Sm-fe-n-based sintered magnet and method for producing same

Abstract

This sintered magnet includes a first phase containing, as the main phase, Sm-Fe-N-based crystal grains having a Th2Zn17-type structure. The sintered magnet includes a second phase formed of an alloy containing at least one group-2 element and / or at least one rare-earth element. The average crystal grain size of the first phase is 5 µm or less. Among the crystal grains in the first phase, the content proportion of crystal grains having a crystal grain size of 1 µm or less is 20% or less.

Description

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

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

[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 both 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 Documents 1 and 2). Patent Document 1 discloses a technique for improving coercivity by setting the average grain size of the crystal grains to be greater than 0.04 μm and 5 μm or less, and the oxygen content to 0.7% by weight or less. Patent Document 2 discloses a technique for producing a powder with excellent crystallinity and an average grain size of 5 μm or less by grinding Sm-Fe-N magnet powder using a dry jet mill.

[0003] Patent No. 6614647 Patent No. 7076740

[0004] However, Patent Documents 1 and 2 do not examine remanent magnetization or prismaticity. In the technology described in Patent Document 2, 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 remanent 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 and prismaticity of Sm-Fe-N sintered magnets.

[0006] This disclosure was 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 this disclosure, Th2Zn 17A sintered magnet is provided, comprising a first phase mainly consisting of Sm-Fe-N crystal grains having a type structure. This sintered magnet comprises a second phase made of an alloy containing at least one of the elements of Group 2 and rare earth elements, the average crystal grain size of the first phase being 5 μm or less, and the content of crystal grains with a crystal grain size of 1 μm or less among the crystal grains of the first phase being 20% ​​or less.

[0008] With this form of sintered magnet, the average grain size of the first phase is 5 μm or less, thus ensuring the minimum coercivity required for a sintered magnet. Furthermore, since the proportion of crystal grains of 1 μm or less in the first phase is 20% or less, remanent magnetization and prismatic shape can be enhanced. In other words, by setting the grain size of the crystal grains of the first phase as described above, it is possible to enhance remanent magnetization and prismatic shape while maintaining the minimum coercivity.

[0009] Furthermore, in this form of sintered magnet, the second phase includes an alloy phase containing at least one element from either the Group 2 elements or rare earth elements, and the second phase functions as a metal binder layer. Although Sm-Fe-N crystal grains are difficult to sinter in liquid phase, by using an alloy with the above composition, it is possible to induce pseudo-liquid phase sintering and obtain a dense sintered body. By using the above composition for the alloy of the second phase, excellent wettability to the Sm-Fe-N crystal grains can be achieved, thereby improving the volume fraction of the first phase and improving the volume magnetization (magnetic force per unit volume) of the sintered magnet.

[0010] <2> In the sintered magnet of the above form, the difference between the 90% diameter D90 and the 10% diameter D10 in the grain size distribution of the crystal grains of the first phase may be 5 μm or less. In this case, the variation in the grain size distribution of the crystal grains of the first phase is small and the proportion of coarse particles is low, so the remanent magnetization can be further increased.

[0011] <3> In the above-described form of sintered magnet, the content of the second phase may be 10 vol% or less. In this case, the content of the second phase per unit volume is reduced, and the alloy that becomes the second phase can be effectively used as an auxiliary agent for densifying the first phase while appropriately suppressing the decrease in magnetization of the sintered magnet. As a result, the degree of densification during sintering can be further increased, and the magnetization of the sintered magnet can be further improved.

[0012] <4>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 an Sm-Fe-N single crystal to obtain the Sm-Fe-N crystalline grains, an alloy powder preparation step of obtaining an 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 concentration atmosphere, the average grain size of the Sm-Fe-N crystalline grains obtained in the grinding step is 5 μm or less, and the content of the Sm-Fe-N crystalline grains with a grain size of 1 μm or less is 20% or less.

[0013] According to this method for manufacturing powder for sintered magnets, 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. Furthermore, since the average crystal grain size of the Sm-Fe-N crystal grains obtained in the grinding process is 5 μm or less, the minimum coercivity required for sintered magnets can be ensured, and since the proportion of crystal grains with a grain size of 1 μm or less is 20% or less, remanent magnetization and prismatic shape can be enhanced. In other words, by setting the average crystal grain size of the Sm-Fe-N crystal grains obtained in the grinding process as described above, it is possible to obtain a sintered magnet with high remanent magnetization and prismatic shape while maintaining the minimum coercivity.

[0014] <5>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 includes a sintering step of pressurizing and sintering the sintered magnet powder produced by the method for manufacturing sintered magnet powder of the above embodiment at a sintering temperature of 600°C or less in a low oxygen concentration atmosphere.

[0015] 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 and prismatic shape can be manufactured.

[0016] Furthermore, this disclosure can be implemented in various forms, for example, as permanent magnets for motors, motors for electric vehicles, motors for motorcycles, industrial robots, drones, home appliances, and the like.

[0017] This is a conceptual diagram illustrating the cross-sectional structure of the sintered magnet of the embodiment. This is a diagram illustrating the prismatic shape. This is a process diagram showing an example of a method for manufacturing a sintered magnet. This is a diagram showing the evaluation results of a sample. This is a diagram illustrating a sample for SEM observation. This is a diagram showing the results of the wettability evaluation of the alloy.

[0018] <Embodiment> Figure 1 is an explanatory diagram conceptually showing 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 element from either a group 2 element or a rare earth element. In other embodiments, the sintered magnet may not contain the second phase.

[0019] 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 a plurality of 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.

[0020] The main phase, Sm-Fe-N crystal grain 10G, is Th2Zn 17 Sm2Fe having a type structure 17 It is N3. The sintered magnet 100 exhibits magnetism due to the Sm-Fe-N crystal grains 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.

[0021] Sm2Fe 17 Because N3 has excellent saturation magnetization and a huge anisotropic magnetic field, the sintered magnet 100 of this embodiment can withstand heat and reverse magnetic fields and generate a high magnetic field.

[0022] The first phase 10 is composed of Sm-Fe-N crystal grains 10G, and Th2Ni 17 The structure may include structures different from the main phase, such as a type structure or a TbCu7 type structure. Here, Tb is terbium and Cu is copper.

[0023] In the sintered magnet 100, the average grain size of the first phase 10 is 5 μm or less, and the proportion of crystal grains 10G with a grain size of 1 μm or less among the crystal grains 10G of the first phase 10 is 20% or less. Here, the proportion is the ratio (%) of the number of crystal grains 10G with a grain size of 1 μm or less to the total number of crystal grains 10G of the first phase 10. If the average grain size of the first phase 10 is greater than 5 μm, for example, sufficient coercivity cannot be obtained as a permanent magnet for a motor. Also, if the proportion of crystal grains 10G with a grain size of 1 μm or less among the crystal grains 10G of the first phase 10 is greater than 20%, the remanent magnetization and prismatic shape are insufficient. In other words, by setting the grain size of the crystal grains 10G of the first phase 10 as described above, it is possible to improve remanent magnetization and prismatic shape while maintaining a minimum coercivity, and as a result, the maximum energy product, which represents the overall performance of the permanent magnet, can be improved.

[0024] Figure 2 is an explanatory diagram of the squareness. As shown in Figure 2, the squareness is expressed by Hk / Hcj (also called the squareness ratio), and indicates the degree to which the demagnetization curve is square. Hk is defined as the value of the external magnetic field when the magnetization drops to 90% of the remanent magnetization Br, and Hcj is the coercivity. The range is 0 < Hk / Hcj ≤ 1, and ideally Hk / Hcj = 1, and the closer Hk / Hcj is to 1, the better the magnet is considered to be. The closer the squareness ratio is to 1, the less the magnet changes in response to disturbances, which is preferable as it makes designing easier when used in motors.

[0025] The average grain size of the first phase 10 of the sintered magnet 100 can be evaluated by acquiring a cross-sectional SEM (Scanning Electron Microscope) image of the sintered magnet 100 and using the planimetric method. The planimetric method, also known as the quadrature method or Jeffries method, is a method for measuring the two-dimensional area of ​​a sample cross-section. The measurement of the average grain size by the planimetric method can be performed according to the method described in the following document: Yoshimasa Takayama, et al., "Influence of grain size distribution on evaluation of average grain size," Journal of the Japan Institute of Metals, 1988, Vol. 52, No. 9, pp. 835-842.

[0026] The difference between the 90% diameter D90 and the 10% diameter D10 in the grain size distribution of the crystal grains 10G of the first phase 10 of the sintered magnet 100 is not particularly limited, but is preferably 5 μm or less. In other words, it is preferable that the variation in the grain size distribution of the crystal grains of the first phase is small, or in other words, that there is less coarse grains and excessively crushed ultrafine powder. The presence of coarse grains causes a decrease in the coercivity of the sintered magnet, and the presence of ultrafine powder causes a decrease in the degree of orientation of the sintered magnet. Therefore, if the grain size distribution of the crystal grains of the first phase is as described above, a balance between the coercivity and remanent magnetization of the sintered magnet is ensured.

[0027] The second phase 20 consists of an alloy containing at least one element from either the Group 2 elements or the rare earth elements. An alloy with such a composition is the main phase (Sm2Fe 17 It exhibits excellent wettability to N3. Therefore, a dense sintered body can be obtained.

[0028] 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).

[0029] 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.

[0030] Although the melting point of the alloy that forms the second phase 20 is not particularly limited, it is preferably 180°C or higher and 620°C or lower. Since the Sm—Fe—N-based magnet undergoes thermal decomposition at 620°C or higher, there has been a limitation on the sintering temperature, and conventionally, a high-density sintered body could not be obtained. In contrast, when the melting point of the alloy that forms the second phase 20 is 620°C or lower, since it is a temperature at which the main phase does not decompose, even when heating at the temperature at which the alloy melts during the production of the sintered magnet 100, the main phase does not decompose. Therefore, by using an alloy with a melting point of 620°C or lower for the second phase 20, liquid-phase sintering can occur, Sm2Fe 17 N3 / Sm2Fe 17 The second phase 20 made of the above alloy can be formed as a grain boundary phase at the interface of N3 / Sm2FeN3. Further, when the melting point of the alloy that forms the second phase 20 is 180°C or higher, for example, the sintered magnet 100 can also be used for equipment such as an EV motor that generates heat and becomes high temperature.

[0031] The melting point of the second phase can be measured using a DSC (differential scanning calorimeter). Weigh 10 to 20 mg of the rapidly quenched liquid foil obtained by melt spinning described later, and use this as the measurement sample. For the measurement, use a pan made of BN (boron nitride) material, set the measurement temperature range from room temperature to 700°C, and the heating rate to 10°C / min. The melting point is determined using the melting peak temperature that appears within the measurement temperature range.

[0032] Although the content of the second phase 20 is not particularly limited, it is preferably 10 vol% or less. While the alloy of the second phase 20 can act as an auxiliary agent for densifying the first phase 10, since the alloy of the second phase 20 is a non-magnetic component, if it is contained in a large amount, there is a risk that the magnetic phase ratio will relatively decrease and the magnetization will decrease. When the content of the second phase 20 is 10 vol% or less, while appropriately suppressing the decrease in the magnetization of the sintered magnet 100 due to the second phase 20, as an auxiliary agent function for densifying the first phase 10, the alloy that becomes the second phase 20 can act effectively. 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. Note that the content of the second phase 20 is preferably 0.1 vol% or more. The content ratio of the second phase 20 can be determined by fluorescent X-ray or ICP analysis, etc.

[0033] The sintered magnet 100 may contain inevitable impurity elements and the like as long as the magnetic properties of the main phase are not impaired. The inevitable impurity elements refer to impurity elements that cannot be avoided when manufacturing the sintered magnet 100 of the embodiment, or impurity elements that would cause a significant increase in manufacturing cost to avoid. Examples of such inevitable impurity elements include impurity elements in raw materials and elements contained in lubricants used during molding.

[0034] FIG. 3 is a process diagram showing an example of a method for manufacturing the sintered magnet 100. The method for manufacturing the sintered magnet 100 of the present embodiment is not particularly limited, but for example, it can be manufactured by the following method. As shown in FIG. 3, in the method for manufacturing the sintered magnet 100, the steps are performed in the order of the manufacturing process P0 of the sintered magnet powder and the sintering process P4. In the manufacturing process P0 of the sintered magnet powder, the steps are performed in the order of the pulverization process P1, the alloy powder production process P2, and the mixing process P3.

[0035] In the pulverization process P1, 17 a coarse powder containing a Sm—Fe—N single crystal having a Th2Zn 17 type structure is pulverized to obtain Sm—Fe—N system crystal grains. As the coarse powder, for example, those having a composition of Sm2Fe

[0036] N3 and an average particle size of 10 μm or more and 200 μm or less can be used. The average particle size of the Sm—Fe—N system crystal grains obtained in the pulverization process P1 is 5 μm or less, and the content ratio of Sm—Fe—N system crystal grains having a crystal grain size of 1 μm or less is 20% or less.

[0037] In the alloy powder production process P2, powder of a predetermined size of an alloy serving as the second phase is produced to obtain alloy powder.

[0038] 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.).

[0039] Since the average grain size of the Sm-Fe-N crystal grains obtained in the grinding step P1 is 5 μm or less, the minimum coercivity required for sintered magnets can be ensured, and since the proportion of grain sizes of 1 μm or less is 20% or less, remanent magnetization and prismatic shape can be enhanced. In other words, by setting the average grain size of the Sm-Fe-N crystal grains obtained in the grinding step P1 as described above, it is possible to obtain a sintered magnet with high remanent magnetization and prismatic shape while maintaining the minimum coercivity.

[0040] The above-described 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.

[0041] 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. Also, because the sintering temperature is low at 600°C or lower, the growth of Sm-Fe-N crystal grains does not progress, and the particle size of the Sm-Fe-N crystal grains in the sintered magnet can be maintained at approximately the same level as the Sm-Fe-N crystal grains obtained in the grinding process P1. Therefore, a sintered magnet with high residual magnetization and prismaticity can be obtained while maintaining the minimum coercivity. Furthermore, by carrying out 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.

[0042] The sintered magnets of this embodiment can be used in, for example, electric vehicle motors, motorcycle motors, industrial robots, drones, home appliances, and the like.

[0043] The present disclosure will be further illustrated by examples. Figure 4 shows the evaluation results of samples 1 to 15. In samples 1 to 3, the second phase contains barium (Ba) as a group 2 element and copper (Cu), which is an element other than group 2 elements and rare earth elements. In sample 4, the second phase contains calcium (Ca) as a group 2 element and silver (Ag), which is an element other than group 2 elements and rare earth elements. In sample 5, the second phase contains calcium (Ca) as a group 2 element and copper (Cu), which is an element other than group 2 elements and rare earth elements. In sample 6, the second phase contains magnesium (Mg) and barium (Ba) as group 2 elements and does not contain any elements other than group 2 elements and rare earth elements. In sample 7, the second phase contains praseodymium (Pr) as a rare earth element and copper (Cu), which is an element other than group 2 elements and rare earth elements. In Figure 4, the columns for Group 2 elements and rare earth elements in the second phase composition are enclosed in double lines. Also in Figure 4, the grinding methods are abbreviated as "JM" for jet mill grinding and "wet grinding" for wet grinding.

[0044] 1. Manufacturing of Samples Samples 1-7, 12, and 13 were manufactured by the manufacturing method illustrated in the above embodiment (Figure 3). Samples 8-11, 14, and 15 do not contain a second phase, so the alloy powder preparation step P2 and mixing step P3 of the manufacturing method illustrated in the above embodiment (Figure 3) were omitted. Instead, the Sm-Fe-N crystalline grains obtained by the grinding step P1 were used to form and sinter in the sintering step P4.

[0045] (1) Grinding process P1 As a coarse powder containing Sm-Fe-N single crystals, Sm2Fe with an average particle size of 30 μm 17N3 powder was used. Samples 1-4, 6, 7, 11-15 The above coarse powder was ground using an air-jet mill with an inert gas (Ar or N2) under the grinding conditions shown in Figure 4. In order to keep the particle size within an appropriate range, the process of grinding the powder discharged from the grinding chamber of the jet mill and grinding it again was repeated up to a maximum of three times in total. In addition, in order to optimize the particle size, the grinding gas pressure was sometimes changed and adjusted as appropriate during the up to three jet mill grinding cycles.

[0046] Specifically, samples 1-3, 7, and 11-13 underwent two repeated grinding cycles at a grinding gas pressure of 0.7 MPa. Samples 4 and 6 underwent three repeated grinding cycles at a grinding gas pressure of 0.7 MPa. Sample 14 underwent one grinding cycle at a grinding gas pressure of 1 MPa. Sample 15 underwent one grinding cycle at a grinding gas pressure of 1 MPa followed by one grinding cycle at a grinding gas pressure of 0.7 MPa (total of two passes).

[0047] In samples 1-4, 6, 7, and 11-13, each grinding process was carried out while removing excessively fine powder using a cyclone (airflow classifier). In samples 1-4, 6, 7, and 11-15, grinding was carried out in a low-oxygen atmosphere inside a glove box connected to a gas-circulating oxygen-moisture purifier to prevent oxidation of the powder.

[0048] - Samples 5, 8-10: Instead of using the jet mill described above, wet grinding was performed using a ball mill. Ball mill grinding was carried out in the following manner: In a glove box where the oxygen concentration was controlled to 0.5 ppm or less, stainless steel pebbles, the above raw material powder, and ethanol as a solvent were placed in a stainless steel pot, and the pot was rotated to grind the coarse powder using a ball mill. The rotation time was 48 hours and the rotation speed was 120 rpm. The obtained slurry was sieved through a sieve with a mesh size of 25 μm in the same glove box and dried in a vibrating dryer. The obtained powder was sieved through a sieve with a mesh size of 250 μm to obtain dried powder.

[0049] (2) Alloy powder production process P2 The following were used as raw materials (granular alloy raw materials) for the alloy powder: ・Mg metal (granular) ・Ca metal (granular) ・Ba metal (granular) ・Al metal (granular) ・Cu metal (granular) ・Ag metal (granular) ・Sn metal (granular) ・Zn metal (granular) ・La metal (granular)

[0050] These granular alloy raw materials were weighed to the composition ratio shown in Figure 4 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 boulders were placed in a stainless steel pot, and ethanol, heptane, or acetonitrile 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 12 hours and the rotation speed was 200 rpm.

[0051] 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 20 μm mesh sieve to obtain a dried alloy powder.

[0052] (3) Mixing step P3 Sm-Fe-N system crystal grains obtained in grinding step P1 (Sm2Fe 17 N3) and the alloy powder obtained in the alloy powder preparation step P2 were ball-milled using isopropanol as a solvent to obtain a mixed powder (slurry) for sintered magnets. In the mixing step P3, the alloy powder was added so that its content was the second phase content (vol%) shown in Figure 4. 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 (volume) relative to the amount of N3) plus the amount of alloy powder represents the second phase content (vol%).

[0053] (4) Sintering process P4 - Samples 1-7, 12, 13 The sintered magnet powder obtained in mixing process 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, and a pressure of 600 MPa to 1200 MPa was applied using a uniaxial press. This was then electrically sintered at a sintering temperature of 400°C to 600°C for 10 minutes under a vacuum atmosphere. As a result, Sm-Fe-N type crystal grains (Sm2Fe 17 A sintered body was obtained comprising a first phase 10 mainly composed of N3) and a second phase 20 made of an alloy. Samples 8-11, 14, 15 Using the Sm-Fe-N system crystal grains, which are dried powder obtained by the grinding process P1, the material was placed in a non-magnetic cemented carbide die (mold) in a glove box with an oxygen concentration controlled to 0.5 ppm or less, similar to the sintering process of Samples 1-7, 12, 13, and a pressure of 600 MPa to 1200 MPa was applied using a uniaxial press. This was then electrically sintered at a sintering temperature of 400°C to 600°C for 10 minutes under a vacuum atmosphere. As a result, Sm-Fe-N system crystal grains (Sm2Fe 17 A sintered body was obtained containing a first phase 10 with N3 as the main phase.

[0054] 2. Evaluation Method (1) Evaluation of the average crystal grain size of the first phase of the sintered body Sm2Fe 17 Because N3 undergoes thermal decomposition at temperatures above 600°C, low-temperature sintering is performed. As a result, grain growth of crystal particles is difficult during the sintering process, and there is no significant change in grain size before and after sintering. Therefore, the average grain size of Sm-Fe-N crystal grains before sintering was evaluated using the HELOS & RODOS (Sympatec), a dry-method grain size distribution analyzer, and compared with the average particle size of the first phase of the sintered body evaluated using the area measurement method. It was confirmed that both yielded similar grain sizes. Thus, the average grain size of Sm-Fe-N crystal grains before sintering can also be applied as the average grain size of the first phase of the sintered body.

[0055] The average particle size of the first phase of the sintered body was calculated using the area measurement method as follows. First, an SEM observation sample was prepared to obtain a cross-sectional SEM image of the sintered magnet. Figure 5 is an explanatory diagram of the SEM observation sample 100S. First, the sintered body (sintered magnet) of the above sample was cut into a cylindrical shape with a diameter of 10 mm and a thickness of 3 mm (Figure 5(A)). Then, a cross-section was made using waterproof abrasive paper (Figure 5(B)). The cross-section was prepared by Ar ion milling to create the SEM observation sample 100S (Figure 5(C)). An SEM image of a 100 μm × 100 μm region was obtained using the SEM observation sample 100S. This was binarized, and the area of ​​each particle was calculated to be a perfect circle (πr). 2 After approximation, the particle size of the first phase of the sintered body is calculated by considering its diameter (2r) as the particle size of each particle. This operation is performed in five regions with different fields of view, and the average particle size of the first phase of the sintered body and the proportion of particles smaller than 1 μm are determined from the frequency distribution obtained by summing the particle sizes of each particle calculated from the five obtained SEM images. For the 90% diameter D90 and 10% diameter D10 in the particle size distribution of the crystal grains of the first phase, the cumulative relative frequency is determined from the frequency distribution obtained above, and the particle size corresponding to the cumulative 90% is taken as D90, and the particle size corresponding to the cumulative 10% is taken as D10, and the difference (D90 - D10) is calculated. Figure 4 shows the average particle size of the first phase of the sintered body using the area measurement method.

[0056] (2) Evaluation of the magnetic properties of the sintered body The magnetic properties of the sintered body were evaluated using a vibrating sample magnetometer (VSM). After applying an external magnetic field of 9T, the demagnetization curve obtained by applying a reverse magnetic field from there to -2T was measured, and the remanent magnetization Br, prismaticity Hk / Hcj, and maximum energy product (BH) max were calculated.

[0057] 3. Evaluation Results (1) Evaluation of the average crystal grain size of the first phase of the sintered body As shown in Figure 4, all of samples 1 to 15 had an average crystal grain size of 5 μm or less in the first phase. In addition, in samples 1 to 8 and 11 to 13, the proportion of crystal grains with a crystal grain size of 1 μm or less in the first phase was 20% or less.

[0058] Furthermore, for samples 1-7 and 9-15, the difference between the 90% diameter D90 and the 10% diameter D10 in the grain size distribution of the first phase crystal grains was 5 μm or less. (2) Evaluation of the magnetic properties of the sintered body In order to confirm the effect of the addition of the second phase on the magnetic properties, it is advisable to compare the remanent magnetization of samples 8-10 and 11, which were pulverized by wet milling and jet milling and sintered without the addition of the second phase, with samples 1-7, which were sintered with the addition of the second phase. Among the samples prepared by wet milling, sample 5 had a higher remanent magnetization than samples 8-10 which had no addition, and among the samples prepared by jet milling, it was confirmed that samples 1-4 and 6 and 7 all had higher remanent magnetization than sample 11 which had no addition. In other words, it was confirmed that all of samples 1-7 had remanent magnetizations that were higher than those of the samples sintered without the addition.

[0059] Samples 1-8 and 11-13 satisfy the following requirements [1] and [2] (Figure 4). [1] The average grain size of the first phase is 5 μm or less. [2] The proportion of grains with a grain size of 1 μm or less among the grains of the first phase is 20% or less. In contrast, samples 9, 10, 14, and 15 satisfy requirement [1] above, but do not satisfy requirement [2] above. That is, by not only making the grain size of the first phase 5 μm or less, but also keeping the proportion of grains with a grain size of 1 μm or less low at 20% or less, it was possible to increase the remanent magnetization and the angularity ratio.

[0060] Furthermore, samples 1 to 7 satisfy the following requirement [3]: [3] They contain a second phase made of an alloy containing at least one of either a group 2 element or a rare earth element. Samples 1 to 7 exhibit the same remanent magnetization as samples 8 and 11 to 13 or higher. Samples 8 and 11 do not contain a second phase, and although samples 12 and 13 contain a second phase, the second phase does not contain either a group 2 element or a rare earth element. In other words, in Sm-Fe-N sintered magnets, the remanent magnetization was improved by containing a second phase, and by making the second phase an alloy containing at least one of either a group 2 element or a rare earth element. Sm-Fe-N crystal grains are difficult to sinter in liquid phase, but by using an alloy with the above composition, it was possible to simulate liquid phase sintering and obtain a dense sintered body. By using the above composition for the second phase alloy, excellent wettability to Sm-Fe-N crystal grains can be achieved, thereby improving the volume fraction of the first phase.

[0061] As described above, samples 1-3 contain barium (Ba) as the Group 2 element in the second phase, samples 4 and 5 contain calcium (Ca) as the Group 2 element in the second phase, and sample 6 contains magnesium (Mg) and barium (Ba) as the Group 2 elements in the second phase. All samples 1-6 showed remanent magnetization of sample 8 and 11-13 or higher, and similar effects were obtained regardless of the type of Group 2 element, and whether one or two elements were used. Sample 7 contains praseodymium (Pr) as the rare earth element in the second phase and, like samples 1-6, showed remanent magnetization of sample 8 and 11-13 or higher. In other words, by including a rare earth element in the second phase, the same effects as when including a Group 2 element were obtained.

[0062] Samples 1 to 7 also satisfy the following requirement [4]: ​​[4] The difference between the 90% diameter D90 and the 10% diameter D10 in the grain size distribution of the first phase crystal grains is 5 μm or less. Generally, the coercivity of a permanent magnet increases as the crystal grain size decreases, but samples 1 to 3 have higher coercivity than sample 8 despite having a larger average grain size than sample 8. Sample 8 does not satisfy the above requirement [4]. Making the difference between the crystal grain sizes D90 and D10 5 μm or less can also be rephrased as reducing the proportion of coarse particles. In this way, the remanent magnetization of the sintered magnet can be increased, as can the coercivity of the sintered magnet, and the overall performance of the sintered magnet can be improved.

[0063] Samples 2 to 6 also satisfy the following requirement [5]: [5] The content of the second phase is 10 vol% or less. Samples 2 to 6 have higher remanent magnetization compared to Sample 1. While the alloy of the second phase can act as an aid to densify the first phase, the alloy of the second phase is a non-magnetic component, so if it is included in large quantities, the proportion of the magnetic phase will relatively decrease, and there is a risk that the magnetization will decrease. Since Samples 2 to 6 have a second phase content of 10 vol% or less, it is thought that the alloy that becomes the second phase was able to effectively act as an aid to densify the first phase while appropriately suppressing the decrease in magnetization of the sintered magnet due to the second phase. As a result, the degree of densification during sintering was increased compared to Sample 1, and the remanent magnetization of the sintered magnet was further improved compared to Sample 1.

[0064] As described above, samples 1 to 7 were able to improve at least one of the remanent magnetization and the square aspect ratio compared to samples 8 to 15. As a result, samples 1 to 7 were able to increase the maximum energy product compared to samples 8 to 15, thus improving the magnetic performance.

[0065] As described above, Samples 1 to 7 satisfy the requirements of [1] to [3] above and are one embodiment of the sintered magnet 100 of the above embodiment. These samples were able to be sintered magnets with higher residual magnetization and prismaticity compared to Samples 8 to 15.

[0066] 4. Wettability of the alloy Prior to the production of the above samples, Sm-Fe-N type crystal grains (Sm2Fe 17 Preliminary experiments were conducted to narrow down the group of elements and alloy compositions that exhibit good wettability to N3). Figure 6 shows the results of the wettability evaluation of the alloys. Alloy powders with the compositions shown in Figure 6 were prepared by step P2 of the alloy powder preparation process (2) of the above sample manufacturing method. Sm-Fe-N system crystal grains (Sm2Fe 17 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 under current pressure at a sintering temperature of 450°C to 600°C, a sintering time of 10 min, a pressure of 600 MPa, and a vacuum atmosphere. 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.

[0067] SEM observation was performed using sample 100S (Figure 5), 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.

[0068] As shown in Figure 6, the metal binders of samples S1 to S4 contain calcium (Ca), a group 2 element; the metal binders of samples S5 to S6 contain barium (Ba), a group 2 element; the metal binders of samples S7, S8, and S11 contain lanthanum (La), a rare earth element; and the metal binders of samples S9 and S10 contain praseodymium (Pr), a rare earth element. The metal binders of samples S12 to S18 do not contain any group 2 elements or rare earth elements. The sintered body of sample S19 has no metal binder added.

[0069] Preliminary experiments revealed a significant decrease in porosity in sintered bodies (samples S1-S11) to which metal binders containing group 2 elements and rare earth elements were added. Specifically, the metal binders in samples S1-S11 contained Sm-Fe-N crystalline grains (Sm2Fe 17 It is thought to exhibit good wettability to N3 fine powder.

[0070] In the preliminary experiments, calcium (Ca) and barium (Ba) were used as Group 2 elements, 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), and radium (Ra).

[0071] 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 material for Sm oxides when chemically synthesizing N3 particles. 17 Since Ca is an element that undergoes a redox reaction with unavoidable oxides present on the particle surface of a N3-dominant phase, alloys containing Ca exhibit a similar effect. 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 of the same group, Be, Mg, Sr, Ba, and Ra, also have a reducing effect on Sm-Fe-O. Therefore, similar effects can be expected with 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 when alloyed, similar to Ca, and can achieve the minimum necessary low melting point as a binder.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] As described above, in Samples 1 to 3 of the above examples, a second phase containing barium (Ba) was exemplified; in Samples 4 and 5, a second phase containing calcium (Ca) was exemplified; in Sample 6, a second phase containing magnesium (Mg) and barium (Ba) was exemplified; and in Sample 7, a second phase containing praseodymium (Pr) was exemplified. However, even when the second phase of the sintered magnet contains other Group 2 elements or rare earth elements, it can be said that it exhibits high remanent magnetization and prismaticity, as well as a high maximum energy product. Furthermore, it can be said that similar effects can be obtained when at least one of the Group 2 elements and rare earth elements is included in two or more types.

[0076] 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.

[0077] This disclosure can also be implemented in the following application examples: [Application Example 1] Th2Zn 17A sintered magnet comprising a first phase mainly consisting of Sm-Fe-N crystal grains having a type structure, comprising a second phase made of an alloy containing at least one of the elements of Group 2 and rare earth elements, wherein the average crystal grain size of the first phase is 5 μm or less, and the content of crystal grains with a crystal grain size of 1 μm or less among the crystal grains of the first phase is 20% or less. [Application Example 2] A sintered magnet according to Application Example 1, wherein the difference between the 90% diameter D90 and the 10% diameter D10 in the grain size distribution of the crystal grains of the first phase is 5 μm or less. [Application Example 3] A sintered magnet according to Application Example 1 or Application Example 2, wherein the content of the second phase is 10 vol% or less. [Application Example 4] A method for producing sintered magnet powder used in molding a sintered magnet as described in any of Application Examples 1 to 3, comprising: a grinding step of grinding a coarse powder containing an Sm-Fe-N single crystal to obtain Sm-Fe-N crystalline grains; an alloy powder preparation step of preparing an 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 concentration atmosphere, the average grain size of the Sm-Fe-N crystalline grains obtained in the grinding step is 5 μm or less, and the content of Sm-Fe-N crystalline grains with a grain size of 1 μm or less is 20% or less. [Application Example 5] A method for manufacturing a sintered magnet according to any one of Application Examples 1 to 3, characterized by comprising a sintering step of pressurizing and sintering the sintered magnet powder, manufactured by the method for manufacturing sintered magnet powder according to Application Example 4, at a sintering temperature of 600°C or lower in a low oxygen concentration atmosphere.

[0078] 10...First phase 10G...Sm-Fe-N crystal grains 20...Second phase 100...Sintered magnet 100S...Sample for SEM observation V...Void

Claims

1. Th2Zn 17 A sintered magnet comprising a first phase mainly consisting of Sm-Fe-N crystal grains having a type structure, comprising a second phase made of an alloy containing at least one of the elements of Group 2 and rare earth elements, wherein the average crystal grain size of the first phase is 5 μm or less, and the content of crystal grains with a crystal grain size of 1 μm or less among the crystal grains of the first phase is 20% or less.

2. A sintered magnet according to claim 1, characterized in that the difference between the 90% diameter D90 and the 10% diameter D10 in the grain size distribution of the crystal grains of the first phase is 5 μm or less.

3. A sintered magnet according to claim 1, characterized in that the content ratio of the second phase is 10 vol% or less.

4. A method for producing sintered magnet powder used in forming a sintered magnet according to any one of claims 1 to 3, comprising: a grinding step of grinding a coarse powder containing an Sm-Fe-N single crystal to obtain Sm-Fe-N crystalline grains; an alloy powder preparation step of preparing an 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 concentration atmosphere, the average grain size of the Sm-Fe-N crystalline grains obtained in the grinding step is 5 μm or less, and the content of Sm-Fe-N crystalline grains with a grain size of 1 μm or less is 20% or less.

5. A method for manufacturing a sintered magnet according to any one of claims 1 to 3, characterized by comprising a sintering step of pressurizing and sintering the sintered magnet powder, manufactured by the method for manufacturing sintered magnet powder according to claim 4, at a sintering temperature of 600°C or lower in a low oxygen concentration atmosphere.

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