Sintered magnet, method for producing powder for sintered magnet, and method for producing sintered magnet

Abstract

The invention relates to a sintered magnet, a method for producing a powder for a sintered magnet, and a method for producing a sintered magnet. [Problem] To provide a technique for improving residual magnetization in an Sm-Fe-N sintered magnet. [Solution] Provided is a sintered magnet which contains a first phase that is mainly composed of Sm-Fe-N-based crystal grains having a Th2Zn17-type structure. The density of the sintered magnet is 6.5 g / cm3 or more, and the full width at half maximum of the peak of the diffraction intensity of the (220) plane obtained by X-ray diffraction is 0.2-0.3 degrees (inclusive).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a Sm-Fe-N sintered magnet. BACKGROUND

[0002] In recent years, as a high-performance magnet, a Sm (samarium)-Fe (iron)-N (nitrogen) system magnet has been developed. The Sm-Fe-N compound is known to have both a high spontaneous magnetization and a high anisotropic field, and in addition, exhibits high heat resistance. Also, a technique for obtaining a Sm-Fe-N system magnet having high magnetic properties has been proposed (for example, refer to Patent Literature 1). In Patent Literature 1, a technique for pulverizing a Sm-Fe-N system magnet powder by a dry jet mill and producing a powder having excellent crystallinity is disclosed.

[0003] [Related Art Documents]

[0004] [Patent Literature]

[0005] Patent Literature 1: Japanese Patent No. 7076740 SUMMARY

[0006] [Problems to be Solved by the Invention]

[0007] However, in the technique described in Patent Literature 1, the surface of the pulverized magnetic particles can be damaged by the pulverization by the jet mill, and there can be regions where the crystallinity is low on a microscopic scale. If these regions expand significantly at the time of sintering, the residual magnetization of the sintered body can decrease.

[0008] The present disclosure was made in order to solve the above-described problems, and aims to provide a technique for improving the residual magnetization in a Sm-Fe-N sintered magnet.

[0009] [Means for Solving the Problems]

[0010] The present disclosure was made in order to solve at least one of the above-described problems, and can be implemented as the following modes.

[0011] <1> According to one embodiment of the present disclosure, a sintered magnet is provided, including a first phase in which Sm-Fe-N system grains having a Th2Zn 17 structure are a main phase. The sintered magnet has a density of 6.5 g / cm 3 The half-value width of the peak of the diffraction intensity of the (220) plane obtained by X-ray diffraction is 0.2 degrees or more and 0.3 degrees or less.

[0012] The sintered magnet according to the embodiment has a density of 6.5 g / cm 3, and thus the saturation magnetization and the residual magnetization can be improved. In addition, when the half-width of the peak (also referred to as a diffraction peak) of the diffraction intensity of the (220) plane is 0.3 degrees or less, the crystallinity of the Sm-Fe-N-based grains of the sintered magnet is improved, and a sintered magnet in which the magnetic components (saturation magnetization and residual magnetization) and the degree of orientation of the magnetic field are further improved can be provided.

[0013] <2> The sintered magnet of the above-described aspect can further include a second phase composed of an alloy containing one or more elements selected from the group consisting of Group 2 elements and rare earth elements, and having a melting point of 180°C or higher and 620°C or lower, and the content of the second phase can be 20% by volume or less. In this way, the alloy of the second phase has a melting point of 180°C or higher and 620°C or lower, which is lower than the temperature at which the Sm-Fe-N-based magnet thermally decomposes (620°C or higher). Therefore, in the case where sintering is performed at a temperature lower than 620°C, the alloy of the second phase can be used as a sintering aid, and the sintering density of the first phase can be improved. In addition, since the alloy of the second phase has a melting point of 180°C or higher, it can be used, for example, in a device that generates heat and becomes high-temperature, such as an electric motor for an EV (electric vehicle). Furthermore, since the content of the second phase is 20% by volume or less, the decrease in the magnetization of the sintered magnet caused by the second phase can be appropriately suppressed, and the alloy that becomes the second phase can effectively function as an aid for densifying the first phase. As a result, the degree of densification at the time of sintering can be further improved, and the residual magnetization of the sintered magnet can be further improved.

[0014] <3> According to another aspect of the present disclosure, a method for manufacturing a sintered magnet powder for molding a sintered magnet of the above-described aspect is provided. The method for manufacturing a sintered magnet powder includes: a pulverization step in which a coarse powder containing a Sm-Fe-N single crystal is pulverized to obtain the Sm-Fe-N-based grains; an alloy powder production step in which an alloy powder that becomes the second phase is obtained; and a mixing step in which the Sm-Fe-N-based grains and the alloy powder are dispersed to obtain the sintered magnet powder as a mixed powder, and the pulverization step, the alloy powder production step, and the mixing step are performed in a low-oxygen-concentration atmosphere.

[0015] According to the method for manufacturing a sintered magnet powder of the aspect, since the above-described steps are performed in a low-oxygen atmosphere, the oxidation of the Sm-Fe-N grains and the alloy powder can be suppressed, and the wettability of the Sm-Fe-N-based grains and the alloy can be ensured. As a result, a sintered magnet having a high residual magnetization can be manufactured.

[0016] <4>According to another aspect of the present disclosure, there is provided a method for manufacturing a sintered magnet according to the above aspect. The method for manufacturing a sintered magnet includes a sintering process in which the sintered magnet powder manufactured by the method for manufacturing a sintered magnet powder according to the above aspect is pressure-sintered at a sintering temperature of 600°C or lower in a low-oxygen concentration atmosphere.

[0017] According to the method for manufacturing a sintered magnet, by setting the sintering temperature to 600°C or lower, thermal decomposition of the Sm-Fe-N main phase can be suppressed, and by manufacturing in a low-oxygen atmosphere, oxidation of the Sm-Fe-N-based grains and the alloy powder can be suppressed. As a result, the sintered magnet can be manufactured with high residual magnetization and high density.

[0018] Further, the present disclosure can be implemented in various ways, for example, as a permanent magnet for a motor or the like. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is an explanatory diagram conceptually showing a cross-sectional configuration of a sintered magnet according to an embodiment.

[0020] Figure 2 is a process diagram showing an example of a method for manufacturing a sintered magnet.

[0021] Figure 3 is a graph showing the evaluation results of samples.

[0022] Figure 4 is a graph showing the results of evaluation of the wettability of an alloy.

[0023] Figure 5 is an explanatory diagram of a sample for SEM observation. DETAILED DESCRIPTION

[0024] <EMBODIMENT>

[0025] Figure 1 is an explanatory diagram conceptually showing a cross-sectional configuration of a sintered magnet 100 according to an embodiment. The sintered magnet 100 according to the embodiment includes a first phase 10 in which Sm-Fe-N-based grains having a Th2Zn 17 structure are a main phase, and a second phase 20 composed of an alloy containing one or more elements selected from at least one of a Group 2 element and a rare earth element, and having a melting point of 180°C or higher and 620°C or lower. In other embodiments, the sintered magnet can not include the second phase.

[0026] In Figure 1In the diagram, the first phase 10 is marked with an upward-sloping shading line on the right, and the second phase 20 is marked with a downward-sloping shading line on the right. As shown, the first phase 10 has multiple Sm-Fe-N grains 10G. The second phase 20 is located at the grain boundaries of the Sm-Fe-N grains 10G. The sintered magnet 100 may also have voids V at the grain boundaries of the Sm-Fe-N grains 10G.

[0027] The Sm-Fe-N system grain 10G, as the main phase, has Th2Zn. 17 Sm2Fe type structure 17 N3. The sintered magnet 100 exhibits magnetism through Sm-Fe-N system grains 10G (main phase). The crystal structure of the main phase can be identified, for example, by X-ray diffraction analysis of the sintered magnet 100. The main phase refers to the compound that determines the properties of the sintered magnet.

[0028] Sm2Fe 17 N3 has excellent saturation magnetization and a huge anisotropic magnetic field, so the sintered magnet 100 according to the embodiment can withstand heat, reverse magnetic field and generate a high magnetic field.

[0029] Phase 10 may also contain Th2Ni 17 Structures different from the main phase, such as the TbCu7 type structure, are represented as Sm-Fe-N system grains 10G. Here, Tb is terbium and Cu is copper.

[0030] The density of sintered magnet 100 is 6.5 g / cm³. 3 The density of sintered magnet 100 can be determined using the Archimedes method in pure water. The density of sintered magnet 100 is 6.5 g / cm³. 3 The high density of the magnets improves saturation magnetization and remanent magnetization. For example, by manufacturing the magnets in a low-oxygen-concentration atmosphere, the oxygen content of the sintered magnets can be suppressed, thereby increasing the density of the sintered magnets.

[0031] The full width at half maximum (FWHM) of the diffraction intensity peaks in the (220) plane obtained by X-ray diffraction of the sintered magnet 100 is 0.2 degrees or more and 0.3 degrees or less. The FWHM of the intensity peaks in the X-ray diffraction pattern is an indicator of the shape of the intensity peaks. When comparing the same particle size, a larger FWHM indicates a wider peak width and lower crystallinity. A FWHM of 0.2 degrees or more and 0.3 degrees or less for the diffraction peaks in the (220) plane indicates improved crystallinity of the Sm-Fe-N grains in the sintered magnet, which can result in high remanent magnetization. For example, in the manufacture of Sm-Fe-N magnetic powder that becomes the first phase 10, wet grinding of coarse powder suppresses the distortion of the magnetic powder crystals, thereby improving the crystallinity of the sintered magnet.

[0032] The metal forming the second phase 20 is not particularly limited, and is preferably composed of an alloy containing one or more elements of at least either one of a Group 2 element and a rare earth element. Such an alloy of the composition is excellent in wettability to the main phase (Sm2Fe 17 N3). Thus, a dense sintered body can be obtained.

[0033] The Group 2 element is an element belonging to Group 2 of the periodic table, and includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The rare earth element includes scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0034] The second phase 20 can also contain elements other than the Group 2 element and the rare earth element. For example, silver (Ag), aluminum (Al), copper (Cu), zinc (Zn), and the like can also be contained.

[0035] The melting point of the alloy forming the second phase 20 is not particularly limited, and is preferably 180°C or higher and 620°C or lower. The Sm-Fe-N-based magnet undergoes thermal decomposition at 620°C or higher, and thus is subject to the constraint of the sintering temperature, and a high-density sintered body has not been obtained in the past. In contrast, when the melting point of the alloy forming the second phase 20 is 620°C or lower, this is a temperature at which the main phase does not decompose, and thus even if heating is performed at a temperature at which the alloy melts when the sintered magnet 100 is manufactured, the main phase does not decompose. Thus, by using an alloy having a melting point of 620°C or lower for the second phase 20, liquid-phase sintering can be induced, and a Sm2Fe 17 N3 / Sm2Fe 17 N3. Furthermore, when the melting point of the alloy forming the second phase 20 is 180°C or higher, the sintered magnet 100 can be used, for example, for an electric motor for EV and the like that generates heat and becomes high-temperature.

[0036] The melting point of the second phase can be measured using a DSC (differential scanning calorimeter). 10 to 20 mg of a liquid-quenched foil obtained by melt spinning described later is weighed and used as a measurement sample. In the measurement, a sample pan of BN (boron nitride) material is used, the measurement temperature range is set to room temperature to 700°C, and the temperature increase rate is set to 10°C / min. The melting peak temperature appearing in the measurement temperature range is adopted to determine the melting point.

[0037] The content of the second phase 20 is not particularly limited, and is preferably 20% by volume or less. The alloy of the second phase 20 can function as an aid for densifying the first phase 10, and on the other hand, the alloy of the second phase 20 is a non-magnetic component, and thus when contained in a large amount, the proportion of the magnetic phase relatively decreases, and the magnetization can decrease. When the content of the second phase 20 is set to 20% by volume or less, the decrease in the magnetization of the sintered magnet 100 due to the second phase 20 can be appropriately suppressed, and the alloy that becomes the second phase 20 can be made to function effectively as an aid for densifying the first phase 10. As a result, the degree of densification at the time of sintering can be further improved, and the magnetization of the sintered magnet 100 can be further improved. Note that the content of the second phase 20 is preferably 0.1% by volume or more. Here, the added amount (volume %) of the alloy powder and the second phase content (volume %) are approximately the same, and the amount of the alloy powder (volume) is the amount obtained by adding the amount of the Sm-Fe-N-based grains (Sm2Fe 17 N3) to the amount of the alloy powder.

[0038] The second phase content (volume %) in the sintered magnet can be obtained by the following method.

[0039] First, the cross section of the sintered magnet to be evaluated is mirror-polished, and then cross-sectional observation is performed using a scanning electron microscope (SEM) to obtain an SEM image at an appropriate magnification (for example, 1,000 to 5,000 times). The SEM image is taken under conditions in which the contrast difference between the binder phase and the main phase becomes clear. Next, the obtained SEM image is subjected to a binarization process using the open-source image analysis software "ImageJ", and a black-and-white image in which the two phases are clearly separated is generated. The area ratio of each phase is calculated for the binarized image, and by assuming that the cross-sectional observation image is a representative random cross section, the obtained area fraction of the second phase is considered to be approximately the same as the volume fraction in the material, and the calculated value of the area fraction can be treated as the volume fraction (volume %) of the second phase.

[0040] The sintered magnet 100 can also contain inevitable impurity elements and the like within a range that does not impair the magnetic properties of the main phase. The inevitable impurity elements refer to impurity elements that cannot be avoided from being contained when manufacturing the sintered magnet 100 and the like of the embodiment, or that would cause a significant increase in manufacturing cost if they were avoided. As such inevitable impurity elements, impurity elements in raw materials, elements contained in lubricants and the like used at the time of molding, and the like can be exemplified.

[0041] Figure 2 is a process chart indicating an example of a method for manufacturing the sintered magnet 100. The method for manufacturing the sintered magnet 100 of the embodiment is not particularly limited, and for example, can be manufactured by the following method.

[0042] like Figure 2 As shown, in the manufacturing method of sintered magnet 100, the processes are carried out in the order of manufacturing powder for sintered magnet P0 and sintering P4. In the manufacturing powder for sintered magnet P0, the processes are carried out in the order of pulverizing P1, alloy powder making P2, and mixing P3.

[0043] In the pulverizing process P1, the material containing Th2Zn is... 17 The coarse powder of Sm-Fe-N single crystals with a morphological structure is pulverized to obtain Sm-Fe-N system grains. For example, Sm2Fe can be used as the coarse powder. 17 N3, coarse powder having an average particle size of 10 μm or more and 200 μm or less. The average particle size of the pulverized Sm-Fe-N system crystals is not particularly limited, but is preferably 0.1 μm or more and 20 μm or less, more preferably 0.4 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less.

[0044] Pulverization can be performed using mills, planetary ball mills, etc. Furthermore, pulverization can be carried out dry or wet. Compared to dry pulverization, wet pulverization of coarse powder can suppress crystal distortion, improve the crystallinity of the sintered magnet, and enhance magnetization, making it a preferred method. In the case of wet pulverization, solvents such as ethanol or isopropanol can be used.

[0045] In the alloy powder production process P2, powder of a predetermined size that will become the second phase of the alloy is produced to obtain alloy powder.

[0046] In the mixing process P3, Sm-Fe-N grains and alloy powder are dispersed to obtain a sintered magnet powder as the mixed powder. The mixing process P3 can be a wet process in which Sm-Fe-N grains and alloy powder are dispersed in a solvent (e.g., ethanol), or a dry process in which Sm-Fe-N grains and alloy powder are dispersed in an inert gas (e.g., argon, helium, nitrogen, etc.).

[0047] The aforementioned pulverization process P1, alloy powder preparation process P2, and mixing process P3 are all carried out under a low-oxygen concentration atmosphere. The oxygen concentration is adjusted by controlling the atmosphere in each process. Low oxygen concentration refers to a concentration lower than the atmospheric oxygen concentration (approximately 21% by volume). The oxygen concentration is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 0.5 ppm or less. For example, a low-oxygen concentration atmosphere can be achieved by injecting an inert gas into a vacuum chamber. By carrying out the above processes under a low-oxygen atmosphere, oxidation of the Sm-Fe-N grains and alloy powder can be prevented, and the wettability of the Sm-Fe-N grains and alloy powder can be ensured. As a result, the density of the sintered magnet can be increased.

[0048] In sintering step P4, sintered magnet powder manufactured in sintered magnet powder manufacturing step P0 is formed and pressure-sintered at a sintering temperature below 600°C in a low-oxygen atmosphere. In sintering step P4, sintering is performed in an oxygen concentration atmosphere similar to that of pulverizing steps P1 to mixing steps P3. By setting the sintering temperature to below 600°C, the thermal decomposition of Sm-Fe-N grains can be suppressed. Furthermore, by performing sintering step P4 in a low-oxygen atmosphere, the oxidation of Sm-Fe-N grains and alloy powder can be suppressed. As a result, density can be improved, and the magnetization of the sintered magnet 100 can be enhanced.

[0049] The sintered magnet of this embodiment can be used as a permanent magnet for various electric motors, such as electric motors for EVs, built-in electric motors for robots, built-in electric motors for drones, and electric motors for elevators.

[0050] [Example]

[0051] The present disclosure will be illustrated in more detail by way of examples.

[0052] Figure 3 This is a graph showing the evaluation results of samples 1-14. In the examples, the second phase contains any one of magnesium (Mg), calcium (Ca), and barium (Ba) as a Group 2 element, and any one of lanthanum (La) and praseodymium (Pr) as a rare earth element. The second phase in the examples contains any one of silver (Ag), copper (Cu), and zinc (Zn) as elements other than Group 2 elements and rare earth elements. Figure 3 In the diagram, Group 2 elements and rare earth elements are shown enclosed in double lines.

[0053] 1. Sample preparation

[0054] Samples 1 to 10 were manufactured using the methods illustrated in the above embodiments. Figure 2Note that Samples 1 and 7 do not contain the second phase, and thus the alloy powder production process P2 and the mixing process P3 are not performed, and the Sm-Fe-N-based grains obtained through the pulverization process PI are used in the sintering process P4. Sample 11 is sintered using Sm-Fe-N-based powder pulverized by dry jet milling as a raw material. Samples 12 and 13 are sintered using Sm-Fe-N-based pulverized powder obtained by pulverization by ball milling under conditions deviating from the pulverization conditions of Samples 1 to 10 described below. Sample 14 is produced by sintering powder obtained by chemical synthesis of Sm-Fe-N-based grains by a reduction diffusion method.

[0055] (1) Pulverization process PI

[0056] As the coarse powder containing Sm-Fe-N single crystals, Sm2Fe 17 N3 powder having an average particle diameter of 30 μm was pulverized by a wet pulverization method.

[0057] First, in a glove box in which the oxygen concentration was controlled to be 0.5 ppm or less, stainless steel balls, the above coarse powder, and acetonitrile as a solvent were put into a stainless steel pot, and the pot was rotated to pulverize the coarse powder by ball milling. Here, the rotation time was 1 hour to 24 hours, and the rotation speed was 120 rpm to 300 rpm. Specifically, the rotation time of Samples 1 to 6 was 12 hours, and the rotation speed was 150 rpm, and the rotation time of Samples 7 to 10 was 18 hours, and the rotation speed was 200 rpm.

[0058] The slurry obtained by the above process was sieved in the glove box using a sieve having a mesh size of 25 μm, and was dried using a vibration dryer. Then, the obtained powder was sieved using a sieve having a mesh size of 250 μm to obtain Sm-Fe-N-based grains as dried powder. The average particle diameter of the Sm-Fe-N-based grains obtained by this process was 0.1 μm or more and 20 μm or less. Here, the particle size distribution was measured by a dry method.

[0059] (2) Alloy powder production process P2

[0060] As a raw material of the alloy powder (granular alloy raw material), the following materials were used.

[0061] • Al metal (granular)

[0062] • Mg metal (granular)

[0063] • Ca metal (granular)

[0064] • Ba metal (granular)

[0065] • Cu metal (granular)

[0066] • Ag metal (granular)

[0067] • Zn metal (granular)

[0068] La metal (granular)

[0069] • Pr metal (granular)

[0070] Weigh these granular alloy raw materials to make them Figure 3 The composition ratio shown was used to melt the alloy ingots in an electric arc melting furnace under argon (Ar) reduced pressure. The ingots were then melted at high frequency under Ar reduced pressure using a liquid quench foil manufacturing apparatus, followed by melt quenching using a copper single roller rotating at 5000 rpm to produce quenched alloy foil. In a glove box where the oxygen concentration was controlled below 1 ppm, the quenched alloy foil and stainless steel balls were added to a stainless steel canister, along with ethanol as a solvent. The canister was rotated, and the quenched alloy foil was pulverized by planetary ball milling. Here, the rotation time was 6 hours, and the rotation speed was 200 rpm.

[0071] The slurry obtained through the above treatment was sieved in a glove box using a 25 μm mesh sieve and dried using a vibrating dryer. The resulting powder was then sieved using a 63 μm mesh sieve to obtain the dried alloy powder. The average particle size of the alloy powder was 0.1 μm or more and 20 μm or less. By setting the average particle size of the alloy powder to 0.1 μm or more and 20 μm or less, the dispersibility of alloy particles in the sintered body's microstructure can be improved, allowing it to function as a sintering aid over a wider range and increasing both remanent magnetization and sintering density.

[0072] (3) Mixing process P3

[0073] Ethanol was used as a solvent to process the Sm-Fe-N system grains (Sm2Fe) obtained in the pulverizing process P1. 17 N3) and alloy powder are ball-milled to obtain a sintered magnet powder as a mixed powder (slurry). In the mixing process P3, alloy powder is added to achieve a content of N3. Figure 3 The second phase content (volume %) is shown. Here, the amount of alloy powder added (volume %) is approximately the same as the second phase content (volume %), relative to the Sm-Fe-N system grains (Sm2Fe). 17 The amount of N3 plus the amount of alloy powder is used to determine the amount of the second phase (volume %). Figure 3 The content (volume %) of the second phase in the data describes the relative content of the Sm-Fe-N system grains (Sm2Fe). 17 The amount of N3 (cm) 3 Add the amount of alloy powder (cm) 3) and the amount of the alloy powder (cm 3 ) in terms of the amount of the alloy powder (cm

[0074] (4) Sintering Process P4

[0075] The sintered magnet powder obtained through the mixing process P3 was put into a non-magnetic super-hard alloy mold (mold) in a glove box controlled to have an oxygen concentration of 0.5 ppm or less. Without exposing it to the atmosphere, a forming magnetic field press device in which a hydraulic press and a magnetic field orientation device are integrated was used to apply a magnetic field of 2 T to perform a magnetic field orientation treatment. In addition, the press forming was performed by applying a pressure of 600 MPa to 1200 MPa to the mixed powder. It was current-sintered at a sintering temperature of 400°C to 600°C for 1 to 10 minutes in a vacuum atmosphere. Thus, a sintered body including a first phase 10 in which Sm-Fe-N-based grains (Sm2Fe 17 N3) as a main phase and a second phase 20 composed of an alloy.

[0076] 2. Evaluation Method

[0077] (1) Density Evaluation of Sintered Body

[0078] The density of the sintered body was measured in pure water using the Archimedes method. The sintered body density was evaluated using the measured density measured using the Archimedes method.

[0079] (2) Evaluation of Crystallinity of Sintered Body Using X-ray Diffraction

[0080] The crystallinity of the sintered body was evaluated using an X-ray diffraction device. Since the Sm2Fe 17 N3 crystal contains a large amount of Fe as a constituent element, the background rises due to the generation of fluorescent X-rays and the like, and the diffraction peak intensity and the SN ratio decrease when measured using a Cu tube commonly used in XRD. Therefore, measurement was performed using a Co tube. Measurement was performed in the range of diffraction angles 20 to 80 degrees, and an X-ray diffraction pattern was obtained. For the obtained X-ray pattern, peak processing was performed excluding the Ka2 line and the background. For the pattern after peak processing, the half-height width of the diffraction peak of the (220) plane of Sm2Fe 17 N3 was calculated.

[0081] (3) Evaluation of Magnetic Properties of Sintered Body

[0082] The residual magnetization B r and the saturation magnetization J s of the sintered body were measured with a vibrating sample magnetometer (VSM). Sm2Fe 17The anisotropic magnetic field of N3 is very large, 260 kOe, and is difficult to fully saturate. Therefore, the saturation magnetization was estimated using a saturation asymptote. The saturation asymptote here was plotted by measuring the saturation magnetization J s9T and the remanent magnetization B r using a VSM by applying a magnetic field of up to 9 T (90 kOe). s9T In addition, the magnetic field orientation degree was evaluated by the ratio J s9T / B r of J r and B s9T obtained by the above method.

[0083] 3. Evaluation Results

[0084] (1) Density Evaluation of Sintered Body

[0085] As shown in Table 1, the densities of samples 1 to 10 and 13 were 6.5 g / cm 3 or more, and sufficient densification was obtained. On the other hand, the densities of samples 11, 12, and 14 were less than 6.5 g / cm 3 , and sufficient densification was not obtained. Figure 3 (2) Evaluation of Crystallinity of Sintered Body by X-ray Diffraction

[0086] It was confirmed that the half-value width of the diffraction peak of the (200) plane of samples 1 to 10 was 0.3 degrees or less, and sufficient crystallinity was obtained. On the other hand, it was confirmed that the half-value widths of samples 11 to 13 were all greater than 0.3 degrees, and the crystallinity was low. In addition, it was confirmed that the half-value width of sample 14 was less than 0.2 degrees.

[0087] (3) Evaluation of Magnetic Properties of Sintered Body

[0088] It was confirmed that the saturation magnetization J s9T of samples 1 to 10 at a magnetic field of 9 T was 11.5 kG or more, the remanent magnetization B r was 10 kG or more, and the magnetic field orientation degree J s9T / B r was improved compared to samples 11 to 14, and high magnetic properties were exhibited.

[0089] Samples 1 to 10 satisfied the following conditions [1] and [2].

[0090] Figure 3 [1] The density was 6.5 g / cm 3 or more.

[0091] [2] The half-value width of the peak of the diffraction intensity of the (220) plane obtained by X-ray diffraction was 0.2 degrees or more and 0.3 degrees or less.

[0092] [2] The half-value width of the peak of the diffraction intensity of the (220) plane obtained by X-ray diffraction was 0.2 degrees or more and 0.3 degrees or less.

[0093] Samples 1 to 10 satisfy the condition of the above [1], and thus can be said to have sufficient densification. In addition, samples 1 to 10 satisfy the condition of the above [2], and thus can be said to have high crystallinity. That is, samples 1 to 10 satisfy the conditions of the above [1] and [2], have sufficient densification, and have high crystallinity, and as a result, can be said to exhibit high magnetic properties.

[0094] On the other hand, samples 11, 12, and 14 are sintered bodies that do not satisfy the conditions of the above [1] and [2], and have low densification and low crystallinity, and thus cannot obtain sufficient magnetic properties. In sample 14, the half-value width of the peak of the diffraction intensity of the (220) plane is less than 0.2 degrees, and has very high crystallinity, but the residual magnetization cannot be sufficiently increased. Sample 14 is sintered using a magnet powder synthesized by a reduction diffusion method as a raw material, and the raw material powder also has very high crystallinity, but the orientation degree cannot be sufficiently increased due to necking between the particles, and thus a sintered magnet having increased residual magnetization cannot be obtained. In this way, Sm2Fe 17 The XRD half-value width in the N3 sintered body strongly depends on the half-value width (crystallinity) of the powder used as a raw material thereof, and thus by sintering a powder whose crystallinity is appropriately adjusted, a Sm2Fe 17 N3 sintered magnet having appropriate crystallinity required to increase the residual magnetization can be obtained. Sample 13 satisfies the condition of the above [1] and has sufficient densification, but does not satisfy the condition [2] above and has low crystallinity, and thus cannot obtain sufficient magnetic properties.

[0095] Further, samples 2 to 6 and 8 to 10 satisfy the conditions of the above [3] and [4]. Figure 3

[0096] [3] contains a second phase composed of one or more elements containing at least either one of a Group 2 element and a rare earth element, and an alloy having a melting point of 180°C or higher and 620°C or lower.

[0097] [4] the content of the second phase is 20% by volume or less.

[0098] ​As described above, the Sm-Fe-N system crystal grains forming the first phase are the same in Samples 1 to 6. Sample 1 does not contain the second phase, and Samples 2 to 6 contain the second phase having a composition different from each other at a content of 20 vol% or less. The composition of the alloy forming the second phase contained in Samples 2 to 6 is different from each other, and thus the melting point of the alloy is different from each other. Samples 2 to 6 have a higher density and improved densification compared to Sample 1. It can be said that this is a result of the alloy of the second phase functioning as a sintering aid. In addition, Samples 2 to 6 have the same degree of magnetic properties (saturation magnetization, residual magnetization) as Sample 1. It can be said that the content of the second phase is 20 vol% or less, and the reduction of the residual magnetization can be appropriately suppressed. That is, it can be said that Samples 2 to 6 can appropriately suppress the reduction of the magnetization of the sintered magnet caused by the second phase, and the alloy becoming the second phase effectively functions as an aid for densifying the first phase, as a result of which the degree of densification can be improved compared to Sample 1, and the reduction of the residual magnetization of the sintered magnet can be suppressed.

[0099] Similarly, the Sm-Fe-N system crystal grains forming the first phase are the same in Samples 7 to 10. Sample 7 does not contain the second phase, and Samples 8 to 10 contain the second phase having a composition different from each other at a content of 20 vol% or less. The composition of the alloy forming the second phase contained in Samples 8 to 10 is different from each other, and thus the melting point of the alloy is different from each other. Samples 8 to 10 have a higher density and improved densification compared to Sample 7. It can be said that this is a result of the alloy of the second phase functioning as a sintering aid. In addition, Samples 8 to 10 have the same degree of magnetic properties (saturation magnetization, residual magnetization) as Sample 7. It can be said that the content of the second phase is 20 vol% or less, and the reduction of the residual magnetization can be appropriately suppressed. That is, it can be said that Samples 8 to 10 can appropriately suppress the reduction of the magnetization of the sintered magnet caused by the second phase, and the alloy becoming the second phase effectively functions as an aid for densifying the first phase, as a result of which the degree of densification can be improved compared to Sample 7, and the reduction of the residual magnetization of the sintered magnet can be suppressed.

[0100] As described above, Samples 1 to 10 satisfy the conditions of [1], [2] described above, and are one embodiment of the sintered magnet 100 of the above-described embodiment. These samples can be made into a sintered magnet having high densification and crystallinity, and having a higher residual magnetization than Samples 11 to 14.

[0101] 4. Wettability of alloy

[0102] Before manufacturing the above-described samples, a preliminary experiment for screening an element group and an alloy composition that show good wettability to Sm-Fe-N system crystal grains (Sm2Fe 17 N3) was performed.

[0103] Figure 4This is a graph showing the results of the wettability evaluation of the alloy. The alloy powder was prepared using the above-described sample manufacturing method (2) alloy powder preparation process P2. Figure 4 The alloy powder shown has the following composition. Sm-Fe-N system grains (Sm2Fe) 17 N3 micro powder was prepared by the pulverization step P1 of the above sample manufacturing method (1). In Sm-Fe-N system grains (Sm2Fe... 17 The above alloy powder was added to N3 micro powder at a ratio of 20% by volume, and sintered under pressure and current under a sintering temperature of 450℃~600℃, a sintering time of 10 min, a pressure of 600MPa, and a vacuum atmosphere. Using the prepared sintered bodies (samples S1~S17), the porosity was calculated using the method described later. These values ​​were compared with those of various alloys to screen for Sm-Fe-N system grains (Sm2Fe). 17 The alloy composition (N3 micro powder) exhibits good wettability.

[0104] Figure 5 This is an explanatory diagram of sample 100S used for SEM observation. First, the sintered body (sintered magnet) prepared using the above method is cut into cylindrical shapes with a diameter of 10mm and a thickness of 3mm. Figure 5 (A)). Then, water-resistant abrasive paper is used to expose the cross-section ( Figure 5 (B)). A sample 100S for SEM observation was fabricated by Ar ion milling of the cross-section. Figure 5 (C)). SEM observation was performed on the 100S sample, capturing secondary electron images at 1000x magnification at five different locations within the field of view. The captured secondary electron images were binarized using Image-J image processing software to calculate the porosity.

[0105] like Figure 4 As shown, the alloy powders of samples S1–S4 contain calcium (Ca), a Group 2 element; the alloy powders of samples S5, S6, and S9 contain lanthanum (La), a rare earth element; and the alloy powders of samples S7 and S8 contain praseodymium (Pr), a rare earth element. The alloy powders of samples S10–S16 do not contain any Group 2 elements or rare earth elements. The sintered body of sample S17 did not contain any alloy powder.

[0106] Preliminary experiments confirmed a significant reduction in porosity in sintered bodies (samples S1–S9) containing alloy powders containing Group 2 elements and rare earth elements. That is, it is believed that the alloy powders in samples S1–S9 significantly reduced the porosity of the Sm-Fe-N grains (Sm2Fe). 17 N3 micro powder exhibits good wettability.

[0107] In the preliminary experiment, calcium (Ca) was used as the Group 2 element, but it is considered that the same effect can be obtained even if beryllium (Be), magnesium (Mg), strontium (Sr), barium (Ba), and radium (Ra) are used as other Group 2 elements for the following reasons.

[0108] In the Ellingham diagram, calcium Ca is on the lower side than Sm, and thus Ca has a function of reducing Sm over the entire temperature range. In fact, in the chemical synthesis of Sm2Fe 17 N3 particles as a reducing material for Sm oxides.

[0109] Thus, for the inevitable oxides present on the surface of the particles in which Sm2Fe 17 N3 is the main phase, Ca is an element that causes a redox reaction, and thus an alloy containing Ca also has the same effect. "Causes a redox reaction" can be replaced with "has reactivity of one stage or more with the surface of the main phase particles", and having wettability can also be understood as one of the reactivity. Ca belongs to Group 2 of the periodic table, and elements of the same group as Ca, Be, Mg, Sr, Ba, and Ra also have a reducing effect on Sm-Fe-O. Thus, the same effect can be expected for other elements of the same group as Ca. In addition, in the binary phase diagram, elements X (Be, Mg, Sr, Ba, and Ra) have eutectic points at the same time as Ca when alloying, and a low melting point that is the minimum requirement as a binder can also be achieved.

[0110] In addition, in the preliminary experiment, lanthanum (La) and praseodymium (Pr) were used as rare earth elements, but it is considered that the same effect can be obtained even if scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) are used as other rare earth elements.

[0111] The main phase particles contain a rare earth element Sm as shown in the composition of Sm2Fe 17 N3. It is expected that Sm shows high similarity / substitution with other lanthanide elements (La, Pr, etc.) as in a complete solid solution system, and has high reactivity. In fact, as one of the reactivity, good wettability is explicitly shown by experiments.

[0112] Thus, by optimizing the composition and the addition amount of the alloy containing at least either of the Group 2 element and the rare earth element, it is aimed to increase the volume fraction of the first phase (magnetic phase).

[0113] Thus, in Samples 2 to 4, 6, and 7 of the above-described embodiments, the second phase containing calcium (Ca) or barium (Ba) was exemplified, but as the second phase of the sintered magnet, it can be said that sufficient densification and high crystallinity are also obtained, and high magnetic properties are exhibited, in the case where a Group 2 element other than calcium (Ca) and barium (Ba) or a rare earth element is contained.

[0114] The present disclosure has been described above based on the embodiments, but the embodiments of the above-described modes are used to make the understanding of the present disclosure easy, and do not limit the present disclosure. The present disclosure can be changed, modified, and the like without departing from the gist thereof and the claims, and equivalents thereof are included in the present disclosure. In addition, if the technical feature is not described as an essential feature in the specification, it can be appropriately deleted.

[0115] The present disclosure can also be implemented as the following application examples.

[0116] [Application Example 1]

[0117] A sintered magnet including a first phase in which Sm-Fe-N-based grains having a Th2Zn 17 a structure are mainly contained as a first phase, characterized by

[0118] a density of 6.5 g / cm 3 Thus,

[0119] The half-value width of the peak of the diffraction intensity of the (220) plane obtained by X-ray diffraction is 0.2 degrees or more and 0.3 degrees or less.

[0120] [Application Example 2]

[0121] The sintered magnet according to Application Example 1, characterized in that

[0122] a second phase is further contained, the second phase being composed of an alloy containing one or more elements of at least any one of a Group 2 element and a rare earth element, and having a melting point of 180°C or more and 620°C or less,

[0123] The content of the second phase is 20% by volume or less.

[0124] [Application Example 3]

[0125] A method for producing a sintered magnet powder used for the formation of the sintered magnet described in Application Example 1 or Application Example 2, characterized by comprising:

[0126] a pulverization process in which a coarse powder containing Sm-Fe-N single crystals is pulverized to obtain Sm-Fe-N-based grains;

[0127] an alloy powder production step in which an alloy powder to be the second phase is produced; and

[0128] a mixing step in which the Sm-Fe-N-based crystal grains and the alloy powder are dispersed to obtain the sintered magnet powder as a mixed powder,

[0129] The pulverization step, the alloy powder production step, and the mixing step are performed in a low-oxygen-concentration atmosphere.

[0130] [Application Example 4]

[0131] The production method of a sintered magnet according to Application Example 1 or Application Example 2, characterized in that,

[0132] a sintering step in which the sintered magnet powder produced by the production method of a sintered magnet powder according to Application Example 3 is pressure-sintered at a sintering temperature of 600°C or lower in a low-oxygen-concentration atmosphere.

[0133] [Explanation of Symbols]

[0134] 10…first phase

[0135] 10G…Sm-Fe-N-based crystal grains

[0136] 20…second phase

[0137] 100…sintered magnet

[0138] 100S…sample for SEM observation

[0139] V…voids

Claims

1. A sintered magnet comprising Th2Zn 17 The first phase, characterized by its Sm-Fe-N system with a grain-dominant structure, is characterized by... The density is 6.5 g / cm³. 3 above, The peak half-width at half-maximum (FWHM) of the diffraction intensity of the (220) plane obtained by X-ray diffraction is greater than 0.2 degrees and less than 0.3 degrees.

2. The sintered magnet according to claim 1, characterized in that, It also includes a second phase, which is composed of an alloy containing at least one of Group 2 elements and rare earth elements, and having a melting point of 180°C or higher and 620°C or lower. The content of the second phase is less than 20% by volume.

3. A method for manufacturing powder for sintered magnets, wherein the powder is used for forming the sintered magnet according to claim 1 or claim 2, the method being characterized by comprising: The crushing process involves crushing coarse powder containing Sm-Fe-N single crystals to obtain Sm-Fe-N system grains. The alloy powder manufacturing process includes manufacturing alloy powder that will become the second phase; and The mixing process involves dispersing the Sm-Fe-N grains and the alloy powder to obtain the sintered magnet powder as a mixed powder. The crushing process, the alloy powder preparation process, and the mixing process are carried out in a low-oxygen atmosphere.

4. A method for manufacturing a sintered magnet, which is the method for manufacturing a sintered magnet as described in claim 1 or claim 2, characterized in that, It includes a sintering process, wherein the sintered magnet powder manufactured by the method for manufacturing sintered magnet powder according to claim 3 is pressure-sintered at a sintering temperature below 600°C in a low oxygen concentration atmosphere.

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