SmFeN spherical powder, preparation method and use thereof

Abstract

This invention relates to SmFeN spherical powder, its preparation method, and its applications. The preparation method of the SmFeN spherical powder of this invention creatively employs the linkage between plasma spheroidization and nitriding, and utilizes a three-stage nitriding process to obtain SmFeN spherical powder with high flowability and high orientation. The nitrogen content fluctuation in the SmFeN spherical powder of this invention is controlled within ±0.2wt%, far superior to traditional processes; the coercivity of the SmFeN spherical powder is ≥20kOe, Hall flow rate ≤30s / 50g, sphericity ≥0.8, and orientation ≥85%; nitrogen is uniformly distributed within the SmFeN spherical powder particles, exhibiting both excellent magnetic properties and molding and processing performance, fully meeting the performance requirements of high-end applications such as 3D printing and injection molding of bonded magnets.

Description

Technical Field

[0001] This invention relates to the field of magnetic powder materials technology, specifically to a SmFeN spherical powder, its preparation method, and its applications. Background Technology

[0002] Traditional SmFeN (SmFeN) powder preparation employs mechanical alloying, which results in irregular powder shapes with poor sphericity and numerous irregular edges. This not only makes complete coating of acidic films difficult but also allows the sharp edges to easily puncture the films, leading to easy oxidation and negatively impacting subsequent molding processes such as injection molding and compression molding. Furthermore, it severely interferes with the consistency of magnetic properties. Simultaneously, traditional solid-state nitriding is constrained by factors such as pressure, temperature, and powder particle size. Pressure has limited effect on promoting nitriding of SmFeN alloys in the solid state; even with increased pressure, the nitriding rate remains low. Small powder particles are prone to oxidation, negatively affecting the nitriding effect and the final product's magnetic properties. These factors combined result in lengthy and ineffective nitriding processes for SmFeN alloys, significantly hindering the industrial production of SmFeN. The traditional chemical coprecipitation method for preparing samarium iron nitrogen (SmFeN) powder can control the powder morphology to a certain extent, but the process is extremely complicated and the stable and accurate control of samarium content is very difficult, making large-scale production extremely challenging. Summary of the Invention

[0003] Addressing the current technical challenges in the preparation of samarium iron nitride (SmFeN) powder, this invention develops a spherical SmFeN powder, its preparation method, and its applications. The SmFeN spherical powder preparation method of this invention utilizes plasma spheroidization technology to transform irregularly shaped SmFeN powder into spherical shapes, significantly improving the sphericity of the powder, effectively enhancing its flowability and packing density, making it more suitable for complex shape forming processes. Simultaneously, this invention utilizes plasma spheroidization technology to precisely control the particle size and morphology of the powder, reducing the generation of sharp corners, enhancing the coating effect, reducing the risk of powder oxidation, and improving the consistency of magnetic properties. In the nitriding stage, the SmFeN spherical powder preparation method of this invention improves nitriding efficiency and uniformity through process improvements, reduces production costs, and promotes the large-scale application of SmFeN materials in the industrial field. The SmFeN spherical powder obtained by the SmFeN spherical powder preparation method of this invention can meet the high-performance requirements of high-end applications.

[0004] On one hand, the present invention provides a method for preparing SmFeN spherical powder, which adopts a plasma spheroidization combined with a fluidized bed three-stage nitriding process, including: step S1: plasma spheroidization to prepare high sphericity Sm-Fe powder; step S2: sieving to obtain a first Sm-Fe raw material powder; step S3: vacuum degassing to obtain a second Sm-Fe raw material powder; and step S4: fluidized bed three-stage nitriding to obtain SmFeN spherical powder.

[0005] The present invention provides a method for preparing SmFeN spherical powder, which specifically includes the following steps: Step S1: Mechanical alloying is used to prepare primary Sm-Fe alloy powder with irregular morphology. The primary Sm-Fe alloy powder is fed into a high-temperature plasma torch at a powder feeding rate of 5~20 g / min for plasma spheroidization.

[0006] The plasma spheroidization process includes: forming spherical droplets from the primary Sm-Fe alloy powder under the action of high-energy plasma at a temperature of 5000~10000K; the spherical droplets entering the cooling zone and being rapidly cooled by argon gas to solidify and form Sm-Fe powder with high sphericity; the argon gas volume concentration in the cooling zone is 100%, and the purity of the argon gas is ≥99.999%.

[0007] Step S2: The high sphericity Sm-Fe powder is sieved to obtain the first Sm-Fe raw material powder, the particle size distribution range of the first Sm-Fe raw material powder is 5~50μm, and the particle size span is ≤3 times.

[0008] Step S3: The first Sm-Fe raw material powder is degassed under vacuum to obtain the second Sm-Fe raw material powder; the vacuum degree of the vacuum degasing process is ≤1Pa and the temperature is 300~400℃.

[0009] Step S4: The second Sm-Fe raw material powder is placed in a fluidized bed nitriding furnace and subjected to a three-stage nitriding process to obtain high-fluidity and high-orientation SmFeN spherical powder; the three-stage nitriding process includes three stages in sequence: low-temperature pre-nitriding stage, medium-temperature main nitriding stage, and high-temperature homogenization stage.

[0010] The low-temperature pre-permeation stage involves maintaining the temperature at 200-300℃ and nitrogen partial pressure at 0.1-0.3MPa for 2-4 hours to allow nitrogen atoms to be uniformly adsorbed onto the surface of the second Sm-Fe raw material powder.

[0011] The intermediate temperature main diffusion stage involves heating to 450~500℃, setting the nitrogen partial pressure to 0.5~1.0MPa, and holding the temperature for 6~10h to allow nitrogen atoms to diffuse into the particles of the second Sm-Fe raw material powder.

[0012] The high-temperature homogenization stage involves maintaining the temperature at 500-550℃ for 2-3 hours under a mixed atmosphere of nitrogen and argon to eliminate the nitrogen concentration gradient inside and outside the particles, thereby obtaining highly fluid and highly oriented SmFeN spherical powder; the volume ratio of nitrogen to argon is 1:1.

[0013] In this invention, Sm2Fe 17 N3 is the basic and core phase of the SmFeN powder system. The lower limit of the high-temperature homogenization stage is 500℃, ensuring that nitrogen atoms still possess sufficient diffusion kinetic energy to migrate rapidly within the powder particles, effectively eliminating the nitrogen-rich surface and nitrogen-poor core concentration gradient formed during the intermediate-temperature main infiltration stage, thus achieving uniform nitriding. The upper limit of the temperature is 550℃: This does not exceed the limits for Sm2Fe 17 The critical temperature threshold for the thermal decomposition of N3 (Sm2Fe) 17 The Curie temperature of N3 is approximately 470℃. The thermodynamic driving force for the decomposition reaction is extremely low at temperatures between 500 and 550℃, making the reaction rate almost negligible. This avoids the possibility of Sm2Fe decomposition due to excessively high temperatures. 17 The N3 bonds break, preventing the precipitation of SmN and α-Fe phases. Simultaneously, the high-temperature homogenization stage is a post-nitriding homogenization process, where the powder has already completed the formation of the main Sm2Fe phase. 17 →Sm2Fe 17 N3 conversion, no unreacted Sm2Fe 17 The continuous nitriding of the parent phase is exothermic, and the system does not experience additional temperature rise, further avoiding decomposition caused by local overheating.

[0014] In this invention, the atmosphere system during the high-temperature homogenization stage is designed as a nitrogen:argon mixture of 1:1 to maintain a reasonable nitrogen potential and suppress denitrification. (Sm2Fe) 17 The high-temperature decomposition of N3 is essentially the desorption and loss of nitrogen atoms, which leads to the collapse of the crystal structure and the precipitation of impurity phases. This invention uses a nitrogen:argon mixture atmosphere of 1:1, rather than pure nitrogen or vacuum, to block the decomposition path from the perspective of nitrogen potential control: 1) Retaining 50% volume fraction of nitrogen: to provide a stable nitrogen potential for the system and suppress Sm2Fe 17 Nitrogen atoms in the N3 lattice desorb at high temperatures, thermodynamically preventing the decomposition reaction Sm2Fe. 17 The forward reaction proceeds from N3 to 2SmN + 17Fe; 2) Introduce 50% volume fraction of argon gas: dilute the nitrogen atmosphere, avoid excessive nitriding under high nitrogen potential, and at the same time, argon gas, as an inert gas, can achieve uniform heat conduction, prevent the formation of local hot spots in the furnace, and avoid powder particles from being decomposed due to local overheating.

[0015] In this invention, the holding time during the high-temperature homogenization stage is strictly controlled to be short, only 2-3 hours, to avoid heat accumulation. Simultaneously, strictly limiting the holding time during the high-temperature homogenization stage to 2-3 hours mitigates the risk of decomposition from a kinetic perspective: Sm2Fe 17 The thermal decomposition of N3 is a time-dependent and slow process. Even in the range of 500~550℃, prolonged holding time will still lead to the slow desorption of nitrogen atoms and trigger phase decomposition. A holding time of 2~3h can satisfy the kinetic requirements of nitrogen atom diffusion to eliminate the concentration gradient, and also avoid the accumulation of heat in the powder in the high temperature range, thus inhibiting the occurrence and progress of the decomposition reaction from the perspective of reaction kinetics.

[0016] In this invention, the three-stage nitriding process utilizes a fluidized bed dynamic environment to enhance system homogeneity and further prevent decomposition. The high-temperature homogenization stage is conducted in a fluidized bed nitriding furnace, where the powder remains suspended under gas disturbance, achieving two major auxiliary decomposition prevention effects: 1) Powder particles are in full contact with the mixed atmosphere, ensuring high uniformity of temperature and nitrogen potential for each particle, preventing localized high temperatures or uneven nitrogen potential caused by particle agglomeration; 2) The fluidized bed has higher dynamic heat exchange efficiency, effectively removing the trace heat effect of the particles and preventing heat accumulation between particles, ensuring the entire system remains stable within the set range of 500-550℃ without localized overheating. The high-temperature homogenization stage of this invention is not simply high-temperature holding, but rather achieves "efficient nitrogen atom diffusion homogenization" and "Sm2Fe" through a four-fold process design: a critical narrow temperature range of 500-550℃, nitrogen potential control using a 1:1 nitrogen-argon ratio, short-time holding for 2-3 hours, and a fluidized bed dynamic homogenization environment. 17 The dual objectives of "stabilizing the N3 phase and preventing decomposition" were cleverly achieved, thus solving the problem of Sm2Fe 17 There is a technical contradiction between the poor thermal stability of N3 and the requirement for high-temperature homogenization.

[0017] In this invention, particle size span refers to the ratio between particle size values ​​represented by a specific percentile in the particle size distribution curve. The particle size span formula in this invention is: Span = (D90 − D10) / D50; where: D10: 10% of the particles in the cumulative distribution are smaller than this particle size value (i.e., the "lower limit particle size"), D50: 50% of the particles in the cumulative distribution are smaller than this particle size value, also known as the median particle size, which is the central tendency of the distribution, and D90: 90% of the particles in the cumulative distribution are smaller than this particle size value (i.e., the "upper limit particle size").

[0018] Furthermore, in the preparation method of SmFeN spherical powder of the present invention, in step S1, the morphological characteristics of the primary Sm-Fe alloy powder are irregular spherical with sharp edges, and the particle size ranges from 60 to 80 μm.

[0019] In this invention, during the plasma spheroidization process, at extremely high temperatures of 5000~10000K, the plasma solidifies rapidly at a rate >100K / s within the cavity. The cooling rate far exceeds the atomic diffusion rate of Sm, Fe, and their intermediate phases. This can lead to the liquid Sm-Fe alloy potentially not having enough time to crystallize if the cooling rate is fast enough, forming a metastable amorphous phase (amorphous structure); or forming a quasi-crystalline phase (a structure with long-range order but no translational symmetry). However, the probability of this phase transformation is low and it may only occur in extremely fine powders or under specific Sm / Fe ratios. Therefore, the particle size range of the primary Sm-Fe alloy powder must be limited to 60~80μm.

[0020] Furthermore, in the method for preparing SmFeN spherical powder according to the present invention, in step S1, the cooling rate is 10³~10⁻¹⁰. 4 K / s, the initial temperature of argon is 25℃, and the gas flow rate is 10~30L / min.

[0021] Furthermore, in the method for preparing SmFeN spherical powder according to the present invention, in step S1, the power range of the high-energy plasma is 30~60kW, and the oxygen content in the cavity of the high-temperature plasma torch is less than 100ppm.

[0022] Furthermore, in the method for preparing SmFeN spherical powder according to the present invention, the nitrogen content fluctuation in the SmFeN spherical powder is controlled within ±0.2wt%.

[0023] Furthermore, in the preparation method of SmFeN spherical powder of the present invention, in step S4, the nitrogen volume concentration in the low-temperature pre-percolation stage and the medium-temperature main percolation stage is 100%, and the nitrogen volume concentration in the high-temperature homogenization stage is 50%.

[0024] In this invention, a 100% nitrogen atmosphere is used in both the low-temperature pre-infiltration stage and the medium-temperature main infiltration stage to maximize the adsorption and diffusion efficiency of nitrogen atoms and ensure sufficient nitriding. In the high-temperature homogenization stage, an equal volume of argon gas is introduced to dilute the nitrogen. This maintains a certain nitrogen potential to prevent nitrogen atom desorption and achieves uniform heat conduction through the mixed atmosphere, more efficiently eliminating the nitrogen concentration gradient inside and outside the particles, while also avoiding Sm2Fe. 17 Risk of N3 high-temperature decomposition. If the nitriding temperature is too low, the time is insufficient, or the N atmosphere concentration is inadequate, Sm2Fe... 17 It cannot be completely converted to Sm2Fe 17 N3, residual Sm2Fe 17 The parent phase becomes a "soft magnetic region," which makes the domain walls easy to move and reduces coercivity. At the same time, it may be accompanied by the residue of SmFe2 phase (low coercivity intermetallic compound), which further dilutes the proportion of the main phase. This invention completely overcomes this phenomenon of incomplete nitriding.

[0025] Furthermore, in the preparation method of SmFeN spherical powder of the present invention, the SmFeN spherical powder has the following characteristics: coercivity ≥20kOe and Hall flow rate ≤30s / 50g.

[0026] Furthermore, in the method for preparing SmFeN spherical powder according to the present invention, the sphericity of the SmFeN spherical powder is ≥0.8 and the orientation degree is ≥85%.

[0027] On the other hand, the present invention also provides a SmFeN spherical powder, wherein the SmFeN spherical powder is a high-flowability, high-orientation SmFeN spherical powder prepared by any of the preparation methods described above.

[0028] In another aspect, the present invention also provides an application of SmFeN spherical powder, wherein the SmFeN spherical powder is a high-flowability, high-orientation SmFeN spherical powder prepared by any of the preparation methods described above, or the SmFeN spherical powder is the SmFeN spherical powder described above; the SmFeN spherical powder is used for 3D printing, or for injection molding of bonded magnets.

[0029] The beneficial effects of this invention are: The present invention innovatively employs a combined approach of plasma spheroidization and nitriding to prepare SmFeN spherical powder, utilizing a three-stage nitriding process to obtain highly fluid and highly oriented SmFeN spherical powder. The nitrogen content fluctuation in the SmFeN spherical powder of the present invention is controlled within ±0.2wt%, far superior to the ±0.5wt% of traditional processes. The SmFeN spherical powder of the present invention exhibits a coercivity ≥20kOe, Hall flow rate ≤30s / 50g, sphericity ≥0.8, and orientation ≥85%. The spherical powder obtained by plasma spheroidization of the present invention has a consistent specific surface area, providing conditions for symmetrical diffusion of nitrogen atoms; the uniformity of nitriding contributes to the consistency of magnetic properties, forming a closed-loop technology in the preparation method. High coercivity (≥20kOe): Uniform nitriding forms a complete SmFeN phase, inhibiting magnetic domain wall movement; High fluidity (Hall flow rate ≤30s / 50g): Improved sphericity significantly enhances powder filling characteristics; High orientation (≥85%): Spherical powder is more easily oriented in a magnetic field.

[0030] This invention represents a revolutionary application of plasma spheroidization technology, replacing traditional mechanical alloying. It utilizes a plasma torch (5000-10000K high temperature) to melt and spheroidize irregular Sm-Fe alloy powder, completely overcoming the fundamental defects of mechanically alloyed powders, such as sharp edges and poor sphericity (sphericity <0.7). This is achieved through a plasma power of 30-60kW, a powder feed rate of 5-20g / min, and a plasma density of 10³-10... 4A cooling rate of K / s and high-purity argon protection enable the preparation of spherical powders with a sphericity ≥0.8 and a bulk density of 3.5-4.2 g / cm³. High-temperature melting eliminates microcracks and oxide layers on the powder surface, forming a smooth substrate that provides an ideal interface for subsequent nitriding and coating. Simultaneously, plasma spheroidization eliminates sharp edges, solving the problem of coating failure in acidic films (where sharp corners puncture the film, leading to oxidation in existing technologies).

[0031] The segmented temperature control and fluidized bed dynamic nitriding of the three-stage nitriding process of this invention significantly shortens the nitriding time from tens of hours to 10-15 hours and improves uniformity; the high-temperature homogenization stage eliminates the concentration gradient; the dynamic fluidized bed nitriding device suspends the powder through gas disturbance, solving the problem of "core nitrogen deficiency" in traditional static nitriding and ensuring that the nitriding depth of each powder is consistent. Attached Figure Description

[0032] Figure 1 This is a microscopic morphology diagram of the SmFeN spherical powder in Example 1 of the present invention; Figure 2 This is a microscopic morphology diagram of the SmFeN spherical powder in Example 2 of the present invention; Figure 3 This is a microscopic morphology image of the SmFeN spherical powder in Example 3 of the present invention; Figure 4 This is a microstructure diagram of the SmFeN magnetic powder in Comparative Example 1 of the present invention. Figure 5 This is a microstructure diagram of the SmFeN magnetic powder in Comparative Example 2 of the present invention; Figure 6 This is a microstructure diagram of the SmFeN magnetic powder in Comparative Example 3 of the present invention. Figure 7 This is a microstructure diagram of the SmFeN magnetic powder in Comparative Example 4 of the present invention. Figure 8 This is a microstructure diagram of the SmFeN magnetic powder in Comparative Example 5 of the present invention. Figure 9 This is a microstructure diagram of the SmFeN magnetic powder in Comparative Example 6 of the present invention. Figure 10 The XRD pattern of SmFeN magnetic powder in Comparative Example 1 of this invention; Figure 11 The image shows the XRD pattern of the SmFeN magnetic powder in Comparative Example 6 of this invention. Detailed Implementation

[0033] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments are now described in detail with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the detailed embodiments, conventional conditions or conditions provided by the manufacturer shall apply.

[0034] In the following description, when referring to the accompanying drawings, the same numbers in different drawings denote the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. Specific Implementation Method 1

[0035] The present invention discloses a method for preparing SmFeN spherical powder, which employs a plasma spheroidization combined with a fluidized bed three-stage nitriding process, comprising: step S1: plasma spheroidization to prepare Sm-Fe powder with high sphericity; step S2: sieving to obtain a first Sm-Fe raw material powder; step S3: vacuum degassing to obtain a second Sm-Fe raw material powder; and step S4: fluidized bed three-stage nitriding to obtain SmFeN spherical powder.

[0036] In some embodiments, a method for preparing SmFeN spherical powder according to the present invention specifically includes the following steps: Step S1: Mechanical alloying is used to prepare primary Sm-Fe alloy powder with irregular morphology. The primary Sm-Fe alloy powder is fed into a high-temperature plasma torch at a powder feeding rate of 5~20 g / min for plasma spheroidization. The aforementioned plasma spheroidization process includes: forming spherical droplets from the primary Sm-Fe alloy powder under the action of high-energy plasma at a temperature of 5000~10000K; the spherical droplets entering a cooling zone and being rapidly cooled by argon gas to solidify and form Sm-Fe powder with high sphericity; the argon gas volume concentration in the cooling zone is 100%, and the argon gas purity is ≥99.999%; Step S2: The above high sphericity Sm-Fe powder is sieved to obtain the first Sm-Fe raw material powder. The particle size distribution range of the first Sm-Fe raw material powder is 5~50μm and the particle size span is ≤3 times. Step S3: The first Sm-Fe raw material powder is subjected to vacuum degassing to obtain the second Sm-Fe raw material powder; the vacuum degree of the above vacuum degassing process is ≤1Pa and the temperature is 300~400℃; Step S4: The above-mentioned second Sm-Fe raw material powder is placed in a fluidized bed nitriding furnace and subjected to a three-stage nitriding process to obtain high-fluidity and high-orientation SmFeN spherical powder; the above-mentioned three-stage nitriding process includes three stages in sequence: low-temperature pre-nitriding stage, medium-temperature main nitriding stage, and high-temperature homogenization stage.

[0037] In some embodiments, the above-mentioned low-temperature pre-permeation stage involves maintaining the temperature at 200~300℃ and nitrogen partial pressure at 0.1~0.3MPa for 2~4 hours to allow nitrogen atoms to be uniformly adsorbed on the surface of the second Sm-Fe raw material powder.

[0038] In some embodiments, the above-mentioned medium-temperature main infiltration stage involves heating to 450~500℃, setting the nitrogen partial pressure to 0.5~1.0MPa, and holding the temperature for 6~10h to allow nitrogen atoms to diffuse into the particles of the second Sm-Fe raw material powder.

[0039] In some embodiments, the above-mentioned high-temperature homogenization stage involves maintaining the temperature at 500~550℃ for 2~3 hours under a mixed atmosphere of nitrogen and argon to eliminate the nitrogen concentration gradient inside and outside the particles, thereby obtaining highly fluid and highly oriented SmFeN spherical powder; the volume ratio of nitrogen to argon in the mixed atmosphere is 1:1.

[0040] In some embodiments, in step S1 above, the morphological characteristics of the primary Sm-Fe alloy powder are irregular spherical shapes with angular edges, and the particle size ranges from 60 to 80 μm.

[0041] In some embodiments, during step S1 and the rapid cooling process described above, the cooling rate is 10³~10 4 K / s, the initial temperature of argon is 25℃, and the gas flow rate is 10~30L / min.

[0042] In some embodiments, in step S1 above, the power range of the high-energy plasma is 30~60kW, and the oxygen content inside the cavity of the high-temperature plasma torch is less than 100ppm.

[0043] In some embodiments, the nitrogen content fluctuation in the above-mentioned SmFeN spherical powder is controlled within ±0.2wt%.

[0044] In some embodiments, in step S4 above, the nitrogen volume concentration is 100% in both the low-temperature pre-percolation stage and the medium-temperature main percolation stage, and the nitrogen volume concentration is 50% in the high-temperature homogenization stage.

[0045] In some embodiments, the coercivity of the above-mentioned SmFeN spherical powder is ≥20kOe and the Hall flow rate is ≤30s / 50g.

[0046] In some embodiments, the sphericity of the above-mentioned SmFeN spherical powder is ≥0.8 and the orientation degree is ≥85%. Specific Implementation Method Two

[0047] The present invention provides a SmFeN spherical powder, wherein the SmFeN spherical powder is a highly fluid and highly oriented SmFeN spherical powder prepared by any of the preparation methods in the first specific embodiment described above. Specific Implementation Method 3

[0048] The present invention discloses an application of SmFeN spherical powder, wherein the SmFeN spherical powder is a high-flowability, high-orientation SmFeN spherical powder prepared by any of the preparation methods in Embodiment 1 above, or the SmFeN spherical powder is the SmFeN spherical powder in Embodiment 2; the SmFeN spherical powder is used for 3D printing, or for injection molding of bonded magnets.

[0049] The present invention will be further described in detail below with reference to specific embodiments.

[0050] Example 1: The present invention provides a method for preparing SmFeN spherical powder, comprising the following steps: Step S1: Mechanical alloying was used to prepare primary Sm-Fe alloy powder with irregular morphology. The primary Sm-Fe alloy powder was fed into a high-temperature plasma torch at a feed rate of 5~20 g / min for plasma spheroidization. The morphology of the primary Sm-Fe alloy powder was characterized by irregular spherical shapes with angular edges, and the particle size ranged from 60 to 80 μm. During rapid cooling, the cooling rate was 10³~10⁻¹⁰. 4 The initial temperature of argon gas is 25℃, and the gas flow rate is 10~30L / min; the power range of the high-energy plasma is 30~60kW, and the oxygen content in the cavity of the high-temperature plasma torch is less than 100ppm; the plasma spheroidization process includes: forming spherical droplets from primary Sm-Fe alloy powder under the action of high-energy plasma at a temperature of 5000~10000K; the spherical droplets enter the cooling zone and are rapidly cooled by argon gas, solidifying to form Sm-Fe powder with high sphericity; the volume concentration of argon gas in the cooling zone is 100%, and the purity of argon gas is ≥99.999%.

[0051] Step S2: The high sphericity Sm-Fe powder is sieved to obtain the first Sm-Fe raw material powder. The particle size distribution range of the first Sm-Fe raw material powder is 5~50μm and the particle size span is ≤3 times.

[0052] Step S3: The first Sm-Fe raw material powder is degassed under vacuum to obtain the second Sm-Fe raw material powder; the vacuum degree of the vacuum degassing process is ≤1Pa and the temperature is 300~400℃.

[0053] Step S4: The second Sm-Fe raw material powder is placed in a fluidized bed nitriding furnace and subjected to a three-stage nitriding process to obtain high-flowability, high-orientation SmFeN spherical powder. The three-stage nitriding process includes three stages: low-temperature pre-nitriding stage, medium-temperature main nitriding stage, and high-temperature homogenization stage. The nitrogen volume concentration in the low-temperature pre-nitriding stage and the medium-temperature main nitriding stage is 100%, and the nitrogen volume concentration in the high-temperature homogenization stage is 50%. Low-temperature pre-permeation stage: The temperature is kept at 200~300℃ and the nitrogen partial pressure is 0.1~0.3MPa for 2~4h to allow nitrogen atoms to be uniformly adsorbed on the surface of the second Sm-Fe raw material powder; Medium-temperature main infiltration stage: heat up to 450~500℃, nitrogen partial pressure is 0.5~1.0MPa, and keep warm for 6~10h to allow nitrogen atoms to diffuse into the particles of the second Sm-Fe raw material powder; High-temperature homogenization stage: The temperature is maintained at 500~550℃ for 2~3h under a mixed atmosphere of nitrogen and argon to eliminate the nitrogen concentration gradient inside and outside the particles, and obtain SmFeN spherical powder with high fluidity and high orientation. The volume ratio of nitrogen to argon in the mixed atmosphere is 1:1.

[0054] The highly fluid and highly oriented SmFeN spherical powder prepared in Example 1 exhibits excellent magnetic properties: (BH)max = 41.55, Br = 14.12, Hcj = 11.01, and has the characteristic microstructure of spherical powder. Figure 1 As shown, the powder exhibits good sphericity, exceeding 0.8 (measured using a laser particle size analyzer combined with image analysis), and an orientation degree ≥85%, eliminating the sharp edges and irregular morphology of mechanically alloyed powders. The nitrogen content fluctuation in the SmFeN spherical powder is controlled within ±0.2wt%, and the coercivity of the SmFeN spherical powder is ≥20kOe, the Hall flow rate is ≤30s / 50g, and the sphericity of the SmFeN spherical powder is ≥0.8.

[0055] Example 2: In this embodiment 2, the plasma spheroidization + fluidized bed three-stage nitriding process of the present invention is used to prepare highly fluid and highly oriented SmFeN spherical powder. The specific steps are as follows: Step S1: Plasma spheroidization to prepare high sphericity Sm-Fe powder Primary Sm-Fe alloy powder with irregular morphology, sharp edges, and a particle size of 60 μm, prepared by mechanical alloying, was used as raw material. Primary Sm-Fe alloy powder was fed into a high-temperature plasma torch at a powder feeding rate of 10 g / min. The plasma power was set to 45 kW, the high-energy plasma temperature inside the torch was controlled at 8000 K, and the oxygen content inside the cavity was controlled at 80 ppm. The molten spherical droplets enter the cooling zone, where 99.999% pure argon is used as the cooling inert gas. The initial temperature of the argon is 25℃, the flow rate is 20L / min, and the cooling rate is controlled at 5×10³K / s. After rapid cooling and solidification, high sphericity Sm-Fe powder is obtained, with argon protection throughout the process.

[0056] Step S2: Sieve to obtain the first Sm-Fe raw material powder High sphericity Sm-Fe powder was sieved through a precision classifying sieve to obtain the first Sm-Fe raw material powder with a particle size distribution of 10~40μm and a particle size span of 2.8 times. The powder was tested and found to have D10=10μm, D50=20μm, D90=46μm, and Span=(46-10) / 20=2.8.

[0057] Step S3: Vacuum degassing to obtain the second Sm-Fe raw material powder The first Sm-Fe raw material powder was placed in a vacuum degassing furnace and kept at a vacuum of 0.8 Pa and a temperature of 350 °C for 3 hours to remove the moisture and impurities adsorbed on the powder surface. After cooling, the second Sm-Fe raw material powder was obtained.

[0058] Step S4: Fluidized bed three-stage nitriding to obtain SmFeN spherical powder The second Sm-Fe raw material powder was placed into a fluidized bed nitriding furnace and subjected to a three-stage nitriding process: low-temperature pre-nitriding, medium-temperature main nitriding, and high-temperature homogenization. The specific parameters are as follows: Low-temperature pre-percolation stage: temperature 250℃, nitrogen partial pressure 0.2MPa, heat preservation for 3h, pure nitrogen atmosphere (nitrogen concentration 100%), to achieve uniform adsorption of nitrogen atoms; Medium-temperature main diffusion stage: heat up to 480℃, nitrogen partial pressure 0.8MPa, keep warm for 8h, pure nitrogen atmosphere (nitrogen concentration 100%), to achieve deep diffusion of nitrogen atoms into the particle interior; High-temperature homogenization stage: The temperature is raised to 520℃, and a mixed atmosphere of nitrogen and argon = 1:1 is introduced. The mixture is kept at this temperature for 2.5 hours to eliminate the nitrogen concentration gradient inside and outside the particles. After cooling in the furnace, high-flowability and high-orientation SmFeN spherical powder is obtained.

[0059] The SmFeN spherical powder prepared in Example 2 was subjected to performance testing. All testing methods adopted industry standards and the methods specified in this invention: laser particle size analyzer + image analysis for sphericity measurement, X-ray fluorescence spectrometry for nitrogen content measurement, magnetic property tester for magnetic properties measurement, Hall effect flowmeter for flowability measurement, and X-ray diffractometer for orientation / phase determination (XRD). The test results are shown in Table 1 below. Figure 2 As shown: Table 1 Performance parameters of SmFeN spherical powder prepared in Example 2

[0060] As can be seen from Table 1, the SmFeN spherical powder prepared in Example 2 is free of oxidized phases such as samarium oxide and iron oxide, and free of α-Fe low coercivity phase. Nitrogen is evenly distributed inside the powder particles, and it has both excellent magnetic properties and molding and processing performance, which fully meets the performance requirements of high-end applications such as 3D printing and injection molding of bonded magnets.

[0061] Example 3: In this embodiment 3, the plasma spheroidization + fluidized bed three-stage nitriding process of the present invention is used to prepare highly fluid and highly oriented SmFeN spherical powder. The specific steps are as follows: Step S1: Plasma spheroidization to prepare high sphericity Sm-Fe powder Primary Sm-Fe alloy powder with irregular morphology, sharp edges, and a particle size of 70 μm, prepared by mechanical alloying, was used as raw material. The powder was fed into a high-temperature plasma torch at a feed rate of 10 g / min, with the plasma power set at 45 kW. The high-energy plasma temperature inside the torch was controlled at 8000 K, and the oxygen content in the cavity was controlled at 80 ppm. The molten spherical droplets entered the cooling zone, where 99.999% pure argon was used as the cooling inert gas. The initial argon temperature was 25 °C, the flow rate was 25 L / min, and the cooling rate was 8 × 10³ K / s. After rapid cooling and solidification, high-sphericity Sm-Fe powder was obtained, with argon protection throughout the process.

[0062] Step S2: Sieve to obtain the first Sm-Fe raw material powder The high sphericity Sm-Fe powder was sieved through a precision classifying sieve to obtain the first Sm-Fe raw material powder with a particle size distribution of 15~45μm and a particle size span of 2.7 times. After testing, D10=15μm, D50=22μm, and D90=54μm, the Span=(54-15) / 22=2.7 was calculated according to the formula Span=(D90−D10) / D50.

[0063] Step S3: Vacuum degassing to obtain the second Sm-Fe raw material powder The first Sm-Fe raw material powder was placed in a vacuum degassing furnace and kept at a vacuum of 0.8 Pa and a temperature of 350 °C for 3 hours to remove the moisture and impurities adsorbed on the powder surface. After cooling, the second Sm-Fe raw material powder was obtained.

[0064] Step S4: Preparation of SmFeN spherical powder by three-stage fluidized bed nitriding The second Sm-Fe raw material powder was placed into a fluidized bed nitriding furnace and subjected to a three-stage nitriding process: low-temperature pre-nitriding, medium-temperature main nitriding, and high-temperature homogenization. The medium-temperature main nitriding holding time was 9 hours, and the other nitriding parameters remained unchanged, as follows: Low-temperature pre-percolation stage: temperature 250℃, nitrogen partial pressure 0.2MPa, heat preservation for 3h, pure nitrogen atmosphere (nitrogen concentration 100%) to achieve uniform adsorption of nitrogen atoms; Medium-temperature main diffusion stage: heat up to 480℃, nitrogen partial pressure 0.8MPa, keep warm for 9h, pure nitrogen atmosphere (nitrogen concentration 100%), to achieve deep diffusion of nitrogen atoms into the particle interior; High-temperature homogenization stage: The temperature is raised to 520℃, and a mixed atmosphere of nitrogen and argon = 1:1 is introduced. The mixture is kept at this temperature for 2.5 hours to eliminate the nitrogen concentration gradient inside and outside the particles. After cooling in the furnace, high-flowability and high-orientation SmFeN spherical powder is obtained.

[0065] The only difference between Example 3 and Example 2 is that the plasma spheroidization cooling rate and the medium-temperature main infiltration holding time are adjusted, while the other steps and parameters remain the same, thus verifying the adjustability of the process parameters within the range and the stability of product performance of the present invention.

[0066] The performance parameters of the SmFeN spherical powders prepared in the three examples of this embodiment were tested using the same industry standard testing methods as in Example 2 (laser particle size analyzer + image analysis for sphericity measurement, X-ray fluorescence spectrometry for nitrogen content measurement, and magnetic property tester for magnetic properties measurement, etc.). The results are shown in Table 2 below. Figure 3 As shown, all performance aspects are excellent.

[0067] Table 2 Performance parameters of SmFeN spherical powder prepared in Example 3

[0068] In this embodiment 3, parameters were fine-tuned within the scope of the invention's protection to achieve a slight performance optimization. The core reasons are as follows: The cooling rate was increased to 8×10³ K / s: The faster cooling rate allowed the Sm-Fe molten droplets to solidify more quickly, resulting in smoother particle surfaces, an increase in sphericity from 0.95 to 0.96, further reduction in inter-powder friction, an optimized Hall flow rate of 24 s / 50 g, and an increased loose packing density of 4.0 g / cm³; The medium-temperature nitriding holding time was extended to 9 h: Extending the holding time at the optimal nitriding temperature of 480℃ allowed for more complete diffusion of nitrogen atoms into the particle interior, resulting in a smaller difference in nitrogen concentration between the particle core and surface, ultimately reducing nitrogen content fluctuations to ±0.12 wt%. 17 To Sm2Fe 17 The N3 conversion is more complete, the purity of the main phase is improved, and the coercivity, remanence, and maximum energy product are all slightly optimized; the parameters are still within the protection range: all adjusted parameters do not exceed the limits of this invention and do not induce Sm volatilization, oxidation phase formation, or Sm2Fe. 17 Problems such as N3 decomposition were addressed to ensure the purity of the phase and the stability of the magnetic properties.

[0069] The SmFeN spherical powder prepared in Example 3 is free of oxidized phases such as samarium oxide and iron oxide, and free of α-Fe low coercivity phase. The uniformity of nitrogen distribution within the powder particles is further improved, and the flowability and magnetic properties are slightly optimized compared to Example 2. It fully meets the performance requirements of high-end applications such as 3D printing and injection molding of bonded magnets. At the same time, it verifies the adjustability of the process parameters of the present invention within the protection range, and the parameters can be finely adjusted according to actual production needs to achieve performance customization.

[0070] Example 4: The only difference between Example 4 and Example 2 is that the plasma spheroidization cooling rate is adjusted to 8×10³K / s, the nitrogen partial pressure in the medium-temperature main infiltration stage is increased to 0.9MPa, and the remaining steps and parameters remain the same, so as to prepare SmFeN spherical powder with high fluidity and high orientation.

[0071] The performance parameters of the SmFeN spherical powder prepared in Example 4 were tested using the same industry standard testing method as in Example 2. The results are shown in Table 3 below, and all properties are excellent.

[0072] Table 3 Performance parameters of SmFeN spherical powder prepared in Example 4

[0073] The increased cooling rate in Example 4 further improved the sphericity of Sm-Fe powder, increased surface smoothness, and optimized flowability and bulk density. The moderately increased partial pressure of the medium-temperature nitriding gas enhanced the diffusion driving force of nitrogen atoms, allowing nitrogen atoms to diffuse more fully into the particle interior, improving nitriding uniformity, further reducing nitrogen content fluctuations, simultaneously optimizing magnetic properties, and preventing the precipitation of impurity phases.

[0074] Example 5: The only difference between Example 5 and Example 2 is that the plasma spheroidization powder feeding rate is adjusted to 15 g / min, and the holding time in the high-temperature homogenization stage is extended to 3 h. The remaining steps and parameters remain the same, and SmFeN spherical powder with high fluidity and high orientation degree is prepared.

[0075] The performance parameters of the SmFeN spherical powder prepared in Example 5 were tested using the same industry standard testing method as in Example 2. The results are shown in Table 4 below, and all properties are excellent.

[0076] Table 4 Performance parameters of SmFeN spherical powder prepared in Example 5

[0077] In the preparation process of Example 5, the powder feeding rate of 15 g / min is moderately increased within the range of this invention. Combined with the plasma power of 45 kW, the powder melts fully and disperses well, maintaining excellent sphericity. The 3-hour holding time in the high-temperature homogenization stage allows nitrogen atoms to diffuse more fully, completely eliminating the nitrogen concentration gradient inside and outside the particles, further improving the orientation and magnetic energy product, while avoiding decomposition problems caused by heat accumulation.

[0078] Example 6: The only difference between Example 6 and Example 2 is that the vacuum degassing temperature is adjusted to 380℃, the temperature of the low-temperature pre-permeation stage is increased to 280℃, and the heat preservation time is shortened to 2h. The remaining steps and parameters remain the same, and high-flowability, high-orientation SmFeN spherical powder is prepared.

[0079] The performance parameters of the SmFeN spherical powder prepared in Example 6 were tested using the same industry standard testing method as in Example 2. The results are shown in Table 5 below, and all properties are excellent.

[0080] Table 5 Performance parameters of SmFeN spherical powder prepared in Example 6

[0081] In the preparation process of Example 6, the vacuum degassing temperature of 380℃ is moderately increased within the range of this invention, which more efficiently removes the moisture and impurities adsorbed on the powder surface, providing a cleaner surface for nitrogen atom adsorption; the low-temperature pre-percolation stage is moderately heated to 280℃ and then kept warm for 2 hours, which ensures uniform adsorption of nitrogen atoms, shortens the process time, improves production efficiency, and is well connected with the subsequent main percolation and homogenization stages, without affecting the overall nitriding effect and magnetic properties.

[0082] Comparative Example 1: The only difference between Comparative Example 1 and Example 2 is that the temperature during the high-temperature homogenization stage was increased to 600°C, resulting in the preparation of SmFeN magnetic powder. The performance parameters of the SmFeN magnetic powder prepared in Comparative Example 1 were fully tested using the same testing methods as in Example 2. The microstructure is as follows: Figure 4 As shown, the XRD pattern is as follows Figure 10 As shown in Table 6 below, the performance results show that all performance indicators have significantly deteriorated, which is in stark contrast to Example 2 of the present invention: Table 6 Performance parameters of SmFeN magnetic powder prepared in Comparative Example 1

[0083] The core reason for this Comparative Example 1 is that the temperature during the high-temperature homogenization stage rises to 600℃, exceeding the temperature of Sm2Fe. 17 The thermal stability critical temperature of N3 triggers an irreversible decomposition phase transition: Sm2Fe17 N3 decomposes at 600℃: Sm2Fe 17 The N3 → 2SmN + 17Fe phase, at high temperatures, Fe precipitates as the α-Fe low-coercivity phase, significantly reducing the coercivity and orientation of the magnetic powder. The decomposition phase transition disrupts the internal crystal structure of the particles, leading to significant desorption and uneven distribution of nitrogen atoms, increasing nitrogen content fluctuations from ±0.15wt% to ±0.45wt%. This crystal destruction causes microcracks on the powder particle surface, resulting in decreased flowability (increased Hall flow rate) and reduced bulk density, failing to meet the molding requirements of 3D printing and injection molding. The precipitation of the α-Fe and SmN phases dilutes Sm2Fe. 17 The proportion of N3 main phase leads to a significant deterioration in core magnetic properties such as remanence and maximum magnetic energy product.

[0084] Comparative Example 1 demonstrates that the temperature parameters during the high-temperature homogenization stage must be strictly controlled within the range of 500~550℃ as described in this invention; exceeding this range will directly trigger Sm2Fe. 17 The thermal decomposition phase transition of N3 leads to a comprehensive deterioration of the magnetic properties and molding and processing performance of the magnetic powder, which fully verifies the scientific, rational and necessary nature of the process parameter settings of this invention. Only parameters within the protection range can produce SmFeN spherical powder with high fluidity and high orientation.

[0085] Comparative Example 2: The only difference between Comparative Example 2 and Example 2 is that in step S1, the plasma power is 20kW; and SmFeN magnetic powder is finally obtained.

[0086] The SmFeN magnetic powder prepared in Comparative Example 2 underwent full performance testing using the same testing method as in Example 2. The microstructure is as follows: Figure 5 As shown in Table 7 below, the performance results show that due to insufficient plasma spheroidization, the powder morphology and magnetic properties are significantly degraded, which is in stark contrast to Example 2 of the present invention.

[0087] Table 7 Performance parameters of SmFeN magnetic powder prepared in Comparative Example 2

[0088] The analysis of the performance degradation of the SmFeN magnetic powder in Comparative Example 2 revealed that the core cause was insufficient plasma power (20kW), leading to incomplete melting of the primary Sm-Fe powder and failure of the plasma spheroidization effect. Specific effects included: Insufficient powder spheroidization: The 20kW power could not provide sufficient energy, resulting in a plasma temperature of only 3800K, far below the temperature required for complete melting of the Sm-Fe alloy. Only the surface of the powder slightly melted, failing to shrink into a spherical shape under surface tension, resulting in a final sphericity of only 0.78, retaining numerous sharp edges and irregular morphology. A sharp drop in flowability and bulk density: Irregular morphology increased friction between powder particles, raising the Hall flow rate to 35s / 50g and reducing the bulk density to 3.1g / cm³, failing to meet the filling requirements for 3D printing and injection molding. Deterioration in nitriding uniformity: The unspheroidized powder had an uneven specific surface area, with nitrogen atoms adsorbing too quickly at sharp edges and too slowly at particle depressions. Even with a three-stage fluidized bed nitriding process, the adsorption differences could not be eliminated, and the nitrogen content fluctuation increased to ±0.32wt%. Significant decrease in magnetic properties: Uneven specific surface area leads to Sm2Fe 17 The N3 main phase is unevenly distributed, and its orientation degree drops to 76% due to the difficulty of the irregular particles aligning in a magnetic field. Coercivity, remanence, and maximum energy product all deteriorate significantly with the decrease in the uniformity of the main phase. No impurity phase precipitation: Comparative Example 2 only involved insufficient spheroidization power and did not involve high-temperature decomposition or oxidation. Therefore, no α-Fe, SmN, or oxide phases precipitated. The performance degradation was solely due to insufficient spheroidization, further verifying the core role of the plasma spheroidization power parameter.

[0089] Comparative Example 2 illustrates that the plasma power during the plasma spheroidization stage must be strictly controlled within the range of 30-60 kW as described in this invention. Below this range, insufficient melting of the Sm-Fe alloy powder leads to complete failure of the spheroidization effect, resulting in a comprehensive deterioration of powder flowability, nitriding uniformity, and magnetic properties. Only within the 30-60 kW power range can complete powder melting and the formation of highly spherical particles be achieved, laying the foundation for subsequent nitriding and high-performance magnetic powder preparation. This fully verifies the scientific validity and necessity of the process parameters set in this invention.

[0090] Comparative Example 3: The only difference between Comparative Example 3 and Example 2 is that the powder feeding rate during the plasma spheroidization stage is 30 g / min, and SmFeN magnetic powder is finally obtained.

[0091] The SmFeN magnetic powder prepared in Comparative Example 3 was tested for its full performance using the same testing method as in Example 2. The results are shown in Table 8 below. Due to the excessively high powder feeding rate, the powder spheroidization was insufficient and the risk of oxidation increased. All properties were inferior to those of the present invention, showing a significant contrast with Example 2.

[0092] Table 8 Performance parameters of SmFeN magnetic powder prepared in Comparative Example 3

[0093] The analysis of the performance degradation of the SmFeN magnetic powder in Comparative Example 3 revealed that the core reason was the excessively high powder feed rate (30 g / min), which was mismatched with the 45 kW energy density of the plasma. This led to the failure of the plasma spheroidization effect and an increased risk of powder oxidation. Specific impacts included: Insufficient powder melting: The powder feed rate of 30 g / min far exceeded the plasma's energy carrying capacity, significantly shortening the residence time of powder particles within the plasma torch. This prevented them from being fully heated to a molten state; only some particle surfaces melted, failing to shrink into regular spheres under surface tension. The final sphericity was only 0.82, retaining some edges and irregular shapes. Increased interparticle friction: The irregular shape resulted in uneven contact area between particles during powder accumulation, increasing friction. The loose packing density decreased to 3.3 g / cm³, and the Hall flow rate increased to 33 s / 50 g, leading to poor flowability and failing to meet the continuous powder feeding and uniform filling requirements of 3D printing and injection molding. Decreased nitriding uniformity: The incompletely nitrided powder exhibits variations in specific surface area, leading to different nitrogen atom adsorption and diffusion rates on sharp edges and smooth surfaces. Even with a fluidized bed three-stage nitriding process, this difference cannot be completely eliminated, resulting in nitrogen content fluctuations of ±0.28 wt% and uneven main phase distribution. Slight oxide phase formation: Excessively high powder feed rates worsen powder dispersion within the plasma torch. Some particles agglomerate and come into contact with trace amounts of oxygen within the torch. Insufficient melting prevents the formation of a dense, smooth surface layer, ultimately resulting in the formation of trace amounts of Sm2O3 oxide phase. Simultaneously, irregular particles struggle to orient themselves in the magnetic field, significantly reducing orientation and coercivity. Overall magnetic performance degradation: The formation of the Sm2O3 oxide phase dilutes Sm2Fe. 17 The proportion of N3 main phase, coupled with uneven nitriding and decreased orientation, ultimately leads to a significant deterioration in core magnetic properties such as remanence and maximum magnetic energy product.

[0094] Comparative Example 3 demonstrates that the powder feeding rate during the plasma spheroidization stage must be strictly controlled within the range of 5–20 g / min as described in this invention. Exceeding this range leads to a mismatch between the powder and plasma energy density, causing a series of problems such as insufficient melting, poor spheroidization, and increased oxidation risk, ultimately resulting in a comprehensive deterioration of powder flowability, nitriding uniformity, and magnetic properties. Only within the powder feeding rate range of 5–20 g / min can the residence time and degree of melting of the powder within the plasma torch be guaranteed, enabling the preparation of high-sphericity Sm-Fe powder. This provides a foundation for the subsequent preparation of high-performance SmFeN magnetic powder, fully verifying the scientific validity, rationality, and necessity of the process parameters set in this invention.

[0095] Comparative Example 4: Comparative Example 4 uses a traditional mechanical alloying method combined with a conventional solid-state nitriding process to prepare SmFeN magnetic powder, without employing the plasma spheroidization and fluidized bed three-stage nitriding process. The specific preparation process is as follows: Step 1: Raw material proportioning and ball milling to prepare Sm-Fe alloy powder According to Sm2Fe 17 Weigh high-purity samarium metal powder (purity ≥99.9%) and high-purity iron metal powder (purity ≥99.9%) according to stoichiometric ratio. Put the raw material powder and stainless steel grinding balls into the ball mill jar at a ball-to-material ratio of 15:1. Introduce high-purity argon gas (purity ≥99.99%) into the ball mill jar as a protective gas to remove air from the jar and prevent the powder from oxidizing.

[0096] The ball mill jar was placed in a planetary ball mill and mechanically alloyed ball milled at a speed of 300 r / min for 25 hours. During the ball milling process, the machine was stopped for 1 hour every 5 hours to avoid excessive temperature inside the ball mill jar, which would cause powder agglomeration and oxidation. After the ball milling was completed, Sm-Fe alloy powder with irregular shape and sharp edges was obtained.

[0097] Step 2: Powder sieving The Sm-Fe alloy powder obtained by ball milling was sieved through a standard sieve to obtain Sm-Fe raw material powder with a particle size distribution of 10~60μm. There was no strict control over the particle size span. The particle size span of the powder was found to be 4.2 times, and the particle size distribution dispersion was large.

[0098] Step 3: Conventional solid nitriding treatment The sieved Sm-Fe raw material powder was evenly spread in an alumina crucible with a powder layer thickness of 5 mm. The crucible was then placed in a tube furnace for static solid-state nitriding. The nitriding process was a single-stage isothermal nitriding: pure nitrogen gas (purity ≥99.99%) was introduced into the tube furnace, the nitrogen partial pressure was controlled at 0.6 MPa, the temperature was raised to 480℃, and held for 15 h. During the nitriding process, the nitrogen gas was kept in unidirectional flow at a flow rate of 5 L / min. After nitriding, the nitrogen gas was turned off, and argon gas was continued to be introduced into the tube furnace. The furnace was then cooled to room temperature to obtain SmFeN magnetic powder.

[0099] Step 4: Post-processing The cooled SmFeN magnetic powder was passed through a 200-mesh sieve to remove a small amount of agglomerated coarse particles, thus obtaining the final SmFeN magnetic powder prepared by the mechanical alloying method.

[0100] The preparation process of Comparative Example 4 lacks a vacuum degassing step, resulting in the failure to remove adsorbed moisture and oxygen impurities from the powder surface. Furthermore, the static nitriding process exhibits a "nitrogen-poor core, nitrogen-rich surface" problem in the powder layer, leading to poor nitriding uniformity. Simultaneously, the powder obtained from mechanical alloying ball milling has sharp edges and poor sphericity, with a microstructure resembling... Figure 7As shown, the protective film is easily punctured during subsequent coating processes, leading to easy oxidation of the powder. Ultimately, the performance test results of the SmFeN magnetic powder in Comparative Example 4 showed low magnetic properties: (BH)max = 30.07 MGOe, Br = 12.27 kGs, Hcj = 10.34 kOe, sphericity < 0.7, Hall flow rate > 45 s / 50 g, and nitrogen content fluctuation ± 0.65 wt%. These results show a significant performance gap compared to the SmFeN spherical powder prepared by the plasma spheroidization + fluidized bed three-stage nitriding process of this invention.

[0101] Comparative Example 5: Comparative Example 5 uses mechanical alloying to prepare Sm-Fe powder, followed by a conventional tube furnace static single-stage nitriding process to prepare SmFeN magnetic powder. It does not employ the plasma spheroidization treatment and fluidized bed three-stage nitriding process of this invention; instead, it only performs conventional solid-state nitriding on the irregular Sm-Fe powder obtained through mechanical alloying. The specific preparation process is as follows: Step 1: Mechanical alloying to prepare irregular Sm-Fe alloy powder According to Sm2Fe 17 High-purity samarium powder (purity ≥99.9%) and high-purity iron powder (purity ≥99.9%) were weighed according to stoichiometry. The raw materials and stainless steel grinding balls were loaded into the ball mill jar at a ball-to-material ratio of 12:1. Argon gas (purity ≥99.99%) was introduced to purge the air and then the jar was sealed. The jar was then placed in a planetary ball mill and milled at 280 r / min for 22 h. The mill was stopped for 0.5 h every 4 h of milling to cool down the powder and prevent oxidation and agglomeration. This yielded Sm-Fe alloy powder with irregular morphology, sharp edges, and a particle size distribution of 8~65 μm, without precise control over the particle size range.

[0102] Step 2: Powder Pretreatment The above Sm-Fe alloy powder was placed in an oven and dried at 120°C for 4 hours to remove some of the adsorbed moisture on the surface (without the high vacuum degassing process of this invention, trace amounts of impurities and adsorbed oxygen still remain on the powder surface). After cooling, it was sieved to remove agglomerated coarse particles, and Sm-Fe raw material powder for nitriding was obtained.

[0103] Step 3: Traditional tubular furnace static single-stage nitriding core process Sm-Fe raw material powder was evenly spread in an alumina crucible with a powder layer thickness of about 8 mm, and placed in a horizontal tube nitriding furnace. The crucible was placed in the constant temperature zone of the furnace. Argon gas (flow rate 8 L / min) was first introduced into the tube furnace to purge the air in the furnace for 30 min to ensure that there was no oxidizing atmosphere in the furnace. Then the argon gas was turned off and pure nitrogen gas (purity ≥99.99%) was introduced. The nitrogen partial pressure in the furnace was controlled at 0.7 MPa, and the temperature was raised to 470℃ at a heating rate of 5℃ / min. A single-stage constant temperature nitriding mode was adopted and the temperature was held for 20 h. During the nitriding process, the nitrogen gas was kept in a unidirectional low-speed flow (flow rate 4 L / min) to achieve only the replacement of the atmosphere in the furnace without disturbing the powder. After the nitriding holding was completed, the nitrogen gas was turned off and argon gas was introduced again (flow rate 10 L / min). The furnace was cooled to room temperature to obtain SmFeN magnetic powder.

[0104] Step 4: Post-processing The cooled magnetic powder was passed through a 200-mesh standard sieve to remove a small amount of sintered and agglomerated hard lumps, thus obtaining the final SmFeN magnetic powder prepared by the traditional nitriding process.

[0105] The correlation between process defects and performance in Comparative Example 5 is explained as follows: Without plasma spheroidization treatment: the powder retains an irregular angular morphology, with a sphericity <0.7, poor flowability, and a tendency for uneven filling during subsequent molding. Static nitriding mode: powder layering leads to insufficient nitriding of the bottom / core powder, resulting in a concentration gradient of "nitrogen-rich surface and nitrogen-poor core," with nitrogen content fluctuations exceeding ±0.6wt%. Without a high-temperature homogenization stage: the difference in nitrogen concentration inside and outside the particles cannot be eliminated, and some particles are not completely converted to Sm2Fe. 17 N3 main phase, residual Sm2Fe 17 The mother phase and a small amount of SmFe2 phase are present; simple pretreatment is used. Low-temperature drying without high-vacuum degassing means that residual moisture and impurities on the powder surface hinder nitrogen atom adsorption and diffusion, further reducing nitriding efficiency and uniformity. The nitriding time is long: single-stage isothermal nitriding requires 20 hours, far longer than the 10-15 hours of the three-stage nitriding of this invention, resulting in extremely low industrial production efficiency.

[0106] The SmFeN magnetic powder prepared in Comparative Example 5 has the following detection properties: (BH)max = 31.52 MGOe, Br = 12.43 kGs, Hcj = 11.09 kOe; the microstructure is as follows. Figure 8 As shown, the powder has poor sphericity and is angular.

[0107] Comparative Example 6: Comparative Example 6 uses a traditional chemical co-precipitation method combined with subsequent heat treatment and nitriding to prepare SmFeN magnetic powder. This process involves preparing a samarium iron precursor through liquid-phase precipitation, followed by calcination, reduction, and nitriding to obtain the final product. The specific preparation process is as follows: Step 1: Raw material preparation and precursor precipitation According to Sm2Fe 17 Stoichiometrically, samarium nitrate hexahydrate (Sm(NO3)3・6H2O, purity ≥99.9%) and ferric nitrate nonahydrate (Fe(NO3)3・9H2O, purity ≥99.9%) were weighed as metal sources and dissolved in deionized water to prepare a samarium-ferric mixed salt solution with a total metal ion concentration of 0.8 mol / L. The solution was magnetically stirred for 30 min until completely dissolved. A 1.0 mol / L ammonium bicarbonate (NH4HCO3) solution was prepared as a precipitant, and a 0.5 mol / L ammonia solution was prepared as a pH adjuster. The precipitant and pH adjuster were mixed thoroughly at a volume ratio of 2:1 to obtain a precipitate mixture. Under constant temperature water bath (temperature 40℃) and magnetic stirring (speed 400r / min) conditions, the precipitated mixture was added dropwise to the samarium iron mixed salt solution at a rate of 5mL / min. During the dropwise addition, the pH value of the system was continuously adjusted with ammonia water to stabilize it at 8.5~9.0. After the dropwise addition was completed, stirring was continued for 2h to allow samarium and iron ions to fully co-precipitate and form a samarium iron hydroxide and carbonate complex precursor suspension.

[0108] Step 2: Precursor solid-liquid separation and drying The precursor suspension was subjected to solid-liquid separation by vacuum filtration (vacuum degree -0.08 MPa). The filter cake was washed repeatedly with deionized water 3-4 times, and then washed twice with anhydrous ethanol to remove residual impurities such as nitrate and ammonium ions. The washed filter cake was placed in a vacuum drying oven and dried at 60℃ and vacuum degree -0.09 MPa for 12 hours to obtain dried samarium-iron composite precursor powder.

[0109] Step 3: Precursor calcination and reduction Samarium-iron composite precursor powder was evenly spread in an alumina crucible and placed in a tube furnace. The furnace was heated to 550°C at a rate of 2°C / min under air atmosphere and held for 4 hours for calcination, causing the precursor to decompose into Sm₂O₃-Fe₂O₃ composite oxide powder. The furnace was then cooled to room temperature. The composite oxide powder was transferred to a reduction furnace, and high-purity hydrogen gas (≥99.999%) was introduced at a flow rate of 15 L / min. The temperature was increased to 850°C at a rate of 3°C / min and held for 6 hours for high-temperature reduction, converting the oxide into Sm-Fe alloy powder. After reduction, hydrogen gas was continuously introduced, and the furnace was cooled to room temperature to obtain primary Sm-Fe alloy powder.

[0110] Step 4: Conventional solid nitriding treatment The Sm-Fe alloy powder obtained from the reduction process was passed through a 200-mesh sieve to remove agglomerated particles, yielding raw material powder for nitriding. The powder was spread evenly in an alumina crucible (3 mm thick) and placed in a tube nitriding furnace. The furnace was first purged with argon gas for 30 minutes, followed by the introduction of pure nitrogen gas (≥99.99% purity), maintaining a nitrogen partial pressure of 0.5 MPa. The temperature was increased to 460°C at a rate of 4°C / min, and nitriding was performed in a single stage at a constant temperature for 18 hours. After nitriding, the mixture was cooled to room temperature by argon gas to obtain SmFeN magnetic powder prepared by the chemical co-precipitation method.

[0111] Step 5: Post-processing The nitrided magnetic powder is ground and sieved to remove a small amount of sintered hard lumps, resulting in the final product SmFeN magnetic powder.

[0112] The core process defects and performance correlation of Comparative Example 6 illustrate the following: Difficulty in composition control: During the liquid-phase co-precipitation process, the precipitation rates of Sm³⁺ and Fe³⁺ differ, easily leading to localized component segregation. This causes the final Sm / Fe stoichiometric ratio of the Sm-Fe alloy powder to deviate from Sm₂Fe. 17 The design value indicates that pure Sm2Fe is difficult to form after nitriding. 17 N3 main phase. Irregular powder morphology: During calcination and reduction, particles are prone to agglomeration and irregular growth, resulting in a mixed morphology of flocculent and blocky particles with a sphericity <0.6 and extremely poor flowability, which cannot meet the molding requirements of 3D printing and injection molding. The microstructure of the finished SmFeN magnetic powder is as follows: Figure 9 As shown. The process is complex, involving multiple steps such as salt dissolution, precipitation, filtration, drying, calcination, reduction, and nitriding. Each step generates losses, and the parameters of each step are highly interconnected, making precise control difficult during large-scale production, resulting in poor batch stability of the product. Nitriding uniformity is poor: the resulting powder has an uneven specific surface area, and conventional static nitriding easily produces "nitrogen-rich areas" and "nitrogen-poor areas," with nitrogen content fluctuations exceeding ±0.7wt%. Furthermore, it easily leaves behind impurities such as Sm₂O₃ and α-Fe, as shown in the XRD pattern. Figure 11 As shown. Magnetic properties are low: Due to problems such as component segregation, residual impurities, and uneven nitriding, the final magnetic powder properties are far lower than those of the product of this invention. The test results of the finished SmFeN magnetic powder of Comparative Example 6 are: (BH) max=29.99MGOe, Br=12.43kGs, Hcj=10.97kOe, Hall flow rate>50s / 50g.

[0113] This invention has been described through the specific embodiments described above. Those skilled in the art should understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Parts not described in detail in this specification are well-known to those skilled in the art. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from the scope of this application. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims of this invention.

Claims

1. A method for preparing SmFeN spherical powder, characterized in that, Includes the following steps: Step S1: Mechanical alloying is used to prepare primary Sm-Fe alloy powder with irregular morphology. The primary Sm-Fe alloy powder is fed into a high-temperature plasma torch at a powder feeding rate of 5~20g / min for plasma spheroidization. The plasma spheroidization process includes: forming spherical droplets from the primary Sm-Fe alloy powder under the action of high-energy plasma at a temperature of 5000~10000K; the spherical droplets entering a cooling zone and being rapidly cooled by argon gas to solidify and form Sm-Fe powder with high sphericity; the argon gas volume concentration in the cooling zone is 100%, and the argon gas purity is ≥99.999%; Step S2: The high sphericity Sm-Fe powder is sieved to obtain the first Sm-Fe raw material powder, the particle size distribution range of the first Sm-Fe raw material powder is 5~50μm, and the particle size span is ≤3 times; Step S3: The first Sm-Fe raw material powder is degassed under vacuum to obtain the second Sm-Fe raw material powder; the vacuum degree of the vacuum degassing process is ≤1Pa and the temperature is 300~400℃; Step S4: The second Sm-Fe raw material powder is placed in a fluidized bed nitriding furnace and subjected to a three-stage nitriding process to obtain high-fluidity and high-orientation SmFeN spherical powder; the three-stage nitriding process includes three stages in sequence: low-temperature pre-nitriding stage, medium-temperature main nitriding stage, and high-temperature homogenization stage; The low-temperature pre-permeation stage involves maintaining the temperature at 200~300℃ and nitrogen partial pressure at 0.1~0.3MPa for 2~4 hours to allow nitrogen atoms to be uniformly adsorbed on the surface of the second Sm-Fe raw material powder. The intermediate temperature main infiltration stage involves heating to 450~500℃, setting the nitrogen partial pressure to 0.5~1.0MPa, and holding the temperature for 6~10h to allow nitrogen atoms to diffuse into the particles of the second Sm-Fe raw material powder. The high-temperature homogenization stage involves maintaining the temperature at 500-550℃ for 2-3 hours in a mixed atmosphere of nitrogen and argon to eliminate the nitrogen concentration gradient inside and outside the particles, thereby obtaining highly fluid and highly oriented SmFeN spherical powder. The volume ratio of nitrogen to argon in the mixed atmosphere is 1:

1.

2. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, In step S1, the primary Sm-Fe alloy powder is characterized by an irregular spherical shape with angular edges, and the particle size ranges from 60 to 80 μm.

3. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, In step S1, during the rapid cooling process, the cooling rate is 10³~10 4 K / s, the initial temperature of argon is 25℃, and the gas flow rate is 10~30L / min.

4. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, In step S1, the power range of the high-energy plasma is 30~60kW, and the oxygen content inside the high-temperature plasma torch is less than 100ppm.

5. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, The nitrogen content in the SmFeN spherical powder is controlled within ±0.2wt%.

6. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, In step S4, the nitrogen volume concentration is 100% in both the low-temperature pre-infiltration stage and the medium-temperature main infiltration stage, and the nitrogen volume concentration is 50% in the high-temperature homogenization stage.

7. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, The coercivity of the SmFeN spherical powder is ≥20kOe and the Hall flow rate is ≤30s / 50g.

8. The method for preparing SmFeN spherical powder according to claim 1, characterized in that, The sphericity of the SmFeN spherical powder is ≥0.8 and the orientation degree is ≥85%.

9. A spherical SmFeN powder, characterized in that, The SmFeN spherical powder is a highly fluid and highly oriented SmFeN spherical powder prepared by the preparation method described in any one of claims 1 to 8.

10. An application of SmFeN spherical powder, characterized in that, The SmFeN spherical powder is a high-flowability, high-orientation SmFeN spherical powder prepared by the preparation method according to any one of claims 1 to 8, or the SmFeN spherical powder is the SmFeN spherical powder according to claim 9; the SmFeN spherical powder is used for 3D printing, or for bonding magnets through injection molding.

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