Sintered magnet, method for manufacturing powder for sintered magnet, and method for manufacturing a sintered magnet

Abstract

This invention provides a technology to improve the remanent magnetization of Sm-Fe-N sintered magnets. [Solution] Th2Zn 17 A sintered magnet is provided, comprising a first phase mainly consisting of Sm-Fe-N crystal grains having a type structure. This sintered magnet has a density of 6.5 g / cm³. 3 The above results indicate that the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction is 0.2 degrees or more and 0.3 degrees or less.

Description

[Technical Field]

[0001] This disclosure relates to Sm-Fe-N sintered magnets. [Background technology]

[0002] In recent years, Sm (samarium)-Fe (iron)-N (nitrogen) magnets have been developed as high-performance magnets. Sm-Fe-N compounds are known to exhibit high spontaneous magnetization and anisotropic magnetic field, as well as high heat resistance. Techniques for obtaining Sm-Fe-N magnets with high magnetic properties have been proposed (see, for example, Patent Document 1). Patent Document 1 discloses a technique for producing a powder with excellent crystallinity by grinding Sm-Fe-N magnet powder using a dry jet mill. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 7076740 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in the technology described in Patent Document 1, the surface of the magnetic particles after pulverization may have microscopic areas of low crystallinity due to damage from jet mill pulverization, and if these areas expand significantly during sintering, there is a risk that the residual magnetization of the sintered body will decrease.

[0005] This disclosure was made to solve the above-mentioned problems and aims to provide a technology to improve the remanent magnetization in Sm-Fe-N sintered magnets. [Means for solving the problem]

[0006] This disclosure is made to solve at least one of the above-mentioned problems and can be implemented in the following forms.

[0007] <1>According to one embodiment of the present disclosure, a sintered magnet including a first phase mainly composed of Sm-Fe-N-based crystal grains having a Th2Zn 17 type structure is provided. This sintered magnet has a density of 6.5 g / cm 3 or more, and the half-value width of the peak of the diffraction intensity at the (220) plane obtained by X-ray diffraction is 0.2 degree or more and 0.3 degree or less.

[0008] According to this type of sintered magnet, since the density is 6.5 g / cm 3 and the compactness is high, the saturation magnetization and the residual magnetization can be increased. In addition, the half-value width of the peak of the diffraction intensity at the (220) plane (also referred to as the diffraction peak) being 0.3 degree or less indicates that the crystallinity of the Sm-Fe-N-based crystal grains of the sintered magnet is increased, and a sintered magnet with improved magnetization components (saturation magnetization and residual magnetization), and in addition, magnetic field orientation degree can be provided.

[0009] <2>The sintered magnet of the above embodiment further includes a second phase made of an alloy containing at least 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, and the content of the second phase may be 20 vol% or less. By doing so, the melting point of the alloy of the second phase is 180°C or more and 620°C or less, which is lower than the temperature (620°C or more) at which the Sm-Fe-N-based magnet undergoes thermal decomposition. Therefore, when sintering 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 melting point of the alloy of the second phase is 180°C or more, it can also be used for devices that generate heat and reach a high temperature, such as motors for electric vehicles (EVs). Furthermore, since the content ratio of the second phase is 20 vol% or less, the alloy serving as the second phase can effectively act as an aid function for densifying the first phase while appropriately suppressing the decrease in the magnetization of the sintered magnet due to the second phase. As a result, the degree of densification during sintering can be further increased, and the residual magnetization of the sintered magnet can be further improved.

[0010] <3> According to another embodiment of the present disclosure, a method for producing sintered magnet powder used in forming the above-described sintered magnet is provided. This method for producing sintered magnet powder includes a grinding step of grinding a coarse powder containing Sm-Fe-N single crystals to obtain the Sm-Fe-N crystalline grains; an alloy powder preparation step of obtaining the alloy powder that will become the second phase; and a mixing step of dispersing the Sm-Fe-N crystalline grains and the alloy powder to obtain the sintered magnet powder, which is a mixed powder, wherein the grinding step, the alloy powder preparation step, and the mixing step are carried out in a low-oxygen atmosphere.

[0011] According to this method for manufacturing sintered magnet powder, the above process is carried out under a low-oxygen atmosphere, which suppresses oxidation of the Sm-Fe-N crystal grains and alloy powder, and ensures wettability between the Sm-Fe-N crystal grains and the alloy. As a result, sintered magnets with high residual magnetization can be manufactured.

[0012] <4> According to another embodiment of the present disclosure, a method for manufacturing a sintered magnet of the above embodiment is provided. This method for manufacturing a sintered magnet comprises a sintering step in which the sintered magnet powder manufactured by the method for manufacturing sintered magnet powder of the above embodiment is pressurized and sintered at a sintering temperature of 600°C or less in a low oxygen concentration atmosphere.

[0013] According to this method of manufacturing sintered magnets, the thermal decomposition of the Sm-Fe-N main phase can be suppressed by keeping the sintering temperature below 600°C, and oxidation of the Sm-Fe-N crystal grains and alloy powder can be suppressed by performing this process in a low-oxygen atmosphere. As a result, the density of the sintered magnet can be improved, and a sintered magnet with high residual magnetization can be manufactured.

[0014] Furthermore, this disclosure can be implemented in various forms, for example, in the form of a permanent magnet for a motor. [Brief explanation of the drawing]

[0015] [Figure 1]This is an explanatory diagram conceptually showing the cross-sectional configuration of the sintered magnet of the embodiment. [Figure 2] This is a process diagram showing an example of a manufacturing method for sintered magnets. [Figure 3] This figure shows the evaluation results of the samples. [Figure 4] This figure shows the results of the wettability evaluation of the alloy. [Figure 5] This is an explanatory diagram of a sample for SEM observation. [Modes for carrying out the invention]

[0016] <Embodiment> Figure 1 is a conceptual diagram illustrating the cross-sectional configuration of the sintered magnet 100 of the embodiment. The sintered magnet 100 of the embodiment is made of Th2Zn 17 The sintered magnet comprises a first phase 10 mainly consisting of Sm-Fe-N (samarium-iron-nitrogen) crystalline grains having a mold structure, and a second phase 20 made of an alloy containing at least one of the group 2 elements and rare earth elements, with a melting point of 180°C to 620°C. In other embodiments, the sintered magnet may not contain the second phase.

[0017] In Figure 1, the first phase 10 is marked with upward-sloping diagonal hatching, and the second phase 20 is marked with downward-sloping diagonal hatching. As shown in the figure, the first phase 10 has multiple Sm-Fe-N crystal grains 10G. The second phase 20 is located at the grain boundaries between the Sm-Fe-N crystal grains 10G and the Sm-Fe-N crystal grains 10G. The sintered magnet 100 may have voids V at the grain boundaries between the Sm-Fe-N crystal grains 10G and the Sm-Fe-N crystal grains 10G.

[0018] The main phase, Sm-Fe-N crystal grain 10G, is Th2Zn 17 Sm2Fe with a type structure 17 It is N3. The sintered magnet 100 exhibits magnetism due to the Sm-Fe-N crystal grain 10G (main phase). The crystal structure of the main phase can be identified by, for example, X-ray diffraction analysis of the sintered magnet 100. The main phase refers to the compound that determines the properties of the sintered magnet.

[0019] Sm2Fe 17 Since N3 has excellent saturation magnetization and a huge anisotropic magnetic field, according to the sintered magnet 100 of the embodiment, it can withstand heat and a reverse magnetic field and generate a high magnetic field.

[0020] The first phase 10 may include a structure different from the main phase, such as a Th2Ni 17 type structure, a TbCu7 type structure, etc. Here, Tb is terbium and Cu is copper.

[0021] The density of the sintered magnet 100 is 6.5 g / cm 3 or more. The density of the sintered magnet 100 can be measured in pure water using the Archimedes method. The sintered magnet 100 has a density of 6.5 g / cm 3 or more and high density, so that the saturation magnetization and the remanent magnetization can be increased. For example, by performing the manufacturing process of the sintered magnet in an atmosphere with a low oxygen concentration and suppressing the oxygen content of the sintered magnet, the density of the sintered magnet can be increased.

[0022] The full width at half maximum of the diffraction peak on the (220) plane obtained from the X-ray diffraction of the sintered magnet 100 is 0.2 degree or more and 0.3 degree or less. The full width at half maximum of the intensity peak of the X-ray diffraction pattern is an index of the shape of the intensity peak. When compared with the same particle size, the larger the full width at half maximum, the broader the peak, indicating lower crystallinity. The fact that the full width at half maximum of the diffraction peak on the (220) plane is 0.2 degree or more and 0.3 degree or less indicates that the crystallinity of the Sm-Fe-N-based crystal grains of the sintered magnet is enhanced, and a high remanent magnetization can be obtained. For example, in the production of the Sm-Fe-N-based magnetic powder that becomes the first phase 10, by wet grinding the coarse powder and suppressing the strain of the crystals of the magnetic powder, the crystallinity of the sintered magnet can be enhanced.

[0023] The metal forming the second phase 20 is not particularly limited, but it is preferably composed of an alloy containing at least one of the Group 2 elements and the rare earth elements. An alloy with such a composition is the main phase (Sm2Fe17 It exhibits excellent wettability to N3. Therefore, a dense sintered body can be obtained.

[0024] Group 2 elements are elements belonging to Group 2 of the periodic table and include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), eurobium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0025] Phase 20 may contain elements other than Group 2 elements and rare earth elements. For example, it may contain silver (Ag), aluminum (Al), copper (Cu), zinc (Zn), etc.

[0026] The melting point of the alloy forming the second phase 20 is not particularly limited, but it is preferably between 180°C and 620°C. Sm-Fe-N magnets undergo thermal decomposition above 620°C, which limits the sintering temperature, and conventionally, it was not possible to obtain high-density sintered bodies. In contrast, if the melting point of the alloy forming the second phase 20 is 620°C or lower, the main phase does not decompose. Therefore, when manufacturing the sintered magnet 100, the main phase does not decompose even when heated at the melting temperature of the alloy. For this reason, by using an alloy with a melting point of 620°C or lower for the second phase 20, liquid-phase sintering can be achieved, resulting in Sm2Fe 17 N3 / Sm2Fe 17 A second phase 20 made of the above alloy can be formed as a grain boundary phase at the N3 interface. Furthermore, if the melting point of the alloy forming the second phase 20 is 180°C or higher, the sintered magnet 100 can be used in equipment that generates heat and becomes hot, such as EV motors.

[0027] The melting point of the second phase can be measured using a DSC (Dynamic Suggestion Calorimeter). 10-20 mg of liquid-quenched foil obtained by melt-spinning (described later) is weighed and used as the measurement sample. For the measurement, a BN (boron nitride) pan was used, with a measurement temperature range of room temperature to 700°C and a heating rate of 10°C / min. The melting point is determined using the melting peak temperature that appears within the measurement temperature range.

[0028] The content of the second phase 20 is not particularly limited, but it is preferably 20 vol% or less. The alloy of the second phase 20 can act as an aid to densify the first phase 10, but since the alloy of the second phase 20 is a non-magnetic component, if it is included in large quantities, the proportion of magnetic phases will relatively decrease, and the magnetization may decrease. By setting the content of the second phase 20 to 20 vol% or less, the decrease in magnetization of the sintered magnet 100 due to the second phase 20 can be appropriately suppressed, while the alloy that becomes the second phase 20 can effectively act as an aid to densify the first phase 10. As a result, the degree of densification during sintering can be further increased, and the magnetization of the sintered magnet 100 can be further improved. The content of the second phase 20 is preferably 0.1 vol% or more. Here, the amount of alloy powder added (vol%) is approximately the same as the second phase content (vol%), and the Sm-Fe-N system crystal grain (Sm2Fe 17 The amount of alloy powder (volume) relative to the amount of N3) plus the amount of alloy powder represents the second phase content (vol%).

[0029] The second phase content (vol%) in a sintered magnet can be determined by the following method. First, the cross-section of the sintered magnet to be evaluated is mirror-polished, and then the cross-section is observed using a scanning electron microscope (SEM), and an SEM image is acquired at an appropriate magnification (e.g., 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 is clear. Next, the obtained SEM image is binarized using the open-source image analysis software "ImageJ" to generate two clearly separated black and white images of the two phases. The area ratio of each phase is calculated from the binarized image, and the obtained area fraction of the second phase is considered to approximately coincide with the volume fraction in the material, assuming that the cross-sectional observation image is a representative random cross-section, and the calculated area fraction value can be treated as the volume fraction (vol%) of the second phase.

[0030] The sintered magnet 100 may contain unavoidable impurity elements, etc., to the extent that it does not impair the magnetic properties of the main phase. Unavoidable impurity elements are impurity elements that cannot be avoided when manufacturing the sintered magnet 100 of the embodiment, or whose inclusion would lead to a significant increase in manufacturing costs if avoided. Examples of such unavoidable impurity elements include impurity elements in the raw materials, elements contained in lubricants used during molding, etc.

[0031] Figure 2 is a process diagram showing an example of a method for manufacturing a sintered magnet 100. The method for manufacturing the sintered magnet 100 in this embodiment is not particularly limited, but for example, it can be manufactured by the following method. As shown in Figure 2, in the manufacturing method of the sintered magnet 100, the processes are carried out in the order of sintered magnet powder manufacturing process P0 and sintering process P4. In sintered magnet powder manufacturing process P0, the processes are carried out in the order of grinding process P1, alloy powder production process P2 and mixing process P3.

[0032] In the grinding process P1, Th2Zn 17 Sm-Fe-N crystalline grains are obtained by grinding a coarse powder containing an Sm-Fe-N single crystal having a specific structure. For example, the coarse powder may have a composition of Sm2Fe 17It can be N3 with an average particle size of 10 μm to 200 μm. The average particle size of the Sm-Fe-N crystal grains after grinding is not particularly limited, but is preferably 0.1 μm to 20 μm, and preferably 0.4 μm to 10 μm. This is more preferable, and even more preferable is a particle size of 1 μm or more and 5 μm or less.

[0033] Grinding can be carried out using, for example, a grinder or a planetary ball mill. Grinding may be carried out dry or wet. Wet grinding of the coarse powder is preferable because it can suppress crystal strain compared to dry grinding, thereby improving the crystallinity of the sintered magnet and enhancing its magnetization. When wet grinding is performed, for example, ethanol or isopropanol can be used as a solvent.

[0034] In the alloy powder preparation process P2, powder of a predetermined size of the alloy that will become the second phase is prepared to obtain alloy powder.

[0035] In mixing step P3, Sm-Fe-N crystal grains and alloy powder are dispersed to obtain a mixed powder, which is a sintered magnet powder. Mixing step P3 may be a wet process in which Sm-Fe-N crystal grains and alloy powder are dispersed in a solvent (e.g., ethanol), or a dry process in which Sm-Fe-N crystal grains and alloy powder are dispersed in an inert gas (e.g., argon gas, helium gas, nitrogen gas, etc.).

[0036] The above-mentioned grinding process P1, alloy powder preparation process P2, and mixing process P3 are all carried out under a low-oxygen atmosphere. The oxygen concentration is adjusted by controlling the atmosphere in each process. A low oxygen concentration is a concentration lower than the oxygen concentration in the atmosphere (approximately 21 vol%). 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 atmosphere can be achieved by injecting an inert gas into a vacuum chamber. By performing the above processes under a low-oxygen atmosphere, oxidation of the Sm-Fe-N crystal grains and alloy powder can be prevented, and the wettability of the Sm-Fe-N crystal grains and alloy powder can be ensured. As a result, the density of the sintered magnet can be improved.

[0037] In the sintering process P4, the sintered magnet powder produced in the manufacturing process P0 is molded and pressure-sintered at a sintering temperature of 600°C or lower in a low-oxygen atmosphere. In the sintering process P4, firing is carried out in an oxygen concentration atmosphere similar to that of the grinding process P1 to the mixing process P3. By setting the sintering temperature to 600°C or lower, thermal decomposition of Sm-Fe-N crystal grains can be suppressed. Furthermore, by performing the sintering process P4 in a low-oxygen atmosphere, oxidation of the Sm-Fe-N crystal grains and alloy powder can be suppressed. As a result, density can be improved, and the magnetization of the sintered magnet 100 can be improved.

[0038] The sintered magnet of this embodiment can be used as a permanent magnet for various motors, such as EV motors, robot motors, drone motors, and elevator motors. [Examples]

[0039] The present disclosure will be further described by examples. Figure 3 shows the evaluation results for samples 1 to 14. In the examples, the second phase contains one of magnesium (Mg), calcium (Ca), and barium (Ba) as a group 2 element, and one of lanthanum (La) and praseodymium (Pr) as a rare earth element. In the examples, the second phase contains one of silver (Ag), copper (Cu), and zinc (Zn), which are elements other than group 2 elements and rare earth elements. In Figure 3, group 2 elements and rare earth elements are enclosed in double lines.

[0040] 1. Sample manufacturing Samples 1 to 10 were manufactured using the manufacturing method illustrated in the above embodiment (Figure 2). Since samples 1 and 7 do not contain a second phase, the alloy powder preparation step P2 and mixing step P3 were omitted, and the sintering step P4 was performed using Sm-Fe-N crystalline grains obtained in the grinding step P1. Sample 11 was prepared by grinding Sm-Fe-N crystalline powder using a dry jet mill and then sintering this as the raw material. Samples 12 and 13 were prepared by sintering Sm-Fe-N pulverized powder obtained by ball mill grinding under conditions different from those used for the production of samples 1 to 10, as described later. Sample 14 was prepared by sintering powder obtained by chemically synthesizing Sm-Fe-N crystalline grains by reduction-diffusion.

[0041] (1) Grinding process P1 As a crude powder containing Sm-Fe-N single crystals, Sm2Fe has an average particle size of 30 μm. 17 N3 powder was used and ground using a wet grinding method. First, in a glove box where the oxygen concentration was controlled to 0.5 ppm or less, stainless steel pebbles and the coarse powder mentioned above were placed in a stainless steel pot, and acetonitrile was added as a solvent. The pot was then rotated to ball-mill the coarse powder. The rotation time ranged from 1 to 24 hours, and the rotation speed from 120 rpm to 300 rpm. Specifically, samples 1 to 6 were rotated for 12 hours at a rotation speed of 150 rpm, while samples 7 to 10 were rotated for 18 hours at a rotation speed of 200 rpm. The slurry obtained by the above process was sieved through a 25 μm mesh sieve in the same glove box and dried in a vibrating dryer. The resulting powder was then sieved through a 250 μm mesh sieve to obtain dried Sm-Fe-N crystalline grains. The average particle size of the Sm-Fe-N crystalline grains obtained by this process was between 0.1 μm and 20 μm. The particle size distribution was measured using a dry method.

[0042] (2) Alloy powder preparation process P2 The following materials were used as raw materials for the alloy powder (granular alloy raw materials). ·Al metal (granular) ·Mg metal (granular) ·Ca metal (granular) • Ba metal (granular) ·Cu metal (granular) ·Ag metal (granular) ·Zn metal (granular) ·La metal (granular) ·Pr metal (granular)

[0043] These granular alloy raw materials were weighed to the composition ratio shown in Figure 3 and melted under reduced argon (Ar) pressure using an arc melting furnace to produce alloy ingots. The prepared ingots were then high-frequency melted under reduced Ar pressure using a liquid quenching foil manufacturing apparatus, and then melt-spinned with a copper single roll rotating at 5000 rpm to produce quenched alloy foil. In a glove box with an oxygen concentration controlled to 1 ppm or less, the quenched alloy foil and stainless steel pebbles were placed in a stainless steel pot, and ethanol was added as a solvent. The pot was then rotated, and the quenched alloy foil was pulverized using a planetary ball mill. The rotation time was 6 hours and the rotation speed was 200 rpm.

[0044] The slurry obtained by the above process was sieved through a 25 μm mesh sieve in the same glove box and dried in a vibrating dryer. The resulting powder was then sieved through a 63 μm mesh sieve to obtain a dried alloy powder. The average particle size of the alloy powder is between 0.1 μm and 20 μm. By setting the average particle size of the alloy powder to between 0.1 μm and 20 μm, the dispersibility of alloy particles in the structure of the sintered body can be improved, allowing it to act as a sintering aid over a wider range, and improving both sintering density and residual magnetization.

[0045] (3) Mixing process P3 Sm-Fe-N crystalline grains (Sm2Fe) obtained in grinding step P1 17 Sintered magnet powder, which is a mixed powder (slurry), was obtained by ball milling N3) and alloy powder using ethanol as a solvent. In mixing step P3, the alloy powder was added so that its content was the second phase content (vol%) shown in Figure 3. Here, the amount of alloy powder added (vol%) was approximately equal to the second phase content (vol%), and the Sm-Fe-N system crystal grains (Sm2Fe) 17 The amount of alloy powder (vol) relative to the amount of N3) plus the amount of alloy powder is the second phase content (vol%). In Figure 3, the second phase content (vol%) is the amount of Sm-Fe-N crystal grains (Sm2Fe 17 (N3) amount (cm³) 3 ) amount of alloy powder (cm 3 The amount of alloy powder (cm) relative to the amount added 3 The percentage (vol%) of ) is listed.

[0046] (4) Sintering process P4 The sintered magnet powder obtained in mixing step P3 was placed into a non-magnetic cemented carbide die (mold) in a glove box with an oxygen concentration controlled to 0.5 ppm or less. Without exposure to the atmosphere, a magnetic field orientation treatment was performed by applying a 2T magnetic field using a forming magnetic field press device that integrates a hydraulic press and a magnetic field orientation device. The mixed powder was then press-formed by applying a pressure of 600 MPa to 1200 MPa. This was then electrically sintered under a vacuum atmosphere at a sintering temperature of 400°C to 600°C for 1 to 10 minutes. As a result, Sm-Fe-N type crystal grains (Sm2Fe) were formed. 17 A sintered body was obtained containing a first phase 10 mainly composed of N3 and a second phase 20 made of an alloy.

[0047] 2. Evaluation Method (1) Density evaluation of sintered body 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 obtained by the Archimedes method. (2) Evaluation of the crystallinity of the sintered body by X-ray diffraction The crystallinity of the sintered body was evaluated using an X-ray diffractometer. Sm2Fe 17 Because N3 crystals contain a large amount of Fe as a constituent element, when measured with a Cu tube commonly used in XRD, the background increases due to the generation of fluorescent X-rays, and the diffraction peak intensity and signal-to-noise ratio decrease. Therefore, measurements were performed using a Co tube. Measurements were performed in the diffraction angle range of 20 to 80 degrees, and X-ray diffraction profiles were obtained. The obtained X-ray profiles were processed to remove Ka2 lines and background, and peak processing was performed. The profile after peak processing was used for Sm2Fe 17 The full width at half maximum (FMAX) of the diffraction peak of the (220) plane of N3 was calculated. (3) Evaluation of the magnetic properties of the sintered body Residual magnetization B of sintered body r and saturation magnetization J s The measurement was performed using a vibrating sample magnetometer (VSM). Sm2Fe 17N3 has a very large anisotropic magnetic field of 260 kOe, making it difficult to completely saturate. Therefore, the saturation magnetization was estimated using a saturation asymptote. Here, the saturation asymptote was drawn by applying a magnetic field up to 9 T (90 kOe) using a VSM, and then determining the saturation magnetization J at that point. s9T , and remanent magnetization B r The magnetic field orientation was measured using the method described above. s9T and B r The ratio of J s9T / B r It was evaluated by [the following method / method].

[0048] 3. Evaluation Results (1) Density evaluation of sintered body As shown in Figure 3, the densities of samples 1-10 and 13 are 6.5 g / cm³. 3 The above results demonstrate that sufficient density was achieved. On the other hand, the densities of samples 11, 12, and 14 were 6.5 g / cm³. 3 It was less than [a certain level], and sufficient density could not be achieved. (2) Evaluation of the crystallinity of the sintered body by X-ray diffraction Samples 1-10 showed sufficient crystallinity, as the full width at half maximum (FMAX) of the diffraction peaks on the (200) plane was 0.3 degrees or less. On the other hand, samples 11-13 all showed low crystallinity, as the FMAX was greater than 0.3 degrees. Furthermore, sample 14 showed a FMAX less than 0.2 degrees. (3) Evaluation of the magnetic properties of the sintered body Samples 1-10 show the saturation magnetization J at a magnetic field of 9T. s9T If the value is 11.5kG or higher, the remanent magnetization B r The magnetic field orientation is 10kG or more, and the magnetic field orientation is J s9T / B r This was an improvement compared to samples 11-14, confirming that it exhibits high magnetic properties.

[0049] Samples 1-10 satisfy the following requirements [1] and [2] (Figure 3). [1] Density is 6.5 g / cm³ 3 That's all. [2] The full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction is 0.2 degrees or more and 0.3 degrees or less.

[0050] Samples 1-10 can be said to have sufficient density as they satisfy requirement [1] above. Furthermore, samples 1-10 can be said to have high crystallinity as they satisfy requirement [2] above. In other words, samples 1-10 satisfy requirements [1] and [2] above, have sufficient density and high crystallinity, and as a result, can be said to exhibit high magnetic properties.

[0051] In contrast, samples 11, 12, and 14 did not meet the requirements of [1] and [2] above, and were sintered bodies with low density and crystallinity, and could not obtain sufficient magnetic properties. In sample 14, the full width at half maximum of the diffraction intensity peak on the (220) plane was less than 0.2 degrees, indicating very high crystallinity, but it was not possible to sufficiently increase the remanent magnetization. Sample 14 was sintered using magnet powder synthesized by reduction-diffusion as the raw material, and this raw material powder also had very high crystallinity, but due to necking between particles, the degree of orientation could not be sufficiently increased, and therefore a sintered magnet with increased remanent magnetization could not be obtained. Thus, Sm2Fe 17 The XRD full width at half maximum (FWHM) in an N3 sintered body strongly depends on the FWHM (crystallinity) of the raw material powder. Therefore, by sintering powder with appropriately adjusted crystallinity, it is possible to increase the remanent magnetization. This is necessary for obtaining Sm2Fe with the appropriate crystallinity. 17 This makes it possible to obtain N3 sintered magnets. Sample 13 met the requirements of [1] above and had sufficient density, but it did not meet the requirements of [2] above, and as a result of its low crystallinity, it was not possible to obtain sufficient magnetic properties.

[0052] Furthermore, samples 2-6 and 8-10 satisfy the requirements of [3] and [4] below (Figure 3). [3] The second phase comprises an alloy containing at least one element from Group 2 and / or rare earth elements, with a melting point of 180°C or higher and 620°C or lower. [4] The content of the second phase is 20 vol% or less.

[0053] As described above, samples 1 to 6 have similar Sm-Fe-N crystal grains forming the first phase. Sample 1 does not contain the second phase, while samples 2 to 6 contain a second phase with different compositions in an amount of 20 vol% or less. Because the alloy compositions forming the second phase in samples 2 to 6 are different, the melting points of the alloys differ. Compared to sample 1, samples 2 to 6 have higher density and improved compactness. This can be attributed to the second phase alloy functioning as a sintering aid. Furthermore, samples 2 to 6 obtained magnetic properties (saturation magnetization, remanent magnetization) similar to those of sample 1. Since the second phase content is 20 vol% or less, it can be said that the decrease in remanent magnetization was appropriately suppressed. In other words, samples 2 to 6 were able to appropriately suppress the decrease in magnetization of the sintered magnet due to the second phase, while effectively utilizing the alloy that becomes the second phase as an aid to densify the first phase. As a result, they were able to increase the degree of compaction compared to sample 1 and suppress the decrease in remanent magnetization of the sintered magnet.

[0054] Similarly, samples 7-10 have similar Sm-Fe-N crystal grains forming the first phase. Sample 7 does not contain a second phase, while samples 8-10 contain a second phase with different compositions in amounts of 20 vol% or less. Because the alloy compositions forming the second phase in samples 8-10 are different, the melting points of the alloys differ. Compared to sample 7, samples 8-10 have higher density and improved compactness. This can be attributed to the second phase alloy functioning as a sintering aid. Furthermore, samples 8-10 obtained magnetic properties (saturation magnetization, remanent magnetization) similar to those of sample 7. Since the second phase content is 20 vol% or less, the decrease in remanent magnetization was appropriately suppressed. In other words, samples 8-10 were able to appropriately suppress the decrease in magnetization of the sintered magnet due to the second phase, while effectively utilizing the alloy that becomes the second phase as an aid to densify the first phase. As a result, they were able to increase the degree of compaction compared to sample 7 and suppress the decrease in remanent magnetization of the sintered magnet.

[0055] As described above, Samples 1 to 10 satisfy the requirements of [1] and [2] above and are one embodiment of the sintered magnet 100 of the above embodiment. These samples were able to be made into sintered magnets with high density and crystallinity and higher residual magnetization compared to Samples 11 to 14.

[0056] 4. Wettability of alloys Prior to the production of the above samples, Sm-Fe-N crystal grains (Sm2Fe 17 Preliminary experiments were conducted to narrow down the group of elements and alloy compositions that exhibit good wettability with N3. Figure 4 shows the results of the wettability evaluation of the alloy. The alloy powder with the composition shown in Figure 4 was prepared by step (2) alloy powder preparation step P2 of the above sample manufacturing method. Sm-Fe-N type crystal grain (Sm2Fe 17 The N3 fine powder was prepared by the grinding step P1 of the above sample manufacturing method. Sm-Fe-N crystalline grains (Sm2Fe 17 The above alloy powder was added to N3 fine powder at a ratio of 20 vol%, and sintering was carried out at a temperature of 450°C to 600°C, a sintering time of 10 min, a pressure of 600 MPa, and under vacuum pressure. The porosity was calculated using the method described later for the fabricated sintered bodies (samples S1 to S17), and by comparing these values ​​for each alloy, the Sm-Fe-N type crystal grain (Sm2Fe) was determined. 17 We selected alloy compositions with good wettability to N3 fine powder.

[0057] Figure 5 is an explanatory diagram of sample 100S for SEM observation. First, the sintered body (sintered magnet) prepared by the method described above was cut into a cylindrical shape with a diameter of 10 mm and a thickness of 3 mm (Figure 5(A)). Then, the cross section was prepared using waterproof abrasive paper (Figure 5(B)). Sample 100S for SEM observation was prepared by Ar ion milling of the cross section (Figure 5(C)). SEM observation was performed using sample 100S, and secondary electron images at a magnification of 1000x were captured at five different locations in the field of view. The porosity was calculated by binarizing the captured secondary electron images using the image processing software Image-J.

[0058] As shown in Figure 4, the alloy powders of samples S1 to 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 to S16 do not contain any group 2 elements or rare earth elements. The sintered body of sample S17 has no alloy powder added.

[0059] Preliminary experiments revealed a significant decrease in porosity in sintered bodies (samples S1-S9) to which alloy powders containing Group 2 elements and rare earth elements were added. Specifically, the alloy powders of samples S1-S9 had Sm-Fe-N crystalline grains (Sm2Fe 17 It is thought to exhibit good wettability to N3 fine powder.

[0060] In the preliminary experiment, calcium (Ca) was used as the group 2 element, but for the following reasons, it is thought that similar effects can be obtained by using other group 2 elements such as beryllium (Be), magnesium (Mg), strontium (Sr), barium (Ba), and radium (Ra).

[0061] In the Ellingham diagram, calcium (Ca) is below Sm, indicating that Ca has the effect of reducing Sm across the entire temperature range. In fact, Sm2Fe 17 It is also used as a reducing agent for Sm oxides when chemically synthesizing N3 particles. Thus, Sm2Fe 17Since Ca is an element that undergoes redox reactions with unavoidable oxides present on the particle surface of a N3-dominant phase, alloys containing Ca exhibit similar effects. The occurrence of a redox reaction can be rephrased as having a certain level of reactivity with the main phase particle surface, and wettability can be considered one aspect of this reactivity. Ca belongs to Group 2 of the periodic table, and elements in the same group as Ca, such as Be, Mg, Sr, Ba, and Ra, also have reducing properties towards Sm-Fe-O. Therefore, similar effects can be expected with other elements in the same group as Ca. In addition, in the binary phase diagram, elements X (Be, Mg, Sr, Ba, and Ra) have eutectic points when alloyed, similar to Ca, and can achieve the minimum necessary low melting point as a binder.

[0062] Furthermore, while lanthanum (La) and praseodymium (Pr) were used as rare earth elements in the preliminary experiments, it is believed that similar effects can be obtained by using other rare earth elements such as scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), eurobium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), for the following reasons.

[0063] The main phase particle is Sm2Fe 17 As represented by the composition of N3, it contains the rare earth element Sm. Sm exhibits high similarity / substitution with other lanthanide elements (such as La and Pr), forming a total solid solution system, and is expected to have high reactivity. In fact, it has been experimentally demonstrated that one of its reactivity characteristics is good wettability.

[0064] Therefore, we aimed to improve the volume fraction of the first phase (magnetic phase) by optimizing the composition and amount of alloys containing at least one of the group 2 elements and rare earth elements.

[0065] As described above, while samples 2-4, 6, and 7 of the examples above illustrate a second phase containing calcium (Ca) or barium (Ba), it can be said that even when the second phase of a sintered magnet contains a group 2 element other than calcium (Ca) or barium (Ba), or a rare earth element, it exhibits sufficient density and high crystallinity, and high magnetic properties.

[0066] The present disclosure has been described above based on embodiments and examples, but the embodiments described above are for the purpose of facilitating understanding of the present disclosure and do not limit it. The present disclosure may be modified and improved without departing from its spirit and the claims, and equivalents thereof are included in the present disclosure. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0067] This disclosure can also be realized in the following application examples. [Application Example 1] Th2Zn 17 A sintered magnet comprising a first phase mainly consisting of Sm-Fe-N crystal grains having a type structure, Density is 6.5 g / cm³ 3 That's all. The characteristic feature is that the full width at half maximum of the diffraction intensity peak in the (220) plane obtained from X-ray diffraction is 0.2 degrees or more and 0.3 degrees or less. Sintered magnet. [Application Example 2] The sintered magnet described in Application Example 1, moreover, The second phase comprises an alloy containing at least one element from Group 2 and / or rare earth elements, with a melting point between 180°C and 620°C. The second phase is characterized by having a content of 20 vol% or less. Sintered magnet. [Application Example 3] A method for producing sintered magnet powder used in molding the sintered magnet described in Application Example 1 or Application Example 2, A grinding step to obtain Sm-Fe-N-based crystal grains by grinding a coarse powder containing Sm-Fe-N single crystals, A process for producing the alloy powder that will become the second phase, A mixing step of dispersing the Sm-Fe-N crystal grains and the alloy powder to obtain the sintered magnet powder, which is a mixed powder; Includes, The pulverization step, the alloy powder production step, and the mixing step are characterized in that they are carried out in a low oxygen concentration atmosphere. A method for manufacturing powder for sintered magnets. [Application Example 4] A method for manufacturing a sintered magnet as described in Application Example 1 or Application Example 2, The method is characterized by comprising a sintering step in which the sintered magnet powder produced by the method for producing sintered magnet powder described in Application Example 3 is pressurized and sintered at a sintering temperature of 600°C or lower in a low oxygen concentration atmosphere. A method for manufacturing sintered magnets. [Explanation of symbols]

[0068] 10…First phase 10G…Sm-Fe-N crystal grain 20…Second phase 100... Sintered magnets 100S…Sample for SEM observation V...Void

Claims

1. Th 2 Zn 17 A sintered magnet comprising a first phase mainly consisting of Sm-Fe-N crystal grains having a type structure, Density is 6.5 g / cm³ 3 That's all. The diffraction intensity peaks in the (220) plane obtained from X-ray diffraction are characterized by having a full width at half maximum of 0.2 degrees or more and 0.3 degrees or less. Sintered magnet.

2. A sintered magnet according to claim 1, moreover, The material includes a second phase consisting of an alloy containing at least one element from Group 2 and / or rare earth elements, with a melting point of 180°C or higher and 620°C or lower. The second phase is characterized in that its content is 20 vol% or less. Sintered magnet.

3. A method for producing sintered magnet powder used in forming a sintered magnet according to claim 1 or claim 2, A grinding step in which a coarse powder containing Sm-Fe-N single crystals is ground to obtain Sm-Fe-N crystalline grains, A process for producing the alloy powder that will become the second phase, A mixing step of dispersing the Sm-Fe-N crystal grains and the alloy powder to obtain the sintered magnet powder, which is a mixed powder, Includes, The pulverization step, the alloy powder production step, and the mixing step are characterized by being carried out in a low oxygen concentration atmosphere. A method for manufacturing powder for sintered magnets.

4. A method for manufacturing a sintered magnet according to claim 1 or claim 2, The method for producing sintered magnet powder according to claim 3 is characterized by comprising a sintering step in which the sintered magnet powder produced by the method for producing sintered magnet powder according to claim 3 is pressurized and sintered at a sintering temperature of 600°C or lower in a low oxygen concentration atmosphere. A method for manufacturing sintered magnets.

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