High-toughness neodymium-iron-boron magnet and method of making

Abstract

This invention relates to a high-toughness NdFeB magnet and its preparation method. First, the sintered NdFeB magnet undergoes surface grinding and polishing. An electrophoretic dispersion is prepared using anhydrous ethanol as the dispersion medium and Cu powder as the solute. A Cu diffusion source coating is deposited on the magnet surface using a two-electrode DC electrophoresis method. Subsequently, high-temperature grain boundary diffusion treatment and low-temperature aging treatment are performed sequentially under vacuum conditions. Through this process, Cu elements preferentially diffuse and enrich along grain boundaries and triple-grain boundaries, improving the wetting ability and continuous encapsulation state of rare-earth-rich grain boundaries relative to the main phase grains, enhancing the strength of the grain boundary phase itself and the bonding strength of the main phase-grain boundary interface, inducing crack deflection and bifurcation, and increasing energy dissipation during fracture. The prepared magnet maintains high magnetic properties while significantly improving bending strength and fracture toughness, making it suitable for fields requiring high reliability in magnet service.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, specifically to a high-toughness NdFeB magnet and its preparation method. The invention utilizes Cu grain boundary diffusion to improve the grain boundary structure of sintered NdFeB magnets, thereby enhancing the bending strength and fracture toughness of the NdFeB magnets. Background Technology

[0002] Sintered NdFeB permanent magnets possess high energy product, high remanence, and high coercivity, making them valuable for applications in new energy vehicles, wind power generation, high-efficiency industrial motors, and aerospace. As service environments evolve towards higher speeds, higher loads, and vibration / shock conditions, magnets must not only maintain excellent magnetic properties but also possess high mechanical reliability and service stability.

[0003] However, sintered NdFeB magnets are typical multiphase brittle materials, with their main phase being Nd2Fe. 14 The presence of fewer B-slip systems results in weak plasticity and compatibility with deformation. Furthermore, rare-earth-rich grain boundary phases and triangular grain boundary regions typically exhibit low strength, making them prime sites for crack initiation and rapid propagation. Under external forces, cracks easily propagate unstably along grain boundary paths, leading to low flexural strength, poor fracture toughness, and susceptibility to spalling during processing and use.

[0004] Existing improvement methods typically enhance the overall performance of magnets through heavy rare earth element control, microalloying, or microstructure design. However, some methods suffer from drawbacks such as high cost, complex processes, or adverse effects on magnetic properties. Therefore, there is an urgent need to develop a grain boundary diffusion method that is simple to implement, low in cost, has a controllable diffusion source, and can improve grain boundary structure and fracture behavior without significantly impairing magnetic properties, thereby enhancing the toughness of sintered NdFeB magnets. Summary of the Invention

[0005] While existing technologies can effectively improve the coercivity of sintered NdFeB magnets through grain boundary diffusion of heavy rare earth elements (such as Dy and Tb), they suffer from drawbacks such as high raw material costs and often sacrifice remanence and energy product. Conventional microalloying or Cu addition through smelting can improve grain boundaries to some extent, but they struggle to overcome the segregation problem caused by the low solid solubility of Cu in the main phase and cannot achieve precise control over grain boundary regions. More importantly, existing processes primarily focus on magnetic performance optimization, neglecting the inherent brittleness of the material. This leads to magnet fracture under machining and high-load service conditions due to weak grain boundary bonding and rapid crack propagation along grain boundaries. There is a lack of an effective solution that can reconstruct the grain boundary phase and significantly improve fracture toughness and flexural strength at low cost while maintaining high magnetic performance.

[0006] To address the problems of weak grain boundary bonding, high brittleness, rapid crack propagation along grain boundaries, and insufficient overall mechanical properties in existing sintered NdFeB magnets, this invention provides a Cu grain boundary diffusion method and a magnet thereof to improve the mechanical properties and fracture toughness of sintered NdFeB magnets. This method constructs a controllable Cu diffusion source on the magnet surface through electrophoretic deposition, and combines this with vacuum diffusion and aging heat treatment to preferentially migrate and enrich Cu elements along grain boundaries and triple-grain boundaries, thereby achieving grain boundary phase reconstruction, interface strengthening, and crack deflection toughening.

[0007] A high-toughness NdFeB magnet comprising a grain boundary phase and Nd2Fe 14 B main phase, the Nd2Fe 14 The grain size of the B main phase is more than 95% in the range of 2 μm-6 μm, and the Cu atom content in the main phase is less than 0.1 at.%.

[0008] The width of the continuous grain boundary phase in the grain boundary phase is greater than 15 nm; the proportion of the grain boundary phase is 7% to 14%;

[0009] The continuous grain boundary phase contains fcc-NdO2 type neodymium-rich oxides;

[0010] The XRD diffraction peak intensity ratio of the (006) and (105) planes of the high-toughness NdFeB magnet ranges from 1.2 to 1.4.

[0011] The half-width at half-maximum (WHM) of the (006) surface ranges from 0.33 to 0.36.

[0012] The crack propagation path of the high-toughness NdFeB magnet is a composite path including deflection, bifurcation, and local transgranular propagation, and Nd2Fe 14 No impurities are generated in the B main phase.

[0013] Preferably, the high-toughness neodymium iron boron magnet has a bending strength of 300 MPa or more and a fracture toughness of 3.0 MPa·m¹ / ² or more.

[0014] Preferably, the atomic composition of the continuous grain boundary phase is: Fe 12.4~23.3 at.%; O 9.7~22.2 at.%; Ga 2.1~4.1 at.%; Nd 25.7~30.0 at.%; Pr 11.6~24.8 at.%; Cu 9.0~16.6 at.%.

[0015] A method for preparing a high-toughness neodymium iron boron magnet includes the following steps:

[0016] S1 substrate pretreatment: The sintered NdFeB magnet is ground and polished step by step, then cleaned and dried with anhydrous ethanol to obtain a clean substrate to be treated.

[0017] S2 Cu deposition: A continuous Cu coating with a thickness of 20~70 μm and a Cu introduction amount of 0.3~1.5 wt.% is formed on the substrate surface;

[0018] S3 gradient heat treatment: The magnet with Cu coating is placed in a crucible with a high-purity molybdenum mesh. Under high vacuum conditions, the temperature is first raised to 700~800 ℃ at 5 ℃ / min and held for 3~5 h for grain boundary diffusion. Then, it is cooled to 80~120 ℃ in the furnace and then raised to 450~550 ℃ at 5 ℃ / min and held for 2~4 h for aging treatment. Finally, it is cooled to room temperature in the furnace.

[0019] Preferably, the Cu deposition is specifically carried out by electrophoresis, including the following steps: preparing an electrophoretic dispersion with a solid-liquid concentration of 15~25 g / L using anhydrous ethanol as the dispersion medium and Cu powder as the solute;

[0020] A dual-electrode DC system was adopted, with the substrate to be treated as the cathode and the conductive electrode as the anode. By adjusting the electrophoresis time under a constant voltage of 100~140 V, a continuous Cu coating with a thickness of 20~70 μm and a Cu introduction amount of 0.3~1.5wt.% was formed on the substrate surface.

[0021] During the preparation of the electrophoretic dispersion, Cu powder is uniformly dispersed by ultrasonic oscillation to reduce particle agglomeration and sedimentation; the solid-liquid concentration of the electrophoretic dispersion is 20 g / L; and the constant voltage is 120 V.

[0022] The method improves the wettability and continuous encapsulation of rare earth-rich grain boundaries relative to the main phase grains by preferentially enriching Cu elements along grain boundaries and triple grain boundaries, enhances the bonding strength of the main phase-grain boundary interface, induces crack deflection and bifurcation, and achieves simultaneous improvement of magnet toughness and strength.

[0023] A sintered NdFeB magnet prepared by the Cu grain boundary diffusion method, wherein Cu, Nd, and Pr are co-enriched in rare-earth-rich grain boundary phases and triangular grain boundary regions, increasing the proportion of grain boundary phases from 4.27% in the original magnet to 7.79%, and the crack propagation path changes from a single intergranular propagation to a composite path including deflection, bifurcation, and local transgranular propagation, and the main phase Nd2Fe 14 B does not produce any impurities.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Using Cu as a low-cost, low-melting-point diffusion source and achieving precise control of the amount of diffusion source introduced through electrophoretic deposition, a uniformly distributed and well-bonded surface coating can be obtained. The process is simple and has good repeatability.

[0026] (2) After diffusion through the vacuum grain boundary, Cu element preferentially diffuses and accumulates along the grain boundary network and the three-way grain boundary region, which can improve the wettability of rare earth-rich grain boundaries relative to the main phase grains, reduce grain boundary pores and discontinuous regions, and promote the formation of continuous grain boundary structure.

[0027] (3) The examples show that when the amount of Cu introduced is within a suitable range, the magnet can significantly improve its bending strength and fracture toughness; among them, the 0.8 wt.% Cu-diffused magnet exhibits the best comprehensive performance, with a bending strength of about 315.8 MPa; the fracture toughness of the 0.8 wt.% Cu-diffused magnet can reach about 2.83 MPa·m. 1 / 2 .

[0028] (4) Microstructure analysis shows that the present invention achieves crack deflection toughening through grain boundary phase reconstruction and interface strengthening, which can effectively suppress the rapid linear propagation of cracks along fragile grain boundaries and improve the service life and reliability of sintered NdFeB magnets under high stress and complex environments. Attached Figure Description

[0029] To more clearly illustrate the technical solution of the present invention, a brief description of the accompanying drawings is provided below. In the drawings, identical or similar parts represent the same or similar meanings.

[0030] Figure 1 These are SEM images of Cu coating sections under different electrophoresis durations and weight gain conditions;

[0031] Figure 2 These are the XRD patterns of the original magnet and the diffused magnet;

[0032] Figure 3 This is a comparison chart of the Vickers hardness, three-point bending, and fracture toughness of the original magnet and the Cu diffused magnet.

[0033] Figure 4 The figures show a comparison of the fracture morphology and crack propagation path of the original magnet and the 0.8 wt.% Cu-diffused magnet; (a) and (c) in the figures are the original magnet, and (b) and (d) in the figures are the magnets after Cu diffusion.

[0034] Figure 5 This is a comparison of the three-point bending and fracture toughness of the original magnet and the 1.0 wt.% Tb diffused magnet. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0036] This invention employs Cu grain boundary diffusion to regulate the microstructure of sintered NdFeB magnets. The process involves constructing a diffusion source through surface electrophoretic deposition and using vacuum heat treatment to achieve the migration, enrichment, and interface reconstruction of Cu elements along grain boundaries, thereby achieving the desired strength and toughness of the magnet.

[0037] A Cu grain boundary diffusion method for improving the mechanical properties and fracture toughness of sintered NdFeB magnets includes the following steps:

[0038] (1) Substrate pretreatment: Sintered NdFeB magnets were selected as the substrate and were successively ground with 400 mesh, 600 mesh, 800 mesh and 1000 mesh silicon carbide sandpaper, and further polished; after polishing, they were cleaned with anhydrous ethanol and dried to obtain a clean and flat magnet to be treated.

[0039] (2) Preparation of electrophoretic dispersion: Anhydrous ethanol is used as the dispersion medium, and high-purity metal Cu powder is added to prepare an electrophoretic dispersion with a solid-liquid concentration of 20 g / L. The Cu powder is uniformly dispersed by ultrasonic oscillation to reduce particle agglomeration and sedimentation.

[0040] (3) Electrophoretic deposition: A dual-electrode DC electrophoresis system is used, with the sintered NdFeB magnet to be treated as the cathode and the conductive counter electrode as the anode, and electrophoretic deposition is carried out under constant voltage conditions; the preferred voltage is 120 V, and a Cu coating with controllable thickness is formed on the magnet surface by controlling the electrophoresis time to obtain a Cu introduction amount in the range of 0.4 wt.% to 1.2 wt.%.

[0041] (4) Grain boundary diffusion heat treatment: After the magnet is deposited, it is placed in a crucible with a high-purity molybdenum mesh, heated to 750 ℃ ​​at a heating rate of 5 ℃ / min under high vacuum and held for 4 h to allow Cu elements to diffuse fully along the grain boundary; then cooled to about 100 ℃ in the furnace, and then heated to 500 ℃ at a heating rate of 5 ℃ / min and held for 3 h for aging treatment, and finally cooled to room temperature in the furnace.

[0042] In the sintered NdFeB magnets obtained by the above process, Cu element is preferentially enriched in the rare earth-rich grain boundary phase and the triangular grain boundary region, which improves the continuity of the grain boundary phase and the encapsulation state of the main phase grains, enhances the strength of the grain boundary phase itself and the interfacial bonding force between the main phase grains and the grain boundary phase.

[0043] The present invention also provides a sintered NdFeB magnet prepared by the above-mentioned Cu grain boundary diffusion method. In the grain boundary region of the magnet, Cu element and rare earth elements such as Nd and Pr are co-enriched and distributed, the continuity of grain boundary phase is improved, and the crack propagation path is changed from a single rapid intergranular propagation to a composite path that is more prone to deflection, bifurcation and local transgranular propagation, thereby obtaining better comprehensive mechanical properties and service reliability.

[0044] Analysis of the impact of Cu deposition:

[0045] Anhydrous ethanol was used as the dispersion medium, and high-Cu powder was added to prepare a suspension with a concentration of 20 g / L. Ultrasonic oscillation was used to uniformly disperse the Cu powder and reduce particle agglomeration. A dual-electrode DC electrophoresis system was employed, with a NdFeB magnet as the cathode and the counter electrode as the anode, and electrophoretic deposition was performed at a constant voltage of 120 V. To ensure a consistent suspension state before each deposition, the electrophoretic solution was ultrasonically oscillated and stirred thoroughly after each sample deposition.

[0046] Different Cu coating amounts can be obtained by adjusting the electrophoresis time. In this embodiment, the Cu deposition amounts were set to five groups: 0.4 wt.%, 0.6 wt.%, 0.8 wt.%, 1.0 wt.%, and 1.2 wt.%, and the corresponding electrophoresis times and coating thicknesses are shown in Table 1. After deposition, the Cu coating spreads continuously and smoothly along the surface of the magnet substrate, and is tightly bonded to the substrate, providing a stable diffusion source for subsequent diffusion.

[0047] The deposited magnet was placed stably in a crucible lined with a high-purity molybdenum mesh and then placed in a vacuum sintering furnace for grain boundary diffusion heat treatment. First, it was heated to 750 °C at a heating rate of 5 °C / min and held for 4 h to allow Cu to diffuse fully along the grain boundaries and the triple grain boundaries. Then, it was cooled in the furnace to about 100 °C, and then heated to 500 °C at a rate of 5 °C / min and held for 3 h for aging treatment. Finally, it was cooled in the furnace to room temperature to obtain a Cu grain boundary diffusion sintered NdFeB magnet.

[0048] Table 1. Correlation between Cu powder electrophoretic deposition time, coating thickness, and weight gain

[0049]

[0050] Analysis of electrophoretic deposition parameters and controllability of diffusion sources:

[0051] See Figure 1 As shown in Table 1, as the electrophoresis time increased from 88 s to 296 s, the Cu coating thickness increased from 24.48 μm to 71.37 μm, and the corresponding Cu introduction amount increased from 0.40 wt.% to 1.20 wt.%, showing a good positive correlation. This indicates that the present invention can achieve precise control of the Cu diffusion source introduction amount by adjusting the electrophoresis time.

[0052] As can be seen from the cross-sectional SEM morphology, within the electrophoretic parameters of this embodiment, the Cu coating is continuous and dense, without obvious pores, cracks and delamination, indicating that the electrophoretic deposition process is stable and the resulting diffusion source coating meets the requirements of subsequent vacuum diffusion heat treatment for coating integrity and interface bonding performance.

[0053] Microstructural characteristics analysis of diffusion magnets:

[0054] See Figure 2 After diffusion treatment, the diffraction peaks of each sample still correspond to those of Nd2Fe. 14 The main phase was well-matched with Cu, and no harmful impurities were observed, indicating that Cu grain boundary diffusion did not disrupt the crystal structure stability of the main phase. An appropriate amount of Cu (0.4 wt.%) can optimize grain orientation (I(006) / I(105) reaches its peak), which is beneficial to improving magnetic properties; while at 0.8 wt.%, grain refinement is most significant (FWHM is the largest), which helps to improve coercivity.

[0055] See Figure 3 Although the Vickers hardness of the magnet decreased slightly after Cu diffusion, the edge chipping and radial cracks at the indentation point were significantly reduced, indicating that the material's resistance to crack initiation and propagation under localized loads was improved. Three-point bending tests showed that the bending strength of the 0.8 wt.% Cu-diffused magnet could be increased to 315.8 MPa; fracture toughness tests showed that the fracture toughness of the 0.8 wt.% Cu-diffused magnet could reach 2.83 MPa·m. 1 / 2 It is significantly superior to the original magnet.

[0056] See Figure 4 (a) shows the fracture morphology, with intergranular fracture (red box) predominating in the original magnet. After Cu diffusion, as shown in (b), the proportion of transgranular fracture (yellow box) in the diffused magnet increases, indicating that both the grain boundary phase strength and the main phase-grain boundary interface bonding state are improved. In (c), the crack propagation path in the original magnet is a long-range linear rapid propagation, and the crack width is relatively wide, destroying the grain boundary phase (red box). After Cu diffusion, as shown in (b), the fracture morphology is improved. Figure 4 In (d), the crack propagation path transforms into a composite path that is more prone to deflection, bifurcation, and local transgranular propagation. Furthermore, the crack propagation path changes from the original magnet's destructive grain boundary phase to the junction between the grain boundary phase and the main phase (yellow box). Thus, it can be seen that the present invention achieves the improvement of the toughness and bending strength of sintered NdFeB magnets through grain boundary phase reconstruction, interface strengthening, and crack deflection toughening mechanisms.

[0057] EDS elemental analysis: The grain boundary phase composition in the original magnet matrix is: Fe 34.0~48.1 at.%; O 6.8~7.2 at.%; Ga 0.2~0.4 at.%; Nd 27.3~35.4 at.%; Pr 15.2~21.3 at.%; Cu 1.7~2.1 at.%; The grain boundary phase composition of the diffused magnet prepared in this invention is: Fe 12.4~23.3 at.%; O 9.7~22.2 at.%; Ga 2.1~4.1 at.%; Nd 25.7~30.0 at.%; Pr 11.6~24.8 at.%; Cu 9.0~16.6 at.%. The Cu content in the main phase is less than 0.1 at.%.

[0058] TEM results show that the grain boundary region in the original magnet was mainly composed of rare-earth-rich oxide phase Nd₂O₃, with a grain boundary width of 13.5 nm. After diffusion, the grain boundary oxide region and the interfacial chemical environment were reconstructed, and the grain boundary phase became fcc-NdO₂, with a grain boundary width of 19.07 nm and a standard deviation of < 4 nm. Both the continuity of the grain boundary phase and the interfacial matching were improved. Simultaneously, the Cu content in the original magnet was significantly lower. After Cu diffusion, Cu showed a clear co-enrichment distribution with Nd and Pr elements, and the continuous grain boundary region became an important enrichment site for Cu, which is beneficial for achieving continuous wetting of the grain boundaries and effective encapsulation of the main phase grains. The addition of Cu enhanced the width of the magnet's grain boundaries, effectively achieving magnetic isolation between the main phases and strengthening the crack resistance of the magnet's grain boundaries. After diffusion, the magnet's grain boundary phase was continuous and wider. From the elemental distribution, Cu, Nd, and Pr elements showed a co-enrichment distribution characteristic in the grain boundary region.

[0059] The grain boundaries of the original magnet are mostly Nd₂O₃. Previous studies have shown that Nd₂O₃ in the original magnet usually exists in a discrete form at grain boundaries or in the TJP region. Its weak intergranular bonding promotes intergranular brittle fracture, negatively impacting mechanical properties. The fcc-NdO₃ distributed in the grain boundaries of the diffused magnet... x The formation of Nd-rich oxides simultaneously enhances both the grain boundary phase strength and the interfacial bonding force between the main phase grains and the grain boundary phase. Furthermore, the segregation of Cu in the grain boundary region can improve Nd₂Fe. 14 B. The interfacial bonding state between the main phase grains and the grain boundary phase, which improves the interfacial bonding strength and reduces the possibility of interfacial debonding and microcrack formation.

[0060] The main phase grain size of the Cu-diffused magnet is concentrated in the range of 2 μm-6 μm, with an average grain size of approximately 4.0 μm. The size distribution range is narrow, with no obvious coarse or fine grain segregation, low grain size dispersion, and good uniformity of the main phase grain distribution. In contrast, the original magnet's grain size distribution range has significantly widened to 1 μm-11 μm, with increased grain size dispersion. The average grain size has rebounded to 4.2 μm. After diffusion, the magnet grains are more uniform, and fcc-NdO forms at the grain boundaries after Cu diffusion. x This continuous network of grain boundary phases effectively optimizes the wettability and continuity of the grain boundary phases. This network effectively pins grain boundaries, inhibits abnormal grain growth, ensures the uniform distribution of the main phase grains, and improves grain flatness and uniformity.

[0061] In Cu-diffused magnets, the grain boundary phase proportion is as follows: 0.4 wt.% Cu grain boundary diffusion magnet: 7.79%; 0.8 wt.% Cu grain boundary diffusion magnet: 9.42%; 1.2 wt.% Cu grain boundary diffusion magnet: 13.24%. The original magnet grain boundary phase proportion is 4.27%. Cu significantly increases the grain boundary phase proportion (from 4.27% to 13.24%) by lowering the melting point of the Nd-rich phase and improving liquid phase fluidity, forming more continuous soft grain boundaries, effectively hindering crack propagation, and greatly improving the material's toughness. However, while excessive Cu (such as 1.2 wt.%) further enhances toughness, it may weaken magnetic coupling due to excessively thick grain boundaries, affecting remanence. Overall, 0.4–0.8 wt.% Cu is the optimal doping range, exhibiting the best performance in terms of mechanical toughness.

[0062] The electrophoresis method and parameter selection, heat treatment process and parameter selection, and Cu content range provided by this invention collectively achieve product effects of low cost, high toughness, and no degradation of magnetic properties. The core difference between this invention and existing technologies lies in the synergistic effect of three factors: the selection of Cu as a diffusion source, the precise control of the diffusion source by electrophoretic deposition, and the selective enrichment of Cu along grain boundaries induced by gradient heat treatment. These three factors achieve the aforementioned product effects: replacing heavy rare earth elements with low-cost Cu avoids a significant decrease in magnetic properties such as remanence and energy product; precisely controlling the Cu introduction amount (0.4~1.2 wt.%) through electrophoretic deposition avoids the formation of brittle phases from excessive Cu; and utilizing the preferential diffusion of Cu along grain boundaries / triangular grain boundaries reconstructs the continuity of the grain boundary phase, rather than simply changing the main phase composition.

[0063] The products of this invention exhibit superior mechanical properties. The 0.8 wt.% Cu diffused magnet achieves a bending strength of 315.8 MPa, and the 1.0 wt.% Cu diffused magnet achieves a fracture toughness of 3.13 MPa·m¹ / ², which is superior to traditional heavy rare earth diffusion or microalloying schemes. Furthermore, the magnetic properties of the prepared products are largely maintained: no harmful impurities were detected by XRD, and the main phase structure is stable. An appropriate amount of Cu (0.4 wt.%) can optimize grain orientation, which is beneficial to improving magnetic properties. Grain refinement is most significant at 0.8 wt.%, which helps to improve coercivity. Although excessive Cu (such as 1.2 wt.%) further enhances toughness, it may weaken magnetic coupling due to excessively thick grain boundaries, affecting remanence.

[0064] Comparative Example

[0065] S1 substrate pretreatment: The sintered NdFeB magnet is ground and polished step by step, then cleaned and dried with anhydrous ethanol to obtain a clean substrate to be treated.

[0066] S2 electrophoretic deposition: An electrophoretic dispersion with a solid-liquid concentration of 15~25 g / L was prepared using anhydrous ethanol as the dispersion medium and high-purity Tb powder as the solute.

[0067] A dual-electrode DC system was adopted, with the substrate to be treated as the cathode and the conductive electrode as the anode. By adjusting the electrophoresis time under a constant voltage of 100~140 V, a continuous pure Tb coating with a Tb introduction amount of 1.0 wt.% was formed on the substrate surface.

[0068] S3 gradient heat treatment: The magnet after depositing a pure Tb coating is placed in a crucible lined with a high-purity molybdenum mesh. Under high vacuum conditions, the temperature is first raised to 800~900 ℃ at 5 ℃ / min and held for 10~15 h to carry out grain boundary diffusion. Then, it is cooled to 80~120 ℃ in the furnace and then raised to 450~550 ℃ at 5 ℃ / min and held for 2~4 h to carry out aging treatment. Finally, it is cooled to room temperature in the furnace.

[0069] See Figure 5 Three-point bending tests on magnets after Tb diffusion showed that the bending strength of the 1.0 wt.% Tb-diffused magnet decreased to 229.7 MPa; fracture toughness tests showed that the fracture toughness of the 1.0 wt.% Tb-diffused magnet decreased to 2.05 MPa·m. 1 / 2 The strength of the magnet is significantly lower than that of the original magnet. This indicates that not all metals can improve the toughness and strength of magnets, but Cu can change the grain boundary phase structure and improve the distribution of grain boundary phases, thereby improving the toughness of the magnet.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. All equivalent substitutions, improvements, or variations made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-toughness neodymium iron boron magnet, characterized in that, Including grain boundary phase and Nd2Fe 14 B main phase, the Nd2Fe 14 The grain size of the B main phase is more than 95% in the range of 2 μm-6 μm, and the Cu atom content in the main phase is less than 0.1 at.%. The continuous grain boundary phase in the grain boundary phase has a width of more than 15 nm and a standard deviation of less than 4 nm; the proportion of the grain boundary phase is 7% to 14%; The continuous grain boundary phase contains fcc-NdO2 type neodymium-rich oxides; The XRD diffraction peak intensity ratio of the (006) and (105) planes of the high-toughness NdFeB magnet ranges from 1.2 to 1.

4. The half-width at half-maximum (WHM) of the (006) surface ranges from 0.33 to 0.

36. The crack propagation path of the high-toughness NdFeB magnet is a composite path including deflection, bifurcation, and local transgranular propagation, and Nd2Fe 14 No impurities are generated in the B main phase; The atomic composition of the grain boundary phase is as follows: Fe 12.4~23.3 at.%; O 9.7~22.2 at.%; Ga 2.1~4.1 at.%; Nd 25.7~30.0 at.%; Pr 11.6~24.8 at.%; Cu 9.0~16.6 at.%; The high-toughness NdFeB magnet is deposited with a continuous Cu coating by electrophoresis, wherein the Cu content in the continuous Cu coating is 0.3~1.5 wt.%.

2. The high-toughness NdFeB magnet as described in claim 1, characterized in that, The bending strength of the neodymium iron boron magnet reaches over 300 MPa.

3. The high-toughness neodymium iron boron magnet as described in claim 1, characterized in that, The fracture toughness of the neodymium iron boron magnet reaches 3.0 MPa·m¹ / ² or higher.

4. The method for preparing a high-toughness NdFeB magnet as described in claim 1, characterized in that, Includes the following steps: S1 substrate pretreatment: The sintered NdFeB magnet is ground and polished step by step, then cleaned and dried with anhydrous ethanol to obtain a clean substrate to be treated. S2 Cu deposition: A continuous Cu coating with a thickness of 20~70 μm and a Cu introduction amount of 0.3~1.5 wt.% is formed on the substrate surface; the Cu deposition is specifically carried out by electrophoresis, including the following steps: preparing an electrophoretic dispersion with a solid-liquid concentration of 15~25 g / L using anhydrous ethanol as the dispersion medium and Cu powder as the solute; A dual-electrode DC system was adopted, with the substrate to be treated as the cathode and the conductive electrode as the anode. By adjusting the electrophoresis time under a constant voltage of 100~140 V, a continuous Cu coating with a thickness of 20~70 μm and a Cu introduction amount of 0.3~1.5wt.% was formed on the substrate surface. During the preparation of the electrophoretic dispersion, ultrasonic oscillation is used to uniformly disperse the Cu powder, reducing particle agglomeration and sedimentation; the solid-liquid concentration of the electrophoretic dispersion is 20 g / L; the constant voltage is 120 V; S3 gradient heat treatment: The magnet with deposited Cu coating is placed in a crucible lined with a molybdenum mesh and subjected to 8×10⁻⁶ heat treatment. -4 Under high vacuum conditions, the temperature was first increased to 750 °C at 5 °C / min and held for 4 h for grain boundary diffusion. Then, the temperature was cooled to 100 °C in the furnace and then increased to 500 °C at 5 °C / min and held for 3 h for aging treatment. Finally, the temperature was cooled to room temperature in the furnace.

5. The method for preparing a high-toughness NdFeB magnet as described in claim 4, characterized in that, The step-by-step grinding and polishing specifically includes: sequentially grinding and polishing with 400-mesh, 600-mesh, 800-mesh, and 1000-mesh silicon carbide sandpaper.

6. The method for preparing a high-toughness NdFeB magnet as described in claim 4, characterized in that, The purity of the Cu powder is above 99.5%.

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