Preparation method of low-cost high-performance nanocrystalline composite material

Abstract

The invention provides a preparation method of a nanocrystalline composite material with low cost and high performance. Iron-based nanocrystalline powder, FeNi powder and FeSiAl powder are mixed, pressing and heat treatment are carried out after resin insulation coating are carried out, the nanocrystalline composite material is obtained, in the process, through quality control over all the powder, resin insulation coating is carried out after inorganic coating is carried out on the powder, and cooperative control over two-step pressing and two-step heat treatment is carried out, so that the composite material is obtained. The nanocrystalline composite material which is low in cost, high in frequency, low in loss, high in magnetic conductivity and high in direct current bias is prepared, and the nanocrystalline composite material is suitable for high-frequency power electronic equipment in the fields of 5G communication, new energy automobiles, aerospace and the like.

Description

Technical Field

[0001] This invention relates to the field of soft magnetic materials technology, and specifically to a method for preparing a low-cost, high-performance nanocrystalline composite material. Background Technology

[0002] To promote the development of power equipment and magnetic devices towards higher frequencies and higher power, the development of soft magnetic materials with high frequency, low loss, high permeability and high DC bias performance is one of the key issues that those skilled in the art are working on. In addition, considering the feasibility of large-scale application, reducing costs is another key issue that urgently needs to be addressed.

[0003] For example, soft magnetic powder cores, as important magnetic core components for manufacturing inductors, are widely used in photovoltaic energy storage, new energy vehicles, communications and other fields. In recent years, with the continuous development of technology, soft magnetic powder cores are usually made by combining metal magnetic powder particles with insulating media and preparing them through powder metallurgy. This results in low-cost soft magnetic powder cores that also have high frequency, low loss, high permeability and high DC bias performance, which is an important foundation for the widespread application of high-frequency and high-power inductors.

[0004] Among many soft magnetic materials, nanocrystals are ideal materials for high-frequency electronic devices due to their excellent soft magnetic properties such as high saturation magnetic induction, low coercivity and high permeability; FeNi has great application potential due to its high saturation magnetic flux density and excellent DC bias performance; FeSiAl soft magnetic materials are favored because of their comprehensive advantages such as zero magnetostriction coefficient, low coercivity, low loss, high resistance and low cost.

[0005] However, existing soft magnetic materials still have some shortcomings in performance, making it difficult to meet the growing demand for high performance. For example, nanocrystalline magnetic powder is brittle, difficult to process, and suffers from significant eddy current losses at high frequencies; FeNi magnetic powder is expensive, limiting its large-scale application; FeSiAl magnetic powder has low saturation magnetic induction (generally less than or equal to 1.6T), poor DC bias performance, and is prone to saturation under light load conditions, failing to meet the requirements for high power density. Summary of the Invention

[0006] In view of the above-mentioned technological status, the present invention aims to provide a method for preparing a low-cost, high-performance nanocrystalline composite material. The nanocrystalline composite material prepared by this method is low in cost and has the characteristics of high frequency, low loss, high magnetic permeability, and high DC bias performance.

[0007] Therefore, the method for preparing the nanocrystalline composite material adopted by the inventors includes the following steps: (1) Iron-based nanocrystalline powder, FeNi powder and FeSiAl powder are mixed to obtain a mixed powder; (2) The mixed powder is added to a solution containing resin binder, lubricant and organic solvent, stirred thoroughly, dried and granulated to obtain a mixed powder with resin insulation coating; (3) Press the resin-insulated mixed powder to obtain a green magnet; (4) The green magnet is heat-treated to obtain a nanocrystalline composite material; In this preparation method, the inventors discovered that by performing the following controls (i) to (iii), a low-cost nanocrystalline composite material that also possesses high frequency, low loss, high permeability, and high DC bias performance can be obtained: (i) In step (1), the iron-based nanocrystalline powder is coated with a SiO2 insulating layer, the FeNi powder is coated with a SiO2 insulating layer, and the FeSiAl powder is coated with an Al2O3 insulating layer. Iron-based nanocrystalline powder coated with a SiO2 insulating layer, FeNi powder coated with a SiO2 insulating layer, and FeSiAl powder coated with an Al2O3 insulating layer are mixed to obtain the mixed powder. According to the mass percentage, the iron-based nanocrystalline powder coated with a SiO2 insulating layer accounts for 50%-60%, the FeNi powder coated with SiO2 accounts for 20%-30%, and the balance is FeSiAl powder coated with an Al2O3 insulating layer. (ii) In step (3), the pressing is divided into two steps. The first step is to hold the pressure for 60s-180s under a pressure of 180MPa-220MPa, and the second step is to hold the pressure for 60s-180s under a pressure of 800MPa-1800MPa. (iii) In step (4), the heat treatment is divided into two steps. The first step is low temperature pretreatment, that is, heating to 180℃-210℃ and holding for 30min-60min. The second step is high temperature annealing, that is, heating to 600℃-660℃ and holding for 60min-120min.

[0008] Through the control measures described in (i) to (iii) above, the obtained nanocrystalline composite material has low cost and can effectively improve the overall performance of the nanocrystalline composite material, resulting in a soft magnetic composite material with high frequency, low loss, high permeability, and high DC bias performance.

[0009] The main component of the iron-based nanocrystalline powder is Fe, and it also includes one or more of Si, Nb, Cu, B, Ni, etc. As one implementation, the elements and their mass percentages in the iron-based nanocrystalline powder are as follows: Fe: 50%-75%; Si: 20%-25%; Nb: 1%-5%; Cu: 0.5%-2%; B: 0-30%.

[0010] In one implementation, the FeNi powder contains the following elements and their mass percentages: 45%-55% Ni, 0%-5% unavoidable impurity elements, and the remainder Fe.

[0011] In one implementation, the elements and their mass percentages in the FeSiAl powder are: 8%-10% Si, 5%-6% Al, 0%-1% unavoidable impurity elements, and the remainder is Fe.

[0012] Preferably, the median particle size of the iron-based nanocrystalline powder is... D 50 The range is 10μm-20μm.

[0013] Preferably, the median particle size of the FeNi powder is... D 50 The range is 1μm-5μm.

[0014] Preferably, the median particle size of the FeSiAl powder is... D 50 The range is 30μm-40μm.

[0015] The method for coating the iron-based nanocrystalline powder with a SiO2 insulating layer is not limited. For example, the sol-gel method can be used to coat the iron-based nanocrystalline powder with a SiO2 insulating layer.

[0016] The method for coating the FeNi powder surface with a SiO2 insulating layer is not limited. For example, the sol-gel method can be used to coat the FeNi powder surface with a SiO2 insulating layer.

[0017] The method for coating the FeSiAl powder surface with an Al2O3 insulating layer is not limited. For example, hydrolysis and heat treatment can be used to coat the FeSiAl powder surface with an Al2O3 insulating layer.

[0018] When coating the surface of the iron-based nanocrystalline powder with a SiO2 insulating layer using the sol-gel method, the following steps are preferred: The surfactant is ultrasonically dispersed in anhydrous ethanol to obtain a dispersion, and then the iron-based nanocrystalline powder is added to obtain surface-activated iron-based nanocrystalline powder. The surface-activated iron-based nanocrystalline powder is dispersed in a sol formed by mixing a silicon source with ethanol, water, and a catalyst. The sol is coated on the surface of the surface-activated iron-based nanocrystalline powder by hydrolysis and condensation to form a wet gel layer. Then, the gel is dried to transform it into a dense SiO2 layer, resulting in iron-based nanocrystalline powder coated with a SiO2 insulating layer. As a further preferred embodiment, the mass ratio of the surface-activated iron-based nanocrystalline powder to the silicon source is controlled to be 100:(3-7).

[0019] When coating the FeNi powder surface with a SiO2 insulating layer using the sol-gel method, the following steps are preferred: The surfactant was ultrasonically dispersed in anhydrous ethanol to obtain a dispersion, and then the FeNi powder was added to obtain surface-activated FeNi powder. The surface-activated FeNi powder was dispersed in a sol formed by mixing a silicon source with ethanol, water, and a catalyst. The sol was coated onto the surface of the surface-activated FeNi powder by hydrolysis and condensation to form a wet gel layer. Then, the gel was dried to transform it into a dense SiO2 layer, resulting in FeNi powder coated with a SiO2 insulating layer. As a further preferred embodiment, the mass ratio of surface-activated iron-based nanocrystalline powder to silicon source was controlled to be 100:(3-7).

[0020] When coating the FeSiAl powder surface with an Al2O3 insulating layer using hydrolysis and heat treatment, the preferred method includes the following steps: The FeSiAl powder is dispersed in a mixed system consisting of aluminum nitrate solution, pH adjuster, and dispersant. A controlled hydrolysis reaction is performed to generate an Al(OH)3·nH2O wet gel layer on the surface of the FeSiAl powder in situ. The gel layer is then dried and followed by heat treatment under an inert atmosphere to transform it into a dense Al2O3 layer, resulting in FeSiAl powder coated with an Al2O3 insulating layer. Preferably, the mass ratio of FeSiAl powder to aluminum nitrate is controlled to be 100:(8-12).

[0021] When the iron-based nanocrystalline powder is coated with a SiO2 insulating layer, the silicon source includes, but is not limited to, at least one of tetraethyl orthosilicate (TEOS), sodium silicate, silica sol, and methyltrimethoxysilane.

[0022] When the iron-based nanocrystalline powder is coated with a SiO2 insulating layer, the catalyst includes, but is not limited to, at least one of hydrochloric acid, ammonia, acetic acid, and cation exchange resin.

[0023] When the FeNi powder is coated with a SiO2 insulating layer, the silicon source includes, but is not limited to, at least one of tetraethyl orthosilicate, sodium silicate, silica sol, and methyltrimethoxysilane.

[0024] When the FeNi powder is coated with a SiO2 insulating layer, the catalyst includes, but is not limited to, at least one of hydrochloric acid, ammonia, acetic acid, and cation exchange resin.

[0025] When the FeSiAl powder is coated with an Al2O3 insulating layer, the pH adjuster includes, but is not limited to, at least one of sodium acetate, acetic acid, sodium carbonate, and ammonia.

[0026] When the FeSiAl powder is coated with an Al2O3 insulating layer, the dispersant includes, but is not limited to, at least one of sodium dodecyl sulfonate (SDS), sodium dodecyl sulfate, and polyvinylpyrrolidone.

[0027] When the FeSiAl powder is coated with an Al2O3 insulating layer, the heat treatment temperature is preferably 700℃-900℃.

[0028] In step (2), the resin adhesive includes, but is not limited to, at least one of epoxy resin, silicone resin, polyimide resin, and phenolic resin.

[0029] In step (2), the lubricant includes, but is not limited to, at least one of zinc stearate, aluminum stearate, and barium stearate.

[0030] In step (2), the organic solvent includes, but is not limited to, at least one of acetone and anhydrous ethanol.

[0031] Preferably, in step (2), the solution contains 1%-2% resin binder and 0.5%-1% lubricant by mass percentage.

[0032] Preferably, in step (4), the vacuum level of the heat treatment process is controlled at 10. -1 Pa-10 0 Pa.

[0033] Preferably, in step (4), during the low-temperature pretreatment, the temperature is increased at a rate of 3℃ / min-5℃ / min.

[0034] Preferably, in step (4), the temperature is increased at a rate of 10℃ / min-12℃ / min during high-temperature annealing.

[0035] As a preferred implementation, the method for coating the iron-based nanocrystalline powder with a SiO2 insulating layer is as follows: 1-3 parts by mass of the surfactant polyvinylpyrrolidone (PVP) are ultrasonically dispersed in anhydrous ethanol to obtain a PVP dispersion. Then, 100 parts by mass of iron-based nanocrystalline powder are added, and the mixture is stirred evenly under a water bath at 40℃-60℃ to obtain a surface-activated iron-based nanocrystalline powder dispersion. A catalyst is added to a silicon source and anhydrous ethanol to adjust the pH, and the mixture is stirred evenly to obtain a silicon source solution. The silicon source solution is slowly added to the surface-activated iron-based nanocrystalline powder dispersion, controlling the mass ratio of iron-based nanocrystalline powder to silicon source to be 100:(3-7). The mixture is stirred to obtain a SiO2-coated iron-based nanocrystalline powder precursor. Subsequently, the mixture is washed several times with anhydrous ethanol and deionized water until the pH of the supernatant is close to neutral, and then vacuum dried to obtain the SiO2-coated iron-based nanocrystalline powder.

[0036] As a preferred embodiment, the method for coating the FeNi powder surface with a SiO2 insulating layer is as follows: 1-3 parts by mass of the surfactant polyvinylpyrrolidone (PVP) were ultrasonically dispersed in anhydrous ethanol to obtain a PVP dispersion. Then, 100 parts by mass of FeNi powder were added, and the mixture was stirred evenly in a water bath at 40℃-60℃ to obtain a surface-activated FeNi powder dispersion. The catalyst was added to a silicon source and anhydrous ethanol to adjust the pH, and the mixture was stirred evenly to obtain a silicon source solution. The silicon source solution was slowly added to the surface-activated FeNi powder dispersion, and the mass ratio of FeNi powder to silicon source was controlled at 100:(3-7). The mixture was stirred to obtain a SiO2-coated FeNi powder precursor. The precursor was then washed several times with anhydrous ethanol and deionized water until the pH of the supernatant was close to neutral, and then vacuum dried to obtain SiO2-coated FeNi powder.

[0037] As a preferred embodiment, the method for preparing the FeSiAl powder coated with the Al2O3 insulating layer includes the following steps: Aluminum nitrate (Al(NO3)3·9H2O) was dispersed in deionized water to obtain an aluminum nitrate solution. Sodium acetate solution was added to adjust the pH to 4-6, and sodium dodecyl sulfonate solution containing 1-3 parts by mass was added to improve particle dispersibility, resulting in a mixed solution. 100 parts by mass of FeSiAl powder was added to the mixed solution and stirred evenly under a water bath at 40℃-60℃. The mixture was then washed several times with anhydrous ethanol and deionized water until the pH of the supernatant was close to neutral. The supernatant was then vacuum dried to obtain a dry Al(OH)3-coated FeSiAl powder precursor. This precursor was placed in a tube furnace and heated under inert gas conditions for heat treatment. After cooling to room temperature, Al2O3-coated FeSiAl powder was obtained.

[0038] Compared with the prior art, the present invention mixes iron-based nanocrystalline powder with FeNi powder and FeSiAl powder, and reduces costs through multi-dimensional synergistic control of the following (1) to (4), and regulates the soft magnetic properties of the nanocrystalline composite material, improves the effective permeability of the nanocrystalline composite material, reduces losses, and maintains excellent DC bias characteristics.

[0039] (1) The present invention controls the mass ratio of three metal powders. This invention uses iron-based nanocrystalline powder as the main component. Since FeNi powder is expensive, FeSiAl powder is cheaper. Therefore, this invention controls the mass of iron-based nanocrystalline powder to account for 50%-60% of the mass of the mixed powder, controls the mass of FeNi powder to account for 20%-30% of the mass of the mixed powder, and the remainder is FeSiAl powder.

[0040] (2) In this invention, each powder is inorganically coated and then mixed, and then the mixed powder is organically coated with resin to form an inorganic-organic double-layer coating. The SiO2 inorganic layer and the resin organic layer have high resistivity, and SiO2 is chemically very stable. Furthermore, the double-layer coating significantly improves the particle coating efficiency. The Al2O3 inorganic layer and the resin organic layer also have high resistivity, and Al2O3 has high thermal conductivity. While ensuring good electrical insulation, they significantly improve the thermal conductivity and heat dissipation capacity of the composite material. Therefore, the "inorganic-organic" composite insulation structure improves the magnetic properties of the material, making it suitable for high-frequency, high-power applications.

[0041] (3) The present invention obtains a green magnet by two-step pressing of double-coated mixed powder. The inventors have discovered that when a double-coated mixed powder is pressed once to obtain a green magnet, the density of the green magnet is relatively low, and there may be tiny voids inside. The friction between particles and the internal stress are relatively large, which are difficult to eliminate during heat treatment, resulting in a decrease in magnetic permeability under a DC magnetic field and a rapid decline. The present invention uses a two-pressing process to effectively release the internal stress during the molding process, thereby improving the magnetic permeability, DC bias characteristics, and reducing magnetic loss.

[0042] (4) The present invention performs two-step heat treatment on the green magnet and controls the temperature of the low-temperature stage and the high-temperature stage. The inventors have discovered that using a single annealing process during heat treatment leads to a deterioration in overall magnetic properties. This is due to the rapid decomposition of the binder and uneven stress relief, resulting in an increase in internal defects. Therefore, this invention employs a two-step temperature control process: low-temperature pretreatment and high-temperature annealing. This promotes the formation of a uniform equiaxed crystal structure within the powder particles, optimizes the crystal structure, enhances the magnetic properties of the material, and increases the saturation magnetization.

[0043] Furthermore, the inventors discovered that when the temperature of the low-temperature pretreatment stage is below 200°C, the overall magnetic permeability decreases. This is because the remaining binder is a non-magnetic material, which is equivalent to introducing more "air gaps" into the magnetic circuit, leading to a deterioration in magnetic properties. When the temperature of the high-temperature annealing stage is above 660°C, the overall magnetic properties deteriorate. This is due to overheating, excessive grain growth, and the formation of harmful phases, which damage the insulation between particles. Therefore, this invention controls the temperature of the low-temperature pretreatment stage at 180°C-210°C and the temperature of the high-temperature annealing stage at 600°C-660°C.

[0044] Through the multi-dimensional synergistic control described in (1) to (4) above, this invention produces a low-cost soft magnetic composite material that also features high frequency, low loss, high permeability, and high DC bias performance. This material is beneficial for large-scale industrial production. The permeability at 1MHz is greater than or equal to 45%, the DC bias performance at a bias field of 100Oe is greater than or equal to 45%, and the power loss at 50mT and 1MHz is less than or equal to 3500mW / cm². 3 .

[0045] As a superior technical solution, the present invention also employs the following control (5).

[0046] (5) The present invention controls the material content of three metal powders during inorganic coating. When using the sol-gel method to coat the surface of the iron-based nanocrystalline powder with a SiO2 insulating layer, the inventors discovered that the content of the silicon source affects the magnetic properties. When the content of the silicon source is too high or too low, the magnetic permeability is significantly reduced, the DC bias characteristics deteriorate, and the loss is greatly increased. Therefore, the present invention controls the mass of the silicon source corresponding to 100 parts by mass of iron-based nanocrystalline powder to be in the range of 3 parts by mass to 7 parts by mass (inclusive of 3 parts by mass and 7 parts by mass).

[0047] When using the sol-gel method to coat the FeNi powder with a SiO2 insulating layer, the inventors discovered that the content of the silicon source affects the magnetic properties. When the content of the silicon source is too high or too low, the magnetic permeability is significantly reduced, the DC bias characteristics deteriorate, and the loss is greatly increased. Therefore, the present invention controls the mass of the silicon source corresponding to 100 parts by mass of FeNi powder to be in the range of 3 parts by mass to 7 parts by mass (inclusive of 3 parts by mass and 7 parts by mass).

[0048] When using hydrolysis and heat treatment to coat the FeSiAl powder with an Al2O3 insulating layer, the inventors discovered that the content of aluminum nitrate also affects the magnetic properties. When the content of aluminum nitrate is too high or too low, the magnetic permeability is significantly reduced, the DC bias characteristics deteriorate, and the loss is greatly increased. Therefore, the present invention controls the mass of aluminum nitrate corresponding to 100 parts by mass of FeSiAl powder to be in the range of 8 parts by mass to 12 parts by mass (including 8 parts by mass and 12 parts by mass).

[0049] Through the multi-dimensional coordinated control described in (1) to (5) above, the present invention achieves a permeability greater than or equal to 60 at 1MHz, a DC bias performance greater than or equal to 60% at a bias field of 100Oe, and a power loss less than or equal to 1500mW / cm at 50mT and 1MHz. 3 This excellent soft magnetic property was unexpected by those skilled in the art. It can meet the requirements for the use of metal soft magnetic powder cores in inductors, and is especially suitable for high-frequency power electronic equipment in fields such as 5G communication, new energy vehicles, and aerospace. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention are still within the protection scope of the present invention.

[0051] In this invention, the terms "including" and "comprising" should be interpreted as including rather than exclusive or exhaustive; that is, they mean "including but not limited to". Example 1:

[0052] The preparation method of low-cost, high-performance nanocrystalline composite materials includes the following steps: S1, Surface coating: ... D 50 Iron-based nanocrystalline FeSiBNbCu powder with a diameter of 15μm D 50 FeNi powder with a diameter of 5μm D 50 FeSiAl powder with a thickness of 35μm was subjected to insulating coating, as detailed below.

[0053] S1.1, Insulation coating with iron-based nanocrystalline powder Two parts by mass of the surfactant polyvinylpyrrolidone (PVP) were ultrasonically dispersed in anhydrous ethanol to obtain a PVP dispersion. Then, 100 parts by mass of iron-based nanocrystalline powder were added and stirred evenly under a water bath at 40℃-60℃ to obtain a surface-activated iron-based nanocrystalline powder dispersion for later use. Ammonia solution was added to a solution containing 5 parts by mass of tetraethyl orthosilicate and 100 parts by mass of anhydrous ethanol to adjust the pH to 10, and stirred until homogeneous to obtain a silicon source solution. The silicon source solution was slowly added to the dispersion of surface-activated iron-based nanocrystalline powder, and the mixture was stirred for 2-4 hours to obtain SiO2-coated nanocrystalline powder precursor. The precursor was then washed several times with anhydrous ethanol and deionized water until the pH of the supernatant was close to neutral. After vacuum drying, SiO2-coated iron-based nanocrystalline powder was obtained.

[0054] S1.2 and FeNi powders are used for insulating coating. Two parts by mass of the surfactant polyvinylpyrrolidone (PVP) were ultrasonically dispersed in anhydrous ethanol to obtain a PVP dispersion. Then, 100 parts by mass of FeNi powder were added and stirred evenly under a water bath at 40℃-60℃ to obtain a surface-activated FeNi powder dispersion for later use. Ammonia solution was added to a solution containing 5 parts by mass of tetraethyl orthosilicate and 100 parts by mass of anhydrous ethanol to adjust the pH to 10, and stirred until homogeneous to obtain a silicon source solution. The silicon source solution was slowly added to the surface-activated FeNi powder dispersion and stirred for 2-4 hours to obtain the SiO2-coated FeNi powder precursor. Then, it was washed several times with anhydrous ethanol and deionized water until the pH of the supernatant was close to neutral. After vacuum drying, the SiO2-coated FeNi powder was obtained.

[0055] Insulating coating with S1.3 and FeSiAl powders 10 parts by mass of aluminum nitrate (Al(NO3)3·9H2O) were dispersed in deionized water to obtain an aluminum nitrate solution. Sodium acetate solution was added to adjust the pH to 4-6, and then sodium dodecyl sulfonate solution containing 2 parts by mass was added to improve particle dispersibility, resulting in a mixed solution. 100 parts by mass of FeSiAl powder were added to the mixed solution and stirred evenly under a water bath at 40℃-60℃. The solution was then washed several times with anhydrous ethanol and deionized water until the pH of the supernatant was close to neutral. After vacuum drying, a dry Al(OH)3-coated FeSiAl powder precursor was obtained. The powder precursor was placed in a tube furnace and heated to a high temperature under Ar environment at a heating rate of 5℃ / min. After cooling to room temperature, Al2O3-coated FeSiAl powder was obtained.

[0056] S2, Powder Mixing The iron-based nanocrystalline powder coated with SiO2, the FeNi powder coated with SiO2, and the FeSiAl powder coated with Al2O3 were mixed to obtain a mixed powder. By mass percentage, the iron-based nanocrystalline powder coated with SiO2 accounted for 50% of the mixed powder, the FeNi powder coated with SiO2 accounted for 20% of the mixed powder, and the FeSiAl powder coated with Al2O3 accounted for 30% of the mixed powder.

[0057] S3, Compression Molding The mixed powder was added to an organic solution, stirred thoroughly, dried, and granulated to obtain magnetic powder. The organic solution contained 2% resin binder and 1% zinc stearate lubricant by weight percentage, with the remainder being acetone. The magnetic powder is then subjected to a two-step pressing process: a pre-pressing step and a secondary pressing step, to obtain a green magnetic ring. The pre-pressing pressure is 200 MPa, and the holding time is 60 s; the secondary pressing pressure is 1200 MPa, and the holding time is 60 s.

[0058] S4, Annealing treatment The green magnetic ring was placed in a quartz tube and subjected to vacuum annealing. The annealing process consisted of two steps. The first step was a low-temperature pretreatment stage, in which the temperature was increased to 200°C at a heating rate of 5°C / min and held for 30 min. The second step was a high-temperature annealing stage, in which the temperature was increased to 600°C at a heating rate of 10°C / min and held for 60 min. Finally, the ring was cooled to room temperature in the furnace and removed to obtain the nanocrystalline composite material. Example 2:

[0059] This embodiment is basically the same as Embodiment 1, except that: [selection / selection] D 50 Iron-based nanocrystalline powder with a diameter of 20 μm was used instead D 50 Iron-based nanocrystalline powder with a diameter of 15 μm. Example 3:

[0060] This embodiment is basically the same as Embodiment 1, except that: [selection / selection] D 50 FeSiAl powder with a diameter of 40 μm was used instead D 50 FeSiAl powder with a diameter of 35 μm. Example 4:

[0061] This embodiment is basically the same as Embodiment 1, except that: by mass percentage, the iron-based nanocrystalline powder coated with SiO2 accounts for 60% of the mixed powder, the FeNi powder coated with SiO2 accounts for 20% of the mixed powder, and the FeSiAl powder coated with Al2O3 accounts for 20% of the mixed powder. Comparative Example 1:

[0062] This comparative example is basically the same as Example 1, except that in step S1, only... D 50 The iron-based nanocrystalline powder with a diameter of 15 μm is used for insulating coating; the mixed powder in step S2 contains only iron-based nanocrystalline powder coated with SiO2. Comparative Example 2:

[0063] This comparative example is basically the same as Example 1, except that in step S1, only... D 50 FeNi powder with a diameter of 5 μm is used for insulating coating; the mixed powder in step S2 contains only SiO2-coated FeNi powder. Comparative Example 3:

[0064] This comparative example is basically the same as Example 1, except that in step S1, only... D 50FeSiAl powder with a thickness of 35 μm is used for insulating coating; the mixed powder in step S2 contains only FeSiAl powder coated with Al2O3. Comparative Example 4:

[0065] This comparative example is basically the same as Example 1, except that in step S1, the following steps are taken: D 50 Insulating coating of iron-based nanocrystalline powder with a diameter of 15 μm, and... D 50 =5μm FeNi powder is used for insulating coating; in step S2, the mixed powder contains only SiO2-coated iron-based nanocrystalline powder and SiO2-coated FeNi powder, with SiO2-coated iron-based nanocrystalline powder accounting for 80% of the mass of the mixed powder and SiO2-coated FeNi powder accounting for 20% of the mass of the mixed powder. Comparative Example 5:

[0066] This comparative example is basically the same as Example 1, except that in step S1, the following steps are taken: D 50 Insulating coating of iron-based nanocrystalline powder with a diameter of 15 μm, and... D 50 =35μm FeSiAl powder is used for insulating coating; in step S2, the mixed powder contains only SiO2-coated iron-based nanocrystalline powder and Al2O3-coated FeSiAl powder, with SiO2-coated iron-based nanocrystalline powder accounting for 80% of the mass of the mixed powder and Al2O3-coated FeSiAl powder accounting for 20% of the mass of the mixed powder. Comparative Example 6:

[0067] This comparative example is basically the same as Example 1, except that in step S1, the following steps are taken: D 50 Insulating coating of FeNi powder with a diameter of 5 μm, and... D 50 =35μm FeSiAl powder is used for insulating coating; in step S2, the mixed powder contains only SiO2-coated FeNi powder and Al2O3-coated FeSiAl powder, with SiO2-coated FeNi powder accounting for 20% of the mass of the mixed powder and Al2O3-coated FeSiAl powder accounting for 80% of the mass of the mixed powder. Comparative Example 7:

[0068] This comparative example is basically the same as Example 1, except that S1 is not performed, that is, D 50 Iron-based nanocrystalline powder with a diameter of 15μm D 50 FeNi powder with a diameter of 5μm D50 The FeSiAl powder with a diameter of 35 μm is not surface coated. Instead, the iron-based nanocrystalline powder, FeNi powder, and FeSiAl powder are directly mixed in S2 to obtain a mixed powder. By mass percentage, the iron-based nanocrystalline powder accounts for 50% of the mixed powder, the FeNi powder accounts for 20% of the mixed powder, and the FeSiAl powder accounts for 30% of the mixed powder. Comparative Example 8:

[0069] This comparative example is basically the same as Example 1, except that S2 is not performed, that is, the mixed powder is not coated with resin insulation, but the mixed powder is directly pressed in the two steps mentioned above. At this time, the green magnetic ring is not formed. Comparative Example 9:

[0070] This comparative example is basically the same as Example 1, except that in step S3, the magnetic ring is pressed in one step, that is, the pressing pressure is 1200MPa and the holding time is 60s, to obtain a green magnetic ring. Comparative Example 10:

[0071] This comparative example is basically the same as Example 1, except that in step S4, during the second high-temperature annealing stage, the temperature is raised to 680°C and held for 60 minutes. Comparative Example 11:

[0072] This comparative example is basically the same as Example 1, except that in step S4, during the first low-temperature pretreatment stage, the temperature is raised to 170°C and kept at that temperature for 30 minutes. Comparative Example 12:

[0073] This comparative example is basically the same as Example 1, except that in step S4, the annealing process is done in one step, that is, the temperature is directly raised to 600°C and held for 60 minutes. Comparative Example 13:

[0074] This embodiment is basically the same as Embodiment 1, except that in steps S1.1 and S1.2, an ammonia solution is added to a solution containing 8 parts by mass of tetraethyl orthosilicate and 100 parts by mass of anhydrous ethanol to adjust the pH to 10, and the solution is stirred evenly to obtain a silicon source solution. Comparative Example 14:

[0075] This embodiment is basically the same as Embodiment 1, except that in steps S1.1 and S1.2, an ammonia solution is added to a solution containing 2 parts by mass of tetraethyl orthosilicate and 100 parts by mass of anhydrous ethanol to adjust the pH to 10, and the solution is stirred evenly to obtain a silicon source solution. Comparative Example 15:

[0076] This embodiment is basically the same as Embodiment 1, except that in step S1.3, 13 parts by mass of aluminum nitrate (Al(NO3)3·9H2O) are dispersed in deionized water to obtain an aluminum nitrate solution. Comparative Example 16:

[0077] This embodiment is basically the same as Embodiment 1, except that in step S1.3, 7 parts by mass of aluminum nitrate (Al(NO3)3·9H2O) are dispersed in deionized water to obtain an aluminum nitrate solution.

[0078] The materials prepared in Examples 1-4 and Comparative Examples 1-16 were subjected to magnetic property testing, and the results are shown in Table 1 below: Table 1: Preparation conditions and magnetic properties of materials in Examples 1-4 and Comparative Examples 1-16

[0079] Comparing Example 1 and Comparative Examples 1-6, it can be seen that: pure nanocrystalline materials have low permeability and excellent DC bias performance but high loss; pure iron-nickel materials have low loss but low permeability and excellent DC bias performance; pure iron-silicon-aluminum materials have high permeability but poor DC bias performance and high loss; the composite material of nanocrystalline materials and FeNi has low permeability and high loss; the composite material of nanocrystalline materials and FeSiAl has low permeability and high loss; and the composite material of FeNi and FeSiAl has poor DC bias performance.

[0080] A comparison of Example 1 and Comparative Examples 7-8 reveals that: inorganic insulating coating layers are formed on the surfaces of iron-based nanocrystalline powder, FeNi powder, and FeSiAl powder, respectively; and an organic insulating coating layer is formed on the inorganically insulating coated metal soft magnetic powder base by resin. The SiO2 and Al2O3 inorganic insulating coating layers are thermodynamically very stable, and the resin not only possesses good insulation properties but is also a flexible polymer material capable of acting as a binder. Both the oxide inorganic layer and the resin organic layer have high resistivity, and the double-layer coating significantly improves the particle coating efficiency and enhances the magnetic properties of the material. However, a single inorganic or organic insulating coating layer is insufficient in terms of coating effect, leading to reduced magnetic properties and increased losses.

[0081] This invention achieves a low-cost, low-core-loss, and high-efficiency permeability and DC bias performance by rationally combining three metal powders, optimizing their ratio, and using an organic-inorganic double-layer coating. This allows it to meet the requirements for use under high-frequency and high-power conditions.

[0082] Comparing Example 1 and Comparative Example 9, it can be seen that the density of the material obtained by single pressing is relatively low, there may be tiny voids inside, the friction between particles and the internal stress are large, and the annealing process is difficult to eliminate them. This leads to a decrease in magnetic permeability under a DC magnetic field and a rapid decrease. In contrast, the two pressing process can effectively release the internal stress during the molding process, thereby preparing a composite material with better performance.

[0083] A comparison of Example 1 and Comparative Examples 10-12 reveals the following: In the low-temperature stage (below 200°C), the overall magnetic permeability decreases because the remaining binder is a non-magnetic material, effectively introducing more "air gaps" into the magnetic circuit, leading to deterioration of magnetic properties. In the high-temperature stage (above 660°C), the overall magnetic properties deteriorate due to overheating, excessive grain growth, and the formation of harmful phases, which damage interparticle insulation. One-step annealing further deteriorates the overall magnetic properties due to rapid binder decomposition, uneven stress relief, and increased internal defects. In contrast, the staged temperature control during annealing promotes the formation of a uniform equiaxed crystal structure within the powder particles, optimizes the crystal structure, enhances the material's magnetic properties, and improves saturation magnetization.

[0084] Comparing Example 1 and Comparative Examples 13-16, it can be seen that the content of tetraethyl orthosilicate affects the magnetic properties of the composite material. The amount of tetraethyl orthosilicate in 100 parts by mass of iron-based nanocrystalline powder or FeNi powder should be controlled between 3 and 7 parts by mass. When the content of tetraethyl orthosilicate is greater than 7 parts by mass or less than 3 parts by mass, the permeability decreases significantly, the loss increases greatly, and the DC bias characteristics deteriorate. Furthermore, the content of aluminum nitrate also affects the magnetic properties of the composite material. The amount of aluminum nitrate in 100 parts by mass of FeSiAl powder should be controlled between 8 and 12 parts by mass. When the content of aluminum nitrate is greater than 12 parts by mass or less than 8 parts by mass, the excessive non-magnetic phase significantly reduces the permeability, greatly increases the loss, and deteriorates the DC bias characteristics. As can be seen from Table 1, the effective permeability, DC bias characteristics and losses of the materials prepared in Examples 1-4 are all better than those in Comparative Examples 1-16, indicating that the preparation method of the present invention can effectively improve the comprehensive performance of the materials.

[0085] The above embodiments provide a detailed description of the technical solution of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a low-cost, high-performance nanocrystalline composite material, comprising the following steps: (1) Iron-based nanocrystalline powder, FeNi powder and FeSiAl powder are mixed to obtain a mixed powder; (2) The mixed powder is added to a solution containing resin binder, lubricant and organic solvent, stirred thoroughly, dried and granulated to obtain a mixed powder with resin insulation coating; (3) Press the resin-insulated mixed powder to obtain a green magnet; (4) The green magnet is heat-treated to obtain a nanocrystalline composite material; Its characteristics are: In step (1), the iron-based nanocrystalline powder is coated with a SiO2 insulating layer, the FeNi powder is coated with a SiO2 insulating layer, and the FeSiAl powder is coated with an Al2O3 insulating layer. Iron-based nanocrystalline powder coated with a SiO2 insulating layer, FeNi powder coated with a SiO2 insulating layer, and FeSiAl powder coated with an Al2O3 insulating layer are mixed to obtain the mixed powder. According to the mass percentage, the iron-based nanocrystalline powder coated with a SiO2 insulating layer accounts for 50%-60%, the FeNi powder coated with SiO2 accounts for 20%-30%, and the balance is FeSiAl powder coated with an Al2O3 insulating layer. In step (3), the pressing is divided into two steps. The first step is to hold the pressure for 60s-180s under a pressure of 180MPa-220MPa, and the second step is to hold the pressure for 60s-180s under a pressure of 800MPa-1800MPa. In step (4), the heat treatment is divided into two steps. The first step is low-temperature pretreatment, that is, heating to 180℃-210℃ and holding for 30min-60min. The second step is high-temperature annealing, that is, heating to 600℃-660℃ and holding for 60min-120min.

2. The preparation method according to claim 1, characterized in that: At least one of the following conditions (i) to (iii) must be met: (i) The main component of the iron-based nanocrystalline powder is Fe, and it also includes one or more of Si, Nb, Cu, B and Ni; (ii) The elements and their mass percentages in the FeNi powder are: 45%-55% Ni, 0%-5% unavoidable impurity elements, and the remainder is Fe; (iii) The elements and their mass percentages in the FeSiAl powder are: 8%-10% Si, 5%-6% Al, 0%-1% unavoidable impurity elements, and the remainder is Fe.

3. The preparation method according to claim 1, characterized in that: At least one of the following conditions (i) to (iii) must be met: (i) The median particle size of the iron-based nanocrystalline powder D 50 The range is 10μm-20μm; (ii) Median particle size of the FeNi powder D 50 The range is 1μm-5μm; (iii) Median particle size of the FeSiAl powder D 50 The range is 30μm-40μm.

4. The preparation method according to claim 1, characterized in that: At least one of the following conditions (i) to (iii) must be met: (i) In step (2), the resin adhesive includes at least one of epoxy resin, silicone resin, polyimide resin, and phenolic resin; (ii) In step (2), the lubricant includes at least one of zinc stearate, aluminum stearate, and barium stearate; (iii) In step (2), the organic solvent includes at least one of acetone and anhydrous ethanol.

5. The preparation method according to claim 1, characterized in that: At least one of the following conditions (i) to (ii) must be met: (i) In step (4), during the low-temperature pretreatment, the temperature is increased at a rate of 3℃ / min-5℃ / min; (ii) In step (4), during high-temperature annealing, the temperature is increased at a rate of 10℃ / min-12℃ / min.

6. The preparation method according to claim 1, characterized in that: At least one of the following conditions (i) to (iii) must be met: (i) A SiO2 insulating layer is coated on the surface of the iron-based nanocrystalline powder using the sol-gel method; (ii) A SiO2 insulating layer is coated onto the surface of the FeNi powder using the sol-gel method; (iii) The FeSiAl powder is coated with an Al2O3 insulating layer by hydrolysis and heat treatment.

7. The preparation method according to claim 6, characterized in that: When coating the surface of the iron-based nanocrystalline powder with a SiO2 insulating layer using the sol-gel method, the following steps are included: The surfactant was ultrasonically dispersed in anhydrous ethanol to obtain a dispersion, and then the iron-based nanocrystalline powder was added to obtain surface-activated iron-based nanocrystalline powder. The surface-activated iron-based nanocrystalline powder was dispersed in a sol formed by mixing silicon source with ethanol, water and catalyst, and the mass ratio of surface-activated iron-based nanocrystalline powder to silicon source was controlled to be 100:(3-7). The sol was coated on the surface of surface-activated iron-based nanocrystalline powder by hydrolysis and condensation to form a wet gel layer. Then, the gel was dried to transform it into a dense SiO2 layer, and iron-based nanocrystalline powder coated with SiO2 insulating layer was obtained. When coating the FeNi powder surface with a SiO2 insulating layer using the sol-gel method, the following steps are included: The surfactant was ultrasonically dispersed in anhydrous ethanol to obtain a dispersion, and then the FeNi powder was added to obtain surface-activated FeNi powder. The surface-activated FeNi powder was dispersed in a sol formed by mixing silicon source with ethanol, water and catalyst, and the mass ratio of surface-activated iron-based nanocrystalline powder to silicon source was controlled to be 100:(3-7). The sol was coated on the surface of surface-activated FeNi powder by hydrolysis and condensation to form a wet gel layer. Then, the gel was dried to transform it into a dense SiO2 layer to obtain FeNi powder coated with a SiO2 insulating layer. When coating the FeSiAl powder surface with an Al2O3 insulating layer using hydrolysis and heat treatment, the following steps are included: The FeSiAl powder is dispersed in a mixed system consisting of aluminum nitrate solution, pH adjuster and dispersant, and the mass ratio of FeSiAl powder to aluminum nitrate is controlled to be 100:(8-12). By controlling the hydrolysis reaction, an Al(OH)3·nH2O wet gel layer is generated in situ on the surface of the FeSiAl powder. Then, it is dried and then heat-treated under an inert atmosphere to transform the gel layer into a dense Al2O3 layer, thus obtaining FeSiAl powder coated with an Al2O3 insulating layer.

8. The preparation method according to claim 7, characterized in that: At least one of the following conditions (i) to (vii) must be met: (i) When the iron-based nanocrystalline powder is coated with a SiO2 insulating layer, the silicon source includes at least one of tetraethyl orthosilicate, sodium silicate, silica sol, and methyltrimethoxysilane; (ii) When the FeNi powder is coated with a SiO2 insulating layer, the silicon source includes at least one of tetraethyl orthosilicate, sodium silicate, silica sol, and methyltrimethoxysilane; (iii) When the iron-based nanocrystalline powder is coated with a SiO2 insulating layer, the catalyst includes at least one of hydrochloric acid, ammonia, acetic acid, and cation exchange resin; (iv) When the FeNi powder is coated with a SiO2 insulating layer, the catalyst includes at least one of hydrochloric acid, ammonia, acetic acid, and cation exchange resin; (v) When the FeSiAl powder is coated with an Al2O3 insulating layer, the pH adjuster includes at least one of sodium acetate, acetic acid, sodium carbonate, and ammonia water; (vi) When the FeSiAl powder is coated with an Al2O3 insulating layer, the dispersant includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, and polyvinylpyrrolidone; (vii) When the FeSiAl powder is coated with an Al2O3 insulating layer, the temperature of the heat treatment is 700℃-900℃.

9. The preparation method according to any one of claims 1 to 5, characterized in that: The nanocrystalline composite material exhibits a magnetic permeability greater than or equal to 45 at 1 MHz, a DC bias performance greater than or equal to 45% at a bias field of 100 Oe, and a power loss less than or equal to 3500 mW / cm² at 50 mT and 1 MHz. 3 .

10. The preparation method according to any one of claims 6 to 8, characterized in that: The nanocrystalline composite material exhibits a magnetic permeability greater than or equal to 60 at 1 MHz, a DC bias performance greater than or equal to 60% at a bias field of 100 Oe, and a power loss less than or equal to 1500 mW / cm² at 50 mT and 1 MHz. 3 .

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