High-permeability nanocrystalline composite transformer iron core material and preparation method thereof

Abstract

The invention discloses a high-permeability nanocrystalline composite transformer iron core material and a preparation method thereof, and the iron core material comprises the following components by weight: 70-82 wt% of alloy powder with a particle size of 20-45 [mu] m; 8-18 wt% of an epoxy resin matrix; the thickness of the boron nitride nanosheet is smaller than 50 nm, and the diameter of the boron nitride nanosheet is 0.5-2 microns; 3-5wt% of a composite system of polytetrafluoroethylene micro powder and aluminum silicate fibers, wherein the weight ratio of the polytetrafluoroethylene micro powder to the aluminum silicate fibers is (0.8-1.2): 1; 2-5wt% of lithium iron phosphate nanoparticles, wherein the particle size of the lithium iron phosphate nanoparticles is 50-100nm; the boron nitride nanosheets, the polytetrafluoroethylene micro powder, the aluminum silicate fibers and the lithium iron phosphate nanoparticles form a multi-scale isolation structure. The preparation method of the nanocrystalline composite transformer iron core material with high magnetic conductivity is used for preparing the iron core material. Through the synergistic effect of the boron nitride nanosheets, the polytetrafluoroethylene micro-powder / aluminum silicate fiber composite system and the lithium iron phosphate nanoparticles, unification of high magnetic conductivity and low eddy-current loss of the nanocrystalline composite iron core material under high frequency is achieved.

Description

Technical Field

[0001] The invention relates to the field of soft magnetic materials, in particular to a high magnetic permeability nanocrystalline composite transformer core material and a preparation method thereof. Background Art

[0002] As the core component of energy transmission and conversion in power systems, the performance of transformer core directly affects the efficiency, loss and stability of the transformer. Since the beginning of the 20th century, transformer core materials have gone through a development process from silicon steel to amorphous alloys and then to nanocrystalline alloys.

[0003] Although the traditional silicon steel sheet core has mature technology, it will produce large iron loss when used in high-frequency applications; although amorphous alloys have advantages such as low coercivity and high resistivity, their saturation magnetic induction intensity is low, and they are brittle and difficult to process. In recent years, iron-based nanocrystalline alloys have become the focus of transformer core material preparation due to their excellent soft magnetic properties, such as high saturation magnetic induction intensity, high magnetic permeability, low coercivity and low loss.

[0004] However, nanocrystalline soft magnetic materials still face the problem of excessive eddy current loss in high-frequency applications, especially in the frequency range above 10kHz. Eddy current loss increases with the square of frequency, becoming the main factor restricting material performance. This problem mainly stems from the following aspects:

[0005] In the prior art, the thickness of nanocrystalline ribbons is generally 20-30 μm. Due to the skin effect, the current is mainly distributed on the surface of the material at high frequencies, resulting in a decrease in the effective cross-sectional area and an increase in losses. Although the resistivity of iron-based nanocrystalline alloys (about 100-120 μΩ·cm) is higher than that of pure iron (about 10 μΩ·cm), it is still not enough in high-frequency applications and cannot effectively suppress the formation of eddy currents; the magnetic domain structure of the material is unreasonable, and under high-frequency alternating magnetic fields, the losses caused by magnetic domain wall movement and magnetic domain rotation are large; Traditional nanocrystalline ribbons are stacked or wound into cores, with poor insulation between layers and air gaps, which increase magnetic resistance and losses.

[0006] At present, the common methods to reduce the high-frequency eddy current loss of nanocrystalline materials include: reducing the thickness of the strip, increasing the resistivity of the material (such as by adding elements such as Si and B), improving the heat treatment process to optimize the magnetic domain structure, and using baking technology to improve interlayer insulation. However, these methods have their own limitations: too thin strips will reduce mechanical strength and filling factor; too much addition of non-magnetic elements will reduce the saturation magnetic induction intensity; traditional heat treatment processes are difficult to accurately control the magnetic domain structure; and simply improving interlayer insulation cannot fundamentally solve the high-frequency loss problem of the material itself.

[0007] Therefore, developing a nanocrystalline composite transformer core material that can simultaneously maintain high saturation magnetic induction intensity and high magnetic permeability while effectively reducing high-frequency eddy current losses is of great significance to improving the efficiency and performance of high-frequency transformers. Summary of the invention

[0008] The purpose of the present invention is to provide a high magnetic permeability nanocrystalline composite transformer core material and a preparation method thereof, so as to solve the problem of excessive eddy current loss of existing nanocrystalline materials in high-frequency applications and achieve the unity of high magnetic permeability and low eddy current loss.

[0009] The above technical objectives of the present invention are achieved through the following technical solutions: A high magnetic permeability nanocrystalline composite transformer core material, the composite material comprising the following components in weight percentage: Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder: 70-82wt%, particle size 20-45μm; Epoxy resin matrix: 8-18wt%; Boron nitride nanosheets (h-BN): 0.5-2.0wt%, thickness less than 50nm, diameter 0.5-2μm; Composite system of polytetrafluoroethylene powder and aluminum silicate fiber: 3-5wt%, wherein the weight ratio of polytetrafluoroethylene powder to aluminum silicate fiber is 0.8-1.2:1; Lithium iron phosphate (LiFePO4) nanoparticles: 2-5wt%, particle size 50-100nm.

[0010] The present invention is further configured that the epoxy resin is bisphenol A epoxy resin E51, and the epoxy resin matrix further comprises the following components: The curing agent is methyltetrahydrophthalic anhydride (MTHPA), and the amount used is 3-5wt% of the weight of the epoxy resin; The accelerator is 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and the amount used is 0.5-1.0wt% of the weight of the epoxy resin; The coupling agent is γ-glycidyloxypropyltrimethoxysilane (KH560), and the amount used is 0.3-0.8wt% of the total weight; The dispersant is polyvinyl pyrrolidone (PVP, K30), and the amount used is 0.2-0.5wt% of the total weight.

[0011] The present invention also provides a method for preparing the above-mentioned high magnetic permeability nanocrystalline composite transformer core material, comprising the following steps: (1) 73.5 Si 13.5The B9Cu1Nb3 alloy strip was prepared into a powder of 20-45 μm by mechanical crushing and ball milling, and vacuum dried at 80°C for 4 hours; (2) γ-glycidyloxypropyltrimethoxysilane coupling agent and anhydrous ethanol were prepared into a solution in a weight ratio of 1:9, the powder was added to the solution, stirred at room temperature for 2 hours, and dried at 80°C for 6 hours; (3) boron nitride nanosheets, polytetrafluoroethylene powder, aluminum silicate fiber and lithium iron phosphate nanoparticles were mixed with a dispersant respectively, and ultrasonically dispersed for 30-60 minutes to form a uniform suspension; (4) epoxy resin was heated to 60°C, and the suspension in step (3) was added in sequence, and stirred for 30 minutes; (5) the surface treated Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder is stirred and mixed for 30 minutes; (6) a curing agent and an accelerator are added, and after stirring for 10 minutes, the mixture is evacuated to -0.095 MPa in a vacuum degassing box and degassed for 10 minutes; (7) the mixture is poured into a mold preheated to 80°C, and initially cured at 80°C for 2 hours and post-cured at 120°C for 4 hours; (8) the cured composite material is placed in a tubular furnace, and under nitrogen protection, the temperature is increased to 520-560°C at a rate of 3-5°C / min, and after keeping warm for 0.5-2 hours, the temperature is cooled to room temperature at a rate of 5°C / min.

[0012] The present invention is further configured such that the purity of the heat treatment nitrogen in step (8) is greater than 99.9% and the oxygen content is less than 10 ppm to prevent the iron-based nanocrystalline particles from being oxidized at high temperatures.

[0013] The present invention is further configured such that the heat treatment temperature in step (8) is 540° C. and the heat preservation time is 1 hour.

[0014] The present invention is further configured such that the heating rate in step (8) is 4° C. / min.

[0015] In summary, the present invention has the following beneficial effects: In the prior art, the addition of non-magnetic components will dilute the volume fraction of magnetic materials, which will theoretically reduce the saturation magnetic induction intensity and magnetic permeability of the composite material; the addition of conductive polymers or semiconductor materials will increase the conductivity of the material, which will theoretically increase eddy current losses. However, the combination in the present invention produces the opposite effect to the prior art, as follows:

[0016] h-BN nanosheets: non-magnetic materials, generally reduce the saturation magnetic induction intensity and magnetic permeability of composite materials, but its two-dimensional sheet structure is preferentially oriented in the epoxy matrix to form an ordered microstructure, which not only cuts off the eddy current path, but also improves the magnetic domain structure through the stress release mechanism, and improves the effective magnetic permeability of the material. The high thermal conductivity of h-BN also accelerates heat dissipation and reduces the degradation of magnetic properties caused by temperature rise.

[0017] PTFE / aluminum silicate fiber composite system: Generally, the magnetic filling rate is reduced, but the micro air gap network structure formed actually optimizes the magnetic flux path, reduces stray magnetic flux and eddy current loss. This air gap network also provides a stress buffer, alleviates the interface detachment problem caused by thermal expansion mismatch, and improves the mechanical stability and service life of the material.

[0018] LiFePO4 nanoparticles: As ionic conductors, they have poor electronic conductivity and generally reduce the overall performance of the material. However, in the present invention, the phosphide / oxide composite interface layer generated by the interface reaction between its structure and iron-based nanocrystals effectively regulates the motion energy of the magnetic domain wall through magnetic ion substitution and electronic transition mechanisms, significantly reduces the hysteresis loss at high frequencies, and improves the temperature stability of the material.

[0019] Moreover, there is a synergistic enhancement effect among the three components, as follows: Interfacial synergistic effect: A small amount of oxygen released by LiFePO4 during heat treatment combines with the B atoms at the edge of h-BN to form BO bonds, which enhances the bonding force between h-BN and the matrix; at the same time, the presence of h-BN promotes a more uniform interfacial reaction between LiFePO4 and iron-based nanocrystals.

[0020] Magnetic domain structure optimization synergy: h-BN nanosheets affect the magnetic domain arrangement through stress regulation; PTFE / aluminum silicate fiber network regulates the magnetic domain size through micro air gaps; LiFePO4 interface layer affects the magnetic domain wall energy through magnetic ion exchange. The three work together to form an optimized magnetic domain structure, which minimizes the motion loss of the magnetic domain wall under high-frequency alternating magnetic fields.

[0021] Resistivity gradient distribution synergy: The three materials form a resistivity gradient distribution from the core of the nanocrystalline particles to the matrix in the composite system. The gradient structure suppresses the formation of eddy currents more effectively than the uniform high-resistance structure while maintaining good magnetic properties.

[0022] In summary, the present invention achieves the unity of high magnetic permeability and low eddy current loss of nanocrystalline composite core materials at high frequencies through the synergistic effect of three components: boron nitride nanosheets, polytetrafluoroethylene powder / aluminum silicate fiber composite system and lithium iron phosphate nanoparticles, as follows: (1) The multi-scale spatial confinement effect and conductive path regulation are realized: the three components form a nano-micro-macro multi-scale structural control system in the material. Boron nitride nanosheets are arranged in a two-dimensional sheet structure perpendicular to the magnetic flux direction; polytetrafluoroethylene micropowder and aluminum silicate fiber are combined to form a micron-scale three-dimensional network; lithium iron phosphate nanoparticles are mainly distributed on the surface of iron-based nanocrystalline particles. This hierarchical isolation structure effectively cuts off the long-range conductive path in the material, making the resistivity of the composite material reach 800-1200μΩ·cm.

[0023] (2) A magnetic-electric-thermal multi-field coupling mechanism was established: the three components form a complementary synergistic effect in electromagnetic-thermal multi-field coupling. Boron nitride nanosheets have high thermal conductivity and can effectively conduct heat while blocking current; the micro-air gap network formed by the polytetrafluoroethylene / aluminum silicate fiber composite system increases resistance and provides thermal stress buffering; lithium iron phosphate nanoparticles increase electron scattering through the interface layer. This multi-field coupling mechanism enables the material to maintain stable magnetic properties when working at high frequencies, significantly reducing the temperature rise of the material.

[0024] (3) Interfacial chemical reactions and mutual catalysis are achieved: The three components undergo interfacial chemical interactions during high-temperature heat treatment. Lithium iron phosphate undergoes partial interfacial reactions with the surface of iron-based nanocrystalline particles to form (Fe, Li)3(PO4)2 and Fe2P phases, increasing the interfacial resistivity; boron nitride nanosheets form BOC bonds with the epoxy matrix, enhancing the bonding strength with the matrix; a hydrogen bond network is formed between lithium iron phosphate and boron nitride, strengthening the overall structure.

[0025] (4) Achieved disorder-to-order structural transformation: The three components induced a disorder-to-order structural transformation of iron-based nanocrystals during the heat treatment process, which promoted the ordered arrangement of Si atoms in the α-Fe(Si) phase. This atomic-scale ordered structure affected the magnetocrystalline anisotropy and magnetic permeability of the material, thereby improving the initial magnetic permeability of the material. DETAILED DESCRIPTION

[0026] A high magnetic permeability nanocrystalline composite transformer core material, the component ratio of which is: Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder (particle size: 25-35μm): 70-82wt%; Epoxy resin (bisphenol A type epoxy resin E51): 8-18wt%; Curing agent (methyltetrahydrophthalic anhydride MTHPA): 3-5wt% of the weight of epoxy resin; Accelerator (2,4,6-tris(dimethylaminomethyl)phenol (DMP-30): 0.5-1.0wt% of the weight of epoxy resin; Coupling agent (γ-glycidyloxypropyltrimethoxysilane (KH560): 0.3-0.8wt% of the weight of epoxy resin; Dispersant (polyvinyl pyrrolidone PVP, K30): 0.2-0.5wt% of the weight of epoxy resin; Boron nitride nanosheets (h-BN, thickness 30nm, diameter 1μm): 0.5-2.0wt%; Composite system of polytetrafluoroethylene micropowder and aluminum silicate fiber: 3-5wt%, wherein the weight ratio of polytetrafluoroethylene micropowder to aluminum silicate fiber is 0.8-1.2:1.

[0027] Lithium iron phosphate (LiFePO4) nanoparticles (particle size 80nm): 2-5wt%.

[0028] The preparation method is as follows: (1) Fe 73.5 Si 13.5 The B9Cu1Nb3 alloy strip was prepared into a powder of 20-45 μm by mechanical crushing and ball milling, and vacuum dried at 80°C for 4 hours; (2) γ-glycidyloxypropyltrimethoxysilane coupling agent and anhydrous ethanol were prepared into a solution in a weight ratio of 1:9, the powder was added to the solution, stirred at room temperature for 2 hours, and dried at 80°C for 6 hours; (3) boron nitride nanosheets, polytetrafluoroethylene powder, aluminum silicate fiber and lithium iron phosphate nanoparticles were mixed with a dispersant respectively, and ultrasonically dispersed for 30-60 minutes to form a uniform suspension; (4) epoxy resin was heated to 60°C, and the suspension in step (3) was added in sequence, and stirred for 30 minutes; (5) the surface treated Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder is stirred and mixed for 30 minutes; (6) a curing agent and an accelerator are added, and after stirring for 10 minutes, the mixture is evacuated to -0.095 MPa in a vacuum degassing box and degassed for 10 minutes; (7) the mixture is poured into a mold preheated to 80°C, and initially cured at 80°C for 2 hours and post-cured at 120°C for 4 hours; (8) the cured composite material is placed in a tubular furnace, and under the protection of 99.9% nitrogen, the temperature is increased to 520-560°C at a rate of 3-5°C / min, and after keeping warm for 0.5-2 hours, it is cooled to room temperature at a rate of 5°C / min.

[0029] In view of the above-mentioned core material and preparation method thereof, the present invention designs the following experiments to verify the above-mentioned technical effects: A total of 7 groups of formulas were designed for the experiment, including 5 experimental groups and 2 control groups. The formula design is shown in Table 1 below: Table 1: Experimental group and control group design table Note: The amount of curing agent and accelerator added is the percentage relative to the weight of epoxy resin.

[0030] Among them, control group 1: basic formula, only containing iron-based nanocrystalline powder and epoxy resin system.

[0031] Control group 2: Commercial Fe 73.5 Si 13.5 B9Cu1Nb3 nanocrystalline ribbon after standard heat treatment (550°C, 1 hour).

[0032] Experimental groups 1-3: Single components were added to evaluate the independent effects of each single component.

[0033] Experimental group 4: adding h-BN and PTFE / aluminum silicate fiber dual components, but without LiFePO4, is used to verify the synergistic effect of the two-dimensional barrier layer and the three-dimensional network structure.

[0034] Experimental Group 5: A complete formula containing three components to verify the complete multi-scale synergistic enhancement mechanism.

[0035] (1) DC magnetic performance test Test method: Vibrating sample magnetometer (VSM) Equipment: LakeShore8600VSM system Test conditions: Room temperature, maximum external field strength ±20kOe, test results are shown in Table 2: Table 2: Magnetic properties test table (2) AC magnetic loss test Test method: AC magnetic loss test system Equipment: IWATSUSY-8232B-H analyzer Test conditions: ring sample, primary coil 100 turns, secondary coil 50 turns, temperature 25℃, the test results are shown in Table 3 below, Table 3: Magnetic loss test table (3) Frequency characteristics test Test method: Impedance analyzer Equipment: AgilentE4 99 1A impedance analyzer test conditions: frequency range 1kHz-1MHz, excitation voltage 0.5V, temperature 25℃, test results are shown in Table 4: Table 4: Frequency characteristics test table (4) Resistivity and skin depth test Test method: four-probe method and impedance analysis method Equipment: RTS-9 room temperature four-probe tester, Agilent E4 991A impedance analyzer test conditions: room temperature, four-probe spacing 1mm, test current 10mA, test results are shown in Table 5: Table 5: Point coarse filtration and skin depth test table (5) Verification of synergistic effects ① Thermal behavior analysis Test method: Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) Equipment: NETZSCHSTA449F3Jupiter thermal analyzer Test conditions: temperature range 25-600℃, heating rate 10℃ / min, N2 atmosphere, test results are shown in Table 6: Table 6: Thermal analysis results test table ②High temperature and long-term performance stability test Test method: High temperature magnetic property retention test equipment: Customized high temperature magnetic property test system Test conditions: 100kHz, 0.05T, temperature 150℃, duration 24 hours, test results are shown in Table 7: Table 7: High temperature and long time performance stability test table ③The influence of heat treatment temperature change on synergistic effect Test method: The performance of the samples in the experimental group 5 at different heat treatment temperatures was compared. Parameter changes: heat treatment at 520℃, 540℃ and 560℃, holding time 1 hour, and the test results are shown in Table 8: Table 8: Performance test table at different heat treatment temperatures ④The influence of heat treatment time on synergistic effect Test method: The performance of the samples in the experimental group 5 at different heat treatment times was compared. Parameter changes: 0.5 hours, 1 hour and 2 hours at 540°C. The test results are shown in Table 9: Table 9: Performance test table under different heat treatment time ⑤The effect of heating rate change on synergistic effect Test method: The performance of the samples in the experimental group 5 at different heating rates was compared. Parameter changes: 2℃ / min, 4℃ / min and 6℃ / min were heated to 540℃ and kept warm for 1 hour. The test results are shown in Table 10: Table 10: Performance test table at different heating rates Based on the above experimental data, the following conclusions can be drawn: 1. Multi-scale spatial confinement effect: Judging from the resistivity data, the resistivity of experimental group 5 (three-component complete formula) reached 950μΩ·cm, which is much higher than that of the single-component experimental group (380-450μΩ·cm) and the two-component experimental group 4 (680μΩ·cm), indicating that the three components formed an efficient multi-scale isolation structure.

[0036] The skin depth test results show that the skin depth of experimental group 5 (255μm) is more than 2.5 times that of control group 1 (100μm), proving that the multi-scale spatial confinement effect effectively improves the high-frequency electromagnetic performance.

[0037] Thermal behavior analysis shows that the thermal conductivity of experimental group 5 (3.5W / m·K) is significantly higher than that of the basic formula (0.8W / m·K), and far exceeds the single-component formula (1.0-2.3W / m·K), verifying the synergistic enhancement of multi-components in thermal conduction.

[0038] The high-temperature and long-term performance stability test showed that the iron loss increase rate of experimental group 5 was only 7.0%, while that of control group 1 was as high as 28.9%, proving that the synergistic effect of multiple components significantly improved the thermal stability of the material.

[0039] The temperature rise test results show that the temperature rise of experimental group 5 after working at 100kHz for 8 hours is only 35℃, which is much lower than control group 1 (85℃) and the single group group (62-70℃), confirming the effectiveness of the multi-field coupling mechanism.

[0040] 2. Influence of process parameters on synergistic effect The results of the process parameter comparison experiment show that: The heat treatment temperature has a significant influence on the synergistic effect. 540℃ is the optimal heat treatment temperature. At this temperature, the thickness of the interface layer is moderate (15nm), the h-BN orientation degree is the highest (85%), and the best comprehensive performance is exhibited.

[0041] The best performance is achieved when the heat treatment time is 1 hour. If the time is too short (0.5 hours), the interface reaction is not sufficient. If the time is too long (2 hours), the interface layer is too thick, which affects the magnetic properties.

[0042] A heating rate of 4°C / min is most conducive to forming a complete PTFE / fiber network structure while ensuring that the nanocrystal particle size is small and uniform.

[0043] This experimental design systematically verifies the synergistic effect of three components: h-BN nanosheets, PTFE / aluminum silicate fiber composite system, and LiFePO4 nanoparticles in nanocrystalline composite transformer core materials. The experimental results show that these three substances synergistically achieve the unity of high magnetic permeability and low eddy current loss of nanocrystalline composite materials in high-frequency applications.

[0044] Especially under the high frequency condition of 100kHz, the iron loss of experimental group 5 is only 185W / kg, which is more than 60% lower than that of the control group, while maintaining a high initial magnetic permeability of 10500, which is about 1.4 times that of control group 1. The three components work synergistically, proving the core technical solution of the present invention.

[0045] In addition, process parameter experiments show that the synergistic effect of components can be further enhanced by optimizing heat treatment temperature, time and heating rate, providing a corresponding reference for subsequent industrialization.

[0046] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A high magnetic permeability nanocrystalline composite transformer core material, characterized in that: The composite material comprises the following components in weight percentage: Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder: 70-82wt%, particle size 20-45μm; Epoxy resin matrix: 8-18wt%; Boron nitride nanosheets: 0.5-2.0wt%, thickness less than 50nm, diameter 0.5-2μm; Composite system of polytetrafluoroethylene powder and aluminum silicate fiber: 3-5wt%, wherein the weight ratio of polytetrafluoroethylene powder to aluminum silicate fiber is 0.8-1.2:1; Lithium iron phosphate nanoparticles: 2-5wt%, particle size 50-100nm; The composite system of boron nitride nanosheets, polytetrafluoroethylene micropowder and aluminum silicate fiber and lithium iron phosphate nanoparticles together form a multi-scale isolation structure, which not only cuts off the long-range conductive path in the material and reduces the eddy current loss under high frequency, but also maintains the continuity of the magnetic flux path.

2. The high magnetic permeability nanocrystalline composite transformer core material according to claim 1, characterized in that: The epoxy resin matrix also includes the following components: Curing agent, methyltetrahydrophthalic anhydride, used in an amount of 3-5wt% of the weight of the epoxy resin; The accelerator is 2,4,6-tris(dimethylaminomethyl)phenol, and the amount used is 0.5-1.0wt% of the weight of the epoxy resin; The coupling agent is γ-glycidyloxypropyltrimethoxysilane, and the amount used is 0.3-0.8wt% of the total weight; The dispersant is polyvinyl pyrrolidone, and the amount used is 0.2-0.5wt% of the total weight.

3. A method for preparing a high magnetic permeability nanocrystalline composite transformer core material as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Fe 73.5 Si 13.5 The B9Cu1Nb3 alloy strip was prepared into 20-45 μm powder by mechanical crushing and ball milling, and vacuum dried at 80 °C for 4 hours; (2) preparing a solution of γ-glycidyloxypropyltrimethoxysilane coupling agent and anhydrous ethanol in a weight ratio of 1:9, adding the powder to the solution, stirring at room temperature for 2 hours, and drying at 80° C. for 6 hours; (3) mixing boron nitride nanosheets, polytetrafluoroethylene powder, aluminum silicate fibers and lithium iron phosphate nanoparticles with a dispersant respectively, and performing ultrasonic dispersion for 30-60 minutes to form a uniform suspension; (4) Heat the epoxy resin to 60° C., add the suspension in step (3) in sequence, and stir and mix for 30 minutes; (5) Adding surface treated Fe 73.5 Si 13.5 B9Cu1Nb3 alloy powder, stirred and mixed for 30 minutes; (6) Add curing agent and accelerator, stir for 10 minutes, evacuate to -0.095 MPa in a vacuum degassing box, and degas for 10 minutes; (7) pouring the mixture into a mold preheated to 80°C, preliminarily curing at 80°C for 2 hours, and post-curing at 120°C for 4 hours; (8) The cured composite material is placed in a tubular furnace, and under nitrogen protection, the temperature is raised to 520-560°C at a rate of 3-5°C / min, and after being kept at this temperature for 0.5-2 hours, the composite material is cooled to room temperature at a rate of 5°C / min.

4. The preparation method according to claim 3, characterized in that: The nitrogen purity in step (8) is greater than 99.9%, and the oxygen content is less than 10 ppm.

5. The preparation method according to claim 3, characterized in that: The heat treatment temperature in step (8) is 540°C and the holding time is 1 hour.

6. The preparation method according to claim 3, characterized in that: The heating rate in step (8) is 4°C / min.

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