A grain boundary diffusion method for high-coercivity neodymium-iron-boron magnets

Abstract

The application provides a grain boundary diffusion method of high-coercivity neodymium-iron-boron magnets, which comprises the following steps: mixing heavy rare earth alloy powder with an organic solvent, coating the mixture on the surface of a neodymium-iron-boron magnet and drying, and then performing heat diffusion treatment. In the application, the heavy rare earth alloy powder for grain boundary diffusion is prepared by using a monodisperse gas atomization method, then mixed with the organic solvent uniformly and coated on the surface of the neodymium-iron-boron magnet, and then subjected to grain boundary diffusion treatment, so that the uniformity of coating is improved, the diffusion of the magnet is more uniform, the diffusion of rare earth elements in the grain is reduced, the problem of reduction of remanence of the magnet caused by the diffusion of the rare earth elements is alleviated or eliminated, and beneficial comprehensive magnetic properties are obtained.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, and relates to grain boundary diffusion of magnets, and particularly to a method for grain boundary diffusion of high coercivity neodymium iron boron magnets. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets, as the third generation of rare-earth permanent magnets, are widely used in all aspects of our lives, such as computer disk drives, nuclear magnetic resonance (NMR) scanners, wind power generation, new energy vehicles, and permanent magnet motors. Modern science and technology, and the information industry, are developing towards integration, thinning, miniaturization, and intelligentization. The emergence of NdFeB permanent magnets has greatly promoted the progress of modern science and technology and the information industry, serving as one of its important material foundations. With the rapid development of new energy vehicles and intelligent manufacturing, the demand for NdFeB permanent magnets is also increasing.

[0003] CN106887323A discloses a method for preparing high coercivity NdFeB magnets via grain boundary diffusion, belonging to the field of magnetic materials. The low-melting-point metal is one of Ga, Zn, and Sn; the low-melting-point alloy composition is RM, where R is one or more of La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, and Y; and M is one or more of Cu, Al, Ga, Zn, Sn, and Ag. The process steps are as follows: first, the surface of the NdFeB magnet is cleaned; then, the magnet is preheated under vacuum; next, it is immersed in a vacuum-melted metal or alloy molten liquid for hot-dip coating to achieve surface coating; finally, the hot-dip coated NdFeB magnet undergoes diffusion heat treatment and subsequent annealing to improve the boundary structure and grain boundary phase distribution of the magnet, obtaining the desired high coercivity NdFeB magnet. The invention produces a uniform and strong coating on the magnet surface, which is beneficial to the grain boundary diffusion process and the uniformity of the magnet's structure and properties. At the same time, the thickness of the coating on the magnet surface can be flexibly controlled by controlling the immersion time and the removal speed, avoiding the waste of diffusion source metals or alloys. This hot-dip immersion process is continuous and fast, and is suitable for mass continuous production.

[0004] CN108831658A discloses a method for preparing high-coercivity NdFeB magnets by grain boundary diffusion under a constant magnetic field, comprising: preparing NdFeB alloy components, vacuum melting to obtain an alloy ingot, and rapidly quenching it into a thin strip; preparing a rare-earth ternary ReAlCu alloy components, vacuum melting to obtain a master alloy ingot, and rapidly quenching it into a thin strip, and then obtaining uniform low-melting-point rare-earth ternary ReAlCu nanopowder through high-energy ball milling; coating the ReAlCu nanopowder onto the free surface and quenched surface of the NdFeB alloy thin strip; and placing the thin strip alloy in parallel in a constant magnetic field annealing furnace with a magnetic field strength of 1.5T for vacuum magnetic field heat treatment. This invention uses a low-melting-point rare-earth ternary ReAlCu nanoalloy as a diffusion source, and by performing diffusion heat treatment on the NdFeB alloy under a constant magnetic field, promotes the alignment of the hard magnetic phase in the NdFeB alloy along the easy magnetization axis, thereby improving the grain boundary characteristics of the NdFeB magnet after diffusion.

[0005] CN112927921A discloses a method for preparing high-coercivity sintered NdFeB magnets via grain boundary diffusion. The method involves preparing a multilayer thin film of heavy rare earth alloy elements on the surface of a sintered NdFeB magnet using magnetron sputtering, followed by a vacuum thermal diffusion process, and finally tempering to obtain the high-coercivity NdFeB magnet. The thermal diffusion process is carried out at a temperature of 600–900°C for 3–10 hours. This method shortens the time required for sputtering the heavy rare earth alloy element thin film and achieves a deeper diffusion depth. Compared to methods that diffuse pure rare earth elements, the deeper diffusion depth further enhances the coercivity of the sintered NdFeB magnet.

[0006] Grain boundary diffusion treatment is a preferred method for improving the coercivity of NdFeB magnets. Heavy rare earth elements or their compounds are attached to the magnet surface through coating, magnetron sputtering, or evaporation. Heat treatment diffusion and tempering optimize the microstructure, enhance the anisotropic field of the epitaxial layer, and suppress demagnetization deformable nuclei. Grain boundary diffusion treatment allows heavy rare earth elements to diffuse along grain boundaries into the magnet interior, effectively reducing the diffusion of heavy rare earth elements into the main phase, avoiding a significant decrease in remanence and maximum energy product, and reducing the need for additional heavy rare earth elements. Therefore, it is urgent to study methods for improving the coercivity of NdFeB magnets through grain boundary diffusion. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a grain boundary diffusion method for high-coercivity NdFeB magnets. In this invention, heavy rare earth alloy powder with grain boundary diffusion is prepared by monodisperse gas atomization, then mixed uniformly with an organic solvent and coated onto the surface of the NdFeB magnet for grain boundary diffusion treatment. This improves the uniformity of the coating, makes the magnet diffusion more uniform, and reduces the diffusion of rare earth elements within the grains. This alleviates or eliminates the problem of reduced remanence of the magnet caused by the diffusion of rare earth elements, thereby obtaining beneficial comprehensive magnetic properties.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a grain boundary diffusion method for high coercivity NdFeB magnets, the grain boundary diffusion method comprising:

[0010] The heavy rare earth alloy powder is mixed with an organic solvent, coated onto the surface of the neodymium iron boron magnet, dried, and then subjected to thermal diffusion treatment.

[0011] In this invention, grain boundary diffusion heavy rare earth alloy powder is prepared by monodisperse gas atomization, then mixed uniformly with an organic solvent and coated on the surface of a NdFeB magnet for grain boundary diffusion treatment. This improves the uniformity of the coating, makes the magnet diffusion more uniform, and reduces the diffusion of rare earth elements inside the grains. This alleviates or eliminates the problem of reduced remanence of the magnet caused by the diffusion of rare earth elements, and obtains beneficial comprehensive magnetic properties.

[0012] As a preferred technical solution of the present invention, the constituent elements of the heavy rare earth alloy, based on a mass of 100 wt.%, include Dy, Tb, Cu, Al, Co, Ni, Nb, Zn, and Ga.

[0013] Preferably, the proportions of Dy and Tb are 85 to 99 wt.%, for example, 85 wt.%, 86 wt.%, 87 wt.%, 88 wt.%, 89 wt.%, 90 wt.%, 91 wt.%, 93 wt.%, 94 wt.%, 95 wt.%, 96 wt.%, 97 wt.%, 98 wt.%, and 99 wt.%, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0014] As a preferred technical solution of the present invention, the heavy rare earth alloy powder is prepared by the following method: the heavy rare earth and other non-rare earth metal raw materials are melted and then prepared by monodisperse gas atomization method to obtain the heavy rare earth alloy powder.

[0015] Preferably, the temperature of the melting process is 1100 to 1600°C, for example, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or 1600°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the monodisperse gas atomization method specifically includes the following steps:

[0017] Heavy rare earth and other non-rare earth metal raw materials are placed in a container and melted. An inert gas is introduced to create a pressure difference. A pulse signal with a certain voltage and frequency is input to make the melt vibrate periodically. Part of the melt is squeezed out from the micro-hole at the bottom of the container and falls freely. Gas is sprayed out from the atomizing nozzles on both sides. The molten metal squeezed out from the bottom of the container is broken into small droplets by the sprayed gas. After cooling and solidification, heavy rare earth alloy powder is formed.

[0018] As a preferred embodiment of the present invention, the monodisperse gas atomization method is carried out under an inert atmosphere.

[0019] Preferably, the inert atmosphere is an argon atmosphere.

[0020] Preferably, the pressure difference during the implementation of the monodisperse gas atomization method is 0 to 100 kPa, for example, it can be 0 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, or 100 kPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] As a preferred technical solution of the present invention, the frequency of the pulse signal is 20 to 200 Hz, for example, it can be 20 Hz, 30 Hz, 40 Hz, 60 Hz, 80 Hz, 100 Hz, 130 Hz, 150 Hz, 180 Hz, or 200 Hz, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the specified voltage is 3 to 100V, for example, it can be 3V, 10V, 20V, 30V, 40V, 50V, 60V, 70V, 80V, 90V, or 100V, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the angle at which the gas is ejected is 15 to 30°, for example, 15°, 17°, 19°, 20°, 21°, 22°, 24°, 26°, 27°, 29°, or 30°, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0024] Preferably, the velocity of the ejected gas is 260–470 m / s, for example, 260 m / s, 280 m / s, 300 m / s, 320 m / s, 340 m / s, 380 m / s, 400 m / s, 420 m / s, 440 m / s, 460 m / s, or 470 m / s, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] As a preferred embodiment of the present invention, the organic solvent includes gasoline and acrylic acid.

[0026] Preferably, the organic solvent also includes ethanol.

[0027] Preferably, the mass ratio of the heavy rare earth alloy powder to the volume ratio of the organic solvent is 20-110 g / 100 mL, for example, it can be 20 g / 100 mL, 30 g / 100 mL, 40 g / 100 mL, 50 g / 100 mL, 60 g / 100 mL, 70 g / 100 mL, 80 g / 100 mL, 90 g / 100 mL, or 100 g / 100 mL, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] This invention specifically limits the volume ratio of heavy rare earth alloy powder to organic solvent to 20-100 g / 100 mL. This is because when the ratio exceeds the limit of 100 g / 100 mL, it will lead to uneven coating. This is because when the ratio exceeds the limit, the powder will not disperse evenly in the organic solvent, thus affecting the coating effect. When the ratio is lower than the limit of 20 g / 100 mL, it will lead to increased production costs. This is because when it is lower than the limit, more coatings are required to achieve the required amount of heavy rare earth coating.

[0029] Preferably, the stirring speed of the mixing process is 60 to 280 r / min, for example, it can be 60 r / min, 80 r / min, 100 r / min, 140 r / min, 160 r / min, 180 r / min, 200 r / min, 220 r / min, 240 r / min, 260 r / min, or 280 r / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] As a preferred technical solution of the present invention, the neodymium iron boron magnet is pretreated before mixing.

[0031] Preferably, the pretreatment process includes:

[0032] After polishing the surface of the neodymium iron boron magnet, it is placed in a degreasing agent solution for ultrasonic cleaning, and then successively subjected to acid washing, water washing, alcohol washing and ultrasonic cleaning before being dried for later use.

[0033] As a preferred technical solution of the present invention, the temperature of the drying process is 55 to 75°C, for example, it can be 55°C, 60°C, 65°C, 68°C, 70°C, 73°C, or 75°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] As a preferred embodiment of the present invention, the vacuum degree of the thermal diffusion process is 1×10⁻⁶. -3 ~1×10 -2 Pa.

[0035] Preferably, the thermal diffusion process includes a thermal diffusion process and a tempering process.

[0036] Preferably, the temperature of the heat diffusion treatment process is 650 to 950°C, for example, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or 950°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] This invention specifically limits the temperature of the thermal diffusion process to 650–950°C. When the temperature exceeds the limit of 950°C, the remanence will decrease and the coercivity will not improve significantly. This is because high temperature will cause heavy rare earth elements to diffuse into the interior of the grains, reducing the saturation magnetization of the magnet and the content of heavy rare earth elements diffused into the interior of the magnet. When the temperature is below the limit of 650°C, the coercivity will not improve significantly. This is because the diffusion efficiency is slow at low temperatures, and only a small amount of heavy rare earth elements diffuse into the magnet.

[0038] Preferably, the heat diffusion treatment process takes 4 to 9 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, or 9 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the temperature of the tempering process is 350 to 600°C, for example, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] This invention specifically limits the tempering process temperature to 350–600°C. When the temperature exceeds the limit of 600°C, the remanence will decrease because the tempering temperature is too high, and heavy rare earth elements will diffuse more into the grain interior. When the temperature is below the limit of 350°C, the coercivity will not increase significantly because the tempering temperature is too low, and heavy rare earth elements will accumulate more at the corners of the grain boundaries, making it impossible to form a uniform core-shell structure.

[0041] Preferably, the tempering process takes 1 to 4 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] As a preferred embodiment of the present invention, the grain boundary diffusion method specifically includes the following steps:

[0043] (I) The heavy rare earth alloy powder is prepared by melting heavy rare earth and other non-rare earth metal raw materials and then using a monodisperse gas atomization method. The melting temperature is 1100-1600℃, the monodisperse gas atomization method is carried out in an argon atmosphere, the pressure difference between the inside and outside of the crucible is 0-100kPa, the input voltage is 3-100V, the input frequency is 20-200Hz, the gas ejection angle is 15-30°, and the flow rate is 260-470m / s.

[0044] (II) Mix the heavy rare earth alloy powder with an organic solvent. The ratio of the mass of the heavy rare earth alloy powder to the volume of the organic solvent is 20-110 g / 100 mL. The stirring speed during the mixing process is 60-280 r / min.

[0045] (III) Before mixing, the surface of the NdFeB magnet is polished, then ultrasonically cleaned in a degreasing agent solution, followed by acid washing, water washing, alcohol washing, and ultrasonic cleaning in sequence, and then dried for later use. The drying temperature is 55-75℃, and the vacuum degree of the heat diffusion treatment process is 1×10⁻⁶. -3 ~1×10 -2 Pa, the temperature of the thermal diffusion process is 650-950℃ and the time is 4-9h, and the temperature of the tempering process is 350-600℃ and the time is 1-4h to complete the grain boundary diffusion.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] In this invention, grain boundary diffusion heavy rare earth alloy powder is prepared by monodisperse gas atomization, then mixed uniformly with an organic solvent and coated on the surface of a NdFeB magnet for grain boundary diffusion treatment. This improves the uniformity of the coating, makes the magnet diffusion more uniform, and reduces the diffusion of rare earth elements inside the grains. This alleviates or eliminates the problem of reduced remanence of the magnet caused by the diffusion of rare earth elements, and obtains beneficial comprehensive magnetic properties. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0049] Example 1

[0050] This embodiment provides a grain boundary diffusion method for high coercivity NdFeB magnets, which specifically includes the following steps:

[0051] (1) The following mass percentages are used to prepare the ingredients: Tb: 90.50%, Al: 4.37% and Cu: 5.13%. The ingredients are put into the crucible cavity and heated to 1500℃ to melt. Argon gas is introduced to make the pressure difference between the inside and outside of the crucible 5kPa. A pulse signal with a driving voltage of 15V and a frequency of 80Hz is input to drive the piezoelectric ceramic to drive the transmission rod to vibrate. Part of the melt is squeezed out from the micropore at the bottom of the crucible and falls freely. Nitrogen gas with a gas pressure of 2.8MPa and a gas velocity of 290m / s is sprayed out at a 25° angle through the atomizing nozzles on both sides. The molten metal squeezed out from the bottom of the crucible is broken into small droplets. After cooling and solidification, heavy rare earth alloy powder for grain boundary diffusion is formed.

[0052] (2) The mass of heavy rare earth alloy powder and the volume of ethanol are prepared at 50g / 100mL, and the mixture is stirred evenly at a speed of 120r / min to obtain a suspension for grain boundary diffusion.

[0053] (3) The surface of the NdFeB magnet was polished with metallographic sandpaper to remove the oxide layer and smooth the surface. Then, it was ultrasonically cleaned for 15 seconds in a solution containing a degreasing agent. Next, the NdFeB magnet was cleaned with a 3-6% (v / v) nitric acid solution to create a microporous structure on the magnet surface for better adsorption of rare earth alloy powder. Finally, it was ultrasonically cleaned with deionized water and anhydrous ethanol in sequence and then dried. The suspension was then uniformly coated on the surface of the NdFeB magnet and dried at 55°C.

[0054] (4) Evacuate the dried neodymium iron boron magnet to a vacuum of 1×10⁻⁶. -2 Pa, heated to 850℃, held for 5 hours, and subjected to thermal diffusion treatment, so that the heavy rare earth elements in the rare earth alloy powder diffuse along the grain boundaries into the interior of the magnet. The magnet after thermal diffusion treatment is then tempered at 480℃ to obtain a diffused magnet.

[0055] Example 2

[0056] This embodiment provides a grain boundary diffusion method for high coercivity NdFeB magnets, which specifically includes the following steps:

[0057] (1) The following mass percentages are used to prepare the ingredients: Tb: 90.50%, Al: 4.37% and Cu: 5.13%. The ingredients are put into the crucible cavity and heated to 1430℃ to melt. Argon gas is introduced to make the pressure difference between the inside and outside of the crucible 5kPa. A pulse signal with a driving voltage of 20V and a frequency of 100Hz is input to drive the piezoelectric ceramic to drive the transmission rod to vibrate. Part of the melt is squeezed out from the micropore at the bottom of the crucible and falls freely. Nitrogen gas with a gas pressure of 2.8MPa and a gas velocity of 270m / s is sprayed out at a 20° angle through the atomizing nozzles on both sides. The molten metal liquid squeezed out from the bottom of the crucible is broken into small droplets. After cooling and solidification, heavy rare earth alloy powder for grain boundary diffusion is formed.

[0058] (2) The mass of heavy rare earth alloy powder and the volume of ethanol are prepared at 70g / 100mL, and the mixture is stirred evenly at a speed of 130r / min to obtain a suspension for grain boundary diffusion.

[0059] (3) The surface of the NdFeB magnet was polished with metallographic sandpaper to remove the oxide layer and smooth the surface. Then, it was immersed in a solution containing a degreasing agent for 15 seconds of ultrasonic cleaning to remove the oil. Next, the NdFeB magnet was cleaned with a 3-6% (v / v) nitric acid solution to create a microporous structure on the magnet surface for better adsorption of rare earth alloy powder. Finally, it was ultrasonically cleaned with deionized water and anhydrous ethanol in sequence and then dried for later use. Subsequently, the suspension was uniformly coated on the surface of the NdFeB magnet and dried at 58°C.

[0060] (4) Evacuate the dried neodymium iron boron magnet to a vacuum of 1×10⁻⁶. -2 Pa, heated to 900℃, held for 6 hours, and subjected to thermal diffusion treatment, so that the heavy rare earth elements in the rare earth alloy powder diffuse along the grain boundaries into the interior of the magnet. The magnet after thermal diffusion treatment is then tempered at 550℃ to obtain a diffused magnet.

[0061] Example 3

[0062] This embodiment provides a grain boundary diffusion method for high coercivity NdFeB magnets. The difference between this embodiment and Embodiment 1 is that in step (4), the dried NdFeB magnet is heated to 600°C for thermal diffusion treatment. The remaining process parameters and operating steps are exactly the same as in Embodiment 1.

[0063] Example 4

[0064] This embodiment provides a grain boundary diffusion method for high coercivity NdFeB magnets. The difference between this embodiment and Embodiment 1 is that in step (4), the dried NdFeB magnet is heated to 1000℃ for thermal diffusion treatment. The remaining process parameters and operating steps are exactly the same as in Embodiment 1.

[0065] The magnetic properties of the neodymium iron boron magnets prepared in each embodiment are shown in Table 1 below.

[0066] Table 1

[0067]

[0068] As can be seen from the data in Table 1:

[0069] Compared to Example 1, the coercivity data of Examples 3 and 4 are significantly lower than those of Example 1. This is because the thermal diffusion treatment temperature in Example 3 is too low, while the thermal diffusion treatment temperature in Example 4 is too high. Both excessively high and low thermal diffusion treatment temperatures affect the coercivity performance. The reason is that when the thermal diffusion treatment temperature exceeds the limit of 950°C, the content of heavy rare earth elements diffused into the magnet decreases, because the temperature is too high, resulting in more heavy rare earth elements diffusing into the grain interior. When the thermal diffusion treatment temperature is below the limit of 650°C, only a small amount of heavy rare earth elements diffuse into the magnet, because the temperature is too low, resulting in slower diffusion efficiency.

[0070] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0071] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A grain boundary diffusion method of high-coercivity neodymium-iron-boron magnets for reducing diffusion of rare earth elements inside the crystal grains, characterized by, The grain boundary diffusion method comprises the following steps: The heavy rare earth alloy powder is mixed with an organic solvent, coated on the surface of a Nd-Fe-B magnet, dried, and then subjected to a heat diffusion treatment; The heavy rare earth alloy powder is prepared by the following method: the heavy rare earth and other non-rare earth metal raw materials are melted, and then the heavy rare earth alloy powder is prepared by a monodisperse gas atomization method; The mass of the heavy rare earth alloy powder and the volume of the organic solvent are in a ratio of 20-110 g / 100 mL; The heat diffusion treatment process comprises a heat diffusion treatment process and a tempering process; The temperature of the heat diffusion treatment process is 650-950 ℃; The organic solvent comprises gasoline and acrylic acid; The monodisperse gas atomization method comprises the following steps: The heavy rare earth and other non-rare earth metal raw materials are melted in a container, inert gas is filled to form a pressure difference, a pulse signal with a certain voltage and frequency is inputted to make the melt vibrate periodically, part of the melt is extruded from the bottom of the container and freely falls under the joint action of the pressure difference, gas is sprayed from both sides of the atomization nozzle, the extruded melt is broken into small droplets by the sprayed gas, and the heavy rare earth alloy powder is formed after cooling and solidification.

2. The grain boundary diffusion method according to claim 1, characterized by, The heavy rare earth alloy powder comprises Dy, Tb, Cu, Al, Co, Ni, Nb, Zn and Ga, with the mass percentage being 100 wt.%.

3. The grain boundary diffusion method according to claim 2, wherein The mass percentage of Dy and Tb is 85-99 wt.%.

4. The grain boundary diffusion method of claim 1, wherein The monodisperse gas atomization method is carried out in an inert atmosphere.

5. The grain boundary diffusion method according to claim 4, wherein The inert atmosphere is an argon atmosphere.

6. The grain boundary diffusion method of claim 1, wherein The pressure difference during the implementation of the monodisperse gas atomization method is 0-100 kPa.

7. The grain boundary diffusion method of claim 1, wherein The temperature of the melting process is 1100-1600 ℃.

8. The grain boundary diffusion method of claim 7, wherein, The certain frequency is 20-200 Hz.

9. The grain boundary diffusion method of claim 7, wherein, The certain voltage is 3-100 V.

10. The grain boundary diffusion method of claim 7, wherein The angle of gas spraying is 15-30°.

11. The grain boundary diffusion method of claim 7, wherein, The flow rate of gas spraying is 260-470 m / s.

12. The grain boundary diffusion method of claim 1, wherein The organic solvent further comprises ethanol.

13. The grain boundary diffusion method of claim 1, wherein, The stirring speed of the mixing process is 60-280 r / min.

14. The grain boundary diffusion method of claim 1, wherein The Nd-Fe-B magnet is pretreated before mixing.

15. The grain boundary diffusion method of claim 14, wherein, The pretreatment process comprises the following steps: After the surface of the Nd-Fe-B magnet is polished, the magnet is placed in a degreasing agent solution for ultrasonic cleaning, and then subjected to acid pickling, water washing, alcohol washing and ultrasonic cleaning in sequence, and finally dried for standby use.

16. The grain boundary diffusion method of claim 1, wherein The temperature of the drying process is 55-75 ℃.

17. The grain boundary diffusion method of claim 1, wherein, The vacuum degree of the heat diffusion treatment process is 1x10 -3 ~1x10 -2 Pa.

18. The grain boundary diffusion method of claim 1, wherein, The time of the heat diffusion treatment process is 4-9 h.

19. The grain boundary diffusion method of claim 1, wherein, The temperature of the tempering process is 350-600 ℃.

20. The grain boundary diffusion method of claim 1, wherein, The time of the tempering process is 1-4 h.

21. The grain boundary diffusion method of claim 1, wherein, The grain boundary diffusion method comprises the following steps: (Ⅰ) The heavy rare earth alloy powder is prepared by the following method: the heavy rare earth and other non-rare earth metal raw materials are melted, and then the heavy rare earth alloy powder is prepared by a monodisperse gas atomization method, the temperature of the melting process is 1100-1600 ℃, the monodisperse gas atomization method is carried out in an argon atmosphere, the pressure difference is 0-100 kPa, the voltage of the input pulse signal is 3-100 V, the frequency is 20-200 Hz, the angle of gas spraying is 15-30°, and the flow rate is 260-470 m / s; (II) Mix the heavy rare earth alloy powder with an organic solvent. The mass ratio of the heavy rare earth alloy powder to the volume of the organic solvent is 20~110g / 100mL. The stirring speed during the mixing process is 60~280r / min. (III) before mixing, the surface of the neodymium iron boron magnet is polished, put into the oil removing agent solution for ultrasonic cleaning, then sequentially through pickling, washing, alcohol washing and ultrasonic cleaning and drying, the drying temperature is 55~75℃, then through the vacuum degree of 1×10 -3 ~1×10 -2 Pa, the temperature of the heat diffusion treatment process is 650~950℃, the time is 4~9h, the temperature of the tempering treatment process is 350~600℃, the time is 1~4h, and the grain boundary diffusion is completed.

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