A thin film grain boundary diffusion source and preparation method, and a method for preparing a neodymium iron boron magnet

Abstract

The present invention discloses a thin-film grain boundary diffusion source and a preparation method, and a method for preparing a neodymium iron boron magnet. The thin-film grain boundary diffusion source comprises a flexible high-temperature resistant carrier; HRE diffusion source films are attached to both sides of the flexible high-temperature resistant carrier; microporous membranes are respectively attached to the outer surfaces of the two HRE diffusion source films; the present invention performs grain boundary diffusion on the magnet using the HRE diffusion source prepared by electrophoretic deposition, which can effectively improve the coercive force of the magnet; at the same time, the microporous membrane prepared by secondary electrophoretic deposition will not hinder the diffusion of the HRE diffusion source into the interior of the magnet, and can also avoid large-area contact between the HRE diffusion source and the magnet surface, reduce the formation of an excessively thick shell layer, and improve the utilization rate of the HRE; the high-temperature resistance and oxidation resistance of the flexible high-temperature resistant carrier avoid oxidation of the diffusion material and reduce unnecessary consumption of the HRE; due to the presence of the flexible high-temperature resistant carrier, contact between magnets will not produce adhesion, thereby increasing the loading capacity and improving production efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnetic materials, and in particular to a thin film grain boundary diffusion source and a preparation method thereof, and a preparation method of a neodymium iron boron magnet. Background Art

[0002] Sintered NdFeB magnets possess superior magnetic properties. Various methods exist to enhance the coercivity of sintered NdFeB magnets, a common approach being grain boundary diffusion, which involves the diffusion of heavy rare earth elements (RREs) such as Dy and Tb. HREs can enhance the magnetic isolation between the main phases by forming an HRE-rich shell with a high anisotropy field (Ha) and a continuous grain boundary phase, thereby improving the Hcj effect. However, a significant increase in HRE usage can lead to a significant increase in cost. In recent years, mixed diffusion sources of HRE and low-melting-point metals have been used, including Dy-Zn, Pr-Tb-Cu, Pr-Tb-Cu-Al, Tb-Dy-Fe, and Pr-Cu-Al. Compared to HRE diffusers, mixed diffusers have a more pronounced effect on Hcj.

[0003] Grain boundary diffusion (GBD) technologies currently in mass production all involve depositing a layer of heavy rare earth elements (HREs) on the magnet surface as a diffusion source. Then, through diffusion processing, the HREs are allowed to penetrate into the magnet along the grain boundaries, achieving GBD. There are two methods for forming mixed diffusion sources on the magnet surface: one involves depositing one or more layers of HREs on the magnet surface using electroplating, spraying, printing, or other methods. The other involves using HRE metal targets and employing vacuum evaporation and PVD. Spraying and printing offer simple processes and high production efficiency, but they lack precise control over the diffusion source. Vapor deposition and PVD are environmentally friendly and can deposit thin, uniform films, but they suffer from low production efficiency, high cost, and difficulty adjusting the diffusion source components.

[0004] In addition, when the diffusion source is directly deposited on the surface of the magnet, the diffusion material is in direct contact with the magnet surface during high-temperature diffusion. The HRE diffusion source will inevitably exchange elements with the surface Nd-Fe-B grains, forming a thicker shell or even an inverse core / shell structure. An excessively thick shell (over 15nm) cannot effectively further improve the coercive force of the magnet. The HRE diffusion depth in thick magnets is limited, the gradient is large, and the formation of an inverse core / shell structure will also have a negative impact on the magnetic properties.

[0005] The invention with patent application number CN 108231322 A proposes to form a dry layer with HRE compounds attached on a flexible high-temperature resistant carrier by spraying to prepare an HRE diffusion source, which is then diffused into a rare earth sintered magnet. This method can reduce the surface area of ​​the HRE compound, adjust its diffusion mode and diffusion speed, and thus improve the diffusion efficiency and diffusion quality. However, this method uses spraying to prepare the HRE diffusion source. The spraying process makes it difficult to control the dissipation and overflow of the slurry, resulting in material waste. At the same time, the thickness of the coating is difficult to control and the structure between the heavy rare earth element powder particles in its internal structure is loose, which affects the diffusion depth in the magnet, resulting in a low coercive force of the subsequently formed magnet.

[0006] In addition, the HRE diffusion source prepared by this method is highly active and easily oxidized when exposed to air. It is difficult to store and cannot be used in large-scale production and application. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a thin film grain boundary diffusion source and a preparation method, as well as a method for preparing NdFeB magnets. The preparation method has a simple process, high production efficiency, can effectively increase the diffusion depth, reduce the formation of excessively thick shells, and improve the HRE utilization rate.

[0008] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a thin film grain boundary diffusion source, including a flexible high-temperature resistant carrier; HRE diffusion source films are attached to both sides of the flexible high-temperature resistant carrier; microporous membranes are respectively attached to the outer surfaces of the two HRE diffusion source films.

[0009] Furthermore, the flexible high-temperature resistant carrier is made of a metal selected from Group IVB, Group VB, Group VIB or Group VIIB of the periodic table, including Mo, W, Nb, Ta, Ti, Hf, Zr, Ti, V, Re, or an alloy of the above materials, and has a thickness of 0.01-0.5 mm.

[0010] Furthermore, the HRE diffusion source is an HRE compound, the HRE is one or more of Dy, Tb, Gd or Ho, the HRE compound is one or more selected from the oxide, fluoride, hydride, chloride or nitrate of HRE, and the thickness of the HRE diffusion source is 10μm-200μm.

[0011] Furthermore, the thickness of the microporous membrane is 10-15 μm, and the pore size is 3-5 nm.

[0012] A method for preparing a thin film grain boundary diffusion source comprises the following steps:

[0013] S1) preparing a flexible high-temperature resistant carrier with a thickness of 0.01-0.5 mm;

[0014] S2) adding a formulating agent to the HRE compound suspension, ultrasonically dispersing it uniformly, and then adding it to the electrolytic cell;

[0015] S3) Using a flexible high-temperature resistant carrier as a cathode and a copper sheet as an anode, setting a deposition voltage of 20-200 V, and using a DC power supply for deposition, a diffusion source substrate having a heavy rare earth compound coating deposited on the surface is obtained.

[0016] S4) preparing an Al(OH)3 precipitate, and then ultrasonically dispersing the Al(OH)3 precipitate in an organic medium to form a transparent and stable Al(OH)3 sol, using a diffusion source substrate as a cathode and a copper sheet as an anode, setting a deposition voltage of 20-100V, and using a DC power supply for deposition to obtain a thin film grain boundary diffusion source with a γ-Al2O3 microporous film deposited on the surface.

[0017] Furthermore, the HRE compound suspension is obtained by adding one or more of HRE oxides, fluorides, hydrides, chlorides or nitrates into anhydrous ethanol.

[0018] Furthermore, the formulating agent is CuCl2·2H2O, MgCl2·6H2O or ZnCl2.

[0019] Furthermore, the Al(OH)3 precipitate is obtained by adding Al(OH)3 into anhydrous ethanol, then adding a formulating agent, and uniformly dispersing the mixture by ultrasonication.

[0020] A method for preparing a neodymium iron boron magnet comprises the following steps:

[0021] S1) preparing a thin film HRE diffusion source on a 0.01-0.5 mm thick flexible high temperature resistant support by electrophoretic deposition;

[0022] S2) preparing a sintered NdFeB blank;

[0023] S3) processing the sintered NdFeB blank into a substrate treated with grain boundary diffusion and performing surface treatment;

[0024] S4) The prepared thin-film HRE diffusion source is then attached to a substrate, and several layers are stacked inside the graphite box in a stacking manner of one layer of HRE diffusion source film and one layer of substrate; wherein the bottom and top layers are HRE diffusion source films;

[0025] S5) The stacked substrate and diffusion source film are sent into a sintering furnace for diffusion heat treatment to obtain a diffusion magnet.

[0026] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0027] The present invention uses HRE diffusion sources prepared by electrophoretic deposition to diffuse into the grain boundaries of the magnet, which can effectively improve the coercive force of the magnet. The microporous membrane prepared by secondary electrophoretic deposition has the characteristic of high temperature resistance. The micropores with a surface pore size of 5nm will not hinder the diffusion of the HRE diffusion source into the interior of the magnet. At the same time, it can also avoid large-area contact between the HRE diffusion source and the magnet surface, reduce the formation of an excessively thick shell layer, and improve the HRE utilization rate.

[0028] In addition, the γ-Al2O3 microporous membrane prepared by secondary electrophoretic deposition can isolate the HRE diffusion source from the air, effectively prevent the oxidation of the HRE diffusion source, and is easy to store and easy to achieve large-scale production and application.

[0029] Secondly, the high temperature resistance and oxidation resistance of the flexible high temperature resistant carrier avoids the oxidation of the diffused material, reduces the unnecessary consumption of HRE, and makes the diffused magnet have better magnetic properties.

[0030] In addition, due to the presence of a flexible, high-temperature resistant carrier, the contact between magnets will not cause adhesion, thereby increasing the loading capacity and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings:

[0032] Figure 1 A schematic structural diagram of a thin film grain boundary diffusion source according to an embodiment of the present invention;

[0033] Among them: flexible high temperature resistant carrier 1, HRE diffusion source film 2, microporous membrane 3. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0035] The present invention provides a method for preparing a grain boundary diffusion source and a high-performance sintered NdFeB magnet, so as to solve the problem in the prior art that the diffusion material is in direct contact with the magnet surface, the HRE diffusion source will inevitably exchange elements with the surface Nd-Fe-B grains, forming a thicker shell, which will have a negative impact on the magnetic properties.

[0036] For ease of understanding, the specific process in the embodiment of this application is described below. Figure 1In an embodiment of the present application, a thin film grain boundary diffusion source includes a flexible high temperature resistant carrier 1; HRE diffusion source films 2 are attached to both sides of the flexible high temperature resistant carrier 1; and microporous membranes 3 are respectively attached to the outer surfaces of the two HRE diffusion source films 2.

[0037] In this embodiment, the flexible high-temperature resistant carrier is made of a metal selected from Group IVB, Group VB, Group VIB or Group VIIB of the periodic table of Mo, W, Nb, Ta, Ti, Hf, Zr, Ti, V, Re, or an alloy of the above materials, with a thickness of 0.01-0.5 mm. The flexible high-temperature resistant carrier is flexible and has excellent adhesion to the diffusion source film 2.

[0038] In this embodiment, the HRE diffusion source is an HRE compound, the HRE is one or more of Dy, Tb, Gd or Ho, the HRE compound is one or more selected from the oxide, fluoride, hydride, chloride or nitrate of HRE, and the thickness of the HRE diffusion source is 10μm-200μm.

[0039] In addition, in order to avoid oxidation of the HRE diffusion source film 2, it is necessary to continue to deposit a layer of γ-Al2O3 microporous membrane with a thickness of 10-15um and a pore size of 5nm on the surface 2 of the HRE diffusion source film through EPD. The microporous membrane has the characteristics of high temperature resistance and the surface pore size of 5nm. This will not hinder the diffusion of the HRE diffusion source into the interior of the magnet. At the same time, it can also avoid large-area contact between the HRE diffusion source and the magnet surface, reduce the formation of an excessively thick shell layer, and improve the HRE utilization rate. Among them, the thickness of the microporous membrane is 10-15um and the pore size is 3~5nm.

[0040] The present invention discloses a method for preparing a thin film grain boundary diffusion source, comprising the following steps:

[0041] S1) preparing a flexible high-temperature resistant carrier with a thickness of 0.01-0.5 mm by die-cutting;

[0042] S2) adding a formulating agent to the HRE compound suspension, ultrasonically dispersing it uniformly, and then adding it to the electrolytic cell;

[0043] S3) using a flexible high-temperature resistant carrier as a cathode and a copper sheet as an anode, setting a deposition voltage of 20-200 V, and using a DC power supply for deposition to obtain a diffusion source substrate having a heavy rare earth compound coating deposited on the surface, wherein the deposition time is controlled within 20-600 s according to the required deposition amount;

[0044] S4) preparing an Al(OH)3 precipitate, and then ultrasonically dispersing the Al(OH)3 precipitate in an organic medium to form a transparent and stable Al(OH)3 sol, wherein the organic medium is a solution of ethanol, acetylacetone, etc., and then using a diffusion source substrate as a cathode and a copper sheet as an anode, setting a deposition voltage of 20-100V, and using a DC power supply for deposition to obtain a thin film grain boundary diffusion source with a γ-Al2O3 microporous film deposited on the surface.

[0045] As a further illustration of the present application, the HRE compound suspension is obtained by adding one or more of HRE oxides, fluorides, hydrides, chlorides or nitrates into anhydrous ethanol, and the concentration of the HRE compound suspension is 1-20 g / L.

[0046] As a further illustration of the present application, the formulating agent is CuCl2·2H2O, MgCl2·6H2O or ZnCl2, and the concentration of the formulating agent is 0.001 to 2 mol / L.

[0047] As a further explanation of the present application, the Al(OH)3 precipitate is obtained by adding Al(OH)3 to anhydrous ethanol, then adding a formulating agent, and ultrasonically dispersing the mixture uniformly. The concentration of the Al(OH)3 precipitate is 0.1-10 g / L, and the preferred concentration is 5 g / L.

[0048] In addition, the preparation method of the thin film grain boundary diffusion source can effectively control the thickness of the deposited rare earth compound by changing the deposition voltage and deposition time to meet different needs.

[0049] The present invention also discloses a method for preparing a neodymium iron boron magnet, comprising the following steps:

[0050] 1) A thin film HRE diffusion source is prepared on a flexible high temperature resistant carrier with a thickness of 0.01-0.5 mm by electrophoretic deposition. The thickness of 0.01-0.5 mm is used to ensure the ductility of the flexible high temperature resistant carrier.

[0051] 2) preparing a sintered NdFeB blank for grain boundary diffusion treatment, wherein the components are composed by mass percentage: Pr-Nd: 29% to 32%, Co: 0.8 to 1.2%, Al: 0.05-0.2%, Nb: 0.5 to 1.0%, B: 1.0% to 1.2%, Cu: 0 to 0.2%, Ti: 0 to 0.2%, Zr: 0.1 to 0.3% and the balance Fe;

[0052] 3) Processing the sintered NdFeB blank into a substrate treated with grain boundary diffusion, the orientation direction of which is similar to the finished product size, within the range of 1mm-10mm, and undergoing surface treatment;

[0053] 4) The prepared thin-film HRE diffusion source is then attached to a substrate, and several layers are stacked inside the graphite box in a stacking manner of one layer of HRE diffusion source film and one layer of substrate; the bottom and top layers are the diffusion source films;

[0054] 5) The stacked substrate and diffusion source film are placed in a sintering furnace for diffusion heat treatment. First, the diffusion treatment is carried out at 750-1000°C for 3-20 hours, followed by low-temperature tempering treatment at 400-600°C for 4-8 hours to obtain a diffusion magnet.

[0055] Among them, during the diffusion heat treatment process, since the carrier of the thin film HRE diffusion source has the characteristics of high temperature resistance, the stacked magnets are separated by flexible high temperature resistant carriers, which can effectively avoid the surface adhesion of magnets in mass production.

[0056] Several examples of the preparation of NdFeB magnets are listed below for illustration.

[0057] Example 1

[0058] 1) A molybdenum sheet with a thickness of 0.5 mm was prepared as a flexible high-temperature resistant carrier by die-cutting, and the surface of the molybdenum sheet was then pickled to remove surface oil stains, and then washed with deionized water and dried for later use.

[0059] 2) Add 2.5 L of anhydrous ethanol solution to the electrophoresis cell, add terbium fluoride powder and CuCl2·2H2O formulating agent, stir thoroughly and disperse by ultrasonication, wherein the mass concentration of terbium fluoride powder is 10 g / L and the concentration of CuCl2·2H2O formulating agent is 0.2 mol / L;

[0060] 3) using a flexible high-temperature resistant carrier as a cathode and a copper sheet as an anode, setting a deposition voltage of 20-100 V and using a DC power supply for deposition; controlling the deposition time to 180-300 s depending on the desired deposition amount, to obtain a diffusion source substrate with an HRE compound coating deposited on the surface;

[0061] 4) Preparing an Al(OH)3 precipitate, and then ultrasonically dispersing the precipitate in an organic medium to form a transparent and stable Al(OH)3 sol. Deposition was performed using a DC power supply with a diffusion source substrate as the cathode and a copper sheet as the anode, and a deposition voltage of 50 V. The deposition time was controlled to 30 seconds depending on the desired deposition amount, resulting in a thin film grain boundary diffusion source with a γ-Al2O3 microporous film deposited on the surface (Examples 1.1-1.9).

[0062] 5) preparing a rare earth sintered magnet having the following composition by mass percentage: Pr-Nd: 29%, Co: 0.8%, Al: 0.15%, Nb: 0.5%, B: 0.97%, Cu: 0.1%, Ti: 0.2%, Zr: 0.1%, and the balance Fe;

[0063] 6) The processed sintered magnet was processed into a square magnet with a size of 10mm*10mm*4mm, with the 4mm direction being the magnetic field orientation direction. After surface cleaning, the processed magnet was tested for magnetic properties using a Mianyang Bipolar 264Y permanent magnet property automatic measuring instrument at a measurement temperature of 20°C. The measurement results were Br: 14.38kGs, Hcj: 15.62kOe, (BH)max: 50.35MGOe, and SQ: 97.8%.

[0064] 7) The prepared thin-film HRE diffusion source is then attached to a substrate, and several layers are stacked inside the graphite box in the order of one layer of HRE diffusion source film and one layer of substrate; the bottom and top layers are diffusion source films.

[0065] 8) Sending the stacked substrate and diffusion source film into a sintering furnace for diffusion heat treatment;

[0066] 9) The diffused magnets were tested for magnetic properties using a 264Y permanent magnet automatic measuring instrument from Mianyang Bipolar, with the measuring temperature being 20°C.

[0067] Table 1 Magnetic performance evaluation of the examples

[0068]

[0069] In Examples 1.1-1.9, no oxidation or rust was observed on the surfaces of the magnets, nor were there blank areas of diffusion source powder. This indicates that the HRE diffusion source of the present invention has excellent adhesion to the diffusion matrix. Furthermore, as shown in Table 1, the coercive force increment increases with increasing deposition voltage and deposition time, but Br (remanence) and SQ (squareness) do not decrease dramatically. The best overall magnetic properties were achieved when the electrophoresis voltage was 100 V and the electrophoresis time was 240 s. Therefore, grain boundary diffusion of the HRE diffusion source prepared by electrophoretic deposition can effectively improve the coercive force of the magnet.

[0070] Example 2

[0071] 1) A tantalum sheet with a thickness of 0.5 mm was prepared by die-cutting as a flexible high-temperature resistant carrier, and the surface of the tantalum sheet was then pickled to remove surface oil stains, and then washed with deionized water and dried for later use;

[0072] 2) Add 2.5 L of anhydrous ethanol solution to the electrophoresis cell, add terbium fluoride powder and CuCl2·2H2O formulating agent, stir thoroughly and disperse by ultrasonication, wherein the mass concentration of terbium fluoride powder is 10 g / L and the concentration of CuCl2·2H2O formulating agent is 0.2 mol / L;

[0073] 3) Using a flexible high-temperature resistant carrier as the cathode and a copper sheet as the anode, deposition was performed using a DC power supply at a deposition voltage of 100 V. The deposition time was controlled at 240 s based on the desired deposition amount, yielding a diffusion source substrate 1 having an HRE compound coating deposited on its surface. The measured weight gain of the HRE diffusion source was 0.75%, meaning that the mass of the heavy rare earth compound coating added to the magnet was 0.75% of the original mass of the magnet.

[0074] 4) preparing an Al(OH)3 precipitate, and then ultrasonically dispersing the precipitate in an organic medium (a solution of ethanol, acetylacetone, etc.) to form a transparent and stable Al(OH)3 sol. Using the diffusion source substrate 1 as the cathode and the copper sheet as the anode, the deposition voltage was set to 50 V and a DC power supply was used for deposition. The deposition time was controlled at 30 seconds according to the required deposition amount, thereby obtaining a thin film grain boundary diffusion source with a γ-Al2O3 microporous film deposited on the surface.

[0075] 5) preparing a rare earth sintered magnet having the following composition by mass percentage: Pr-Nd: 29%, Co: 0.8%, Al: 0.15%, Nb: 0.5%, B: 0.97%, Cu: 0.1%, Ti: 0.2%, Zr: 0.1%, and the balance Fe;

[0076] 6) The processed sintered magnet was processed into a square magnet with a size of 10mm*10mm*4mm, with the 4mm direction being the magnetic field orientation direction. After surface cleaning, the processed magnet was tested for magnetic properties using a Mianyang Bipolar 264Y permanent magnet property automatic measuring instrument at a measurement temperature of 20°C. The measurement results were Br: 14.38kGs, Hcj: 15.62kOe, (BH)max: 50.35MGOe, and SQ: 97.8%;

[0077] 7) The prepared thin-film HRE diffusion source is then attached to a substrate, and several layers are stacked inside the graphite box in a stacking manner of one layer of HRE diffusion source film and one layer of substrate; the bottom and top layers are the diffusion source films;

[0078] 8) The stacked substrate and diffusion source film are sent to a sintering furnace for diffusion heat treatment to obtain a diffusion magnet (Example 2.1);

[0079] 9) The diffused magnets were tested for magnetic properties using a 264Y permanent magnet automatic measuring instrument from Mianyang Bipolar at a temperature of 20°C.

[0080] 10) Using the method of CN 108231322 A, a tantalum sheet was sprayed with 0.75% terbium hydride powder by weight, and then the tantalum sheet with 0.75% terbium hydride powder was attached to a substrate and the same treatment as steps (7-9) was performed to obtain Comparative Example 2.1;

[0081] 11) A single-layer terbium hydride diffusion film was deposited on a diffusion substrate using conventional screen printing, PVD coating, and electrophoresis methods as a comparative example, wherein the weight gain ratio of the terbium hydride diffusion source was controlled at 0.75% (Comparative Examples 2.2-2.3).

[0082] Table 2 Magnetic performance evaluation of the examples

[0083]

[0084] As can be seen from Table 2, the performance of the diffusion magnet prepared by the present invention is close to that of the diffusion magnet prepared by PVD under the premise of the same HRE diffusion source dosage. However, PVD has disadvantages such as low production efficiency, high price, and difficulty in adjusting the diffusion source elements.

[0085] The performance of the diffusion magnet prepared by the present invention is superior to that of the diffusion magnet prepared by the method with patent number CN 108231322 A, and is also superior to that of the diffusion magnet prepared by traditional screen printing and traditional electrophoresis. This is because the γ-Al2O3 microporous membrane has the characteristics of high temperature resistance, and the surface pores with a diameter of 5nm do not hinder the diffusion of the HRE diffusion source into the interior of the magnet. At the same time, it can also avoid large-area contact between the HRE diffusion source and the magnet surface, reduce the formation of an excessively thick shell layer, and improve the utilization rate of the HRE.

[0086] At the same time, during the entire diffusion process, the high temperature resistance and oxidation resistance of the tantalum sheet avoid the oxidation of the diffusion material and reduce unnecessary consumption of HRE. Therefore, under the same HRE diffusion source dosage, the diffusion magnet prepared by the present invention has better magnetic properties.

[0087] In addition, due to the presence of tantalum sheets, the contact between magnets will not cause adhesion, thereby increasing the loading capacity and improving production efficiency.

[0088] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a thin film grain boundary diffusion source, characterized in that: The thin film grain boundary diffusion source comprises a flexible high temperature resistant carrier; HRE diffusion source films are attached to both sides of the flexible high temperature resistant carrier; microporous membranes are attached to the outer surfaces of the two HRE diffusion source films respectively; the flexible high temperature resistant carrier is made of a metal selected from the group consisting of Mo, W, Nb, Ta, Ti, Hf, Zr, V, Re, and a metal of Group IVB, VB, VIB, or VIIB of the periodic table, or an alloy of the above materials, and has a thickness of 0.01-0.5 mm; the HRE diffusion source is an HRE compound, the HRE is one or more of Dy, Tb, Gd, or Ho, the HRE compound is one or more of the oxides, fluorides, hydrides, chlorides, or nitrates of HRE, and the thickness of the HRE diffusion source is 10 μm-200 μm; The method for preparing the thin film grain boundary diffusion source comprises the following steps: S1) preparing a flexible, high-temperature-resistant carrier having a thickness of 0.01-0.5 mm; S2) adding a formulating agent to the HRE compound suspension, ultrasonically dispersing the suspension to uniformity, and then adding the suspension to the electrolytic cell; S3) using a flexible high-temperature resistant carrier as a cathode and a copper sheet as an anode, setting a deposition voltage of 20-200 V, and using a DC power supply for deposition to obtain a diffusion source substrate having a heavy rare earth compound coating deposited on its surface; S4) Prepare Al(OH)3 precipitate, then ultrasonically disperse the Al(OH)3 precipitate in an organic medium to form a transparent and stable Al(OH)3 sol, use the diffusion source substrate as the cathode and the copper sheet as the anode, set the deposition voltage to 20-100V, and use a DC power supply for deposition to obtain a thin film grain boundary diffusion source with a γ-Al2O3 microporous film deposited on the surface.

2. The method for preparing a thin film grain boundary diffusion source according to claim 1, wherein: The HRE compound suspension is obtained by adding one or more of HRE oxides, fluorides, hydrides, chlorides or nitrates into anhydrous ethanol.

3. The method for preparing a thin film grain boundary diffusion source according to claim 1, wherein: The formulating agent is CuCl2·2H2O, MgCl2·6H2O or ZnCl2.

4. The method for preparing a thin film grain boundary diffusion source according to claim 1, wherein: The Al(OH)3 precipitate is obtained by adding Al(OH)3 into anhydrous ethanol, then adding a formulating agent, and uniformly dispersing the mixture through ultrasonication.

5. A method for preparing a neodymium iron boron magnet, characterized in that: The steps include: S1) preparing a thin film HRE diffusion source using the method for preparing a thin film grain boundary diffusion source according to claim 1; S2) preparing a sintered NdFeB blank; S3) processing the sintered NdFeB blank into a substrate treated with grain boundary diffusion and performing surface treatment; S4) The prepared thin-film HRE diffusion source is then attached to a substrate, and several layers are stacked inside the graphite box in a stacking manner of one layer of HRE diffusion source film and one layer of substrate, wherein the bottom and top layers are HRE diffusion source films; S5) The stacked substrate and diffusion source film are sent into a sintering furnace for diffusion heat treatment to obtain a diffusion magnet.

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