Sintered neodymium-iron-boron magnet material with good mechanical property and preparation method of sintered neodymium-iron-boron magnet material

Abstract

The invention relates to the technical field of modified magnet materials, and provides a sintered neodymium-iron-boron magnet material with good mechanical properties and a preparation method. The sintered neodymium-iron-boron magnet is prepared through the following steps that S1, burdening, smelting and sheet casting are conducted, and an alloy sheet is obtained; s2, hydrogen decrepitation and jet milling are conducted, and alloy powder is obtained; s3, uniformly mixing the alloy powder and the additive powder to obtain mixed powder; s4, orientation profiling and secondary pressing are carried out, and an anisotropic magnet is obtained; and S5, performing sintering and heat treatment to obtain the sintered neodymium-iron-boron magnet. Wherein TiC serves as a core layer of the additive powder, Ti3SiC2 serves as a shell layer of the additive powder, and the mass ratio of the alloy powder to the additive powder is 100: (0.4-1). The sintered neodymium-iron-boron magnet material is subjected to grain boundary addition modification by adopting the additive powder, so that the bending strength of the material is improved, and the fracture toughness of the material is improved.

Description

Technical Field

[0001] The invention relates to the technical field of modified magnetic materials, and provides a sintered NdFeB magnetic material with good mechanical properties and a preparation method thereof. Background Art

[0002] Sintered NdFeB magnets have excellent magnetic properties and are widely used in electronic power, medical equipment, petrochemical, aviation and other fields. Sintered NdFeB magnets are mainly composed of the main phase (Nd 2 Fe 14 B) and grain boundary phase (Nd-rich phase). The grain boundary phase is evenly distributed around the main phase. The main phase provides the magnetic source, and the Nd-rich phase plays the role of demagnetizing coupling and improving coercive force.

[0003] Although sintered NdFeB magnet material has good magnetic properties, its mechanical properties are poor, mainly reflected in: First, the main phase Nd 2 Fe 14 B belongs to the tetragonal system, with few slip systems, and will break during the elastic deformation stage, without toughness and plasticity. Therefore, the fracture toughness of sintered NdFeB magnets is low, showing intergranular fracture. Secondly, since the elastic modulus of the grain boundary Nd-rich phase is much lower than that of the main phase, the bending strength of sintered NdFeB magnets is low.

[0004] It can be seen that sintered NdFeB magnet materials are prone to cracks or bending deformation during processing and use, which reduces the production qualification rate and processing accuracy, leads to material failure, reduces safety, and limits its application in high-impact, high-precision occasions or high-strength demand fields. Therefore, improving the bending strength and fracture toughness of sintered NdFeB magnets has important practical significance. Summary of the invention

[0005] In view of the above situation, the present invention proposes a sintered NdFeB magnet material with good mechanical properties and a preparation method, aiming to improve the bending strength and fracture toughness of the sintered NdFeB magnet material.

[0006] To achieve the above purpose, the specific technical solution of the present invention is as follows: First, the present invention provides a method for preparing a sintered NdFeB magnet material with good mechanical properties, comprising the following preparation steps: S1, batching, smelting, and casting to obtain alloy sheets; S2, hydrogen crushing and air flow grinding to obtain alloy powder; S3, mixing the alloy powder and the additive powder uniformly to obtain a mixed powder; S4, orientation pressing and secondary pressing to obtain anisotropic magnets; S5, sintering and heat treatment to obtain the sintered NdFeB magnet.

[0007] The additive powder has a core-shell structure, the core layer is TiC, the shell layer is Ti 3 SiC 2 .

[0008] Preferably, the additive powder is prepared by: using TiCl 4 As titanium source, CH 3 SiCl 3 As silicon source and carbon source, high-purity hydrogen is used as reaction gas and carrier gas, and high-purity argon is used as dilution gas to perform chemical vapor deposition on the surface of SiC nanoparticles to form Ti 3 SiC 2 The coating layer is obtained with TiC as the core layer and Ti 3 SiC 2 It is an additive powder for the shell layer.

[0009] Further preferably, in the above preparation method, the deposition temperature is 1100° C., the deposition pressure is 5 kPa, the volume concentration of hydrogen is 50%, and the deposition time is 5-10 min.

[0010] Preferably, the mass ratio of alloy powder to additive powder is 100:0.4-1.

[0011] Preferably, the casting in S1 adopts a rapid solidification casting process, and the solidification cooling rate is 10 4 -10 5 ℃ / s.

[0012] Preferably, in S2, the particle size of the alloy powder after hydrogen crushing is in the range of 50-200 μm.

[0013] Preferably, in S2, the particle size of the alloy powder after air flow milling is in the range of 3-5 μm.

[0014] Preferably, the mixing method in S3 is: adding the additive powder to ethanol in a glove box filled with nitrogen, ultrasonically dispersing for 20-40 minutes, then adding the alloy powder, ultrasonically dispersing for 10-20 minutes, and then volatilizing to remove the ethanol to obtain a mixed powder.

[0015] Preferably, in S4, the magnetic field intensity of the orientation pressing is 2T.

[0016] Preferably, in S4, the secondary pressing pressure is 200-300 MPa, and the holding time is 20-40 s.

[0017] Preferably, in S5, the sintering process is first sintering at 1050-1060° C. for 1-2 h, and then sintering at 1060-1070° C. for 3-5 h.

[0018] Preferably, in S5, the heat treatment process is first tempering at 900-920°C for 2-4h, and then tempering at 470-490°C for 4-5h.

[0019] The present invention also provides a sintered NdFeB magnet material prepared by the above preparation method.

[0020] Ti 3 SiC 2 It is a flexible ceramic material with a ternary layered hexagonal crystal structure. In the unit cell, the CTi 6 The octahedron is separated by closely packed parallelogram Si atomic layers, among which Ti and C are connected by typical strong covalent bonds, while the planar Si atomic layer and Ti are connected by weak bonds similar to those between graphite layers. It is based on this structural feature that Ti 3 SiC 2 The material has the excellent properties of both metals and ceramics. It has electrical and thermal conductivity, room temperature ductility, processing plasticity, etc. similar to metals, as well as high temperature resistance, corrosion resistance, oxidation resistance, and high yield strength of ceramics.

[0021] Ti 3 SiC 2 The material can be prepared by methods such as vapor deposition, self-propagating high temperature synthesis, solid-liquid reaction, and spark plasma sintering. Chemical vapor deposition can form a layer of Ti with good uniformity on the surface of the substrate. 3 SiC 2 The chemical composition of the deposited layer is easy to control. 4 -CH 3 SiCl 3 -H 2 -Ar precursor reaction system, chemical vapor deposition is carried out on the surface of TiC nanoparticles to obtain TiC as the core layer and Ti 3 SiC 2 The additive powder for the shell layer. In addition, TiC nanoparticles are selected as the substrate because TiC and Ti 3 SiC 2 There is a certain similarity in composition. 3 SiC 2 The Si in the core layer can form a weak bond with the Ti on the surface of the core layer, which is beneficial to the coating stability of the deposited layer.

[0022] The present invention uses the above-mentioned additive powder to add to the grain boundary of sintered NdFeB. After the alloy powder and the additive powder are mixed and oriented and pressed, in the subsequent sintering process, at the sintering temperature, the main phase (melting point higher than the sintering temperature) is a solid phase, and the neodymium-rich phase (melting point lower than the sintering temperature) is a liquid phase. The neodymium-rich phase flows between the main phases to promote sintering densification. The additive powder is distributed in the neodymium-rich phase in a solid form and is distributed around the main phase as the neodymium-rich phase flows. In the final sintered NdFeB magnet material, the additive powder is concentrated in the neodymium-rich grain boundary phase. In the additive powder, the core layer TiC is a rigid ceramic particle with high strength but poor flexibility, while the shell layer Ti 3 SiC 2 It is a flexible ceramic with significantly higher fracture toughness than TiC (the fracture toughness of TiC is 4MPa·m 1 / 2 Left and right, Ti 3 SiC 2 The fracture toughness is 11.2MPa·m 1 / 2 After the additive powder is used for grain boundary modification, on the one hand, the core layer TiC of the additive powder has strong rigidity, which strengthens the grain boundary phase, thereby improving the bending strength of the sintered NdFeB magnet material; on the other hand, the shell layer Ti 3 SiC 2 It is flexible and can absorb the energy of external forces, reduce the generation of microcracks, and hinder the development of cracks, thereby improving the fracture toughness of sintered NdFeB magnet materials.

[0023] The present invention provides a sintered NdFeB magnet material with good mechanical properties and a preparation method. Compared with the prior art, the present invention has outstanding characteristics and excellent effects in that the present invention adopts the following steps to prepare the sintered NdFeB magnet: S1, batching, smelting, casting, obtaining alloy sheets; S2, hydrogen crushing, air flow milling, obtaining alloy powder; S3, uniformly mixing the alloy powder and additive powder to obtain mixed powder; S4, oriented pressing, secondary pressing, obtaining anisotropic magnets; S5, sintering, heat treatment, obtaining the sintered NdFeB magnet. The additive powder has TiC as the core layer and Ti 3 SiC 2 The alloy powder and the additive powder have a mass ratio of 100:0.4-1. By using the additive powder to modify the grain boundary of the sintered NdFeB magnet material, not only the bending strength of the material can be improved, but also the fracture toughness of the material can be improved. DETAILED DESCRIPTION

[0024] The following examples are only for further explanation of the present invention and are not intended to limit the scope of protection of the present invention. Example 1

[0025] First, TiCl 4 As titanium source, CH 3 SiCl 3 As silicon source and carbon source, high-purity hydrogen is used as reaction gas and carrier gas, and high-purity argon is used as dilution gas to perform chemical vapor deposition on the surface of SiC nanoparticles to form Ti 3 SiC 2 The coating layer is obtained with TiC as the core layer and Ti 3 SiC 2 The additive powder of the shell layer. The average particle size of TiC nanoparticles is 200nm, purchased from Shanghai Chaowei Nano Technology Co., Ltd. The deposition temperature is 1100℃, the deposition pressure is 5kPa, the volume concentration of hydrogen is 50%, and the deposition time is 8min.

[0026] Then, the obtained additive powder is used as a grain boundary modifier to prepare sintered NdFeB magnets: S1, ingredients, smelting, rapid solidification casting, to obtain alloy sheet; alloy composition is Nd 29.9 Fe bal Co 0.6 Ga 0.6 B 0.98 ; Solidification cooling rate is 10 5 °C / s; S2, firstly hydrogen crushing the alloy flakes into alloy particles of 100±20μm, and then jet milling into alloy powder of 4±0.2μm; S3, adding the additive powder to ethanol in a glove box filled with nitrogen, ultrasonically dispersing for 30 minutes, then adding the alloy powder, ultrasonically dispersing for 15 minutes, and then volatilizing to remove the ethanol to obtain a mixed powder; S4, orientation pressing with a magnetic field strength of 2T, and then pressing at 250MPa for 30s to obtain anisotropic magnets; S5, first sintering at 1055°C for 1.5h, then sintering at 1065°C for 4h; first tempering at 910°C for 3h, then tempering at 480°C for 4.5h, to obtain the sintered NdFeB magnet.

[0027] In S3, the mass ratio of alloy powder to additive powder is 100:0.4. Example 2

[0028] The difference from Example 1 is that in S3, the mass ratio of the alloy powder to the additive powder is 100:0.6. Example 3

[0029] The difference from Example 1 is that in S3, the mass ratio of the alloy powder to the additive powder is 100:0.8. Example 4

[0030] The difference from Example 1 is that in S3, the mass ratio of the alloy powder to the additive powder is 100:1.

[0031] Performance Test: (1) With reference to GB / T 232-2010 standard, the bending strength of the material was tested by three-point bending test method, the sample size was 5mm×5mm×30mm, the test span was 25mm, the loading speed was 0.1mm / min, the loading direction was perpendicular to the magnetic field orientation direction during molding, the test temperature was room temperature, and the average value was taken after 10 tests. The bending strengths of the sintered NdFeB magnet materials prepared in Example 1, Example 2, Example 3, and Example 4 were measured to be 254.8 MPa, 274.5 MPa, 289.9 MPa, and 299.4 MPa, respectively.

[0032] (2) Referring to GB / T 4161-2007 standard, a three-point bending specimen was used to test the fracture toughness of the material by the single-side notched beam method. The specimen size was 7mm×7mm×30mm. A crack with a width of 0.18mm was introduced by wire cutting. The test span was 25mm. The loading speed was 0.1mm / min. The loading direction was perpendicular to the magnetic field orientation direction during molding. The test temperature was room temperature. The average value was obtained after 10 tests. The fracture toughness of the sintered NdFeB magnet materials prepared in Example 1, Example 2, Example 3, and Example 4 was measured to be 0.82 MPa·m 1 / 2 、0.87 MPa·m 1 / 2 , 0.92 MPa·m 1 / 2 、0.95 MPa·m 1 / 2 .

[0033] In addition, a sintered NdFeB magnet material without additive powder was prepared by the same process as in the example, and the bending strength and fracture toughness were obtained according to the above test method, which were 226.5 MPa and 0.76 MPa·m 1 / 2 It can be seen that the bending strength and fracture toughness of the sintered NdFeB magnet material are improved by the method of the present invention.

Claims

1. A method for preparing a sintered NdFeB magnet material with good mechanical properties, comprising the following preparation steps: S1, batching, smelting, and casting to obtain alloy sheets; S2, hydrogen crushing and air flow grinding to obtain alloy powder; S3, mixing the alloy powder and the additive powder uniformly to obtain a mixed powder; S4, orientation pressing and secondary pressing to obtain anisotropic magnets; S5, sintering and heat treatment to obtain the sintered NdFeB magnet; It is characterized in that The additive powder has a core-shell structure, the core layer is TiC, and the shell layer is Ti3SiC2.

2. The preparation method according to claim 1, characterized in that: The preparation method of the additive powder is as follows: using TiCl4 as a titanium source, CH3SiCl3 as a silicon source and a carbon source, using high-purity hydrogen as a reaction gas and a carrier gas, and using high-purity argon as a dilution gas, chemical vapor deposition is performed on the surface of SiC nanoparticles to form a Ti3SiC2 coating layer, thereby obtaining an additive powder with TiC as a core layer and Ti3SiC2 as a shell layer.

3. The preparation method according to claim 2, characterized in that: The deposition temperature is 1100°C, the deposition pressure is 5 kPa, the volume concentration of hydrogen is 50%, and the deposition time is 5-10 min.

4. The preparation method according to claim 1, characterized in that: The mass ratio of alloy powder to additive powder is 100:0.4-1.

5. The preparation method according to claim 1, characterized in that: The S1 casting adopts the rapid solidification casting process, and the solidification cooling rate is 10 4 -10 5 ℃ / s.

6. The preparation method according to claim 1, characterized in that: In S2, the particle size range of the alloy powder after hydrogen crushing is 50-200 μm, and the particle size range of the alloy powder after air flow milling is 3-5 μm.

7. The preparation method according to claim 1, characterized in that: The mixing method in S3 is to add the additive powder to ethanol in a glove box filled with nitrogen, ultrasonically disperse for 20-40 minutes, then add the alloy powder, ultrasonically disperse for 10-20 minutes, and then volatilize to remove the ethanol to obtain a mixed powder.

8. The preparation method according to claim 1, characterized in that: In S4, the magnetic field intensity of the orientation pressing is 2T; the pressure of the secondary pressing is 200-300MPa, and the holding time is 20-40s.

9. The preparation method according to claim 1, characterized in that: In S5, the sintering process is to first sinter at 1050-1060°C for 1-2h, and then sinter at 1060-1070°C for 3-5h; the heat treatment process is to first temper at 900-920°C for 2-4h, and then temper at 470-490°C for 4-5h.

10. The sintered NdFeB magnet material prepared by the preparation method according to any one of claims 1 to 9.