R-t-b permanent magnet having high coercivity, preparation method therefor and use thereof

Abstract

An R-T-B permanent magnet having high coercivity, a preparation method therefor and the use thereof. The preparation method for the R-T-B permanent magnet of the present invention comprises: (1) preparing composite magnetic powder, specifically, coating surfaces of base material powder particles with coating material particles so as to obtain the composite magnetic powder; and (2) subjecting the composite magnetic powder in step (1) to press molding treatment and thermal treatment, and optionally performing diffusion treatment, so as to prepare the R-T-B permanent magnet. In the present invention, the surface layers of the base material powder particles are uniformly coated with a grain boundary alloy having a low melting point, which effectively lowers the melting point of a grain boundary phase and reduces the sintering temperature of the permanent magnet, thus greatly reducing the production cost of the permanent magnet; in addition, the bulk phase in the magnet can be uniformly encapsulated by the grain boundary phase, so as to effectively isolate the magnetic exchange coupling effect between bulk-phase grains, and reduce grain boundary defects, thus significantly improving the coercivity of the permanent magnet.

Description

A high coercivity RTB permanent magnet, its preparation method and application

[0001] This application claims priority to an earlier application filed on May 27, 2024, with the China National Intellectual Property Administration, patent application number 202410659498.6, entitled "A High Coercivity RTB Permanent Magnet and Its Preparation Method and Application". The entire contents of the earlier application are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of rare earth permanent magnet material preparation technology, and particularly relates to a high coercivity R-Fe-B permanent magnet, its preparation method and application. Background Technology

[0003] Sintered NdFeB, as a third-generation rare-earth permanent magnet material, is mainly composed of rare-earth elements such as PrNd, iron, and boron. Due to its excellent magnetic properties and high cost-effectiveness, it is widely used in various rare-earth permanent magnet motors, smart consumer electronics, and medical devices. With the rapid development of the low-carbon, energy-saving economy and high technology, downstream products of rare-earth permanent magnets are gradually moving towards lower costs and smaller equipment, requiring sintered NdFeB magnets to possess high performance, high magnetic flux, and low heavy rare-earth element usage. Currently, methods to improve the performance of sintered NdFeB magnets include particle size refinement, grain boundary diffusion, and the addition of heavy rare-earth elements to grain boundaries. These processes can effectively reduce the amount of heavy rare-earth elements used while maintaining high magnetic properties, achieving high-cost-effective magnet manufacturing.

[0004] However, the above-mentioned process for preparing sintered NdFeB still has the following problems: First, poor powder flowability leads to reduced blank formability; the irregular edges on the surface of powder particles reduce powder flowability, resulting in uneven powder filling, and hindering grain deflection during magnetic field orientation, reducing the degree of orientation and making it difficult to prepare high remanence magnets. Second, the grain boundary phase distribution is discontinuous; when there is a lack of grain boundary phase between adjacent main phase grains, defects at the grain boundaries increase, and antimagnetic domains are prone to nucleation, making it difficult for the magnet to obtain high coercivity. In addition, as the main diffusion channel, the lack of grain boundary phase will reduce the grain boundary diffusion effect and weaken the ability of heavy rare earth elements to enhance magnetic properties. Although some literature has disclosed methods such as double alloying or grain boundary addition to increase the proportion of grain boundary phase and optimize the distribution morphology, it is very easy to cause the remanence of the magnet to decrease due to excessive increase in the proportion of grain boundary phase, making it difficult to effectively control the grain boundary phase. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an RTB permanent magnet with high coercivity, its preparation method, and its application.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for preparing an RTB permanent magnet, the method comprising:

[0008] (1) Preparation of composite magnetic powder: The composite magnetic powder is obtained by coating the packaging material particles onto the surface of the parent material powder particles;

[0009] (2) The composite magnetic powder in step (1) is subjected to molding treatment, heat treatment, and optionally diffusion treatment to prepare the RTB permanent magnet.

[0010] According to an embodiment of the present invention, in step (1), the method for preparing the composite magnetic powder is as follows: using high-speed gas as a power source, the packaging material particles are impacted onto the surface of the parent material powder particles by mechanical collision, and the packaging material particles deform and adhere to the surface of the parent material powder particles, thereby achieving the coating of the parent material powder particles.

[0011] Preferably, the high-speed gas is an inert gas, such as argon or nitrogen.

[0012] Preferably, the mechanical collision refers to mixing the packaging material particles with the parent material powder particles by ball milling or air jet milling to obtain the composite magnetic powder.

[0013] Preferably, the packaging material particles are selected from softer packaging material particles, which can deform through collision during the mixing process, thereby coating the surface of the parent material particles.

[0014] According to an embodiment of the present invention, in step (1), the components of the parent material powder particles include the following:

[0015] R, 26wt% to 35wt%; R is a rare earth element selected from at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y;

[0016] B, 0.7wt%~1.1wt%;

[0017] Co, 0wt%~3.0wt%;

[0018] M, 0.05wt% to 4.0wt%; M is selected from at least one of Ga, Cu, Al, Zr, and Ti;

[0019] The balance consists of iron and unavoidable impurities.

[0020] According to an exemplary embodiment of the present invention, the composition of the main phase grains includes: 29% Nd, 0.9% B, 1.0% Co, 0.5% Ga, 0.15% Cu, 0.25% Al, 0.1% Zr, 0.18% Ti, with the balance being iron and unavoidable impurities.

[0021] According to an embodiment of the present invention, the base material powder particles can be obtained using a conventional neodymium iron boron powder preparation process. Exemplarily, the components of the base material powder particles are melted in an argon atmosphere, and the melt is cast onto a quenching roller to obtain a base material alloy sheet; the base material alloy sheet is then subjected to hydrogenation treatment and air jet milling to obtain the base material powder particles.

[0022] According to an embodiment of the present invention, the average particle size of the parent material powder particles is 1-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0023] According to an embodiment of the present invention, the average particle size of the packaging material particles differs from the average particle size of the parent material powder particles by an order of magnitude. For example, the average particle size of the packaging material particles is one order of magnitude higher than the average particle size of the parent material powder particles (e.g., the average particle size of the packaging material particles is 10-100 μm), or for example, the average particle size of the packaging material particles is one order of magnitude lower than the average particle size of the parent material powder particles (e.g., the particle size of the packaging material particles is 0.1-1 μm).

[0024] According to an embodiment of the present invention, the ratio of the average particle size of the packaging material particles to the average particle size of the parent material powder particles is 0.1-1:1-10 or 10-100:1-10, for example, 0.2:2.8 or 20:2.8.

[0025] According to an embodiment of the present invention, the components of the packaging material particles include at least the rare earth element R'.

[0026] Preferably, R' is selected from one or more of Pr, Nd, Tb, Dy, Ho, Gd, Ce, Y, and La. Preferably, the components of the packaging material particles include at least Pr and / or Nd.

[0027] According to an embodiment of the present invention, the composition of the packaging material particles optionally includes M1. Preferably, M1 includes one or more of Cu, Ga, Al, Zr, Ti, Sn, Mn, B, Fe, Co, V, and Se.

[0028] According to a preferred embodiment of the present invention, the packaging material particles also include unavoidable impurities, such as metallic impurity elements silicon (Si), manganese (Mn), oxygen (O), carbon (C), etc.

[0029] According to an embodiment of the present invention, the packaging material particles are alloys.

[0030] According to a preferred embodiment of the present invention, the component R' of the packaging material particles includes R1 and R2, wherein, based on the mass percentage of the packaging material particles, R1 is selected from Pr, Nd, Tb, Dy, Ho, and Gd, and the proportion of R1 is 60wt%-98wt% (e.g., 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 98wt%), and R2 is selected from Ce, Y, and La, and the proportion of R2 is 2wt%-40wt% (e.g., 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%). Exemplarily, the components of the packaging material particles are Pr and Ce, with a mass ratio of, for example, 75:25. Exemplarily, the components of the packaging material particles are Nd and Y. Exemplarily, the components of the packaging material particles are Tb and Ce. Exemplarily, the components of the packaging material particles are Pr, Tb, and Y.

[0031] Furthermore, the packaging material particles are selected from at least one of Pr-Ce alloy powder, Nd-Y alloy powder, Tb-Ce alloy powder, and Pr-Tb-Y alloy powder; for example, a 75% Pr-25% Ce alloy is used.

[0032] According to a preferred embodiment of the present invention, the packaging material particles comprise R' and M1, wherein, based on the mass percentage of the packaging material particles, R' accounts for 80wt%-99.5wt% (e.g., 80wt%, 85wt%, 90wt%, 99.5wt%), and M1 accounts for 0.5wt%-20wt% (e.g., 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%).

[0033] Furthermore, the packaging material particles comprise R' and M1, wherein, based on the mass percentage of the packaging material particles, R' is selected from Pr and / or Nd, and the percentage of R' is 80wt%-99.5wt%; and M1 is selected from B, and the percentage of M1 is 0.5wt%-20wt%.

[0034] For example, the packaging material particles are composed of Pr and B in a mass ratio of, for example, 90:1. For example, the packaging material particles are composed of Pr and Cu. For example, the packaging material particles are composed of Nd and B. For example, the packaging material particles are composed of Pr, Tb, and B.

[0035] Furthermore, the packaging material particles are selected from at least one of Pr-B alloy powder, Pr-Cu alloy powder, Nd-B alloy powder, and Pr-Tb-B alloy powder; for example, 99% Pr-1% B alloy is used.

[0036] The inventors discovered that the best results are achieved when Pr and / or Nd and B alloy powders are used as packaging material particles (e.g., PrB or NdB alloys, PrNdB).

[0037] According to an embodiment of the present invention, the amount of packaging material particles added to the composite magnetic powder is 0.1-10%, for example, 0.1%, 0.5%, 1%, 2%, or 10%. Preferably, the amount of packaging material particles added is 0.5%-5%. In the present invention, the amount of packaging material particles added specifically refers to the mass ratio of packaging material particles to parent material powder particles.

[0038] According to an embodiment of the present invention, the composite magnetic powder includes a core-shell structure, wherein the core is the parent material powder particle and the shell includes the packaging material particle; preferably, the shell is deformed after being adsorbed onto the surface of the parent material powder particle by the packaging material particle.

[0039] According to an embodiment of the present invention, in step (2), before the molding process, the composite magnetic powder can be further sorted by a sorting device. The present invention does not specifically limit the particle size of the composite magnetic powder, as long as it can be used to prepare RTB permanent magnets. For example, the particle size of the composite magnetic powder is 2-5 μm.

[0040] According to an embodiment of the present invention, in step (2), the pressing process can be performed using methods known in the art. Exemplarily, the composite magnetic powder is mixed with a lubricant to obtain a mixed powder, and the mixed powder is pressed into a compact under magnetic field conditions, wherein the amount of lubricant added is 0.1-0.5 wt% of the composite magnetic powder. Preferably, the mixing time is 0.1-3 hours. Preferably, the lubricant can be any lubricant known in the art; the present invention does not impose specific limitations.

[0041] According to an embodiment of the present invention, in step (2), the magnetic field can be a magnetic field known in the art, such as a magnetic field with a magnetic field strength of 2T.

[0042] According to an embodiment of the present invention, in step (2), after pressing and molding, the compact can be subjected to cold isostatic pressing to further improve the density of the compact.

[0043] According to an embodiment of the present invention, in step (2), the conditions of the heat treatment include: a sintering temperature of 800 to 1100°C (e.g., 800°C, 900°C) and a sintering time of 2 to 10 hours.

[0044] According to an embodiment of the present invention, in step (2), the heat treatment optionally includes a first-stage aging treatment and / or a second-stage aging treatment, wherein the temperature of the first-stage aging treatment is 700-950°C and the holding time is 30-400 min; the temperature of the second-stage aging treatment is 400-600°C and the holding time is 30-400 min, for example, 50 min, 100 min, 200 min, or 300 min.

[0045] According to an embodiment of the present invention, in step (2), the diffusion treatment includes arranging a diffusion source on the surface of the magnet substrate obtained after heat treatment, heating under vacuum conditions, and when the heating temperature rises to the temperature of the grain boundary diffusion treatment, introducing an inert gas of 10 kPa to 30 kPa, holding at the temperature, and then cooling to room temperature. Preferably, the temperature of the grain boundary diffusion treatment is 800 to 1000°C. Preferably, the holding time is 3 hours or more, for example, 3 to 10 hours. Preferably, an aging treatment is also performed after the diffusion treatment, and the aging treatment temperature is 400 to 600°C, for example, 500°C.

[0046] According to an embodiment of the present invention, the diffusion source includes a heavy rare earth element, which may be any heavy rare earth element known in the art for diffusion. The present invention does not make specific limitations, such as dysprosium (Dy), terbium (Tb), oxides of dysprosium (Dy) and / or hydrides of terbium (Tb).

[0047] According to an embodiment of the present invention, the arrangement method of the diffusion source is selected from thermal spraying, coating, sputtering or immersion.

[0048] According to an embodiment of the present invention, in step (2), after heat treatment and / or diffusion treatment, the RTB permanent magnet is subjected to conventional treatment, such as being processed to the required size, or being cleaned, degreased, or pickled.

[0049] The present invention also provides an RTB permanent magnet, wherein the RTB permanent magnet comprises at least a grain boundary phase and a main phase grain;

[0050] The grain boundary phase is distributed in the form of clumps or thin bands of uniform thickness at or between any two or more main phase grains.

[0051] The main phase grains have an RTB-type phase structure, such as an R2T14B-type crystal structure.

[0052] According to an embodiment of the present invention, the main phase grains are nearly spherical. Preferably, the aspect ratio of the main phase grains is between 1:1 and 1:1.2, for example, 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19, and 1:1.20.

[0053] According to an embodiment of the present invention, in the grain boundary phase, the bulky grain boundary phase refers to a grain boundary with a maximum size greater than 100 nm when projected in any direction, such as the bulky structure shown in Figure 1.

[0054] According to an embodiment of the present invention, the thin-ribbon-shaped grain boundary phase refers to a grain boundary with a maximum size less than 100 nm when projected in any direction, such as the thin-ribbon-shaped structure shown in Figure 2.

[0055] According to an embodiment of the present invention, the volume percentage of the aggregated grain boundary phase in the grain boundary phase is ≤80%, for example, 70%, 60%, 50%, 40%, 30%, 20%, or 10%. Preferably, the volume percentage of the aggregated grain boundary phase is 50%-80%.

[0056] According to an embodiment of the present invention, the volume percentage of the thin-banded grain boundary phase in the grain boundary phase is ≥20%, for example, 30%, 40%, 50%, 60%, 70%, or 80%. Preferably, the volume percentage of the thin-banded grain boundary phase is 20%-50%.

[0057] According to an embodiment of the present invention, in the grain boundary phase, the volume ratio of the bulk grain boundary phase to the thin band grain boundary phase is 3:1 to 1:1.

[0058] According to an embodiment of the present invention, the RTB permanent magnet is obtained by the above-described method for preparing an RTB permanent magnet.

[0059] The present invention also provides applications of the above-mentioned RTB permanent magnet, such as in rare earth permanent magnet motors, smart consumer electronics products, medical devices and other fields. Beneficial effects

[0060] 1. The permanent magnet powder particles prepared by this invention have an approximately spherical appearance and good powder flowability, which can significantly optimize the flowability of powder particles and improve powder formability. At the same time, it is beneficial for the powder particles to deflect under the orientation magnetic field, further improving the orientation degree of the main phase grains (such as the main phase grains being nearly spherical).

[0061] 2. This invention coats the surface of the base powder particles with RR or RM alloys. These alloys have lower hardness and higher plasticity than the base powder particles, effectively reducing the deformation stress of the powder particles during pressing, minimizing cracks in the pressed blank due to elastic aftereffects, and significantly improving the appearance of the pressed blank. Simultaneously, the reduction in powder particle deformation stress decreases the number of demagnetization nucleation points, thereby further improving the coercivity of the permanent magnet.

[0062] 3. This invention effectively reduces the melting point of the grain boundary phase and the sintering temperature of the magnet by uniformly coating the surface of the base material powder particles with a low-melting-point grain boundary alloy, thus significantly reducing the production cost of permanent magnets. Simultaneously, it allows the main phase within the permanent magnet to be uniformly enveloped by the grain boundary phase, effectively isolating the magnetic exchange coupling between the main phase grains, reducing grain boundary defects, and thereby significantly improving the coercivity of the permanent magnet.

[0063] 4. By adjusting the particle size and addition ratio of the packaging material, this invention can accurately and effectively control the proportion and distribution morphology of the grain boundary phase. The resulting low-melting-point continuously distributed grain boundary phase greatly enhances the channels for grain boundary diffusion, allowing the diffusion source to penetrate deep into the magnet. This significantly improves the performance enhancement effect of heavy rare earth elements on the magnet, enhances the consistency of the composition and performance of the permanent magnet obtained by grain boundary diffusion, and further increases the diffusion thickness of grain boundary diffusion in the permanent magnet. Attached Figure Description

[0064] Figure 1 is a TEM image of the magnet matrix of Example 11, showing the grain boundary phase with a bulk structure.

[0065] Figure 2 is a TEM image of the magnet matrix of Example 11, showing the grain boundary phase with a thin band structure.

[0066] Figure 3 is a TEM image of the magnet substrate of Example 11.

[0067] Figure 4 is a TEM image of the magnet substrate in Comparative Example 1. Detailed Implementation

[0068] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0069] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0070] Examples 1-16, Comparative Example 1

[0071] (I) Preparation of parent material powder particles:

[0072] Prepare raw materials according to the following RTB permanent magnet composition, melt the raw materials in an argon atmosphere, and cast the melt onto a quenching roller to form a base alloy sheet; after hydrogenation treatment and air jet milling, the base alloy sheet is used to obtain base powder particles with an average particle size of 2.8 μm.

[0073] The composition of the RTB-based permanent magnets is as follows: 29% Nd, 0.9% B, 1.0% Co, 0.5% Ga, 0.15% Cu, 0.25% Al, 0.1% Zr, and 0.18% Ti.

[0074] (II) Preparation of Packaging Material Particles:

[0075] The target component alloy of the packaging material particles is melted into packaging material alloy sheets in a nitrogen atmosphere. The packaging material alloy sheets are then initially crushed using a ball mill, and finally pulverized using an air jet mill to achieve the target average particle size, thus producing packaging material particles. Specifically, the target components and target average particle size of the packaging material particles are shown in Table 1.

[0076] Table 1

[0077] (III) Preparation of NdFeB Sintered Magnets

[0078] (1) The base material powder particles and the packaging material particles are thoroughly mixed as follows: using high-speed argon gas as the driving force, the packaging material particles are impacted onto the surface of the base material powder particles by mechanical collision. At this time, the packaging material particles are deformed and attached to the surface of the base material powder particles, thereby obtaining the coated powder particles. The composition, average particle size and addition amount of the packaging material particles are shown in Table 1.

[0079] (2) The coated powder particles are sorted by a sorting device to collect powder particles with a particle size of 2-5μm into a material tank. After adding 0.5wt% lubricant, the mixture is mixed for 3h to obtain mixed powder particles, which are then pressed into compacts.

[0080] (3) The pressed blank is first heat-treated, and then processed to obtain a magnet matrix with dimensions of 48.5*11*5mm; wherein,

[0081] The specific conditions for heat treatment are: sintering under vacuum conditions, sintering temperature of 900℃, and sintering time of 8h;

[0082] After sintering, a second aging treatment is performed. The specific conditions are as follows: the temperature of the first aging treatment is 700℃ and the time is 60min; the temperature of the second aging treatment is 400℃ and the time is 120min.

[0083] The processed magnet substrate is cleaned, degreased, and acid-washed for later use.

[0084] (iv) Diffusion treatment

[0085] Diffusion sources, made of metallic Tb, were arranged on the surface of the aforementioned magnet substrate using a vacuum sputtering method. The magnet substrate with the diffusion sources was then heated under vacuum conditions. When the heating temperature reached the temperature for grain boundary diffusion treatment, an inert gas of 10 kPa was introduced. After holding at this temperature, the substrate was cooled to room temperature. The temperature for grain boundary diffusion treatment was 800°C, and the holding time was 3 hours. The magnet after diffusion treatment was then subjected to aging treatment at a temperature of 400°C. After cooling to room temperature, the magnet after diffusion treatment was cleaned, degreased, and acid-washed to obtain a sintered NdFeB permanent magnet.

[0086] Test case

[0087] (1) By testing the magnet matrix prepared in step (iii) of the above embodiments and comparative examples, it can be seen that the magnet produced after being coated with the parent material powder particles has the main phase in the magnet being uniformly wrapped by the grain boundary phase, which effectively isolates the magnetic exchange coupling between the main phase grains, reduces grain boundary defects, and thus significantly improves the coercivity of the magnet. The specific test results are shown in Table 1.

[0088] (2) The magnet substrates of Example 11 and Comparative Example 1 were subjected to TEM detection and analysis. The detection equipment was a JEOL-2010F scanning transmission electron microscope. The TEM detection results are as follows:

[0089] The magnet matrix of Example 11 was observed using a scanning transmission electron microscope. The aspect ratios of the main phase grains containing points A1, A2, A3, and A4 within the field of view are recorded in Table 2. The TEM image of point A1 within this field of view is shown in Figure 3.

[0090] Table 2

[0091] The magnet matrix of Comparative Example 1 was observed using scanning transmission electron microscopy. The main phase grains containing points B1, B2, B3, and B4 within the field of view are shown in Table 3, with their major and minor diameters as shown. The TEM image of point B1 within this field of view is shown in Figure 4.

[0092] Table 3

[0093] The above test results show that:

[0094] The magnet matrix includes at least a grain boundary phase and a main phase grain; the main phase grain has an RTB-type phase structure;

[0095] The grain boundary phase is distributed in the form of clumps or thin bands of uniform thickness at or between the main phase grains; wherein, the clump-shaped grain boundary phase refers to a grain boundary with a maximum size greater than 100 nm when projected in any direction, as shown in the clump structure in Figure 1; the thin band-shaped grain boundary phase refers to a grain boundary with a maximum size less than 100 nm when projected in any direction, as shown in the thin band structure in Figure 2.

[0096] TEM observation of the grain boundary state in Example 11 revealed that, within the visual detection range, the volume percentage of the bulky grain boundary phase was 65%, and the volume percentage of the thin-banded grain boundary phase was 35%. Within the visual detection range, the main phase grains were nearly spherical, with an aspect ratio between 1:1 and 1:1.2.

[0097] TEM observation of the grain boundary state of Comparative Example 1 revealed that, within the visual detection range, 85% of the grain boundary phase was clumpy, and 15% was ribbon-like, indicating a high proportion of clumpy grain boundary phase. Within the visual detection range, the aspect ratio of the main phase grains was not between 1:1 and 1:1.2, and many grains were not nearly spherical.

[0098] (3) Take the sintered NdFeB permanent magnets prepared in Example 11 and Comparative Example 1 respectively, and test their Hcj after diffusion. The results are recorded in Table 4.

[0099] Table 4

[0100] As can be seen from Table 4, the NdFeB magnet matrix made using the powder particles coated in this invention exhibits greater magnetic enhancement after diffusion treatment.

[0101] The inventors believe that this invention, by including at least a grain boundary phase and main phase grains in the magnet matrix, wherein the main phase grains have an RTB-type phase structure, and the grain boundary phase is distributed in a clump-like or uniformly thick, continuous thin band at or between the main phase grains, can achieve precise control over the microstructure of the magnet, thereby improving its magnetic properties. By controlling the average particle size and amount of the packaging material particles to obtain the aforementioned coated powder particles, when used to prepare the magnet matrix, the proportion and distribution morphology of the grain boundary phase in the magnet matrix can be precisely and effectively controlled, thereby forming a low-melting-point, continuously distributed grain boundary phase, which greatly enhances the channels for grain boundary diffusion.

[0102] During diffusion treatment, the diffusion source can penetrate deep into the interior of the magnet matrix, thereby significantly improving the enhancement effect of heavy rare earth elements on magnetic properties, thus improving the performance of grain boundary diffused magnets and the consistency of magnetic properties in different parts of the magnet, and further increasing the thickness of grain boundary diffusion.

[0103] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An R-T-B permanent magnet, characterized by, The R-T-B permanent magnet comprises at least a grain boundary phase and a main phase grain; The grain boundary phase is distributed in the form of lumps or thin strips with uniform thickness at the junction or between any two or more main phase grains; The main phase grain has an R-T-B type phase structure; The main phase grain has a near-circular shape; In the grain boundary phase, the volume percentage of the lump-shaped grain boundary phase is ≤80%, and the volume percentage of the thin strip-shaped grain boundary phase is ≥20%.

2. The method of producing an R-T-B magnet as claimed in claim 1, characterized by, The preparation method comprises: (1) preparing a composite magnetic powder by coating a wrapper particle on the surface of a base material powder particle to obtain the composite magnetic powder; (2) preparing the R-T-B permanent magnet by subjecting the composite magnetic powder in step (1) to compression treatment, heat treatment, and optionally diffusion treatment.

3. The production method according to claim 2, characterized by, In step (1), the composite magnetic powder comprises a core-shell structure, wherein the core is the base material powder particle, and the shell layer comprises the wrapper particle; the shell layer is obtained by deforming the wrapper particle after being adsorbed on the surface of the base material powder particle; The addition amount of the wrapper particle in the composite magnetic powder is 0.1-10%.

4. The production method according to claim 2, characterized by, The average particle size of the base material powder particle is 1-10 μm; The average particle size of the wrapper particle differs from the average particle size of the base material powder particle by one order of magnitude; The ratio of the average particle size of the wrapper particle to the average particle size of the base material powder particle is 0.1-1:1-10 or 10-100:1-10.

5. The preparation method according to claim 2, characterized in that, The components of the wrapper particle at least comprise a rare earth element R'; R' is selected from one or more of Pr, Nd, Tb, Dy, Ho, Gd, Ce, Y, and La; Alternatively, the components of the wrapper particle further comprise M1; M1 comprises one or more of Cu, Ga, Al, Zr, Ti, Sn, Mn, B, Fe, Co, V, and Se.

6. The production method according to claim 5, wherein The components of the wrapper particle comprise R' and M1, wherein the proportion of R' is 80wt%-99.5wt%, and the proportion of M1 is 0.5wt%-20wt%.

7. The preparation method according to claim 6, characterized in that, The components of the wrapper particle comprise R' and M1, wherein R' is selected from Pr or / and Nd, and the proportion of R' is 80wt%-99.5wt%; M1 is selected from B, and the proportion of M1 is 0.5wt%-20wt%.

8. The preparation method according to claim 2, characterized in that, In step (2), the heat treatment conditions comprise a sintering temperature of 800-1100 ℃ and a sintering time of 2-10 h.

9. The preparation method according to claim 2, characterized in that, In step (2), the diffusion treatment comprises arranging a diffusion source on the surface of the magnet substrate obtained after heat treatment, heating under vacuum conditions, filling 10 kPa-30 kPa of inert gas when the heating temperature rises to the temperature of the grain boundary diffusion treatment, and cooling to room temperature after holding; the diffusion source comprises a heavy rare earth element.

10. Application of the R-T-B permanent magnet of claim 1 in the fields of rare earth permanent magnet motors, intelligent consumer electronics, and medical devices.

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