Sm-Fe-N sintered magnet and method for manufacturing the same

Abstract

Disclosed is an Sm-Fe-N-based sintered magnet that comprises crystal grains which contain samarium, iron, and nitrogen and which include main phase grains that contain not less than 9 atom% but less than 13 atom% of samarium and sub-phase grains that contain 13 atom% or more of samarium, iron, and nitrogen. The ratio (M2 / M1) of the average value M2 of the X-ray magnetic circular dichroism intensities of the iron of the sub-phase grains to the average value M1 of the X-ray magnetic circular dichroism intensities of the iron of the main phase grains, which is obtained in a plane that is perpendicular to the easy axis of magnetization in an environment in which a static magnetic field of 4T is applied in a direction that is parallel to the direction of the easy axis of magnetization is 10% to 83% inclusive.

Description

[Technical Field]

[0001] The present invention relates to an Sm-Fe-N sintered magnet and a method for manufacturing the same. [Background technology]

[0002] Sm-Fe-N sintered magnets are representative of rare-earth-transition-metal-nitrogen magnets and possess high anisotropic magnetic fields and remanent magnetization. Furthermore, Sm-Fe-N sintered magnets have superior heat resistance due to their relatively higher Curie temperature compared to other rare-earth-transition-metal-nitrogen magnets. On the other hand, it is said that the coercivity of Sm-Fe-N sintered magnets decreases during the firing process.

[0003] Patent Document 1 describes SmFe3N as a secondary phase. x A rare earth magnet based on Sm-Fe-N is disclosed that contains a phase (1.0 ≤ x ≤ 2.5) in an area ratio of 5% or less (excluding 0) of the cross-sectional area. According to Patent Document 1, SmFe3N is selectively used as a secondary phase. x Because the phase is oxidized, the main phase is Sm2Fe 17 The oxidation of the N3 phase is suppressed, thereby reducing the degradation of magnetic properties. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6520337 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the coercivity of the magnet in Patent Document 1 is not sufficient.

[0006] This invention has been made in view of the aforementioned problems, and aims to provide a sintered magnet of the Sm-Fe-N system that has high coercivity. [Means for solving the problem]

[0007] According to one aspect of the present invention, A crystalline grain containing samarium, iron, and nitrogen, comprising a main phase grain containing 9 atomic percent or more and less than 13 atomic percent of samarium, It comprises a subphase grain containing 13 atomic percent or more of samarium, iron, and nitrogen, A Sm-Fe-N sintered magnet is provided, in which, under conditions where a static magnetic field of 4T is applied in a direction parallel to the easy magnetization axis, the ratio (M2 / M1) of the average value M2 of the X-ray magnetic circular dichroism intensity of the secondary phase iron grains to the average value M1 of the main phase iron grains, obtained in a plane perpendicular to the easy magnetization axis, is between 10% and 83%.

[0008] According to another aspect of the present invention, A method for manufacturing an Sm-Fe-N sintered magnet is provided, comprising pressurizing and firing a magnetic material containing Sm-Fe-N magnetic powder in a sintering machine under reduced pressure of 10 Pa to 200 Pa containing an inert gas. [Effects of the Invention]

[0009] According to the present invention, an Sm-Fe-N sintered magnet having high coercivity is provided. [Brief explanation of the drawing]

[0010] [Figure 1] This flowchart shows an example of a method for manufacturing a sintered magnet according to the present disclosure. [Figure 2A] This is an example of an SEM image (magnification 2000x) used for segmentation in the example. [Figure 2B] This is an example of an SEM image obtained by binarizing Figure 2A, in which the main phase grains are shown in black. [Figure 2C] This is an example of an SEM image obtained by binarizing Figure 2A, in which the grain boundaries between the main phase grains and the secondary phase grains are shown in black. [Modes for carrying out the invention]

[0011] (composition) The Sm-Fe-N sintered magnet (samarium-iron-nitrogen sintered magnet) according to the present disclosure contains crystal grains (Sm-Fe-N crystal grains) containing samarium, iron, and nitrogen. The Sm-Fe-N crystal grains are a sintered body of a magnetic material containing Sm-Fe-N magnetic powder.

[0012] The Sm-Fe-N crystal grains contain main phase grains containing 9 atomic % or more and less than 13 atomic % of samarium. The Sm-Fe-N sintered magnet according to the present disclosure further contains sub-phase grains containing 13 atomic % or more of samarium, iron, and nitrogen.

[0013] The main phase grains contain 9 atomic % or more and less than 13 atomic % of samarium, iron, and nitrogen. The main phase grains have a Sm-Fe-N crystal structure. The main phase grains form the main phase of the Sm-Fe-N sintered magnet (hereinafter, also simply referred to as a magnet). The main phase grains are the target substances when synthesizing the Sm-Fe-N crystal grains.

[0014] The sub-phase grains contain 13 atomic % or more of samarium, iron, and nitrogen. The sub-phase grains may contain more nitrogen than the main phase grains on an atomic % basis. The sub-phase grains (hereinafter, also referred to as Sm-rich phase) may be amorphous. The Sm-rich phase is a by-product that is inevitably generated for the purpose of suppressing the precipitation of the α-Fe phase that significantly deteriorates the magnetic properties when synthesizing the Sm-Fe-N crystal grains. It has been found that when the average magnetic moment of iron in the inevitably generated Sm-rich phase is large, the coercive force of the magnet decreases.

[0015] Although the reason for this is not clear, it is considered that when the average magnetic moment of iron in the Sm-rich phase is large, the magnetization reversal of the main phase grains existing around the Sm-rich phase is likely to be induced.

[0016] The average magnetic moment m2 of iron in the Sm-rich phase changes, for example, depending on the degree of oxidation of the Sm-rich phase. When the Sm-rich phase is oxidized, oxygen (O) enters while nitrogen (N) desorbs. It is considered that the average magnetic moment m2 of iron in the Sm-rich phase increases due to the distance between iron elements being reduced by the desorption of nitrogen.

[0017] Since the main phase grains are less susceptible to oxidation than the Sm-rich phase, the average magnetic moment m1 of iron in the main phase grains is considered to not change much depending on firing conditions, etc. In this disclosure, the ratio of the average magnetic moment m2 of iron in the Sm-rich phase (corresponding to the average value M2 of the XMCD intensity of iron in the Sm-rich phase described later) to the average magnetic moment m1 of iron in the main phase grains (corresponding to the average value M1 of the XMCD intensity of iron in the main phase grains described later) was used as an indicator of the coercivity.

[0018] The average magnetic moment m1 of iron in the main phase grain can be obtained as the average value M1 of the X-ray magnetic circular dichroism (XMCD) intensity of the iron in the main phase grain. The XMCD intensity is obtained in a plane perpendicular to the easy magnetization axis under the environment in which a static magnetic field of 4T is applied in a direction parallel to the easy magnetization axis. Similarly, the average magnetic moment m2 of iron in the Sm-rich phase can be obtained as the average value M2 of the XMCD intensity of iron in the subphase grain.

[0019] High coercivity can be obtained when the ratio (M2 / M1) of the average values ​​of the XMCD intensities is between 10.0% and 83%. The ratio (M2 / M1) may be 82.5% or less, 82.0% or less, or 81.8% or less. The ratio (M2 / M1) may be 20.0% or more, or 30.0% or more. The ratio (M2 / M1) can be reduced, for example, by suppressing oxidation during the pressurized firing of the magnetic material. The pressurized firing conditions will be described later.

[0020] The magnet may contain no oxygen or may contain less than 0.5% by mass of oxygen. An oxygen content of 0.5% by mass or less in the magnet indicates that oxidation of both the main phase grains and the secondary phase grains is suppressed during the firing process, particularly the oxidation of the Sm-rich phase. Therefore, the ratio (M2 / M1) tends to be smaller, and higher coercivity can be expected. The oxygen content of the magnet may be 0.48% by mass or less, or 0.47% by mass or less.

[0021] The oxygen content can be measured by inert gas fusion-nondispersive infrared absorption (NDIR). The magnets to be measured are those immediately after pressurized firing, or those stored in a low-oxygen atmosphere with a cumulative oxygen concentration of 2 ppm or less after pressurized firing.

[0022] The relative density (%) of the magnet can be, for example, 78% or more, or 79% or more. The relative density is based on the representative Sm2Fe particles that make up the main phase grains. 17 Known true density of N3 phase (7.67 g / cm³) 3 This is the ratio of the magnet's volume density to its apparent volume. The magnet's volume density can be determined from its apparent volume and mass. Generally, a higher relative density results in higher magnetization. The relative density (%) of a magnet is less than 100%.

[0023] Sm-Fe-N sintered magnets are obtained by sintering a magnetic material containing Sm-Fe-N crystal grains under high temperature and pressure. Sm-Fe-N sintered magnets can consist substantially of a sintered body of main phase grains and sub-phase grains.

[0024] <Identification of main phase grains and secondary phase grains> The main phase grains and secondary phase grains can be identified as follows. First, the elemental distribution of the cross-section of the magnet is obtained by energy-dispersive X-ray (EDX) analysis. This elemental distribution is typically measured using a SEM-EDX analyzer.

[0025] EDX analysis is performed, for example, under the following conditions:

[0026] [Table 1]

[0027] Images obtained using a scanning electron microscope (SEM) for EDX analysis can be obtained, for example, under the following conditions.

[0028] [Table 2]

[0029] Next, based on the elemental distribution obtained by SEM-EDX analysis, the region is segmented into two parts: a region where the atomic percentage of samarium is 13 atomic percent or more (corresponding to the subphase grain (Sm-rich phase)) and a region where the atomic percentage of samarium is 9 atomic percent or more but less than 13 atomic percent (corresponding to the main phase grain). Through segmentation, the grain boundaries between the main phase grain and the subphase grain are determined, and the main phase grain and subphase grain are identified, respectively.

[0030] Segmentation can be performed by processing the above SEM images using deep learning image processing software (for example, "MIPAR" from MIPAR Software LLC). The specific procedure for this method is as follows.

[0031] [Table 3]

[0032] Segmentation may also be performed by dividing the above SEM images based on contrast. The specific procedure for this method is as follows.

[0033] [Table 4]

[0034] <Obtaining the average value of the XMCD strength of iron> Based on the measurement results of XMCD imaging at an applied magnetic field of 4T, the XMCD intensity and its distribution can be obtained as a signal proportional to the magnetic moment of iron. The number average of the XMCD intensities is taken as the average value of the XMCD intensity.

[0035] XMCD imaging measurements can be performed using a scanning X-ray microscope installed at BL25SU of the large synchrotron radiation facility SPring-8®, or, from April 2024 onwards, a scanning X-ray microscope installed at BL14U of the 3GeV high-brightness synchrotron radiation facility (NanoTerasu®) following equipment relocation from SPring-8.

[0036] In this disclosure, the ratio (M2 / M1) is based on values ​​measured by SPring-8®. When XMCD imaging is obtained based on values ​​measured by NanoTerasu®, the ratio (M2 / M1) calculated from these values ​​is subtracted by 4.6% to be used as the ratio (M2 / M1) in this disclosure.

[0037] XMCD imaging measurements and analyses are performed as follows: First, the cross-section perpendicular to the easy magnetization axis of the sample (sintered magnet) is exposed as the sample surface. This can be achieved by precision polishing in a water-free environment or by vertical Ar ion milling.

[0038] The right-handed and left-handed circularly polarized X-rays generated by the twin helical undulator light source are monochromatized to a predetermined absorption edge energy. Under an environment where a static magnetic field of 4T is applied in a direction parallel to the normal to the sample surface, these high-energy X-rays are focused onto the sample surface by a zone plate, while the sample is sequentially scanned in the in-plane direction. Let R be the X-ray absorption intensity obtained at each scanning step using the right-handed circularly polarized X-rays. Let L be the X-ray absorption intensity obtained at each scanning step using the left-handed circularly polarized X-rays. The ratio of the difference (RL) to the sum of R and L (R+L) is calculated as the XMCD intensity for each scanning step, and these in-plane distributions are output as an XMCD image.

[0039] XMCD imaging is performed under the following conditions, for example. • Measurement absorption edge: Fe L3 edge (Energy value is determined to maximize XMCD intensity) • Detection method: Total electron yield method (sample current measurement) ·X-ray beam size: 0.1 μm or less ·Scanning range: A rectangle with one side being 40 - 60 μm at an arbitrary position on the sample surface ·Scanning step: 0.1 μm

[0040] <Obtaining the average values M1 and M2 of the XMCD intensity of iron in the main phase grains and secondary phase grains> Apply the above segmentation information to the XMCD image to segment the XMCD image into main phase grains and secondary phase grains. The XMCD intensity of each particle can be grasped from the XMCD image. The number average of the XMCD intensity of all main phase grains is defined as the average value M1 of the XMCD intensity of the main phase grains. The number average of the XMCD intensity of all secondary phase grains is defined as the average value M2 of the XMCD intensity of the secondary phase grains. These series of data processing can be carried out using image processing software (for example, the above MIPAR).

[0041] <Main phase grains> The main phase grains form the main phase of the magnet. The main phase grains are Sm-Fe-N system crystal grains, containing 9 atomic% or more and less than 13 atomic% of samarium, iron, and nitrogen. The quantification of samarium can be carried out by EDX analysis method.

[0042] The main phase grains have, at least in part, a crystal structure of the Th2Zn 17 type or Th2Ni 17 type. Specifically, as the crystal structure of the main phase grains, there are SmFe9N 1.5 structure, Sm2Fe 17 N3 structure. The crystal structure of the main phase grains is not limited to this, and it may be any crystal structure composed of Sm, Fe, and N. A typical crystal structure of the main phase grains is Sm2Fe 17 N3 structure.

[0043] The average particle size of the main phase grains may be, for example, 0.5 μm or more and 3.0 μm or less. By having an average particle size of 0.5 μm or more, oxidation and superparamagnetization of Sm-Fe-N crystal grains can be effectively suppressed. By having an average particle size of 3.0 μm or less, many of the main phase grains can become single-domain particles (small regions where the particle magnetic moment is aligned in one direction). By reducing the number of multi-domain particles with low coercivity, the coercivity of the magnet can be further improved. The average particle size of the main phase grains may be 2.0 μm or less, or 1.5 μm or less.

[0044] The method for calculating the average particle size of the main phase grains is as follows: First, a cross-section of the magnet is photographed using a field emission scanning electron microscope (FE-SEM) so that it contains at least 50 particles in total. The main phase grains and sub-phase grains in the captured image are identified in the same manner as described above. Next, the total area A1 of the main phase grain cross-sections and the number N1 of main phase grains in the captured image are determined. The average cross-sectional area per main phase grain (A1 / N1) is calculated. The diameter of a circle (equivalent circle) with the same area as the average cross-sectional area is the average particle size of the main phase grains.

[0045] <Subphase grains> The subphase grains contain 13 atomic percent or more of samarium. The subphase grains may be amorphous, containing samarium, iron, and nitrogen. The amount of nitrogen (atomic percent) in the subphase grains may be equal to or greater than the amount of nitrogen (atomic percent) in the main phase grains. The amount of samarium in the subphase grains may be 14 atomic percent or less.

[0046] Whether the subphase grains are amorphous can be confirmed by electron diffraction patterns obtained using a TEM (transmission electron microscope) or by EBSD (electron backscatter diffraction). If the TEM electron diffraction pattern is a halo pattern, or if a Kikuchi pattern cannot be obtained with EBSD, the subphase grains can be said to be amorphous. In the case of the main phase grains, a spot diffraction pattern can be obtained in the TEM electron diffraction pattern, and a Kikuchi pattern can be obtained with EBSD.

[0047] The average particle size of the subphase grains is not particularly limited. For example, the average particle size of the subphase grains is between 0.2 μm and 5.0 μm.

[0048] The average particle size of the subphase grains can be calculated, similar to the average particle size of the main phase grains, from the total area A2 of the subphase grain cross-sections and the number N2 of subphase grains in the captured image.

[0049] The content of subphase grains in a magnet is, for example, between 0.3 volume% and 5 volume%. A subphase grain content of 0.3 volume% or more makes it easier to achieve an improvement in coercivity. A subphase grain content of 5 volume% or less suppresses the decrease in remanent magnetization.

[0050] The content of the subphase particles may be 0.5% by volume or more, or 0.7% by volume or more. The content of the subphase particles may be 4.8% by volume or less, or 4.6% by volume or less.

[0051] The proportion of subphase grains can be considered as the ratio of the total area of ​​subphase grains to the cross-sectional area of ​​the magnet. The above area ratio (%) of subphase grains is obtained using the formula 100 × A² / A, from the total area A² of the subphase grain cross-section and the cross-sectional area A of the entire magnet, which are obtained in the same manner as when determining the average particle size of the main phase grains and subphase grains. The area ratio (%) obtained by 100 × A² / A can be directly considered as the proportion of subphase grains (volume %) in the magnet.

[0052] <Other ingredients> The magnet contains at least the main phase grains and subphase grains described above. The magnet may also contain other materials, such as α-Fe and trace elements that inevitably become mixed in. Examples of trace elements that inevitably become mixed in include carbon (C), silicon (Si), and aluminum (Al).

[0053] The magnet may contain a sintered body of magnetic powders other than Sm-Fe-N magnetic powder. Examples of other magnetic powders include magnetic powders consisting of rare earth elements other than Sm, Fe, and N, and magnetic powders consisting of rare earth elements containing Sm, Fe, transition metal elements other than Fe, and N. Examples of rare earth elements other than Sm include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). Examples of transition metal elements other than Fe include cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), titanium (Ti), Zr (zirconia), niobium (Nb), tungsten (W), and vanadium (V).

[0054] The presence or absence and location of sintered bodies of other magnetic powders can be determined by the same method as the segmentation described above. The proportion of sintered bodies of other magnetic powders can be considered as the ratio of the total area of ​​sintered bodies of other magnetic powders to the cross-sectional area of ​​the magnet, similar to the ratio of the area of ​​subphase grains to the cross-sectional area of ​​the magnet. The above area ratio (%) of sintered bodies of other magnetic powders can be obtained from the total area A3 of sintered bodies of other magnetic powders and the cross-sectional area A of the magnet using the formula 100 × A3 / A.

[0055] 100 × A3 / A (the area ratio of the sintered body of other magnetic powders to the cross-sectional area of ​​the magnet) may be 5% or less, or 3% or less.

[0056] The magnet may contain, in addition to magnetic powder, at least one of a metal or alloy having a melting point below the pressurized firing temperature, and an alloy having eutectic, peritectic, or petechic points below the pressurized firing temperature (hereinafter also referred to as a low-melting-point metal). The low-melting-point metal can coat at least a portion of the Sm-Fe-N crystal grains (especially the main phase grains), or can form a magnetically separated phase at the grain boundaries between Sm-Fe-N crystal grains. Further improvement in coercivity can be expected with the low-melting-point metal.

[0057] When pressurized firing is performed at a temperature between 300°C and 600°C, at least one of the melting point, eutectic point, peritectic point, or epochic point of the low-melting-point metal must be 600°C or lower. Examples of metals or alloys where at least one of the melting point, eutectic point, peritectic point, or epochic point is 600°C or lower include zinc (Zn), gallium (Ga), germanium (Ge), indium (In), tin (Sn), bismuth (Bi), Zn-Al alloy, Zn-Ga alloy, Zn-Ge alloy, Zn-In alloy, Zn-Sn alloy, and Zn-Bi alloy.

[0058] The presence or absence of low-melting-point metals and their regions can be determined by the same method as the segmentation described above. The proportion of low-melting-point metals can be considered as the ratio of the total area of ​​low-melting-point metals to the cross-sectional area of ​​the magnet, similar to the ratio of the area of ​​subphase grains to the cross-sectional area of ​​the magnet. The above area ratio (%) of low-melting-point metals can be obtained from the total area Am of the low-melting-point metals and the cross-sectional area A of the magnet using the formula 100 × Am / A.

[0059] 100 × Am / A (area ratio of low-melting-point metal to the cross-sectional area of ​​the magnet) may be 2.0% or more, or 3.0% or more. 100 × Am / A may be 15.0% or less, or 10.0% or less.

[0060] (Manufacturing method) The magnets of this disclosure can be manufactured by a method comprising pressurizing a magnetic material containing Sm-Fe-N magnetic powder under a reduced pressure atmosphere containing an inert gas at 10 Pa to 200 Pa.

[0061] Firing is usually carried out in a vacuum atmosphere (see Patent Document 1) or an inert gas atmosphere. A vacuum atmosphere is created by removing gas from inside the furnace using a vacuum pump or the like. However, as gas is removed, it is impossible to prevent air from flowing into the furnace through gaps in the apparatus, making it difficult to prevent oxidation of the magnetic material. An inert gas atmosphere is created by filling a sealed furnace with inert gas. In this case, while the inflow of air from the outside can be suppressed, it is not possible to remove moisture contained in the magnetic powder or moisture generated during heating. Therefore, oxidation of the magnetic material due to moisture may occur.

[0062] In this disclosure, the inside of the sintering machine is depressurized to between 10 Pa and 200 Pa (within the range of low vacuum to medium vacuum as classified by JIS Z 8261-1) in the presence of an inert gas. Because the vacuum inside the furnace is at a low to medium vacuum level, it is difficult for outside air to flow in. In addition, because an inert gas is present, even if air does flow in, contact between the magnetic material and the air is suppressed. Furthermore, when exhausting to maintain the reduced pressure, moisture is also discharged from the furnace. Therefore, firing in a reduced-pressure atmosphere containing an inert gas effectively suppresses oxidation of the magnetic material.

[0063] When pressure firing is performed under the above conditions, the ratio (M2 / M1) of the average XMCD intensity M1 of the iron in the main phase grains of the resulting magnet to the average XMCD intensity M2 of the iron in the Sm-rich phase is between 10% and 83%.

[0064] A reduced-pressure atmosphere containing an inert gas is created, for example, by introducing an inert gas into the sintering machine while simultaneously discharging the gas from the machine. In this case, moisture is removed more easily, further improving the oxidation suppression effect.

[0065] From the standpoint of suppressing oxidation, pressurized firing may be carried out in a low-oxygen atmosphere where the volume-based oxygen concentration is 2.0 ppm or less.

[0066] The following shows an example of a method for manufacturing a sintered magnet. Figure 1 is a flowchart of an example of a method for manufacturing a sintered magnet according to this disclosure.

[0067] (1) Preparation of Sm-Fe-N magnetic powder (S11) The Sm-Fe-N magnetic powder may be a commercially available product. The Sm-Fe-N magnetic powder may also be prepared by nitriding an alloy powder containing Sm and Fe (Sm-Fe alloy).

[0068] (2) Crushing or pulverization, and classification (S12) Sm-Fe-N magnetic powder may be pulverized (or crushed) and classified. The pulverization (crushing) and classification should be carried out under conditions such that the average particle size of the Sm-Fe-N magnetic powder is between 0.5 μm and 5 μm. Fine particles are removed by classification.

[0069] Crushing or grinding can be carried out using, but is not limited to, agate mortars, jet mills (air-jet type, etc.), ball mills, etc. Examples of air-jet type jet mills include, but are not limited to, the MC44 manufactured by Micromacinazione. Classification can be carried out using, but is not limited to, an air-jet classifier, etc.

[0070] (3) Addition of low-melting-point metal (S13) Before pressurized firing, a low-melting-point metal powder may be added to the Sm-Fe-N magnetic powder. The amount of low-melting-point metal added may be, for example, 1% to 20% by mass of the Sm-Fe-N magnetic powder. When the amount of low-melting-point metal added is 1.0% by mass or more, the effect of the low-melting-point metal is easily exhibited. When the amount of low-melting-point metal added is 20.0% by mass or less, the effect on the remanent magnetization of the resulting magnet is small. The amount of low-melting-point metal added may be 2.0% by mass or more, or 3.0% by mass or more. The amount of low-melting-point metal added may be 15.0% by mass or less, or 10.0% by mass or less.

[0071] (4) Molding in magnetic field (S14) Before pressurized firing, the magnetic material may be molded in a magnetic field. Molding in a magnetic field is a process in which the magnetic material is molded while a magnetic field is applied. For example, a powder press equipped with a magnetic field generator can be used for molding in a magnetic field. Molding in a magnetic field aligns the orientation of the easy magnetization axes of the Sm-Fe-N magnetic powder, resulting in higher magnetic properties.

[0072] The conditions for forming in a magnetic field are not particularly limited. The applied magnetic field may be, for example, a static magnetic field of 1T or more, or a pulsed magnetic field. Forming in a magnetic field may be performed on magnetic material filled into a mold used for pressurized firing.

[0073] All of the above steps may be carried out in a low-oxygen atmosphere where the volume-based oxygen concentration is 10 ppm or less (particularly 2 ppm or less). The above steps are carried out, for example, in a glove box purged with an inert gas (one or more mixed gases such as nitrogen, argon, and helium), preferably in a glove box connected to a gas-circulating oxygen-moisture purifier.

[0074] From the preparation of the Sm-Fe-N magnetic powder until pressurized firing (or magnetic field molding), it is permissible to immerse the Sm-Fe-N magnetic powder in an organic solvent that prevents oxidation and leave it in the atmosphere for material handling purposes.

[0075] (5) Pressure firing (S15) A material containing Sm-Fe-N magnetic powder, filled into a mold, is subjected to pressure firing. This yields an Sm-Fe-N sintered magnet. The mold used may have any shape; for example, a cylindrical mold can be used, but is not limited to this.

[0076] Pressurized firing is performed by reducing the pressure inside the sintering machine to between 10 Pa and 200 Pa in the presence of an inert gas. This suppresses oxidation of the magnetic material during firing, resulting in a ratio (M2 / M1) of 83% or less, and producing magnets with high coercivity. The reduced pressure atmosphere containing the inert gas may be created by introducing the inert gas into the sintering machine while simultaneously discharging the gas from inside the sintering machine.

[0077] The pressure inside the sintering machine may be 15 Pa or more, or 20 Pa or more. The pressure inside the sintering machine may be 150 Pa or less, or 100 Pa or less.

[0078] Examples of inert gases include helium, neon, argon, and nitrogen. These can be used individually or in combination of two or more. The inert gas may be argon.

[0079] Any pressurized firing method can be used for pressurized firing, including electrostatic pressurized firing. Pressurized firing may be carried out, for example, by hot pressing or by electrostatic sintering. The pressure applied to the magnetic material in the mold should be higher than atmospheric pressure and sufficient to form a sintered magnet. The pressure applied to the magnetic material in the mold may be, for example, in the range of 100 MPa to 2000 MPa. The pressurized firing time is, for example, 30 seconds to 10 minutes.

[0080] Pressure firing is carried out at a temperature of, for example, 300°C to 600°C. The pressure firing temperature may be 350°C or higher, or 400°C or higher. The pressure firing temperature may be 580°C or lower, or 550°C or lower.

[0081] This disclosure is not limited to the embodiments described above, and design modifications are possible without departing from the gist of this disclosure. [Examples]

[0082] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is by no means limited by the examples below, and it is certainly possible to implement it with appropriate modifications to the extent that it is applicable to the spirit of the preceding and following, and all such modifications are included within the technical scope of the present disclosure.

[0083] [Example 1] A Sm-Fe-N magnet was fabricated using the following procedure. (i) Preparation of Sm-Fe-N magnetic powder Composition is Sm2Fe 17 A Sm-Fe-N magnetic powder with an average particle size of approximately 25 μm and a mineral content of N3 was prepared.

[0084] (ii) Grinding and Classification Using an air-jet mill, Sm-Fe-N magnetic powder was ground at a grinding pressure of 0.7 MPa.

[0085] Grinding was performed in a glove box under a low-oxygen atmosphere of 2 ppm or less. After grinding, fine particles (particles with a particle size of less than 0.04 μm) were removed using an air-flow classifier. This adjusted the average particle size of the Sm-Fe-N magnetic powder to 1.6 μm.

[0086] (iii) Molding in magnetic field A slurry was prepared by immersing 0.2 g of the obtained magnetic powder in heptane in a glove box under a low-oxygen atmosphere of 2 ppm or less. The obtained slurry was filled into a cemented carbide mold. The mold was removed from the glove box and placed in a powder press equipped with a magnetic field generator. While applying a static magnetic field of 1.5 T to the powder press, press molding was performed with a pressure of 1250 MPa perpendicular to the magnetic field.

[0087] (iv) Pressurized firing Next, the mold described above was placed inside a pulse current sintering machine equipped with a servo-controlled press mechanism. Ar gas was introduced into the pulse current sintering machine while evacuating it with a vacuum pump to create a reduced pressure atmosphere of 100 Pa. While maintaining this reduced pressure atmosphere, a pressure of 1250 MPa was applied to the mold, and sintering was performed at 350°C for 2 minutes to obtain a sintered magnet.

[0088] [Example 2] A sintered magnet was obtained in the same manner as in Example 1, except that a magnetic material was used which consisted of 100% by mass of Sm-Fe-N magnetic powder mixed with 9.2% by mass of Zn-Al alloy (10% by mass of Al, melting point 381°C), and the pressurization conditions were changed as shown in Table 1.

[0089] [Comparative Examples 1-2] A sintered magnet was obtained in the same manner as in Example 1, except that the pressure firing conditions were changed as shown in Table 5.

[0090] [evaluation] (oxygen content) The oxygen content of Sm-Fe-N magnetic powder was measured using inert gas fusion-nondispersive infrared absorption (NDIR) spectroscopy.

[0091] (Average particle size, area ratio) The cross-section of the magnet was segmented as described above, and the average particle size and area ratio of the main phase grains and sub-phase grains were calculated.

[0092] Figure 2A shows an example of an SEM image of a cross-section of the sintered magnet used in the calculation. In the SEM image, the light gray areas represent the Sm-rich phase, and the black or dark gray areas represent the main phase grains. Figure 2B is an image obtained by binarizing Figure 2A, with the main phase grains shown in black. 2 C is an image obtained by binarizing Figure 2A, with the Sm-rich phase shown in black.

[0093] (Average XMCD strength of iron) Segmentation information and XMCD imaging at an applied magnetic field of 4T were acquired as described above, and the average values ​​M1 and M2 of the XMCD intensities of iron in the main phase grains and Sm-rich phase grains were obtained. The XMCD imaging was performed at the large synchrotron radiation facility SPring-8(registered trademark). For Comparative Example 2, XMCD imaging was also performed using the 3GeV high-brightness synchrotron radiation facility (NanoTerasu(registered trademark)).

[0094] (Relative density) Representative Sm2Fe particles that make up the main phase 17 Known true density of N3 phase (7.67 g / cm³) 3 The ratio of the volume density of the sintered magnet to the volume of the magnet was calculated as the relative density. The volume density of the sintered magnet was determined from the volume and mass of the sintered magnet.

[0095] (coercive force, residual magnetization) The measurements were taken using a vibrating sample magnetometer (VSM).

[0096] [Table 5]

[0097] [Example 3] The following procedure will enable the Sm-Fe-N system Grill A magnet was fabricated. (i) Preparation of Sm-Fe-N magnetic powder Composition is Sm2Fe 17 A Sm-Fe-N magnetic powder with an average particle size of approximately 25 μm and a mineral content of N3 was prepared.

[0098] 5.0% by mass of Zn-Al alloy (Al content 20% by mass, melting point 395°C) was mixed with 100% by mass of Sm-Fe-N magnetic powder.

[0099] (ii) Grinding and Classification Using an air-jet mill, Sm-Fe-N magnetic powder was ground at a grinding pressure of 0.7 MPa.

[0100] Grinding was performed in a glove box under a low-oxygen atmosphere of 2 ppm or less. After grinding, fine particles (particles with a particle size of less than 0.04 μm) were removed using an air-flow classifier. This adjusted the average particle size of the Sm-Fe-N magnetic powder to 2.0 μm.

[0101] (iii) Molding in magnetic field A slurry was prepared by immersing 0.2 g of the obtained magnetic powder in heptane in a glove box under a low-oxygen atmosphere of 2 ppm or less. The obtained slurry was filled into a cemented carbide mold. The mold was removed from the glove box and placed in a powder press equipped with a magnetic field generator. A static magnetic field of 1.5 T was applied to the powder press, and a magnetic field of 1250 MP was applied perpendicular to the magnetic field. a Press molding was performed under this pressure.

[0102] (iv) Pressurized firing Next, the mold described above was placed inside a pulse current sintering machine equipped with a servo-controlled press mechanism. Ar gas was introduced into the pulse current sintering machine while evacuating it with a vacuum pump, creating a reduced pressure atmosphere of 200 Pa. While maintaining this reduced pressure atmosphere, a pressure of 1470 MPa was applied to the mold, and sintering was performed at 400°C for 2 minutes to obtain a sintered magnet.

[0103] [Example 4] A sintered magnet was obtained in the same manner as in Example 3, except that the pressure firing conditions were changed as shown in Table 6.

[0104] [Example 5] A sintered magnet was obtained in the same manner as in Example 3, except that 10.0% by mass of Zn-Al alloy (Al content 20% by mass, melting point 395°C) was mixed in and the pressure firing conditions were changed as shown in Table 6.

[0105] [Comparative Example 3] A sintered magnet was obtained in the same manner as in Example 3, except that the pressure firing conditions were changed as shown in Table 6.

[0106] [evaluation] The evaluation was carried out in the same manner as in Example 1. The results are shown in Table 6. However, for Examples 3 to 5 and Comparative Example 3, the average values ​​M1 and M2 of the XMCD intensities of iron in the main phase grains and Sm-rich phase grains were obtained based on XMCD imaging measurements using the 3 GeV high-brightness synchrotron radiation facility (NanoTerasu®), and after calculating the ratio (M2 / M1), the value obtained by subtracting 4.6% was shown.

[0107] [Table 6]

[0108] <1> A crystalline grain containing samarium, iron, and nitrogen, comprising a main phase grain containing 9 atomic percent or more and less than 13 atomic percent of samarium, It comprises a subphase grain containing 13 atomic percent or more of samarium, iron, and nitrogen, An Sm-Fe-N sintered magnet in which, under conditions where a static magnetic field of 4T is applied in a direction parallel to the easy magnetization axis, the ratio (M2 / M1) of the average value M2 of the X-ray magnetic circular dichroism intensity of the secondary phase iron grains to the average value M1 of the main phase iron grains, obtained in a plane perpendicular to the easy magnetization axis, is between 10% and 83%. <2> The content of the aforementioned subphase particles is 0.3% by volume or more and 5% by volume or less. <1> The Sm-Fe-N sintered magnet described above. <3> The average particle size of the main phase grains is 0.5 μm or more and 3.0 μm or less. <1> or <2> The Sm-Fe-N sintered magnet described above. <4> It contains no oxygen, or contains oxygen at a concentration of 0.5% by mass or less. <1> from <3> Sm-Fe-N sintered magnet as described in any of the following. <5> A method for manufacturing an Sm-Fe-N sintered magnet, comprising pressurizing and firing a magnetic material containing Sm-Fe-N magnetic powder in a sintering machine under reduced pressure of 10 Pa to 200 Pa containing an inert gas. <6> The aforementioned reduced pressure atmosphere is formed by introducing the inert gas into the sintering machine while simultaneously discharging the gas from within the sintering machine. <5> A method for manufacturing Sm-Fe-N sintered magnets as described above. <7> The aforementioned pressurized firing is carried out in a low-oxygen atmosphere where the volume-based oxygen concentration is 2 ppm or less. <5> or <6> A method for manufacturing Sm-Fe-N sintered magnets as described above. <8> The aforementioned pressurized firing is carried out at a temperature of 300°C to 600°C. <5> from <7> A method for manufacturing an Sm-Fe-N sintered magnet as described in any of the following. <9> The magnetic material includes at least one of a metal or alloy having a melting point below the pressurized firing temperature, and an alloy having eutectic, peritectic, or petechic points below the pressurized firing temperature. <5> from <8> A method for manufacturing an Sm-Fe-N sintered magnet as described in any of the following. <10> The method further comprises molding the magnetic material in a magnetic field prior to the aforementioned pressurized firing. <5> from <9> A method for manufacturing an Sm-Fe-N sintered magnet as described in any of the following. <11> The method further comprises grinding and classifying the Sm-Fe-N magnetic powder before the aforementioned pressurized firing. <5> from <10> A method for manufacturing an Sm-Fe-N sintered magnet as described in any of the following. [Industrial applicability]

[0109] The sintered magnets and magnetic powders of the present invention can be used in a wide range of applications in the field of various motors. For example, they can be used in automotive auxiliary motors, main motors for EVs / HEVs, and more specifically, in motors for oil pumps, motors for electric power steering, motors for EVs / HEVs, and so on.

[0110] This application claims priority under Japanese Patent Application No. 2024-111634, filed in Japan on 11 July 2024, the entirety of which is incorporated herein by reference.

Claims

1. Crystal grains containing samarium, iron, and nitrogen, comprising a main phase grain containing 9 atomic percent or more and less than 13 atomic percent of samarium, It comprises a subphase grain containing 13 atomic percent or more of samarium, iron, and nitrogen, In an environment where a static magnetic field of 4T is applied in a direction parallel to the easy magnetization axis, the ratio (M2 / M1) of the average value M2 of the X-ray magnetic circular dichroism intensity of the secondary phase iron grains to the average value M1 of the main phase iron grains, obtained in a plane perpendicular to the easy magnetization axis, is between 10% and 83%. Sm-Fe-N sintered magnets that are oxygen-free or contain 0.5% by mass or less of oxygen.

2. The Sm-Fe-N sintered magnet according to claim 1, wherein the content of the aforementioned subphase grains is 0.3 volume% or more and 5 volume% or less.

3. The Sm-Fe-N sintered magnet according to claim 1 or 2, wherein the average particle size of the main phase grains is 0.5 μm or more and 3.0 μm or less.

4. A method for manufacturing an Sm-Fe-N sintered magnet, comprising: immersing a magnetic material containing Sm-Fe-N magnetic powder in an organic solvent capable of preventing oxidation; introducing an inert gas while discharging the gas to create a reduced pressure atmosphere of 10 Pa to 200 Pa containing an inert gas in a sintering machine; and pressurizing the magnetic material at a temperature of 300°C to 600°C in a low-oxygen atmosphere where the volume-based oxygen concentration is 2 ppm or less.

5. The method for manufacturing an Sm-Fe-N sintered magnet according to claim 4, wherein the magnetic material comprises at least one of a metal or alloy having a melting point below the pressurized firing temperature, and an alloy having a eutectic, peritectic, or petechic point below the pressurized firing temperature.

6. A method for manufacturing an Sm-Fe-N sintered magnet according to claim 4 or 5, further comprising molding the magnetic material in a magnetic field before the aforementioned pressurized firing.

7. A method for producing an Sm-Fe-N sintered magnet according to claim 4 or 5, further comprising grinding and classifying the Sm-Fe-N magnetic powder before the aforementioned pressurized firing.

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