R-t-b based permanent magnet and method for producing the same

Abstract

An R-T-B based permanent magnet containing at least a rare earth element, Fe, Zr, Cu, B, C, O, and N, the content of the rare earth element being 28.50 mass% or more and 32.00 mass% or less, the content of Zr being 0.01 mass% or more and 0.50 mass% or less, the content of Cu being 0.04 mass% or more and 0.50 mass% or less, the content of Al being 0 mass% or more and 0.60 mass% or less, the content of Ga being 0 mass% or more and 0.80 mass% or less, the content of Co being 0 mass% or more and 3.50 mass% or less, the content of B being 0.88 mass% or more and 1.00 mass% or less, the content of C being 0.05 mass% or more and 0.12 mass% or less, the content of O being 0.11 mass% or more and 0.30 mass% or less, the content of N being 0.015 mass% or more and 0.07 mass% or less, and Fe being a substantial remainder, containing a heavy rare earth element as the rare earth element, the content of the heavy rare earth element being 0.03 mass% or more and 0.20 mass% or less.

Description

Technical Field

[0001] This disclosure relates to RTB-based permanent magnets and methods for manufacturing the same. Background Technology

[0002] Patent document 1 discloses an RTB-based permanent magnet that improves magnetic properties by having a composition within a specific range.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-8212 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] The purpose of this disclosure is to provide an RTB-based permanent magnet with low content of heavy rare earth elements and excellent magnetic properties, and a method for manufacturing the same.

[0008] Technical solutions for solving technical problems

[0009] To achieve the above objectives, this disclosure provides an RTB-based permanent magnet, wherein...

[0010] It contains at least rare earth elements, Fe, Zr, Cu, B, C, O, and N.

[0011] The rare earth element content is between 28.50% and 32.00% by mass.

[0012] The Zr content is between 0.01% by mass and 0.50% by mass.

[0013] The Cu content is between 0.04% and 0.50% by mass.

[0014] The Al content is between 0% by mass and 0.60% by mass.

[0015] The Ga content is between 0% by mass and 0.80% by mass.

[0016] The Co content is between 0% and 3.50% by mass.

[0017] The content of B is 0.88% by mass or more and 1.00% by mass or less.

[0018] The content of C is between 0.05% and 0.12% by mass.

[0019] The content of O is 0.11% by mass or more and 0.30% by mass or less, and

[0020] The nitrogen content is between 0.015% by mass and 0.07% by mass.

[0021] Fe is the actual remaining part.

[0022] It contains heavy rare earth elements as rare earth elements, with the content of heavy rare earth elements being more than 0.03% by mass and less than 0.20% by mass.

[0023] The residual magnetic flux density Br can also be above 1400mT, and the coercivity HcJ can also be above 1900kA / m.

[0024] The RTB-based permanent magnet may also include a main phase and a grain boundary triangular point surrounded by three or more main phases. The grain boundary triangular point may also be composed of rare earth oxide phase and low melting point grain boundary phase. The average equivalent circle diameter of the low melting point grain boundary phase may also be above 0.40 μm and below 1.00 μm.

[0025] The total area ratio of the low-melting-point grain boundary phase can also be above 1.5% and below 7.5%.

[0026] To achieve the above objectives, this disclosure provides a method for manufacturing an RTB-based permanent magnet, comprising:

[0027] The process of crushing an alloy to obtain alloy powder;

[0028] The process of compressing the alloy powder to obtain a shaped body;

[0029] The process of firing the shaped body to obtain a sintered body; and

[0030] The process of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment.

[0031] in,

[0032] The oxygen content of the alloy powder is controlled before the alloy powder is compressed and formed.

[0033] The alloy can also be coarsely pulverized by hydrogen adsorption to obtain coarse powder, or the coarse powder can be micro-pulverized to obtain alloy powder.

[0034] The coarse powder can also be finely pulverized using an air jet mill.

[0035] Alternatively, the coarse powder can be heat-treated under conditions where the oxygen concentration in the atmosphere is set to be between 0.5% and 23%, and the oxygen content of the alloy powder can be controlled.

[0036] Alternatively, the micro-pulverization can be carried out under the condition that the oxygen concentration in the atmosphere inside the airflow pulverizer is set to be between 0.01% and 0.30%, and the oxygen content of the alloy powder is controlled.

[0037] Alternatively, the micro-pulverization can be carried out under conditions where the internal atmosphere of the airflow pulverizer is a mixture of rare gases and oxygen, and the oxygen content of the alloy powder is controlled.

[0038] Alternatively, the coarse powder can be heat-treated under conditions where the oxygen concentration in the atmosphere is set to between 0.5% and 23%, and the micro-pulverization can be performed under conditions where the atmosphere inside the air jet mill is a mixture of rare gas and oxygen or a rare gas, while controlling the oxygen content of the alloy powder.

[0039] Alternatively, a step of performing a first aging treatment on the sintered body may be included before the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, and / or after the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment.

[0040] Alternatively, the first aging treatment step may be performed before the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment.

[0041] The aging temperature of the first aging treatment can also be above 850℃ and below 950℃, and the aging time of the first aging treatment can also be above 1.5 hours and below 10 hours.

[0042] Alternatively, after the first aging treatment, there may be a second aging treatment of the sintered body.

[0043] Alternatively, after the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, there is a step of performing the second aging treatment step. 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 the cross section of the sintered body before grain boundary diffusion in sample number 4.

[0046] Figure 3 This is a SEM image of the cross section of the sintered body before grain boundary diffusion in sample number 4.

[0047] Figure 4This is a SEM image of the cross-section of the sintered body before grain boundary diffusion in sample number 63.

[0048] Figure 5 This is a SEM image of the cross section of the sintered body before grain boundary diffusion in sample number 41.

[0049] Figure 6 This is a SEM image of the cross section of the sintered body before grain boundary diffusion in sample number 41.

[0050] Figure 7 It is Figure 2 The image obtained by binarization.

[0051] Figure 8 It is Figure 4 The image obtained by binarization. Detailed Implementation

[0052] The present disclosure will now be described based on embodiments shown in the accompanying drawings.

[0053] <RTB series permanent magnets>

[0054] The RTB-based permanent magnet of this embodiment has main phase particles, which contain R2T 14 B-type crystal structure grains. The RTB-based permanent magnet of this embodiment also has grain boundaries formed by two or more adjacent main phase grains. In particular, a line-shaped grain boundary formed by two adjacent main phase grains is called a two-grain grain boundary, and a grain boundary formed by three or more main phase grains is called a grain boundary trifle. A grain boundary trifle is, for example, a point.

[0055] In RTB system permanent magnets and R2T 14 In the B-type crystal structure, R represents rare earth elements, T represents transition metal elements, and B represents boron.

[0056] In RTB system permanent magnets and R2T 14 In a B-type crystal structure, the rare earth elements included as R can be Sc, Y, and lanthanides, or Y and lanthanides. Rare earth elements are not included among the transition metal elements included as T. The transition metal elements included as T can also be iron group elements. Part of the boron included as B can also be replaced by carbon.

[0057] There are no particular limitations on the shape of the RTB-type permanent magnet in this embodiment.

[0058] The RTB-based permanent magnet of this embodiment improves magnetic properties by containing multiple specific elements in a specific range, particularly increasing remanent magnetic flux density Br, coercivity HcJ, and rectangularity ratio Hk / HcJ. Furthermore, the aforementioned magnetic properties are all at room temperature (23±1℃).

[0059] Specifically, Br can be above 1400 mT, and the coercivity HcJ can be above 1900 kA / m. In addition, Hk / HcJ can be above 93.0%.

[0060] Furthermore, the RTB-based permanent magnet of this embodiment may also have a concentration distribution of heavy rare earth elements that decreases from the outside to the inside of the RTB-based permanent magnet. There are no particular limitations on the type of heavy rare earth element. For example, it can be Dy or Tb, or it can be Tb.

[0061] Specifically, such as Figure 1 As shown, the cuboid-shaped RTB-based permanent magnet 1 of this embodiment has a surface portion and a central portion. Based on mass, the content of heavy rare earth elements in the surface portion can be 2% or more, 5% or more, or 10% or more higher than the content of heavy rare earth elements in the central portion. Furthermore, the aforementioned surface portion refers to the surface of the RTB-based permanent magnet 1. For example, Figure 1 Point C and point C' ( Figure 1 The center of gravity of the opposing surfaces in the image is 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 1 Point M (the midpoint between point C and point C') is the center. Furthermore, Figure 1 Points C and C' can also be the centroid of the surface with the largest area in the RTB system permanent magnet 1, and the centroid of the surface opposite to that surface.

[0062] Generally, rare earth elements are divided into light rare earth elements and heavy rare earth elements. In this embodiment, the light rare earth elements in the RTB-based permanent magnet 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.

[0063] There are no particular limitations on the method for forming the aforementioned concentration distribution of heavy rare earth elements in the RTB-based permanent magnet of this embodiment. For example, the concentration distribution of heavy rare earth elements can be formed in the RTB-based permanent magnet through grain boundary diffusion of heavy rare earth elements, as described later.

[0064] Furthermore, the main phase particles of the RTB-based permanent magnet in this embodiment can also be core-shell particles consisting of a core and a shell enclosing the core. Moreover, heavy rare earth elements may be present in at least the shell, or Dy or Tb may be present, or Tb may be present.

[0065] By including heavy rare earth elements in the shell, the magnetic properties of RTB-based permanent magnets can be effectively improved.

[0066] 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 center of the main phase particles is defined as the shell. Furthermore, the aforementioned ratio in the center of the main phase particles may, for example, be defined as the aforementioned ratio in the portion extending from the particle surface of the main phase particles at a depth of 30% or more of the particle diameter.

[0067] There are no particular restrictions on the shell thickness, and the average value can be less than 500 nm. Similarly, there are no particular restrictions on the particle size of the main phase particles, and the average value can be between 1.0 μm and 6.5 μm. Furthermore, when calculating the above average values, the cross-section of the RTB-based permanent magnet can be observed using SEM (Scanning Electron Microscopy). Moreover, the observation range can be set to include the size of more than 50 core-shell particles. Furthermore, the shell thickness of all core-shell particles within the observation range can be measured and averaged. Additionally, the particle size of all main phase particles within the observation range can be measured and averaged. Furthermore, the observation range can be set to, for example, 100 μm × 100 μm.

[0068] There are no particular limitations on the method of setting the main phase particles as the core-shell particles described above. For example, there is the method of diffusion through grain boundaries, which will be described later. By diffusing heavy rare earth elements into the grain boundaries and replacing the rare earth elements on the surface of the main phase particles with those heavy rare earth elements, a shell with a high proportion of heavy rare earth elements is formed, thus creating the core-shell particles described above.

[0069] The RTB-based permanent magnet of this embodiment may contain at least one light rare earth element selected from Nd and Pr, and may also contain at least one heavy rare earth element selected from Dy and Tb. Furthermore, the RTB-based permanent magnet of this embodiment preferably contains at least Nd and Tb.

[0070] Regarding the RTB-based permanent magnet of this embodiment, when the total mass of the RTB-based permanent magnet is set to 100% by mass, the total content of rare earth elements other than Nd, Pr, Dy and Tb can be 0.3% by mass or less, and the total content of rare earth elements other than Nd, Pr and Tb can also be 0.3% by mass or less.

[0071] Regarding the total rare earth element (TRE) content in the RTB-based permanent magnet of this embodiment, when the total mass of the RTB-based permanent magnet is set to 100% by mass, the total rare earth element (TRE) content is 28.50% by mass or more and 32.00% by mass or less. When TRE is low, HcJ and Hk / HcJ tend to decrease. When TRE is high, Hk / HcJ tends to decrease.

[0072] There is no particular limitation on the total content of light rare earth elements in the RTB-based permanent magnet of this embodiment. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the total content of the light rare earth elements can be 28.30% by mass or more and 31.97% by mass or less.

[0073] When the RTB-based permanent magnet contains one or more of Nd and Pr, the Pr content can be 0.0% by mass or more and 10.0% by mass or less, or 0.0% by mass or more and 8.5% by mass or 0.0% by mass or less and 7.6% by mass or less.

[0074] Based on quality standards, the value obtained by dividing the Pr content by the total Nd and Pr content can also be above 0 and below 0.35.

[0075] Furthermore, regarding the RTB-based permanent magnet of this embodiment, when the total mass of the RTB-based permanent magnet is set to 100% by mass, the total content of heavy rare earth elements (TRH) is 0.03% by mass or more and 0.20% by mass or less. When the heavy rare earth elements are too low, HcJ is less likely to increase compared to the case where heavy rare earth elements are not present. When the heavy rare earth elements are too high, the raw material cost increases. Moreover, Br and Hk / HcJ tend to decrease.

[0076] The Fe content is essentially the remainder in RTB-based permanent magnets. This means that in RTB-based permanent magnets, besides the aforementioned rare earth elements and the elements B, Zr, Cu, Al, Ga, Co, C, O, and N (described later), the remainder is essentially only Fe.

[0077] When the Fe content is essentially the remainder of RTB-based permanent magnets, elements other than rare earth elements, Fe, B, Zr, Cu, Al, Ga, Co, C, O, and N do not have a significant impact on the magnetic properties of RTB-based permanent magnets.

[0078] For example, when the total mass of an RTB-based permanent magnet is set to 100% by mass, the content of elements other than rare earth elements, Fe, B, Zr, Cu, Al, Ga, Co, C, O, and N can be less than 0.10% by mass each, or less than 1.0% by mass in total. When the content of elements other than rare earth elements, Fe, B, Zr, Cu, Al, Ga, Co, C, O, and N is less than 0.10% by mass each, and less than 1.0% by mass in total, the Fe content is essentially the remaining portion of the RTB-based permanent magnet.

[0079] Regarding the boron (B) content in the RTB-based permanent magnet of this embodiment, when the total mass of the RTB-based permanent magnet is set to 100% by mass, the aforementioned B content is 0.88% by mass or more and 1.00% by mass or less. It can be 0.90% by mass or more and 1.00% by mass or less, or 0.92% by mass or more and 1.00% by mass or less. When B is low, the Hk / HcJ ratio tends to decrease. When B is high, the HcJ ratio tends to decrease.

[0080] The RTB-based permanent magnet of this embodiment also contains Zr. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the Zr content is 0.01% by mass to 0.50% by mass. It can be 0.04% by mass to 0.50% by mass, or 0.05% by mass to 0.50% by mass. Without Zr, HcJ and Hk / HcJ tend to decrease. With a high Zr content, Br tends to decrease.

[0081] The RTB-based permanent magnet of this embodiment also contains Cu. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the Cu content is 0.04% by mass to 0.50% by mass. It can be 0.08% by mass to 0.50% by mass, or 0.08% by mass to 0.30% by mass. With less Cu, HcJ tends to decrease. With more Cu, Br tends to decrease. Furthermore, regardless of the amount of Cu, Hk / HcJ tends to decrease.

[0082] The RTB-based permanent magnet of this embodiment may also contain Al. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the Al content is 0% by mass or more and 0.60% by mass or less. It may also be 0% by mass or more and 0.40% by mass or less. The RTB-based permanent magnet may not contain Al, but the less Al there is, the easier it is to reduce HcJ. In addition, when there is more Al, Br tends to decrease.

[0083] The RTB-based permanent magnet of this embodiment may also contain Ga. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the Ga content is 0% by mass or more and 0.80% by mass or less. It may also be 0.05% by mass or more and 0.70% by mass or less. The RTB-based permanent magnet may not contain Ga, but the less Ga there is, the easier it is to reduce HcJ. In addition, when there is more Ga, the easier it is to reduce Br.

[0084] The RTB-based permanent magnet of this embodiment may also contain Co. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the Co content is 0% by mass or less than 3.50% by mass. It can be 0.2% by mass or less than 3.20% by mass, or 0.3% by mass or less than 3.20% by mass. The RTB-based permanent magnet may also not contain Co, but the lower the Co content, the easier it is to reduce corrosion resistance. Furthermore, a higher Co content increases the cost.

[0085] The RTB-based permanent magnet of this embodiment also contains C. When the total mass of the RTB-based permanent magnet is set to 100% by mass, the C content is 0.05% by mass or more and 0.12% by mass or less. It can also be 0.05% by mass or more and 0.11% by mass or less. When C is low, HcJ tends to decrease. When C is high, HcJ and Hk / HcJ tend to decrease.

[0086] The RTB-based permanent magnet of this embodiment also contains oxygen (O). When the total mass of the RTB-based permanent magnet is set to 100% by mass, the O content is 0.11% by mass to 0.30% by mass. It can be 0.13% by mass to 0.29% by mass, or 0.13% by mass to 0.26% by mass. With less O, HcJ tends to decrease. With more O, Br and HcJ tend to decrease.

[0087] The RTB-based permanent magnet of this embodiment also contains nitrogen (N). When the total mass of the RTB-based permanent magnet is set to 100% by mass, the N content is 0.015% by mass or more and 0.07% by mass or less. It can also be 0.02% by mass or more and 0.07% by mass or less. Regardless of whether there is too much or too little N, HcJ tends to decrease.

[0088] The method for determining the various components contained in the RTB-based permanent magnet of this embodiment can employ conventionally known methods. The content of various elements can be determined, for example, by fluorescence X-ray analysis and inductively coupled plasma atomic emission spectrometry (ICP analysis). The content of O can be determined, for example, by inert gas melting-non-dispersive infrared absorption method. The content of C can be determined, for example, by combustion in an oxygen stream-infrared absorption method. The content of N can be determined, for example, by inert gas melting-thermal conductivity method.

[0089] There are no particular limitations on the shape of the RTB-type permanent magnet in this embodiment. For example, cuboid, C-shaped, and other shapes can be used.

[0090] Hereinafter, as an example of the manufacturing method of RTB-based permanent magnets in this embodiment, the manufacturing method of RTB-based sintered magnets will be described in detail. However, the manufacturing method of RTB-based permanent magnets is not limited to this, and other known methods may also be used.

[0091] [Preparation process of raw material powder]

[0092] The raw material powder can be produced by known methods. In this embodiment, the "single alloy method" using one alloy is described, but the so-called "two alloy method" can also be used, in which two or more alloys with different compositions are mixed to produce the raw material powder.

[0093] First, a raw material alloy for the RTB-based permanent magnet is prepared (alloy preparation process). In the alloy preparation process, after melting a raw material metal corresponding to the composition of the RTB-based permanent magnet of this embodiment using a known method, a raw material alloy having the desired composition is produced by casting.

[0094] As raw material metals, for example, elemental rare earth elements, elemental metallic elements such as Fe, or compounds composed of multiple elements (e.g., ferroborone) can be appropriately used. There are no particular restrictions on the casting method for casting the raw material alloy from the raw material metal. To obtain RTB-based permanent magnets with high magnetic properties, the strip casting method can also be used. The resulting raw material alloy can also be homogenized as needed using known methods.

[0095] After the above-mentioned raw material alloy is produced, it is pulverized (pulverization process). Furthermore, from the viewpoint of obtaining high magnetic properties, the atmosphere in each process from the pulverization process to the sintering process can be set to a low oxygen concentration. For example, the oxygen concentration in the atmosphere in each process can be set to 200 ppm or less (0.02% or less). However, in any process before the micro-pulverized powder is shaped into the target shape, the oxygen concentration in the atmosphere can be increased in order to control the O content of the alloy powder. Details will be described later.

[0096] The following describes the above-mentioned pulverizing process in two stages: a coarse pulverizing process to a particle size of several hundred μm to several mm, and a fine pulverizing process to a particle size of several μm. However, it is also possible to implement the process in only one stage: the fine pulverizing process.

[0097] In the coarse grinding process, the particles are ground to a size of several hundred μm to several mm. This yields coarse powder. There are no particular limitations on the method of coarse grinding; it can be carried out using known methods such as hydrogen adsorption grinding.

[0098] In hydrogen adsorption pulverization, the following steps are performed: hydrogen adsorption, which causes the alloy to adsorb hydrogen; and hydrogen crushing, which breaks down the alloy by dehydrogenating the hydrogen-adsorbed alloy. The coarse powder obtained by hydrogen crushing is heat-treated in an atmosphere with an oxygen concentration of 0.5% to 23%, thereby controlling the O content of the final alloy powder. Furthermore, the N content can sometimes be controlled along with the O content. The heat treatment temperature can be set to 50°C to 200°C. The heat treatment time can be set to 5 minutes to 4 hours. Additionally, the heat treatment of the coarse powder can be carried out in a stirring apparatus equipped with a screw or the like.

[0099] Next, the coarse powder is micronized to an average particle size of about a few μm (micronization process). This yields micronized powder (raw material powder). The average particle size of the micronized powder can also be 1 μm to 10 μm, 2 μm to 6 μm, or 2 μm to 4 μm.

[0100] There are no particular restrictions on the method of micronization. For example, it can be carried out by using an air jet mill.

[0101] By setting the oxygen concentration in the atmosphere during micronization to between 0.01% and 0.30%, the oxygen content of the final alloy powder can be controlled. The oxygen concentration can be set to between 0.02% and 0.30%, or between 0.03% and 0.30%. Furthermore, the nitrogen content can sometimes be controlled along with the oxygen content.

[0102] When controlling the oxygen content of the final alloy powder, it is preferable to supply oxygen, or a mixture of rare gas and oxygen, in a manner such that the oxygen concentration in the atmosphere during micro-grinding is not lower than the lower limit of the aforementioned oxygen concentration range. Even if the oxygen concentration in the atmosphere at the start of micro-grinding is above the lower limit of the aforementioned oxygen concentration range, the oxygen concentration in the atmosphere will decrease if oxygen is not adequately supplied to the atmosphere during micro-grinding. This is because the powder absorbs oxygen during micro-grinding.

[0103] By performing the above-mentioned micro-pulverization under an atmosphere of a mixture of rare gases and oxygen inside the air jet mill, the oxygen content of the final alloy powder can be controlled. Furthermore, the nitrogen content can sometimes be controlled along with the oxygen content. There are no particular restrictions on the type of rare gas. For example, Ar gas, He gas, and mixtures of Ar and He gas can be used.

[0104] When the coarsely ground powder is further pulverized, by adding various pulverizing aids such as laurylamide and oleamide, it is possible to obtain pulverized powder whose grains easily orient themselves in a specific direction when pressed and shaped in a magnetic field. Furthermore, by changing the amount of pulverizing aids added, the C and N content in the RTB-based permanent magnet can be controlled.

[0105] Furthermore, regarding the control of O content, for example, by heat-treating the coarse powder under conditions where the oxygen concentration in the atmosphere is set to 0.5% to 23% as described above, and by performing the aforementioned micro-pulverization under conditions where the atmosphere inside the air jet mill is a mixture of rare gas and oxygen, or a rare gas, the O content of the final alloy powder can be controlled. Additionally, sometimes the N content can also be controlled along with the O content. There are no particular restrictions on the type of rare gas. For example, Ar gas, He gas, and mixtures of Ar and He gas can be cited.

[0106] [Forming process]

[0107] In the forming process (compression forming), the aforementioned micronized powder is shaped into the target shape. There are no particular limitations on the forming method. In this embodiment, the aforementioned micronized powder is filled into a mold and pressurized under a magnetic field. The resulting molded body has RTB-based permanent magnets with higher Br content because the grains are oriented in a specific direction.

[0108] The pressure applied during molding can be between 20 MPa and 300 MPa. The applied magnetic field can be set to 950 kA / m or higher, and between 950 kA / m and 1600 kA / m. The applied magnetic field is not limited to a static magnetic field, but can also be a pulsed magnetic field. Furthermore, a static magnetic field and a pulsed magnetic field can be used together.

[0109] In addition to dry forming, which involves directly forming micronized powder as described above, wet forming, which involves forming a slurry (obtained by dispersing micronized powder in a solvent such as oil), can also be applied as a forming method.

[0110] There are no particular limitations on the shape of the molded article obtained by shaping the micronized powder. Furthermore, the density of the molded article at this point can be set to 4.0 Mg / m³. 3 ~4.3Mg / m 3 .

[0111] [Sintering process]

[0112] The sintering process is a process of obtaining a sintered body by sintering a shaped body in a vacuum or an inert gas atmosphere. The sintering conditions need to be adjusted according to various factors such as composition, pulverization method, particle size, and particle size distribution. For example, for a shaped body, sintering may be performed by heating at 1000°C to 1200°C for 1 to 20 hours in a vacuum or inert gas atmosphere. By sintering under the above conditions, a high-density sintered body is obtained. In this embodiment, a density of at least 7.45 Mg / m³ is obtained. 3 The above refers to the sintered body. The density of the sintered body can also be 7.50 Mg / m³. 3 above.

[0113] [Aging Process]

[0114] The aging process is a process of heat-treating (aging) the sintered body at 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. Hereinafter, an implementation method in which two aging treatments are performed will be described, but in the case of performing only one aging treatment, the aging process in which this aging treatment is performed will be referred to as the first aging process described later.

[0115] 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.

[0116] In the RTB-based permanent magnet of this embodiment, the dispersion state of the grain boundary tripartite points (described later) changes depending on the conditions of the first aging process. There are no particular limitations on the atmosphere of the first aging process. For example, it can be an argon atmosphere, a vacuum atmosphere, or an argon-reduced atmosphere in which argon flows in a vacuum. There are no particular limitations on T1. T1 can be 700°C to 1000°C, 700°C to 950°C, or 850°C to 950°C. There are no particular limitations on the aging time of the first aging process. The aging time of the first aging process can be 1.0 hour to 15 hours, 1.0 hour to 10 hours, or 1.5 hours to 10 hours.

[0117] The RTB-based permanent magnet of this embodiment has a composition within a specified range, specifically the carbon, oxygen, and nitrogen content are within specified ranges. When such an RTB-based permanent magnet is subjected to a first aging process under the aforementioned conditions, the composition of the liquid phase at the grain boundary junctions is appropriately controlled during the first aging process. Furthermore, the viscosity of the liquid phase becomes suitable. As a result, a network structure connecting the grain boundary junctions to each other is formed, and the liquid phase is supplied from the grain boundary junctions to the two-grain boundaries. Moreover, while maintaining the volume ratio of the main phase, the dispersion state of the grain boundary junctions becomes suitable, and the two-grain boundaries thicken. As a result, the magnetic properties are easily improved.

[0118] The first aging process can be performed before or after the grain boundary diffusion process described later. By performing the first aging process before the grain boundary diffusion process described later, the equivalent circle diameter and total area ratio of the low-melting-point grain boundary phase can be easily and appropriately controlled. In addition, the first aging process can also serve as the heat treatment in the grain boundary diffusion process described later.

[0119] There are no special restrictions on T2 and aging time in the second aging process. T2 can be set to 450℃ or higher and 700℃ or lower. The aging time can be set to 1 hour or higher and 10 hours or lower.

[0120] The second aging process can also be performed after the first aging process and before the grain boundary diffusion process described later. Alternatively, the second aging process can be performed after the grain boundary diffusion process described later.

[0121] [Processing steps (before grain boundary diffusion)]

[0122] It may also include a process for processing the sintered body of this embodiment into a desired shape, as needed. Examples of processing methods include, for instance, cutting, grinding, or chamfering, such as rolling.

[0123] [Grain boundary diffusion process]

[0124] The grain boundary diffusion process can be carried out by attaching a diffusion material to the surface of a sintered body and heating the sintered body with the diffusion material attached. Then, an RTB-based permanent magnet is obtained.

[0125] (Diffusion material attachment process)

[0126] In this embodiment, there are no particular limitations on the type of diffusion material. The diffusion material may contain hydrides of heavy rare earth elements (e.g., Tb), or it may contain heavy rare earth elements and Cu. The diffusion material may also be an elemental form of heavy rare earth elements (e.g., metallic Tb).

[0127] The diffusion material can also be a slurry containing a solvent in addition to hydrides of the aforementioned heavy rare earth elements. The solvent in the slurry can be any solvent other than water. For example, it can be an organic solvent such as an alcohol, aldehyde, or ketone. Furthermore, the diffusion material can also contain a binder. There are no particular limitations on the type of binder. For example, it can contain resins such as acrylic resin as a binder. By including a binder, the diffusion material can easily adhere to the surface of the sintered body.

[0128] Diffusion materials can also be pastes containing solvents and binders in addition to hydrides of the aforementioned heavy rare earth elements. Pastes have fluidity and high viscosity. The viscosity of pastes is higher than that of slurries.

[0129] Prior to the diffusion treatment described later, the sintered body with attached slurry or paste may also be dried to remove solvents and remove binders.

[0130] The drying temperature can be kept below 200℃, and the drying time can be between 3 minutes and 1 hour.

[0131] The holding temperature during binder removal can be between 200°C and 800°C, and the holding time can be between 10 minutes and 10 hours. Especially at high holding temperatures during binder removal, grain boundary diffusion of heavy rare earth elements can occur during binder removal. The atmosphere during binder removal is set to an inert gas atmosphere. By removing the binder from the sintered body with the attached slurry or paste, the formation of heavy rare earth element carbides on the surface of the magnet substrate can be suppressed, further reducing the amount of heavy rare earth elements used.

[0132] Alternatively, the elemental form of heavy rare earth elements (such as metallic Tb) can be sputtered onto the surface of the sintered body as a diffusing material. There are no particular limitations on the sputtering apparatus used; magnetron sputtering can also be used. Especially when the amount of diffusing material is small, the method of attaching the diffusing material by sputtering is preferred.

[0133] (Heating process)

[0134] In the heating process of grain boundary diffusion, as the temperature rises, the grain boundary phase with a high concentration of rare earth elements (especially the low-melting-point grain boundary phase) present at the grain boundaries of the magnetic substrate (sintered body) becomes a liquid phase. By melting the diffusion material into this liquid phase, the components of the diffusion material diffuse from the surface of the magnetic substrate to the interior of the magnetic substrate. Alternatively, when the diffusion material (e.g., elemental heavy rare earth elements) is attached to the surface of the sintered body by sputtering, the components of the diffusion material can also diffuse by heating the substrate on which the sintered body is provided.

[0135] The diffusion process in the grain boundary diffusion step of this embodiment can also be performed continuously after the removal of the adhesive described above. Alternatively, the diffusion process can be performed by cooling to room temperature after the adhesive is removed and then reheating. The holding temperature during the diffusion process can also be between 700°C and 1000°C. In the grain boundary diffusion step, the temperature of the magnet substrate can also be slowly increased from a temperature lower than the diffusion process temperature to the diffusion process temperature.

[0136] The time for maintaining the substrate temperature at the diffusion treatment temperature (diffusion treatment time) can be, for example, more than 1 hour and less than 50 hours. The atmosphere surrounding the substrate during the diffusion treatment process can be a non-oxidizing atmosphere. A non-oxidizing atmosphere can be, for example, a rare gas such as argon. The pressure of the atmosphere surrounding the magnetic substrate during the diffusion process can be less than 1 kPa. When the diffusion material is a hydride of a heavy rare earth element, setting it to such a reduced pressure atmosphere can promote the dehydrogenation reaction of the hydride. As a result, the melting of the diffusion material into the liquid phase is facilitated.

[0137] The second aging process described above can also be performed after the grain boundary diffusion process. Alternatively, the first aging process described above can be performed before the grain boundary diffusion process. By performing the first aging process before the grain boundary diffusion process and the second aging process described above after the grain boundary diffusion process, it is easier to appropriately control the equivalent circle diameter and total area ratio of the low-melting-point grain boundary phase, and easier to improve the magnetic properties of the final RTB-based sintered magnet.

[0138] [Processing steps (after grain boundary diffusion)]

[0139] After the grain boundary diffusion process, grinding can be performed to remove the diffusion material remaining on the surface of the RTB-based permanent magnet. Other processing can also be performed on the RTB-based permanent magnet. Surface finishing processes such as cutting, grinding, chamfering, etc., can also be performed. Grinding can be performed before or after the second aging process.

[0140] In addition, processing steps before and after grain boundary diffusion were performed in this embodiment, but these steps are not necessary.

[0141] In particular, RTB-based permanent magnets that have undergone grain boundary diffusion tend to exhibit a heavy rare earth element concentration distribution that decreases from the outside to the inside of the RTB-based permanent magnet. Furthermore, the main phase particles contained in RTB-based permanent magnets that have undergone grain boundary diffusion tend to possess the aforementioned core-shell structure.

[0142] The RTB-based permanent magnet obtained in this embodiment, despite having a low content of heavy rare earth elements, still possesses the desired characteristics. Specifically, it has high Br, HcJ, and Hk / HcJ content.

[0143] The RTB-based permanent magnet of this embodiment obtained by the above method is magnetized to become a magnetic RTB-based permanent magnet.

[0144] The reasons why the RTB-based permanent magnet of this embodiment still has the desired properties despite having a low content of heavy rare earth elements will be explained below.

[0145] The two-grain grain boundaries of sintered bodies before grain boundary diffusion (hereinafter, sometimes referred to as substrates) with compositions within the above range (especially carbon content, oxygen content, and nitrogen content within the above range) tend to thicken.

[0146] For substrates produced by controlling oxygen content primarily through the above manufacturing methods, the grain boundaries of the second grain tend to thicken.

[0147] Specifically, regarding the substrate that serves as the precursor to the RTB-based permanent magnet in this embodiment, such as Figures 2-4 As shown, the grain boundary between the two grains is thick enough that the interface between the two grains can be confirmed by using an image of the cross-section obtained by SEM (SEM image). Figure 2 This is a 2500x SEM image of the substrate of sample number 4 in the embodiment described later. Figure 3 This is a 5000x SEM image of the substrate of sample number 4 in the embodiment described later. Figure 4 This is a 2500x SEM image of the substrate of sample number 63 in the embodiment described later. Furthermore, all SEM images in this embodiment are reflectance electron images.

[0148] Thus, by making the grain boundary thickness sufficient to confirm the interface between the two grain boundaries in the substrate, the HcJ of the substrate is improved. Moreover, even with reduced diffusion of heavy rare earth elements, the magnetic properties of the RTB-based permanent magnets obtained through grain boundary diffusion are also improved.

[0149] also, Figure 5 This is a 2500x SEM image of the substrate of specimen number 41 in the comparative example described later. Figure 6 This is a 5000x SEM image of the substrate from sample number 41 of the comparative example described later. The interface between the two grain boundaries cannot be identified in either image. Furthermore, the width of the two grain boundaries in this case can be confirmed using TEM (transmission electron microscopy). When the width of the two grain boundaries was actually confirmed, it was approximately 5 nm.

[0150] The width of the two-grain boundary that can be confirmed in the SEM image is approximately 15 nm or more. The width of the two-grain boundary can also be 15 nm or more but less than 50 nm. Alternatively, within the field of view of a sufficiently large SEM image observed at 5000x magnification, an arbitrary 20 μm × 15 μm area can be selected as the observation object. If the observation object contains at least five two-grain boundary interfaces with a length of 0.5 μm or more, it is considered that the two-grain boundary of the sintered body is sufficiently thick.

[0151] Furthermore, for the RTB-based permanent magnet of this embodiment, by having a composition within the aforementioned range (particularly carbon, oxygen, and nitrogen content within the aforementioned range) and undergoing a prescribed heat treatment (particularly a prescribed first aging treatment) under conditions within the aforementioned range, the dispersion state of the grain boundary triangular points becomes suitable. As a result, it is easier to thicken the two-grain boundaries while maintaining the volume ratio of the main phase. Consequently, it is believed that the magnetic properties are easily improved.

[0152] To evaluate the dispersion state of grain boundary triangulation points, rare earth oxide phases and low-melting-point grain boundary phases were extracted from all grain boundary triangulation points contained within the field of view of the SEM image. Low-melting-point grain boundary phases refer to grain boundary phases other than the high-melting-point rare earth oxide phases.

[0153] Rare earth oxide phases, in addition to containing rare earth elements and oxygen, may also contain nitrogen and / or carbon. There are no particular restrictions on the composition of rare earth oxide phases. For example, the content of rare earth elements in a rare earth oxide phase can be 30–70 at%. The content of oxygen in a rare earth oxide phase can be 10–60 at%. The content of carbon in a rare earth oxide phase can be 0–40 at%. The content of nitrogen in a rare earth oxide phase can be 0–30 at%. Moreover, rare earth oxide phases can also be mainly composed of rare earth elements, oxygen, carbon, and nitrogen. "Mainly composed of rare earth elements, oxygen, carbon, and nitrogen" means that the total content of elements other than rare earth elements, oxygen, carbon, and nitrogen is between 0 at% and 20 at%.

[0154] The total area ratio of low-melting-point grain boundary phases in an RTB-based permanent magnet can be calculated by dividing the total area of ​​the low-melting-point grain boundary phases (i.e., the total area of ​​grain boundary phases other than rare-earth oxide phases) contained in a cross-section of the magnet by the area of ​​that cross-section. The area of ​​that cross-section is calculated based on the magnification and pixel count of the SEM image.

[0155] Furthermore, by calculating the equivalent circle diameters of each low-melting-point grain boundary phase contained in a cross-section of an RTB-based permanent magnet, and then taking the arithmetic mean of the equivalent circle diameters of each low-melting-point grain boundary phase, the average equivalent circle diameter of the low-melting-point grain boundary phase can be calculated. The equivalent circle diameter of the low-melting-point grain boundary phase is a parameter obtained by converting the area of ​​the low-melting-point grain boundary phase into the diameter of a circle with the same area.

[0156] These parameters can be used to evaluate the dispersion state of grain boundary triangulation points.

[0157] The reason for not considering the total area of ​​the rare earth oxide phases and the equivalent circle diameter of each rare earth oxide phase is that it is believed that the rare earth oxide phases have little impact on the dispersion of the grain boundary triangular points. The reason for believing that the rare earth oxide phases have little impact on the dispersion of the grain boundary triangular points is that the rare earth oxide phases have high melting points and are difficult to become liquid phases through the first aging treatment or heat treatment in grain boundary diffusion, making them difficult to flow.

[0158] There are no particular limitations on the method for distinguishing between low-melting-point grain boundary phases (grain boundary phases other than rare-earth oxide phases) and the rest (main phase and rare-earth oxide phases). For example, brightness-based binarization can also be performed on SEM images. By performing binarization on SEM images, the SEM images become black and white. There are no particular limitations on the type of image processing software used for binarization. Any image processing software capable of determining the shape of the low-melting-point grain boundary phase after binarization is acceptable.

[0159] The threshold for binarization is set between the low-melting-point grain boundary phase and the portion outside the low-melting-point grain boundary phase. The threshold can be set automatically using image processing software or by visually examining the SEM image. The contrast of the image differs between the portion outside the low-melting-point grain boundary phase (main phase and rare earth oxide phase) and the low-melting-point grain boundary phase; therefore, they can be clearly distinguished through binarization.

[0160] There are no particular restrictions on the total area ratio of the low-melting-point grain boundary phase. It can be between 1.5% and 7.5%, or between 3.5% and 6.8%. There are also no particular restrictions on the average equivalent circle diameter of the low-melting-point grain boundary phase. It can be between 0.40 μm and 1.00 μm, or between 0.46 μm and 0.92 μm. In short, when the total area ratio and the average equivalent circle diameter of the low-melting-point grain boundary phase are within the above ranges, the dispersion of the grain boundary junctions is good.

[0161] The RTB-type permanent magnet of this embodiment is suitable for use in electric motors, generators, and the like.

[0162] Example

[0163] The present disclosure will now be described with reference to more detailed embodiments, but the present disclosure is not limited to these embodiments.

[0164] (The fabrication of RTB-type permanent magnets)

[0165] The raw material alloys were prepared using a thin-strip continuous casting method, with the composition of the final RTB-based permanent magnets as shown in Tables 1 to 9. Tb is not included in the raw material alloys, but only in the diffusion material paste described later. Other elements not listed in Tables 1 to 9, such as H, Si, Ca, La, Ce, and Cr, were sometimes detected. Si may mainly be introduced from the ferroboron raw material and the crucible during alloy melting. Ca, La, and Ce may be introduced from rare earth raw materials. In addition, Cr may be introduced from electrolytic iron. The reason why the Fe content is recorded as "balance" in Tables 1 to 9 is that the Fe content represents the substantial remainder when the entire RTB-based permanent magnet containing these other elements is set at 100% by mass.

[0166] Next, hydrogen gas was allowed to flow at room temperature for 1 hour to allow the above-mentioned raw material alloy to adsorb hydrogen. Then, the atmosphere was switched to Ar gas, and dehydrogenation treatment was carried out at 500°C for 1 hour, thereby pulverizing the raw material alloy by hydrogen adsorption to obtain coarse powder.

[0167] Next, the obtained coarse powder was fed into a stirring device equipped with a screw. Then, heat treatment was performed while stirring the coarse powder in an atmosphere with an oxygen concentration of 0.5% to 23%. The heat treatment temperature was set to 140°C, and the heat treatment time was set to 2.5 hours. The oxygen concentration of the alloy powder obtained after micronization was controlled by changing the oxygen concentration in the atmosphere.

[0168] Next, 0.1% by mass of oleamide was added to the heat-treated coarse powder as a pulverizing aid, and the powder was mixed using a Nota mixer.

[0169] Next, the material is micronized in a nitrogen stream using a collision plate-type air jet mill to obtain micronized powder (raw material powder) with an average particle size of approximately 3.0 μm. Furthermore, the aforementioned average particle size is the average particle size D50 measured using a laser diffraction particle size analyzer.

[0170] The obtained micro-powder is shaped in a magnetic field to produce a molded body. The applied magnetic field is a static magnetic field of 1200 kA / m. Furthermore, the pressure applied during shaping is set to 120 MPa. Additionally, the direction of the applied magnetic field and the direction of the applied pressure are orthogonal.

[0171] Next, the shaped body is sintered to obtain a sintered body. The optimal sintering conditions vary depending on the composition, but for example, it is maintained at 1030°C to 1070°C for 4 hours. The sintering atmosphere is set to vacuum. At this point, the sintering density is 7.51 Mg / m³. 3 ~7.55Mg / m 3 Within the specified range. Then, under atmospheric pressure (1 atm), a first aging treatment was performed while Ar flowed. The first aging treatment temperature T1 was set to 900°C, and the first aging treatment time was set to 2 hours. Thus, sintered bodies of the samples shown in Tables 1 to 9 were produced by grain boundary diffusion.

[0172] (Preparation of diffusion material paste)

[0173] Next, a diffusion material paste for grain boundary diffusion was prepared for samples other than 71a and 72.

[0174] First, hydrogen gas was circulated at room temperature to allow 99.9% pure metallic Tb to adsorb hydrogen. Next, the atmosphere was switched to Ar gas, and a dehydrogenation treatment was performed at 500°C for 1 hour to pulverize the metallic Tb through hydrogen adsorption. Then, 0.05% by mass of zinc stearate was added as a pulverizing aid relative to 100% by mass of metallic Tb, and the mixture was stirred using a Nota mixer. Finally, the mixture was micronized using an air jet mill in an atmosphere containing 3000 ppm oxygen to obtain micronized Tb hydride powder with an average particle size of approximately 10.0 μm.

[0175] A diffusion material paste was prepared by mixing 60 parts by weight of micronized Tb hydride powder, 10 parts by weight of metallic Cu powder, 25 parts by weight of alcohol, and 5 parts by weight of acrylic resin. The alcohol was used as a solvent, and the acrylic resin as a binder.

[0176] (Coating and heat treatment of diffusion material paste)

[0177] The sintered body described above was processed to a length of 11 mm × width of 11 mm × thickness of 4.2 mm (4.2 mm in the direction of the easily magnetized axis). Then, an etching process was performed as follows: the body was immersed in a mixed solution of nitric acid and ethanol (3 parts by mass relative to 100 parts by mass of ethanol) for 3 minutes, followed by immersion in ethanol for 1 minute. This process of immersion in the mixed solution for 3 minutes followed by immersion in ethanol for 1 minute was repeated twice.

[0178] Next, the above-mentioned diffusion material paste is applied to the entire surface of the etched sintered body. The amount of diffusion material paste applied is set such that the Tb content in the final RTB-based permanent magnet is the value recorded in Tables 1 to 9.

[0179] Sample number 71 was processed and etched, but the diffusion material paste was not applied.

[0180] The following describes sample numbers 71a and 72.

[0181] For samples 71a and 72, Tb was attached to the sintered body after the above processing and etching by sputtering with metal Tb as the target. Magnetron sputtering was used in the sputtering process.

[0182] The amount of Tb adhering to the sintered body was set so that the Tb content in the final RTB-based permanent magnet was the value recorded in Tables 1 to 9.

[0183] Next, the sintered body is dried. Specifically, the sintered bodies coated with diffusion material paste (excluding the sintered body without diffusion material paste of sample number 71, and the sintered bodies with Tb attached by sputtering of sample numbers 71a and 72) are placed in an oven at 160°C for 45 minutes in the atmosphere to remove the solvent from the diffusion material paste.

[0184] Next, the binder of the sintered body was removed. Specifically, the sintered bodies after the diffusion material paste was dried (except for the sintered body without diffusion material paste in sample number 71, and the sintered bodies with Tb attached by sputtering in samples 71a and 72) were placed in an oven at 400°C for 3 hours in an Ar gas atmosphere to remove residual binder from the dried diffusion material. Then, under atmospheric pressure (1 atm), the bodies were heated at 900°C for 30 hours while Ar was flowing to allow heavy rare earth elements to diffuse across grain boundaries. Then, a second aging treatment was performed by heating at 500°C for 1 hour while Ar was flowing at atmospheric pressure (1 atm). Thus, RTB-based permanent magnets for each sample shown in Tables 1 to 9 were obtained.

[0185] For the surface of RTB-based permanent magnets, the composition, fine structure, elemental distribution, and magnetic properties were evaluated after scraping off 0.1 mm from each surface.

[0186] The RTB-based permanent magnet was machined to a length of 11 mm × width of 11 mm × thickness of 4.2 mm (4.2 mm in the direction of easy magnetization axis) using a vertical milling machine, and its magnetic properties at room temperature were evaluated using a BH tracer. Furthermore, the RTB-based permanent magnet was magnetized with a pulsed magnetic field of 4000 kA / m before the magnetic properties were measured. Additionally, because the RTB-based permanent magnet is thin, three magnets were stacked together to evaluate the magnetic properties. Furthermore, in this embodiment, when calculating Hk / HcJ, in the second quadrant of the magnetization J-magnetic field H curve (J-H demagnetization curve), the magnetic field at which 90% of Br is magnetized was set as Hk (kA / m), and Hk / HcJ × 100 (%) was calculated.

[0187] In this embodiment, a Br value of 1400 mT or higher for an RTB-based permanent magnet is defined as "good," and a Br value of 1430 mT or higher is defined as "better." Similarly, an HcJ value of 1900 kA / m or higher for an RTB-based permanent magnet is defined as "good," a HcJ value of 1915 kA / m or higher is defined as "better," and a HcJ value of 1950 kA / m or higher is defined as "especially good." Finally, an Hk / HcJ ratio of 93.0% or higher for an RTB-based permanent magnet is defined as "good," and a Hk / HcJ ratio of 95.0% or higher is defined as "better."

[0188] The cross-section of the sintered body (substrate) before grain boundary diffusion was observed using SEM. Measurement conditions were set at an accelerating voltage of 5.0 kV. Within the field of view of a sufficiently large SEM image observed at 5000x magnification, an arbitrary area of ​​20 μm × 15 μm was selected as the observation object. The presence of an observation object (i.e., the identification of more than 5 two-grain boundary interfaces with a length of 0.5 μm or more within that observation object) was classified as "good." The absence of an observation object (i.e., the identification of more than 5 two-grain boundary interfaces with a length of 0.5 μm or more within that observation object) was classified as "poor." The results are shown in Tables 1 to 9.

[0189] Table 1

[0190]

[0191] Table 2

[0192]

[0193] Table 3

[0194]

[0195] Table 4

[0196]

[0197] Table 5

[0198]

[0199] Table 6

[0200]

[0201] Table 7

[0202]

[0203] Table 8

[0204]

[0205] Table 9

[0206]

[0207] As shown in Tables 1 to 9, in all embodiments within the specific composition range, a sufficient number of two-grain boundary interfaces were identified before grain boundary diffusion. Furthermore, good magnetic properties were obtained in all embodiments.

[0208] As shown in Table 1, the HcJ and Hk / HcJ decreased in sample number 1, which had too little TRE (total rare earth element content). The Hk / HcJ decreased in sample number 7, which had too much TRE.

[0209] As shown in Table 2, the Hk / HcJ ratio decreased in sample number 11, which had too low a B content. The HcJ ratio decreased in sample number 16, which had too high a B content.

[0210] As shown in Table 3, the HcJ and Hk / HcJ of sample number 21, which does not contain Zr, decreased. The Br content of sample number 28, which has excessive Zr, decreased.

[0211] As shown in Table 4, the HcJ of sample number 31, which had too little Cu, decreased. The Br of sample number 36, which had too much Cu, decreased.

[0212] As shown in Table 5, neither sample number 41 (with insufficient O content) nor sample number 47 (with excessive O content) showed a sufficient number of two grain boundaries in the substrate. Furthermore, the HcJ of sample number 41 decreased, and the Br and HcJ of sample number 47 decreased.

[0213] As shown in Table 6, neither sample number 51 (with insufficient C content) nor sample number 56 (with excessive C content) showed a sufficient number of two grain boundaries in the substrate. Furthermore, the HcJ of sample number 51 decreased, and the HcJ and Hk / HcJ of sample number 56 also decreased.

[0214] As shown in Table 7, neither sample number 61 (with insufficient N content) nor sample number 66 (with excessive N content) showed a sufficient number of two grain boundaries in the substrate. Furthermore, the HcJ values ​​of both samples 61 and 66 were reduced.

[0215] As shown in Table 8, the HcJ of sample number 71, which did not undergo Tb grain boundary diffusion, was reduced. In sample number 76, which had excessive TRH (total content of heavy rare earth elements), the heavy rare earth elements were not sufficiently reduced. Furthermore, compared to the examples with sufficiently low TRH, its Hk / HcJ was low.

[0216] As shown in Table 8, in samples 41 and 51 with insufficient O and C content, even when TRE was increased to the same level as in sample 75, sufficient two-grain boundary interfaces were not identified in the substrate. Furthermore, HcJ was not sufficiently increased.

[0217] For sample number 4, except for the change in the conditions of the first aging treatment, RTB-based permanent magnets of sample numbers 90-97 were essentially produced under the same conditions.

[0218] For the obtained RTB-based permanent magnets, SEM images were obtained in the same manner as for other samples. Then, within the field of view of the SEM images, an arbitrarily selected area of ​​20 μm × 15 μm was used as the observation object. The portion of the SEM image selected as the observation object was binarized using image processing software. Based on the image obtained through binarization, the total area ratio of the low-melting-point grain boundary phase and the average equivalent circle diameter of the low-melting-point grain boundary phase were calculated.

[0219] Table 10 shows the oxygen, carbon, and nitrogen contents of each sample, the conditions of the first aging treatment, various parameters related to fine structure, and magnetic properties. Furthermore, conditions other than the first aging treatment are assumed to be the same as those for sample number 4.

[0220] Table 10

[0221]

[0222] As shown in Table 10, in all embodiments with compositions within a specific range, a sufficient number of two-grain boundary interfaces were identified before grain boundary diffusion. Furthermore, good magnetic properties were obtained in all embodiments.

[0223] right Figure 2 The image obtained by binarizing the SEM image (SEM image of the substrate in sample number 4 at 2500x magnification) is as follows: Figure 7 .right Figure 4 The image obtained by binarizing the SEM image (SEM image of the substrate of sample number 63 at 2500x magnification) is as follows: Figure 8 .according to Figure 7 and Figure 8 It can be seen that, for the magnets with sample numbers 4 and 63 that have undergone the prescribed first aging treatment, the dispersion of the grain boundary triangular points is good.

[0224] As shown in Table 10, for RTB-based permanent magnets with sample numbers 91, 4, 92, 94 to 96, the average equivalent circle diameter of the low-melting-point grain boundary phase is 0.40 μm to 1.00 μm or the area fraction of the low-melting-point grain boundary phase is 1.5% to 7.5%, which can improve HcJ while maintaining high Br.

[0225] Furthermore, for RTB-based permanent magnets with sample numbers 91, 4, 92, and 95-96, the average equivalent circle diameter of the low-melting-point grain boundary phase is 0.40 μm to 1.00 μm and the total area ratio of the low-melting-point grain boundary phase is 1.5% to 7.5%, which in particular can improve HcJ while maintaining high Br.

[0226] Furthermore, for the magnet of sample number 63, which underwent the first aging treatment under the same conditions as sample number 4, the average equivalent circle diameter of its low-melting-point grain boundary phase is 0.40 μm to 1.00 μm and the total area fraction of the low-melting-point grain boundary phase is 1.5% to 7.5%, which in particular improves HcJ while maintaining high Br.

[0227] [Explanation of reference numerals in the attached figures]

[0228] 1: RTB is a permanent magnet.

Claims

1. An RTB-based permanent magnet, wherein, It contains at least rare earth elements, Fe, Zr, Cu, B, C, O, and N. The rare earth element content is between 28.50% and 32.00% by mass. The Zr content is between 0.01% by mass and 0.50% by mass. The Cu content is between 0.04% and 0.50% by mass. The Al content is between 0% by mass and 0.60% by mass. The Ga content is between 0% by mass and 0.80% by mass. The Co content is between 0% and 3.50% by mass. The content of B is 0.88% by mass or more and 1.00% by mass or less. The content of C is between 0.05% and 0.12% by mass. The content of O is 0.11% by mass or more and 0.30% by mass or less, and The nitrogen content is between 0.015% by mass and 0.07% by mass. Fe is the actual remaining part. It contains heavy rare earth elements as rare earth elements, with the content of heavy rare earth elements being more than 0.03% by mass and less than 0.20% by mass.

2. The RTB-based permanent magnet according to claim 1, wherein, The residual magnetic flux density Br is above 1400mT and the coercivity HcJ is above 1900kA / m.

3. The RTB-based permanent magnet according to claim 1 or 2, wherein, The RTB-based permanent magnet comprises a main phase and a grain boundary triangular point surrounded by three or more main phases. The grain boundary triangular point is composed of rare earth oxide phases and low-melting-point grain boundary phases, and the average equivalent circle diameter of the low-melting-point grain boundary phases is above 0.40 μm and below 1.00 μm.

4. The RTB-based permanent magnet according to claim 3, wherein, The total area ratio of the low-melting-point grain boundary phase is above 1.5% and below 7.5%.

5. A method for manufacturing an RTB-based permanent magnet, in, include: The process of crushing an alloy to obtain alloy powder; The process of compressing the alloy powder to obtain a shaped body; The process of firing the shaped body to obtain a sintered body; and The process of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment. in, The oxygen content of the alloy powder is controlled before the alloy powder is compressed and formed.

6. The method for manufacturing an RTB-based permanent magnet according to claim 5, wherein, The alloy is coarsely pulverized by hydrogen adsorption to obtain coarse powder, and then the coarse powder is finely pulverized to obtain alloy powder.

7. The method for manufacturing an RTB-based permanent magnet according to claim 6, wherein, The coarse powder is finely pulverized using an air jet mill.

8. The method for manufacturing an RTB-based permanent magnet according to claim 6 or 7, wherein, The coarse powder is heat-treated under conditions where the oxygen concentration in the atmosphere is set to be between 0.5% and 23%, and the oxygen content of the alloy powder is controlled.

9. The method for manufacturing an RTB-based permanent magnet according to claim 7, wherein, The micro-pulverization is carried out under the condition that the oxygen concentration in the atmosphere inside the airflow pulverizer is set to be between 0.01% and 0.30%, and the oxygen content of the alloy powder is controlled.

10. The method for manufacturing an RTB-based permanent magnet according to claim 7, wherein, The micro-pulverization is carried out under the condition that the internal atmosphere of the airflow pulverizer is a mixture of rare gas and oxygen, and the oxygen content of the alloy powder is controlled.

11. The method for manufacturing an RTB-based permanent magnet according to claim 7, wherein, The coarse powder is heat-treated under conditions where the oxygen concentration in the atmosphere is set to be between 0.5% and 23%, and the micro-pulverization is performed under conditions where the atmosphere inside the air jet mill is a mixture of rare gas and oxygen or a rare gas, and the oxygen content of the alloy powder is controlled.

12. The method for manufacturing an RTB-based permanent magnet according to claim 5, wherein, Before the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, and / or after the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, there is a step of performing a first aging treatment on the sintered body.

13. The method for manufacturing an RTB-based permanent magnet according to claim 12, wherein, Prior to the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, there is a step of performing the first aging treatment.

14. The method for manufacturing an RTB-based permanent magnet according to claim 12 or 13, wherein, The aging temperature of the first aging treatment is above 850℃ and below 950℃, and the aging time of the first aging treatment is above 1.5 hours and below 10 hours.

15. The method for manufacturing an RTB-based permanent magnet according to claim 12 or 13, wherein, After the first aging treatment, there is a second aging treatment of the sintered body.

16. The method for manufacturing an RTB-based permanent magnet according to claim 15, wherein, After the step of contacting the sintered body with a diffusion material containing heavy rare earth elements and performing heat treatment, there is a step of performing the second aging treatment step.

Images