rare earth magnet having a high relative density and excellent magnetic properties.

The method for producing a rare earth magnet of the present invention includes the following preparation step, coating step, heat treatment step, nitriding step, and forming step.
Preparatory process: The process of preparing the powder of the Sm-Fe-type alloy which uses the Sm-Fe-type compound containing Sm and Fe as a main phase.
Coating step: A step of coating the surface of the particles of the Sm—Fe alloy powder with a nonmagnetic metal material.
Heat treatment step: a step of heat-treating the Sm—Fe-based alloy powder coated with the metal material to form a surface layer containing the metal element of the metal material on the particle surface layer of the powder.
Nitriding step: nitriding the Sm-Fe-based alloy powder with the surface layer formed in a magnetic field and nitriding the Sm-Fe-based compound of the main phase, thereby producing a Sm-Fe-N-based compound as a main component. A step of obtaining Sm—Fe—N alloy powder as a phase.
Molding step: a step of compression-molding the Sm—Fe—N alloy powder in a magnetic field to obtain an Sm—Fe—N magnet.

  The method for producing a rare earth magnet of the present invention can provide a rare earth magnet having a high relative density and excellent magnetic properties.

  The inventors of the present invention coated a non-magnetic metal material on a powder of an Sm—Fe-based alloy, heat-treated to form a surface layer, and then nitriding and compressing this to increase the density of the magnet. And found that the magnetic properties can be improved. Based on the above findings, the present inventors have completed the present invention.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

(1) The manufacturing method of the rare earth magnet according to the embodiment includes the following preparation process, covering process, heat treatment process, nitriding process, and forming process.
Preparatory process: The process of preparing the powder of the Sm-Fe-type alloy which uses the Sm-Fe-type compound containing Sm and Fe as a main phase.
Coating step: A step of coating a non-magnetic metal material on the particle surface of the Sm-Fe alloy powder.
Heat treatment step: a step of heat-treating the Sm—Fe-based alloy powder coated with the metal material to form a surface layer containing the metal element of the metal material on the particle surface layer of the powder.
Nitriding step: Sm-Fe-N-based compound powder having a surface layer formed therein is nitrided in a magnetic field to nitride the Sm-Fe-based compound of the main phase, thereby using the Sm-Fe-N-based compound as the main phase. A step of obtaining a powder of an Sm—Fe—N alloy.
Molding step: a step of obtaining a Sm-Fe-N-based magnet by compression-molding a powder of an Sm-Fe-N-based alloy in a magnetic field.

  According to the above rare earth magnet manufacturing method, the surface of the Sm-Fe alloy powder is coated with a nonmagnetic metal material and then heat-treated, so that the metal element of the metal material is applied to the particle surface layer of the Sm-Fe alloy powder. The surface layer containing can be formed uniformly. Further, since the heat treatment is performed on the Sm—Fe-based alloy powder before nitriding, the heat treatment temperature is not limited to the thermal decomposition temperature of the Sm—Fe—N alloy. The metal material includes an alloy including a metal element in addition to a metal composed of a single metal element.

  The surface layer functions as a binder when compression-molding the Sm—Fe—N alloy powder. Most of the metal elements contained in the surface layer are considered to exist in the form of a compound by reacting with a part of Sm and Fe of the Sm—Fe based alloy (Sm—Fe based compound). Specifically, by heat-treating the Sm—Fe alloy powder coated with the metal material, at least a part of the metal element of the metal material diffuses into the particle surface layer of the powder, and the Sm—Fe alloy (Sm— It reacts with Sm and Fe in the Fe-based compound) to form a compound. When the surface layer contains the metal element and the compound of the metal element and Sm or Fe exists in the surface layer, the surface layer is soft and easily deformed. Therefore, when the Sm—Fe—N alloy powder is compression-molded, the surface layer is plastically deformed so that the particles can be bonded to each other, and the density can be increased. For example, a rare earth magnet having a relative density of 85% or more can be obtained. Therefore, a dense rare earth magnet having a high relative density and a high ratio of the hard magnetic phase can be obtained.

  Further, the surface layer contains the above-mentioned nonmagnetic metal element, and in the final magnet state, has a function of cutting the magnetic coupling between the particles of the Sm—Fe—N alloy powder, and has a coercive force. Improve magnetic properties. Specifically, when the particles of the Sm—Fe-based alloy powder are single crystal particles (particles consisting of only single main phase crystal grains), a surface layer is formed on the particle surface layer of the powder by heat treatment, and finally In addition, the surface layer is interposed at the boundary between the particles of the Sm—Fe—N alloy powder and functions to cut the magnetic coupling between the particles. On the other hand, when the particles of the Sm—Fe-based alloy powder are polycrystalline particles (particles composed of crystal grains of a plurality of main phases), a surface layer is formed on the particle surface layer of the powder by heat treatment, and the crystal grains of the main phase The metal element diffuses along the boundary to form a grain boundary phase containing the metal element. And finally, the surface layer is interposed at the boundary between the particles of the Sm—Fe—N based alloy powder to cut the magnetic coupling between the particles, and the grain boundary phase is the Sm—Fe—N based. It exists in the grain boundary of the main phase of the compound and works to break the magnetic coupling between the main phases.

  In addition, N is easily diffused by nitriding the Sm—Fe alloy powder in a magnetic field, and N is selectively introduced between Fe—Fe atoms in the crystal lattice of the main phase (Sm—Fe compound). It becomes easy. As a result, the nitriding reaction of the Sm—Fe compound is promoted, the Sm—Fe compound can be nitrided well, and the magnetic anisotropy is improved. Further, by compressing the Sm—Fe—N alloy powder in a magnetic field, the grains can be oriented with the crystal orientation of the main phase (Sm—Fe—N compound) aligned in the direction of the magnetic field. As a result, it is possible to obtain a rare earth magnet that easily aligns the easy magnetization axis (c-axis) of the Sm—Fe—N-based compound in one direction, has high magnetic anisotropy, and excellent magnetic properties.

  The coating of the metal material on the particle surface of the Sm-Fe-based alloy powder in the coating step is, for example, (a) depositing the metal material on the particle surface of the Sm-Fe-based alloy powder by a vapor phase method, or (B) It may be performed by mixing the powder of the Sm—Fe alloy and the powder of the metal material.

  (2) As one form of the manufacturing method of the rare earth magnet, in the coating step, the metal material is coated on the particle surface of the Sm—Fe based alloy powder. Is performed by vapor deposition by a vapor phase method.

  (3) As one form of the manufacturing method of the rare earth magnet, in the coating step, the coating of the metal material on the particle surface of the Sm—Fe based alloy powder is performed by using the Sm—Fe based alloy powder, the metallic material powder, Is performed by mixing.

  By depositing the metal material on the particle surface of the Sm-Fe-based alloy powder by a vapor phase method, or mixing the Sm-Fe-based alloy powder and the powder of the metal material, particles of the Sm-Fe-based alloy powder are obtained. A metal material can be satisfactorily coated on the surface. Vapor deposition of the metal material on the particle surface of the Sm-Fe alloy powder is more effective on the particle surface of the powder than when the Sm-Fe alloy powder and the metal material powder are mixed. There is an advantage that it is easy to uniformly coat the metal material.

  (4) As one form of the manufacturing method of the rare earth magnet, the metal material is a metal composed of at least one metal element selected from Cu, Zn, Al, Sn, Nb, Zr, and Ti, or a metal thereof It is mentioned that it is an alloy containing an element.

  The metal material is suitable as a surface layer forming material by containing at least one selected from Cu, Zn, Al, Sn, Nb, Zr, and Ti as a metal element. Specifically, the metal element is easily diffused into the particle surface layer of the powder by heat treatment after coating the particle surface of the Sm—Fe-based alloy powder, and a uniform surface layer is easily formed. Further, the metal element easily reacts with Sm or Fe to form a compound, and a relatively soft surface layer is easily formed. Furthermore, the metal element is non-magnetic, and the surface layer (including the grain boundary phase in the case of polycrystalline particles) contains the metal element, so that the particles of the Sm—Fe—N alloy powders (grain boundary In the case of the phase, it is possible to effectively break the magnetic coupling of the main phases of the Sm—Fe—N compound).

(5) as a form of the method for manufacturing the rare earth magnet, the _alloy, Cu ₆ Sn 5, CuTi, CuAl, and the like be at least one alloy selected from TiZn _5.

  The above alloy is suitable as a material for forming the surface layer. Examples of the other alloy include an alloy of Sm and the above metal element (any one of Cu, Zn, Al, Sn, Nb, Zr, and Ti).

  (6) As one form of the manufacturing method of the said rare earth magnet, in the said heat processing process, heat processing is mentioned so that the thickness of a surface layer may be 1 nm or more and 27 nm or less.

  When the thickness of the surface layer is 1 nm or more, the surface layer is easily plastically deformed when the Sm—Fe—N alloy powder is compression-molded, and the particles are easily bonded to each other. That is, the surface layer easily exhibits a function as a binder when the Sm—Fe—N alloy powder is compression-molded, the compression molding is facilitated, and a dense rare earth magnet having a high relative density is easily obtained. Further, when the thickness of the surface layer is 1 nm or more, the magnetic coupling between the particles of the Sm—Fe—N alloy powder can be sufficiently separated, and the magnetic characteristics can be effectively improved. . On the other hand, when the thickness of the surface layer is 27 nm or less, when the Sm—Fe-based alloy powder is nitrided, the surface layer hardly inhibits the diffusion of N, and the Sm—Fe-based compound can be sufficiently nitrided. Moreover, since the thickness of the surface layer is 27 nm or less, the ratio (volume ratio) of the surface layer (compound of metal element of the metal material and Sm or Fe) in the particles of the Sm—Fe—N alloy powder is reduced. A decrease in magnetic properties due to the increase can be suppressed. Furthermore, the production | generation of (alpha) -Fe by the erosion of the metal element of the said metal material can be suppressed, and the fall of the magnetic characteristic resulting from the production | generation of (alpha) -Fe can be suppressed.

  The thickness of the surface layer can be appropriately adjusted by controlling the heat treatment conditions in the heat treatment step, and the thickness of the surface layer increases as the heat treatment temperature is increased or the heat treatment time is increased. Tend. The heat treatment temperature is preferably set as appropriate according to the type of the metal material coated on the surface of the Sm—Fe-based alloy powder.

  (7) As one form of the manufacturing method of the rare earth magnet, in the nitriding treatment step, the strength of the magnetic field is 3T or more and 12T or less.

  By setting the strength of the magnetic field to 3 T or more, N easily penetrates the surface layer and diffuses into the particles, promotes the nitriding reaction of the Sm—Fe-based compound, and sufficiently nitrifies the Sm—Fe-based compound. On the other hand, by setting the intensity of the magnetic field to 12 T or less, inhibition of the nitriding reaction due to excessive increase in the diffusion rate of N can be suppressed, and deterioration in magnetic characteristics can be suppressed. Moreover, the production | generation of (alpha) -Fe and a-Sm ("a-" means an amorphous) by excessive nitriding can be suppressed, and the fall of a magnetic characteristic can be suppressed.

[Details of the embodiment of the present invention]
The specific example of the manufacturing method of the rare earth magnet which concerns on embodiment of this invention is demonstrated. In addition, this invention is not limited to these illustrations, is shown by the claim, and is intended that all the changes within the meaning and range equivalent to the claim are included.

<Rare earth magnet manufacturing method>
The method for manufacturing a rare earth magnet includes a preparation step, a covering step, a heat treatment step, a nitriding step, and a forming step. Hereinafter, each step will be described in detail.

(Preparation process)
The preparation step is a step of preparing a powder of an Sm—Fe based alloy containing a Sm—Fe based compound containing Sm and Fe as a main phase. The Sm—Fe alloy typically includes Sm ₂ Fe ₁₇ alloy containing Sm and Fe as main components and Sm ₂ Fe ₁₇ as a main phase. The Sm—Fe-based alloy can be manufactured by a casting method or a reduction diffusion method. Examples of the casting method include rapid solidification methods such as a melt span method and a strip cast method.

<Sm-Fe alloy>
The Sm—Fe alloy contains Sm as an essential element as a rare earth element. The Sm content is preferably 25% by mass or more and 26.5% by mass or less. By setting the Sm content within the above range, an Sm—Fe compound having a stoichiometric composition of Sm ₂ Fe ₁₇ can be easily obtained. Further, a part of Sm may be substituted with another rare earth element. Examples of other rare earth elements to be substituted include at least one rare earth element selected from Nd, Dy, Pr, Tb, Ce, and Y. When substituting a part of Sm with another rare earth element, the amount of substitution with respect to Sm is preferably less than 50 atomic%, more preferably 30 atomic% or less, in order to avoid deterioration of magnetic properties.

  In the Sm—Fe based alloy, a part of Fe may be substituted with at least one element selected from, for example, Co, Ni, Ga, Cu, Al, Si, Ti, Mn, and Nb. For example, heat resistance can be improved by replacing part of Fe with Co. However, when a part of Fe is substituted with the above element, the substitution amount with respect to Fe is preferably less than 50 atomic%, more preferably 35 atomic%, since the magnetic property is deteriorated when the substitution amount is excessive. It is as follows. For example, when a part of Fe is replaced with Co, the Co content in the Sm—Fe-based alloy is preferably 6% by mass or less.

<Sm-Fe alloy powder>
Sm—Fe based alloy powder can be obtained by appropriately pulverizing the Sm—Fe based alloy. For the pulverization of the Sm—Fe alloy, a known pulverizer such as a jet mill, a hammer mill, a pin mill, a disk mill, or a jaw crusher can be used. The particle diameter of the Sm—Fe-based alloy powder is, for example, 0.5 μm or more and 50 μm or less, particularly 1 μm or more and 30 μm or less, from the viewpoint of easy nitriding in the subsequent nitriding step or compression forming in the forming step. It is preferable. Here, the particle diameter of the Sm—Fe-based alloy powder is a particle diameter value (D50: 50) in which accumulation is 50% from the small diameter side of the volume-based particle size distribution when measured by a laser diffraction particle size distribution measuring device. Volume% particle size). The particles constituting the Sm—Fe-based alloy powder may be single crystal particles or polycrystalline particles.

In addition, the Sm—Fe alloy or powder thereof may be subjected to HDDR (Hydrogenation Deposition Decomposition Recombination) treatment (hydrogenation / disproportionation / dehydrogenation / recombination). The HDDR treatment is a Sm—Fe-based compound (eg, Sm ₂ Fe ₁₇₎ of a main phase by heat-treating a Sm—Fe-based alloy or a powder thereof in a hydrogen-containing atmosphere by heat-treating at or above the disproportionation temperature. ) Is decomposed into a phase of Sm hydride (SmH ₂ ) and Fe. Then, it is the process which recombines the hydrocracked Sm-Fe-type compound by heat-processing in an inert atmosphere or a pressure-reduced atmosphere above a recombination temperature, and dehydrogenating. By this treatment, the crystal grains of the main phase are refined, and a polycrystalline structure (polycrystal particles) composed of fine main phase crystal grains having an average crystal grain size of 500 nm or less is obtained. In the case of HDDR-treated HDDR powder, the crystal grain size of the main phase is usually about 100 nm to 300 nm. Known conditions can be applied to the HDDR treatment conditions (temperature and time of heat treatment for hydrogenation, temperature and time of heat treatment for dehydrogenation). The temperature of the heat treatment for hydrogenation is, for example, 600 ° C. or higher (more 650 ° C. or higher) 1100 ° C. or lower, preferably 700 ° C. or higher (further 750 ° C. or higher) 950 ° C. or lower (further 900 ° C. or lower). The heat treatment time for hydrogenation is, for example, 30 minutes or more and 5 hours or less. The temperature of the heat treatment for dehydrogenation is, for example, 600 ° C. or higher (further 650 ° C. or higher, particularly 700 ° C. or higher) 1000 ° C. or lower. The heat treatment time for dehydrogenation is, for example, 10 minutes or more and 10 hours or less.

(Coating process)
The coating step is a step of coating the surface of the particles of the Sm—Fe-based alloy powder with a nonmagnetic metal material. The coating of the metal material on the particle surface of the Sm-Fe-based alloy powder is, for example, (1) depositing the metal material on the particle surface of the Sm-Fe-based alloy powder by a vapor phase method, or (2) Sm- It may be performed by mixing the powder of the Fe-based alloy and the powder of the metal material.

<Coating by vapor phase method (evaporation)>
The metal material can be coated on the particle surface of the Sm-Fe alloy powder by vapor-depositing the metal material on the particle surface of the Sm-Fe alloy powder. Specific examples of the vapor phase method include a physical vapor deposition (PVD) method such as a vacuum vapor deposition method, a sputtering method, and an ion plating method, and a chemical vapor deposition (CVD) method. By vapor-depositing a metal material by a vapor phase method, it is easy to uniformly coat the metal material on the particle surface of the Sm-Fe alloy powder. What is necessary is just to set suitably the thickness of the metal material vapor-deposited (coating) on the particle | grain surface of Sm-Fe type alloy powder according to the thickness of the surface layer formed by the heat treatment process of a post process, and the thickness of the metal material to coat | cover For example, the thickness may be 1 nm or more and 27 nm or less. In addition, the vapor deposition is preferably performed in a vacuum atmosphere from the viewpoint of preventing oxidation of the Sm—Fe-based alloy powder and entry of impurities.

<Coating by mixing>
By mixing the powder of the Sm-Fe alloy and the powder of the metal material, the particles of the metal material adhere to and coat the particle surfaces of the Sm-Fe alloy powder. For mixing the powder of the Sm—Fe alloy and the powder of the metal material, for example, various mixers / mixers such as a ball mill and a V-type mixer can be used. What is necessary is just to set the addition amount of the powder of a metal material suitably according to the thickness of the surface layer formed by the heat treatment process of a post process, and the addition amount of a metal material shall be 3 mass% or more and 10 mass% or less, for example Is mentioned. Although the particle diameter of the metal material powder is not particularly limited, it may be less than or equal to the particle diameter of the Sm—Fe-based alloy powder. The particle diameter of the metal material powder is 50% by volume (D50), similar to the particle diameter of the Sm—Fe alloy powder. What is necessary is just to set mixing conditions suitably so that the particle | grains of the powder of a metal material may adhere uniformly to the particle | grain surface of Sm-Fe-type alloy powder, and mixing time shall be 3 hours or more and 15 hours or less, for example. . Further, the mixing is preferably performed in an inert atmosphere, specifically, in an inert gas atmosphere such as Ar or N ₂ from the viewpoint of preventing oxidation of the Sm—Fe based alloy powder.

<Coating material>
The metal material used for the coating material may be a metal composed of a single metal element or an alloy containing a metal element. Examples of the metal material include a metal composed of at least one metal element selected from Cu, Zn, Al, Sn, Nb, Zr, and Ti, or an alloy containing the metal element. As the _{alloy, Cu 6 Sn 5, CuTi,} CuAl, and at least one alloys are selected from TiZn _5. These metal materials are suitable as a material for forming the surface layer described later.

(Heat treatment process)
The heat treatment step is a step of heat-treating the Sm—Fe-based alloy powder coated with the metal material to form a surface layer containing the metal element of the metal material on the particle surface layer of the powder. The surface layer containing the metal element of the metal material can be uniformly formed on the particle surface layer of the Sm-Fe-based alloy powder by performing heat treatment after coating the surface of the particle of the Sm-Fe-based alloy powder.

<Surface layer>
The metal element contained in the surface layer is considered to exist in the form of a compound by reacting with a part of Sm or Fe of the Sm—Fe based alloy (Sm—Fe based compound). Specifically, by heat treatment, at least a part of the metal element of the metal material coated on the particle surface of the Sm—Fe—N alloy powder is diffused into the particle surface layer of the powder, and the Sm—Fe alloy (Sm— It reacts with Sm and Fe in the Fe-based compound) to form a compound. When the metal material contains at least one selected from Cu, Zn, Al, Sn, Nb, Zr, and Ti as a metal element, the metal element is easily diffused into the particle surface layer by heat treatment, and a uniform surface layer is formed. Easy to do.

  The surface layer functions as a binder when compression-molding the Sm—Fe—N-based alloy powder in a subsequent forming step. The surface layer contains a metal element, and the presence of a compound of the metal element and Sm or Fe in the surface layer makes the surface layer soft and easily deformed. In particular, the metal elements (Cu, Zn, Al, Sn, Nb, Zr, and Ti) easily react with Sm and Fe to form a compound, and a relatively soft surface layer is easily formed. Therefore, when the Sm—Fe—N alloy powder is compression-molded, the surface layer is plastically deformed so that the particles can be bonded to each other, and the density can be increased. For example, a rare earth magnet having a relative density of 85% or more can be obtained. Therefore, a dense rare earth magnet having a high relative density and a high ratio of the hard magnetic phase can be obtained.

  Further, the surface layer contains a non-magnetic metal element, and in the final magnet state, it has a function of cutting the magnetic coupling between the particles of the Sm-Fe-N alloy powder, and has a magnetic property. Improve. Specifically, when the particles of the Sm—Fe-based alloy powder are single crystal particles (particles consisting of only single main phase crystal grains), a surface layer is formed on the particle surface layer of the powder by heat treatment, and finally In addition, the surface layer is interposed at the boundary between the particles of the Sm—Fe—N alloy powder and functions to cut the magnetic coupling between the particles. On the other hand, when the particles of the Sm—Fe-based alloy powder are polycrystalline particles (particles composed of crystal grains of a plurality of main phases), a surface layer is formed on the particle surface layer of the powder by heat treatment, and the crystal grains of the main phase A grain boundary phase containing a metal element is formed by diffusing the metal element along the boundary. And finally, the surface layer is interposed at the boundary between the particles of the Sm—Fe—N based alloy powder to cut the magnetic coupling between the particles, and the grain boundary phase is the Sm—Fe—N based. It exists in the grain boundary of the main phase of the compound and works to break the magnetic coupling between the main phases. In particular, the metal elements (Cu, Zn, Al, Sn, Nb, Zr, and Ti) are all non-magnetic, and the surface layer (including the grain boundary phase in the case of polycrystalline particles) contains the metal element. By doing so, it is possible to effectively break the magnetic coupling between the particles of the Sm—Fe—N alloy powder (in the case of a grain boundary phase, the main phases of the Sm—Fe—N compound). .

<Surface layer thickness>
The thickness of the surface layer is preferably 1 nm or more and 27 nm or less. By setting the thickness of the surface layer to 1 nm or more, the surface layer is easily plastically deformed when the Sm—Fe—N alloy powder is compression-molded, and the particles are easily bonded to each other. That is, the surface layer easily exhibits a function as a binder when the Sm—Fe—N alloy powder is compression-molded, the compression molding is facilitated, and a dense rare earth magnet having a high relative density is easily obtained. Further, by setting the thickness of the surface layer to 1 nm or more, it is possible to sufficiently break the magnetic coupling between the particles of the Sm—Fe—N-based alloy powder, and to effectively improve the magnetic characteristics. . On the other hand, when the thickness of the surface layer is set to 27 nm or less, the Sm—Fe compound is difficult to inhibit the diffusion of N when the Sm—Fe alloy powder is nitrided in the nitriding process in the subsequent step. Can be sufficiently nitrided. Further, by setting the thickness of the surface layer to 27 nm or less, the ratio (volume ratio) of the surface layer (compound of metal element of metal material and Sm or Fe) in the particles of the Sm—Fe—N alloy powder is increased. It is possible to suppress a decrease in magnetic properties due to the operation. In other words, it is possible to suppress a decrease in magnetic properties due to a decrease in the ratio of the Sm—Fe—N-based compound (eg, Sm ₂ Fe ₁₇ N ₃ ) that is a hard magnetic phase. Furthermore, the production | generation of (alpha) -Fe by the erosion of the metal element of a metal material can be suppressed, and the fall of the magnetic characteristic resulting from the production | generation of (alpha) -Fe can be suppressed.

<Heat treatment>
The heat treatment is preferably performed so that the thickness of the surface layer is 1 nm to 27 nm. The thickness of the surface layer can be adjusted as appropriate by controlling the conditions of the heat treatment. For example, the thickness of the surface layer tends to increase as the heat treatment temperature is increased or the heat treatment time is increased. There is. In particular, when the heat treatment temperature is raised to some extent, the metal element of the metal material coated on the particle surface of the Sm—Fe—N alloy powder is sufficiently diffused into the particle surface layer of the powder and reacts with Sm and Fe to form a compound. It is easy to form a surface layer. If the heat treatment temperature is too low, the metal element is not sufficiently diffused and it is difficult to form a surface layer having a predetermined thickness. On the other hand, if the heat treatment temperature is too high, the diffusion of the metal element proceeds too much, and the thickness of the surface layer becomes too thick, or α-Fe is likely to be generated.

  The heat treatment temperature is preferably set as appropriate according to the type of metal material coated on the surface of the Sm—Fe-based alloy powder. An example of the range of the heat treatment temperature according to various metal materials is shown below.

Cu: more than 620 ° C. and less than 750 ° C., preferably 630 ° C. or more and 730 ° C. or less Zn: more than 430 ° C. and less than 500 ° C., preferably 440 ° C. or more and 490 ° C. or less Al: more than 680 ° C. and less than 800 ° C., preferably 700 ° C. or more and 780 ° C. Sn: More than 650 ° C. and less than 830 ° C., preferably 660 ° C. or more and 800 ° C. or less Nb: More than 700 ° C. and less than 810 ° C., preferably 720 ° C. or more and 800 ° C. or less Zr: More than 660 ° C. and less than 790 ° C., preferably 680 ° C. or more and 780 ° C. Ti: 710 ° C. or more and less than 850 ° C., preferably 730 ° C. or more and 830 ° C. or less Cu ₆ Sn ₅ : 570 ° C. or more and less than 690 ° C., preferably 590 ° C. or more and 670 ° C. or less CuTi: More than 650 ° C. and less than 770 ° C., preferably 660 ° C. or higher and 750 ° C. or lower CuAl: Over 640 ° C. and lower than 760 ° C., preferably 650 ° C. or higher and 740 ° C. or lower iZn _5: 600 ℃ ultra 720 below ° C., preferably not more than 700 ° C. 610 ° C. or higher

  The heat treatment time may be set as appropriate so that the thickness of the surface layer falls within the above range, and may be 0.5 hours or more and 2 hours or less, for example, depending on the heat treatment temperature. Moreover, it is preferable to perform heat processing in inert gas atmosphere, specifically, inert gas atmosphere, such as Ar, from a viewpoint of preventing the oxidation of Sm-Fe type alloy powder.

(Nitriding process)
In the nitriding step, the Sm—Fe—N based compound powder having the surface layer formed therein is nitrided in a magnetic field to nitride the Sm—Fe based compound of the main phase, thereby making the Sm—Fe—N based compound a main phase. This is a step of obtaining Sm—Fe—N alloy powder. Typically, Sm ₂ Fe ₁₇ is nitrided to Sm ₂ Fe ₁₇ N ₃ .

<Nitriding treatment>
The nitriding treatment may be performed by performing a heat treatment in a nitrogen-containing atmosphere at a nitriding temperature or higher. Examples of the nitrogen-containing atmosphere include an N ₂ gas atmosphere, a mixed gas atmosphere of N ₂ gas and H ₂ gas, an NH ₃ gas atmosphere, or a mixed gas atmosphere of NH ₃ gas and H ₂ gas. Moreover, the temperature of the heat treatment at the time of nitriding is, for example, 200 ° C. or higher (preferably 300 ° C. or higher) and 550 ° C. or lower (preferably 500 ° C. or lower).

Furthermore, by performing the nitriding treatment in a magnetic field, it is easy for N to diffuse and to selectively introduce N between Fe—Fe atoms in the crystal lattice of the main phase (Sm—Fe-based compound). As a result, the nitriding reaction of the Sm—Fe compound is promoted, the Sm—Fe compound can be nitrided well, and the magnetic anisotropy is improved. In particular, the strength of the magnetic field is preferably 3T or more and 12T or less. By setting the strength of the magnetic field to 3 T or more, N easily penetrates the surface layer and diffuses into the particles, promotes the nitriding reaction of the Sm—Fe-based compound, and sufficiently nitrifies the Sm—Fe-based compound. In addition, it is possible to suppress a decrease in moldability due to the remaining Sm—Fe-based compound (eg, Sm ₂ Fe ₁₇ ) in the subsequent molding step. On the other hand, by setting the intensity of the magnetic field to 12 T or less, inhibition of the nitriding reaction due to excessive increase in the diffusion rate of N can be suppressed, and deterioration in magnetic characteristics can be suppressed. Moreover, the production | generation of (alpha) -Fe and a-Sm by excessive nitriding can be suppressed, and the fall of a magnetic characteristic can be suppressed. In addition, the composition distribution of the crystal phase of the Sm—Fe—N-based alloy powder is less likely to be biased due to the influence of the magnetic field, and a decrease in formability due to the bias of the composition distribution of the crystal phase can be suppressed. For the application of the magnetic field, for example, a known magnetic field application device such as a superconducting magnet or a normal conducting magnet can be used. If a superconducting magnet is used, it is easy to apply a strong magnetic field of 3T or more.

(Molding process)
The forming step is a step in which an Sm—Fe—N-based magnet is obtained by compression-molding an Sm—Fe—N-based alloy powder in a magnetic field.

<Compression molding>
Conditions of the compression molding, from the viewpoint of increasing the density of the magnet, the molding pressure for example 294MPa (3ton / cm ²⁾ or more 1960MPa (20ton / cm ²⁾ include to be less. More preferred molding pressure is, 588MPa (6ton / cm ²⁾ or more, and 980MPa (10ton / cm ²⁾ or more. The higher the molding pressure, the easier it is to obtain a rare earth magnet with a higher relative density. The relative density of the rare earth magnet is preferably 80% or more, and more preferably 85% or more and 90% or more. A higher relative density is preferable in that a rare earth magnet having a dense and hard magnetic phase ratio can be obtained. Here, the relative density _(in the case of Sm _{2 Fe} 17 _{N 3,} about ^{7.92g / cm 3) Sm-Fe} -N -based true density of the alloy actual density to ([ "bulk density of the magnet" / " It is the percentage of the true density of the alloy.

  Furthermore, by performing compression molding in a magnetic field, it is possible to align the crystal orientation of the main phase (Sm—Fe—N compound) in the direction of the magnetic field and to orient the particles. As a result, it is possible to obtain a rare earth magnet that easily aligns the easy magnetization axis (c-axis) of the Sm—Fe—N-based compound in one direction, has high magnetic anisotropy, and excellent magnetic properties. The magnetic field strength of the magnetic field is preferably, for example, 3.99 kA / cm or more, more preferably 7.98 kA / cm or more, 23.9 kA / cm or more. The higher the magnetic field strength, the easier it is to align the crystal orientation of the particles in the direction of the magnetic field. However, if the magnetic field strength is increased too much, no further effect can be expected. And so on. The direction of the magnetic field is not particularly limited, and examples thereof include a direction parallel to the compression direction and a perpendicular direction. In addition, by appropriately heating the molding die during compression molding, deformation of the powder is promoted, and high density is facilitated.

[Example 1]
An Sm-Fe-based alloy having a composition containing 25% by mass of Sm and the balance of Fe and inevitable impurities was manufactured, and pulverized to prepare an Sm-Fe-based alloy powder. The Sm-Fe alloy was produced by melting and casting a raw material containing Sm and Fe so as to have the above composition by a strip casting method. Further, in this example, this Sm—Fe alloy was subjected to HDDR treatment. Thereafter, this Sm—Fe alloy was pulverized and then sieved to obtain a raw material powder of an Sm—Fe alloy having a particle diameter (D50) of 1.0 μm. The Sm-Fe-based alloy _{is Sm} 2 _{Fe 17} alloy as a main phase of Sm 2 _{Fe 17.}

The prepared Sm ₂ Fe ₁₇ alloy powder was used as a raw material powder, and the production conditions were changed to produce a rare earth magnet (Sm—Fe—N based magnet). 1-1-No. 1-4 and No.1. 1-11-No. 1-14 was obtained. And the magnet characteristic was evaluated about the sample of the obtained magnet.

<Sample No. 1-1>
Zn was deposited on the surface of the particles of the Sm ₂ Fe ₁₇ alloy powder by a vacuum deposition method to cover the Zn. The thickness of the coated Zn is 18 nm. Thereafter, the Zn-coated Sm ₂ Fe ₁₇ alloy powder was heat-treated at 450 ° C. for 1 hour in an Ar gas atmosphere.

A part of the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was collected, and crystal phase analysis was performed using an X-ray diffractometer (XRD; SmartLab, manufactured by Rigaku Corporation). As a result of the analysis, Sm ₂ Fe ₁₇ and Fe ₃ Zn ₁₀ were present. Further, a part of the Sm ₂ Fe ₁₇ alloy powder was embedded in a resin and polished to prepare an observation sample, and a cross section thereof was observed with a transmission electron microscope (TEM; H-9500 manufactured by Hitachi High-Technologies Corporation). And the thickness of the surface layer containing Zn was calculated | required from the elemental mapping by the energy dispersive X-ray analyzer (EDX) attached to TEM. Specifically, line analysis was performed from the powder particle surface toward the center, and the thickness of the surface layer containing Zn was measured. Here, the thickness of the surface layer was measured at 10 or more points per particle, the thickness of the surface layer was determined for at least 10 particles, and the average value was obtained. As a result, the thickness of the surface layer was 19 nm. From the TEM image of the cross section and the elemental mapping of Zn, it was confirmed that the surface layer was uniformly formed over the entire circumference of the particle.

Furthermore, from the TEM image of the cross section and the elemental mapping of Zn, the particles of this Sm ₂ Fe ₁₇ alloy powder are polycrystalline particles composed of crystal grains of a plurality of main phases (Sm ₂ Fe ₁₇ ), and Zn is present at the grain boundaries. It was confirmed that a grain boundary phase containing was formed. The grain boundary phase was present uniformly around the main phase crystal grains. Further, the crystal grain size of the main phase was determined from the TEM image of the cross section. For the crystal grain size of the main phase, the equivalent area circle equivalent diameter of each crystal grain was calculated and averaged for at least 10 grains. As a result, the crystal grain size of the main phase was about 300 nm.

Next, the Sm ₂ Fe ₁₇ alloy powder on which the surface layer was formed was subjected to nitriding treatment at 400 ° C. for 10 hours in a mixed gas atmosphere having a volume concentration ratio of NH ₃ gas and H ₂ gas of 1: 3. The nitriding treatment was performed while applying a 3T magnetic field.

As a result of crystal phase analysis of a part of the Sm ₂ Fe ₁₇ alloy powder after nitriding by XRD, Sm ₂ Fe ₁₇ N ₃ and Fe ₃ Zn ₁₀ were present. That is, the alloy powder _is a powder of _Sm 2 _Fe 17 _{N 3} alloy of which main phase Sm _{2 Fe} 17 _{N 3.}

Finally, Sm ₂ Fe ₁₇ N ₃ alloy powder was subjected to high pressure press molding by applying a surface pressure of 980 MPa in a magnetic field of 13.5 kA / cm, and Sm ₂ Fe ₁₇ N ₃ alloy powder was compression molded. -N magnets were produced. This magnet is connected to sample No. 1-1.

<Sample No. 1-2>
The coating material was changed to Cu, and an Sm—Fe—N magnet was produced.

Cu was deposited on the surface of the particles of the Sm ₂ Fe ₁₇ alloy powder by a vacuum deposition method to cover the Cu. The thickness of the coated Cu is 4.3 nm. Thereafter, the Cu-coated Sm ₂ Fe ₁₇ alloy powder was heat-treated at 700 ° C. for 0.5 hour in an Ar gas atmosphere. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was analyzed by XRD to find that Sm ₂ Fe ₁₇ and SmCu ₅ were present. Moreover, when the thickness of the surface layer containing Cu was calculated | required by TEM analysis, the thickness of the surface layer was 5.0 nm. Further, from the cross-sectional TEM image and Cu element mapping, the sample No. As in 1-1, it was confirmed that the surface layer was formed uniformly over substantially the entire circumference of the particle, and a grain boundary phase containing Cu was formed at the crystal grain boundary.

Next, the Sm ₂ Fe ₁₇ alloy powder with the surface layer formed thereon was subjected to nitriding treatment at 450 ° C. for 8 hours in a mixed gas atmosphere in which the volume concentration ratio of NH ₃ gas and H ₂ gas was 1: 3. The nitriding treatment was performed while applying a 5T magnetic field. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ N ₃ , SmCu ₅ , Cu, and a-Sm were present. It is considered that the reason why Cu and a-Sm were produced was that a part of SmCu ₅ reacted with N and decomposed into Cu and a-Sm during nitriding.

Finally, sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet is connected to sample No. 1-2.

<Sample No. 1-3>
The coating material was changed to Al, and an Sm—Fe—N magnet was produced.

Al was deposited on the particle surfaces of the Sm ₂ Fe ₁₇ alloy powder by a vacuum deposition method to coat the Al. The thickness of the coated Al is 1 nm. Thereafter, the Al-coated Sm ₂ Fe ₁₇ alloy powder was heat-treated at 750 ° C. for 0.5 hour in an Ar gas atmosphere. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ and FeAl ₃ were present. Moreover, when the thickness of the surface layer containing Al was calculated | required by TEM analysis, the thickness of the surface layer was 1.3 nm. Further, from the TEM image of the cross section and the elemental mapping of Al, the sample No. As in 1-1, it was confirmed that the surface layer was formed uniformly over substantially the entire circumference of the particle, and a grain boundary phase containing Al was formed at the crystal grain boundary.

Next, the Sm ₂ Fe ₁₇ alloy powder having the surface layer formed thereon was subjected to nitriding treatment at 475 ° C. for 12 hours in a mixed gas atmosphere in which the volume concentration ratio of NH ₃ gas and H ₂ gas was 1: 4. The nitriding treatment was performed while applying a 5T magnetic field. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ N ₃ and FeAl ₃ were present.

Finally, sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet is connected to sample No. 1-3.

<Sample No. 1-4>
The coating material was changed to Cu ₆ Sn ₅ to produce an Sm—Fe—N magnet.

Cu ₆ Sn ₅ was deposited on the particle surface of the Sm ₂ Fe ₁₇ alloy powder by a vacuum deposition method to cover the Cu ₆ Sn ₅ . The thickness of the coated Cu ₆ Sn ₅ is 6.5 nm. Thereafter, the Sm ₂ Fe ₁₇ alloy powder coated with Cu ₆ Sn ₅ was heat-treated at 630 ° C. for 1 hour in an Ar gas atmosphere. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ , SmCu ₅ and Cu ₆ Sn ₅ were present. Moreover, when the thickness of the surface layer containing Cu or Sn was determined by TEM analysis, the thickness of the surface layer was 7.2 nm. Furthermore, from the TEM image of the cross section and elemental mapping of Cu and Sn, sample No. As in 1-1, it was confirmed that the surface layer was uniformly formed over the entire circumference of the particle, and a grain boundary phase containing Cu or Sn was formed at the crystal grain boundary. .

Next, the Sm ₂ Fe ₁₇ alloy powder on which the surface layer was formed was subjected to nitriding treatment at 420 ° C. for 8 hours in a mixed gas atmosphere in which the volume concentration ratio of NH ₃ gas and H ₂ gas was 1: 3. The nitriding treatment was performed while applying a 4T magnetic field. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after nitriding was analyzed by XRD, and as a result, Sm ₂ Fe ₁₇ N ₃ , SmCu ₅ , Cu ₆ Sn ₅ , Cu, a-Sm, and Sn were Existed. The reason why Cu, a-Sm, and Sn were generated is that a part of SmCu ₅ and Cu ₆ Sn ₅ reacted with N and decomposed into Cu and a-Sm and Cu and Sn, respectively, during nitriding. It is considered a thing.

Finally, sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet is connected to sample No. 1-4.

<Sample No. 1-11, No. 1 1-12>
Except for changing the heat treatment conditions in the heat treatment step, Sample No. An Sm—Fe—N-based magnet was produced under the same production conditions as 1-1.

Sample No. In _1-11, after covering by vacuum deposition of Zn on the surface of the particles of the Sm 2 _{Fe 17} alloy powder, a _Sm 2 _{Fe 17} alloy powder Zn is coated, in an Ar gas atmosphere, and heat-treated for 1 hour at 500 ° C. . Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ , Fe ₃ Zn ₁₀ , and α-Fe were present. Moreover, when the thickness of the surface layer was calculated | required by TEM analysis, the thickness of the surface layer was 43 nm.

Next, sample No. The Sm ₂ Fe ₁₇ alloy powder on which the surface layer was formed was nitrided under the same nitriding conditions as 1-1. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after nitriding was analyzed by XRD, and as a result, Sm ₂ Fe ₁₇ N ₃ , Fe ₃ Zn ₁₀ , α-Fe, Sm ₂ Fe ₁₇ was present. It was.

Finally, sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet was connected to Sample No. 1-11.

Sample No. In _1-12, after covering by vacuum deposition of Zn on the surface of the particles of the Sm 2 _{Fe 17} alloy powder, a _Sm 2 _{Fe 17} alloy powder Zn is coated, in an Ar gas atmosphere, 0.5 hours at 430 ° C. Heat treated. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after heat treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ and Fe ₃ Zn ₁₀ were present. Moreover, when the thickness of the surface layer was calculated | required by TEM analysis, the thickness of the surface layer was 0.5 nm.

Next, sample No. The Sm ₂ Fe ₁₇ alloy powder on which the surface layer was formed was nitrided under the same nitriding conditions as 1-1. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ N ₃ and Fe ₃ Zn ₁₀ were present.

Finally, sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet is connected to sample No. 1-12.

<Sample No. 1-13, No. 1 1-14>
Except for changing the nitriding conditions in the nitriding step (specifically, the strength of the applied magnetic field), the sample No. An Sm—Fe—N-based magnet was produced under the same production conditions as 1-1.

Sample No. 1-13, No. 1 In No. 1-14, after coating the surface of the particles of the Sm ₂ Fe ₁₇ alloy powder with Zn by a vacuum deposition method, The Sm ₂ Fe ₁₇ alloy powder coated with Zn was heat-treated under the same heat treatment conditions as 1-1. The result of XRD crystal phase analysis of the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was Sm ₂ Fe ₁₇ and Fe ₃ Zn ₁₀ and the thickness of the surface layer was 19 nm.

Sample No. In No. 1-13, the Sm ₂ Fe ₁₇ alloy powder having the surface layer formed thereon was subjected to 400 in a mixed gas atmosphere having a volume concentration ratio of NH ₃ gas and H ₂ gas of 1: 3 while applying a 1T magnetic field. Nitriding was performed at a temperature of 10 ° C. for 10 hours. Sample No. As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ N ₃ , Fe ₃ Zn ₁₀ , and Sm ₂ Fe ₁₇ were present. And sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet was connected to Sample No. 1-13.

Sample No. In No. 1-14, the Sm ₂ Fe ₁₇ alloy powder having the surface layer formed thereon was subjected to 400 in a mixed gas atmosphere in which the volume concentration ratio of NH ₃ gas and H ₂ gas was 1: 3 while applying a magnetic field of 17T. Nitriding was performed at a temperature of 10 ° C. for 10 hours. Sample No. Similar to 1-1, the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ N ₃ , Fe ₃ Zn ₁₀ , Sm ₂ Fe ₁₇ , α-Fe, a- Sm was present. And sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet is connected to sample No. 1-14.

<Evaluation of magnet properties>
Sample No. 1-1-No. 1-4 and No.1. 1-11-No. The relative density was determined for 1-14. The relative density is calculated by calculating the dimensional density (measured density) from the volume and mass of the magnet, and assuming that the true density is equivalent to the true density of the Sm ₂ Fe ₁₇ N ₃ alloy (7.92 g / cm ³ ). / “True density”] × 100. The results are shown in Table 1.

  Sample No. 1-1-No. 1-4 and No.1. 1-11-No. For 1-14, coercive force and remanent magnetization were measured as magnetic properties. The coercive force and residual magnetization were measured using a vibrating sample magnetometer (VSM-5SC-5HF type manufactured by Toei Kogyo Co., Ltd.). The results are shown in Table 1.

  As shown in Table 1, the Sm—Fe-based alloy powder is coated with a non-magnetic metal material, heat-treated to form a surface layer, and then subjected to nitriding treatment. It can be seen that a rare earth magnet having high magnetic properties can be obtained. In particular, the sample No. obtained by the production method of Example 1 was obtained. 1-1-No. 1-4 has magnetic properties of a relative density of 85% or more, a coercive force of 798 kA / m (10 kOe) or more, and a residual magnetization of 0.8 T or more, and has both high heat resistance and high magnetic force.

Sample No. 1-1-No. 1-4 and Sample No. 1-11, No. 1 From the comparison result with 1-12, it can be seen that the heat treatment can be performed so that the thickness of the surface layer is 1 nm or more and 27 nm or less, so that the density of the magnet can be increased and the magnetic characteristics can be significantly improved. Sample No. 1-1-No. 1-4 and Sample No. 1-13, No. 1 From the comparison result with 1-14, it can be seen that the density of the magnet and the magnetic characteristics can be greatly improved by setting the strength of the magnetic field during nitriding in the nitriding step to 3T or more and 12T or less. Sample No. The relative density of 1-13 is Sample No. The reason for lower compared to like _1-1, the deformation of the _Sm 2 _Fe 17 _{N 3} alloy powder is inhibited by the residual of Sm 2 _{Fe 17,} is believed to be caused by the density has been difficult up. Sample No. The relative density of 1-14 indicates sample no. The reason why it was lower than 1-1 and the like was that the composition distribution of the crystal phase of the Sm ₂ Fe ₁₇ N ₃ alloy powder was biased due to the influence of the magnetic field at the time of nitriding, so that it was difficult to increase the density. Possible cause.

[Example 2]
Using the powder of the Sm ₂ Fe ₁₇ alloy used in Example 1 as a raw material powder, a rare earth magnet (Sm—Fe—N-based magnet) was manufactured by changing the coating method in Example 1 and the coating process. Sample No. shown 2-1. 2-3 was obtained. And the magnet characteristic was evaluated about the sample of the obtained magnet.

<Sample No. 2-1>
Sm ₂ Fe ₁₇ alloy powder and Nb powder having a particle diameter (D50) of 0.3 μm were mixed in a toluene solvent in a toluene solvent in an Ar gas atmosphere at room temperature for 6 hours to obtain a particle surface of Sm ₂ Fe ₁₇ alloy powder. Was coated with Nb. The amount of Nb powder added is 4.0% by mass. Thereafter, the Sm ₂ Fe ₁₇ alloy powder coated with Nb was heat-treated at 750 ° C. for 2 hours in an Ar gas atmosphere. Sample No. 1 of Example 1 As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the heat treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ and NbFe ₂ were present. Moreover, when the thickness of the surface layer containing Nb was calculated | required by TEM analysis, the thickness of the surface layer was 1.6 nm. Furthermore, from the TEM image of the cross section and the elemental mapping of Nb, the sample No. As in 1-1, it was confirmed that the surface layer was formed uniformly over substantially the entire circumference of the particle, and a grain boundary phase containing Nb was formed at the crystal grain boundary.

Next, the Sm ₂ Fe ₁₇ alloy powder having the surface layer formed thereon was subjected to nitriding treatment at 500 ° C. for 10 hours in a mixed gas atmosphere having a volume concentration ratio of NH ₃ gas and H ₂ gas of 1: 4. The nitriding treatment was performed while applying a 6T magnetic field. Sample No. 1 of Example 1 As in 1-1, the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment was subjected to crystal phase analysis by XRD. As a result, Sm ₂ Fe ₁₇ N ₃ and NbFe ₂ were present.

Finally, sample no. In the same compression molding conditions as 1-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet is connected to sample No. 2-1.

<Sample No. 2-2>
Sm ₂ Fe ₁₇ alloy powder and Zr powder having a particle size (D50) of 0.5 μm were mixed in a toluene solvent in a toluene solvent in an Ar gas atmosphere at room temperature for 6 hours to obtain a particle surface of Sm ₂ Fe ₁₇ alloy powder. Was coated with Zr. The amount of Zr powder added is 3.7% by mass. Thereafter, the Sm ₂ Fe ₁₇ alloy powder coated with Zr was heat-treated at 730 ° C. for 1.5 hours in an Ar gas atmosphere. Sample No. As in the case of 2-1, as a result of crystal phase analysis of the Sm ₂ Fe ₁₇ alloy powder after the heat treatment by XRD, Sm ₂ Fe ₁₇ and ZrFe ₂ were present. Further, when the thickness of the surface layer containing Zr was determined by TEM analysis, the thickness of the surface layer was 2.4 nm. Furthermore, from the TEM image of the cross section and elemental mapping of Cu and Sn, sample No. As in 2-1, it was confirmed that the surface layer was formed uniformly over substantially the entire circumference of the particle and a grain boundary phase containing Zr was formed at the crystal grain boundary.

Next, the Sm ₂ Fe ₁₇ alloy powder having the surface layer formed thereon was subjected to nitriding treatment at 480 ° C. for 12 hours in a mixed gas atmosphere having a volume concentration ratio of NH ₃ gas and H ₂ gas of 1: 4. The nitriding treatment was performed while applying a 7T magnetic field. Sample No. As in the case of 2-1, as a result of XRD crystallographic analysis of the nitrided Sm ₂ Fe ₁₇ alloy powder, Sm ₂ Fe ₁₇ N ₃ and ZrFe ₂ were present.

Finally, sample no. In the same compression molding conditions as 2-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet was connected to Sample No. 2-2.

<Sample No. 2-3>
Sm ₂ Fe ₁₇ alloy powder and TiZn ₅ powder having a particle diameter (D50) of 1.0 μm were mixed in a toluene solvent in a toluene solvent in an Ar gas atmosphere at room temperature for 6 hours to obtain particles of Sm ₂ Fe ₁₇ alloy powder. The surface was coated with TiZn ₅ . The amount of TiZn ₅ powder added is 8.0% by mass. Thereafter, the Sm ₂ Fe ₁₇ alloy powder coated with TiZn ₅ was heat-treated at 650 ° C. for 1 hour in an Ar gas atmosphere. Sample No. As in the case of 2-1, as a result of crystal phase analysis of the Sm ₂ Fe ₁₇ alloy powder after the heat treatment by XRD, Sm ₂ Fe ₁₇ , Fe ₃ Zn ₁₀ and TiFe ₂ were present. Moreover, when the thickness of the surface layer containing Ti or Zn was determined by TEM analysis, the thickness of the surface layer was 23 nm. Further, from the cross-sectional TEM image and elemental mapping of Ti and Zn, sample No. As in the case of 2-1, it was confirmed that the surface layer was uniformly formed over substantially the entire circumference of the particle and that a grain boundary phase containing Ti or Zn was formed at the crystal grain boundary. .

Next, the Sm ₂ Fe ₁₇ alloy powder having the surface layer formed thereon was subjected to nitriding treatment at 405 ° C. for 8 hours in a mixed gas atmosphere in which the volume concentration ratio of NH ₃ gas and H ₂ gas was 1: 5. The nitriding treatment was performed while applying a 10T magnetic field. Sample No. As in the case of 2-1, as a result of crystal phase analysis of the Sm ₂ Fe ₁₇ alloy powder after the nitriding treatment by XRD, Sm ₂ Fe ₁₇ N ₃ , Fe ₃ Zn ₁₀ and TiFe ₂ were present.

Finally, sample no. In the same compression molding conditions as 2-1, _Sm 2 _Fe 17 _{N 3} alloy powder was pressure press _molding, to produce a Sm-Fe-N magnet obtained by compressing molding the Sm _{2 Fe} 17 _{N 3} alloy powder. This magnet was connected to Sample No. 2-3.

<Evaluation of magnet properties>
In the same manner as in Example 1, Sample No. 2-1. The relative density was determined for 2-3. Similarly to Example 1, using a vibrating sample magnetometer, the sample No. 2-1. The coercive force and residual magnetization of 2-3 were measured. The results are shown in Table 2.

  As shown in Table 2, even if the method of coating the nonmagnetic metal material on the Sm—Fe alloy powder is changed to the coating by mixing the Sm—Fe alloy powder and the metal material powder, It can be seen that a rare earth magnet having a high relative density and excellent magnetic properties can be obtained in the same manner as the manufacturing method. In particular, Sample No. obtained by the production method of Example 2 was used. 2-1. 2-3 has a magnetic property of a relative density of 85% or more, a coercive force of 798 kA / m (10 kOe) or more, and a residual magnetization of 0.8 T or more, and has both high heat resistance and high magnetic force.

  Sample No. 2-1. Sample No. 1 of Example 1 shown in 2-3 and Table 1. 1-11, No. 1 From the comparison result with 1-12, it can be seen that the heat treatment can be performed so that the thickness of the surface layer is 1 nm or more and 27 nm or less, so that the density of the magnet can be increased and the magnetic characteristics can be significantly improved. Sample No. 2-1. 2-3 and Sample No. 1 shown in Table 1. 1-13, No. 1 From the comparison result with 1-14, it can be seen that the density of the magnet and the magnetic characteristics can be greatly improved by setting the strength of the magnetic field during nitriding in the nitriding step to 3T or more and 12T or less.

  The method for producing a rare earth magnet of the present invention can be suitably used for producing a rare earth magnet having a high relative density and excellent magnetic properties.

Claims (7)

A preparation step of preparing a powder of an Sm-Fe-based alloy containing a Sm-Fe-based compound containing Sm and Fe as a main phase;
A coating step of coating a particle surface of the Sm-Fe-based alloy powder with a nonmagnetic metal material;
A heat treatment step of heat-treating the Sm-Fe-based alloy powder coated with the metal material to form a surface layer containing the metal element of the metal material on a particle surface layer of the powder;
The Sm—Fe—N based compound powder having the surface layer formed thereon is nitrided in a magnetic field to nitride the Sm—Fe based compound of the main phase, thereby using the Sm—Fe—N based compound as the main phase. A nitriding step for obtaining a powder of an Sm-Fe-N alloy;
A step of compression-molding the Sm-Fe-N-based alloy powder in a magnetic field to obtain an Sm-Fe-N-based magnet;
A method for producing a rare earth magnet.   In the coating step, the metal material is coated on the particle surface of the Sm-Fe-based alloy powder by depositing the metal material on the particle surface of the Sm-Fe-based alloy powder by a vapor phase method. Item 2. A method for producing a rare earth magnet according to Item 1.   2. The coating step according to claim 1, wherein the coating of the metal material onto the particle surface of the Sm—Fe alloy powder is performed by mixing the powder of the Sm—Fe alloy and the powder of the metal material. Method for producing rare earth magnets.   The metal material is a metal composed of at least one metal element selected from Cu, Zn, Al, Sn, Nb, Zr, and Ti, or an alloy containing the metal element. A method for producing a rare earth magnet according to claim 1. The method for producing a rare earth magnet according to claim 4, wherein the alloy is at least one alloy selected from Cu ₆ Sn ₅ , CuTi, CuAl, and TiZn ₅ .   The method for producing a rare earth magnet according to any one of claims 1 to 5, wherein in the heat treatment step, heat treatment is performed so that the thickness of the surface layer is 1 nm or more and 27 nm or less.   The method for producing a rare earth magnet according to any one of claims 1 to 6, wherein in the nitriding step, the strength of the magnetic field is 3T or more and 12T or less.