A method for grain boundary diffusion of sintered neodymium-iron-boron magnets

Abstract

The application provides a sintered neodymium-iron-boron magnet grain boundary diffusion method, which comprises the following steps: taking a sintered neodymium-iron-boron magnet as a substrate, placing the substrate in a vacuum chamber of an ion implantation device, taking a heavy rare earth metal or a non-rare earth metal as an ion source material, and generating an ion beam to implant the magnet surface; and placing the magnet in a high-vacuum sintering furnace to perform multistage heat treatment, thereby obtaining a high-coercivity sintered neodymium-iron-boron magnet. Compared with a traditional coating or sputtering diffusion technology, the method has the advantages of high heavy rare earth utilization rate, strong interface bonding force and high diffusion efficiency. The prepared neodymium-iron-boron magnet has a significantly improved coercivity while maintaining a high remanence, thereby meeting the needs of high-end application fields such as new energy automobile motors and wind power generation.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, and particularly relates to a method for grain boundary diffusion in sintered NdFeB magnets. Background Technology

[0002] Sintered neodymium iron boron (NdFeB) rare earth permanent magnet materials are prized for their excellent magnetic properties, especially their extremely high maximum energy product (BH). max ) and remanence (B r Neodymium iron boron (NdFeB) magnets, hailed as the "King of Magnets" of our time, have been widely used in high-end fields such as new energy vehicle drive motors, wind turbines, servo motors, consumer electronics, medical devices (such as MRI), and industrial robots since their invention by Masato Sagawa and others in 1983. The demand for high-performance NdFeB magnets from new energy vehicles and energy-saving appliances is experiencing explosive growth.

[0003] However, a major weakness of neodymium iron boron magnets is their Curie temperature (Ti). c The intrinsic coercivity (H0.05) is relatively low (approximately 312 °C), and decreases sharply with increasing temperature. In high-temperature operating environments (such as the operating temperature of new energy vehicle motors often exceeding 150 °C), magnets are prone to irreversible demagnetization. To ensure the stability of magnets at high temperatures, industry must significantly increase the intrinsic coercivity (H0.05) at room temperature. cj ).

[0004] Traditionally, improving the coercivity of NdFeB magnets mainly employs the "alloying method," which involves directly adding heavy rare earth elements (HREE, such as Dy and Tb) during the raw material smelting stage to replace Nd2Fe. 14 Some Nd atoms in the B principal phase lattice form a magnetocrystalline anisotropic field (H). A Higher (Nd,Dy)2Fe 14 B or (Nd,Tb)2Fe 14 Phase B. However, this method has two major drawbacks: first, the antiferromagnetic coupling between Dy / Tb and Fe atoms leads to a decrease in the saturation magnetization of the main phase (M). s Firstly, HREE is reduced; secondly, although HREE is uniformly distributed in the magnet particles, demagnetization domain nucleation only occurs at defects on the grain surface. Therefore, only HREE in the outer shell of the grain is effective, while HREE in the core region is severely wasted. Given that Dy / Tb is a scarce strategic resource and is expensive, this method of addition not only wastes resources but also drives up the cost of magnet production.

[0005] To address the magnetic dilution effect (such as decreased remanence) and waste of heavy rare earth resources caused by traditional alloying methods, grain boundary diffusion (GBD) technology has emerged. This technology involves attaching heavy rare earth sources (such as Dy / Tb oxides or metals) to the surface of sintered magnets and then subjecting them to high-temperature heat treatment to allow the heavy rare earths to penetrate along the grain boundaries and form a rare earth-rich "core-shell" structure. This significantly improves coercivity while almost eliminating the loss of remanence, and the amount of heavy rare earths used is only 10% to 20% of that used in traditional alloying methods. However, current mainstream surface coating processes still have significant drawbacks: coating / dip coating methods are difficult to control in terms of coating thickness and uniformity, and are prone to residual carbon impurities that affect the chemical properties of grain boundary phases. In addition, oxide / fluoride diffusion efficiency is low and may release fluoride ions, causing environmental problems. Although magnetron sputtering produces dense and pure films, the target utilization rate is low (<30%), the equipment is expensive, and there is a "line-of-sight deposition" limitation on complex-shaped magnets, resulting in uneven coverage. Furthermore, the film has weak adhesion to the substrate, and the surface oxide layer hinders diffusion, often requiring higher temperatures to cause abnormal grain growth. Evaporation methods are only suitable for small-sized magnets and are difficult to process large-sized or complex-shaped magnets. They also have extremely high requirements for vacuum and heating temperature. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the problems existing in the prior art, such as low utilization rate of heavy rare earth elements, poor interfacial bonding force, difficulty in processing irregular parts, and surface oxide layer hindering diffusion in grain boundary diffusion technology. The present invention provides a grain boundary diffusion method for sintered NdFeB magnets, which uses semiconductor ion implantation technology to inject heavy rare earth elements into the grain boundary diffusion of NdFeB magnets. Ion implantation, a core doping technology in semiconductor manufacturing, has been introduced into the grain boundary diffusion pretreatment of NdFeB magnets due to its precise dosage control, high purity, and non-equilibrium implantation characteristics. It has shown significant advantages over traditional coating technologies: high-energy ion beams (tens to hundreds of keV) bombarding the surface can produce a sputtering cleaning effect, physically breaking the Nd oxide layer to open diffusion channels; implanted ions embed into the substrate surface to form a gradient mixing layer, effectively solving the problem of film-substrate adhesion and preventing coating peeling; precise dosage control allows the Dy / Tb implantation amount to be precisely adjusted as needed, avoiding the waste of precious Tb elements; plasma immersion implantation (PIII) technology can achieve omnidirectional uniform implantation of irregularly shaped magnets, overcoming the line-of-sight deposition limitations of magnetron sputtering.

[0007] To address the aforementioned technical problems, this invention provides a method for grain boundary diffusion in sintered NdFeB magnets, comprising the following steps: S1. Using sintered NdFeB magnets as the substrate, place them in the vacuum chamber of an ion implantation device, and use heavy rare earth metals or non-rare earth metals as ion source materials to generate an ion beam that is implanted into the surface of the magnet. S2. The magnet is placed in a high-vacuum sintering furnace for multi-stage heat treatment to obtain a high-coercivity sintered NdFeB magnet.

[0008] In the above-described method for grain boundary diffusion in sintered NdFeB magnets, the heavy rare earth metal is one or more combinations of Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; and the non-rare earth metal in S2 is one or more combinations of Ga, Cu, Al, Mg, Ni, and Zn.

[0009] In the above-described method for grain boundary diffusion in sintered NdFeB magnets, the energy injected into the magnet surface is further described as 10 keV to 200 keV.

[0010] In the above-described method for grain boundary diffusion in sintered NdFeB magnets, the dose range of the ion source material implanted in step S1 is 1 × 10⁻⁶. 10 ions / cm 2 Up to 9×10 20 ions / cm 2 .

[0011] Furthermore, in the above-mentioned grain boundary diffusion method for sintered NdFeB magnets, the temperature is controlled below 200 °C during the ion beam implantation process on the magnet surface.

[0012] The above-mentioned grain boundary diffusion method for sintered NdFeB magnets can be further improved by equipping a water-cooled sample stage or controlling the pulse duty cycle to achieve temperature control below 200 °C.

[0013] The above-mentioned method for grain boundary diffusion in sintered NdFeB magnets further includes a multi-stage heat treatment comprising two stages of annealing: a first-stage diffusion treatment at a temperature of 500 ℃ to 1000 ℃ and a holding time of 1 hour to 96 hours; and a second-stage aging treatment at a temperature of 460 ℃ to 600 ℃ and a holding time of 1 hour to 96 hours.

[0014] Compared with the prior art, the advantages of the present invention are as follows: (1) This invention provides a grain boundary diffusion method for sintered NdFeB magnets. This method utilizes ion beam implantation technology to precisely inject heavy rare earth atoms into the surface layer of sintered NdFeB magnets, forming a non-equilibrium supersaturated solid solution layer. The oxide layer on the magnet surface is removed in situ using the sputtering effect of high-energy ions, eliminating the diffusion barrier. Subsequently, through a heat treatment process, heavy rare earth elements are driven to penetrate deeply into the interior along the liquid phase grain boundaries, forming highly magnetocrystalline anisotropic (Nd,HREE)2Fe on the surface of the main phase grains. 14 B-shell structure. Compared with traditional coating or sputtering diffusion techniques, this method has advantages such as extremely high utilization of heavy rare earth elements, strong interfacial bonding, and high diffusion efficiency. The prepared NdFeB magnets exhibit significantly improved coercivity while maintaining high remanence, meeting the needs of high-end applications such as new energy vehicle motors and wind power generation.

[0015] (2) This invention provides a grain boundary diffusion method for sintered NdFeB magnets. Ion implantation technology exhibits multiple advantages in NdFeB magnet processing: its atomic-level operation characteristics enable extremely high utilization of heavy rare earth elements, and the dosage can be precisely controlled to the single-atom-layer level. Compared with coating and sputtering methods, it saves 30% to 50% of the amount of heavy rare earth elements while achieving the same increase in coercivity; the ballistic effect of high-energy ions (such as 100 keV Dy) can penetrate and disperse the surface Nd oxide layer (average range 30 to 50). The plasma immersion injection (PIII) mode effectively solves adhesion problems and eliminates diffusion barriers, significantly improving diffusion depth. When using plasma immersion injection (PIII) mode, irregularly shaped parts (such as motor tiles and ring magnets) can be uniformly processed without complex mechanical rotation, ensuring consistent coercivity on the inner and outer surfaces and overcoming dead zones in the line of sight deposition. By adjusting the injection energy, the depth distribution of heavy rare earth elements can be precisely preset (such as forming a gradient Dy concentration), reducing lattice stress. At the same time, combined with the co-implantation of low-melting-point metal ions such as Al, Cu, and Ga, the low-melting-point eutectic phase is used to improve grain boundary wettability, further accelerating the deep diffusion of heavy rare earth elements and achieving high-efficiency optimization of the entire process. Attached Figure Description

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0017] Figure 1 This is a flowchart of a grain boundary diffusion method for sintered NdFeB magnets according to the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to specific preferred embodiments, but this does not limit the scope of protection of the present invention. The materials, reagents, and instruments used in the following embodiments can all be purchased commercially. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods in the art.

[0019] This invention discloses a method for grain boundary diffusion in sintered NdFeB magnets, the process of which is as follows: Figure 1 As shown, the specific process is as follows: Step 1: Select sintered NdFeB magnets as the substrate, and perform mechanical polishing, degreasing cleaning and acid pickling activation on the magnet surface to remove macroscopic oil stains and loose oxide layers, exposing fresh metal surfaces.

[0020] Step 2: Place the magnet processed in step S1 into the vacuum chamber of the ion implantation device, and use heavy rare earth metals or non-rare earth metals as ion source materials to generate an ion beam to be implanted into the surface of the magnet.

[0021] This method utilizes ion beam implantation technology to precisely implant heavy rare earth atoms into the surface layer of sintered NdFeB magnets, forming a non-equilibrium supersaturated solid solution layer. Specifically, the ion implantation energy ranges from 10 keV to 200 keV; the ion implantation dose ranges from 1 × 10⁻⁶. 10 ions / cm 2 Up to 9×10 20 ions / cm 2 The temperature of the neodymium iron boron magnet is controlled below 200 °C during the ion implantation process, which is achieved by equipping a water-cooled sample stage or controlling the pulse duty cycle to prevent premature oxidation of the substrate or deterioration of the microstructure.

[0022] Furthermore, the energies for Al and Dy ion implantation are 50 keV to 150 keV; the doses for Al and Dy ion implantation are 1 × 10⁻⁶. 15 ions / cm 2 ~1×10 17 ions / cm 2 .

[0023] Step 3: Place the magnet processed in step S2 into a high vacuum sintering furnace for multi-stage heat treatment to obtain a high coercivity sintered NdFeB magnet.

[0024] Specifically, the multi-stage heat treatment includes two-stage annealing: a first-stage diffusion treatment at 500℃ to 1000℃, with a holding time of 1 to 96 hours; and a second-stage aging treatment at 460℃ to 600℃, with a holding time of 1 to 96 hours. Further, the first-stage diffusion treatment is at 800℃ to 900℃, with a holding time of 40 to 50 hours; and the second-stage aging treatment is at 450℃ to 550℃, with a holding time of 1 to 3 hours.

[0025] The present invention will now be described in detail with reference to several specific embodiments.

[0026] Example 1 A method for grain boundary diffusion in sintered NdFeB magnets, comprising the following specific steps: Step 1: Select commercially available sintered NdFeB magnet grade N50 (size: 20 mm × 20 mm × 5 mm) as the matrix. Its original magnetic properties are: remanence B r =14.0 kGs, intrinsic coercivity H cj =12.0 kOe. The magnet surface is mechanically polished, degreased, and acid-washed to remove macroscopic oil stains and loose oxide layers, exposing a fresh metal surface.

[0027] Step 2: Place the magnet processed in step S1 into the vacuum chamber of the ion implantation device, and sequentially use non-rare earth metal Al and heavy rare earth metal Dy as ion source materials to generate ion beams for implantation onto the magnet surface. The energies for Al and Dy ion implantation are both set to 100 keV; the doses for Al and Dy ion implantation are both set to 1×10⁻⁶. 16 ions / cm 2 The temperature of the neodymium iron boron magnet is controlled below 80 °C during the ion implantation process, which is achieved by equipping a water-cooled sample stage or controlling the pulse duty cycle to prevent premature oxidation of the substrate or deterioration of the microstructure.

[0028] Step 3: The magnet processed in step S2 is placed in a high-vacuum sintering furnace for multi-stage heat treatment, which includes two-stage annealing: a first-stage diffusion treatment at 880 ℃ for 48 hours; and a second-stage aging treatment at 500 ℃ for 2 hours. This yields a high-coercivity sintered NdFeB magnet.

[0029] Example 2 A method for grain boundary diffusion in sintered NdFeB magnets, comprising the following specific steps: Step 1: Select commercially available sintered NdFeB magnet grade N50 (size: 20 mm × 20 mm × 5 mm) as the matrix. Its original magnetic properties are: remanence B r =14.0 kGs, intrinsic coercivity H cj =12.0 kOe. The magnet surface is mechanically polished, degreased, and acid-washed to remove macroscopic oil stains and loose oxide layers, exposing a fresh metal surface.

[0030] Step 2: Place the magnet processed in step S1 into the vacuum chamber of the ion implantation device, and use the heavy rare earth metal Dy as the ion source material to generate an ion beam to implant onto the magnet surface. The energy of Dy ion implantation is set to 100 keV; the dose of Dy ion implantation is set to 1×10⁻⁶. 16 ions / cm 2 The temperature of neodymium iron boron magnets is controlled below 80°C during ion implantation, which is achieved by equipping a water-cooled sample stage or controlling the pulse duty cycle to prevent premature oxidation of the substrate or deterioration of the microstructure.

[0031] Step 3: The magnet processed in step S2 is placed in a high-vacuum sintering furnace for multi-stage heat treatment, which includes two-stage annealing: a first-stage diffusion treatment at 880 ℃ for 48 hours; and a second-stage aging treatment at 500 ℃ for 2 hours. This yields a high-coercivity sintered NdFeB magnet.

[0032] Comparative Example 1 A method for grain boundary diffusion in sintered NdFeB magnets (magnetron sputtering) includes the following steps: Step 1: Select commercially available sintered NdFeB magnet grade N50 (size: 20 mm × 20 mm × 5 mm) as the matrix. Its original magnetic properties are: remanence B r =14.0 kGs, intrinsic coercivity H cj =12.0 kOe. The magnet surface is mechanically polished, degreased, and acid-washed to remove macroscopic oil stains and loose oxide layers, exposing a fresh metal surface.

[0033] Step 2: Place the magnet processed in step S1 into the vacuum chamber of the magnetron sputtering equipment, and sputter non-rare earth metal Al and heavy rare earth metal Dy into the magnet surface in sequence.

[0034] Step 3: The magnet processed in step S2 is placed in a high-vacuum sintering furnace for multi-stage heat treatment, which includes two-stage annealing: a first-stage diffusion treatment at 880 ℃ for 48 hours; and a second-stage aging treatment at 500 ℃ for 2 hours. This yields a high-coercivity sintered NdFeB magnet.

[0035] Comparative Example 2 A method for grain boundary diffusion (coating method) in sintered NdFeB magnets, the specific steps of which are as follows: Step 1: Select commercially available sintered NdFeB magnet grade N50 (size: 20 mm × 20 mm × 5 mm) as the matrix. Its original magnetic properties are: remanence B r = 14.0 kGs, intrinsic coercivity H cj = 12.0 kOe. The magnet surface is mechanically polished, degreased, and acid-washed to remove macroscopic oil stains and loose oxide layers, exposing a fresh metal surface.

[0036] Step 2: Place the magnet processed in step S1 into the vacuum chamber of the coating equipment, and coat the magnet surface with a slurry made of non-rare earth metal Al powder and heavy rare earth metal Dy powder in sequence.

[0037] Step 3: The magnet processed in step S2 is placed in a high-vacuum sintering furnace for multi-stage heat treatment, which includes two-stage annealing: a first-stage diffusion treatment at 880 ℃ for 48 hours; and a second-stage aging treatment at 500 ℃ for 2 hours. This yields a high-coercivity sintered NdFeB magnet.

[0038] The high coercivity sintered NdFeB magnets prepared in Examples 1-2 and Comparative Examples 1-2 were used as samples for magnetic performance testing. The test results are listed in Table 1.

[0039] Table 1: Test Results of Magnetic Properties of Sintered NdFeB Magnets

[0040]

[0041] The results in Table 1 show that the sample obtained in Example 1 exhibits the largest increase in intrinsic coercivity Hcj after diffusion, while simultaneously experiencing the smallest remanence loss. A comparison of the results from Example 1 and Example 2 indicates that diffusion using elements such as Al or Cu can lower the melting point of grain boundaries in the magnet, improve wettability, and facilitate the subsequent diffusion of heavy rare earth elements within the grain boundaries, thereby further enhancing the intrinsic coercivity performance of the magnet. A comparison of the results from Example 1, Comparative Example 1, and Comparative Example 2 demonstrates that the effect of grain boundary diffusion using ion implantation technology in improving magnet performance is significantly superior to traditional magnetron sputtering and coating methods.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for grain boundary diffusion in sintered NdFeB magnets, characterized in that, Includes the following steps: S1. Using sintered NdFeB magnets as the substrate, place them in the vacuum chamber of an ion implantation device, and use heavy rare earth metals or non-rare earth metals as ion source materials to generate an ion beam that is implanted into the surface of the magnet. S2. The magnet is placed in a high-vacuum sintering furnace for multi-stage heat treatment to obtain a high-coercivity sintered NdFeB magnet.

2. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that, The heavy rare earth metal is one or more combinations of Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; the non-rare earth metal in S2 is one or more combinations of Ga, Cu, Al, Mg, Ni, and Zn.

3. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that, The energy injected into the surface of the magnet is between 10 keV and 200 keV.

4. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that, The dose range of the ion source material implanted in S1 is 1×10⁻⁶. 10 ions / cm 2 Up to 9×10 20 ions / cm 2 .

5. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that, During the ion beam injection process onto the magnet surface, the temperature is controlled below 200 ℃.

6. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 5, characterized in that, Temperature control can be achieved below 200 °C by equipping a water-cooled sample stage or controlling the pulse duty cycle.

7. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that, The multi-stage heat treatment includes two-stage annealing: the first-stage diffusion treatment has a temperature of 500 ℃ to 1000 ℃ and a holding time of 1 hour to 96 hours; the second-stage aging treatment has a temperature of 460 ℃ to 600 ℃ and a holding time of 1 hour to 96 hours.

8. The method for grain boundary diffusion in sintered NdFeB magnets according to any one of claims 1 to 7, characterized in that, The sintered NdFeB magnet in S1 is pretreated by the following method: the surface of the sintered NdFeB magnet is mechanically polished, degreased and cleaned and acid-washed to remove macroscopic oil stains and loose oxide layer, exposing fresh metal surface.

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