HIGHLY HEAT-RESISTANT Sm-Fe-N-BASED MAGNETIC POWDER AND METHOD FOR PRODUCING SAME

Abstract

[Problem] To improve heat resistance of an Sm-Fe-N-based magnetic powder in an oxidizing atmosphere. [Solution] The problem is solved by a highly heat-resistant Sm-Fe-N-based magnetic powder comprising Sm-Fe-N-based magnetic particles with an Al-Ae-based alloy coating layer on the surface, wherein Ae represents an alkaline earth metal element. In the powder, the Sm / Fe molar ratio is, for example, 0.09-0.25 (inclusive), and the N / Fe molar ratio is, for example, 0.06-0.30 (inclusive). The powder has a cumulative 50% particle diameter D50 in the volume-based particle size distribution by the laser diffraction scattering method of, for example, 0.5-5.0 μm (inclusive). As the alkaline earth metal element Ae, for example, one or more elements selected from Mg and Ca can be employed. The coating layer can be formed by performing co-sputtering of Al and Ae using, for example, a sputtering film forming device.

Description

Highly heat-resistant Sm-Fe-N magnetic powder and its manufacturing method

[0001] The present invention relates to a highly heat-resistant Sm-Fe-N magnetic powder that exhibits excellent resistance to coercive force loss when heated in the air, and a method for producing the same.

[0002] Sm ２ Fe １７ A material in which nitrogen is introduced into an intermetallic compound (the typical composition formula is Sm ２ Fe １７ N ３ ) is known to be a ferromagnetic material that exhibits excellent hard magnetic properties. ２ Fe １７ Powder of a substance in which nitrogen is introduced into an Sm—Fe alloy having a stoichiometric composition or a composition close to this, and which is a ferromagnetic material, is called "Sm—Fe—N magnetic powder." Sm—Fe—N magnetic powder is useful as a material for bonded magnets.

[0003] Since the production of bonded magnets requires a process of heat-treating magnetic powder together with a resin binder, the Sm-Fe-N magnetic powder for bonded magnets must be "heat-resistant" so that the deterioration of its magnetic properties (especially coercive force) due to the heat treatment is minimized.

[0004] Patent Document 1 discloses an Sm—Fe—N magnetic powder that has a core-shell structure with a shell layer containing Sm and Fe in a specific composition and also contains phosphorus (P). This magnetic powder has excellent heat resistance and can be molded at high temperatures using a binder such as polyphenylene sulfide resin, which has high heat resistance (paragraph 0094).

[0005] Japanese Patent Application Laid-Open No. 2022-177699

[0006] In recent years, there has been a demand for Sm-Fe-N bonded magnets made with SPS (syndiotactic polystyrene) resin or PPS (polyphenylene sulfide) resin, which have excellent strength and chemical properties, for automotive motor applications. Industrial mass production of bonded magnets made with these resins requires heating to approximately 300°C in air. Patent Document 1, as mentioned above, describes polyphenylene sulfide resin. However, the heat resistance evaluation conducted in Patent Document 1 involves heating at 300°C for 90 minutes in an argon atmosphere (paragraph 0106). The technology disclosed in Patent Document 1 for forming a shell layer primarily composed of Sm and Fe makes it difficult to sufficiently suppress the decrease in coercivity when heated to approximately 300°C in air, which is an oxidizing atmosphere.

[0007] To advance the practical application of Sm-Fe-N bonded magnets using the above-mentioned SPS resin or PPS resin, it is necessary to improve the heat resistance of Sm-Fe-N magnetic powder in an oxidizing atmosphere. An object of the present invention is to provide an Sm-Fe-N magnetic powder with improved heat resistance in an oxidizing atmosphere.

[0008] The inventors discovered that coating the surfaces of Sm—Fe—N magnetic particles with an alloy film of Al (aluminum) and an alkaline earth metal element significantly improves the heat resistance of the powder comprising the magnetic particles in air, i.e., the resistance to coercivity loss when heated in air at approximately 300°C. As a result of their research, they concluded that the alloy film functions as a barrier layer to prevent oxygen intrusion. The alloy film can be formed by a vapor deposition method that is less likely to cause thermal damage to the Sm—Fe—N magnetic particles. Furthermore, the coating layer can be densified by subjecting the Sm—Fe—N magnetic powder, after the formation of the Al-alkaline earth metal alloy coating layer, to a heat treatment in which the powder is heated to a predetermined temperature in a non-oxidizing atmosphere. This densification treatment further improves the resistance to coercivity loss when heated in air at approximately 300°C. The present invention is based on this finding.

[0009] The above object can be achieved by the following inventions. [1] A highly heat-resistant Sm-Fe-N magnetic powder comprising Sm-Fe-N magnetic particles having an Al-Ae alloy coating layer on the surface, where Ae is an alkaline earth metal element. [2] The highly heat-resistant Sm-Fe-N magnetic powder according to [1], wherein the Sm / Fe molar ratio is 0.09 or more and 0.25 or less, and the N / Fe molar ratio is 0.06 or more and 0.30 or less. [3] A particle diameter D at 50% of the cumulative average particle diameter in a volume-based particle size distribution measured by a laser diffraction / scattering method is 0.09 or more and 0.25 or less, and the N / Fe molar ratio is 0.06 or more and 0.30 or less. ５０ The highly heat-resistant Sm—Fe—N magnetic powder according to the above [1] or [2], wherein the surface roughness is 0.5 μm or more and 5.0 μm or less, and the coating amount index R expressed by the following formula (1) is 0.10 μm or more and 2.00 μm or less. Coating amount index R=[(Al+Ae) / Fe]×D ５０ ... (1) Here, the value of the (Al + Ae) / Fe molar ratio in the powder having an Al-Ae based alloy coating layer is substituted for [(Al + Ae) / Fe] in formula (1), and D ５０ The cumulative 50% particle diameter D ５０ [4] The highly heat-resistant Sm-Fe-N magnetic powder according to [3] above, wherein the coating amount index R is 0.10 μm or more and 1.00 μm or less. [5] The highly heat-resistant Sm-Fe-N magnetic powder according to any one of [1] to [4] above, wherein the alkaline earth metal element Ae is one or more elements selected from Mg and Ca. [6] When subjected to a heating test in which the powder is held in air at 300°C for 120 minutes, the coercivity reduction rate δH is expressed by the following formula (2): ｃ The highly heat-resistant Sm—Fe—N magnetic powder according to any one of the above [1] to [5], wherein δH is 60% or less. ｃ = 100 × (H ｃ０ -H ｃ１ ) / H ｃ０ ...(2) Here, H ｃ０ is the coercive force (kA / m) of the powder before the heating test, H ｃ１ is the coercive force (kA / m) of the powder after the heating test.

[0010] [7] A method for producing a highly heat-resistant Sm-Fe-N magnetic powder, comprising a film-forming step of forming a coating layer of an Al-Ae alloy on the surfaces of particles constituting the Sm-Fe-N magnetic powder as a film-forming material by a vapor phase growth method, where Ae is an alkaline earth metal element. [8] A method for producing a highly heat-resistant Sm-Fe-N magnetic powder as described in [7] above, wherein the vapor phase growth method is a sputtering method, and in the film-forming step, a coating layer of an Al-Ae alloy is formed on the surfaces of particles constituting the Sm-Fe-N magnetic powder by a sputtering method while stirring and fluidizing the Sm-Fe-N magnetic powder as the film-forming material in a sputtering film-forming apparatus. [9] The method for producing a highly heat-resistant Sm-Fe-N magnetic powder according to the above [7] or [8], wherein the Sm-Fe-N magnetic powder, which is a material to be deposited, has a composition in which the Sm / Fe molar ratio is 0.09 or more and 0.25 or less, and the N / Fe molar ratio is 0.06 or more and 0.30 or less.

[10] The Sm-Fe-N magnetic powder, which is a material to be deposited, has a cumulative 50% particle diameter D ５０

[10] A method for producing a highly heat-resistant Sm-Fe-N magnetic powder according to any one of [7] to [9] above, wherein in the film-forming step, Al and an alkaline earth metal element Ae are deposited so that the coating amount index R expressed by the above formula (1) is 0.10 μm or more and 1.00 μm or less.

[11] A method for producing a highly heat-resistant Sm-Fe-N magnetic powder according to

[10] above, wherein in the film-forming step, Al and an alkaline earth metal element Ae are deposited so that the coating amount index R expressed by the above formula (1) is 0.10 μm or more and 1.00 μm or less.

[12] The method for producing a highly heat-resistant Sm—Fe—N magnetic powder according to any one of [7] to

[11] above, wherein the Sm—Fe—N magnetic powder, which is a film-forming material, is obtained by a production method comprising the following steps: a heat treatment step of heating a powder of an Sm—Fe alloy having an Sm / Fe molar ratio of 0.09 or more and 0.25 or less, formed in a solidification process by a gas atomization method, to a temperature of 900°C or more and 1200°C or less, thereby coarsening the crystal grains of the powder particles; a crushing step of crushing the Sm—Fe alloy powder whose crystal grains have been coarsened by the heat treatment step, thereby reducing the particles of the powder by fracture, including intragranular fracture; and a nitriding step of heating and maintaining the Sm—Fe alloy powder crushed by the crushing step in a non-oxidizing gas atmosphere containing a nitrogen compound or nitrogen, at a temperature of 500°C or less, thereby introducing nitrogen into the powder particles.

[13] A method for producing a highly heat-resistant Sm—Fe—N magnetic powder according to any one of the above [7] to

[12] , further comprising a densification step of heating the Sm—Fe—N magnetic powder obtained in the film-forming step in a non-oxidizing atmosphere to a temperature T (° C.) that satisfies the following formula (4): 450≦T (° C.)≦550 (4)

[14] In the film-forming step, the melting start temperature T Ｍ The method for producing the highly heat-resistant Sm—Fe—N magnetic powder according to any one of the above [7] to

[12] further comprises a densification treatment step of forming an Al—Ae alloy coating layer having a composition in which the temperature of the Sm—Fe—N magnetic powder obtained in the film-forming step is increased in a non-oxidizing atmosphere to a temperature T (° C.) that satisfies the following formula (3): T Ｍ (°C) -100≦T(°C)≦550 ... (3)

[0011] According to the present invention, it is possible to significantly improve the resistance to coercivity degradation of Sm-Fe-N magnetic powder when heated in air. The present invention can be applied to the production of bonded magnets, which involve a process of heating the powder to approximately 300°C in air, and can contribute to the practical application of Sm-Fe-N bonded magnets that use resins such as SPS resin and PPS resin, which have excellent strength, heat resistance, and chemical properties, as the binder component.

[0012] 6 is a diagram showing a schematic configuration of a gas atomization apparatus used in Examples and Comparative Examples.

[0023] FIG. 6 is a diagram showing a schematic cross-sectional structure near the bottom of the crucible of the gas atomization apparatus used in Examples and Comparative Examples.

[0024] FIG. 6 is a diagram showing a schematic configuration of a sputtering deposition apparatus used in Examples.

[0025] FIG. 6 is a diagram showing a schematic configuration of the interior of the deposition chamber 51 of the sputtering deposition apparatus shown in FIG. 3.

[0026] FIG. 6 is a graph showing the photoelectron peak spectra of Mg and Fe at etching times of 0 seconds and 600 seconds measured by X-ray photoelectron spectroscopy for the Sm—Fe—N magnetic powder obtained in Example 1.

[0027] FIG. 6 is a diagram showing an example of a high-angle annular dark-field (HAADF) image observed by STEM (scanning transmission electron microscope) for powder particles of the Sm—Fe—N magnetic powder obtained in Example 1 after heating in air at 300° C. for 120 minutes.

[0028] FIG. 6 is a graph showing the element concentration profiles of O, Fe, and Al measured along the line AB shown in FIG.

[0013] [Sm—Fe—N-based magnetic particles] The Sm (samarium)—Fe (iron)—N (nitrogen)-based magnetic powder of the present invention is composed of Sm—Fe—N-based magnetic particles having a coating layer made of an alloy of Al (aluminum) and an alkaline earth metal on the surface of a particle of Sm—Fe—N-based magnetic material. The Sm—Fe—N-based magnetic particles can be said to be particles with a so-called core-shell structure, with the Sm—Fe—N-based magnetic material portion as the core and the coating layer portion as the shell.

[0014] [Magnetic Material] The magnetic material corresponding to the core of the Sm—Fe—N based magnetic particles is Th ２ Zn １７ Sm type crystal structure ２ Fe １７ It is mainly composed of a magnetic phase in which N (nitrogen) atoms are introduced into the crystal lattice.２ Fe １７ It is thought that the N atoms are interstitial in the crystal lattice, and the Th ２ Zn １７ The crystal structure is maintained. ２ Fe １７ When N atoms are introduced into the Sm—Fe—N system, the magnetic crystal anisotropy changes from in-plane to uniaxial, and the Curie point rises, making it a practical magnetic material. ２ Fe １７ N ３ The Sm / Fe molar ratio, which means the molar ratio of Sm to Fe, and the N / Fe molar ratio, which means the molar ratio of N to Fe, are ２ Fe １７ N ３ The closer to the stoichiometric composition, the more advantageous it is in terms of magnetic properties, but hard magnetism is also exhibited in the composition range around this. ２ Fe １７ N ３ The stoichiometric Sm / Fe molar ratio is 0.118, and the N / Fe molar ratio is 0.176. In the Sm-Fe-N magnetic material of the present invention, taking into consideration that an effective coercive force as a material for a bonded magnet can be stably obtained in a temperature range including room temperature, it is preferable that the composition is adjusted so that the Sm / Fe molar ratio is in the range of 0.09 to 0.25, and the N / Fe molar ratio is in the range of 0.06 to 0.30. Since Sm, Fe, and N are not used as constituent elements of the coating layer, it is preferable that the Sm / Fe molar ratio and N / Fe molar ratio are also in the above ranges for the composition of the Sm-Fe-N magnetic powder of the present invention, which includes the magnetic material and the constituent elements of the coating layer. Note that the magnetic material corresponding to the core contains Sm containing N. ２ Fe １７ In addition to the phase, for example, TbCu ７ SmFe with a crystalline structure ７ Although there may be cases where a different phase such as a hydroxy phase is mixed in, the presence of the different phase is permissible as long as it does not impede the object of the present invention.

[0015] [Coating Layer] The coating layer, which corresponds to the shell of the Sm—Fe—N magnetic particles, is composed of an alloy of Al and an alkaline earth metal. In this specification, alkaline earth metal elements are referred to as Ae, and alloys of Al and alkaline earth metals are referred to as "Al-Ae alloys." Here, Ae in Al-Ae alloys refers to one or more alkaline earth metal elements. Representative Al-Ae alloys include Al-Mg (magnesium) alloys, Al-Ca (calcium) alloys, and Al-Mg-Ca alloys. Sm-Fe-N magnetic powders composed of particles having an Al-Ae alloy coating layer formed thereon exhibit excellent resistance to coercivity degradation, i.e., excellent resistance to coercivity degradation, by which the problem of coercivity degradation that occurs after heating at approximately 300°C in air is significantly suppressed. The reason for this is thought to be that the coating layer made of an Al-Ae alloy functions as a barrier layer that prevents oxygen from penetrating from the outside into the portion of the Sm-Fe-N magnetic material that corresponds to the core when the Sm-Fe-N magnetic powder is heated in an oxidizing gas such as air to, for example, about 300°C. The composition of the Al-Ae alloy may be set, for example, in a range of 0.05 to 0.95 in terms of the Ae / (Al+Ae) molar ratio, depending on the type of alkaline earth metal element used, and may also be controlled in a range of 0.20 to 0.60 or 0.25 to 0.50. An appropriate Al-Ae alloy composition depending on the type of alkaline earth metal element can be determined, for example, by conducting preliminary experiments with several different compositions.

[0016] As described below, the coating layer can be formed by, for example, a sputtering deposition method. While the coating layer in its post-deposition state improves the resistance to coercive force degradation, the resistance to coercive force degradation can be further improved by performing the densification heat treatment described below. Considering the need to efficiently perform the densification heat treatment in a short time, the composition of the Al—Ae alloy is preferably adjusted to a composition range in which the melting initiation temperature is approximately 600°C or less. From this perspective, for example, when an Al—Mg binary alloy is used, a preferable composition range can be exemplified by a Mg / (Al+Mg) molar ratio in the range of 0.10 to 0.95, and when an Al—Ca binary alloy is used, a preferable composition range can be exemplified by a Ca / (Al+Ca) molar ratio in the range of 0.35 to 0.90.

[0017] By using a powder sputtering deposition device capable of performing sputtering deposition on the particle surfaces while stirring the powder particles, it is possible to cover the entire surface of the core particles with a coating layer having a highly uniform thickness. Such a highly uniform coating layer is believed to exhibit excellent resistance to coercivity degradation when heated in air at approximately 300°C by ensuring an average thickness of, for example, 10 nm or more. It is more preferable to set the deposition conditions so that the average thickness of the coating layer is in the range of 20 nm to 100 nm. The thickness of the coating layer can be confirmed, for example, by a high-angle annular dark-field (HAADF) image of the particles observed using a scanning transmission electron microscope (STEM).

[0018] The amount of the coating layer can also be determined from the chemical composition and particle size of the powder. For example, the ratio of the total amount of Al and alkaline earth metal element Ae, which are constituent elements of the coating layer, to Fe, which is a constituent element of the magnetic particle corresponding to the core, i.e., the (Al + Ae) / Fe molar ratio, is an index indicating the quantitative proportion of the coating layer in the powder particle. Furthermore, if the (Al + Ae) / Fe molar ratio is the same, the larger the particle size, the larger the average thickness of the coating layer is considered to be. It is preferable that the amount of the coating layer is adjusted to an effective range depending on the particle size. As a result of various studies, it has been found that the coating amount index R, expressed by the following formula (1), is preferably 0.10 μm or more and 2.00 μm or less, and a coating amount index R of 0.10 μm or more and 1.00 μm or less is particularly preferable from the perspective of balancing heat resistance and cost. Coating amount index R = [(Al + Ae) / Fe] × D ５０ ... (1) Here, the value of the (Al + Ae) / Fe molar ratio in the powder having an Al-Ae based alloy coating layer is substituted for [(Al + Ae) / Fe] in formula (1), and D ５０ The cumulative 50% particle diameter D ５０ The value of (μm) is substituted.

[0019] [Particle diameter] When the Sm—Fe—N magnetic powder of the present invention is used as a magnetic material for a bonded magnet, the cumulative 50% particle diameter D in the volume-based particle size distribution measured by a laser diffraction / scattering method is５０ is preferably 0.5 μm or more and 5.0 μm or less.

[0020] [Heat Resistance of Sm—Fe—N Magnetic Powder] In the case of Sm—Fe—N magnetic powder for use in bonded magnets that use resins known as engineering plastics (such as the above-mentioned SPS resin and PPS resin) as binders, which have high heat resistance and strength, the coercivity reduction rate δH, expressed by the following formula (2), is obtained when the powder is subjected to a heating test in which it is held in air at 300° C. for 120 minutes in order to be fully adapted to the mass production process of such bonded magnets. ｃ It is preferable that the coercive force reduction rate δH is 60% or less. ｃ It is more preferable that the coercive force reduction rate δH is 45% or less, and even more preferable that the coercive force reduction rate δH is 35% or less. ｃ The lower limit of δH is not particularly limited, but it is preferable that the lower limit of δH can be obtained without causing excessive process load. ｃ The range of δH can be, for example, 15% or more. ｃ = 100 × (H ｃ０ -H ｃ１ ) / H ｃ０ ...(2) Here, H ｃ０ is the coercive force (kA / m) of the powder before the heating test, H ｃ１ is the coercive force (kA / m) of the powder after the heating test.

[0021] [Film Formation Process] The Sm—Fe—N magnetic powder used as the film formation material can be prepared using known synthesis methods such as reduction-diffusion and gas atomization. Vapor deposition is a suitable method for forming the coating layer, as it is less likely to thermally damage the Sm—Fe—N magnetic material and can form an Al—Ae alloy coating of any composition. A specific example, as shown in the examples below, is a method in which the Sm—Fe—N magnetic powder used as the film formation material is stirred and fluidized in a sputtering film formation apparatus, forming an Al—Ae alloy coating layer on the surfaces of the particles that make up the Sm—Fe—N magnetic powder. Here, "stirring and fluidizing" refers to the operation of applying a stirring force to the powder contained in the film formation apparatus to fluidize the powder particles. This operation allows the powder particles to circulate continuously, ensuring that each particle is evenly exposed to the space where the atoms to be deposited are present. By applying such a film-forming method, the surfaces of the magnetic particles corresponding to the cores can be covered with a film of an Al-Ae alloy, resulting in a significant improvement in heat resistance. Note that the film-forming method for the coating layer is not limited to vapor deposition methods such as sputtering, and it is believed that other known film-forming techniques or newly developed film-forming techniques may also be applied if it is confirmed that an Al-Ae alloy film that is less likely to cause thermal damage to the magnetic material and has a highly uniform film thickness can be formed on the powder particle surfaces.

[0022] [Densification Treatment Step] In the case of Al-Ae based alloys, it is sometimes possible to find a composition range in which the melting initiation temperature is low, for example, 600°C or less, depending on the type of alkaline earth metal used. In such a composition range in which the melting initiation temperature is low, the crystal structure of the Sm-Fe-N based magnetic material (Th with N introduced) is formed on the Sm-Fe-N based magnetic powder after the formation of the Al-Ae based alloy coating layer. ２ Zn １７By subjecting the coating layer to a heat treatment at a temperature of, for example, 550°C or lower, at which the ferrite core (the mold structure) does not decompose, diffusion involving a liquid phase or solid phase diffusion rapidly progresses in the coating layer, thereby densifying the coating layer. This densification treatment can further improve the resistance to coercivity degradation when heated in air at about 300°C. Therefore, this densification treatment can be performed as needed.

[0023] Specifically, first, in the film formation process, the melting start temperature T Ｍ The Sm—Fe—N magnetic powder is prepared by forming an Al—Ae alloy coating layer having a composition in which the melting temperature T Ｍ can be known from, for example, the equilibrium phase diagram of an Al-Ae alloy. Next, the Sm-Fe-N magnetic powder obtained in the film-forming process is heated in a non-oxidizing atmosphere such as Ar (argon) gas to a temperature T (°C) that satisfies the following formula (3): T Ｍ (℃) -100≦T (℃)≦550...(3) Heating temperature T is melting start temperature T Ｍ If the temperature is above this, the Al-Ae alloy coating layer will enter the solid-liquid coexistence region and will begin to melt partially. In this case, the coating layer will rapidly become dense due to diffusion involving the liquid phase. On the other hand, if the heating temperature T is higher than the melting start temperature T Ｍ If the temperature is lower than this, the densification of the coating layer will proceed due to solid-state diffusion. Ｍ In order to rapidly promote diffusion, it is advantageous to raise the temperature to a temperature close to the "T Ｍ (°C)-100”, T Ｍ The densification can be efficiently achieved by raising the temperature to a temperature where the difference between the heating temperature T and T is within 100°C. Ｍ If greater than or equal to T Ｍ In either case, the crystal structure of the Sm—Fe—N magnetic material (Th ２ Zn １７In order to prevent decomposition of the mold structure, the heating temperature T must be set in the range of 550°C or less, and more preferably in the range of 520°C or less. The holding time at the heating temperature T (°C) may be set, for example, in the range of 0 seconds or more and 3600 seconds or less. Here, a holding time of 0 seconds at the heating temperature T (°C) means a heat pattern in which the material temperature starts to decrease immediately after it reaches T (°C).

[0024] In addition, the melting start temperature T Ｍ Even when a coating layer having an Al--Ae alloy composition range where the melting temperature exceeds 600°C is formed, the coating layer can be subjected to a densification treatment by heating to a temperature range of 550°C or less. Ｍ Al-Ae alloys having a melting temperature T Ｍ Regardless of the Sm-Fe-N magnetic powder having any coating layer formed thereon, made of an Al-Ae alloy having a temperature exceeding 600°C, it is effective to perform a densification treatment in which the temperature is raised to a temperature T (°C) that satisfies the following formula (4) in a non-oxidizing atmosphere such as Ar (argon) gas: 450≦T (°C)≦550 ... (4) In this case, too, the holding time at the heating temperature T (°C) may be set within the range of, for example, 0 to 3600 seconds. Note that the melting start temperature T Ｍ In the case of Sm-Fe-N magnetic powder having an Al-Ae alloy coating layer with a temperature of 600° C. or less, it is more preferable to control the heating temperature T to satisfy the above formula (3) as described above.

[0025] [Example of a method for manufacturing Sm—Fe—N-based magnetic powder, which is a film-forming material] As described above, synthesis methods such as reduction-diffusion and gas atomization can be used to manufacture Sm—Fe—N-based magnetic powder, which is a film-forming material. However, processes using gas atomization have the advantage of not causing an environmental burden due to alkaline waste liquid. A typical example of a process using this gas atomization method is a method in which the steps of gas atomization, heat treatment, pulverization, and nitriding are performed in the above order. Hydrogen treatment can be performed as needed before the pulverization. The applicant has disclosed the technology for the above process in detail in Japanese Patent Application No. 2023-061046. Each step is briefly described below.

[0026] (Gas atomization) As the metal raw material for generating the molten metal to be subjected to gas atomization, a pre-melted Sm-Fe based master alloy, metallic Sm, metallic Fe, etc., whose composition is known, can be used. ２ Fe １７ It is desirable to adjust the Sm / Fe molar ratio to a value relatively close to the stoichiometric composition, specifically, to a range of 0.09 to 0.25. While the inclusion of metal elements other than Sm and Fe is permissible to the extent that the required properties of the magnetic powder finally obtained are not impaired, the total content of Sm and Fe in the molten metal is preferably 95.0 mass% or more, and more preferably 98.0 mass% or more. It is desirable to generate the molten metal in an inert gas atmosphere excluding nitrogen or in a vacuum.

[0027] The molten metal, which has been maintained at a predetermined temperature and made sufficiently uniform, is discharged from the nozzle into the gas phase space, and cooling gas is forcefully sprayed onto the molten metal immediately after discharge. This causes the molten metal to turn into fine liquid phase particles, which fly through the gas phase space and solidify. The molten metal temperature at the time of discharge may be set within the range of 1400 to 1900°C. The pressurizing gas for discharging the molten metal, the injection gas sprayed onto the molten metal, and the ambient gas in the gas phase space through which the liquid phase particles fly are all preferably inert gases other than nitrogen. The particle size of the gas atomized powder is determined by the cumulative 50% particle diameter D in the volume-based particle size distribution determined by the laser diffraction / scattering method. ５０ For example, the particle size of the gas atomized powder is preferably 70.0 μm or less, more preferably 50.0 μm or less, and even more preferably 25.0 μm or less. ５０ It is sufficient to adjust the thickness to a range of 5.0 μm or more, and it may be controlled to a range of 10.0 μm or more.

[0028] (Heat Treatment) In the heat treatment process, the gas-atomized powder of Sm—Fe alloy is heat-treated at high temperatures to coarsen the crystal grains. Specifically, by heating to 900°C or higher, the crystal grains can be coarsened to a size such that the average crystal grain size in the cross-sectional structure of the particles is, for example, approximately 3 to 15 μm in equivalent circle diameter. This coarsening of the crystal grains facilitates intragranular fracture during subsequent pulverization, making it easier to obtain fine Sm—Fe alloy powder with a high proportion of particles consisting of single crystal grains. Heating to 930°C or higher is more preferable. Since excessive heating is uneconomical, the heating temperature is preferably set in the range of 1200°C or less, and may be controlled to 1100°C or less, or 1000°C or less. The holding time in the temperature range of 900°C to 1200°C can be, for example, 10 seconds to 10 minutes, or may be set to 30 seconds to 5 minutes. The heating atmosphere is preferably an inert gas atmosphere other than nitrogen, or a vacuum.

[0029] (Hydrogen Treatment) In order to facilitate the occurrence of intragranular fracture in the subsequent milling process, it is effective to perform hydrogen treatment by heating in a hydrogen gas atmosphere before milling. Hydrogen treatment causes hydrogen to penetrate into the crystal grains of the Sm—Fe alloy, which makes intragranular fracture more likely to occur due to the so-called hydrogen embrittlement phenomenon. Therefore, hydrogen treatment can be performed as necessary. The heating temperature for hydrogen treatment is preferably set in the range of 200°C to 600°C, and the holding time in that temperature range may be set in the range of, for example, 30 minutes to 600 minutes.

[0030] (Pulverization) When mechanical pulverization is performed on the powder of Sm—Fe alloy whose crystal grains have become coarse by the heat treatment, the individual particles are fractured by fracture at the grain boundaries (intergranular fracture) as well as fracture within the grains (intragranular fracture). When the powder particles are refined by such "fracture including intragranular fracture," a fine Sm—Fe alloy powder having a high proportion of particles consisting of single crystal grains can be obtained. As a pulverization method, for example, a wet ball mill can be used. The particle diameter after pulverization is determined by the cumulative 50% particle diameter D in the volume-based particle size distribution determined by the laser diffraction / scattering method. ５０It is preferable to adjust the particle size D to 5.0 μm or less, and more preferably to 3.0 μm or less. If the particle size is made too small, the application of an excessive external force may increase the crystal lattice distortion, which may adversely affect the magnetic properties. ５０ It is desirable to carry out pulverization so that the particle size is 0.5 μm or more, and pulverization may be carried out so that the particle size is 1.0 μm or more.

[0031] (Nitriding Treatment) Next, nitriding treatment is carried out to obtain Sm—Fe—N magnetic powder. The nitriding treatment can be carried out by heating and holding the Sm—Fe alloy powder pulverized by the above-mentioned pulverization in a non-oxidizing gas atmosphere containing a nitrogen compound or nitrogen. If the heating temperature is too high, Sm ２ Fe １７ Sm crystal with nitrogen atoms inserted ２ Fe １７ N ３ The structure based on this becomes unstable, making nitriding difficult. The heating temperature for nitriding is preferably 500°C or lower. If the temperature is too low, it takes a long time for nitriding to proceed, which is disadvantageous in terms of diffusing nitrogen atoms uniformly into the interior of the particles. It is effective to set the heating temperature to 300°C or higher. The atmospheric gas for nitriding is ammonia (NH ３ ) and hydrogen (H ２ For example, a reducing atmosphere consisting of a mixture of ammonia and hydrogen in a ratio of NH ３ : H ２ The ratio can be in the range of 10:90 to 60:40. Other atmospheric gases used in the nitriding treatment include hydrogen, ammonia, and nitrogen (N ２ Examples of suitable gases for the nitriding treatment include a mixture of hydrogen, ammonia, and argon (Ar), ammonia alone, a mixture of ammonia and nitrogen, a mixture of ammonia and argon, nitrogen alone, and a mixture of nitrogen and hydrogen. These gases are used to form a non-oxidizing atmosphere. The optimum time for the nitriding treatment varies somewhat depending on the average particle size of the powder, the composition of the atmospheric gas, and the temperature, but the optimum time can usually be found in the range of 15 to 240 minutes. This nitriding treatment allows the nitriding of Sm ２ Fe １７Nitrogen is introduced into the crystals, and an Sm--Fe--N magnetic powder having an N / Fe molar ratio in the range of 0.06 to 0.30 is obtained, which exhibits excellent magnetic properties.

[0032] In the following examples, elemental analysis, measurement of particle size distribution of powder, measurement of magnetic properties of powder, and X-ray diffraction measurement were carried out by the following methods.

[0033] (Elemental Analysis) Metal element analysis was performed by heating and dissolving the analytical sample in hydrochloric acid in a glove box filled with argon (Ar) gas, followed by dilution to prepare a sample solution for analysis, and analyzing this solution with an ICP optical emission spectrometer (Agilent Technologies, Agilent 720). Nitrogen analysis was performed by the inert gas fusion-thermal conductivity method using an oxygen / nitrogen analyzer (Horiba, Ltd., EMGA-920).

[0034] (Measurement of particle size distribution of powder) The cumulative 50% particle diameter D in the volume-based particle size distribution was measured using a laser diffraction particle size distribution measuring device (Helos / Rodos, manufactured by Sympatec). ５０ asked for.

[0035] (Magnetic Measurement of Powder) A sample cell filled with 20 mg of sample powder and paraffin was placed at the center of an electromagnet, and the sample cell was heated at 80°C for 2 minutes using a hot air generator. The amount of paraffin filled here was the amount that filled the container of the sample cell with the sample powder and paraffin. Next, while the sample cell was heated at 80°C, an external magnetic field of 1.0 T (tesla) was applied to the sample cell by the electromagnet for 2 minutes. Next, the sample cell was cooled to room temperature with the magnetic field of 1.0 T still applied. In this way, a magnetically oriented measurement sample was obtained. This measurement sample was placed in a VSM (VSM-5HSC, manufactured by Toei Kogyo Co., Ltd.) so that the direction of the applied magnetic field was parallel to the magnetic field orientation direction of the measurement sample, and the coercive force H ｃ The measurement conditions were a maximum applied magnetic field of 4.79 MA / m and a sweep rate of 8 kA / ms.

[0036] (X-ray Diffraction Measurement) The X-ray diffraction pattern of the powder sample was measured using Co-Kα rays at a tube voltage of 45 kV and a tube current of 40 mA.

[0037] Example 1 (Synthesis of Sm—Fe-based powder by gas atomization) Figure 1 shows a schematic diagram of the gas atomization apparatus used in this example. A chamber contains two independent upper and lower spaces that can be evacuated using a vacuum exhaust device 10. These spaces can be converted into gas-phase spaces with a predetermined gas atmosphere by introducing gas from atmospheric gas supply sources 11a and 11b. The upper space contains a crucible 1, in which raw materials are melted by induction heating using a high-frequency coil 4 to form a molten metal 5. A molten metal discharge nozzle member 2 is attached to the bottom of the crucible 1 for discharging the molten metal 5 into the lower gas-phase space. A stopper 3 is pressed against the molten metal discharge nozzle member 2 to block the molten metal flow path until the molten metal 5 is discharged. After the molten metal 5 has been sufficiently homogenized and attained a predetermined temperature, gas is supplied at a predetermined pressure from the molten metal discharge gas supply device 13 to the surface of the molten metal in the crucible 1. The stopper 3 is then raised, and the molten metal 5 is discharged from the tip of the molten metal discharge nozzle member 2 into the lower gas phase space. The lower gas phase space is equipped with a gas injection nozzle 6 for spraying gas onto the discharged molten metal 5. Prior to discharge, gas is supplied from the gas supply device 12 to the gas injection nozzle 6, and the gas is injected from the gas injection nozzle 6 at high pressure. By impinging the strong jet of injected gas on the molten metal 5, fine particles of the molten metal 5 are formed, and the fine particles are rapidly cooled and solidified. The solidified metal particles 7 are deposited at the bottom of the lower gas phase space.

[0038] 2 shows a schematic diagram of an example of the cross-sectional structure near the bottom of the crucible of a gas atomizing device. The molten metal discharge nozzle member 2 attached to the bottom of the crucible 1 has a discharge port 21, which is an opening at the tip of the nozzle, and a stopper abutment surface 22. The stopper 3 is movable in the vertical direction, and has the function of blocking the flow path of the nozzle by abutting against the stopper abutment surface 22 of the molten metal discharge nozzle member 2, and opening the flow path of the nozzle by moving away from the stopper abutment surface 22 when the molten metal is discharged. In this example, the entire crucible 1 is made of boron nitride (BN), the entire molten metal discharge nozzle member 2 is made of boron nitride (BN), and at least the entire portion of the stopper 3 that is immersed in the molten metal 5 is made of yttrium oxide (Y ２ O ３The inner diameter of the molten metal discharge nozzle member 2 was 3.0 mm.

[0039] A pre-melted Sm-Fe alloy was used as the raw material. Elemental analysis revealed that the Sm / Fe molar ratio of this raw material alloy was 0.16. 996.7 g of this raw material was placed in a crucible and melted by high-frequency induction heating in an Ar atmosphere. After the raw material alloy was completely molten, 27 minutes after the start of heating, the entire molten metal at 1637°C was ejected from the nozzle into the lower gas phase space. The maximum supply pressure of the molten metal ejection gas was 65 kPa, calculated as the differential pressure from the atmospheric gas pressure. Ar was used as the ejection gas. The lower gas phase space was also an Ar atmosphere. The resulting powder was collected and sieved through a 16 μm mesh sieve in a glove box under a nitrogen atmosphere to remove excessively small particles. In this way, gas-atomized powder was obtained. Elemental analysis of the gas-atomized powder revealed that the Sm / Fe molar ratio was 0.16, equivalent to that of the raw material alloy. In addition, the cumulative 50% particle diameter D in the volume-based particle size distribution of the gas atomized powder by the laser diffraction / scattering method ５０ was 22.8 μm.

[0040] (Heat Treatment) An electrically heated tubular furnace connected to a glove box filled with argon (Ar) gas was used as the heat treatment furnace. The Sm—Fe-based gas-atomized powder was placed in a sealed container filled with argon gas, transferred to the glove box, and then loaded into the tubular furnace without being exposed to the atmosphere. While flowing argon gas through the tubular furnace, the temperature was increased from room temperature to 950°C at a rate of 150°C / min, and then held at 950°C for 1 minute. Thereafter, the temperature was cooled to 50°C or less while flowing argon gas to obtain a heat-treated powder.

[0041] (Hydrogen Treatment) The obtained heat-treated powder was transferred to another tubular furnace and heated with hydrogen (H ２ While flowing hydrogen gas, the temperature was raised to 300°C at a rate of 10°C / min, and then held at 300°C for 180 minutes. Next, while continuing to flow hydrogen gas, the temperature was cooled to 50°C or less, and the atmosphere inside the furnace was replaced with argon gas. In this way, hydrogen-treated powder was obtained.

[0042] (Crushing) The obtained hydrogen-treated powder was placed in an airtight container filled with argon gas and transferred from the tubular furnace to another glove box filled with argon gas. Grinding was performed using a wet ball mill in this glove box. A 240 mL stainless steel mill pot was charged with 5.0 g of hydrogen-treated powder, 250 g of 2.5 mm diameter stainless steel balls, and acetonitrile as a solvent. The amount of acetonitrile was the minimum amount necessary to immerse all of the stainless steel balls in acetonitrile. Next, the mill pot containing the hydrogen-treated powder was placed on a ball mill rotating stand (AV-1 model, manufactured by Asahi Rika Seisakusho), and grinding was performed at a rotation speed of 120 rpm for 2 hours. The contents of the mill pot were then passed through a sieve to remove the stainless steel balls remaining on the sieve, and the slurry that passed through the sieve was recovered. The recovered slurry was then allowed to stand, the supernatant liquid was discarded, and the remaining slurry was vacuum-dried to obtain a crushed powder. The above operations from grinding to drying were carried out in a glove box under an argon gas atmosphere.

[0043] (Nitriding Treatment) The pulverized powder obtained as described above was transferred into an electrically heated tubular furnace under an argon gas atmosphere, and then ammonia (NH ３ ) gas 35% by volume, hydrogen (H ２ A mixed gas containing 65% by volume of hydrogen (H ) gas was then flowed to replace the gas in the tubular furnace. Thereafter, while flowing the mixed gas, the temperature was raised to 420°C at a rate of 5°C / min and held at 420°C for 30 minutes to perform nitriding treatment. Next, the gas flowing in the tubular furnace was changed to hydrogen (H ). ２ The gas flowing through the tubular furnace was then changed to argon gas, and the temperature was maintained at 420°C for another 120 minutes. After that, the gas flowing through the tubular furnace was changed to argon gas, and the temperature was maintained at 420°C for 90 minutes. After that, heating was stopped, and the material was cooled to a temperature near room temperature while argon gas was being flowed, to obtain nitrided powder.

[0044] (Washing and crushing) Next, the obtained nitrided powder was transferred from the tubular furnace into a glove box filled with argon gas, and then placed in a 20 mL glass bottle with a screw cap, and 15 mL of heptane was added as a solvent. Next, this glass bottle was placed in an ultrasonic disperser (UH-150 model, manufactured by SMT Corporation) and operated for 100 minutes under output conditions of 20 kHz, 0.3 second transmission, 0.7 second pause. Next, the supernatant liquid in the glass bottle was removed, and the remaining heptane was removed by vacuum drying, thereby obtaining a Sm—Fe—N-based magnetic powder. As a result of X-ray diffraction measurement, the obtained Sm—Fe—N-based magnetic powder was found to be Th ２ Zn １７ The Sm—Fe—N magnetic powder was confirmed to have a crystalline structure. ５０ was 1.8 μm.

[0045] (Film Formation) Using the Sm—Fe—N magnetic powder obtained as described above as the material to be film-formed, a coating layer of Al—Mg alloy was formed on the surface of the powder particles by sputtering film formation. The film formation method will be described below.

[0046] Figure 3 shows a schematic diagram of the sputtering deposition apparatus used in this example. The left figure corresponds to a side view, and the right figure corresponds to a front view. The deposition chamber 51 of the sputtering deposition apparatus main body is connected to a narrow glove box 52 filled with argon gas on the front side, and sample powder can be manually introduced into the deposition chamber 51 through a glove port 53. A sliding door is installed between the deposition chamber 51 and the glove box 52, and can be opened and closed from inside the glove box 52. By closing this door, the deposition chamber 51 can be evacuated to a vacuum while the glove box 52 side is filled with argon gas. Two sputter cathodes 54 are installed at the top of the deposition chamber 51.

[0047] FIG. 4 is a schematic diagram showing the internal configuration of the film formation chamber 51 of the sputtering film formation apparatus shown in FIG. 3. The hatched area in FIG. 4 represents a cross-sectional shape in a plane including the rotation axis of the stepping motor 57. This film formation apparatus is equipped with two sputtering cathodes 54, enabling co-sputtering using two types of targets. In this example, metallic Al was attached to one sputtering cathode 54, and metallic Mg was attached to the other sputtering cathode 54. Each target material was a disk-shaped material with a thickness of 5 mm and a diameter of 2 inches. Magnetron sputtering was enabled by the magnetic field generated by a neodymium magnet built into the back of the target material. A powder container 55 with a circular bottom and a diameter of 65 mm was installed at the focal position of the two cathodes, and a stirring rod 56 was inserted into the powder container 55. The powder container 55 is connected to a stepping motor 57 installed below the film formation chamber 51, and the sample powder, which is the material to be film formed, can be continuously stirred and fluidized by rotating the powder container 55 while it is held in the powder container 55. When this sputtering film formation device is used, the sample powder is automatically and continuously stirred and fluidized while being sputtered to form a film, so that the surfaces of the powder particles can be coated with elements of the target material attached to the sputtering cathode 54.

[0048] The Sm—Fe—N magnetic powder, which is the material to be deposited, was transferred into the glove box 52 while being kept in an argon gas atmosphere. The sliding door at the connection to the deposition chamber 51 was opened, and 10 g of Sm—Fe—N magnetic powder was placed in the powder container 55 under an argon gas atmosphere. Thereafter, the sliding door was closed to seal the deposition chamber 51. The deposition chamber 51 was temporarily filled with approximately 1×10 －３After evacuating the chamber to 0.5 Pa, argon process gas was introduced into the film-forming chamber 51, and the flow rate of argon was adjusted so that the argon gas pressure in the film-forming chamber 51 was maintained at approximately 0.5 Pa. While continuously stirring the Sm-Fe-N magnetic powder, the material to be film-formed, by rotating the powder container 55 at 50 rpm, two sputtering cathodes 54 were used to perform dual sputtering of Al and Mg, thereby coating the surfaces of the powder particles with an Al-Mg alloy. The film-forming time was adjusted so that the average film thickness of the coating layer was approximately 50 nm. In this example, a coating layer with an Al:Mg molar ratio of 54:46 was formed by adjusting the output ratio of both sputtering cathodes.

[0049] (Densification Treatment) After the film formation, the Sm—Fe—N magnetic powder was transferred to a heat treatment furnace while being kept in an argon gas atmosphere, and subjected to heat treatment at 500° C. for 1 minute in an argon atmosphere. In an Al—Mg alloy having a composition in which the molar ratio of Al to Mg is around 54:46, the melting start temperature T Ｍ Since the temperature is thought to be around 450°C, it is presumed that the formed Al-Mg alloy coating layer entered a solid-liquid coexistence region when heated to 500°C and was rapidly densified. The Sm-Fe-N magnetic powder that had undergone this densification treatment was used as the test powder for this example and was subjected to the following investigation.

[0050] (X-ray Photoelectron Spectroscopy Measurement) The element distribution near the particle surface layer of the test powder in this example was measured using an X-ray photoelectron spectrometer (PHI-5000 VersaProbe II, manufactured by ULVAC-PHI) by the following method. Al-Kα rays (1486.6 eV) were used as the X-ray source, and the energy of the emitted photoelectrons was analyzed with a hemispherical electron analyzer at a pass energy of 23.5 eV and an energy interval of 0.1 eV. In addition, as a depth profile analysis, the distribution in the depth direction from the surface was evaluated by alternately repeating etching of the sample surface by Ar sputtering and measurement. The acceleration voltage of Ar ions was 2 kV. The etching depth corresponding to an etching time of 600 seconds was 0.01 eV. ２ O ３ This is estimated to be approximately 43 nm.

[0051] Figure 5 shows the Mg (magnesium) 2p level and Fe (iron) 2p level measured by X-ray photoelectron spectroscopy. ３／２ The photoelectron peaks of the levels were measured after etching for 0 seconds (i.e., the outermost surface) and 600 seconds (i.e., Fe ２ O ３ The figure shows the spectrum at a depth of approximately 43 nm (equivalent to a depth of 43 nm). At an etching time of 0 seconds, a significant peak intensity of Mg was observed, but no significant peak intensity of Fe was observed. On the other hand, at an etching time of 600 seconds, the peak intensity of Mg was significantly reduced, and a significant peak intensity of Fe was observed. From this, it can be evaluated that the test powder particles in this example are covered on the surface with a coating layer formed by the above-mentioned film formation to such an extent that the exposure of the base (the Sm—Fe—N magnetic material portion corresponding to the core) cannot be confirmed.

[0052] (Composition) Elemental analysis of the test powder was performed using the analytical method described above. The results are shown in Table 1 (the same applies to each of the following examples). The test powder in this example had an Sm / Fe molar ratio of 0.16, an N / Fe molar ratio of 0.22, and an (Al+Ae) / Fe molar ratio of 0.23.

[0053] (Particle size distribution) The particle size distribution of the test powder was measured by the method described above. As a result, the test powder of this example had a cumulative 50% particle diameter D ５０ was 1.9 μm.

[0054] (Coating Amount Index R) The coating amount index R of the test powder was calculated using the above formula (1). As a result, the coating amount index R of the test powder in this example was 0.43 μm.

[0055] (Coercive force) The magnetic properties of the test powder were measured by the above method. As a result, the coercive force H ｃ was 1060 kA / m (13.3 kOe).

[0056] (Evaluation of Heat Resistance) 0.1 g of the test powder sample was placed on a stainless steel tray and placed in a constant temperature dryer (DRA-630DB, manufactured by ADVANTEC) heated to 300°C, and subjected to a heating test in which the sample was heated and held at 300°C for 120 minutes in an atmospheric atmosphere (i.e., in air). Thereafter, the stainless steel tray was removed from the constant temperature dryer, and the powder sample was allowed to cool in air at room temperature. After this heating test, magnetic measurements were carried out on the powder sample in the same manner as above, and the coercive force H after the heating test was 1.0 g. ｃ The coercive force reduction rate δH ｃ was calculated using the following formula (2): ｃ = 100 × (H ｃ０ -H ｃ１ ) / H ｃ０ ...(2) Here, H ｃ０ is the coercive force (kA / m) of the powder before the heating test, H ｃ１ is the coercive force (kA / m) of the powder after the heating test. ｃ was 100 × (1060 − 780) / 1060 ≒ 26.4%.

[0057] Figure 6 shows an example of a high-angle annular dark-field (HAADF) image observed by STEM (scanning transmission electron microscope) of the particles constituting the test powder of this example after a 120-minute heating test at 300°C in air. The white portion represents the Sm—Fe—N magnetic material portion corresponding to the core, and the gray portion along its outline represents the coating layer. Figure 7 shows an example of the element concentration profile of O (oxygen), Fe (iron), and Al (aluminum) measured by EDS (energy dispersive X-ray spectroscopy) line analysis along the line segment AB shown in Figure 6. The portion with a high Al concentration approximately 0.27 μm away from A represents the location of the coating layer. It can be seen that the coating layer prevents oxygen from penetrating into the Sm—Fe—N magnetic material portion corresponding to the core. In other words, it is inferred that the coating layer according to the present invention functions as a barrier layer that prevents oxygen from penetrating during heating in air, thereby achieving excellent resistance to coercivity degradation.

[0058] [Example 2] In this example, the properties of an Al-Mg alloy-coated Sm-Fe-N magnetic powder that had not been subjected to densification treatment were examined as a test powder. Specifically, an Sm-Fe-N magnetic powder was obtained through the steps of gas atomization, heat treatment, pulverization, hydrogen treatment, nitriding, cleaning, and film formation under the same conditions as in Example 1. This powder (corresponding to the powder before densification treatment in Example 1) was used as a test powder and subjected to elemental analysis, particle size distribution measurement, magnetic measurement, and heat resistance evaluation using the same methods as described above.

[0059] The properties of the test powder in this example were as follows: Sm / Fe molar ratio was 0.17, N / Fe molar ratio was 0.23, and (Al+Ae) / Fe molar ratio was 0.23. The cumulative 50% particle diameter D in the volume-based particle size distribution measured by the laser diffraction / scattering method was ５０ The coating thickness index R was 0.47 μm. ｃ The coercive force H of the powder after the heating test at 300°C for 120 minutes in the atmosphere was 1170 kA / m (14.7 kOe). ｃ is 560 kA / m (7.0 kOe), and the coercive force reduction rate δH calculated by the above formula (2) is ｃ The figure was 52.1%.

[0060] Comparative Example 1 In this example, the characteristics of an Al-Mg alloy-coated Sm-Fe-N magnetic powder without a coating layer were examined as a test powder. Specifically, an Sm-Fe-N magnetic powder was obtained through the steps of gas atomization, heat treatment, pulverization, hydrogen treatment, nitriding, and washing under the same conditions as in Example 1. This powder (corresponding to the film-forming material in Example 1) was used as a test powder and subjected to elemental analysis, particle size distribution measurement, magnetic measurement, and heat resistance evaluation using the same methods as described above.

[0061] The properties of the test powder in this example were as follows: Sm / Fe molar ratio was 0.17, N / Fe molar ratio was 0.21, and (Al+Ae) / Fe molar ratio was 0.00. The cumulative 50% particle diameter D in the volume-based particle size distribution measured by the laser diffraction / scattering method was ５０ The thickness was 1.8 μm. Since no coating layer was formed, the coating amount index R was 0.00 μm. ｃThe coercive force H of the powder after the heating test at 300°C for 120 minutes in the atmosphere was 750 kA / m (9.4 kOe). ｃ is 120 kA / m (1.5 kOe), and the coercive force reduction rate δH calculated by the above formula (2) is ｃ was 84.0%.

[0062] [Example 3] (Synthesis of Sm—Fe-based powder by gas atomization method) A gas atomized powder was obtained in the same manner as in Example 1, except that 1700 g of an Sm—Fe alloy with a Sm / Fe molar ratio of 0.15 was used as the raw material, the molten metal temperature during discharge was 1500°C, and particle removal by sieving was not performed after powder recovery. Elemental analysis of the gas atomized powder revealed that the Sm / Fe molar ratio was 0.15, which was equivalent to that of the raw material alloy. Furthermore, the cumulative 50% particle diameter D ５０ was 52.5 μm.

[0063] (Heat Treatment) An electrically heated tubular furnace capable of treatment in a gas atmosphere was used as the heat treatment furnace. The Sm—Fe gas-atomized powder was placed in a sample container and loaded into the furnace. The temperature was raised from room temperature to 990° C. at a rate of 10° C. / min while flowing argon gas, and then held at 990° C. for 60 minutes. Thereafter, the temperature was cooled to 50° C. or less while flowing argon gas to obtain a heat-treated powder.

[0064] (Pulverization) 500 g of heat-treated powder was pulverized using a vibration mill (YAMP-6SND, manufactured by Uras Techno Co., Ltd.). 500 g of heat-treated powder, 12,500 g of 3.2 mm diameter chrome steel balls, and 5.9 g of 2-propanol were placed in a 3 L stainless steel pot in a glove box filled with nitrogen gas, sealed, and pulverized for 84 minutes at an amplitude of ±2.5 mm and a frequency of 29.1 Hz. The pulverized sample was separated from the balls in the glove box filled with nitrogen gas, and the pulverized powder was obtained.

[0065] (Nitriding Treatment) The pulverized powder obtained as described above was transferred into an electrically heated tubular furnace under a nitrogen gas atmosphere, and then ammonia (NH ３ ) gas 35% by volume, hydrogen (H ２A mixed gas of 65% by volume of hydrogen (H ) gas was then flowed to replace the gas inside the furnace. Then, while flowing the mixed gas, the temperature was raised to 390°C at a rate of 5°C / min and held at 390°C for 260 minutes to perform nitriding treatment. Next, the gas flowing in the tubular furnace was changed to hydrogen (H ). ２ The gas flowing through the tubular furnace was changed to argon gas and the temperature was maintained at 390°C for another 130 minutes. After that, the gas flowing through the tubular furnace was changed to argon gas and the temperature was maintained at 390°C for 90 minutes. After that, the heating was stopped and the mixture was cooled to a temperature near room temperature while the argon gas was being flowed, to obtain a Sm-Fe-N magnetic powder.

[0066] (Film Formation) Using the Sm—Fe—N magnetic powder obtained by the above procedure as the film-forming material, the surfaces of the powder particles were coated with an Al—Mg alloy in the same manner as in Example 1, except that the output ratio settings of both sputtering cathodes were changed and the film-forming time was adjusted so that the average film thickness of the coating layer would be about 29 nm. In this example, a coating layer with an Al:Mg molar ratio of 67:33 was formed.

[0067] (Densification Treatment) After the film formation, the Sm-Fe-N magnetic powder was subjected to the same heat treatment as in Example 1 to perform densification treatment, thereby obtaining a test powder.

[0068] The obtained Sm-Fe-N magnetic powder (test powder) was subjected to elemental analysis, particle size distribution measurement, magnetic measurement, and evaluation of heat resistance in the same manner as in Example 1 (the same applies to each of the following examples). As a result, the Sm / Fe molar ratio was 0.14, the N / Fe molar ratio was 0.18, the (Al+Ae) / Fe molar ratio was 0.09, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by the laser diffraction / scattering method was 0.09. ５０ is 3.2 μm, the coverage index R is 0.29 μm, and the coercive force H ｃ is 490 kA / m (6.2 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 330 kA / m (4.1 kOe), and the coercive force reduction rate δH calculated by the above formula (2) ｃ The figure was 32.7%.

[0069] Example 4 A Sm-Fe-N magnetic powder (test powder) was obtained in the same manner as in Example 3, except that in the film-forming step, the film-forming time was adjusted so that the average film thickness of the coating layer was about 55 nm. In this example, a coating layer with an Al to Mg molar ratio of 66:34 was formed. The Sm / Fe molar ratio of this test powder was 0.14, the N / Fe molar ratio was 0.18, the (Al + Ae) / Fe molar ratio was 0.18, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by laser diffraction / scattering method was 0.14. ５０ is 3.3 μm, the coverage index R is 0.59 μm, and the coercive force H ｃ is 510 kA / m (6.4 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 370 kA / m (4.6 kOe), and the coercive force reduction rate δH calculated by the above formula (2) ｃ was 27.5%.

[0070] [Example 5] A Sm-Fe-N magnetic powder (test powder) was obtained in the same manner as in Example 3, except that in the film-forming step, the film-forming time was adjusted so that the average film thickness of the coating layer was about 82 nm. In this example, a coating layer with an Al to Mg molar ratio of 66:34 was formed. The Sm / Fe molar ratio of this test powder was 0.13, the N / Fe molar ratio was 0.18, the (Al + Ae) / Fe molar ratio was 0.27, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by laser diffraction / scattering method was 0.02. ５０ is 3.4 μm, the coverage index R is 0.92 μm, and the coercive force H ｃ is 510 kA / m (6.4 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 350 kA / m (4.4 kOe), and the coercive force reduction rate δH calculated by the above formula (2) ｃ The figure was 31.4%.

[0071] [Example 6] A Sm-Fe-N magnetic powder (test powder) was obtained in the same manner as in Example 3, except that in the film-forming process, the output ratio settings of both sputtering cathodes were changed, and the film-forming time was adjusted so that the average film thickness of the coating layer was about 53 nm. In this example, a coating layer with an Al to Mg molar ratio of 54:46 was formed. The Sm / Fe molar ratio of this test powder was 0.14, the N / Fe molar ratio was 0.18, the (Al + Ae) / Fe molar ratio was 0.17, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by laser diffraction / scattering method was 0.14. ５０ is 3.2 μm, the coverage index R is 0.54 μm, and the coercive force H ｃ is 530 kA / m (6.7 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 410 kA / m (5.2 kOe), and the coercive force reduction rate δH calculated by the above formula (2) is ｃ was 22.6%.

[0072] Example 7 A Sm-Fe-N magnetic powder (test powder) was obtained in the same manner as in Example 6, except that in the film-forming step, the film-forming time was adjusted so that the average film thickness of the coating layer was about 99 nm. In this example, a coating layer with an Al to Mg molar ratio of 55:45 was formed. The Sm / Fe molar ratio of this test powder was 0.14, the N / Fe molar ratio was 0.18, the (Al + Ae) / Fe molar ratio was 0.33, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by laser diffraction / scattering method was 0.14. ５０ is 3.2 μm, the coverage index R is 1.06 μm, and the coercive force H ｃ is 530 kA / m (6.7 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 410 kA / m (5.2 kOe), and the coercive force reduction rate δH calculated by the above formula (2) is ｃ was 22.6%.

[0073] [Example 8] A Sm-Fe-N magnetic powder (test powder) was obtained in the same manner as in Example 3, except that in the film formation process, Mg was replaced with Ca as the alkaline earth metal element Ae, the output ratio settings of both sputtering cathodes were changed, and the film formation time was adjusted so that the average film thickness of the coating layer was approximately 45 nm. In this example, a coating layer was formed with an Al to Ca molar ratio of 72:28. The Sm / Fe molar ratio of this test powder was 0.14, the N / Fe molar ratio was 0.18, the (Al + Ae) / Fe molar ratio was 0.11, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by laser diffraction / scattering method was 0.14. ５０ is 3.1 μm, the coverage index R is 0.34 μm, and the coercive force H ｃ is 490 kA / m (6.2 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 350 kA / m (4.4 kOe), and the coercive force reduction rate δH calculated by the above formula (2) ｃ was 28.6%.

[0074] Example 9 A Sm-Fe-N magnetic powder (test powder) was obtained in the same manner as in Example 8, except that in the film-forming step, the film-forming time was adjusted so that the average film thickness of the coating layer was about 124 nm. In this example, a coating layer with an Al to Ca molar ratio of 72:28 was formed. The Sm / Fe molar ratio of this test powder was 0.13, the N / Fe molar ratio was 0.18, the (Al + Ae) / Fe molar ratio was 0.32, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by laser diffraction / scattering method was 0.13. ５０ is 3.1 μm, the coverage index R is 0.99 μm, and the coercive force H ｃ is 600 kA / m (7.5 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 370 kA / m (4.6 kOe), and the coercive force reduction rate δH calculated by the above formula (2) ｃ The rate was 38.3%.

[0075] [Comparative Example 2] In this example, by omitting the film-forming process and densification process in Example 3, an Sm-Fe-N magnetic powder without a coating layer was produced, and its properties were investigated. That is, the test powder in this example corresponds to an Sm-Fe-N magnetic powder at the stage where the process up to the nitriding treatment was completed in the same manner as in Example 3. The Sm / Fe molar ratio of this test powder was 0.15, the N / Fe molar ratio was 0.19, the (Al + Ae) / Fe molar ratio was 0.00, and the cumulative 50% particle diameter D in the volume-based particle size distribution measured by the laser diffraction / scattering method was 0.00. ５０ is 3.0 μm, the coating amount index R is 0.00 μm, and the coercive force H ｃ is 590 kA / m (7.4 kOe), and the coercive force H after a heating test in air at 300°C for 120 minutes ｃ is 180 kA / m (2.3 kOe), and the coercive force reduction rate δH calculated by the above formula (2) ｃ The result is shown in Table 1.

[0076]

[0077] The Sm-Fe-N magnetic powder of the example on which the Al-Ae alloy coating layer was formed had a coercive force reduction rate δH when subjected to a severe heating test in which the powder was heated in air at 300°C for 120 minutes. ｃ The coercivity reduction resistance was significantly improved compared to the Sm—Fe—N magnetic powders of Comparative Examples 1 and 2, which did not have the coating layer. It was also confirmed that the coercivity reduction resistance was further improved by applying the densification treatment (comparison between Example 1 and Example 2).

[0078] REFERENCE SIGNS LIST 1 crucible 2 molten metal discharge nozzle member 3 stopper 4 high frequency coil 5 molten metal 6 gas injection nozzle 7 solidified metal particles 10 vacuum exhaust device 11a, 11b atmospheric gas supply source 12 injection gas supply device 13 molten metal discharge gas supply device 21 discharge port 22 stopper contact surface 51 film formation chamber 52 glove box 53 glove port 54 sputtering cathode 55 powder storage container 56 stirring rod 57 stepping motor

Claims

1. Highly heat-resistant Sm-Fe-N magnetic powder, which is composed of Sm-Fe-N magnetic particles having an Al-Ae alloy coating layer on the surface, where Ae is an alkaline earth metal element.

2. High heat resistance Sm-Fe-N magnetic powder according to claim 1, wherein the Sm / Fe molar ratio is from 0.09 to 0.25, and the N / Fe molar ratio is from 0.06 to 0.

30.

3. Cumulative 50% particle diameter D in volume-based particle size distribution by laser diffraction / scattering method ５０ The highly heat-resistant Sm-Fe-N magnetic powder according to claim 1, wherein the surface roughness is 0.5 μm or more and 5.0 μm or less, and the coating amount index R expressed by the following formula (1) is 0.10 μm or more and 2.00 μm or less. ５０ ...(1) Here, the value of the (Al+Ae) / Fe molar ratio in the powder having an Al-Ae based alloy coating layer is substituted for [(Al+Ae) / Fe] in the formula (1), and D ５０ The cumulative 50% particle diameter D ５０ The value of (μm) is substituted.

4. High heat resistance Sm-Fe-N magnetic powder according to claim 3, wherein the coating amount index R is 0.10 μm or more and 1.00 μm or less.

5. The highly heat-resistant Sm-Fe-N magnetic powder according to claim 1, wherein the alkaline earth metal element Ae is one or more elements selected from the group consisting of Mg and Ca.

6. When subjected to a heating test in which the material is held in air at 300°C for 120 minutes, the coercive force reduction rate δH expressed by the following formula (2) ｃ 2. The highly heat-resistant Sm—Fe—N magnetic powder according to claim 1, wherein δH ｃ = 100 × (H ｃ０ -H ｃ１ ) / H ｃ０ ... (2) Here, H ｃ０ is the coercive force (kA / m) of the powder before the heating test, H ｃ１ is the coercive force (kA / m) of the powder after the heating test.

7. A method for producing highly heat-resistant Sm-Fe-N magnetic powder, comprising a film-forming process for forming a coating layer of an Al-Ae alloy on the surfaces of particles constituting the Sm-Fe-N magnetic powder, which is a film-forming material, by a vapor phase growth method, when an alkaline earth metal element is represented as Ae.

8. A method for producing a highly heat-resistant Sm-Fe-N magnetic powder as described in claim 7, wherein the vapor phase growth method is a sputtering method, and in the film formation step, a coating layer of an Al-Ae alloy is formed on the surfaces of particles constituting the Sm-Fe-N magnetic powder by a sputtering method while stirring and flowing the Sm-Fe-N magnetic powder as the film formation material in a sputtering film formation device.

9. A method for producing a highly heat-resistant Sm-Fe-N magnetic powder as described in claim 7, wherein the Sm-Fe-N magnetic powder, which is the material to be filmed, has a composition in which the Sm / Fe molar ratio is 0.09 or more and 0.25 or less, and the N / Fe molar ratio is 0.06 or more and 0.30 or less.

10. The Sm-Fe-N magnetic powder, which is the material to be coated, has a cumulative 50% particle diameter D in the volume-based particle size distribution measured by the laser diffraction / scattering method. ５０ 8. The method for producing a highly heat-resistant Sm-Fe-N magnetic powder according to claim 7, wherein the thickness of the powder is 0.5 μm or more and 5.0 μm or less, and in the film-forming step, Al and an alkaline earth metal element Ae are deposited so that a coverage index R expressed by the following formula (1) is 0.10 μm or more and 2.00 μm or less. Coverage index R=[(Al+Ae) / Fe]×D ５０ ...(1) Here, the value of the (Al+Ae) / Fe molar ratio in the powder having an Al-Ae based alloy coating layer is substituted for [(Al+Ae) / Fe] in the formula (1), and D ５０ The cumulative 50% particle diameter D ５０ The value of (μm) is substituted.

11. A method for producing a highly heat-resistant Sm-Fe-N magnetic powder as set forth in claim 10, wherein in the film-forming step, Al and an alkaline earth metal element Ae are deposited so that the coverage index R is 0.10 μm or more and 1.00 μm or less.

12. A method for producing a highly heat-resistant Sm-Fe-N magnetic powder as set forth in claim 7, wherein the Sm-Fe-N magnetic powder as a film-forming material is obtained by a production method comprising the steps of: a heat treatment step of heating a powder of Sm-Fe alloy having a Sm / Fe molar ratio of 0.09 or more and 0.25 or less, formed during a solidification process by a gas atomization method, to a temperature of 900°C or more and 1200°C or less, thereby coarsening the crystal grains of the powder particles; a crushing step of crushing the Sm-Fe alloy powder whose crystal grains have been coarsened by the heat treatment step, thereby reducing the particles of the powder by fracture, including intragranular fracture; and a nitriding step of heating and maintaining the Sm-Fe alloy powder refined by the crushing step at a temperature of 500°C or less in an atmosphere of a nitrogen compound or nitrogen-containing non-oxidizing gas, thereby introducing nitrogen into the powder particles.

13. The method for producing a highly heat-resistant Sm-Fe-N magnetic powder according to claim 7, further comprising a densification step of heating the Sm-Fe-N magnetic powder obtained in the film-forming step in a non-oxidizing atmosphere to a temperature T (°C) that satisfies the following formula (4): 450≦T(°C)≦550 ... (4) 14. In the film forming process, the melting start temperature T Ｍ The method for producing the highly heat-resistant Sm-Fe-N magnetic powder according to claim 7 further comprises a densification treatment step of heating the Sm-Fe-N magnetic powder obtained in the film-forming step in a non-oxidizing atmosphere to a temperature T (°C) that satisfies the following formula (3): T Ｍ (°C)-100≦T(°C)≦550 ... (3)

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