Neodymium-iron-boron magnet grain boundary diffusion method and application of neodymium-iron-boron magnet grain boundary diffusion method in cerium-containing magnet

Abstract

The invention discloses a neodymium-iron-boron magnet grain boundary diffusion method and application of the neodymium-iron-boron magnet grain boundary diffusion method in a cerium-containing magnet, and relates to the field of rare earth permanent magnets. The grain boundary diffusion method comprises an ion beam auxiliary thermal diffusion technology, the surface of a heavy rare earth diffusion source is covered with an anti-sputtering layer composed of a carbon film, sputtering loss of heavy rare earth and neodymium iron boron can be prevented, and the heavy rare earth is further promoted to be diffused inwards along the grain boundary. Due to the strong diffusion promoting force, the thermal diffusion temperature of the grain boundary is extremely low, the heavy rare earth has strong selectivity on the grain boundary compared with that in the grain, the diffusion has small influence on the residual magnetism of the magnet, and the method is particularly suitable for grain boundary diffusion of the cerium-containing magnet with relatively low residual magnetism.

Description

Technical Field

[0001] The invention relates to the field of rare earth permanent magnetic materials, and in particular to a NdFeB magnet grain boundary diffusion method and an application thereof in a cerium-containing magnet. Background Art

[0002] Adding modified components represented by heavy rare earth elements to NdFeB magnets through grain boundary diffusion is an important means to improve the magnetic properties of magnets, especially their intrinsic coercivity. Compared with traditional alloy additions, grain boundary additions and other methods, the amount of modified components added by the grain boundary diffusion method is relatively small. However, since the diffusion efficiency mainly depends on the temperature, in practice, it is often necessary to carry out grain boundary diffusion in a high temperature environment above 800°C; and as the temperature increases, the difference between the grain boundary diffusion and intracrystalline diffusion rates decreases, allowing more heavy rare earth elements to enter the interior of the crystal, which in turn leads to a decrease in the remanence of the NdFeB magnet. In particular, cerium-containing magnets with low remanence themselves cannot accept a serious decrease in remanence when using grain boundary diffusion processing.

[0003] It is easy to think that grain boundary diffusion can be carried out at a lower temperature, and certain methods can be taken to greatly increase the grain boundary diffusion rate to offset the effect of temperature reduction. Experiments have long proved that ion bombardment can significantly accelerate the thermal diffusion process, and it has been applied in production. The Chinese invention with announcement number CN108231394B discloses a low-temperature preparation method for high-coercivity neodymium iron boron magnets, in which this ion beam-assisted vacuum thermal diffusion treatment process is used to reduce the temperature of grain boundary diffusion to 600-800°C, and the time is greatly shortened to 6-12h. However, the bombardment of high-energy ion beams will sputter and peel off part of the atoms on the surface of the magnet, causing the loss of the magnet and heavy rare earth elements and the pollution of the diffusion cavity, and is not conducive to the inward diffusion of heavy rare earth elements; in addition, the energy used in the ion beam at the order of hundreds of electron volts can only increase the diffusion coefficient to a depth of hundreds of microns at most, which limits the effect of this method on thicker magnets. If the ion beam energy is to be increased to enhance the penetration ability, the aforementioned sputtering loss problem must be solved. Summary of the invention

[0004] The purpose of the present invention is to provide a method for grain boundary diffusion of NdFeB magnets and its application in cerium-containing magnets, including an ion beam assisted thermal diffusion method, wherein a sputtering-resistant layer composed of a carbon film is further covered on the surface of a heavy rare earth diffusion source, and the sputtering-resistant layer not only has an extremely low sputtering rate itself, but also can prevent the sputtering loss of heavy rare earth and NdFeB.

[0005] The present invention provides a method for grain boundary diffusion of NdFeB magnets, comprising the following steps:

[0006] A heavy rare earth diffusion source and an anti-sputtering layer are sequentially attached to the surface of the NdFeB magnet, and then thermal diffusion is performed with the aid of ion beam irradiation to wash away the anti-sputtering layer, thereby obtaining a NdFeB magnet modified by grain boundary diffusion;

[0007] The energy of the ion beam is 3 to 10 keV;

[0008] The thermal diffusion temperature is 400-550° C. and the time is 5-10 hours.

[0009] Further on the basis of the technical solution of the present invention, before attaching the heavy rare earth diffusion source and the anti-sputtering layer, a wetting agent and a barrier agent are sequentially attached to the surface of the NdFeB magnet and pre-diffusion is performed.

[0010] The present invention also provides an application of the above-mentioned NdFeB magnet grain boundary diffusion method in a cerium-containing magnet.

[0011] The technical solution of the present invention has the following beneficial effects:

[0012] 1. The NdFeB magnet grain boundary diffusion method of the present invention uses an anti-sputtering layer, which greatly reduces the sputtering loss of heavy rare earth and NdFeB materials under the condition of low ion beam energy loss; this enables higher energy ion beams to be put into use, increases the depth of change in the magnet diffusion coefficient, and thus allows for more selective grain boundary diffusion at lower temperatures.

[0013] 2. The anti-sputtering layer of the present invention is composed of a carbon film, which has high conductivity and can be irradiated by a DC ion source. The operation and equipment are relatively simple and the cost is low. In addition, the carbon anti-sputtering layer has low compatibility with the inner metal layer and is easy to remove.

[0014] 3. In some embodiments of the present invention, the NdFeB magnet subjected to ion beam assisted thermal diffusion is first pre-diffused with a wetting agent and a barrier agent, and its grain boundary wettability and fluidity are improved, and a rare earth oxide shell is formed at the grain boundary and the grain boundary, which is beneficial to further improve the selectivity of grain boundary diffusion. DETAILED DESCRIPTION

[0015] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the specific implementation of the present invention is further described below. Obviously, the embodiments described therein are only part of the implementation of the present invention, which is an explanation of the technical solution of the present invention rather than a limitation.

[0016] A method for grain boundary diffusion of NdFeB magnets of the present invention comprises the following steps:

[0017] A heavy rare earth diffusion source and an anti-sputtering layer are sequentially attached to the surface of the NdFeB magnet, and then thermal diffusion is performed with the aid of ion beam irradiation to wash away the anti-sputtering layer, thereby obtaining a NdFeB magnet modified by grain boundary diffusion;

[0018] The energy of the ion beam is 3 to 10 keV;

[0019] The thermal diffusion temperature is 400-550° C. and the time is 5-10 hours.

[0020] Due to the effect of the anti-sputtering layer, the ion beam energy of the ion beam irradiation assisted thermal diffusion of the present invention is increased by an order of magnitude, and the depth of the ion beam to improve the diffusion coefficient reaches the millimeter level. The method of washing away the anti-sputtering layer includes but is not limited to ultrasonic cleaning, laser cleaning and solvent cleaning.

[0021] Furthermore, the anti-sputtering layer is composed of a carbon film with a thickness of 1 to 10 μm. Due to the barrier of the heavy rare earth layer and the low temperature, the diffusion of carbon to the NdFeB magnet is very weak and has no significant effect on the magnet composition.

[0022] Furthermore, the method for attaching the carbon film to the surface of the NdFeB magnet includes: directly attaching multilayer graphene of a specified thickness to the surface of the NdFeB magnet, and depositing the carbon film on the surface of the NdFeB magnet by magnetron sputtering.

[0023] Furthermore, the ion beam is an inert gas ion beam with a beam current density of 5 to 20 mA / cm 2 , the incident direction is perpendicular to the surface of the NdFeB magnet. The beam density should not be too large, because the reflected positive ions will shield the subsequent ions.

[0024] Furthermore, during the thermal diffusion, each surface of the NdFeB magnet attached with the heavy rare earth diffusion source and the anti-sputtering layer is irradiated with ion beam for no less than 1.5 hours. Obviously, the thermal diffusion assisted by ion beam irradiation includes ion beam irradiation of the entire or part of the thermal diffusion process.

[0025] Furthermore, before attaching the heavy rare earth diffusion source and the anti-sputtering layer, a wetting agent and a barrier agent are sequentially attached to the surface of the NdFeB magnet and pre-diffusion is performed.

[0026] Furthermore, the wetting agent is a non-rare earth metal or an alloy thereof with at least one of Pr and Nd, and the non-rare earth metal includes at least one of Cu, Al, Ga, Ni and Co; the barrier agent is one or more of Al2O3, MgO, ZnO, Cr2O3.

[0027] The wetting agent is a transition metal or an alloy thereof with a light rare earth metal, which can improve the fluidity of the grain boundary; the barrier agent is a partial non-rare earth oxide, preferably MgO and ZnO, which can react at the edge of the grain boundary to generate a light rare earth oxide phase, thereby improving the coercive force and thermal stability of the magnet, and providing a reflection site for the solitary wave generated by the ion beam, thereby increasing the defect rate of the grain boundary during irradiation.

[0028] Furthermore, the pre-diffusion is: in a vacuum environment, diffusing at 500-650° C. for 1-4 hours, and then diffusing at 900-1000° C. for 0.5-1 hour.

[0029] The low-temperature first stage pre-diffusion is intended to diffuse the wetting agent into the grain boundaries to improve the subsequent diffusion efficiency; while the high-temperature, rapid second stage pre-diffusion allows the oxide to penetrate deep into the grain boundaries to form the light rare earth oxide phase and minimize the wetting agent and barrier agent from entering the interior of the grains.

[0030] Furthermore, after the pre-diffusion is completed, the surface of the NdFeB magnet to which the heavy rare earth diffusion source is to be attached is cleaned and activated by ion beam irradiation with an energy of 200 to 500 eV and a working gas of an inert gas containing 0 to 5% by volume of hydrogen. In addition to ion beam cleaning, plasma cleaning can also be used to remove excess oxides.

[0031] The application of the above-mentioned NdFeB magnet grain boundary diffusion method in the present invention in cerium-containing magnets includes but is not limited to application in common dual-phase cerium-containing NdFeB magnets. For magnets that require a two-stage annealing process, pre-diffusion can replace the first stage annealing (about 1000°C), and ion beam assisted thermal diffusion can replace the second stage annealing (about 500°C).

[0032] The present invention is described in detail below with reference to the examples. The experimental methods are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0033] Example 1

[0034] Dual-phase Ce-containing NdFeB magnets: Magnequench MQP-7-8 and MQP-15-12 (nominal compositions are Nd 4.0 Pr 1.9 Ce 23.6 Fe 69.5 B 1.0 and Nd 26.0 Nb 1.9 Fe 71.1 B 1.0 ) are mixed in a mass ratio of 1:1, oriented and formed, and sintered in a spark plasma sintering furnace (40MPa, 750℃ for 5min). The obtained NdFeB magnet is cut into small pieces of φ5mm×4mm and tempered at 900℃ in vacuum for 8h.

[0035] Ion beam assisted thermal diffusion: A 3μm thick heavy rare earth diffusion source (Dy) was attached to the pre-diffused surface of the obtained NdFeB magnet by magnetron sputtering, and then a 5μm thick carbon film was deposited by reactive magnetron sputtering (according to the existing technology: the synthesis gas is 4% H2 / Ar, the reaction gas is C3F6, C2F6, diethylamine, and the total pressure is 2.6Pa). Then, the diffusion was carried out at 500℃ for 6h in a vacuum environment, with a pressure of 5keV, 12mA / cm 2 The surface with the heavy rare earth diffusion source and carbon film attached was uniformly irradiated with an argon ion beam vertically for 1.5 hours each. The surface was cleaned and decarbonized by laser to obtain a magnet with grain boundary diffusion.

[0036] Example 2

[0037] The difference between this embodiment and embodiment 1 is that the ion beam assisted thermal diffusion is carried out at 400°C for 9 hours, with a temperature of 10 keV and 10 mA / cm 2 The surface to which the heavy rare earth diffusion source and the carbon film were attached was uniformly irradiated with an argon ion beam vertically for 3 hours each.

[0038] Example 3

[0039] The difference between this embodiment and embodiment 1 is that instead of using reactive magnetron sputtering to form a carbon film, an electrodeposition method is used to deposit artificial graphene on the heavy rare earth diffusion source to form a 10 μm thick carbon film. (The process is consistent with the method described in the Chinese invention with publication number CN118109882A, and the surface does not need to be cleaned)

[0040] Example 4

[0041] The difference between this embodiment and embodiment 1 is that no 900° C. tempering is performed before ion beam assisted thermal diffusion, and the following two steps are added:

[0042] Pre-diffusion: Coat the two surfaces of the obtained dual-phase Ce-containing NdFeB magnet that are not perpendicular to the magnetization direction and the pressing direction with a 2 μm thick wetting agent (Pr 0.3 Cu 0.4 Al 0.4 ) and 5μm barrier (MgO), diffused at 600℃ for 3h and then at 1000℃ for 0.5h in a vacuum environment.

[0043] Pre-diffusion cleaning: high-purity argon gas is introduced into the vacuum chamber to ionize and clean the pre-diffused surface of the NdFeB magnet. In the process, hydrogen gas is used to make its volume account for 3% of the total gas. The pressure in the vacuum chamber is 0.5 Pa, the ion beam energy is 300 eV, and the cleaning time is 20 minutes.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that no carbon film is prepared, and ion beam irradiation is directly used to assist thermal diffusion.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that direct thermal diffusion is performed without using ion beam irradiation assistance.

[0048] Comparative Example 3

[0049] The difference between this comparative example and Example 1 is that ion beam irradiation assistance is not used, and vacuum thermal diffusion is carried out at 800° C. for 6 hours.

[0050] The magnetic properties of the magnets obtained in the above embodiments and comparative examples are tested below, including their remanence (Br), intrinsic coercivity (H cj ) and maximum energy product ((BH) max ), the results are shown in Table 1.

[0051] Table 1 Comparison of magnetic properties of cerium-containing NdFeB magnets

[0052] Group Br(kGs) <![CDATA[H cj (no)]]> <![CDATA[(BH) max (MGOe)]]> Example 1 12.46 14.30 36.32 Example 2 12.68 14.11 37.45 Example 3 12.44 14.24 36.40 Example 4 12.97 14.82 38.24 Comparative Example 1 12.50 12.75 36.79 Comparative Example 2 12.72 9.64 37.89 Comparative Example 3 11.45 14.86 34.37

[0053] The cerium-containing magnets prepared by the preparation method of the present invention have excellent magnetic properties, especially coercive force. At the same time, due to the less invasion of heavy rare earth elements into the main phase, the remanence is particularly improved compared with the product obtained by ordinary grain boundary diffusion (Comparative Example 3). All samples in the embodiments can meet the requirements of N38M grade.

[0054] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and the obvious changes or modifications derived therefrom should still be considered as the protection scope of the present invention.

Claims

1. A method for grain boundary diffusion of NdFeB magnets, characterized in that: The steps include: A heavy rare earth diffusion source and an anti-sputtering layer are sequentially attached to the surface of the NdFeB magnet, and then thermal diffusion is performed with the aid of ion beam irradiation to wash away the anti-sputtering layer, thereby obtaining a NdFeB magnet modified by grain boundary diffusion; The energy of the ion beam is 3 to 10 keV; The thermal diffusion temperature is 400-550° C. and the time is 5-10 hours.

2. The method for grain boundary diffusion of NdFeB magnets according to claim 1, characterized in that: The anti-sputtering layer is composed of a carbon film and has a thickness of 1 to 10 μm.

3. The method for grain boundary diffusion of NdFeB magnets according to claim 2, characterized in that: The method for attaching the carbon film to the surface of the NdFeB magnet comprises: directly attaching multilayer graphene of a specified thickness to the surface of the NdFeB magnet, and depositing the carbon film on the surface of the NdFeB magnet by magnetron sputtering.

4. The NdFeB magnet grain boundary diffusion method according to claim 1, characterized in that: The ion beam is an inert gas ion beam with a beam current density of 5 to 20 mA / cm 2 , the incident direction is perpendicular to the surface of the NdFeB magnet.

5. The method for grain boundary diffusion of NdFeB magnets according to claim 1, characterized in that: During the thermal diffusion, each surface of the NdFeB magnet attached with the heavy rare earth diffusion source and the anti-sputtering layer is irradiated with the ion beam for no less than 1.5 hours.

6. The NdFeB magnet grain boundary diffusion method according to claim 1, characterized in that: Before attaching the heavy rare earth diffusion source and the anti-sputtering layer, a wetting agent and a barrier agent are sequentially attached to the surface of the NdFeB magnet and pre-diffusion is performed.

7. The method for grain boundary diffusion of NdFeB magnets according to claim 6, characterized in that: The wetting agent is a non-rare earth metal or an alloy thereof with at least one of Pr and Nd, and the non-rare earth metal includes at least one of Cu, Al, Ga, Ni and Co; the barrier agent is one or more of Al2O3, MgO, ZnO and Cr2O3.

8. The method for grain boundary diffusion of NdFeB magnets according to claim 6, characterized in that: The pre-diffusion is: in a vacuum environment, diffusing at 500-650° C. for 1-4 hours, and then diffusing at 900-1000° C. for 0.5-1 hour.

9. The method for grain boundary diffusion of NdFeB magnets according to claim 6, characterized in that: After the pre-diffusion is completed, the surface of the NdFeB magnet to which the heavy rare earth diffusion source is to be attached is cleaned and activated by ion beam irradiation with an energy of 200-500 eV and a working gas of an inert gas containing 0-5% by volume of hydrogen.

10. Use of the NdFeB magnet grain boundary diffusion method according to any one of claims 1 to 9 in a cerium-containing magnet.