Rare earth sintered magnet, method for manufacturing rare earth sintered magnet, rotor, and rotating machine

Abstract

The rare earth sintered magnet (1) includes: a plurality of main phases (2) that contain at least Nd as the rare earth element R and have an R2Fe 14 B crystal structure; and a grain boundary phase (3) that is formed between the main phases (2). The grain boundary phase (3) has: a Sm-enriched portion (4) in which Sm is substituted in the crystalline NdO phase and Sm is enriched; and a heavy rare earth element RH-enriched portion (5) in which the heavy rare earth element RH is enriched in at least a part of the periphery of the Sm-enriched portion (4). Thereby, while suppressing the deterioration of magnetic properties, the heavy rare earth element RH can be further diffused into the interior of the rare earth sintered magnet (1).

Description

Technical Field

[0001] The present disclosure relates to a rare earth sintered magnet, a method for manufacturing a rare earth sintered magnet, a rotor using the rare earth sintered magnet, and a rotating machine using the rare earth sintered magnet. Background Art

[0002] The R-T-B based rare earth sintered magnet is a magnet having rare earth element R, Fe, or a transition metal element T such as Fe in which a part thereof is replaced with Co, and boron B as main constituent elements. The R-T-B based rare earth sintered magnet is used for an industrial motor or the like, and the use environment temperature is a high temperature exceeding 100°C. Therefore, in the conventional R-T-B based rare earth sintered magnet, in order to improve heat resistance, it contains heavy rare earth elements RH such as Dy and Tb. However, regarding the heavy rare earth element RH, due to uneven resources and limited production, there is anxiety about its supply.

[0003] As a means of reducing the usage amount of the heavy rare earth element RH, there is the grain boundary diffusion method. For example, in Patent Document 1, the heavy rare earth element RH is subjected to grain boundary diffusion into an R-T-B based rare earth sintered magnet in which neodymium fluoride is dispersed in the grain boundary phase. Thereby, the heavy rare earth element RH is not oxidized in the grain boundary phase but is subjected to grain boundary diffusion, and the usage amount of the scarce heavy rare earth element RH can be reduced.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-82467 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, if the F-containing neodymium fluoride that does not contribute to the magnetic properties remains as a compound inside the rare earth sintered magnet, the concentrations of the rare earth elements R and Fe that bear the magnetic properties are relatively reduced, and thus the magnetic properties are reduced. In addition, if the content of neodymium fluoride is small, although the reduction of the magnetic properties can be suppressed, the heavy rare earth element RH cannot be diffused into the inside of the rare earth sintered magnet. Thus, in the grain boundary diffusion method, there is a problem that it is difficult to diffuse the heavy rare earth element RH into the inside of the rare earth sintered magnet while suppressing the reduction of the magnetic properties.

[0009] The present disclosure has been completed to solve the above problems, and an object thereof is to provide a rare earth sintered magnet, a method for manufacturing a rare earth sintered magnet, a rotor using the rare earth sintered magnet, and a rotating machine using the rare earth sintered magnet in which the heavy rare earth element RH is further diffused into the inside of the rare earth sintered magnet while suppressing the reduction of the magnetic properties.

[0010] Means for Solving the Problems

[0011] The rare earth sintered magnet according to the present disclosure includes: a plurality of main phases that contain at least Nd and Sm as rare earth element R and have an R2Fe 14 B crystal structure; and a grain boundary phase that is formed between the main phases, has a high concentration of Sm compared to the main phases, and has: a Sm enrichment portion in which Sm is substituted and Sm is enriched (concentrated) in a crystalline NdO phase; and a heavy rare earth element RH enrichment portion in which a heavy rare earth element RH is enriched in at least a part of the periphery of the Sm enrichment portion.

[0012] The method for manufacturing a rare earth sintered magnet according to the present disclosure includes: a pulverization step of pulverizing an R-Fe-B-based rare earth magnet alloy containing Nd and Sm as rare earth element R; a molding step of molding the powder of the R-Fe-B-based rare earth magnet alloy to produce a molded body; a sintering and aging step of sintering the molded body at a temperature of 600°C or higher and 1300°C or lower and performing an aging treatment at a temperature lower than the sintering temperature to produce a sintered body; and a grain boundary diffusion step of attaching a heavy rare earth element RH to the sintered body and performing a heat treatment to cause the heavy rare earth element RH to diffuse along the grain boundary.

[0013] Effects of the Invention

[0014] According to the present disclosure, by including a grain boundary phase having a Sm enrichment portion in which Sm is substituted and Sm is enriched in a crystalline NdO phase and a heavy rare earth element RH enrichment portion in which a heavy rare earth element RH is enriched in at least a part of the periphery of the Sm enrichment portion, it is possible to further diffuse the heavy rare earth element RH into the interior of the rare earth sintered magnet while suppressing a decrease in magnetic properties. Description of the Drawings

[0015] Figure 1 A schematic diagram of a part of the rare earth sintered magnet according to Embodiment 1.

[0016] Figure 2 A flowchart showing the steps of the method for manufacturing a rare earth sintered magnet according to Embodiment 2.

[0017] Figure 3 A schematic diagram showing the operation of the raw material alloy production step 11 according to Embodiment 2.

[0018] Figure 4 A to Figure 4 E are diagrams obtained by analyzing a cross section of a rare earth sintered magnet manufactured by the method for manufacturing a rare earth sintered magnet according to Embodiment 2 using EPMA.

[0019] Figure 5 A to Figure 5 E are diagrams obtained by analyzing a cross section of a rare earth sintered magnet manufactured by the method for manufacturing a rare earth sintered magnet according to Embodiment 2 using EPMA.

[0020] Figure 6 Schematic cross-sectional view of the rotor according to Embodiment 3.

[0021] Figure 7 Schematic cross-sectional view of the rotating machine according to Embodiment 4. Detailed Embodiments

[0022] Embodiment 1.

[0023] The rare earth sintered magnet 1 in Embodiment 1 is an R-Fe-B-based rare earth sintered magnet containing light rare earth elements RL and heavy rare earth elements RH as the main rare earth elements R. Among them, the light rare earth elements RL at least include Nd and Sm. In addition, other light rare earth elements RL may also be included. The heavy rare earth elements RH at least include any one of Dy or Tb.

[0024] Regarding the rare earth sintered magnet 1 in Embodiment 1, Figure 1 is described. Figure 1 Schematic view of a part of the rare earth sintered magnet 1. The rare earth sintered magnet 1 includes: a main phase 2 having an R2Fe 14 B crystal structure containing at least Nd as the rare earth element R, and a grain boundary phase 3 formed between a plurality of main phases 2. The grain boundary phase 3 has: a Sm enrichment part 4 in which Sm is substituted and Sm is enriched in the crystalline NdO phase; and a heavy rare earth element RH enrichment part 5 in which the heavy rare earth element RH is enriched in at least a part of the periphery of the Sm enrichment part 4.

[0025] The main phase 2 is, for example, grains based on the Nd2Fe 14 B crystal structure. Regarding the grains of the main phase 2, for example, by making the average particle size 100 μm or less, the magnetic properties can be improved. In addition, a part of the Nd sites of the Nd2Fe 14 B crystal structure of the main phase 2 can be substituted with other rare earth elements R containing Sm and heavy rare earth elements RH.

[0026] The grain boundary phase 3 has a Sm enrichment part 4 in which Sm is substituted and Sm is enriched in the crystalline NdO phase. As Figure 1 shown, the Sm enrichment part 4 is enriched in a part of the grain boundary phase 3. In addition, the Sm enrichment part 4 is dispersed not only on the surface layer of the rare earth sintered magnet 1 but also in the entire grain boundary phase 3 up to the central part.

[0027] In at least a part of the grain boundary phase 3 on the periphery of the Sm enrichment part 4, there is a heavy rare earth element RH enrichment part 5. The heavy rare earth element RH enrichment part 5 is a grain boundary phase 3 in which the heavy rare earth element RH is enriched compared to the other grain boundary phases 3 and the main phase 2 including the Sm enrichment part 4. The heavy rare earth element RH enrichment part 5 is as Figure 1At least a part that can exist in the periphery of the Sm-rich portion 4 may also exist in such a manner as to surround the entire periphery of the Sm-rich portion 4.

[0028] Next, the functions and effects of the present embodiment will be described.

[0029] For example, in Patent Document 1, F, which is an element irrelevant to magnetic properties, remains as a compound inside the rare earth sintered magnet. As a result, the concentrations of the rare earth element R and Fe that bear the magnetic properties are relatively reduced, and the magnetic properties are degraded. In contrast, with respect to the Sm-rich portion 4, Sm substitution is performed at a part of the Nd sites in the crystal structure of the NdO phase in the grain boundary phase 3 as a light rare earth element the same as Nd. Therefore, an element irrelevant to magnetic properties is not added, and Sm substitution is performed in the crystalline NdO phase, whereby a decrease in magnetic properties can be suppressed.

[0030] In addition, in the conventional grain boundary diffusion method, the concentration difference of the heavy rare earth element RH at the interface between the main phase and the grain boundary phase is used as a driving force, and the heavy rare earth element RH diffuses in the main phase. As a result, there is a problem of consuming the heavy rare earth element RH diffused in the grain boundary phase. Further, if the heavy rare earth element RH substitution is performed in the R2Fe 14 B crystal structure, since the magnetic moment of the heavy rare earth element RH is antiferromagnetically coupled with the magnetic moment of Fe, the residual magnetic flux density decreases. In contrast, in the rare earth sintered magnet 1 of the present embodiment, a grain boundary phase 3 is formed, and the grain boundary phase 3 has a heavy rare earth element RH enrichment portion 5 in which the heavy rare earth element RH is enriched in at least a part of the periphery of the Sm-rich portion 4. It is considered that this is the result of the heavy rare earth element RH selectively diffusing to at least a part of the periphery of the Sm-rich portion 4 in the grain boundary phase 3 in the grain boundary diffusion step 31. Therefore, by the selective grain boundary diffusion of the heavy rare earth element RH in the periphery of the Sm-rich portion 4, the penetration of the heavy rare earth element RH into the main phase 2 can be suppressed. Thereby, a decrease in magnetic properties can be suppressed. Further, since the heavy rare earth element RH that has conventionally penetrated into the main phase and has been wasted diffuses into the grain boundary phase 3, the heavy rare earth element RH can be diffused into the rare earth sintered magnet 1 compared with the conventional grain boundary diffusion method.

[0031] In addition, the Sm-rich portion 4 is distributed not only on the surface layer of the rare earth sintered magnet 1 but also in the entire grain boundary phase 3 up to the central portion. Therefore, the selective grain boundary diffusion of the heavy rare earth element RH in the periphery of the Sm-rich portion 4 distributed from the surface layer to the central portion of the rare earth sintered magnet 1 occurs. As a result, the heavy rare earth element RH remaining in the grain boundary phase 3 such as the grain boundary multiple point phase (grain boundary multiple point phase) is reduced, and the heavy rare earth element RH can be diffused into the rare earth sintered magnet 1 compared with the conventional grain boundary diffusion method.

[0032] Thus, regarding the rare earth sintered magnet 1 in the present embodiment, it is formed into a structure having a grain boundary phase 3, and the grain boundary phase 3 has: a Sm-enriched portion 4 in which Sm substitution and Sm enrichment are performed in a crystalline NdO phase; and a heavy rare earth element RH-enriched portion 5 in which a heavy rare earth element RH is enriched in at least a part of the periphery of the Sm-enriched portion 4. Therefore, while suppressing a decrease in magnetic properties, the heavy rare earth element RH can be further diffused into the interior of the rare earth sintered magnet 1.

[0033] In addition, by further diffusing the heavy rare earth element RH into the interior of the rare earth sintered magnet 1, the grain boundary diffusion rate is increased, and effects such as shortening of the grain boundary diffusion time, resource saving of the heavy rare earth element RH, and reduction of the coercivity difference between the surface layer and the central portion of the rare earth sintered magnet 1 are achieved.

[0034] It should be noted that if the content of Sm is too large, the content of Nd, which is an element with a high magnetic anisotropy constant and high saturation magnetic polarization, is relatively reduced, and a decrease in magnetic properties may be caused. Therefore, the composition ratio of Nd and Sm in the entire rare earth sintered magnet 1 can be set to Nd > Sm, and regarding Sm, it can be made to have a high concentration in the grain boundary phase 3 compared to the main phase 2. Thus, it is possible to reduce Sm that substitutes for the Nd site in the Nd2Fe 14 B crystal structure and suppress a decrease in the magnetic properties of the main phase 2.

[0035] In addition, regarding the heavy rare earth element RH, if it exists in the main phase 2, it contributes to an increase in coercivity. However, regarding the magnetic moment of the heavy rare earth element RH, since it is antiferromagnetically coupled with the magnetic moment of Fe, the residual magnetic flux density is reduced. Therefore, by making the heavy rare earth element RH have a high concentration in the grain boundary phase 3 compared to the main phase 2, it is possible to maintain magnetic properties that take both high residual magnetic flux density and coercivity into account, and at the same time save resources of the scarce heavy rare earth element RH.

[0036] In addition, as the light rare earth element RL, La can be contained. If the heavy rare earth element RH is diffused along the grain boundary in the rare earth sintered magnet 1 containing La, the heavy rare earth element RH substitutes for La existing in the grain boundary phase 3. Thus, it is possible to further diffuse the heavy rare earth element RH into the interior of the rare earth sintered magnet 1.

[0037] In addition, an additive element for improving magnetic properties may also be contained. Regarding the additive element, for example, it is one or more elements selected from Al, Cu, Co, Zr, Ti, Ga, Pr, Nb, Mn, Gd, and Ho.

[0038] Embodiment 2.

[0039] This embodiment is a method for manufacturing the rare earth sintered magnet 1 in Embodiment 1. Use Figure 2 and Figure 3 will be described. Figure 2A flowchart showing the steps of the method for manufacturing the rare earth sintered magnet 1 in the present embodiment. Figure 3 A schematic diagram showing the operations of the raw material alloy production process 11. Hereinafter, the raw material alloy production process 11, the sintered magnet production process 21, and the grain boundary diffusion process 31 will be described.

[0040] (Raw material alloy production process 11)

[0041] As Figure 2 and Figure 3 shown in, the raw material alloy production process 11 includes: a melting process 12 of heating the raw materials of the rare earth magnet alloy 47 to a temperature of 1000 K or higher to melt them; a primary cooling process 13 of cooling the molten raw materials on a rotating body 44 to obtain a solidified alloy 45; and a secondary cooling process 14 of further cooling the solidified alloy 45 in a tray container 46.

[0042] The melting process 12 melts the raw materials of the rare earth magnet alloy 47 to produce an alloy melt 42. The raw materials include Nd, Fe, B, and Sm. Additionally, La, Dy, and Tb may also be included, and as additive elements, one or more elements selected from Al, Cu, Co, Zr, Ti, Ga, Pr, Nb, Mn, Gd, and Ho may also be included. For example, as Figure 3 shown in, in an atmosphere containing an inert gas such as Ar or in a vacuum, the raw materials of the rare earth magnet alloy 47 are heated to a temperature of 1000 K or higher in a crucible 41 to be melted, producing an alloy melt 42.

[0043] Regarding the primary cooling process 13, for example, as Figure 3 shown in, the alloy melt 42 is poured into a tundish 43 and rapidly cooled on a rotating body 44 to produce a solidified alloy 45 that is thinner in thickness than an ingot alloy. Additionally, Figure 3 shows an example where a single roll is used as the rotating body 44, and it is also possible to rapidly cool by contacting a twin roll, a rotating disk, or a rotating cylindrical mold, etc. To efficiently produce a solidified alloy 45 with a thin thickness, the cooling rate in the primary cooling process 13 is 10 to 10 7 °C / second, preferably 10 3 to 10 4 °C / second. The thickness of the solidified alloy 45 is 0.03 mm or more and 10 mm or less. Regarding the alloy melt 42, solidification starts from the part in contact with the rotating body 44, and crystals grow in a columnar or needle-like shape in the thickness direction from the contact surface with the rotating body 44.

[0044] Regarding the secondary cooling process 14, for example, as Figure 3As shown, the solidified alloy 45 is cooled in the tray container 46. When the thin solidified alloy 45 enters the tray container 46, it is crushed into flaky rare-earth magnet alloy 47 and cooled. In addition, an example where the rare-earth magnet alloy 47 is flaky is shown, but depending on the cooling rate, a ribbon-shaped rare-earth magnet alloy 47 is manufactured. In order to obtain a rare-earth magnet alloy 47 having an optimal internal structure in the rare-earth magnet alloy, the cooling rate in the secondary cooling process 14 is 0.01 to 10 5 °C / second, preferably 0.1 to 10 2 °C / second.

[0045] Through the raw material alloy production process 11 like this, an R-Fe-B-based rare-earth magnet alloy 47 containing Nd and Sm as the rare-earth element R is produced.

[0046] (Sintered magnet production process 21)

[0047] As Figure 2 shown, the sintered magnet production process 21 includes: a crushing process 22 for crushing the rare-earth magnet alloy 47 produced in the above raw material alloy production process 11; a molding process 23 for molding the crushed rare-earth magnet alloy 47 to produce a molded body; and a sintering aging process 24 for sintering and aging the molded body.

[0048] In the crushing process 22, the R-Fe-B-based rare-earth magnet alloy 47 containing Nd and Sm as the rare-earth element R produced through the above raw material alloy production process 11 is crushed to produce powder with a particle size of 200 μm or less, preferably 0.5 μm or more and 100 μm or less. Regarding the crushing of the rare-earth magnet alloy 47, for example, an agate mortar, a disintegrator, a jaw crusher, a jet mill, etc. are used. In addition, in order to reduce the particle size of the powder, the crushing process 22 can be carried out in an atmosphere containing an inert gas. Furthermore, the crushing of the rare-earth magnet alloy 47 is carried out in an atmosphere containing an inert gas, thereby being able to suppress the mixing of oxygen into the powder. When the atmosphere during crushing has no influence on the magnetic properties of the magnet, the crushing of the rare-earth magnet alloy 47 can also be carried out in the air.

[0049] In the molding process 23, the powder of the rare-earth magnet alloy 47 is molded to produce a molded body. Regarding molding, for example, the powder of the rare-earth magnet alloy 47 can be directly compression molded, or a product obtained by mixing the powder of the rare-earth magnet alloy 47 and an organic binder can be compression molded. In addition, molding can also be carried out while applying a magnetic field. The applied magnetic field is, for example, 2T.

[0050] The sintering aging process 24 includes a sintering process and an aging process.

[0051] In the sintering process, the green compact is heat-treated. Regarding the conditions for sintering treatment, the temperature is 600°C or higher and 1300°C or lower, and the time is 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter. Additionally, for magnetic anisotropy and coercivity improvement, hot working can be added.

[0052] Next, in the aging process, the green compact is heat-treated at a temperature lower than that of the sintering process to produce a sintered body. Regarding the conditions for aging treatment, at a temperature lower than that of the sintering process, for example, 300°C or higher and 1000°C or lower, and the time is 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter. Additionally, for example, it can be divided into two stages such as a primary aging process and a secondary aging process. At this time, the primary aging process is at a temperature below the sintering temperature, preferably 300°C or higher and 1000°C or lower. The time is 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter. The secondary aging process is at a temperature lower than that of the primary aging process, and is 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter.

[0053] Regarding the sintering and aging process 24, in order to suppress oxidation, it is preferably carried out in an atmosphere containing an inert gas or in a vacuum. Additionally, it can be carried out while applying a magnetic field.

[0054] Through the sintering and aging process 24, a sintered body can be produced, which includes: multiple main phases 2 having an R2Fe 14 B crystal structure containing at least Nd as the rare earth element R; and a grain boundary phase 3 having a Sm enrichment part 4 in which Sm is substituted and Sm is enriched in the crystalline NdO phase.

[0055] (Grain boundary diffusion process 31)

[0056] As Figure 2 shown, the grain boundary diffusion process 31 includes: an attachment process 32 for attaching a heavy rare earth element RH to the sintered body produced in the above sintered magnet manufacturing process 21 to produce a diffusion precursor; and a diffusion process 33 for heat-treating the diffusion precursor to cause the heavy rare earth element RH to undergo grain boundary diffusion. In the diffusion process 33, the heavy rare earth element RH is selectively diffused into at least a part of the grain boundary phase 3 surrounding the Sm enrichment part 4. Regarding the grain boundary diffusion process 31, a known grain boundary diffusion method can be used. Regarding the grain boundary diffusion method, various techniques have been proposed according to the supply form of the heavy rare earth element RH, and the coating diffusion method, the sputtering diffusion method, and the vapor diffusion method are representative. Additionally, the grain boundary diffusion process 31 can also be carried out simultaneously with the sintering and aging process 24.

[0057] The grain boundary diffusion process 31 using the coating and diffusion method will be described. In the attaching process 32, a slurry obtained by mixing a powdery heavy rare earth element RH compound in water, an organic solvent, or the like is attached to the surface of the sintered body to produce a diffusion precursor. For the attachment, spraying, dip coating, spin coating, screen printing, electrodeposition, or the like is used. In the diffusion process 33, the heavy rare earth element RH is diffused into the interior of the diffusion precursor by heat-treating the diffusion precursor at a temperature lower than the sintering treatment temperature. Regarding the heat treatment conditions, the temperature is lower than the temperature of the sintering process, for example, 300°C or higher and 1000°C or lower, and the time is set to 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter.

[0058] Next, the grain boundary diffusion process 31 using the sputtering diffusion method will be described. In the attaching process 32, a thin film composed of a heavy rare earth element RH elemental metal or alloy is formed on the surface of the sintered body in a dry environment to produce a diffusion precursor. In the diffusion process 33, the heavy rare earth element RH is diffused into the interior of the diffusion precursor by heat-treating the diffusion precursor at a temperature lower than the sintering treatment temperature. Regarding the heat treatment conditions, the temperature is lower than the temperature of the sintering process, for example, 300°C or higher and 1000°C or lower, and the time is set to 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter.

[0059] Next, the grain boundary diffusion process 31 using the vapor diffusion method will be described. In the attaching process 32, the sintered body and the heavy rare earth element RH supply source are arranged in a vacuum furnace. In the diffusion process 33, the heavy rare earth element RH is diffused into the interior of the diffusion precursor by heat-treating the diffusion precursor at a temperature lower than the sintering treatment temperature. Regarding the heat treatment, the heavy rare earth element RH is supplied to the diffusion precursor through vacuum heating via the gas phase. Regarding the heat treatment conditions, the temperature is lower than the temperature of the sintering process, for example, 600°C or higher to 900°C or lower, and the time is set to 0.1 hour or longer and 100 hours or shorter, preferably 1 hour or longer and 20 hours or shorter. In addition, regarding the vapor diffusion method, since the attaching process 32 and the diffusion process 33 of the heavy rare earth element RH can be performed simultaneously, the time of the grain boundary diffusion process 31 can be shortened.

[0060] Through the grain boundary diffusion process 31, the rare earth sintered magnet 1 having the grain boundary phase 3 can be produced. The grain boundary 3 has a heavy rare earth element RH enrichment portion 5 in which at least a part of the heavy rare earth element RH is enriched on the periphery of the Sm enrichment portion 4. In addition, regarding the rare earth sintered magnet 1 having a thickness of 10 mm produced by the manufacturing method of the present embodiment, the coercivity difference between the surface layer and the central portion of the rare earth sintered magnet 1 is 20% or less. It is considered that this is because the heavy rare earth element RH diffuses into the interior of the rare earth sintered magnet 1, so the coercivity difference between the surface layer and the central portion of the rare earth sintered magnet 1 becomes smaller.

[0061] Thus, regarding the manufacturing method of the rare earth sintered magnet 1 in the present embodiment, the R-Fe-B-based rare earth magnet alloy 47 containing Nd and Sm as the rare earth element R is pulverized. For the compact of the powder of the R-Fe-B-based rare earth magnet alloy 47, a sintered body having a Sm-rich portion 4 with Sm enrichment in a part of the grain boundary phase 3 is produced through the sintering aging process 24, and the heavy rare earth element RH is diffused into the sintered body at the grain boundary. Thus, the rare earth sintered magnet 1 having a heavy rare earth element RH-rich portion 5 in which the heavy rare earth element RH is enriched in at least a part of the periphery of the Sm-rich portion 4 in the grain boundary phase 3 can be produced. Thereby, while suppressing the deterioration of magnetic properties, the heavy rare earth element RH can be further diffused into the interior of the rare earth sintered magnet 1.

[0062] In addition, for example, as described in Patent Document 1, if a fluoride powder is mixed in the rare earth magnet alloy, it is possible that the rare earth magnet alloy and the fluoride powder are not uniformly mixed. In contrast, regarding the manufacturing method of the rare earth sintered magnet 1 of the present embodiment, in the melting process 12 of the raw material alloy manufacturing process 11, the raw materials of the rare earth magnet alloy 47 containing Sm are melted to produce an alloy melt 42. Therefore, elements such as Nd, Fe, and B are uniformly mixed with Sm. Thereby, the rare earth sintered magnet 1 in which the Sm-rich portion 4 is uniformly distributed not only on the surface layer of the rare earth sintered magnet 1 but also in the entire grain boundary phase 3 up to the central portion can be produced.

[0063] In addition, regarding the manufacturing method of the rare earth sintered magnet 1 of the present embodiment, instead of forming a new compound such as neodymium fluoride in the grain boundary phase, a part of the Nd sites of the crystal structure of the NdO phase of the grain boundary phase 3 generated during the above-mentioned sintered magnet manufacturing process 21 is replaced with Sm, which is the same light rare earth element as Nd, to form a Sm-rich portion 4 with Sm enrichment. Thereby, the deterioration of magnetic properties can be suppressed.

[0064] It should be noted that although an example of producing a compact by compression molding in the molding process 23 is shown, a product obtained by mixing the powder of the rare earth magnet alloy 47 and a resin may be heat-molded. The resin may be a thermosetting resin such as an epoxy resin, or a thermoplastic resin such as a polyphenylene sulfide resin may be used.

[0065] In addition, regarding the above-mentioned sintered body, a product produced by the single alloy method (one alloy method) or the double alloy method (two alloy methods) may also be used, and the rare earth sintered magnet 1 may be produced by diffusing the heavy rare earth element RH at the grain boundary therein.

[0066] Further, if La is added to the raw material of the rare earth magnet alloy 47, a sintered body in which La has a higher concentration in the grain boundary phase 3 than in the main phase 2 is produced. If the heavy rare earth element RH is subjected to grain boundary diffusion in this sintered body, the heavy rare earth element RH is replaced with La, thereby having an effect of promoting grain boundary diffusion. Thus, the heavy rare earth element RH can be further diffused into the interior of the rare earth sintered magnet 1 while suppressing a decrease in magnetic properties.

[0067] Next, the evaluation results of the magnetic properties of the rare earth sintered magnet 1 produced by the manufacturing method of the present embodiment will be described using Table 1. Table 1 is a table summarizing the evaluation results of the magnetic properties, with Examples 1 to 12 and Comparative Examples 1 to 8 in which the contents of Sm, La, Dy and Tb as the heavy rare earth element RH of the rare earth sintered magnet 1 or the thickness of the rare earth sintered magnet 1 are different as specimens. The coercivity difference in Table 1 is a value obtained by subtracting the coercivity of a magnet thickness of 7 mm from the coercivity of a magnet thickness of 1.75 mm.

[0068] Table 1 Evaluation Results of Magnetic Properties of Rare Earth Sintered Magnet 1

[0069]

[0070] Regarding the method for evaluating magnetic properties, a pulse excitation type BH tracer is used to measure the residual magnetic flux density and coercivity of the specimen. Regarding the maximum applied magnetic field using the BH tracer, it is 5 T or more to achieve a state where the specimen is completely magnetized. In addition to the pulse excitation type BH tracer, as long as a maximum applied magnetic field of 5 T or more can be generated, a DC self-recording fluxmeter, also known as a DC type BH tracer, a vibrating sample magnetometer (VSM), a magnetic property measurement system (MPMS), a physical property measurement system (PPMS), etc. can also be used. For the measurement, it is carried out in an atmosphere of an inert gas containing nitrogen and evaluated at room temperature.

[0071] Regarding the shape of each specimen, the specimen with a magnet thickness of 7 mm has a cubic shape with a length, width, and height all of 7 mm. Regarding the specimen with a magnet thickness of 1.75 mm, four products processed into a length of 7 mm, a width of 7 mm, and a height of 1.75 mm are overlapped and measured in a cubic shape of 7 mm.

[0072] The measurement error is ±1%.

[0073] Comparative Example 1 and Comparative Example 2 are specimens produced by using Nd, Fe, and B as raw materials for a rare earth magnet alloy in such a way that the general formula becomes Nd-Fe-B, according to the above manufacturing method, without performing the grain boundary diffusion process 31. Regarding the magnet thickness, it is 1.75 mm in Comparative Example 1 and 7 mm in Comparative Example 2. The magnetic properties of these specimens were evaluated by the above method. The remanent flux density is 1.39 T in both Comparative Example 1 and Comparative Example 2. The coercive forces are 1500 kA / m and 1502 kA / m, respectively. The coercivity difference is -2 kA / m, which is at the measurement error level. Regarding Comparative Example 1 and Comparative Example 2, since the grain boundary diffusion process 31 was not performed, almost no coercivity difference due to the magnet thickness was found.

[0074] Comparative Example 3 and Comparative Example 4 are specimens produced by using Nd, Sm, La, Fe, and B as raw materials for a rare earth magnet alloy in such a way that the general formula becomes (Nd, Sm, La)-Fe-B, according to the above manufacturing method, without performing the grain boundary diffusion process 31. Regarding the magnet thickness, it is 1.75 mm in Comparative Example 3 and 7 mm in Comparative Example 4. The magnetic properties of these specimens were evaluated by the above method. Regarding the remanent flux density, it is 1.36 T in Comparative Example 3 and 1.37 T in Comparative Example 4. The coercive forces are 1428 kA / m and 1425 kA / m, respectively. The coercivity difference is 3 kA / m, which is at the measurement error level. Regarding Comparative Example 3 and Comparative Example 4, since the grain boundary diffusion process 31 was not performed, almost no coercivity difference due to the magnet thickness was found.

[0075] Comparative Example 5 and Comparative Example 6 are specimens in which Dy is subjected to grain boundary diffusion according to the above manufacturing method by using Nd, Fe, and B as raw materials for a rare earth magnet alloy in such a way that the general formula becomes (Nd, Dy)-Fe-B. Regarding the magnet thickness, it is 1.75 mm in Comparative Example 5 and 7 mm in Comparative Example 6. The magnetic properties of these specimens were evaluated by the above method. Regarding the remanent flux density, it is 1.34 T in Comparative Example 5 and 1.33 T in Comparative Example 6. When comparing these results with those of Comparative Example 1 and Comparative Example 2, the remanent flux density decreased by adding Dy. The coercive forces are 1941 kA / m and 1720 kA / m, respectively. The coercivity difference is 221 kA / m. From this result, it is considered that for Comparative Example 6 with a magnet thickness of 7 mm, Dy did not sufficiently diffuse into the center of the magnet, resulting in a coercivity difference from Comparative Example 5 with a magnet thickness of 1.75 mm. In addition, compared with Comparative Example 1 and Comparative Example 2, the coercive force increased, but the remanent flux density decreased. This is the result that although the coercive force increased by performing grain boundary diffusion of Dy, the remanent flux density decreased because Dy penetrated into the main phase 2.

[0076] Comparative Example 7 and Comparative Example 8 are specimens in which Nd, Fe, and B are used as raw materials for a rare earth magnet alloy in such a way that the general formula becomes (Nd, Tb)-Fe-B, and Tb is subjected to grain boundary diffusion according to the above manufacturing method. Regarding the magnet thickness, it is 1.75 mm for Comparative Example 7 and 7 mm for Comparative Example 8. The magnetic properties of these specimens were evaluated by the above method. Regarding the residual magnetic flux density, it is 1.33 T for Comparative Example 7 and 1.34 T for Comparative Example 8. When comparing these results with Comparative Example 1 and Comparative Example 2, the residual magnetic flux density decreased by adding Tb. The coercivities were 2013 kA / m and 1821 kA / m, respectively. The coercivity difference was 92 kA / m. From these results, it is considered that for Comparative Example 8 with a magnet thickness of 7 mm, Tb did not sufficiently diffuse into the central part of the magnet, resulting in a coercivity difference from Comparative Example 7 with a magnet thickness of 1.75 mm. In addition, compared with Comparative Example 1 and Comparative Example 2, the coercivity increased, but the residual magnetic flux density decreased. This is the result that although the coercivity increased due to grain boundary diffusion of Tb, the residual magnetic flux density decreased because Tb penetrated into the main phase 2.

[0077] Examples 1 to 6 are specimens in which Nd, Sm, La, Fe, and B are used as raw materials for a rare earth magnet alloy 47 in such a way that the general formula becomes (Nd, Sm, La, Dy)-Fe-B, and Dy is subjected to grain boundary diffusion according to the above manufacturing method. The magnetic properties of these specimens were evaluated by the above method. As a result, compared with Comparative Example 5 and Comparative Example 6, the residual magnetic flux densities of Examples 1 to 6 were high values. This reflects the result of selectively diffusing Dy at least partially around the Sm-rich portion 4, thereby suppressing the penetration of Dy into the main phase 2. In addition, compared with Comparative Example 5 and Comparative Example 6, the coercivity difference became smaller. Furthermore, as the contents of Sm and La increased, the coercivity difference became smaller. This reflects the result of selectively diffusing Dy around the Sm-rich portion 4 distributed from the surface layer to the central part of the rare earth sintered magnet 1, thereby diffusing Dy into the rare earth sintered magnet 1 more than in the conventional grain boundary diffusion method. In addition, La exists in the grain boundary phase 3 and has the effect of promoting the penetration of Dy into the grain boundary.

[0078] Examples 7 to 12 are samples in which Nd, Sm, La, Fe, and B are used as raw materials for the rare-earth magnet alloy 47 in such a way that the general formula becomes (Nd, Sm, La, Tb)-Fe-B, and Tb is subjected to grain-boundary diffusion according to the above manufacturing method. The magnetic properties of these samples were evaluated by the above method. As a result, the residual magnetic flux density was a high value compared with Comparative Example 7 and Comparative Example 8. This is a result of selectively performing grain-boundary diffusion of Tb in at least a part of the periphery of the Sm-rich portion 4, thereby suppressing the penetration of Tb into the main phase 2. In addition, the difference in coercivity became smaller compared with Comparative Example 7 and Comparative Example 8. This is a result of selectively performing grain-boundary diffusion of Tb in the periphery of the Sm-rich portion 4 distributed from the surface layer to the central portion of the rare-earth sintered magnet 1, thereby diffusing Tb into the rare-earth sintered magnet 1 compared with the conventional grain-boundary diffusion method. In addition, La is present in the grain-boundary phase 3 and has the effect of promoting the penetration of Tb into the grain boundary. Furthermore, the difference in coercivity of Examples 7 to 12 became smaller compared with Examples 1 to 6. Thus, with respect to the heavy rare-earth element RH, Tb can obtain a higher effect than Dy.

[0079] Next, the evaluation results of the internal structure of the magnet of the rare-earth sintered magnet 1 produced by the manufacturing method of the present embodiment will be described.

[0080] Regarding the internal structure of the magnet, evaluation was performed by elemental analysis using a scanning electron microscope (SEM) and an electron probe micro analyzer (EPMA). Among them, as the SEM and EPMA, a field emission type electron probe micro analyzer (JXA-8530F manufactured by JEOL Ltd.) was used, and elemental analysis was performed under the evaluation conditions of acceleration voltage: 15.0 kV, irradiation current: 3.05 e -007 A, irradiation time: 10 ms, number of pixels: 256 pixels × 256 pixels, magnification: 5000 times, and number of accumulations: 5 times.

[0081] Figure 4 FIG. is for evaluating the cross section of the rare-earth sintered magnet 1 of Example 1 under the above evaluation conditions, Figure 4 A is a backscattered electron compositional image, Figure 4 B is a surface scan map (mapping diagram) of Nd, Figure 4 C is a surface scan map of Sm, Figure 4 D is a surface scan map of Dy, Figure 4 E is a surface scan map of La.

[0082] Figure 5 FIG. is for evaluating the cross section of the rare-earth sintered magnet 1 of Example 7 under the above evaluation conditions, Figure 5 A is a backscattered electron compositional image,Figure 5 B is the surface scan image of Nd, Figure 5 C is the surface scan image of Sm, Figure 5 D is the surface scan image of Tb, Figure 5 E is the surface scan image of La.

[0083] From Figure 4 and Figure 5 it can be confirmed that the rare earth sintered magnet 1 produced by the manufacturing method of the present embodiment has the following internal magnet structure.

[0084] From Figure 4 A and Figure 5 A, there is a grain boundary phase 3 formed between multiple main phases 2. From Figure 4 B and Figure 5 B, Nd exists throughout the grain boundary phase 3. From Figure 4 C and Figure 5 C, there is a Sm enrichment part 4 in a part of the grain boundary phase 3, and Sm is at a high concentration in the grain boundary phase 3 compared with the main phase 2. In addition, from Figure 4 D and Figure 5 D, at least a part of the grain boundary phase 3 on the periphery of the Sm enrichment part 4 has a heavy rare earth element RH enrichment part 5, and for the heavy rare earth element RH, it is at a high concentration in the grain boundary phase 3 compared with the main phase 2. From Figure 4 E and Figure 5 E, La exists throughout the grain boundary phase 3 in the same way as Nd.

[0085] Embodiment 3.

[0086] This embodiment uses the rotor 51 with the rare earth sintered magnet 1 in Embodiment 1. For the rotor 51 in this embodiment, Figure 6 will be described. Figure 6 is a schematic cross-sectional view perpendicular to the axial direction of the rotor 51.

[0087] The rotor 51 can rotate around the rotation axis 54. The rotor 51 includes: a rotor core 52, and the rare earth sintered magnet 1 inserted into the magnet insertion hole 53 provided along the circumferential direction of the rotor 51. In Figure 6 an example of using 4 magnet insertion holes 53 and 4 rare earth sintered magnets 1 is shown, but the numbers of the magnet insertion holes 53 and the rare earth sintered magnets 1 can be changed according to the design of the rotor 51. Regarding the rotor core 52, a disk-shaped electromagnetic steel sheet is laminated in the axial direction of the rotation axis 54 to form it.

[0088] The rare earth sintered magnet 1 is manufactured by the manufacturing method in Embodiment 2. Four rare earth sintered magnets 1 are respectively inserted into the magnet insertion holes 53. The four rare earth sintered magnets 1 are magnetized in such a manner that the magnetic poles of the rare earth sintered magnets 1 on the radially outer side of the rotor 51 are different from those of the adjacent rare earth sintered magnets 1.

[0089] Thus, for the rotor 51 in the present embodiment, by using the rare earth sintered magnet 1 in Embodiment 1 which can suppress the reduction of magnetic properties and at the same time enable the heavy rare earth element RH to further diffuse into the interior of the rare earth sintered magnet 1, the coercivity difference in the rare earth sintered magnet 1 is small while maintaining a high residual magnetic flux density. Therefore, even in a high-temperature environment exceeding 100°C, the reduction of magnetic properties is suppressed. As a result, even in a high-temperature environment exceeding 100°C, the operation of the rotor 51 can be stabilized.

[0090] Embodiment 4.

[0091] The present embodiment is a rotating machine 61 equipped with the rotor 51 in Embodiment 3. For the rotating machine 61 in the present embodiment, the following is used for Figure 7 explanation. Figure 7 It is a schematic cross-sectional view perpendicular to the axial direction of the rotating machine 61.

[0092] The rotating machine 61 includes: the rotor 51 in Embodiment 3, and an annular stator 62 which is arranged coaxially with the rotor 51 and is disposed opposite to the rotor 51. The stator 62 is formed by laminating a plurality of electromagnetic steel sheets in the axial direction of the rotating shaft 54. The configuration of the stator 62 is not limited thereto, and an existing configuration can be adopted. The stator 62 may be provided with a winding 63. The winding method of the winding 63 can be, for example, concentrated winding or distributed winding. The number of magnetic poles of the rotor 51 in the rotating machine 61 can be two or more, that is, the rare earth sintered magnet 1 can be two or more. In addition, in Figure 7 it shows an example of the magnet-inserted type rotor 51, and it can also be a surface magnet type rotor 51 in which the rare earth magnet is fixed to the surface of the outer peripheral portion with an adhesive.

[0093] Thus, for the rotating machine 61 in the present embodiment, by using the rare earth sintered magnet 1 in Embodiment 1 which can suppress the reduction of magnetic properties and at the same time enable the heavy rare earth element RH to further diffuse into the interior of the rare earth sintered magnet 1, the coercivity difference in the rare earth sintered magnet 1 is small while maintaining a high residual magnetic flux density. Therefore, even in a high-temperature environment exceeding 100°C, the reduction of magnetic properties is suppressed. As a result, even in a high-temperature environment exceeding 100°C, the rotor 51 can be stably driven and the operation of the rotating machine 61 can be stabilized.

[0094] Explanation of reference numerals

[0095] 1 Rare earth sintered magnet, 2 Main phase, 3 Grain boundary phase, 4 Sm enrichment part, 5 Heavy rare earth element RH enrichment part, 11 Raw material alloy production process, 12 Melting process, 13 Primary cooling process, 14 Secondary cooling process, 21 Sintered magnet production process, 22 Crushing process, 23 Forming process 23, 24 Sintering aging process, 31 Grain boundary diffusion process, 32 Coating process, 33 Diffusion process, 41 Crucible, 42 Alloy melt, 43 Tundish, 44 Rotating body, 45 Solidified alloy, 46 Tray container, 47 Rare earth magnet alloy, 51 Rotor, 52 Rotor core, 53 Magnet insertion hole, 54 Rotating shaft, 61 Rotating machine, 62 Stator, 63 Coil winding.

Claims

1. A rare earth sintered magnet, characterized in that, It includes: A plurality of main phases, each containing at least Nd and Sm as rare earth elements R and having an R2Fe 14 B crystal structure; and a grain boundary phase formed between the main phases, compared with the main phase, the grain boundary phase has a high concentration of Sm. In a part of the grain boundary phase, it has: a Sm enrichment part where Sm substitutes in the crystalline NdO phase and Sm is enriched; and a heavy rare earth element RH enrichment part where the heavy rare earth element RH is enriched in at least a part of the periphery of the Sm enrichment part, the heavy rare earth element RH enrichment part is selectively formed in the periphery of the Sm enrichment part, the Sm enrichment part is enriched to an extent that can be confirmed by elemental analysis using an electron probe microanalyzer.

2. The rare earth sintered magnet according to claim 1, wherein The heavy rare earth element RH enrichment part is formed in a manner that surrounds the entire periphery of the Sm enrichment part.

3. The rare earth sintered magnet according to claim 1 or 2, characterized in that, The heavy rare earth element RH enrichment part is enriched to an extent that can be confirmed by elemental analysis using an electron probe microanalyzer.

4. The rare earth sintered magnet according to claim 1 or 2, characterized in that, The Sm enrichment part is dispersed throughout the grain boundary phase from the surface layer to the central part of the rare earth sintered magnet.

5. The rare earth sintered magnet according to claim 1 or 2, characterized in that, Compared with the main phase, the heavy rare earth element RH has a high concentration in the grain boundary phase.

6. The rare earth sintered magnet according to claim 1 or 2, characterized in that, The rare earth element R includes La.

7. A method for manufacturing a rare earth sintered magnet according to any one of claims 1 to 6, which includes: a crushing step of crushing an R-Fe-B based rare earth magnet alloy containing Nd and Sm as the rare earth element R; a molding step of molding the powder of the R-Fe-B based rare earth magnet alloy to produce a molded body; a sintering and aging step of sintering the molded body at a temperature of 600 °C or higher and 1300 °C or lower and performing aging treatment at a temperature lower than the sintering temperature, thereby producing a sintered body; and a grain boundary diffusion step of attaching the heavy rare earth element RH to the sintered body and performing heat treatment, thereby causing the heavy rare earth element RH to undergo grain boundary diffusion.

8. The manufacturing method of the rare earth sintered magnet according to claim 7, characterized in that, The heat treatment in the grain boundary diffusion step is performed at a temperature lower than the sintering temperature.

9. A rotor, which includes: a rotor core; and the rare earth sintered magnet according to any one of claims 1 to 6 provided on the rotor core.

10. A rotating machine, which includes: the rotor according to claim 9; and a stator disposed opposite to the rotor.

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