Method for improving coercive force of nanocrystalline RECo5 permanent magnet material

Abstract

The invention discloses a method for improving the coercive force of a nanocrystalline RECo5 permanent magnet material, and belongs to the technical field of functional materials. According to the method, nano ceramic particles are doped into nanocrystalline RECo5 magnetic powder, uniform distribution of the ceramic particles is achieved through high-energy ball milling, the RECo5 magnetic powder is non-crystallized, and the stable ceramic particles enable the non-crystalline magnetic powder to be uniformly crystallized in the hot pressing process; abnormal growth of crystal grains is hindered in the thermal deformation process, so that the coercive force is improved, but the ceramic particles hinder the growth of the crystal grains, and the residual magnetism is slightly reduced; the stress is released and the impurity phase proportion is reduced through isothermal annealing subsequently, so that the residual magnetism is recovered and even slightly improved, and the coercive force is improved under the condition that the maximum magnetic energy product is not reduced basically.

Description

Technical Field

[0001] The present invention relates to a method for improving the coercivity of nanocrystalline RECo5 permanent magnet material, belonging to the technical field of functional materials. The present invention adopts ceramic particles to replace traditional α-Fe as a soft magnetic phase. The high strength of the ceramic particle alloy is utilized to coordinate the deformation of the soft and hard phases during the thermal deformation process, enhance the c-axis texture, and improve the magnetic properties of the magnet. Background Art

[0002] Rare earth permanent magnet materials are essential functional materials in the field of high-tech in today's society. They are closely related to people's lives and are widely used in communications, machinery, medical treatment, instrumentation, computers, transportation, energy, aerospace, national defense and other fields. As modern science and technology and the information industry develop towards integration, miniaturization and intelligence, rare earth permanent magnet devices also tend to be miniaturized and efficient, which inevitably requires the cooling method of the device to change from liquid cooling to air cooling, which puts higher requirements on the temperature stability of permanent magnet materials.

[0003] Among rare earth permanent magnet compounds, SmCo5 compounds have ultra-high magnetocrystalline anisotropy field and temperature stability, and are suitable for high-temperature applications. Nanocrystalline permanent magnets are easy to obtain high coercivity and low coercivity temperature coefficient due to the strong pinning effect brought by abundant grain boundaries, see DTZhang, WCLv, M.Yue, JJYang, WQLiu, JXZhang, Y.Qiang.Nanocrystalline SmCo5 magnet synthesized by spark plasma sintering, Journal of Applied Physics 107 (2010) 09A701, but because the prepared isotropic magnet, its remanence is low, only 5kG. In order to improve the magnetic properties, it is necessary to introduce c-axis texture to improve the remanence and maximum magnetic energy product. Since nanocrystalline magnetic powder cannot obtain texture through magnetic field orientation, the current thermal deformation method is an effective method for obtaining texture in nanocrystalline permanent magnet materials. However, there is no liquid phase in nanocrystalline RECo5 magnetic powder, and the main phase is hexagonal with low symmetry, so it is difficult to obtain texture through deformation. This is completely different from nanocrystalline Nd-Fe-B magnetic powder. Recent studies have shown that nanocrystalline RECo5 magnets can induce c-axis texture through high temperature and large deformation rate (more than 90% deformation), see M. Yue, JH Zuo, WQ Liu, WCL v, DT Zhang, JX Zhang, ZH Guo, W. Li; Magnetic anisotropy in bulk nanocrystalline SmCo5 permanent magnet prepared by hot deformation, J. Appl. Phys. 109 (2011) 07A711. However, high deformation temperature leads to abnormal grain growth and a significant reduction in coercivity. This patent provides a method for improving the coercivity of nanocrystalline RECo5 permanent magnet materials, by adding nano-ceramic particles and achieving uniform distribution through ball milling. These stable ceramic particles make the amorphous magnetic powder uniformly crystallized during the hot pressing process; during the hot deformation process, the abnormal grain growth is hindered, thereby improving the coercivity.This is completely different from adding high melting point WC to hot-deformed Nd-Fe-B permanent magnet materials to improve the comprehensive magnetic properties, see ZX Wang, K. Pei, JJ Zhang, RJ Chen, WXXia, JZ Wang, M. Li, ARYan, Correlation between the microstructure and magnetic configuration in coarse-grain inhibited hot-deformed Nd-Fe-B magnets, Acta Materialia 167 (2019) 103-111. Summary of the invention

[0004] The purpose of the present invention is to improve the coercive force of nanocrystalline RECo5 permanent magnet material. The method comprises the following steps: adding nano-ceramic particles into nano-crystalline RECo5 magnetic powder, and achieving uniform distribution of ceramic particles and amorphization of RECo5 magnetic powder through high-energy ball milling. These stable ceramic particles make amorphous magnetic powder uniformly crystallized during hot pressing. During thermal deformation, abnormal growth of grains is hindered, thereby improving the coercive force. However, the ceramic particles hinder grain growth and also slightly reduce remanence. Subsequently, isothermal annealing is performed to release stress and reduce the proportion of impure phases so that the remanence is restored or even slightly improved, thereby improving the coercive force without substantially reducing the maximum magnetic energy product.

[0005] The present invention provides a method for improving the coercive force of nanocrystalline RECo5 permanent magnet material, which is characterized in that it specifically comprises the following steps:

[0006] (1) Preparation or screening of ceramic particles with a particle size of less than or equal to 20 nm, such as TiN and TiC;

[0007] (2) After weighing the rare earth element RE and Co raw materials in proportion, the nanocrystalline RECo5 magnetic powder is prepared by melt rapid quenching method;

[0008] (3) mixing the prepared RECo5 magnetic powder and ceramic particles in proportion to obtain a mixture, and then performing high-energy ball milling to prepare amorphous RECo5 magnetic powder with dispersed ceramic particles;

[0009] (4) hot pressing the ball-milled magnetic powder to obtain a nanocrystalline dense deformed precursor;

[0010] (5) thermally deforming the deformed precursor to obtain a thermally deformed RECo5 magnet;

[0011] (6) Isothermal annealing of the hot deformed magnet.

[0012] Further, the ceramic particles in step (1) are selected from high-stability ceramic particle materials such as TiN, TiC, SiC, TiB2, etc., and must have high stability to ensure that they do not decompose during the ball milling process and do not react with the main phase;

[0013] Furthermore, the rare earth element described in step (2) is one or more of Sm, Pr, Ce, La, etc.

[0014] In step (2), the rare earth content must be ensured to be RECo5, and the molar ratio of RE to Co in the stoichiometric ratio is (1.03-1.08):5, that is, the chemical formula of RE1.03-1.08Co5 is used for the mixing, so as to ensure the presence of rare earth-rich nanoparticles in the nanocrystalline magnet, and an additional 3% of the Sm element must be added to compensate for the burn loss during the melting process.

[0015] In the further step (3), the proportion of the ceramic particles in the mixture is 0.1wt.%-1wt.%, preferably 0.5wt.%. The high-energy ball milling process is preferably: high-energy ball milling for 5h, a ball-to-material ratio of 20:1, and a rotation speed of 700r / min.

[0016] In the hot pressing process in step (4), the temperature is 650°C-750°C and the pressure is 200MPa-500MPa. There are no special requirements for the hot pressing equipment, but it is necessary to ensure that the prepared deformed precursor is a well-crystallized nanocrystalline (grain size 30nm-100nm) structure and the magnet density exceeds 98% of the theoretical density.

[0017] In the further step (5), the temperature of the heat deformation process is 750-850°C, the pressure is 100MPa-300MPa, and the deformation amount is 70%-90%, preferably 80%. There is no special requirement for the heat deformation equipment, and the deformation method can be roughening, back extrusion, or front extrusion.

[0018] In the further isothermal annealing process in step (6), the annealing temperature is 750°C-850°C, and the annealing time is 1-3 hours. The annealing temperature varies slightly with the type of rare earth element. The selection principle is to use a temperature as high as possible under the premise of being lower than the decomposition temperature of the RECo5 phase (about 850°C).

[0019] Advantages of the present invention: The present invention incorporates nano-ceramic particles into nano-crystalline RECo5 magnetic powder, and achieves uniform distribution of ceramic particles and amorphization of RECo5 magnetic powder through high-energy ball milling. These stable ceramic particles make the amorphous magnetic powder uniformly crystallized during the hot pressing process; during the thermal deformation process, the abnormal growth of grains is hindered, thereby improving the coercive force, but the ceramic particles hinder the grain growth and also slightly reduce the remanence; subsequently, isothermal annealing is performed to release stress and reduce the proportion of impurities so that the remanence is restored or even slightly improved, thereby achieving the improvement of coercive force without substantially reducing the maximum magnetic energy product. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0021] Example 1

[0022] The specific implementation steps for preparing the hot-deformed (Sm0.4Pr0.6)Co5 magnet with TiN added in this case are as follows:

[0023] (1) Sm, Pr and Co with a purity of 99.9% are prepared in a stoichiometric ratio of (Sm0.4Pr0.6)1.05Co5, and 3% of Sm is added to supplement the volatilization during smelting. A melt quenching device is used to prepare a quenching strip at a rotation speed of 30 m / s.

[0024] (2) TiN particles with a size below 20 nm were screened and mixed with (Sm0.4Pr0.6)Co5 quenched strip in a mass ratio of 0.5:99.5, and high-energy ball milling was performed under gas protection for 5 h, with a ball-to-material ratio of 20:1 and a rotation speed of 700 r / min.

[0025] (3) The milled magnetic powder is loaded into a cemented carbide mold using an induction hot pressing device and hot pressed at 700°C and 300 MPa to obtain a deformed precursor.

[0026] (4) The nanocrystalline thermal deformation precursor is thermally deformed at 830° C. and a pressure of 200 MPa, with a deformation amount of 80%.

[0027] (5) The hot deformed magnet was annealed at 850°C for 2 hours under argon protection to obtain the final magnet.

[0028] Example 2

[0029] The specific implementation steps for preparing hot-deformed SmCo5 magnets with added TiN in this case are as follows:

[0030] (1) Sm element with a purity of 99.9% and Co element were mixed in a stoichiometric ratio of Sm1.05Co5, and 3% of Sm was added to supplement the volatilization during smelting. The melt quenching equipment was used to prepare the quenching strip at a rotation speed of 30 m / s.

[0031] (2) TiN particles with a size below 20 nm were screened and mixed with SmCo5 quenched strips in a mass ratio of 0.5:99.5, and high-energy ball milling was performed under gas protection for 5 h, with a ball-to-material ratio of 20:1 and a rotation speed of 700 r / min.

[0032] (3) The milled magnetic powder is loaded into a cemented carbide mold using an induction hot pressing device and hot pressed at 700°C and 300 MPa to obtain a deformed precursor.

[0033] (4) The nanocrystalline thermal deformation precursor is thermally deformed at 830° C. and a pressure of 200 MPa, with a deformation amount of 80%.

[0034] (5) The hot deformed magnet was annealed at 850°C for 2 hours under argon protection to obtain the final magnet.

[0035] Implementation Case 3

[0036] The specific implementation steps for preparing the hot-deformed PrCo5 magnet with TiN added in this case are as follows:

[0037] (1) Pr element with a purity of 99.9% and Co element are mixed in a stoichiometric ratio of Pr1.05Co5, and an additional 3% of Pr is added to supplement the volatilization during smelting. A melt quenching device is used to prepare a quenching strip at a rotation speed of 30 m / s.

[0038] (2) TiN particles with a size below 20 nm were screened and mixed with PrCo5 quenched strips in a mass ratio of 0.5:99.5, and high-energy ball milling was performed under gas protection for 5 h, with a ball-to-material ratio of 20:1 and a rotation speed of 700 r / min.

[0039] (3) The milled magnetic powder is loaded into a cemented carbide mold using an induction hot pressing device and hot pressed at 700°C and 300 MPa to obtain a deformed precursor.

[0040] (4) The nanocrystalline thermal deformation precursor is thermally deformed at 830° C. and a pressure of 200 MPa, with a deformation amount of 80%.

[0041] (5) The hot deformed magnet was annealed at 850°C for 2 hours under argon protection to obtain the final magnet.

[0042] Comparative Example 1

[0043] The specific implementation steps for preparing the hot-deformed (Sm0.4Pr0.6)Co5 magnet in this comparative case are as follows:

[0044] (1) Sm, Pr and Co with a purity of 99.9% are prepared in a stoichiometric ratio of (Sm0.4Pr0.6)1.05Co5, and 3% of Sm is added to supplement the volatilization during smelting. A melt quenching device is used to prepare a quenching strip at a rotation speed of 30 m / s.

[0045] (2) The (Sm0.4Pr0.6)Co5 rapid quenching strip was subjected to high-energy ball milling for 5 h under gas protection, with a ball-to-material ratio of 20:1 and a rotation speed of 700 r / min.

[0046] (3) The milled magnetic powder is loaded into a cemented carbide mold using an induction hot pressing device and hot pressed at 700°C and 300 MPa to obtain a deformed precursor.

[0047] (4) The nanocrystalline thermal deformation precursor is thermally deformed at 830° C. and a pressure of 200 MPa, with a deformation amount of 80%.

[0048] Comparative Example 2

[0049] The specific implementation steps for preparing the hot-deformed PrCo5 magnet with added TiN in this comparative case are as follows:

[0050] (1) Pr element with a purity of 99.9% and Co element are mixed in a stoichiometric ratio of Pr1.05Co5, and an additional 3% of Pr is added to supplement the volatilization during smelting. A melt quenching device is used to prepare a quenching strip at a rotation speed of 30 m / s.

[0051] (2) TiN particles with a size below 20 nm were screened and mixed with PrCo5 quenched strips in a mass ratio of 0.5:99.5, and high-energy ball milling was performed under gas protection for 5 h, with a ball-to-material ratio of 20:1 and a rotation speed of 700 r / min.

[0052] (3) The milled magnetic powder is loaded into a cemented carbide mold using an induction hot pressing device and hot pressed at 700°C and 300 MPa to obtain a deformed precursor.

[0053] (4) The nanocrystalline thermal deformation precursor is thermally deformed at 830° C. and a pressure of 200 MPa with a deformation amount of 80% to obtain a thermally deformed magnet.

[0054] Table 1 Magnetic properties of various implementation cases and comparative cases

[0055]

[0056]

[0057] Comparison of the magnetic properties of Implementation Case 1 and Comparative Case 1 as well as Implementation Case 3 and Comparative Case 2 can further prove that the incorporation of ceramic particles into RECo5 magnets can effectively improve the coercive force, but the hindrance of grain growth will slightly reduce the remanent magnetism, which can be restored by isothermal annealing, thereby achieving an increase in coercive force without substantially reducing the maximum magnetic energy product.

[0058] Although the present invention has been described in detail above by general description, specific implementation methods and experiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for improving the coercivity of nanocrystalline RECo5 permanent magnet material, characterized in that: The specific steps include: (1) preparing or screening ceramic particles with a particle size of less than or equal to 20 nm; (2) After weighing the rare earth element RE and Co raw materials in proportion, the nanocrystalline RECo5 magnetic powder is prepared by melt rapid quenching method; (3) mixing the prepared RECo5 magnetic powder and ceramic particles in proportion to obtain a mixture, and then performing high-energy ball milling to prepare amorphous RECo5 magnetic powder with dispersed ceramic particles; (4) hot pressing the ball-milled magnetic powder to obtain a nanocrystalline dense deformed precursor; (5) thermally deforming the deformed precursor to obtain a thermally deformed RECo5 magnet; (6) Isothermal annealing of the hot deformed magnet.

2. The method according to claim 1, characterized in that The ceramic particles in step (1) are selected from high-stability ceramic particle materials such as TiN, TiC, SiC, TiB2, etc., and must have high stability to ensure that they do not decompose during the ball milling process and do not react with the main phase.

3. The method according to claim 1, characterized in that The rare earth element described in step (2) is one or more of Sm, Pr, Ce, La, etc.

4. The method according to claim 1, characterized in that In step (2), the rare earth content must be ensured to be RECo5, and the molar ratio of RE to Co in the stoichiometric ratio is (1.03-1.08):5, and an additional 3% of Sm element must be added to compensate for the burn loss during the melting process.

5. The method according to claim 1, characterized in that The ceramic particles in step (3) account for 0.1wt.% to 1wt.% of the mixture, preferably 0.5wt.%.

6. The method according to claim 1, characterized in that In the hot pressing process in step (4), the temperature is 650°C-750°C and the pressure is 200MPa-500MPa. The prepared deformed precursor is a well-crystallized nanocrystalline structure with a grain size of 30nm-100nm, and the magnet density exceeds 98% of the theoretical density.

7. The method according to claim 1, characterized in that In the thermal deformation process in step (5), the temperature is 750°C-850°C, the pressure is 100MPa-300MPa, the deformation amount is 70%-90%, preferably 80%; the deformation method is roughening, or back extrusion, or front extrusion.

8. The method according to claim 1, characterized in that In the isothermal annealing process in step (6), the annealing temperature is 750°C-850°C, and the annealing time is 1-3 hours. The annealing temperature varies slightly with the type of rare earth element. The selection principle is to select a temperature as high as possible under the premise of being lower than the decomposition temperature of the RECo5 phase.

9. The method according to claim 1, characterized in that High-energy ball milling process: high-energy ball milling for 5 hours, ball-to-material ratio of 20:1, rotation speed of 700r / min.

10. Nanocrystalline RECo5 permanent magnet material prepared according to the method according to any one of claims 1 to 9.

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