Highly heat-resistant Sm-Fe-N-based magnetic powder and method for producing same

Abstract

The purpose of the present invention is to improve the heat resistance of an Sm-Fe-N magnetic powder in an oxidizing atmosphere. The above-mentioned problem is achieved by 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 when an alkaline earth metal element is represented by Ae. The Sm / Fe molar ratio of the powder 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. In addition, the cumulative 50% particle diameter D50 of the powder in the volume-based particle size distribution obtained by a laser diffraction scattering method is 0.5 [mu] m or more and 5.0 [mu] m or less, for example. More than one of Mg and Ca can be adopted as the alkaline earth metal element Ae. The coating layer can be formed by co-sputtering Al and Ae using, for example, a sputtering film formation device.

Description

Technical Field

[0001] This invention relates to a highly heat-resistant Sm-Fe-N magnetic powder exhibiting excellent resistance to coercivity reduction when heated in an atmospheric atmosphere, and its manufacturing method. Background Technology

[0002] It is known that in Sm2Fe 17 Intermetallic compounds in which nitrogen has been introduced (a representative example is Sm2Fe). 17 N3) is a strongly magnetic material exhibiting excellent hard magnetism. In this specification, Sm2Fe will be used... 17 Powders containing nitrogen-containing substances in Sm-Fe alloys with a stoichiometric composition or its peripheral composition are called "Sm-Fe-N magnetic powders". Sm-Fe-N magnetic powders can be used as raw materials for bonding magnets.

[0003] In order to manufacture bonded magnets, a process is required to heat-treat the magnetic powder together with the resin used as a binder. Therefore, for Sm-Fe-N magnetic powders used for bonded magnets, the heat resistance should be as low as possible to minimize the reduction in magnetic properties (especially coercivity) caused by the aforementioned heat treatment.

[0004] Patent Document 1 discloses an Sm-Fe-N based magnetic powder having a core-shell structure containing Sm and Fe in a specific composition, and also containing P (phosphorus). This magnetic powder is said to have excellent heat resistance, enabling high-temperature molding of adhesives such as polyphenylene sulfide resins, which have high heat resistance themselves (paragraph 0094).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2022-177699 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In recent years, Sm-Fe-N bonded magnets made of SPS (syndiotactic polystyrene) resin and PPS (polyphenylene sulfide) resin, which possess excellent strength and chemical properties, have been required for automotive engine applications. To mass-produce bonded magnets using these resins industrially, heating at approximately 300°C in atmospheric conditions is necessary. Patent Document 1 describes polyphenylene sulfide resin as mentioned above. However, the heat resistance evaluation in Patent Document 1 uses heating at 300°C for 90 minutes in an argon atmosphere (paragraph 0106). In the technique disclosed in Patent Document 1 for forming a shell layer primarily composed of Sm and Fe, it is difficult to sufficiently suppress the decrease in coercivity when heated to approximately 300°C in an oxidizing atmosphere.

[0010] To advance the practical application of Sm-Fe-N based bonded magnets using the aforementioned SPS and PPS resins, it is necessary to improve the heat resistance of Sm-Fe-N based magnetic powders in oxidizing atmospheres. The object of this invention is to provide Sm-Fe-N based magnetic powders with improved heat resistance in oxidizing atmospheres.

[0011] Methods for solving problems

[0012] The inventors discovered that by coating the surface of Sm-Fe-N magnetic particles with an alloy film of Al (aluminum) and alkaline earth metals, the heat resistance of powder composed of these magnetic particles in the atmosphere, specifically the resistance to coercivity reduction when heated to approximately 300°C in the atmosphere, can be significantly improved. The research results indicate that the aforementioned alloy film functions as a barrier layer to prevent oxygen intrusion. This alloy film can be formed using a vapor-phase growth method that does not easily cause thermal damage to the Sm-Fe-N magnetic particles. Furthermore, by subjecting the Sm-Fe-N magnetic powder with the Al-alkaline earth metal alloy coating to a heat treatment at a specified temperature in a non-oxidizing atmosphere, the coating layer can be densified. This densification process further improves the resistance to coercivity reduction when heated to approximately 300°C in the atmosphere. This invention was made based on this understanding.

[0013] The above objectives are achieved through the following invention.

[0014] [1] High heat-resistant Sm-Fe-N magnetic powder, which is formed by Sm-Fe-N magnetic particles with an Al-Ae alloy coating on the surface when the alkaline earth metal element is represented as Ae.

[0015] [2] According to the high heat resistance Sm-Fe-N magnetic powder described in [1] above, 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.

[0016] [3] According to the high heat-resistant Sm-Fe-N magnetic powder described in [1] or [2] above, wherein laser diffraction is employed. The cumulative 50% particle size D in the volume-based particle size distribution of the scattering method 50 For a thickness of 0.5 μm or more and 5.0 μm or less, the coverage index R, expressed by the following formula (1), is 0.10 μm or more and 2.00 μm or less.

[0017] Coverage index R = [(Al + Ae) / Fe] × D 50 …(1)

[0018] In equation (1), the value of the (Al+Ae) / Fe molar ratio in the powder with the Al-Ae alloy coating is substituted into [(Al+Ae) / Fe], and D is obtained. 50 Substitute the cumulative 50% particle size D into the value. 50 The value of (μm).

[0019] [4] According to the high heat resistance Sm-Fe-N magnetic powder described in [3] above, wherein the coating index R is above 0.10 μm and below 1.00 μm.

[0020] [5] The high heat-resistant Sm-Fe-N magnetic powder according to any one of [1] to [4] above, wherein the alkaline earth metal element Ae is selected from one or more elements of Mg and Ca.

[0021] [6] The high heat-resistant Sm-Fe-N magnetic powder according to any one of [1] to [5] above, wherein, when subjected to a heating test at 300°C in the atmosphere for 120 minutes, the coercivity reduction rate δH expressed by the following formula (2) is given. c Below 60%,

[0022] δH c =100×(H) c0 -H c1 ) / H c0 …(2)

[0023] Among them, H c0 H represents the coercivity (kA / m) of the powder before the heating test. c1 The coercivity (kA / m) of the powder after the heating test.

[0024] [7] A method for manufacturing high heat-resistant Sm-Fe-N magnetic powder, which includes a film-forming process, wherein when the alkaline earth metal element is represented as Ae, an Al-Ae alloy coating is formed on the surface of the particles constituting the Sm-Fe-N magnetic powder as the film-forming material by vapor phase growth.

[0025] [8] According to the manufacturing method of high heat resistance Sm-Fe-N magnetic powder described in [7] above, wherein the vapor phase growth method is a sputtering method, and in the film forming process, while stirring and flowing the Sm-Fe-N magnetic powder as the film forming material in the sputtering film forming device, an Al-Ae alloy coating layer is formed on the surface of the particles constituting the Sm-Fe-N magnetic powder by sputtering.

[0026] [9] According to the manufacturing method of the high heat-resistant Sm-Fe-N magnetic powder described in [7] or [8] above, the Sm-Fe-N magnetic powder used as the film-forming material 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.

[0027]

[10] The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to any one of [7] to [9] above, wherein the Sm-Fe-N magnetic powder used as the film-forming material is subjected to laser diffraction. The cumulative 50% particle size D in the volume-based particle size distribution of the scattering method 50 The coating thickness is 0.5 μm or more and 5.0 μm or less. In the film-forming process, Al and alkaline earth metal element Ale are coated in such a way that the coating thickness index R, as expressed by the formula (1), is 0.10 μm or more and 2.00 μm or less.

[0028]

[11] In the method for manufacturing high heat-resistant Sm-Fe-N magnetic powder as described in

[10] above, in the film-forming process, Al and alkaline earth metal element Ale are coated such that the coating amount index R is 0.10 μm or more and 1.00 μm or less.

[0029]

[12] The method for manufacturing high 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 the film-forming material, is obtained by a manufacturing method having the following steps:

[0030] In the heat treatment process, powder of Sm-Fe alloy with an Sm / Fe molar ratio of 0.09 or higher and 0.25 or lower, formed during solidification using a gas atomization method, is heated to a temperature of 900°C or higher and 1200°C or lower, thereby coarsening the grain size of the powder particles.

[0031] The pulverization process, wherein the powder of an Sm-Fe alloy, whose grains have been coarsened by the heat treatment process, is pulverized, thereby refining the powder particles through fracture involving intragranular damage; and

[0032] The nitriding process involves introducing nitrogen into the powder particles by heating the finely pulverized Sm-Fe alloy powder in a non-oxidizing gas atmosphere containing nitrogen compounds or nitrogen and maintaining the temperature range below 500°C.

[0033]

[13] The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to any one of [7] to

[12] above further includes a densification process, wherein the Sm-Fe-N magnetic powder obtained in the film-forming process is heated in a non-oxidizing atmosphere to a temperature T (°C) that satisfies the following formula (4).

[0034] 450≤T(℃)≤550 …(4).

[0035]

[14] The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to any one of [7] to

[12] above, wherein, in the film-forming process, the melting start temperature T is formed. M The coating is an Al-Ae alloy with a composition below 600°C, and also includes a densification process in which the Sm-Fe-N magnetic powder obtained in the film-forming process is heated in a non-oxidizing atmosphere to a temperature T (°C) that satisfies the following formula (3).

[0036] T M (°C) -100≤T(°C)≤550 …(3).

[0037] The effects of the invention

[0038] According to the present invention, the coercivity reduction resistance during atmospheric heating can be significantly improved in Sm-Fe-N based magnetic powders. The present invention can be applied to the manufacture of bonded magnets involving processes of heating to approximately 300°C in the atmosphere, and can facilitate the practical application of Sm-Fe-N based bonded magnets using resins with excellent strength, heat resistance, and chemical properties, such as SPS resin and PPS resin, as binder components. Attached Figure Description

[0039] Figure 1 This diagram schematically illustrates the configuration of the gas atomizing device used in the embodiments and comparative examples.

[0040] Figure 2 This diagram schematically illustrates the cross-sectional structure near the bottom of the crucible in the gas atomizing apparatus used in the embodiments and comparative examples.

[0041] Figure 3 This diagram schematically illustrates the configuration of the sputtering film-forming apparatus used in the embodiments.

[0042] Figure 4 To illustrate Figure 3A diagram showing the internal structure of the film-forming chamber 51 of the sputtering film-forming apparatus.

[0043] Figure 5 The graph shows the energy spectrum of the photoelectron peaks of Mg and Fe, measured by X-ray photoelectron spectrometry for the Sm-Fe-N magnetic powder obtained in Example 1 at etching times of 0 seconds and 600 seconds.

[0044] Figure 6 For example, the image shows a HAADF (High Angle Circular Dark Field) image of the powder particles obtained in Example 1 after heating them at 300°C in the atmosphere for 120 minutes.

[0045] Figure 7 For example, along Figure 6 The graph shown is a distribution of the elemental concentrations of O, Fe, and Al measured by line segment AB. Detailed Implementation

[0046] [Sm-Fe-N system magnetic particles]

[0047] The Sm(samarium)-Fe(iron)-N(nitrogen) based magnetic powder of the present invention consists of Sm-Fe-N based magnetic particles having a coating layer formed of an alloy of Al(aluminum) and alkaline earth metals on the surface of the particles of the Sm-Fe-N based magnetic body. These Sm-Fe-N based magnetic particles can be referred to as core-shell structured particles, with a portion of the Sm-Fe-N based magnetic body as the core and a portion of the coating layer as the shell.

[0048] [Magnetic material]

[0049] The magnetic body, equivalent to the nucleus of the aforementioned Sm-Fe-N system magnetic particles, introduces N (nitrogen) atoms as Th2Zn. 17 Sm2Fe with a crystal structure of type 17 The magnetic phase of the crystal lattice is the main component. It is assumed that N atoms enter Sm₂Fe. 17 The invasive position of the lattice remains Th2Zn even after the introduction of N atoms. 17 Type-shaped crystal structure. If in Sm₂Fe 17 Introducing nitrogen atoms into the crystal changes its magnetic anisotropy from in-plane to uniaxial, and simultaneously increases the Curie temperature, making it a practical magnet material. A representative composition of Sm-Fe-N magnetic materials with excellent magnetic properties is Sm₂Fe. 17 N3. It is believed that the closer the Sm / Fe molar ratio (representing the molar ratio of Sm to Fe) and the N / Fe molar ratio (representing the molar ratio of N to Fe) are to Sm2Fe, the better. 17The more favorable the stoichiometric composition of N3 is in terms of magnetic properties, the more hard magnetism will be exhibited in the surrounding compositional regions. (Sm2Fe) 17 The stoichiometric Sm / Fe molar ratio of N3 is 0.118, and the N / Fe molar ratio is 0.176. In the Sm-Fe-N magnetic body of the present invention, considering that the effective coercivity as a raw material for bonding magnets can be stably obtained within a temperature range including room temperature, it is preferable to adjust the composition to a range where the Sm / Fe molar ratio is 0.09 or higher and 0.25 or lower, and the N / Fe molar ratio is 0.06 or higher and 0.30 or lower. Since Sm, Fe, and N are not used in the constituent elements of the coating layer, the composition of the Sm-Fe-N magnetic powder of the present invention, which includes both the magnetic body and the coating layer, preferably has Sm / Fe molar ratios and N / Fe molar ratios within the above-mentioned ranges. It should be noted that in the magnetic body corresponding to the core, besides Sm2Fe containing N... 17 In addition to the TbCu7 phase, other phases such as the SmFe7 phase with a TbCu7 crystal structure are sometimes mixed in, but the presence of other phases is permissible as long as it does not hinder the purpose of this invention.

[0050] [Covering layer]

[0051] The coating layer of the aforementioned Sm-Fe-N magnetic particles is formed by an alloy of Al and alkaline earth metals. In this specification, alkaline earth metals are represented 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 powder composed of particles coated with an Al-Ae alloy exhibits excellent resistance to coercivity reduction, a problem that arises when heated to approximately 300°C in air. The reason for this is that the coating formed by the Al-Ae alloy functions as a barrier layer to prevent oxygen from penetrating the Sm-Fe-N magnetic body, which corresponds to the core, when the Sm-Fe-N magnetic powder is heated to approximately 300°C in an oxidizing gas such as air. Regarding the composition of the Al-Ae alloy, depending on the type of alkaline earth metal element used, the Ae / (Al+Ae) molar ratio only needs to be set within the range of 0.05 to 0.95, and can be managed to a range of 0.20 to 0.60 or 0.25 to 0.50. An appropriate Al-Ae alloy composition based on the type of alkaline earth metal element can be determined, for example, through preliminary experiments with several compositions.

[0052] As described below, the aforementioned coating layer can be formed, for example, by sputtering. The coating layer in this film-forming state also improves resistance to coercivity reduction, and this resistance can be further improved by performing the densification heat treatment described later. Regarding the composition of the Al-Ae alloy, considering the need for efficient densification heat treatment in a short time, it is preferable to adjust the composition to a melting start temperature of approximately 600°C or lower. From this viewpoint, for example, a preferred composition range when using an Al-Mg binary alloy is a Mg / (Al+Mg) molar ratio of 0.10 to 0.95, and for example, a preferred composition range when using an Al-Ca binary alloy is a Ca / (Al+Ca) molar ratio of 0.35 to 0.90.

[0053] If a powder sputtering apparatus capable of simultaneously agitating powder particles and sputtering a film onto the particle surface is used, the entire surface of the nucleated particles can be covered with a coating layer exhibiting high uniformity in film thickness. With such a highly uniform coating layer, it is believed that by ensuring an average film thickness of, for example, 10 nm or more, excellent resistance to coercivity reduction can be achieved even when heated to approximately 300°C in the atmosphere. More preferably, the film formation conditions are set such that the average film thickness of the coating layer is in the range of 20 nm or more and 100 nm or less. The thickness of the coating layer can be confirmed, for example, by observing a HAADF (High Angle Annular Dark Field) image of the particles using STEM (Scanning Transmission Electron Microscopy).

[0054] The amount of coating can also be determined by the chemical composition and particle size of the powder. For example, the molar ratio of (Al+Ae) / Fe relative to the total amount of Fe, the constituent element of the magnetic particles corresponding to the core, Al, and the alkaline earth metal element Ae in the coating is used as an indicator of the proportion of the amount of coating in the powder particles. In addition, it has been found that if the (Al+Ae) / Fe molar ratio is the same, the particle size becomes larger and the average film thickness of the coating becomes larger. It is preferable to adjust the amount of coating to an effective range according to the particle size. As a result of various studies, in the Sm-Fe-N magnetic powder of the present invention, it is preferable that the coating amount index R, expressed by the following formula (1), is 0.10 μm or more and 2.00 μm or less. From the viewpoint of balancing heat resistance and cost, it is particularly preferable that the coating amount index R is 0.10 μm or more and 1.00 μm or less.

[0055] Coverage index R = [(Al + Ae) / Fe] × D 50 …(1)

[0056] In equation (1), the value of the (Al+Ae) / Fe molar ratio in the powder with the Al-Ae alloy coating is substituted into [(Al+Ae) / Fe], and D is obtained. 50Substitute the cumulative 50% particle size D into the value. 50 The value of (μm).

[0057] [Particle size]

[0058] Regarding the Sm-Fe-N based magnetic powder of the present invention, if its use as a magnetic material for bonding magnets is considered, laser diffraction is preferred. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 It is between 0.5μm and 5.0μm.

[0059] [Heat resistance of Sm-Fe-N based magnetic powder]

[0060] In Sm-Fe-N based magnetic powders used in bonded magnets with high-temperature-resistant and high-strength resins (such as the aforementioned SPS resin, PPS resin, etc.) as binders, in order to fully adapt to the mass production process of such bonded magnets, for example, when subjected to a heating test at 300°C in the atmosphere for 120 minutes, it is preferable to have a coercivity reduction rate δH expressed by the following formula (2). c Achieving a heat resistance of less than 60%. More preferably, it exhibits a coercivity reduction rate δH. c The heat resistance is preferably 45% or less, and more preferably 35% or less. The reduction rate of coercivity δH c There is no particular lower limit, which is defined as δH that can be manufactured without generating excessive process load. c The range, for example, can be exemplified as a range of 15% or more.

[0061] δH c =100×(H) c0 -H c1 ) / H c0 …(2)

[0062] Among them, H c0 H represents the coercivity (kA / m) of the powder before the heating test. c1 The coercivity (kA / m) of the powder after the heating test.

[0063] [Film Forming Process]

[0064] Sm-Fe-N magnetic powder, the material to be formed, can be obtained using known synthesis methods such as reduction diffusion and gas atomization. Vapor phase growth is preferred as a film-forming method that minimizes thermal damage to the Sm-Fe-N magnetic material during coating formation and can form Al-Ae alloys of arbitrary composition. Specifically, as illustrated in the embodiments described later, an Al-Ae alloy coating layer is formed on the surface of the particles constituting the Sm-Fe-N magnetic powder while it is stirred and flowed within a sputtering film-forming apparatus. Here, "stirring and flowing" refers to the operation of applying a stirring force to the powder contained within the film-forming apparatus and causing the powder particles to flow. Through this operation, the powder particles can be continuously circulated in a manner that ensures each particle is equally exposed in the space where the coated atoms exist. By applying this film-forming method, the surface of magnetic particles, which are equivalent to the nucleus, can be covered with an Al-Ae alloy coating, resulting in a significant improvement in heat resistance. Furthermore, the film-forming method is not limited to vapor-phase growth methods such as sputtering. It is believed that as long as it is confirmed that the Al-Ae alloy coating will not easily cause thermal damage to the magnetic material and can form a highly uniform Al-Ae alloy coating on the surface of the powder particles, other known film-forming techniques and newly developed film-forming techniques can also be applied.

[0065] [Densification Process]

[0066] In Al-Ae alloys, depending on the type of alkaline earth metal used, it is sometimes possible to find compositional ranges where the melting start temperature is reduced to, for example, below 600°C. Within such a low melting start temperature range, by heating the Sm-Fe-N magnetic powder that forms the Al-Ae alloy coating, the crystal structure of the Sm-Fe-N magnetic material (Th₂Zn with introduced N) can be improved. 17 A heat treatment at a temperature range below 550°C (for example, a non-decomposing heat treatment) allows for rapid diffusion of the liquid or solid phase within the coating, achieving densification of the coating. This densification process further improves resistance to coercivity reduction when heated to approximately 300°C in atmosphere. Therefore, this densification process can be implemented as needed.

[0067] Specifically, firstly, in the aforementioned film-forming process, a melting start temperature T is pre-established. M This refers to Sm-Fe-N magnetic powder with an Al-Ae alloy coating composition below 600℃. Here, the melting initiation temperature T... M For example, this can be obtained from the equilibrium state diagram of Al-Ae alloys.

[0068] Next, the Sm-Fe-N magnetic powder obtained in the film-forming process is heated in a non-oxidizing atmosphere such as Ar to a temperature T (°C) that satisfies the following formula (3).

[0069] T M (°C) -100 ≤ T (°C) ≤ 550 … (3)

[0070] The heating temperature T is the melting start temperature T. M At the above temperatures, entering the solid-liquid coexistence region, the coating of the Al-Ae alloy partially begins to melt. In this case, the coating rapidly densifies through diffusion accompanied by the liquid phase. On the other hand, when the heating temperature T is higher than the melting initiation temperature T... M At low temperatures, densification of the coating occurs through solid-phase diffusion. In this case, the temperature is raised as close as possible to T. M Temperature rapidly favors diffusion. Specifically, as in equation (3), "T" M As shown in (°C) -100”, by heating to the same temperature as T M The temperature difference becomes within 100°C, thus enabling effective densification. However, when the heating temperature T is T... M The above situations and less than T M In the case of Sm-Fe-N magnetic materials (Th2Zn with N introduced), in order to prevent the crystal structure of Sm-Fe-N magnetic materials (Th2Zn with N introduced), 17 For the decomposition of the (type structure), the heating temperature T needs to be set in the range below 550°C, and more preferably in the range below 520°C. The holding time at the heating temperature T (°C) only needs to be set in the range of, for example, 0 seconds or more and 3600 seconds or less. Here, the so-called holding time of 0 seconds at the heating temperature T (°C) means a heating mode in which the material temperature begins to cool down immediately after reaching T (°C).

[0071] In addition, at the melting start temperature T, M Even with coatings containing Al-Ae alloys with compositions exceeding 600°C, densification treatment can be performed at temperatures below 550°C. That is, even when a melting start temperature T is reached... M Al-Ae alloys below 600℃, melting start temperature T M Densification treatment of Sm-Fe-N magnetic powder with any coating layer of Al-Ae alloy exceeding 600°C by heating it to a temperature T (°C) that satisfies the following formula (4) in a non-oxidizing atmosphere such as Ar gas is also effective.

[0072] 450≤T(°C)≤550 …(4)

[0073] In this case, the holding time at the heating temperature T (°C) can be set within, for example, a range of 0 seconds to 3600 seconds.

[0074] Furthermore, at the melting start temperature T, M In Sm-Fe-N magnetic powder with an Al-Ae alloy coating at 600°C or below, it is more preferable to manage the heating temperature T to satisfy the above formula (3) as described above.

[0075] [Example of a method for manufacturing Sm-Fe-N based magnetic powder as a film-forming material]

[0076] As mentioned above, in the manufacture of Sm-Fe-N magnetic powders as film-forming materials, synthesis methods such as reduction diffusion and gas atomization can be used. The gas atomization method has the advantage of not generating alkaline waste liquid, which would lead to environmental impact.

[0077] As a representative method using this gas atomization method, an example can be given of a process in which gas atomization, heat treatment, pulverization, and nitriding are performed in the order described above. Prior to the pulverization, hydrogen treatment may be performed as needed.

[0078] The applicant has disclosed the technology of the above method in detail in Japanese Patent Application 2023-061046. The following is a brief description of each step.

[0079] (Gas atomization)

[0080] As the metal raw material for generating the molten metal for gas atomization, pre-melted Sm-Fe master alloys with known compositions, metallic Sm, metallic Fe, etc., can be used. The composition of the molten metal is preferably close to that of Sm₂Fe. 17 The stoichiometric composition of the metal is adjusted, specifically, the Sm / Fe molar ratio is within the range of 0.09 or higher and 0.25 or lower. The inclusion of metal elements other than Sm and Fe is permitted within a range that does not impede the desired properties of the final magnetic powder. Preferably, the total content of Sm and Fe in the molten metal is 95.0% by mass or higher, more preferably 98.0% by mass or higher. The molten metal is preferably generated in a nitrogen-free, inert gas atmosphere or in a vacuum.

[0081] While discharging fully homogenized molten metal, maintained at a specified temperature, from a nozzle into the gas phase space, cooling gas is violently injected into the discharged molten metal. This causes the molten metal to become fine liquid particles, which then fly and solidify in the gas phase space. The temperature of the discharged molten metal only needs to be set within the range of 1400–1900°C. The pressurized gas used to discharge the molten metal, the injection gas injected into the molten metal, and the atmosphere gas in the gas phase space for the flight of liquid particles are preferably all inert gases that do not contain nitrogen. The particle size of the gas atomized powder can be determined using laser diffraction. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The particle size is preferably 70.0 μm or less, more preferably 50.0 μm or less, and even more preferably 25.0 μm or less. There is no particular limitation on the lower limit of the particle size of the gas atomizing powder; generally, as long as the above-mentioned D... 50 Adjustments can be made within a range of 5.0 μm and above, and the range can be managed up to 10.0 μm and above.

[0082] (Heat treatment)

[0083] In the heat treatment process, grain coarsening is achieved by subjecting the gas-atomized powder of Sm-Fe alloy to high-temperature heat treatment. Specifically, by heating to 900°C or higher, grain coarsening is achieved until the average grain diameter, measured in terms of circumference equivalent diameter, in the cross-sectional microstructure of the particles becomes, for example, about 3 to 15 μm. This grain coarsening facilitates intragranular destruction during subsequent pulverization, resulting in fine Sm-Fe alloy powder with a high proportion of particles composed of single grains. Heating to 930°C or higher is more preferable. Since excessive heating becomes uneconomical, it is preferable to set the heating temperature to a range below 1200°C, which can be managed to a range below 1100°C or 1000°C. The holding time in the temperature range of 900°C or higher and 1200°C or lower can be set to, for example, 10 seconds or more and 10 minutes or less, or 30 seconds or more and 5 minutes or less. The heating atmosphere is preferably a nitrogen-free inert gas atmosphere or a vacuum.

[0084] (Hydrogen treatment)

[0085] In the subsequent pulverization process, it is effective to perform a hydrogen treatment in a hydrogen atmosphere before pulverization to facilitate intragranular damage. During hydrogen treatment, hydrogen penetrates into the grains of the Sm-Fe alloy, making intragranular damage more likely through a phenomenon known as hydrogen embrittlement. Therefore, hydrogen treatment can be performed as needed. The heating temperature for hydrogen treatment is preferably set in the range of 200°C to 600°C, and the holding time within this temperature range is, for example, set in the range of 30 minutes to 600 minutes.

[0086] (Crush)

[0087] When mechanically pulverizing Sm-Fe alloy powder with coarsened grains through the aforementioned heat treatment, individual particles undergo not only grain boundary failure (grain boundary failure) but also intragranular failure (intragranular failure), resulting in fracture. By employing this "fracture involving intragranular failure" to refine the powder particles, fine Sm-Fe alloy powder with a high proportion of particles composed of single grains can be obtained. Examples of pulverizing methods include wet ball mills. Regarding the particle size after pulverization, it is preferable to adjust it to the point of using laser diffraction. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The particle size should be 5.0 μm or less, and more preferably adjusted to 3.0 μm or less. Excessive miniaturization can lead to increased lattice strain due to the application of excessive external force, potentially negatively impacting magnetic properties. Generally, a particle size D of 5.0 μm or less is preferred. 50 It can be pulverized in the range of 0.5μm or larger, and can be pulverized in the range of 1.0μm or larger.

[0088] (Nitriding treatment)

[0089] Next, nitriding is performed to obtain Sm-Fe-N based magnetic powder. Nitriding can be carried out by heating and holding the finely pulverized Sm-Fe alloy powder in a non-oxidizing gas atmosphere containing nitrogen compounds or nitrogen. If the heating temperature is too high, nitrogen atoms will penetrate Sm₂Fe. 17 Sm2Fe crystal 17 The basic structure of N3 becomes unstable, making nitriding difficult. The heating temperature for nitriding is preferably set below 500°C. If the temperature is too low, nitriding requires a long time, which is detrimental to the uniform diffusion of nitrogen atoms into the particle interior. A heating temperature of 300°C or higher is effective. A reducing atmosphere consisting of a mixture of ammonia (NH3) and hydrogen (H2) is practical for nitriding. For example, the ammonia to hydrogen mixing ratio (NH3:H2) can be in the range of 10:90 to 60:40. Furthermore, as atmospheres for nitriding, the following can be listed: mixtures of hydrogen, ammonia, and nitrogen (N2); mixtures of hydrogen, ammonia, and argon (Ar); ammonia only; mixtures of ammonia and nitrogen; mixtures of ammonia and argon; nitrogen only; and mixtures of nitrogen and hydrogen, used to create a non-oxidizing atmosphere. The optimal nitriding time varies slightly depending on the average particle size of the powder, the composition of the atmosphere, and the temperature, and can generally be found in the range of 15 to 240 minutes.

[0090] This nitriding treatment introduces nitrogen into Sm2Fe.17 Crystals were obtained, and Sm-Fe-N magnetic powder with an N / Fe molar ratio in the range of 0.06 to 0.30 was obtained, exhibiting excellent magnetic properties.

[0091] Example

[0092] In the following examples, elemental analysis, particle size distribution determination, magnetic properties determination, and X-ray diffraction determination were performed using the following methods.

[0093] (Elemental analysis)

[0094] For metal element analysis, the analytical sample is dissolved in hydrochloric acid by heating in a glove box filled with argon (Ar) gas, then diluted to prepare an analytical sample solution. The solution is then analyzed using an ICP-based luminescence spectrophotometer (Agilent Technologies, Agilent 720).

[0095] In terms of nitrogen analysis, oxygen is used The nitrogen analysis apparatus (manufactured by Horiba Manufacturing Co., Ltd., EMGA-920) employs the inactive gas melting-thermal conductivity method.

[0096] (Particle size distribution determination)

[0097] The cumulative 50% particle size D in the volumetric particle size distribution was determined using a laser diffraction particle size distribution measuring instrument (Sympatec, Helos / Rodos). 50 .

[0098] (Magnetic determination of powder)

[0099] A sample cell containing 20 mg of sample powder and paraffin was placed at the center of an electromagnet, and heated at 80°C for 2 minutes using a hot air generator. The amount of paraffin used was defined as the amount that completely filled the sample cell with the sample powder and paraffin. Next, while heated at 80°C, an external magnetic field of 1.0 T (Tesla) was applied to the sample cell using the electromagnet for 2 minutes. Then, the sample cell was cooled to room temperature while the 1.0 T magnetic field was applied. This yielded a test sample oriented to the magnetic field. The test sample was placed on a VSM (manufactured by Toei Kogyo Co., Ltd., VSM-5HSC) with the direction of the applied magnetic field parallel to the magnetic field orientation direction of the test sample, and the coercivity H was measured. c The measurement conditions were set as follows: maximum applied magnetic field 4.79 MA / m, scan rate 8 kA / m. Second.

[0100] (X-ray diffraction measurement)

[0101] For the powder sample, the X-ray diffraction pattern was determined using Co-Kα radiation at a tube voltage of 45 kV and a tube current of 40 mA.

[0102] [Example 1]

[0103] (Synthesis of Sm-Fe based powders using gas atomization)

[0104] exist Figure 1 The diagram schematically illustrates the configuration of the gas atomizing device used in this example. The chamber contains two independent spaces, upper and lower, capable of being evacuated using a vacuum exhaust device 10. These spaces are evacuated by introducing gas from atmospheric gas supply sources 11a and 11b, thus creating separate gas phase spaces with defined gas atmospheres. A crucible 1 is located in the upper space, where induction heating using a high-frequency coil 4 melts the raw material, forming molten metal 5. A molten metal discharge nozzle component 2 is installed at the bottom of the crucible 1 to discharge the molten metal 5 into the lower gas phase space. By pressing a stop 3 against the molten metal discharge nozzle component 2, the molten metal flow path is blocked until the molten metal 5 is discharged. After the molten metal 5 is sufficiently homogenized to obtain a molten metal at a defined temperature, with a defined pressure of gas supplied to the surface of the molten metal in the crucible 1 from the molten metal discharge gas supply device 13, the stop 3 is lifted, discharging the molten metal 5 from the top of the molten metal discharge nozzle component 2 into the lower gas phase space. In the lower gas phase space, a gas injection nozzle 6 is provided for injecting gas into the discharged molten metal 5. Before discharge begins, 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 injecting this strong jet of gas into the molten metal 5, fine particles of the molten metal 5 are formed, and these fine particles are rapidly cooled and solidified. The solidified metal particles 7 accumulate at the bottom of the lower gas phase space.

[0105] exist Figure 2 The diagram schematically illustrates an example of a cross-sectional structure near the bottom of the crucible in a gas atomizing apparatus. A molten metal discharge nozzle component 2, mounted at the bottom of the crucible 1, has an opening at the nozzle tip, i.e., a discharge outlet 21, and a stop block contact surface 22. The stop block 3 is movable in the vertical direction and functions to block the nozzle flow path by contacting the stop block contact surface 22 of the molten metal discharge nozzle component 2, and to open the nozzle flow path by separating from the stop block contact surface 22 during molten metal discharge. In this example, the entire crucible 1 is constructed of boron nitride (BN), the entire molten metal discharge nozzle component 2 is constructed of boron nitride (BN), and the portion of the stop block 3 at least immersed in the molten metal 5 is constructed entirely of yttrium oxide (Y₂O₃). The nozzle inner diameter of the molten metal discharge nozzle component 2 is set to 3.0 mm.

[0106] Pre-melted Sm-Fe alloy was used as the raw material. Elemental analysis showed 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 using high-frequency induction heating in an Ar atmosphere. After the raw material alloy was completely molten, at a time 27 minutes after the start of heating, the total volume of molten metal at 1637°C was discharged from the nozzle into the lower gas phase space. The maximum supply pressure of the gas for molten metal discharge was set to 65 kPa with a pressure difference from the atmosphere gas pressure. Ar was used as the injection gas. The lower gas phase space was also set to an Ar atmosphere. The generated powder was recovered and excessively small particles were removed using a 16 μm mesh sieve in a glove box under a nitrogen atmosphere. This yielded gas-atomized powder.

[0107] Elemental analysis of the gas-atomized powder was performed, and the Sm / Fe molar ratio was found to be 0.16, consistent with the raw material alloy. Furthermore, laser diffraction was used to analyze the gas-atomized powder. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 It is 22.8 μm.

[0108] (Heat treatment)

[0109] As the heat treatment furnace, a tubular furnace with electric heating connected to a glove box filled with argon (Ar) gas was used. The aforementioned Sm-Fe 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 exposure to the atmosphere. While allowing argon gas to flow into the tubular furnace, the temperature was raised from room temperature to 950°C at a rate of 150°C / min, held at 950°C for 1 minute, and then cooled to below 50°C while allowing argon gas to flow, thus obtaining the heat-treated powder.

[0110] (Hydrogen treatment)

[0111] The obtained heat-treated powder was transferred to another tubular furnace, and heated to 300°C at a rate of 10°C / min while hydrogen (H2) gas flowed through it. This temperature was then maintained at 300°C for 180 minutes. Next, the powder was cooled to below 50°C while hydrogen gas flowed through it, and then the furnace was purged with argon gas. This yielded the hydrogen-treated powder.

[0112] (Crush)

[0113] 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 the glove box at the transfer destination. 5.0 g of hydrogen-treated powder, 250 g of stainless steel balls with a diameter of 2.5 mm, and acetonitrile as a solvent were placed in a 240 mL stainless steel grinding jar. The amount of acetonitrile was set to the minimum required to immerse all the stainless steel balls in acetonitrile. Next, the grinding jar containing the hydrogen-treated powder was placed on a ball mill rotating stand (Asahie Rika Co., Ltd., AV-1 type), and grinding was performed at a speed of 120 rpm for 2 hours. Next, the contents of the grinding jar were sieved to remove the stainless steel balls from the sieve, and the slurry that passed through the sieve was recovered. Next, the recovered slurry was allowed to stand, the supernatant was discarded, and the remaining slurry was vacuum dried to obtain the pulverized powder. The above grinding and drying operations were carried out in a glove box under an argon atmosphere.

[0114] (Nitriding treatment)

[0115] The pulverized powder obtained as described above was transferred to a tubular furnace under an argon atmosphere and heated electrically. A mixed gas consisting of 35% by volume ammonia (NH3) and 65% by volume hydrogen (H2) was then introduced into the furnace to displace the existing gas. The mixture was then heated to 420°C at a rate of 5°C / min while continuing to flow through it, and held at 420°C for 30 minutes for nitriding. Next, the gas flowing into the furnace was changed to hydrogen (H2), and the furnace was held at 420°C for an additional 120 minutes. Then, the gas was changed to argon, and the furnace was held at 420°C for 90 minutes. Finally, heating was stopped, and the furnace was cooled to near room temperature while continuing to flow through it, yielding the nitrided powder.

[0116] (Washing and shredding)

[0117] Next, the obtained nitrided powder was transferred from the tubular furnace to a glove box filled with argon gas, and then placed into a 20 mL glass bottle with a screw cap. 15 mL of heptane was added as a solvent. The glass bottle was then placed in an ultrasonic disperser (SMT Corporation, UH-150 model) and run for 100 minutes at an output frequency of 20 kHz, a transmission time of 0.3 seconds, and a rest time of 0.7 seconds. The supernatant in the glass bottle was then removed, and the remaining heptane was removed by vacuum drying, thus obtaining Sm-Fe-N magnetic powder.

[0118] X-ray diffraction analysis of the obtained Sm-Fe-N magnetic powder confirmed that it possessed Th2Zn content. 17 The Sm-Fe-N magnetic powder exhibits a crystal structure. Furthermore, laser diffraction was used to analyze this Sm-Fe-N magnetic powder. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 It is 1.8μm.

[0119] (film formation)

[0120] Using the Sm-Fe-N magnetic powder obtained as described above as the film-forming material, an Al-Mg alloy coating was formed on the surface of the powder particles by sputtering. The film-forming method is described below.

[0121] exist Figure 3 The diagram schematically illustrates the configuration of the sputtering film deposition apparatus used in this example. The left image corresponds to a side view, and the right image corresponds to a front view. The front side of the film deposition chamber 51 of the main body of the sputtering film deposition apparatus is connected to a narrow-depth glove box 52 filled with argon gas, allowing sample powder to be manually introduced into the film deposition chamber 51 through a glove hole 53. A sliding door is provided between the film deposition chamber 51 and the glove box 52, which can be opened and closed from inside the glove box 52. By closing the door, the vacuum inside the film deposition chamber 51 can be vented while the glove box 52 side is filled with argon gas. Two sputtering cathodes 54 are provided at the upper part of the film deposition chamber 51.

[0122] exist Figure 4 The diagram shows Figure 3 The internal structure of the film-forming chamber 51 of the sputtering film-forming apparatus shown. Figure 4 The shaded portion in the diagram represents the cross-sectional shape within the plane containing the rotation axis of the stepper motor 57. This film-forming apparatus has two sputtering cathodes 54, enabling binary co-sputtering using two types of targets. In this example, metallic Al is mounted on one sputtering cathode 54, and metallic Mg is mounted on the other as the target material. Each target is a 5mm thick, 2-inch diameter circular plate. Magnetron sputtering is achieved using the magnetic field generated by a neodymium magnet embedded on the back of the target. A powder container 55 with a circular bottom surface of 65mm in diameter is positioned at the focal point of the two cathodes, and a stirring rod 56 is inserted into the powder container 55. The powder container 55 is connected to the stepper motor 57 located below the film-forming chamber 51. By rotating the powder container 55 while holding the sample powder, which is the film-forming material, within it, the sample powder can be continuously stirred and flowed. If this sputtering film-forming apparatus is used, by automatically and continuously stirring and flowing the sample powder while sputtering, the surface of the powder particles can be coated with the elements of the target material installed on the sputtering cathode 54.

[0123] The Sm-Fe-N magnetic powder, used as the film-forming material, is transferred to the glove box 52 under an argon atmosphere. The sliding door connecting to the film-forming chamber 51 is opened, and 10g of the Sm-Fe-N magnetic powder is loaded into the powder container 55 under an argon atmosphere. Then, the sliding door is closed, sealing the film-forming chamber 51. A temporary vacuum is then evacuated from the film-forming chamber 51 to approximately 1 × 10⁻⁶. -3 After Pa, argon, the process gas, is introduced into the film-forming chamber 51, and the argon introduction flow rate is adjusted to maintain the argon pressure in the film-forming chamber 51 at approximately 0.5 Pa. While continuously stirring the Sm-Fe-N magnetic powder used as the film-forming material by rotating the powder container 55 at 50 rpm, binary co-sputtering of Al and Mg is performed using two sputtering cathodes 54, coating the surface of the powder particles with an Al-Mg alloy. The film-forming time is adjusted so that the average film thickness of the coating layer is approximately 50 nm. In this example, by adjusting the output ratio of the two sputtering cathodes, a coating layer with an Al to Mg molar ratio of 54:46 is formed.

[0124] (Densification treatment)

[0125] The Sm-Fe-N magnetic powder, after film formation, was transferred to a heat treatment furnace under an argon atmosphere and heat-treated at 500°C for 1 minute. In Al-Mg alloys with an Al:Mg molar ratio of approximately 54:46, the melting initiation temperature T is considered to be... M The temperature is around 450℃. It is speculated that the Al-Mg alloy coating that forms the film enters the solid-liquid coexistence region during heating at 500℃ and rapidly densifies.

[0126] The Sm-Fe-N magnetic powder that has undergone densification treatment was used as the test powder in this example for the following investigation.

[0127] (X-ray photoelectron spectrometry)

[0128] For the test powder in this example, the elemental distribution near the particle surface was determined using an X-ray photoelectron spectrometer (ULVAC-PHI, PHI-5000Versa ProbeII) as follows. Al-Kα rays (1486.6 eV) were used as the X-ray source, and the energy of the released photoelectrons was analyzed using a hemispherical electron analyzer at a channel energy of 23.5 eV and an energy interval of 0.1 eV. Furthermore, for depth distribution analysis, etching and measurement of the sample surface using Ar sputtering were alternately repeated to evaluate the distribution in the depth direction originating from the surface. The accelerating voltage for Ar ions was set to 2 kV. The etching depth corresponding to an etching time of 600 seconds, converted to Fe2O3, was estimated to be approximately 43 nm.

[0129] exist Figure 5 The figure shows the 2p energy levels of Mg (magnesium) and Fe (iron) obtained by X-ray photoelectron spectroscopy. 3 / 2 The photoelectron peaks of the energy levels were observed at etching times of 0 seconds (i.e., the outermost surface) and 600 seconds (i.e., the Fe₂O₃ equivalent depth of approximately 43 nm). At etching time 0 seconds, a significant peak intensity was observed for Mg, but no significant peak intensity was observed for Fe. Conversely, at etching time 600 seconds, the peak intensity of Mg decreased significantly, while a significant peak intensity was observed for Fe. Therefore, the tested powder particles in this example were evaluated as having a surface coating formed using the aforementioned film deposition method, to the extent that the exposure of the substrate (corresponding to the Sm-Fe-N magnetic core portion) could not be confirmed.

[0130] (composition)

[0131] Elemental analysis of the test powder was performed using the analytical methods described above. The results are shown in Table 1 (the same applies to the following examples). In this example, the Sm / Fe molar ratio of the test powder was 0.16, the N / Fe molar ratio was 0.22, and the (Al+Ae) / Fe molar ratio was 0.23.

[0132] (Particle size distribution)

[0133] The particle size distribution of the test powder was determined using the method described above. As a result, the particle size distribution of the test powder in this example was determined by laser diffraction. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 It is 1.9μm.

[0134] (Coverage index R)

[0135] Based on equation (1) above, the coverage index R of the test powder was calculated. As a result, the coverage index R of the test powder in this example is 0.43 μm.

[0136] (Coercivity)

[0137] The magnetic properties of the test powder were determined using the method described above. The results showed that the coercivity H of the test powder in this example was... c It is 1060 kA / m (13.3 kOe).

[0138] (Evaluation of heat resistance)

[0139] A 0.1 g sample of the test powder was placed on a stainless steel container and then placed in a thermostatic dryer (ADVANTEC, DRA-630DB) heated to 300 °C for a heating test in atmospheric atmosphere (air) at 300 °C for 120 minutes. The stainless steel container was then removed from the dryer, and the powder sample was allowed to cool in air at room temperature. The powder sample that had undergone this heating test was then subjected to magnetic determination using the same method as described above. The results showed that the coercivity H after the heating test... c It is 780 kA / m (9.8 kOe).

[0140] The coercivity reduction rate δH caused by the heating test was calculated according to the following equation (2). c .

[0141] δH c =100×(H) c0 -H c1 ) / H c0 …(2)

[0142] Among them, H c0 H represents the coercivity (kA / m) of the powder before the heating test. c1 The coercivity (kA / m) of the powder after the heating test.

[0143] The coercivity reduction rate δH of the test powder in this example c It is 100×(1060-780) / 1060≒26.4%.

[0144] exist Figure 6 The image shown is a HAADF (High Angle Circular Dark Field) image of the test powder particles that underwent a heating test at 300°C for 120 minutes in the atmosphere. The whitish parts are the Sm-Fe-N magnetic core, and the grayish parts along its outline are the coating.

[0145] exist Figure 7 The example in Figure 6 The line segment AB shown represents the elemental concentration distribution of O (oxygen), Fe (iron), and Al (aluminum) determined by EDS (energy-dispersive X-ray spectroscopy). The portion where the Al concentration increases at a distance of approximately 0.27 μm from A marks the location of the coating layer. It can be seen that the coating layer prevents oxygen from penetrating into the Sm-Fe-N magnetic body, which corresponds to the core. That is, the coating layer according to the present invention functions as a barrier layer to prevent oxygen penetration when heated in the atmosphere, presumably achieving excellent resistance to coercivity reduction.

[0146] [Example 2]

[0147] In this example, the properties of Al-Mg alloy coated with Sm-Fe-N magnetic powder without densification treatment were investigated.

[0148] Specifically, under the same conditions as in Example 1, Sm-Fe-N magnetic powder was obtained through gas atomization, heat treatment, pulverization, hydrogen treatment, nitriding, cleaning, and film formation. This powder (equivalent to the powder before densification treatment in Example 1) was used as the test powder, and elemental analysis, particle size distribution determination, magnetic properties determination, and heat resistance evaluation were performed using the same methods described above.

[0149] The characteristics of the test powder in this example are described below.

[0150] The Sm / Fe molar ratio is 0.17, the N / Fe molar ratio is 0.23, and the (Al+Ae) / Fe molar ratio is 0.23. Laser diffraction was employed. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 2.0 μm. The coverage index R is 0.47 μm. The coercivity H... c The coercivity H of the powder was 1170 kA / m (14.7 kOe). The heating test at 300°C for 120 minutes in the atmosphere was completed. c The coercivity reduction rate δH is 560 kA / m (7.0 kOe), calculated according to equation (2) above. c It is 52.1%.

[0151] [Comparative Example 1]

[0152] In this example, Al-Mg alloy coated with Sm-Fe-N magnetic powder without a coating was used as the test powder, and its properties were investigated.

[0153] Specifically, under the same conditions as in Example 1, Sm-Fe-N magnetic powder was obtained through gas atomization, heat treatment, pulverization, hydrogen treatment, nitriding, and cleaning. This powder (equivalent to the film-forming material in Example 1) was used as the test powder, and elemental analysis, particle size distribution determination, magnetic properties determination, and heat resistance evaluation were performed using the same methods described above.

[0154] The characteristics of the test powder in this example are described below.

[0155] The Sm / Fe molar ratio is 0.17, the N / Fe molar ratio is 0.21, and the (Al+Ae) / Fe molar ratio is 0.00. Laser diffraction was employed. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50The thickness is 1.8 μm. Since no coating layer was formed, the coating index R is 0.00 μm. Coercivity H c The coercivity H of the powder was 750 kA / m (9.4 kOe). The heating test at 300°C for 120 minutes in the atmosphere was completed. c The coercivity reduction rate δH is 120 kA / m (1.5 kOe), calculated according to equation (2) above. c It is 84.0%.

[0156] [Example 3]

[0157] (Synthesis of Sm-Fe based powders using gas atomization)

[0158] As raw material, 1700g of Sm-Fe alloy with a Sm / Fe molar ratio of 0.15 was used. The temperature of the melt at discharge was set to 1500°C. Particles that were not recovered were removed by sieving. Otherwise, gas atomized powder was obtained by the same method as in Example 1.

[0159] Elemental analysis of the gas-atomized powder was performed, revealing an Sm / Fe molar ratio of 0.15, consistent with the raw material alloy. Furthermore, laser diffraction was used to analyze the gas-atomized powder. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 It is 52.5 μm.

[0160] (Heat treatment)

[0161] As the heat treatment furnace, a tubular furnace with an electric heating method capable of processing in a gaseous atmosphere was used. The above-mentioned Sm-Fe gas atomized powder was loaded into a sample container and placed inside the furnace. While argon gas was flowing, the temperature was raised from room temperature to 990°C at a rate of 10°C / min, and then maintained at 990°C for 60 minutes. Then, while argon gas was flowing, the temperature was cooled to below 50°C to obtain the heat-treated powder.

[0162] (Crush)

[0163] 500g of heat-treated powder was pulverized using a vibratory mill (manufactured by Yurastecno Co., Ltd., YAMP-6SND). In a 3L stainless steel container filled with nitrogen, 500g of heat-treated powder, 12500g of chromium steel balls (3.2mm in diameter), and 5.9g of 2-propanol were added, sealed, and pulverized for 84 minutes at an amplitude of ±2.5mm and a frequency of 29.1Hz. The pulverized sample was then separated from the balls in a nitrogen-filled glove box to obtain the pulverized powder.

[0164] (Nitriding treatment)

[0165] The pulverized powder obtained as described above was transferred to a tubular furnace under a nitrogen atmosphere and heated electrically. A mixed gas consisting of 35% by volume ammonia (NH3) and 65% by volume hydrogen (H2) was circulated within the furnace to replace the existing gas. Then, while continuing the flow of this mixed gas, the temperature was increased to 390°C at a rate of 5°C / min and maintained at 390°C for 260 minutes for nitriding treatment. Next, the gas flowing into the tubular furnace was changed to hydrogen (H2), and the temperature was maintained at 390°C for an additional 130 minutes. Then, the gas flowing into the tubular furnace was changed to argon, and the temperature was maintained at 390°C for 90 minutes. Finally, heating was stopped, and the furnace was cooled to near room temperature while continuing to circulate argon, yielding Sm-Fe-N magnetic powder.

[0166] (film formation)

[0167] Using the Sm-Fe-N magnetic powder obtained through the above steps as the film-forming material, the output ratio of the sputtering cathodes was changed, and the film-forming time was adjusted to make the average film thickness of the coating layer approximately 29 nm. Otherwise, the surface of the powder particles was coated with an Al-Mg alloy using the same method as in Example 1. In this example, a coating layer with an Al to Mg molar ratio of 67:33 was formed.

[0168] (Densification treatment)

[0169] The test powder was obtained by performing the same heat treatment as in Example 1 on the Sm-Fe-N magnetic powder that had completed film formation.

[0170] The obtained Sm-Fe-N magnetic powder (test powder) was subjected to elemental analysis, particle size distribution determination, magnetic determination, and heat resistance evaluation using the same methods as in Example 1 (as in the following examples).

[0171] The results showed that the Sm / Fe molar ratio was 0.14, the N / Fe molar ratio was 0.18, and the (Al+Ae) / Fe molar ratio was 0.09, obtained using laser diffraction. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.2 μm, the coverage index R is 0.29 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 490 kA / m (6.2 kOe). c The coercivity reduction rate δH is 330 kA / m (4.1 kOe), calculated according to equation (2) above. c It is 32.7%.

[0172] [Example 4]

[0173] In the film-forming process, the film-forming time was adjusted so that the average film thickness of the coating layer was approximately 55 nm. Otherwise, Sm-Fe-N magnetic powder (test powder) was obtained using the same method as in Example 3. In this example, a coating layer with a molar ratio of Al to Mg of 66:34 was formed.

[0174] The tested powder had an Sm / Fe molar ratio of 0.14, an N / Fe molar ratio of 0.18, and a (Al+Ae) / Fe molar ratio of 0.18. Laser diffraction was used to analyze the sample. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.3 μm, the coverage index R is 0.59 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 510 kA / m (6.4 kOe). c The coercivity reduction rate δH is 370 kA / m (4.6 kOe), calculated according to equation (2) above. c It is 27.5%.

[0175] [Example 5]

[0176] In the film-forming process, the film-forming time was adjusted so that the average film thickness of the coating layer was approximately 82 nm. Otherwise, Sm-Fe-N magnetic powder (test powder) was obtained using the same method as in Example 3. In this example, a coating layer with a molar ratio of Al to Mg of 66:34 was formed.

[0177] The tested powder had an Sm / Fe molar ratio of 0.13, an N / Fe molar ratio of 0.18, and a (Al+Ae) / Fe molar ratio of 0.27. Laser diffraction was used to analyze the sample. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.4 μm, the coverage index R is 0.92 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 510 kA / m (6.4 kOe). c The coercivity reduction rate δH is 350 kA / m (4.4 kOe), calculated according to equation (2) above. c It is 31.4%.

[0178] [Example 6]

[0179] In the film formation process, the output ratio of the sputtering cathodes was changed, and the film formation time was adjusted to make the average film thickness of the coating layer approximately 53 nm. Otherwise, Sm-Fe-N magnetic powder (test powder) was obtained using the same method as in Example 3. In this example, a coating layer with a molar ratio of Al to Mg of 54:46 was formed.

[0180] The tested powder had an Sm / Fe molar ratio of 0.14, an N / Fe molar ratio of 0.18, and a (Al+Ae) / Fe molar ratio of 0.17. Laser diffraction was used to analyze the sample. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.2 μm, the coverage index R is 0.54 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 530 kA / m (6.7 kOe). c The coercivity reduction rate δH is 410 kA / m (5.2 kOe), calculated according to equation (2) above. c It is 22.6%.

[0181] [Example 7]

[0182] In the film-forming process, the film-forming time was adjusted so that the average film thickness of the coating layer was approximately 99 nm. Otherwise, Sm-Fe-N magnetic powder (test powder) was obtained using the same method as in Example 6. In this example, a coating layer with a molar ratio of Al to Mg of 55:45 was formed.

[0183] The tested powder had an Sm / Fe molar ratio of 0.14, an N / Fe molar ratio of 0.18, and a (Al+Ae) / Fe molar ratio of 0.33. Laser diffraction was used to analyze the sample. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.2 μm, the coverage index R is 1.06 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 530 kA / m (6.7 kOe). c The coercivity reduction rate δH is 410 kA / m (5.2 kOe), calculated according to equation (2) above. c It is 22.6%.

[0184] [Example 8]

[0185] In the film-forming process, Mg was replaced with Ca as the alkaline earth metal element Al, the output ratio of the two sputtering cathodes was changed, and the film-forming time was adjusted so that the average film thickness of the coating layer was about 45 nm. Otherwise, Sm-Fe-N magnetic powder (test powder) was obtained using the same method as in Example 3. In this example, a coating layer with a molar ratio of Al to Ca of 72:28 was formed.

[0186] The tested powder had an Sm / Fe molar ratio of 0.14, an N / Fe molar ratio of 0.18, and a (Al+Ae) / Fe molar ratio of 0.11. Laser diffraction was used to analyze the powder. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.1 μm, the coverage index R is 0.34 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 490 kA / m (6.2 kOe). c The coercivity reduction rate δH is 350 kA / m (4.4 kOe), calculated according to equation (2) above. c It is 28.6%.

[0187] [Example 9]

[0188] In the film-forming process, the film-forming time was adjusted so that the average film thickness of the coating layer was approximately 124 nm. Otherwise, Sm-Fe-N magnetic powder (test powder) was obtained using the same method as in Example 8. In this example, a coating layer with a molar ratio of Al to Ca of 72:28 was formed.

[0189] The tested powder had an Sm / Fe molar ratio of 0.13, an N / Fe molar ratio of 0.18, and a (Al+Ae) / Fe molar ratio of 0.32. Laser diffraction was used to analyze the sample. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.1 μm, the coverage index R is 0.99 μm, and the coercivity H is... c The coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 600 kA / m (7.5 kOe). c The coercivity reduction rate δH is 370 kA / m (4.6 kOe), calculated according to equation (2) above. c It is 38.3%.

[0190] [Comparative Example 2]

[0191] In this example, by omitting the film-forming and densification processes in Example 3, Sm-Fe-N magnetic powder without a coating was prepared, and its properties were examined. That is, the test powder in this example is equivalent to Sm-Fe-N magnetic powder that has undergone the same process up to the nitriding treatment as in Example 3.

[0192] The tested powder had an Sm / Fe molar ratio of 0.15, an N / Fe molar ratio of 0.19, and a (Al+Ae) / Fe molar ratio of 0.00. Laser diffraction was used to analyze the sample. The cumulative 50% particle size D in the volume-based particle size distribution obtained by scattering method 50 The thickness is 3.0 μm, the coverage index R is 0.00 μm, and the coercivity H is... cThe coercivity H after a heating test at 300℃ for 120 minutes in the atmosphere is 590 kA / m (7.4 kOe). c The coercivity reduction rate δH is 180 kA / m (2.3 kOe), calculated according to equation (2) above. c It is 69.5%.

[0193] The results are shown in Table 1.

[0194] [Table 1]

[0195]

[0196] The coercivity reduction rate δH of the Sm-Fe-N magnetic powder, which formed the Al-Ae alloy coating, was tested under a severe heating test at 300°C for 120 minutes in the atmosphere. c With a content of less than 60%, compared with the Sm-Fe-N magnetic powders of Comparative Examples 1 and 2 that did not form the above-mentioned coating layer, the resistance to coercivity reduction was significantly improved.

[0197] In addition, it was confirmed that the coercivity reduction resistance was further improved by implementing densification treatment (comparison between Example 1 and Example 2).

[0198] Explanation of reference numerals in the attached figures

[0199] 1. Crucible

[0200] 2. Molten metal discharge nozzle component

[0201] 3 stops

[0202] 4. High-frequency coil

[0203] 5. Molten Metal

[0204] 6. Gas injection nozzle

[0205] 7. Solidified metal particles

[0206] 10 Vacuum Exhaust Device

[0207] 11a, 11b Atmospheric gas supply sources

[0208] 12. Gas supply device for injection

[0209] 13 Gas supply device for molten liquid discharge

[0210] 21 Discharge outlet

[0211] 22. Stop block contact surface

[0212] 51 Film-forming chamber

[0213] 52 Glove Box

[0214] 53 Glove holes

[0215] 54 Sputtered cathode

[0216] 55 Powder Containing Container

[0217] 56 Stirring rod

[0218] 57 Stepper Motor

Claims

1. High heat-resistant Sm-Fe-N magnetic powder, which is formed by Sm-Fe-N magnetic particles with an Al-Ae alloy coating on the surface when the alkaline earth metal element is represented as Ae.

2. The high heat-resistant Sm-Fe-N magnetic powder according to claim 1, wherein, The Sm / Fe molar ratio is ≥0.09 and ≤0.25, and the N / Fe molar ratio is ≥0.06 and ≤0.

30.

3. The high heat-resistant Sm-Fe-N magnetic powder according to claim 1, wherein, Using laser diffraction The cumulative 50% particle size D in the volume-based particle size distribution of the scattering method 50 For a thickness of 0.5 μm or more and 5.0 μm or less, the 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) In equation (1), the value of the (Al+Ae) / Fe molar ratio in the powder with the Al-Ae alloy coating is substituted into [(Al+Ae) / Fe], and D is obtained. 50 Substitute the cumulative 50% particle size D into the value. 50 The value of (μm).

4. The high heat-resistant Sm-Fe-N magnetic powder according to claim 3, wherein, The coverage index R is greater than 0.10 μm and less than 1.00 μm.

5. The high heat-resistant Sm-Fe-N magnetic powder according to claim 1, wherein, Alkaline earth metal element Ae is selected from one or more elements from Mg and Ca.

6. The high heat-resistant Sm-Fe-N magnetic powder according to claim 1, wherein, The coercivity reduction rate δH, expressed by the following formula (2), is given by the heating test conducted at 300°C in the atmosphere for 120 minutes. c Below 60%, δH c =100×(H c0 -H c1 ) / H c0 …(2) Among them, H c0 H represents the coercivity (kA / m) of the powder before the heating test. c1 The coercivity (kA / m) of the powder after the heating test.

7. A method for manufacturing high heat-resistant Sm-Fe-N magnetic powder, comprising a film-forming process, wherein, When alkaline earth metal elements are represented as Ae, an Al-Ae alloy coating is formed on the surface of particles constituting the Sm-Fe-N magnetic powder, which serves as the film-forming material, using a vapor phase growth method.

8. The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 7, wherein, The vapor phase growth method is a sputtering method. In the film formation process, while stirring and flowing the Sm-Fe-N magnetic powder, which is the film-forming material, in the sputtering film formation device, an Al-Ae alloy coating layer is formed on the surface of the particles constituting the Sm-Fe-N magnetic powder by sputtering.

9. The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 7, wherein, The Sm-Fe-N magnetic powder used as the film-forming material 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 method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 7, wherein, The Sm-Fe-N magnetic powder used as the film-forming material was subjected to laser diffraction. The cumulative 50% particle size D in the volume-based particle size distribution of the scattering method 50 The film-forming process involves coating Al and alkaline earth metal element Ale with a coating thickness of 0.5 μm or more and 5.0 μm or less, expressed by the following formula (1), such that the coating thickness index R is 0.10 μm or more and 2.00 μm or less. Coverage index R = [(Al + Ae) / Fe] × D 50 …(1) In equation (1), the value of the (Al+Ae) / Fe molar ratio in the powder with the Al-Ae alloy coating is substituted into [(Al+Ae) / Fe], and D is obtained. 50 Substitute the cumulative 50% particle size D into the value. 50 The value of (μm).

11. The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 10, wherein, In the film-forming process, Al and alkaline earth metal element Ale are coated such that the coating amount index R is 0.10 μm or more and 1.00 μm or less.

12. The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 7, wherein, The Sm-Fe-N magnetic powder used as the film-forming material is obtained by a manufacturing method comprising the following steps: In the heat treatment process, powder of Sm-Fe alloy with an Sm / Fe molar ratio of 0.09 or higher and 0.25 or lower, formed during solidification using a gas atomization method, is heated to a temperature of 900°C or higher and 1200°C or lower, thereby coarsening the grain size of the powder particles. The pulverization process, wherein the powder of an Sm-Fe alloy, whose grains have been coarsened by the heat treatment process, is pulverized, thereby refining the powder particles through fracture involving intragranular damage; and The nitriding process involves introducing nitrogen into the powder particles by heating the finely pulverized Sm-Fe alloy powder in a non-oxidizing gas atmosphere containing nitrogen compounds or nitrogen and maintaining the temperature range below 500°C.

13. The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 7, further comprising a densification process, wherein, The Sm-Fe-N magnetic powder obtained in the film-forming process is heated in a non-oxidizing atmosphere to a temperature T (°C) that satisfies the following formula (4). 450≤T（℃）≤550 …（4）。 14. The method for manufacturing high heat-resistant Sm-Fe-N magnetic powder according to claim 7, wherein, In the film-forming process, the melting start temperature T is formed. M It is an Al-Ae alloy coating with a composition below 600℃. It also includes a densification process in which the Sm-Fe-N magnetic powder obtained in the film-forming process is heated in a non-oxidizing atmosphere to a temperature T (°C) that satisfies the following formula (3). T M (℃)-100≤T(℃)≤550 …(3)。

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