Low-loss nanocrystalline powder preparation method, nanocrystalline powder and inductor

Abstract

The invention discloses a low-loss nanocrystalline powder preparation method, nanocrystalline powder and an inductor, and relates to the technical field of inductor preparation. The method comprises the following steps: preparing nano atomized powder and carrying out high-temperature smelting to obtain a master alloy; carrying out primary atomization operation on the mother alloy by utilizing high-speed airflow to form liquid drops; carrying out secondary atomization operation on the liquid drops on the basis of a centrifugal atomization mode to obtain nanocrystalline powder in water; and drying and granulating the nanocrystalline powder in the water to obtain the nanocrystalline powder. According to the method, the nanocrystalline components are adjusted so as to improve the magnetic conductivity and the direct current bias capacity of the nanocrystalline powder, the nanocrystalline powder is prepared through a centrifugal rotation water vapor atomization method, the good nanocrystalline cooling rate is kept, and efficient and low-loss preparation of the nanocrystalline powder is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of inductor preparation, and in particular to a low-loss nanocrystalline powder preparation method, nanocrystalline powder and inductor. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Currently, the frequency stability of one-piece molded inductor alloy powder is poor, and the magnetic permeability decreases significantly at higher frequencies. Due to the low resistivity of the powder, surface passivation treatment is required to increase its resistivity, but this will result in a significant increase in the eddy current loss of the powder.

[0004] Due to its long-range disordered structure, Fe-based nanocrystalline alloys offer electromagnetic properties comparable to those of alloy powders. In particular, they possess excellent combined electromagnetic properties, such as low coercivity and high resistivity, resulting in lower losses and suitable for use as raw materials in high-current, one-piece molded inductors. However, currently, spraying nanocrystalline powders with excellent performance presents significant challenges in the cooling rate of the equipment. To achieve optimal nanocrystalline formation, the magnetic phase content of the nanocrystalline powder must be controlled. Fe-based nanocrystalline magnetic powders incorporate a high level of non-magnetic elements (such as Si, B, C, and P) to improve the alloy's nanocrystalline formation, resulting in a low Ms and difficulty achieving high DC bias capability. To address this issue, some methods incorporate Ni into the nanocrystalline powder preparation. While this improves the nanocrystalline powder's magnetic permeability and DC bias capability to a certain extent, meeting the powder requirements for one-piece molded inductors, its higher cost compared to traditional FeSiCr and carbonyl iron powders used in one-piece inductors makes it less competitive. Furthermore, the ability to form nanocrystals is limited, and large nanocrystalline powders may contain internal crystallization, resulting in high power losses (>300mW / cm³). Due to this limitation, the added nanocrystalline phase content is often too high. Excessive levels of single non-magnetic phase elements such as Si, B, C, and Cr can result in a sprayed nanocrystalline powder with a magnetic permeability between 10-25, severely reducing DC bias capability. Furthermore, because existing integrated inductors use embedded coils, the magnetic properties of nanocrystalline powder cannot be fully utilized without annealing.

[0005] In summary, how to achieve efficient preparation of low-loss and high-permeability nanocrystalline powder in one-piece molded inductors has become a technical problem that needs to be urgently solved in the existing technology. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a low-loss nanocrystalline powder preparation method, nanocrystalline powder and inductor. The nanocrystalline composition is adjusted to improve the magnetic permeability and DC bias capability of the nanocrystalline powder. The nanocrystalline powder is prepared by centrifugal rotating water vapor atomization method, maintaining a good nanocrystalline cooling rate, and realizing efficient and low-loss preparation of nanocrystalline powder.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions: A first aspect of the present invention provides a method for preparing low-loss nanocrystalline powder, comprising the following steps: Prepare nano-atomized powder and perform high-temperature smelting to obtain a master alloy; The master alloy is atomized for the first time using a high-speed airflow to form droplets; The droplets are subjected to a second atomization operation based on centrifugal atomization to obtain nanocrystalline powder in water; The nanocrystalline powder in water is dried and granulated to obtain the nanocrystalline powder.

[0008] Furthermore, the nano-atomized powder composition includes Fe (100-a-b-c-x) Si a B b P c Nb x Mn y La z , where 7≤a≤10, 4≤b≤8, 0.2≤c≤2.0, 0.1≤x≤3.5, 0.5≤y≤1.0, 0.5≤z≤1.0, and the remainder is Fe.

[0009] Furthermore, the high temperature smelting temperature is 1470-1570°C.

[0010] Furthermore, the first atomization operation medium is nitrogen.

[0011] Furthermore, the specific steps of performing the first atomization operation on the master alloy using high-speed airflow are as follows: The liquid master alloy passes through the ladle and nozzle in turn and is dispersed by the high-speed airflow to complete the first atomization, and then dives to the centrifugal disk at high speed.

[0012] Furthermore, the specific steps of performing a second atomization operation on the semi-solidified droplets based on the centrifugal atomization method are as follows: The droplets are impacted and rubbed by the high-speed rotating centrifugal disk, completing the second atomization and cooling. The rotation speed of the centrifugal disk is 5000r / min. The centrifugal disk is made of copper as the body, and there is cooling water on the upper and lower surfaces.

[0013] Furthermore, the specific steps of drying and granulating the nanocrystalline powder in water are as follows: The nanocrystalline powder in the water is subjected to a solid-liquid separation operation and then vacuum dried; The vacuum-dried powder is subjected to annealing pretreatment; The annealed crystal powder is passivated, insulated and coated, and granulated and dried to obtain the final nanocrystalline powder.

[0014] Furthermore, the annealing temperature is 540°C, the reducing atmosphere is 3% concentration of hydrogen, and the annealing time is 3 h.

[0015] The second aspect of the present invention provides a nanocrystalline powder, which is prepared by the low-loss nanocrystalline powder preparation method of the first aspect.

[0016] A third aspect of the present invention provides an inductor, which is an integrally formed inductor and includes the nanocrystalline powder of the second aspect.

[0017] One or more of the above technical solutions have the following beneficial effects: The present invention discloses a method for preparing low-loss nanocrystalline powder, nanocrystalline powder, and inductor. By incorporating trace amounts of Mn and P elements to reduce the coercive force (Hc) of the nanocrystalline powder, and incorporating a certain amount of Nb elements with a large atomic radius to maintain the grain size at a micro-nano scale, the magnetic permeability of the nanocrystalline powder can be significantly improved. The prepared nanocrystalline powder has high magnetic permeability, low loss, and good DC bias capability. The powder also has good sphericity, is easy to press, and has low loss. It can replace iron, silicon, chromium, and carbonyl iron powders as a conventional powder for integrally molded inductors, particularly those with higher operating currents. Inductors pressed using this nanocrystalline powder have a low temperature-rise current.

[0018] The present invention employs a water-gas combined with secondary atomization to address the difficulties in forming and pressing high-iron nanocrystalline formulations. In some implementations, centrifugal atomization is used to enhance the amorphous-forming ability, enabling the spraying of raw materials with an Fe content of approximately 78% into nanocrystalline powders, ensuring that the sprayed powder possesses superior DC bias capability. Furthermore, the addition of a certain amount of rare earth metal improves the powder's toughness, making it easier to press.

[0019] After the powder is sprayed, the powder is pre-treated and annealed in a weak reducing atmosphere at 540° C. to further reduce the oxygen content on the surface of the nanocrystalline powder to reduce its loss.

[0020] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0022] Figure 1 It is a schematic structural diagram of the vacuum melting equipment in the present invention; Figure 2 This is a schematic diagram of the finished nanocrystalline powder of the present invention; Figure 3 This is a particle size distribution diagram of the nanocrystalline powder used in the integrally formed inductor of the present invention; Figure 4 The XRD patterns before and after the formation of nanocrystals in the present invention; Figure 5 This is a diagram of loss test results in the present invention; Among them, 1. melting furnace, 2. vacuum environment, 3. leakage package, 4. injection structure. DETAILED DESCRIPTION

[0023] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations; The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] The present invention provides a method for preparing low-loss nanocrystalline powder, comprising the following steps: Step 1: Prepare nano-atomized powder and perform high-temperature smelting to obtain a master alloy.

[0026] Preferably, the nano-atomized powder composition includes Fe (100-a-b-c-x) Sia B b P c Nb x Mn y La z , wherein 7≤a≤10, 4≤b≤8, 0.2≤c≤2.0, 0.1≤x≤3.5, 0.5≤y≤1.0, 0.5≤z≤1.0, and the balance is Fe. Further preferably, Fe79.5 parts, Si 6.5 parts, B 5 parts, P 1.95 parts, Nb 3.0 parts, Mn 1.05 parts, La 1.0 parts. The present invention improves the nano-atomized powder based on the problems of low magnetic permeability and poor DC bias capability of existing nanocrystalline powders. The Nb element with a large atomic radius can effectively hinder the growth of grain size, so that a large number of nano-type crystal particles are distributed inside the nanocrystalline powder, thereby improving the magnetic permeability. The increase in the content of Fe element in the magnetic phase also helps to improve the magnetic permeability of the powder. The P element has a strong diffusion ability, which is beneficial to the outer layer of the nanocrystalline powder to form a glassy solid, thereby increasing the resistance of the nanocrystalline powder and reducing the loss. The added Mn element helps to reduce the coercive force of the nanocrystalline powder and increase the saturation magnetization intensity (Ms) of the powder, which is beneficial to reducing the hysteresis loss of the powder and can increase the magnetic permeability of the powder.

[0027] Preferably, the nano-atomized powder is prepared according to the above formula and smelted at high temperature to obtain a master alloy. The master alloy is prepared using vacuum melting equipment, such as Figure 1 As shown, the smelting furnace 1 includes a vacuum environment 2 inside, and is provided with a ladle 3 and a spray structure 4. The ladle 3 serves to keep the molten steel warm during its downward flow. The spray structure 4 includes a nozzle and a spray disc. The spray disc is used for rate adjustment. The nozzle controls the particle size of the powder by combining the diameter of the leak hole, the airflow, the rotation speed of the turntable, etc. The diameter of the nozzle leak hole is set at 3-6mm. The high-temperature smelting temperature is 1470-1570℃, and the ladle will be heated to ensure that the temperature of the molten steel is above 1200℃, so that the molten steel has a lower surface tension and is easily dispersed into finer particles and formed into balls after atomization.

[0028] Step 2: Use high-speed airflow to perform the first atomization operation on the master alloy to form droplets.

[0029] To ensure good sphericity of the powder, the initial atomization process uses nitrogen as a shielding gas to prevent oxidation. The sphericity of nanocrystalline powders is related to gas velocity. Gas molecules have a smaller impulse than liquid molecules, so using nitrogen as the operating medium to impact the molten steel ensures good sphericity.

[0030] The liquid master alloy passes through the ladle and nozzle, where it is dispersed by a high-speed airflow, achieving the initial atomization. It then dives down at high speed onto the centrifugal disk. The high-speed airflow is nitrogen, which impacts the falling molten steel, breaking it up and atomizing it. The concentration is 99.9%, and the rate is determined by the nozzle disk structure. The air pressure is controlled between 8 and 12 MPa.

[0031] Step 3: The droplets are subjected to a second atomization operation based on a centrifugal atomization method to obtain nanocrystalline powder in water.

[0032] Preferably, in order to break through the drop surface paint film and improve the cooling rate of powder, atomization adopts centrifugal atomization mode for the second time.The steel droplet obtained through the first atomization operation now is a droplet or a semi-solidified droplet, and collides and rubs with the centrifugal copper disk of high-speed rotation, completes the second atomization operation and cools down.Wherein, centrifugal disk is contained in the position of about 0.3-0.8m below the nozzle, realizes rotation by motor.The rotating speed of centrifugal disk is 5000r / min, and centrifugal disk adopts the copper with higher heat dissipation efficiency as body, and copper disk upper and lower surfaces all have cooling water, i.e. thinner water layer of high-speed rotation, can break through the molten steel surface gas film and reach fast cooling, and simultaneously, the water film on the upper surface also can play a buffering effect, avoids nanocrystalline powder from being torn into band or strip in atomization process.

[0033] Specifically, the centrifugal disc features a concave, aspherical surface with a central outlet to control water flow. Centrifugal force spun the water out of the outlet, forming a high-velocity, flowing water film. When the nitrogen-flushed molten steel falls onto the disc, its copper surface rapidly removes heat and cools it. The water on the disc acts primarily as a buffer, minimizing the likelihood of the powder being torn apart by the disc and ensuring its sphericity.

[0034] Step 4: Drying and granulating the nanocrystalline powder in water to obtain nanocrystalline powder.

[0035] Step 4.1: Perform solid-liquid separation on the nanocrystalline powder in the water, and then vacuum dry it. Preferably, a magnetic powder separation device is used to separate the nanocrystalline powder in the water from the cooling water through filter cloth compression separation, and the collected nanocrystalline powder is vacuum dried. Step 4.2: The vacuum-dried powder is subjected to annealing pretreatment. Preferably, the annealing temperature is 540° C., the reducing atmosphere is 3% hydrogen, and the annealing time is 3 hours.

[0036] Step 4.3: The annealed crystal powder is passivated, insulated, coated, granulated and dried to obtain the final nanocrystalline powder.

[0037] The present invention also provides a nanocrystalline powder, which is prepared by the above-mentioned low-loss nanocrystalline powder preparation method.

[0038] The present invention also provides an inductor, which is an integrally formed inductor, comprising the above-mentioned nanocrystalline powder, and its particle size distribution diagram is as shown in FIG. Figure 3 As shown, the purple line represents the percentage, and the blue line represents the cumulative percentage. It can be seen that the nanocrystalline powder prepared by the method of the present invention can match the water vapor atomization particle size level of the conventional powdered iron silicon chromium powder used in integrated inductors on the market.

[0039] The present invention adopts a centrifugal disk rotating water vapor combined atomization powder making method, which can make the iron content formula components nano-crystallized while improving the cooling rate of the powder spraying equipment, and improve the formula of nano-crystalline powder. Figure 2 As shown, the nanocrystalline powder prepared by the present invention has good sphericity, and the D50 powder size is about 13 μm.

[0040] Compared to the classic K107 nanocrystalline composition, the nanocrystalline powder prepared with this formulation can achieve an Fe content exceeding 80%, enhancing its DC bias resistance. The addition of a certain amount of Nb prevents grain growth, allowing it to form micro-nanocrystalline particles, thereby increasing its magnetic permeability. The resulting nanocrystalline powder exhibits a high effective magnetic permeability (μe = 25-30) and a DC bias resistance of 70-75% μe @ 150 Oe. Small amounts of P and Mn are added to reduce the coercivity (Hc) of the nanocrystalline powder, thereby lowering its power loss, achieving a Pc as low as 183 mW / cm³ (at Bm = 50 mT, f = 100 kHz). The addition of La improves the nanocrystalline's toughness and facilitates compaction. Compared to powdered iron, silicon, and chromium and carbonyl iron powders used in integrally molded inductors, this nanocrystalline powder performs equally well, exhibiting superior permeability and loss. The formulation of the nano-atomized powder in this invention was developed through numerous refinements and experiments. In the process of preparing the nano-atomized powder, the present invention uses Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6 and Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 to conduct tests and compare the effects. The specific formulas and effects of the comparative examples and examples are shown in Table 1.

[0041] Table 1. Comparative Examples and Examples formulations and effects.

[0042]

[0043] As shown in Table 1, Comparative Examples 1-4 are nanocrystalline powders composed primarily of Fe, Si, B, C, and Cr. When the iron content exceeds 83.5%, nanocrystals cannot form, resulting in low magnetic permeability and very high losses. Comparative Examples are nanocrystalline powders doped with only Nb, Mn, and P. While the magnetic permeability is improved, the losses are still above 1000 mW·cm⁻³. Examples 1-5 are improved versions, incorporating a certain amount of Nb, P, and Mn simultaneously. Not only is the magnetic permeability improved, but the DC bias capability is acceptable, and the losses are all below 900 mW·cm⁻³. Figure 4 The diagram shows the powder state of Example 4 before and after annealing. Before annealing, the powder has not formed nanocrystals and is still in an amorphous state. After annealing, nanocrystals are formed, which is used to indicate that nanocrystals have grown. Figure 5 The loss comparison of Examples 3 and 4 is shown below. Because the iron content in Comparative Example 4 is too high, requiring extremely cold conditions, the powder material prematurely crystallizes, resulting in significantly higher losses than the nanocrystalline powder. In Example 6, due to the excessively high iron content and crystallization, the magnetic permeability drops significantly, and the corresponding losses are also particularly high.

[0044] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any technical object of a person skilled in the art that can be easily conceived of within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing low-loss nanocrystalline powder, characterized in that: The following steps are involved: Prepare nano-atomized powder and perform high-temperature smelting to obtain a master alloy; The master alloy is atomized for the first time using a high-speed airflow to form droplets; The droplets are subjected to a second atomization operation based on centrifugal atomization to obtain nanocrystalline powder in water; The nanocrystalline powder in water is dried and granulated to obtain the nanocrystalline powder.

2. The method for preparing low-loss nanocrystalline powder according to claim 1, wherein: Nano atomized powder components include Fe (100-a-b-c-x) Si a B b P c Nb x Mn y La z , where 7≤a≤10, 4≤b≤8, 0.2≤c≤2.0, 0.1≤x≤3.5, 0.5≤y≤1.0, 0.5≤z≤1.0, and the remainder is Fe.

3. The method for preparing low-loss nanocrystalline powder according to claim 1, wherein: The high temperature smelting temperature is 1470-1570℃.

4. The method for preparing low-loss nanocrystalline powder according to claim 1, wherein: The first atomization operating medium is nitrogen.

5. The method for preparing low-loss nanocrystalline powder according to claim 1, wherein: The specific steps for the first atomization operation of the master alloy using high-speed airflow are as follows: The liquid master alloy passes through the ladle and nozzle in turn and is dispersed by the high-speed airflow to complete the first atomization, and then dives to the centrifugal disk at high speed.

6. The method for preparing low-loss nanocrystalline powder according to claim 5, characterized in that: The specific steps of performing the second atomization operation on the semi-solidified droplets based on the centrifugal atomization method are as follows: The droplets are impacted and rubbed by the high-speed rotating centrifugal disk, completing the second atomization and cooling. The rotation speed of the centrifugal disk is 5000r / min. The centrifugal disk is made of copper as the body, and there is cooling water on the upper and lower surfaces.

7. The method for preparing low-loss nanocrystalline powder according to claim 1, wherein: The specific steps for drying and granulating the nanocrystalline powder in water are as follows: The nanocrystalline powder in the water is subjected to a solid-liquid separation operation and then vacuum dried; The vacuum-dried powder is subjected to annealing pretreatment; The annealed crystal powder is passivated, insulated and coated, and granulated and dried to obtain the final nanocrystalline powder.

8. The method for preparing low-loss nanocrystalline powder according to claim 7, wherein: The annealing temperature is 540°C, the reducing atmosphere is 3% hydrogen, and the annealing time is 3 h.

9. A nanocrystalline powder, characterized in that: The low-loss nanocrystalline powder is prepared by the method for preparing the nanocrystalline powder according to any one of claims 1 to 8.

10. An inductor, characterized in that: The inductor is an integrally formed inductor, comprising the nanocrystalline powder according to claim 9.

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