Micron-sized low-loss magnetically soft alloy powder and preparation method thereof

Abstract

The invention belongs to the technical field of magnetic metal powder preparation, and particularly relates to micron-sized low-loss magnetically soft alloy powder and a preparation method thereof. The powder is composed of enriched Fe (Si) or Fe (Ni) solid solution cell crystals, and non-magnetic second phases such as silicon oxide, nitride or carbide are distributed at the boundaries of the cell crystals in a nanoscale continuous net form, so that an insulating network is naturally formed in the powder. The structure is realized through specific component design in combination with ultra-high-speed gas atomization and a controllable cooling rate technology. In the rapid solidification process, alloy elements (such as Si) and impurity elements (such as O and N) are subjected to microscopic segregation, and a nano insulating phase is generated in situ at the cell crystal boundary. The powder disclosed by the invention does not need an additional surface insulation coating process, and an inherent insulation network in the powder can effectively segment a magnetic domain and block an eddy current path, so that high-frequency eddy current loss and magnetic hysteresis loss are remarkably reduced. The powder is particularly suitable for preparing a high-frequency, low-loss and high-strength integrally-formed soft magnetic composite material magnetic core.

Description

Technical Field

[0001] This invention belongs to the field of magnetic metal powder preparation technology, and particularly relates to a micron-sized low-loss soft magnetic alloy powder and its preparation method. Background Technology

[0002] The improvement of soft magnetic composite material performance strongly depends on the control of eddy current losses. Existing technologies mainly rely on post-processing surface insulation coating, but this method faces many challenges such as insufficient interfacial bonding, lack of uniformity, and insufficient thermal stability. The insulation coating method is essentially an "external solution." Another approach is to start from the powder itself and improve performance by adjusting its internal structure. For example, preparing alloy powders with uniform composition (such as Fe-Si alloy powder) can effectively change the internal atomic structure of pure iron, but its resistivity is higher than that of pure iron, which is still insufficient to meet the application requirements above MHz frequency; for mechanically alloyed powders, oxide dispersed phases can be introduced into them through ball milling, but this process is energy-intensive, easily introduces impurities, and the powder shape is irregular, leading to a decrease in filling density and permeability; for oxygen-containing iron powder, the inherent oxygen in the powder can be used to form oxides at the grain boundaries, but this structure is usually random and discontinuous, with limited insulation effect, and excessive oxygen content will seriously impair magnetization.

[0003] Existing alloy powders prepared by atomization methods typically exhibit dendritic or equiaxed crystal microstructures, with a dispersed and discontinuous second phase distribution, failing to form an effective three-dimensional insulating network. Therefore, developing a micron-sized alloy powder capable of directly forming an internal continuous insulating network during atomization, while possessing good sphericity to ensure high packing density, has significant technological and economic value. Summary of the Invention

[0004] The purpose of this invention is to provide a micron-sized soft magnetic alloy powder with an internal insulating network that requires no subsequent insulating coating, and a highly efficient preparation method thereof. This method, through ingenious composition design and atomization process control, achieves spontaneous regulation of the powder's internal structure, fundamentally resolving the contradiction between insulation and magnetic permeability.

[0005] Technical solution of the present invention: A micron-scale low-loss soft magnetic alloy powder, wherein the powder is composed of micron-scale metal cells, and at the boundaries of the cells, there is a continuous network of non-magnetic insulating film phases, thereby forming a three-dimensional insulating network inside the powder and having obvious compositional gradient characteristics.

[0006] The metal cell is composed of Fe-Si, Fe-Ni, or Fe-Si-Al solid solution, with a cell size of 0.5-3 μm; wherein the Fe-Si alloy has a Si content of 2.0-6.5 wt%, the Fe-Ni alloy has a Ni content of 30-50 wt%, and the Fe-Si-Al solid solution has a Si content of 2.0-6.5 wt% and an Al content of 0.5-4.0 wt%.

[0007] The thickness of the non-magnetic insulating thin film phase is 5-50 nm, and its composition is SiO2, Si3N4, and SiO2. x N y A combination of one or more of them.

[0008] The compositional gradient is a continuous gradient distribution of the concentrations of Si, O, and N elements from the cell center to the cell boundary, with significant enrichment at the boundary.

[0009] The soft magnetic alloy powder is spherical or near-spherical, with a sphericity greater than 0.9 and a particle size range of 5-150 μm.

[0010] The method for preparing the micron-scale low-loss soft magnetic alloy powder employs a gas atomization method and is achieved through the following steps: a) Melting an iron-based alloy containing Si and controllable amounts of O and N elements, wherein the Si content is 2.0-6.5 wt%, the O content is 0.1-0.5 wt%, and the N content is 0.05-0.3 wt%; b) Superheating the alloy melt to 1500-1650℃, and then performing ultra-high-speed gas atomization using an atomizing gas with a pressure of not less than 5 MPa; c) In an atmosphere containing nitrogen or a mixture of nitrogen and trace amounts of oxygen, controlling the cooling process of the atomized droplets to cause rapid solidification and in-situ precipitation of cellular structures and grain boundary insulating film phases.

[0011] In step b), the atomizing gas is nitrogen or argon.

[0012] In step c), the cooling rate of the atomized droplets is greater than 10. 5 ℃ / s The beneficial effects of this invention: Unlike traditional surface-coating insulation strategies, this invention adopts a "bulk insulation" design. This preparation method eliminates the need for any post-coating processes; the powder inherently possesses a uniform, continuous, and stable three-dimensional insulating network, fundamentally eliminating interface problems and potential failure risks associated with the coating layer. The micron-sized soft magnetic alloy powder with gradient composition and cellular structure obtained by this method exhibits extremely low high-frequency losses. Its internal insulating network electromagnetically divides the powder into countless micron-scale insulating cellular units, maximizing the extension of the eddy current path and resulting in extremely low eddy current losses. Simultaneously, the small cellular size also helps reduce hysteresis losses. Furthermore, the in-situ generated ceramic phase bonds firmly to the metal matrix, ensuring high thermal stability of the soft magnetic alloy powder, enabling it to withstand high-temperature annealing and service environments. Moreover, the grain boundary ceramics can simultaneously provide dispersion strengthening, improving the compact strength. This soft magnetic alloy powder also exhibits high magnetic flux density and good magnetic permeability. This is because the insulating phase exists only at the nanoscale grain boundaries, and the magnetic volume fraction of the powder (>95%) is much higher than that of traditional coated powders (typically 85%-92%), resulting in higher saturation magnetization and effective magnetic permeability. The preparation method of this invention is simple and has significant cost advantages. It eliminates the complex and time-consuming chemical coating and heat treatment steps, realizing a "one-step" preparation of high-performance SMC powder. The process is short, the overall cost is low, and it is environmentally friendly. Detailed Implementation

[0013] Invention Principle: Magnetic alloy powders are generally treated with subsequent surface coating to achieve insulation and improve eddy current loss control. However, the soft magnetic composite materials prepared by this method suffer from poor interfacial bonding, poor coating uniformity, and poor thermal stability. By combining composition design and process innovation, a three-dimensional insulating network can be formed within the powder through self-assembly by manipulating the rapid solidification process. Unlike traditional methods that coat the powder from the outside, the self-assembly of the three-dimensional insulating network within the powder relies on sophisticated composition design, extreme process control, and intrinsic structural self-generation. Composition design requires the active introduction of specific amounts of "impurity" elements into the iron-based alloy; extreme process control utilizes ultra-high-speed gas atomization to generate extremely high cooling rates, forcing the alloy droplets to undergo non-equilibrium rapid solidification, forming a micron-scale cellular crystal structure. During the final stage of rapid solidification, solute elements (such as Si, O, and N) are pushed to the boundaries of the final solidified crystal cells. These enriched elements can undergo in-situ reactions at the boundaries, generating a continuous, nanoscale insulating film (such as SiO2 or Si3N4). Therefore, each metal cell becomes a magnetic unit encased in a natural insulating layer, forming a complete insulating network within the powder. In other words, through the synergistic effect of compositional design and ultrafast solidification technology, the powder material is guided to spontaneously assemble its internal components into an ideal microstructure where "cells" and "grain boundary insulating networks" meet during solidification, effectively endowing the powder with low-loss soft magnetic properties.

[0014] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description of the embodiments is merely exemplary and is not intended to limit the scope and application of the present invention.

[0015] A micron-sized low-loss soft magnetic alloy powder has the following macroscopic morphology and composition: the powder is spherical or near-spherical with a sphericity greater than 0.9 and a particle size range of 5-150 μm. The interior is composed of micron-scale metal cells, and at the boundaries of these cells, a continuous network of non-magnetic insulating film phases exists, thus forming a three-dimensional insulating network within the powder. The metal cells are composed of Fe-Si, Fe-Ni, or Fe-Si-Al solid solutions, specifically Fe-Si alloys (Si content 2.0-6.5 wt%), Fe-Ni alloys (Ni content 30-50 wt%), or Fe-Si-Al alloys (Si content 2.0-6.5 wt%, Al content 0.5-4.0 wt%). The cell size is 0.5-3 μm. The thickness of the non-magnetic insulating film phase is 5-50 nm, and its composition is SiO2, Si3N4, SiO2 ... x N y It is a composite of one or more of the following: The sphericity of the soft magnetic alloy powder is greater than 0.9, and the particle size ranges from 5 to 150 μm.

[0016] The core microstructure includes a cellular crystal structure and a grain boundary insulating network, exhibiting a distinct compositional gradient. The cellular crystal structure consists of micro-cells with a size of 0.5-3 μm within the powder, each cell containing a supersaturated Fe(Si) or Fe(Ni) solid solution, serving as the primary channel for magnetic flux conduction. The grain boundary insulating network is a continuous network-like thin film phase with a thickness of 5-50 nm existing at the cell boundaries. This film phase is non-magnetic, such as SiO2, Si3N4, and SiO2. x N y The network, or its complexes, can effectively isolate metal cells both physically and electrically; the compositional gradient is a continuous gradient distribution of the concentrations of elements such as Si, O, and N from the cell center to the cell boundary, with significant enrichment at the boundary.

[0017] A method for preparing micron-sized low-loss soft magnetic alloy powder, the method comprising the following steps: (1) Melting an iron-based alloy containing Si and controllable amounts of O and N elements, wherein the Si content is 2.0-6.5 wt%, the O content is 0.1-0.5 wt%, and the N content is 0.05-0.3 wt%; wherein O is introduced by adding Fe2O3 or SiO2, and N is introduced by nitriding the melt or adding nitrides. Melting is carried out under vacuum or a controlled atmosphere to ensure that the alloying elements and trace amounts of O and N are uniformly dissolved in the melt.

[0018] (2) The alloy melt is superheated to 1500-1650℃, and a tightly coupled annular nozzle is used. Then, nitrogen or argon atomizing gas with a pressure of not less than 5MPa is used for ultra-high speed gas atomization. The metal liquid is broken into extremely fine droplets by the extremely high gas kinetic energy, and the droplets are provided with an extremely high initial cooling rate (>105℃ / s).

[0019] (3) In an atmosphere containing nitrogen or a mixture of nitrogen and trace amounts of oxygen, the cooling process of the atomized droplets is controlled by precisely controlling the atmosphere inside the atomization tower (such as slightly positive pressure N2 or N2-Ar mixture containing trace amounts of O2) and the flight distance, wherein the cooling rate of the atomized droplets is greater than 10. 5 The extremely rapid cooling rate of ℃ / s inhibits the precipitation of equilibrium phases (such as coarse silicides), forcing solute elements (Si, O, N) to be expelled to the final solidified grain boundary region at the end of the rapid solidification process. Under specific composition and cooling conditions, these enriched elements react in situ at the cell boundaries, generating nanoscale amorphous or nanocrystalline films such as SiO2 and Si3N4, which then self-assemble to form the aforementioned three-dimensional continuous insulating network. This causes the alloy melt to solidify rapidly and precipitate cellular structures and grain boundary insulating film phases in situ, ultimately producing micron-sized low-loss soft magnetic alloy powder with gradient composition and cellular structure.

[0020] Example 1 A micrometer-scale low-loss soft magnetic alloy powder is disclosed. The powder is composed of micrometer-scale metal cells, with a continuous network of non-magnetic insulating film phases distributed at the boundaries of these cells, thus forming a three-dimensional insulating network within the powder. The metal cells are composed of Fe-Si solid solution with a cell size of 1-2 μm. The non-magnetic insulating film phase has a thickness of 10-20 nm and is composed of SiO2. The soft magnetic alloy powder has a sphericity of 0.91 and a particle size range of 15-50 μm.

[0021] A micron-sized low-loss soft magnetic alloy powder and its preparation method, the method comprising the following steps: (1) Melting an iron-based alloy containing Si and controllable amounts of O and N elements in an argon atmosphere, wherein the Si content is 2.0 wt%, the O content is 0.5 wt%, and the N content is 0.2 wt%; (2) The alloy melt is superheated to 1600℃ and then introduced into the ultra-high speed gas atomization equipment. Then, high-purity argon gas with a pressure of 8MPa is used as the atomization medium for ultra-high speed gas atomization. The atomization tower is kept in a slightly positive pressure (~110kPa) argon atmosphere. (3) In an argon atmosphere, the cooling process of the atomized droplets is controlled, wherein the cooling rate of the atomized droplets is 2×10 5The temperature is increased by ℃ / s, which causes the alloy melt to solidify rapidly and precipitate cellular structures and grain boundary insulating film phases in situ, ultimately producing micron-sized low-loss soft magnetic alloy powder with gradient composition and cellular structure, with a particle size range of 15-50 μm.

[0022] Electron microscopy revealed that the powder was spherical with a sphericity of 0.91. Its interior consisted of cellular crystals approximately 1-2 μm in size, with continuous amorphous SiO2 films of about 10-20 nm thickness at the cell boundaries. The powder resistivity reached 10⁻⁶. 5 On the order of Ω·cm.

[0023] Example 2 A micron-scale low-loss soft magnetic alloy powder is disclosed. The powder is composed of micron-sized metal cells, with a continuous network of non-magnetic insulating film phases distributed at the cell boundaries, forming a three-dimensional insulating network within the powder. The metal cells are Fe-Si or Fe-Ni solid solutions with a cell size of 2-3 μm. The non-magnetic insulating film phase has a thickness of 35-50 nm and is a composite of SiO2 and Si3N4. The soft magnetic alloy powder has a sphericity of 0.95 and a particle size range of 100-150 μm.

[0024] A micron-sized low-loss soft magnetic alloy powder and its preparation method, the method comprising the following steps: (1) Smelting an iron-based alloy containing Si and controllable amounts of O and N elements, wherein the Si content is 6.5 wt%, the Ni content is 30 wt%, the O content is 0.3 wt%, and the N content is 0.3 wt%; (2) The alloy melt is superheated to 1500℃ and then introduced into the ultra-high speed gas atomization equipment. Then, high-purity nitrogen gas with a pressure of 6MPa is used as the atomization medium for ultra-high speed gas atomization. The atomization tower is kept in a slightly positive pressure (~110kPa) nitrogen atmosphere. (3) In a mixed atmosphere of nitrogen and trace amounts of oxygen, the cooling process of the atomized droplets is controlled, wherein the cooling rate of the atomized droplets is 1.5 × 10⁻⁶. 5 The temperature is increased by ℃ / s, which causes the alloy melt to solidify rapidly and precipitate cellular structures and grain boundary insulating film phases in situ, ultimately producing micron-sized low-loss soft magnetic alloy powder with gradient composition and cellular structure, with a particle size range of 100-150 μm.

[0025] Electron microscopy revealed that the powder was spherical with a sphericity of 0.95. Its interior consisted of cellular crystals approximately 2-3 μm in size, with continuous amorphous SiO2 and Si3N4 composite films of approximately 35-50 nm thickness at the cell boundaries. The powder resistivity reached 10⁻¹⁰. 4 On the order of Ω·cm.

[0026] Example 3 A micron-sized low-loss soft magnetic alloy powder is disclosed. The powder is composed of micron-sized metal cells, with a continuous network of non-magnetic insulating film phases distributed at the boundaries of these cells, thus forming a three-dimensional insulating network within the powder. The metal cells are composed of Fe-Si or Fe-Si-Al solid solutions, with a cell size of 0.5-1 μm. The non-magnetic insulating film phase has a thickness of 5-15 nm and is composed of SiO2 or SiO2. x N y The composite of the soft magnetic alloy powder has a sphericity of 0.92 and a particle size range of 5-20 μm.

[0027] A micron-sized low-loss soft magnetic alloy powder and its preparation method, the method comprising the following steps: (1) Smelting an iron-based alloy containing Si, Al, and controllable amounts of O and N elements, wherein the Si content is 4.0 wt%, the Al content is 4.0 wt%, the O content is 0.1 wt%, and the N content is 0.05 wt%; (2) The alloy melt is superheated to 1650°C and then introduced into an ultra-high speed gas atomization device. Then, high-purity nitrogen gas with a pressure of 7.5 MPa is used as the atomization medium for ultra-high speed gas atomization. A slightly positive pressure (~110 kPa) nitrogen atmosphere is maintained in the atomization tower. (3) In a nitrogen atmosphere, control the cooling process of the atomized droplets, wherein the cooling rate of the atomized droplets is 3×10 5 The temperature is increased by ℃ / s, which causes the alloy melt to solidify rapidly and precipitate cellular structures and grain boundary insulating film phases in situ, ultimately producing micron-sized low-loss soft magnetic alloy powder with gradient composition and cellular structure, with a particle size range of 5-20 μm.

[0028] Electron microscopy revealed that the powder was spherical with a sphericity of 0.92. Its interior consisted of cellular crystals approximately 0.5-1 μm in size, with continuous amorphous SiO2 and SiO2 layers of approximately 5-15 nm thickness at the crystal boundaries. x N y Composite thin film. Powder resistivity test reaches 10. 5 On the order of Ω·cm.

[0029] Example 4 A micrometer-scale low-loss soft magnetic alloy powder is disclosed. The powder is composed of micrometer-scale metal cells, with a continuous network of non-magnetic insulating film phases distributed at the boundaries of these cells, thus forming a three-dimensional insulating network within the powder. The metal cells are composed of Fe-Si-Al solid solution with a cell size of 1.5-3 μm. The non-magnetic insulating film phase has a thickness of 20-40 nm and is composed of SiO₂. x Ny The sphericity of the soft magnetic alloy powder is 0.93, and the particle size ranges from 80 to 120 μm.

[0030] A micron-sized low-loss soft magnetic alloy powder and its preparation method, the method comprising the following steps: (1) Smelting an iron-based alloy containing Si and controllable amounts of O and N elements, wherein the Si content is 5.0 wt%, the Al content is 0.5 wt%, the O content is 0.4 wt%, and the N content is 0.15 wt%; (2) The alloy melt is superheated to 1600℃ and then introduced into the ultra-high speed gas atomization equipment. Then, high-purity nitrogen gas with a pressure of 5.5MPa is used as the atomization medium for ultra-high speed gas atomization. The atomization tower is kept in a slightly positive pressure (~110kPa) nitrogen atmosphere. (3) In a mixed atmosphere of nitrogen and trace amounts of oxygen, the cooling process of the atomized droplets is controlled, wherein the cooling rate of the atomized droplets is 1.8 × 10⁻⁶. 5 The temperature is increased by ℃ / s, which causes the alloy melt to solidify rapidly and precipitate cellular structures and grain boundary insulating film phases in situ, ultimately producing micron-sized low-loss soft magnetic alloy powder with gradient composition and cellular structure, with a particle size range of 80-120 μm.

[0031] Electron microscopy revealed that the powder was spherical with a sphericity of 0.93. Its interior consisted of cellular crystals approximately 1.5-3 μm in size, with continuous amorphous SiO₂ layers of approximately 20-40 nm thickness at the crystal boundaries. x N y Thin film. Powder resistivity test reaches 10. 5 On the order of Ω·cm.

[0032] The above description, in conjunction with specific / preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the inventive concept, and all such substitutions or modifications should be considered within the scope of protection of the present invention.

Claims

1. A micron-sized low-loss soft magnetic alloy powder, characterized in that, The powder is composed of micron-scale metal cells, and at the boundaries of the cells, there is a continuous network of non-magnetic insulating film phases, thus forming a three-dimensional insulating network inside the powder with obvious compositional gradient characteristics.

2. The micron-sized low-loss soft magnetic alloy powder as described in claim 1, characterized in that, The metal cell is composed of Fe-Si, Fe-Ni, or Fe-Si-Al solid solution, with a cell size of 0.5-3 μm; wherein the Fe-Si alloy contains 2.0-6.5 wt% Si, the Fe-Ni alloy contains 30-50 wt% Ni, and the Fe-Si-Al solid solution contains 2.0-6.5 wt% Si and 0.5-4.0 wt% Al.

3. The micron-sized low-loss soft magnetic alloy powder as described in claim 1, characterized in that, The thickness of the non-magnetic insulating thin film phase is 5-50 nm, and its composition is SiO2, Si3N4, and SiO2. x N y A combination of one or more of them.

4. The micron-sized low-loss soft magnetic alloy powder as described in any one of claims 1-3, characterized in that, The compositional gradient is a continuous gradient distribution of the concentrations of Si, O, and N elements from the cell center to the cell boundary, with significant enrichment at the boundary.

5. The micron-sized low-loss soft magnetic alloy powder as described in any one of claims 4, characterized in that, The soft magnetic alloy powder is spherical or near-spherical, with a sphericity greater than 0.9 and a particle size range of 5-150 μm.

6. A method for preparing micron-sized low-loss soft magnetic alloy powder as described in any one of claims 1-5, characterized in that, The gas atomization method is adopted and implemented through the following steps: a) Melting an iron-based alloy containing Si and controllable amounts of O and N elements, wherein the Si content is 2.0-6.5 wt%, the O content is 0.1-0.5 wt%, and the N content is 0.05-0.3 wt%; b) Superheating the alloy melt to 1500-1650℃, and then performing ultra-high-speed gas atomization using an atomizing gas with a pressure of not less than 5 MPa; c) In an atmosphere containing nitrogen or a mixture of nitrogen and trace amounts of oxygen, controlling the cooling process of the atomized droplets to cause rapid solidification and in-situ precipitation of cellular structures and grain boundary insulating film phases.

7. The method for preparing micron-sized low-loss soft magnetic alloy powder as described in claim 6, characterized in that, In step b), the atomizing gas is nitrogen or argon.

8. The method for preparing micron-sized low-loss soft magnetic alloy powder according to claim 6, characterized in that, In step c), the cooling rate of the atomized droplets is greater than 10. 5 ℃ / s.