RTB permanent magnets and their manufacturing methods, motors and automobiles

Abstract

This invention provides an R-T-B series permanent magnet with high remanent magnetic flux density Br and coercivity Hcj. R is one or more rare earth elements, with Tb or Dy as essential; T is one or more iron group elements, with Fe or Fe and Co as essential; B is boron; and the R-T-B series permanent magnet also contains Cu. The total content of R is 28.35% by mass to 29.95% by mass, the content of Cu is 0.05% by mass to 0.40% by mass, and the content of B is 0.93% by mass to 1.00% by mass. The concentration distribution of Tb or Dy decreases from the outside to the inside of the R-T-B series permanent magnet.

Description

Technical Field

[0001] This invention relates to an RTB-based permanent magnet, its manufacturing method, a motor, and an automobile. Background Technology

[0002] Rare-earth permanent magnets with an RTB (Remanent Magnetic Flux) composition possess excellent magnetic properties, and much research has been conducted to further improve these properties. As indicators of magnetic properties, remanent magnetic flux density (remanent magnetization) Br and coercivity Hcj are commonly used. It can be said that magnets with high values ​​of these parameters exhibit superior magnetic properties.

[0003] Patent document 1 describes a rare earth permanent magnet obtained by immersing a magnet body in a slurry made by dispersing micro-powders containing various rare earth elements in water or an organic solvent, and then heating it to allow the grain boundaries to diffuse.

[0004] Patent document 2 describes an RTB-type permanent magnet that uses Ga to improve coercivity.

[0005] Patent document 3 discloses a technique for obtaining high coercivity by reducing carbon content through dehydrogenation treatment without coarse crushing.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2006 / 043348

[0009] Patent Document 2: Japanese Patent Application Publication No. 2018-93202

[0010] Patent Document 3: International Publication No. 2014 / 017249 Summary of the Invention

[0011] The technical problem that the invention aims to solve

[0012] The purpose of this invention is to provide an RTB-based permanent magnet with high residual magnetic flux density Br and high coercivity Hcj.

[0013] Technical solutions for solving technical problems

[0014] To achieve the above objectives, a first aspect of the present invention provides an RTB-based permanent magnet.

[0015] R is one or more rare earth elements, with Tb or Dy as essential; T is one or more iron group elements, with Fe or Fe and Co as essential; B is boron; and the RTB-type permanent magnet also contains Cu.

[0016] The total content of R is 28.35% by mass or more and 29.95% by mass or less.

[0017] The Cu content is between 0.05% and 0.40% by mass.

[0018] The content of B is 0.93% by mass or more and 1.00% by mass.

[0019] The concentration distribution of Tb or Dy decreases from the outside to the inside of the RTB-based permanent magnet.

[0020] The residual magnetic flux density is above 1485 mT and the coercivity is above 1800 kA / m.

[0021] The RTB-type permanent magnet of the first aspect of the present invention, by having the above-described configuration, becomes a magnet with high remanent magnetic flux density and coercivity, specifically a magnet with a remanent magnetic flux density of 1485 mT or more and a coercivity of 1800 kA / m or more.

[0022] R can also be one or more rare earth elements for which Tb is essential.

[0023] The C content can also be below 750 ppm.

[0024] The nitrogen content can also be below 500 ppm.

[0025] The content of O can also be below 650 ppm.

[0026] It may also contain light rare earth elements as R, and the total concentration of light rare earth elements is distributed from the outside to the inside of the RTB-based permanent magnet.

[0027] The concentration distribution of Cu can also be a distribution that decreases from the outside to the inside of the RTB-based permanent magnet.

[0028] It may also contain Al, and the Al concentration distribution may decrease from the outside to the inside of the RTB-based permanent magnet.

[0029] It may also contain Co, and the concentration distribution of Co may decrease from the outside to the inside of the RTB-based permanent magnet.

[0030] It may also contain Ga, and the concentration distribution of Ga may decrease from the outside to the inside of the RTB-based permanent magnet.

[0031] The motor of the present invention has the aforementioned RTB-based permanent magnet.

[0032] The automobile of the present invention has the above-described motor.

[0033] A second aspect of this invention provides an RTB-based permanent magnet, wherein R is one or more rare earth elements essential as light rare earth elements, T is one or more iron group elements essential as Fe or Fe and Co, and B is boron. The RTB-based permanent magnet also contains Cu.

[0034] The total content of light rare earth elements is between 27.95% and 29.55% by mass.

[0035] The Cu content is between 0.05% and 0.40% by mass.

[0036] The content of B is 0.93% by mass or more and 1.00% by mass.

[0037] The C content is less than 750 ppm.

[0038] The nitrogen content is less than 500 ppm.

[0039] The O content is less than 650 ppm.

[0040] The second aspect of the present invention provides an RTB-based permanent magnet that, by having the above-described configuration, becomes an RTB-based permanent magnet whose magnetic properties are significantly improved through grain boundary diffusion.

[0041] The manufacturing method of the RTB-based permanent magnet of the present invention includes: a step of absorbing hydrogen into a raw material alloy, and a step of performing a dehydrogenation treatment on the raw material alloy after hydrogen absorption.

[0042] When performing dehydrogenation treatment on the hydrogen-absorbed raw material alloy, the dehydrogenation temperature is set to 50°C or higher and 200°C or lower, and the dehydrogenation time is set to 5 minutes or higher and 600 minutes or lower.

[0043] The H content in the coarsely crushed powder obtained by dehydrogenating the raw alloy after hydrogen absorption can also be above 2100ppm and below 3100ppm. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the RTB-based permanent magnet in this embodiment.

[0045] Figure 2 This is a SEM image of an RTB-based permanent magnet before grain boundary diffusion.

[0046] Figure 3 This is a SEM image of an RTB-based permanent magnet after grain boundary diffusion. Detailed Implementation

[0047] The present invention will now be described based on the embodiments shown in the accompanying drawings.

[0048] <RTB series permanent magnets>

[0049] The RTB-based permanent magnet 1 in this embodiment has an R2T 14 B crystals consist of the main phase particles and grain boundaries. Grain boundaries may also contain secondary phases that are not part of the main phase particles.

[0050] Furthermore, the main phase volume fraction of the RTB-based magnet is preferably 95.0% or higher. By having the main phase volume fraction within this range, the magnetic properties are easily improved. Specifically, regarding the main phase volume fraction, the RTB-based magnet capable of severing grain boundary diffusion is observed using SEM. The area fraction and main phase volume fraction of the main phase particles within this observation range are the same, and the main phase volume fraction is measured. In the SEM observation, an observation range is set to observe the size of at least 200 main phase particles at a magnification of 1000 to 3000x. Moreover, this observation range is set to 10 locations, and the main phase volume fraction within each observation range is measured and averaged. Thus, the main phase volume fraction of this embodiment can be determined.

[0051] The RTB-type permanent magnet 1 in this embodiment can be made into any shape.

[0052] The RTB-based permanent magnet 1 of this embodiment contains a variety of specific elements in a specific range, which can improve the remanent magnetic flux density Br and coercivity Hcj. Specifically, Br is 1485 mT or more, and Hcj is 1800 kA / m or more.

[0053] Furthermore, the RTB-based permanent magnet 1 of this embodiment has a distribution in which the concentration of Tb or Dy decreases from the outside to the inside of the RTB-based permanent magnet 1. In the following description, the case where the concentration of Tb decreases from the outside to the inside will be explained, but the same applies even if part or all of Tb is replaced with Dy. Among these, from the viewpoint of easily increasing Hcj, containing Tb is more preferable than containing Dy.

[0054] Specifically, such as Figure 1 As shown, in the case of the cuboid-shaped RTB-based permanent magnet 1 of this embodiment having a surface portion and a center portion, the Tb content of the surface portion can be 2% or more higher than the Tb content of the center portion, and can also be set to 5% or more or 10% or more. Furthermore, the aforementioned surface portion refers to the surface of the RTB-based permanent magnet 1. For example, Figure 1 Points C and C′ Figure 1 The center of gravity of the mutually facing surfaces is defined as the surface portion. The aforementioned center portion refers to the center of the RTB-based permanent magnet 1. For example, it refers to the portion that is half the thickness of the RTB-based permanent magnet 1. Figure 1Point M (the midpoint between point C and point C′) is the center.

[0055] Furthermore, the RTB-based permanent magnet 1 of this embodiment may also contain one or more light rare earth elements as R, and the concentration of the one or more light rare earth elements has a distribution that decreases from the outside to the inside of the RTB-based permanent magnet 1. In addition, the concentration of Cu may also have a distribution that decreases from the outside to the inside of the RTB-based permanent magnet 1.

[0056] There are no particular limitations on the method for achieving the aforementioned Tb concentration distribution. Tb concentration distribution within the magnet can be generated through Tb grain boundary diffusion, as described later. Furthermore, regarding the concentrations of one or more light rare earth elements, Cu, Al, Co, and Ga, by including Tb in the diffusion material used for grain boundary diffusion, it is possible to produce a concentration distribution for each element. Details will be described later. There are no particular limitations on the type of light rare earth element. For example, it can be Nd and / or Pr, or it can be only Nd.

[0057] R represents a rare earth element. Rare earth elements include Sc and Y, belonging to Group IIIB of the long-period periodic table, as well as lanthanides. Lanthanides include, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Furthermore, in the RTB-based permanent magnet of this embodiment (the RTB-based permanent magnet after grain boundary diffusion described later), Tb is included as R. As mentioned above, some or all of this Tb can be replaced with Dy. Additionally, it is preferable to include Nd as R.

[0058] Rare earth elements are generally classified into light rare earth elements and heavy rare earth elements. The light rare earth elements in the RTB-type permanent magnet of this embodiment are Sc, Y, La, Ce, Pr, Nd, Sm, and Eu, and the heavy rare earth elements are Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0059] T indicates that one or more iron group elements are essential, either Fe or Fe and Co. The iron group elements are Fe, Co, and Ni.

[0060] B stands for boron.

[0061] The RTB-type permanent magnet in this embodiment may also contain Cu, Al, Ga, Zr, O, C, and N.

[0062] The composition of the RTB-based permanent magnet of this embodiment will be described below. Unless otherwise specified, the parameters of the content of each element are the same as those of the magnet as a whole.

[0063] The total content of R is 28.35% by mass or more and 29.95% by mass or less. When the total content of R is less than 28.35% by mass, Hcj decreases. When the total content of R exceeds 29.95% by mass, Br decreases. Alternatively, the total content of R can also be set to 28.75% by mass or more and 29.95% by mass or less.

[0064] When the total content of light rare earth elements is set as TRL, TRL can be 27.95% by mass or 29.55% by mass, or 28.35% by mass or 29.55% by mass. Within this TRL range, it is possible to further increase the content of Br and Hcj.

[0065] As the aforementioned light rare earth elements, it may also contain at least Nd and / or Pr.

[0066] Alternatively, the total content of heavy rare earth elements can be less than 1.0% by mass. When the total content of heavy rare earth elements is less than 1.0% by mass, Br is easily maintained well. As a heavy rare earth element, it can be essentially only Tb. In this case, the Tb content can be between 0.20% by mass and 1.0% by mass, or between 0.40% by mass and 0.65% by mass. When the Tb content is less than 0.20% by mass, Hcj tends to decrease. When the Tb content exceeds 1.0% by mass, Br tends to decrease.

[0067] In this embodiment, the total content of R is relatively low, therefore, a higher Br content is expected. However, when the total content of R is low, sinterability sometimes decreases, and Hcj decreases drastically in cases of incomplete sintering.

[0068] There is no particular limitation on the Co content. It can be 0% by mass or more and 2.0% by mass or less. That is, it can also be Co-free. The Co content can also be 0.5% by mass or more and 1.5% by mass or less. When the Co content is within the above range, Br tends to be higher. Furthermore, in this embodiment, even when the Co content is low or Co is not present, sufficient corrosion resistance can be easily ensured. This is because the total R content is relatively low.

[0069] There are no particular restrictions on the Ni content, and it may also be Ni-free. For example, the Ni content may be less than 0.5% by mass.

[0070] The content of B is 0.93% to 1.00% by mass. It can also be 0.93% to 0.99% by mass, or 0.95% to 0.98% by mass. Regardless of whether the B content is too low or too high, the secondary phase tends to increase, making it difficult to increase Br. By keeping the B content within the above range, it is possible to further increase Br and Hcj.

[0071] The Cu content is 0.05% by mass to 0.40% by mass. When the Cu content is below 0.05% by mass, Br and Hcj decrease. When the Cu content exceeds 0.40% by mass, Br decreases. Alternatively, the Cu content can be 0.06% by mass to 0.30% by mass, or 0.06% by mass to 0.20% by mass. By containing 0.06% by mass or more of Cu, the deviation in properties becomes smaller. That is, manufacturing stability tends to improve.

[0072] There is no particular limitation on the Ga content. The Ga content can also be 0% by mass or less than 0.05% by mass. That is, it can also be Ga-free. The higher the Ga content, the easier it is to reduce Br. This is because the higher the Ga content, the easier it is to reduce the volume fraction of the main phase particles. Magnets with low B content and high Ga content have been known, but compared with the RTB-based permanent magnet of this embodiment, Br is easier to reduce.

[0073] There are no particular restrictions on the Al content. The Al content can also be between 0% by mass and 0.30% by mass. That is, it can also be Al-free. The Al content can also be between 0.06% by mass and 0.30% by mass.

[0074] There are no particular restrictions on the Zr content. It can be between 0% by mass and 0.40% by mass. That is, it can also be Zr-free. The Zr content can also be between 0.05% by mass and 0.40% by mass, or between 0.10% by mass and 0.25% by mass. By keeping the Zr content within the above ranges, Br and Hcj tend to increase. The lower the Zr content, the easier it is to decrease Hcj. The higher the Zr content, the easier it is to decrease Br.

[0075] There are no particular restrictions on the C content. It can be below 1000 ppm, below 790 ppm, or below 750 ppm. By setting the C content within the above range, it is easy to increase Br and Hcj. It is also possible to produce C-free permanent magnets, but manufacturing RTB-type permanent magnets with low C content places a heavy burden on the process, becoming the main reason for increased costs. The C content can be above 250 ppm or above 450 ppm.

[0076] There are no particular restrictions on the nitrogen (N) content. It can be below 900 ppm, 540 ppm, or 500 ppm. By setting the N content within the above range, it is easy to increase Br and Hcj. It is also possible to produce N-free permanent magnets, but manufacturing RTB-type permanent magnets with low N content places a heavy burden on the process, becoming a major reason for increased costs. The N content can be above 150 ppm or above 210 ppm.

[0077] There are no particular restrictions on the O content. It can be below 1000 ppm, below 700 ppm, or below 650 ppm. By setting the O content within the above range, it is easy to increase Br and Hcj. It is also possible to produce O-free permanent magnets, but manufacturing RTB-type permanent magnets with low O content places a heavy burden on the process and becomes the main reason for increased costs. The O content can be above 350 ppm or above 590 ppm.

[0078] There is no particular restriction on the Fe content. Fe can also be the substantial remainder in RTB-based permanent magnets. "Substantial remainder in RTB-based permanent magnets" means that the content of Fe and elements other than those mentioned above, i.e., the total content of elements other than R, Fe, Co, Ni, Cu, Al, Ga, Zr, O, C, and N, is less than 5% by mass. The total content of Fe and elements other than those mentioned above can also be less than 1% by mass or less than 0.1% by mass.

[0079] Furthermore, the determination of various components contained in the RTB-type permanent magnet of this embodiment can be performed using methods that are generally known. The amounts of various elements are determined by, for example, fluorescence X-ray analysis and inductively coupled plasma optical emission spectrometry (ICP analysis). The content of O is determined by, for example, inert gas melting-nondispersive infrared absorption. The content of C is determined by, for example, combustion in an oxygen stream-infrared absorption method. The content of N is determined by, for example, inert gas melting-thermal conductivity method.

[0080] Furthermore, the RTB-based permanent magnet of this embodiment contains multiple principal phase particles and grain boundaries. The principal phase particles can also be core-shell particles consisting of a core and a shell enclosing the core. Moreover, heavy rare earth elements, including Tb, can be present at least in the shell.

[0081] By including heavy rare earth elements in the shell, the magnetic properties of RTB-based permanent magnets can be effectively improved.

[0082] In this embodiment, the portion in which the ratio of heavy rare earth elements to light rare earth elements (heavy rare earth elements / light rare earth elements (molar ratio)) is more than twice the aforementioned ratio in the central part (core) of the main phase particle is defined as the shell.

[0083] There are no particular restrictions on the thickness of the shell; it can be less than 100 nm or less than 50 nm. Additionally, there are no particular restrictions on the particle size of the main phase particles; it can be between 2.5 μm and 6.0 μm.

[0084] The method for forming the core-shell particles described above from the main phase particles is arbitrary. For example, a method involving grain boundary diffusion, described later, can be used. Heavy rare earth elements diffuse at the grain boundaries, replacing the rare earth elements R on the surface of the main phase particles, thereby forming a shell with a high proportion of heavy rare earth elements, thus becoming the core-shell particles described above.

[0085] The manufacturing method of RTB-based permanent magnets will be described in detail below, but the manufacturing method of RTB-based permanent magnets is not limited to this and other known methods may also be used.

[0086] [Preparation process for raw material powder]

[0087] The raw material powder can be produced by known methods. In this embodiment, the single alloy method using a single alloy is described, but the raw material powder can also be produced by mixing a first alloy and a second alloy with different compositions, a so-called dual alloy method.

[0088] First, a raw material alloy for the RTB-based permanent magnet is prepared (alloy preparation process). In the alloy preparation process, a raw material metal corresponding to the composition of the RTB-based permanent magnet of this embodiment is melted using a known method and then cast, thereby producing a raw material alloy with the desired composition.

[0089] The raw material metals can be, for example, rare earth metals or rare earth alloys, pure iron, ferroborone, Co or Cu, and their alloys or compounds. The casting method for casting the raw material alloy from the raw material metal can be any method. To obtain RTB-type permanent magnets with high magnetic properties, thin-strip continuous casting can also be used.

[0090] After the above-mentioned raw material alloy is produced, it is pulverized (pulverization process). Hereinafter, as the above-mentioned pulverization process, it is described that it is carried out in two stages: a coarse pulverization process in which the particle size is pulverized to a degree of several hundred μm to several mm, and a micro pulverization process in which the particle size is pulverized to a degree of several μm.

[0091] In the coarse grinding process, the material is coarsely ground to a particle size of several hundred μm to several mm. This yields coarsely ground powder. In this embodiment, coarse grinding is performed by hydrogen absorption grinding. Hydrogen absorption grinding is a process in which the raw material alloy is subjected to hydrogen absorption followed by dehydrogenation treatment, thereby pulverizing the raw material alloy.

[0092] Furthermore, during the dehydrogenation process after hydrogen absorption, the dehydrogenation conditions were set to a lower temperature and shorter time than before. As a result, dehydrogenation was not fully carried out, intentionally leaving hydrogen (H) residues in the coarsely ground powder. Specifically, the dehydrogenation temperature was set to 50°C to 200°C, and the dehydrogenation time was set to 5 minutes to 600 minutes. The dehydrogenation time is preferably 5 minutes to 120 minutes, and more preferably 5 minutes to 30 minutes.

[0093] In this embodiment, when the total content of R is relatively low, the content of O, C, and N in the magnet tends to decrease. O, C, and N mostly combine with R other than the main phase particles to enter the magnet. When the total content of R is low, the amount of R combined with O, C, and N decreases, therefore, the content of O, C, and N also tends to decrease.

[0094] Here, by intentionally leaving H in the coarsely ground powder, R combines with H. As a result, the amount of R combined with O, C, and N is further reduced, and therefore, the content of O, C, and N is also easily reduced further. There is no particular limitation on the H content contained in the coarsely ground powder, but it is preferably set to 2100 ppm or more and 3100 ppm or less.

[0095] In existing sintered magnets manufactured by compression molding, if dehydrogenation treatment is not sufficiently performed during this stage, the pulverized powder is easily oxidized, resulting in a decrease in the final magnetic properties. However, by keeping the total R content relatively low, oxidation of the pulverized powder is suppressed even without sufficient dehydrogenation treatment, leading to excellent magnetic properties after grain boundary diffusion.

[0096] Alternatively, dehydrogenation can be omitted, but performing dehydrogenation at low temperature and for a short time is more likely to yield magnets with higher magnetic properties. Furthermore, without dehydrogenation, the excessive hydrogen content after coarse grinding makes it prone to cracking during sintering.

[0097] Furthermore, by controlling the nitrogen concentration in the atmosphere during the dehydrogenation process, the N content in the RTB-based permanent magnet can be further controlled. Similarly, by controlling the oxygen concentration in the atmosphere during the dehydrogenation process, the O content in the RTB-based permanent magnet can be further controlled. Specifically, it is preferable to set the nitrogen concentration in the atmosphere to 50 ppm or less, and it is also preferable to set the oxygen concentration to 50 ppm or less.

[0098] In addition, by setting the oxygen concentration in the atmosphere from the crushing process to the sintering process to below 100 ppm, the O content in RTB-based permanent magnets can be reduced.

[0099] Next, the coarsely ground powder is further pulverized to an average particle size of approximately several μm (micro-pulverization process). This yields micro-pulverized powder (raw material powder). The average particle size of the micro-pulverized powder can be between 2 μm and 5 μm. Furthermore, by controlling the nitrogen concentration in the atmosphere of the micro-pulverization process, the nitrogen content in the RTB-based permanent magnet can be controlled.

[0100] Micronization can be carried out by any method. For example, it can be carried out by using various micronizers.

[0101] When micronizing the aforementioned coarsely ground powder, by adding various pulverizing aids such as laurylamide and oleamide, it is possible to obtain micronized powder with high orientation during molding. Furthermore, by varying the amount of pulverizing aids added, the carbon content of the RTB-based permanent magnet can be controlled.

[0102] [Molding Process]

[0103] In the molding process, the aforementioned micro-pulverized powder is molded into the desired shape. Molding can be performed by any method. In this embodiment, the aforementioned micro-pulverized powder is filled into a mold and pressurized in a magnetic field. The principal phase particles of the resulting molded body are oriented in a specific direction, thus obtaining an RTB-based permanent magnet with a higher residual magnetic flux density Br.

[0104] The pressure applied during molding can be from 20 MPa to 300 MPa. The applied magnetic field can be set to 950 kA / m or higher, or from 950 kA / m to 1600 kA / m. The applied magnetic field is not limited to a static magnetic field and can also be set as a pulsed magnetic field. In addition, a static magnetic field and a pulsed magnetic field can be used together.

[0105] In addition, as described above, as a molding method, besides dry molding which directly shapes the micronized powder, wet molding can also be used to shape a slurry made by dispersing the micronized powder in a solvent such as oil.

[0106] The shape of the molded body obtained by molding the micronized powder can be set to any shape. Furthermore, the density of the molded body at this time can be set to 4.0 Mg / m³. 3 ~4.3Mg / m 3 .

[0107] [Sintering process]

[0108] The sintering process involves sintering a molded body in a vacuum or inert gas atmosphere to obtain a sintered body. The sintering temperature needs to be adjusted according to various conditions such as composition, grinding method, particle size, and particle size distribution. However, for molded bodies, for example, sintering is performed by heating at 1000°C to 1200°C for 1 to 20 hours in a vacuum or in the presence of an inert gas. This results in a high-density sintered body. In this embodiment, a minimum Mg / m³ of 7.45 was obtained. 3 The density of the sintered body is above that of the above-mentioned density. The density of the sintered body can also be 7.50 Mg / m³. 3 above.

[0109] [Aging Process]

[0110] The aging process is a heat treatment process that involves subjecting the sintered body to a temperature lower than the sintering temperature. There are no particular restrictions on whether or not to perform aging treatment, nor are there any particular restrictions on the number of aging treatments; the process is implemented appropriately based on the desired magnetic properties. Furthermore, the grain boundary diffusion process described later can also serve as an aging treatment process. In the RTB-based permanent magnet of this embodiment, two aging treatments are performed.

[0111] The first aging process is designated as the first aging process, the second aging process is designated as the second aging process, the aging temperature of the first aging process is designated as T1, and the aging temperature of the second aging process is designated as T2.

[0112] There are no particular restrictions on the temperature T1 and aging time in the first aging process. It can be set to 1 to 10 hours at temperatures between 700°C and 900°C.

[0113] There are no particular restrictions on the temperature T2 and aging time in the second aging process. It can be set to 1 hour to 10 hours at temperatures between 500℃ and 700℃.

[0114] Such aging treatment can improve the magnetic properties of the final RTB-based permanent magnets, especially Hcj.

[0115] The magnetic properties of the RTB-based permanent magnet obtained at this time are lower than those of existing RTB-based permanent magnets without grain boundary diffusion. However, when Tb grain boundaries are diffused through the process described later, Hcj increases significantly. Moreover, the RTB-based permanent magnet with Tb grain boundary diffusion exhibits higher magnetic properties than existing RTB-based permanent magnets with Tb grain boundary diffusion.

[0116] Furthermore, there are no particular restrictions on the composition of the RTB-based permanent magnets obtained at this time. For example,

[0117] It can also be an RTB-based permanent magnet, where R is one or more rare earth elements essential as light rare earth elements, T is one or more iron group elements essential as Fe or Fe and Co, B is boron, and it also contains Cu.

[0118] Alternatively, the total content of light rare earth elements can be between 27.95% and 29.55% by mass.

[0119] The Cu content is between 0.05% and 0.40% by mass.

[0120] The content of B is 0.93% by mass or more and 1.00% by mass.

[0121] The C content is less than 750 ppm.

[0122] The nitrogen content is less than 500 ppm.

[0123] The O content is less than 650 ppm.

[0124] In this embodiment, the content of R in the magnet before grain boundary diffusion is relatively low. Therefore, the overall composition of the magnet is close to R²T. 14 The stoichiometric ratio of B. As a result, R²T 14 The amount of rare earth elements (R) other than the main phase particles (B) is low. Furthermore, the contents of O, C, and N are also relatively low. Therefore, it is difficult for R to combine with O, R with C, and R with N. That is, it is difficult to form secondary phases other than the main phase particles. In addition, the proportion of active rare earth elements is increased, thus, even with a relatively low R content, it possesses sufficient sinterability.

[0125] In this embodiment, in the magnet before grain boundary diffusion, the proportion of principal phase particles increases, while the proportion of secondary phase particles other than principal phase particles decreases. Furthermore, the proportion of grain boundaries decreases. Figure 2 This is a SEM image obtained by observing the magnet before grain boundary diffusion. Compared with existing RTB-based permanent magnets, the grain boundary triple point is smaller, and the two-particle grain boundary phase is significantly finer, in particular. Furthermore, there are regions where the observed main phase particles are directly connected to each other without being connected by the two-particle grain boundary phase. Specifically, the average thickness of the two-particle grain boundary phase can be less than 5 nm or less than 2 nm. Moreover, at this point, the Hcj is significantly lower than that of existing magnets before grain boundary diffusion.

[0126] However, when the magnet before grain boundary diffusion described above is subjected to grain boundary diffusion using a Tb-containing diffusion material, Hcj is significantly increased. Furthermore, the proportion of the secondary phase is small, thus it is easier to obtain a magnet with high Br.

[0127] This is because even with a fine two-particle grain boundary phase, the diffusion of the diffusing material can proceed sufficiently. This sufficient diffusion is due to the smaller proportion of the secondary phase and the smaller size of the grain boundary triple point, which reduces the segregation of the diffusing material towards the secondary phase or the grain boundary triple point, and also because of the higher proportion of active rare earth elements as mentioned above. Furthermore, the relatively low total content of R suppresses the melting of the main phase particles caused by grain boundary diffusion. As a result, in the core-shell structure of the main phase particles after grain boundary diffusion, the thickness of the Tb-containing shell becomes thinner. Moreover, the Tb concentration in the shell increases. Therefore, the increase in Hcj caused by Tb diffusion is greater, resulting in a significant increase in Hcj.

[0128] The following describes a method for grain boundary diffusion of the sintered body obtained in the Tb direction as an RTB-based permanent magnet.

[0129] [Processing steps (before grain boundary diffusion)]

[0130] It may also include a process of machining the RTB-based permanent magnet of this embodiment into a desired shape as needed before grain boundary diffusion. Examples of machining methods include cutting, grinding, chamfering, etc.

[0131] [Grain boundary diffusion process]

[0132] Grain boundary diffusion can be achieved by attaching a diffusion material, such as a metal containing heavy rare earth elements, a compound containing heavy rare earth elements, or an alloy containing heavy rare earth elements, to the surface of an RTB-based permanent magnet through coating or vapor deposition, followed by heat treatment. In this embodiment, the heavy rare earth element is Tb. Grain boundary diffusion of heavy rare earth elements can further improve the Hcj of the final RTB-based permanent magnet. Tb is preferably used as the heavy rare earth element for grain boundary diffusion in the sintered body. Using Tb results in a higher Hcj.

[0133] In the embodiments described below, a coating containing Tb is prepared as a diffusion material and applied to the surface of an RTB-based permanent magnet.

[0134] The method of preparing the coating is arbitrary. What is used as the Tb-containing compound, or as the solvent or dispersion medium, is also arbitrary. Furthermore, the concentration of Tb in the coating is arbitrary. An example of a coating preparation method will be described below.

[0135] First, the raw material metal for the diffusion material is prepared. Tb is prepared as the raw material metal for the diffusion material. The raw material metal for the diffusion material can be Tb alone, or a combination of raw material metals containing Tb can be prepared. For example, light rare earth elements (e.g., Nd, Pr), Cu, Co, Fe, Al, Ga, Dy, or Nd, Cu, Co, and Pr can be prepared as raw material metals for the diffusion material other than Tb. In particular, Nd, Cu, and Tb can be used together as diffusion materials. Next, the molten metal obtained by melting the raw material metal for the diffusion material using a roller is quenched by high-frequency induction heating to produce a raw material alloy for the quenched thin strip of diffusion material. The obtained quenched thin strip is coarsely pulverized using a pulverizer in a glove box with Ar purging. Further, the coarsely pulverized raw material alloy of the diffusion material is sealed in a sealed container purged with an Ar atmosphere and pulverized to obtain diffusion material powder with an average particle size of 5–20 μm. Next, a slow oxidation treatment is performed. Specifically, air is gradually introduced into the sealed container with an Ar atmosphere. Slow oxidation is performed because there is a fire hazard when the powder is rapidly exposed to air.

[0136] Here, compared to the case where the diffusion material is only Tb, it is more preferable to use a diffusion material containing at least one element selected from Nd, Cu, Co, Pr, Al, and Ga in addition to Tb. The diffusion material may also contain at least one element selected from Nd, Cu, Co, and Pr in addition to Tb. There is no particular limitation on the proportion of Tb in the diffusion material. For example, the total diffusion material may be 100 parts by mass, or it may be 50 parts by mass or more. The melting point of Tb alone is 1356°C. In contrast, alloys containing at least one element selected from Nd, Cu, Co, Pr, Al, and Ga in addition to Tb have lower melting points. For example, the melting point of a Tb-Nd-Cu alloy varies depending on the content ratio of each element, but it can be set to 890°C or lower. That is, when the diffusion material contains at least one element selected from Nd, Cu, Co, Pr, Al, and Ga in addition to Tb, grain boundary diffusion can occur at low temperatures. Furthermore, Nd, Cu, Co, Pr, Al, and Ga are all components that form two-particle grain boundary phases. The two-particle grain boundary phase before grain boundary diffusion is very thin, thereby allowing the components that form the two-particle grain boundary phase to diffuse effectively. In the RTB-based permanent magnet of this embodiment, the two-particle grain boundary phase before grain boundary diffusion is very thin, therefore, the content of the components that form the two-particle grain boundary phase is low. Therefore, when the diffusion material contains components that form the two-particle grain boundary phase in addition to Tb, the concentration gradient generated by the concentration difference between the concentration of the components that form the two-particle grain boundary phase contained in the diffusion material and the concentration of the components that form the two-particle grain boundary phase contained in the two-particle grain boundary phase becomes larger. Moreover, the concentration gradient of the components that form the two-particle grain boundary phase becomes the driving force for the rapid diffusion of the components that form the two-particle grain boundary phase. As a result, it is believed that because the two-particle grain boundary phase before grain boundary diffusion is very thin, the components that form the two-particle grain boundary phase can diffuse effectively. Furthermore, the RTB-based permanent magnet of this embodiment can increase the volume fraction of the main phase after grain boundary diffusion compared to conventional RTB-based permanent magnets. As a result, it is able to maintain high Br and significantly increase Hcj.

[0137] Furthermore, if grain boundary diffusion is performed at low temperatures, the melting of the main phase particles generated during heat treatment can be reduced during the grain boundary diffusion process. As a result, the thickness of the shell containing the diffusing material in the core-shell structure of the main phase particles after grain boundary diffusion is reduced. Consequently, the concentration of Tb in the shell can be increased, and Hcj can be significantly improved.

[0138] Next, binder resin and alcohol are added to the obtained diffusion material powder, and the resulting mixture is coated using a ball mill to produce a coating material.

[0139] Next, a coating material is applied to the sintered body before grain boundary diffusion. Alternatively, the sintered body can be etched before coating. Then, the coating material is applied to the etched sintered body. There is no particular limitation on the number of surfaces coated. For example, all surfaces of the sintered body can be coated, or only two opposite surfaces of the sintered body can be coated.

[0140] In this embodiment, the diffusion temperature in the grain boundary diffusion process can be set to 650°C to 930°C. The diffusion time can be set to 5 hours to 24 hours. Furthermore, the grain boundary diffusion process can also be combined with the aforementioned aging process.

[0141] By setting the diffusion treatment temperature and time as described above, manufacturing costs are kept low, and the Tb concentration distribution can be easily set to an appropriate level. Furthermore, when using metal elements other than Tb (e.g., light rare earth elements (e.g., Nd, Pr), Cu, Co, Fe, Al, Ga, Dy) as the diffusion material, the concentration distribution of these metal elements can also be easily set to an appropriate level. Moreover, for… Figure 2 By performing a grain boundary diffusion process on the magnet, one can obtain... Figure 3 The magnet described. It can be known that in Figure 2 Very fine two-particle grain boundary phase in Figure 3 The thickness increases from medium to thick.

[0142] Alternatively, after grain boundary diffusion, further heat treatment can be performed. The heat treatment temperature can be set to 480℃~680℃, and the heat treatment time can be set to 0.5 hours~3 hours. This heat treatment can improve the magnetic properties, especially Hcj, of the final RTB-based permanent magnet.

[0143] [Processing steps (after grain boundary diffusion)]

[0144] Various processing techniques for RTB-based permanent magnets can be performed after the grain boundary diffusion process. There are no particular restrictions on the types of processing performed. For example, surface processing such as cutting, grinding, chamfering, etc., can also be performed.

[0145] The RTB-based permanent magnet obtained through the above method in this embodiment becomes an RTB-based permanent magnet product after being magnetized.

[0146] The RTB-based permanent magnet obtained in this embodiment possesses the desired characteristics. Specifically, it exhibits high remanent magnetic flux density Br and coercivity Hcj, as well as excellent corrosion resistance and manufacturing stability.

[0147] The RTB-type permanent magnet of this embodiment is preferably used in motors, generators, and the like. It is also preferably used in automobiles equipped with this motor.

[0148] Furthermore, the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention.

[0149] Example

[0150] The present invention will now be described with reference to more detailed embodiments, but the present invention is not limited to these embodiments.

[0151] (Experimental Example 1)

[0152] (Fabrication of RTB-based sintered magnets)

[0153] As raw materials, Nd, Pr, electrolytic iron, and low-carbon ferroborone alloys were prepared. Furthermore, Al, Ga, Cu, Co, and Zr were prepared in the form of pure metals or alloys with Fe.

[0154] Using the above-mentioned raw materials, raw material alloys were prepared by thin-strip continuous casting, with the final magnet composition obtained via grain boundary diffusion as described later, as shown in Table 1. The content of each component shown in Table 1 represents its content relative to the total mass of the magnet. The Fe content is defined as the remainder (bal.), meaning the portion remaining after removing impurities not listed in the table. Specifically, the total amount of impurities not listed in the table in each magnet is less than 5% by mass, provided it does not affect the magnetic properties. The alloy thickness of the above-mentioned raw material alloys is set to 0.2 mm to 0.4 mm.

[0155] Next, hydrogen gas was passed through the raw alloy at room temperature for 1 hour to allow it to absorb hydrogen. Then, the atmosphere was switched to Ar, and dehydrogenation treatment was performed at the dehydrogenation temperatures and times recorded in Tables 1 and 2. The raw alloy was then subjected to hydrogen-absorbing pulverization (coarse pulverization) to obtain coarsely pulverized powder. Furthermore, the nitrogen and oxygen concentrations in the atmosphere were controlled for each sample to ensure that the O and N content ratios in the final RTB-based sintered magnets were as recorded in Table 1. For each example and comparative example, the nitrogen concentration was kept to approximately 50 ppm and the oxygen concentration to approximately 50 ppm and below. After cooling, the powder was sieved to a particle size of 425 μm or less. Furthermore, from hydrogen-absorbing pulverization to the sintering process described later, a low-oxygen atmosphere with an oxygen concentration below 100 ppm was always maintained. Then, the hydrogen content of the cooled coarsely pulverized powder was determined using an inert gas-nondispersive infrared absorption spectrometer. The results are shown in Tables 1 and 2.

[0156] Next, oleic acid amide was added and mixed as a pulverizing aid to the powder of the raw alloy after hydrogen absorption pulverization and sieving, so that the content of C in the final RTB permanent magnet was as recorded in Table 1.

[0157] Next, the particles were micronized using a collision plate type spray mill to obtain micronized powder with an average particle size of 3.9 μm to 4.2 μm. Furthermore, the aforementioned average particle size is the average particle size D50 measured by a laser diffraction particle size analyzer.

[0158] The obtained micro-powder was shaped into molded bodies in a magnetic field. The applied magnetic field was a static magnetic field of 1200 kA / m. The applied pressure during shaping was set to 98 MPa. Furthermore, the direction of the applied magnetic field was orthogonal to the direction of the applied pressure. The density of the molded bodies was measured at this time, and the density of all molded bodies was found to be 4.10 Mg / m³. 3 ~4.25Mg / m 3 Within the range.

[0159] Next, the shaped body was sintered to obtain a sintered body. Sintering conditions were varied appropriately according to the composition, but maintained within the range of 1040℃ to 1100℃ for 5 hours. The sintering atmosphere was set to vacuum. At this point, the sintered density was 7.45 Mg / m³. 3 ~7.55Mg / m 3 The range is then determined. Then, in an Ar atmosphere and at atmospheric pressure, a first aging treatment is performed at a first aging temperature of 900°C for 2 hours, followed by a second aging treatment at a second aging temperature of 550°C for 2 hours.

[0160] Then, the sintered body after aging treatment is vertically machined into a size of 12mm×12mm×4.5mm (thickness 4.5mm in the direction of easy magnetization axis) to produce the sintered body before grain boundary diffusion, as described later.

[0161] Separated from the sintered body before grain boundary diffusion, Tb-containing coatings were prepared as diffusion materials. In Experimental Example 1, only Tb was prepared as the raw material metal for the diffusion material. Next, molten metal at 1370°C obtained by melting the raw material metal of the above diffusion material through high-frequency induction heating was quenched using a roller to prepare a raw material alloy (raw material alloy 1) for the quenched thin strip of diffusion material. The obtained quenched thin strip was coarsely pulverized using a stainless steel pulverizer under an Ar atmosphere. Then, the coarsely pulverized raw material alloy of diffusion material was sealed together with a stainless steel medium in a sealed container purged with an Ar atmosphere, and pulverized using a ball mill to obtain diffusion material powder with an average particle size of 10–20 μm. Next, a slow oxidation treatment was performed. Specifically, air was gradually introduced into the sealed container inside a glove box under an Ar atmosphere. The slow oxidation treatment was performed because there is a fire hazard when the powder is rapidly exposed to air.

[0162] A coating material for application was prepared by adding a binder resin (butyral micro powder) and ethanol to a prepared diffusion material powder. Specifically, firstly, 2 parts by weight of binder resin and 100 parts by weight of ethanol were added to 100 parts by weight of the diffusion material powder and mixed to obtain a mixture. Next, the resulting mixture was placed in a resin-made cylindrical container with a lid under an Ar atmosphere, and the container was placed on a ball mill stand and rotated to coat the material, thus preparing the coating material for application. The rotation time was set to 24 hours, and the rotation speed was set to 120 rpm.

[0163] Next, a coating material was applied to the sintered body before grain boundary diffusion. First, the sintered body before grain boundary diffusion was etched. During etching, the sintered body was immersed in a mixed solution of nitric acid and ethanol (100% by mass of ethanol and 3% by mass of nitric acid) for 3 minutes, followed by immersion in ethanol for 1 minute. This process was repeated twice. Next, the coating material was uniformly applied to both 12mm × 12mm surfaces of the etched sintered body. Furthermore, the coating material was applied to each sample with the final magnet composition shown in Table 1.

[0164] After the coating material was applied and dried, a diffusion treatment was performed at 950°C for 10 hours under atmospheric pressure while Ar was flowing through it. Following this, a heat treatment was performed at 550°C for 2 hours. Then, 0.1 mm was removed from each surface of the sample to obtain the RTB-based sintered magnets shown in Tables 1 and 2. Furthermore, TRL represents the total content of light rare earth elements (Nd and Pr), and TRE represents the total content of rare earth elements (Nd, Pr, and Tb).

[0165] The average composition of each RTB-based sintered magnet was determined. Each sample was pulverized using a pulverizer for analysis. The amounts of various elements were determined by fluorescence X-ray diffraction. The boron (B) content was determined by ICP analysis. The oxygen content was determined by inert gas melting-nondispersive infrared absorption spectrometry, the carbon content by combustion in an oxygen stream-infrared absorption spectrometry, and the nitrogen content by inert gas melting-thermal conductivity spectrometry. The results are recorded in Table 1.

[0166] The magnetic properties of the sintered body before and after grain boundary diffusion were evaluated using a BH hysteresis loop analyzer. Magnetization was performed using a pulsed magnetic field of 4000 kA / m, and the magnetic properties were then evaluated. Because the sintered magnets were thin, two overlapping sheets were used for evaluation. The results are shown in Table 2. Furthermore, the magnetic properties of the RTB-based sintered magnets after grain boundary diffusion were defined as good if Br ≥ 1485 mT and Hcj ≥ 1800 kA / m, and even better if Br ≥ 1500 mT and Hcj ≥ 1850 kA / m. The difference in Hcj before and after grain boundary diffusion is also recorded in Table 2.

[0167] In addition, the volume fraction of the main phase in the RTB-based magnet after grain boundary diffusion was measured. Specifically, the RTB-based magnet after grain boundary diffusion was cut off and observed using SEM. In the SEM observation, an observation range was set at 2500x magnification to observe at least 200 main phase particles. Furthermore, the area fraction and volume fraction of the main phase particles within this observation range were the same, and the main phase volume fraction was measured. In addition, a total of 10 such observation ranges were set in different locations, and the main phase volume fraction was measured within each observation range and averaged. The results are shown in Table 2.

[0168]

[0169] According to Table 1, all examples of samples 1-3, whose dehydrogenation temperature and time were set to increase the hydrogen content after coarse grinding, exhibited good magnetic properties. In particular, sample 2, with a low N content, and sample 3, with a low C content, showed even better magnetic properties. In contrast, all comparative examples of samples 4-6, whose dehydrogenation temperature and time were set to decrease the hydrogen content after coarse grinding, resulted in poor magnetic properties.

[0170] Furthermore, for all the RTB-based sintered magnets in the embodiments and comparative examples, the concentration distribution of Tb was analyzed using an electron probe microanalyzer (EPMA), confirming that the concentration distribution of Tb decreased from the outside to the inside.

[0171] (Experimental Example 2)

[0172] In Experiment 2, the same procedures as in Experiment 1 were followed, except for the points described below. The results are shown in Tables 3 and 4. Furthermore, the portions of Experiment 1 recorded in Table 1 are replaced with Table 3, and the portions recorded in Table 2 are replaced with Table 4.

[0173] In Experiment 2, the coating material was changed from that in Experiment 1. In Experiment 2, firstly, Tb, Nd, and Cu were prepared as elemental raw materials for the diffusion material. Next, each raw material metal was weighed in a mass ratio of Tb:Nd:Cu = 68.8:15.6:15.6. Then, the weighed raw materials were melted in an arc melting furnace and cast, and this process was repeated three times. The resulting alloy, melted at 1300°C by high-frequency induction heating, was quenched using a roller to produce a raw material alloy (raw material alloy 2) for the quenched thin strip of diffusion material. Subsequent processes were performed in the same manner as in Experiment 1 to produce the coating material for Experiment 2.

[0174] In grain boundary diffusion, after the above-mentioned coating material is applied and dried, a diffusion treatment is performed at 900°C for 10 hours while Ar flows under atmospheric pressure, followed by a heat treatment at 550°C for 2 hours.

[0175]

[0176]

[0177] According to Tables 3 and 4, all embodiments exhibit good magnetic properties. In contrast, in sample number 19 (total rare earth element content too low), samples 22 and 43 (total rare earth element content too high), sample number 24 (total Cu content too low), sample number 27 (total Cu content too high), sample numbers 28 and 29 (total B content too low), and sample number 39 (total Ga and C content high), Br and / or Hcj are all reduced. Furthermore, in cases of excessive total rare earth element content, excessive Cu content, insufficient B content, and high Ga and C content, the volume fraction of the main phase after grain boundary diffusion is small, and the difference in Hcj before and after grain boundary diffusion is also small. Comparative examples 40 and 41, where the dehydrogenation temperature and time were set to reduce the hydrogen content after coarse grinding, all showed poor magnetic properties. Additionally, samples 42 and 43, which did not undergo dehydrogenation treatment, developed cracks during sintering. This is attributed to the excessive hydrogen content after coarse grinding.

[0178] Furthermore, for all RTB-based sintered magnets in the embodiments and comparative examples, the concentration distributions of Tb, Nd, and Cu were analyzed using electron probe microanalysis (EPMA). The results confirmed that the concentration distributions of Tb, Nd, and Cu all decreased from the outside to the inside.

[0179] (Experimental Example 3)

[0180] In Experiment 3, the same procedures as in Experiment 2 were followed, except for the points described below. The results are shown in Tables 6 to 9. Furthermore, the portions of Experiment 2 recorded in Table 3 were replaced with Tables 6 and 8, and the portions recorded in Table 4 were replaced with Tables 7 and 9. Additionally, TRE represents the total content of rare earth elements (Nd, Pr, Tb, and Dy).

[0181] In Experiment 3, firstly, the raw materials for the diffusion materials were prepared in elemental form as shown in Table 5, including heavy rare earth elements, light rare earth elements, and metallic elements. Next, the raw materials for each diffusion material were weighed according to the mass ratios shown in Table 5. Then, the weighed raw materials for each diffusion material were melted in an electric arc melting furnace and cast. This process was repeated three times. The molten metal obtained by melting the alloy using high-frequency induction heating at a temperature of 1300°C was quenched using rollers to produce raw material alloys (raw material alloys 3-12) for the quenched thin strips of diffusion materials. Subsequent procedures were performed in the same manner as in Experiment 2 to produce the coating material for Experiment 3.

[0182] [Table 5]

[0183]

[0184] In Experiment 3, the coating of the coating material was adjusted so that the total amount of heavy rare earth elements adhering to the sintered body before grain boundary diffusion was 0.6 parts by mass relative to 100 parts by mass of the sintered body before grain boundary diffusion.

[0185] Regarding the magnetic properties of RTB-based sintered magnets after Tb grain boundary diffusion, the condition satisfying Br≥1485mT and Hcj≥1800kA / m is considered good, and the condition satisfying Br≥1500mT and Hcj≥1850kA / m is considered even better. Regarding the magnetic properties of RTB-based sintered magnets after Dy grain boundary diffusion, the condition satisfying Br≥1485mT and Hcj≥1400kA / m is considered good.

[0186]

[0187]

[0188]

[0189] Examples and comparative examples where Tb diffusion was performed are recorded in Tables 6 and 7. Samples 44-50, 52, and 53, whose dehydrogenation temperature and time were set to ensure sufficiently high hydrogen content after coarse grinding, all exhibited good magnetic properties. In contrast, comparative examples 54-60, 62, and 63, whose dehydrogenation temperature and time were set to ensure low hydrogen content after coarse grinding, similarly involved Tb diffusion, all showed poor magnetic properties.

[0190] Examples and comparative examples of Dy diffusion are described in Tables 8 and 9. Sample No. 51, in which the dehydrogenation temperature and time were set to ensure a sufficiently high hydrogen content after coarse grinding, exhibited good magnetic properties. In contrast, Sample No. 61, in which Dy was diffused in the same manner as Sample No. 51, but the dehydrogenation temperature and time were set to ensure a lower hydrogen content after coarse grinding, resulted in poor magnetic properties.

[0191] Furthermore, for all the RTB-based sintered magnets in the embodiments and comparative examples, the concentration distribution of elements contained in the raw material alloy of the diffusion material was analyzed using an electron probe microanalysis (EPMA). The results confirmed that the concentration distribution of the metallic elements in the raw material alloy of the diffusion material decreased from the outside to the inside.

[0192] Explanation of symbols

[0193] 1…RTB series permanent magnets

Claims

1. An RTB-based permanent magnet, wherein, R is one or more rare earth elements, with Tb or Dy as essential; T is one or more iron group elements, with Fe or Fe and Co as essential; B is boron; and the RTB-type permanent magnet also contains Cu. The total content of R is 28.35% by mass or more and 29.95% by mass or less. The Cu content is between 0.05% and 0.40% by mass. The content of B is 0.93% by mass or more and 1.00% by mass. The R element contains one or more light rare earth elements, and the concentration distribution of the one or more light rare earth elements decreases from the outside to the inside of the RTB-based permanent magnet. The concentration distribution of Tb or Dy decreases from the outside to the inside of the RTB-based permanent magnet. The residual magnetic flux density is above 1485 mT and the coercivity is above 1800 kA / m.

2. The RTB-based permanent magnet according to claim 1, wherein, R is one or more rare earth elements for which Tb is essential.

3. The RTB-based permanent magnet according to claim 1 or 2, wherein, The C content is less than 750 ppm.

4. The RTB-based permanent magnet according to claim 1 or 2, wherein, The nitrogen content is less than 500 ppm.

5. The RTB-based permanent magnet according to claim 1 or 2, wherein, The O content is less than 650 ppm.

6. The RTB-based permanent magnet according to claim 1 or 2, wherein, The concentration distribution of Cu decreases from the outside to the inside of the RTB-based permanent magnet.

7. The RTB-based permanent magnet according to claim 1 or 2, wherein, The RTB-based permanent magnet also contains Al, and the Al concentration distribution decreases from the outside to the inside of the RTB-based permanent magnet.

8. The RTB-based permanent magnet according to claim 1 or 2, wherein, The RTB-based permanent magnet also contains Co, and the concentration of Co decreases from the outside to the inside of the RTB-based permanent magnet.

9. The RTB-based permanent magnet according to claim 1 or 2, wherein, The RTB-based permanent magnet also contains Ga, and the Ga concentration distribution decreases from the outside to the inside of the RTB-based permanent magnet.

10. An RTB-based permanent magnet, wherein, R is one or more rare earth elements, with Tb or Dy as essential; T is one or more iron group elements, with Fe or Fe and Co as essential; B is boron; and the RTB-type permanent magnet also contains Cu. The total content of R is 28.35% by mass or more and 29.95% by mass or less. The Cu content is between 0.05% and 0.40% by mass. The content of B is 0.93% by mass or more and 1.00% by mass. The Ga content is between 0% by mass and 0.05% by mass. The concentration distribution of Tb or Dy decreases from the outside to the inside of the RTB-based permanent magnet. The residual magnetic flux density is above 1485 mT and the coercivity is above 1800 kA / m.

11. The RTB-based permanent magnet according to claim 10, wherein, R is one or more rare earth elements for which Tb is essential.

12. The RTB-based permanent magnet according to claim 10 or 11, wherein, The C content is less than 750 ppm.

13. The RTB-based permanent magnet according to claim 10 or 11, wherein, The nitrogen content is less than 500 ppm.

14. The RTB-based permanent magnet according to claim 10 or 11, wherein, The O content is less than 650 ppm.

15. The RTB-based permanent magnet according to claim 10 or 11, wherein, The R contains one or more light rare earth elements, and the concentration distribution of the one or more light rare earth elements decreases from the outside to the inside of the RTB-based permanent magnet.

16. The RTB-based permanent magnet according to claim 10 or 11, wherein, The concentration distribution of Cu decreases from the outside to the inside of the RTB-based permanent magnet.

17. The RTB-based permanent magnet according to claim 10 or 11, wherein, The RTB-based permanent magnet also contains Al, and the Al concentration distribution decreases from the outside to the inside of the RTB-based permanent magnet.

18. The RTB-based permanent magnet according to claim 10 or 11, wherein, The RTB-based permanent magnet also contains Co, and the concentration of Co decreases from the outside to the inside of the RTB-based permanent magnet.

19. The RTB-based permanent magnet according to claim 10 or 11, wherein, The concentration distribution of Ga decreases from the outside to the inside of the RTB-based permanent magnet.

20. A motor, wherein, It has an RTB-type permanent magnet as described in any one of claims 1 to 19.

21. A type of automobile, wherein, It has the motor as described in claim 20.

22. An RTB-based permanent magnet, wherein, R is one or more rare earth elements that are essential light rare earth elements, T is one or more iron group elements that are essential Fe or Fe and Co, B is boron, and the RTB-type permanent magnet also contains Cu. The total content of light rare earth elements is between 27.95% and 29.55% by mass. The Cu content is between 0.05% and 0.40% by mass. The Ga content is between 0% by mass and 0.05% by mass. The content of B is 0.93% by mass or more and 1.00% by mass. The C content is less than 750 ppm. The nitrogen content is less than 500 ppm. The O content is less than 650 ppm.

23. A method for manufacturing an RTB-based permanent magnet according to any one of claims 1 to 19 and 22, wherein, include: The process of absorbing hydrogen from the raw material alloy, and the process of dehydrogenating the raw material alloy after hydrogen absorption. When performing dehydrogenation treatment on the hydrogen-absorbed raw material alloy, the dehydrogenation temperature is set to 50°C or higher and 200°C or lower, and the dehydrogenation time is set to 5 minutes or higher and 600 minutes or lower.

24. The method for manufacturing an RTB-based permanent magnet according to claim 23, wherein, The H content in the coarsely crushed powder obtained by dehydrogenating the raw alloy after hydrogen absorption is above 2100ppm and below 3100ppm.

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