Mim injection molding high-performance sintered samarium iron-nitrogen magnet and preparation process thereof

Abstract

The application relates to a MIM injection-molded samarium-iron-nitrogen magnet and a preparation process thereof. 17 In the application, Nb elements are added in Sm2Fe 17 , a Nb nano-modified layer is formed through high-energy ball milling and heat treatment, then a ternary binder system with a mass ratio of 60:30:10 of paraffin-poly-lactic acid-stearic acid and gradient debinding are adopted to obtain a debinding blank, the debinding blank is sintered, nitriding treatment is carried out through a three-stage process, and then ultrasonic cleaning and other treatments are carried out to obtain a samarium-iron-nitrogen magnet with high magnetism.

Description

Technical Field

[0001] This invention belongs to the field of injection-molded magnetic materials technology, and relates to a rare earth permanent magnet material, particularly to a samarium iron nitrogen magnet formed by MIM injection molding and its preparation process. Background Technology

[0002] Currently, the permanent magnet material with the highest magnetic performance is rare-earth neodymium iron boron (NdFeB) permanent magnet material. Among them, the maximum energy product of sintered NdFeB permanent magnet material has exceeded 56 MGOe, which is very beneficial for the miniaturization and lightweighting of devices. In recent years, it has been widely used in wind power generation, new energy vehicles, and elevators. However, NdFeB materials have the disadvantage of poor high-temperature resistance, which seriously limits their application in high-temperature fields.

[0003] Samarium iron nitride (Sm-Fe-N) magnets are ideal alternatives to neodymium iron boron magnets for high-temperature applications due to their high remanence, high coercivity, and excellent temperature stability. Traditional manufacturing processes typically employ powder metallurgy, mixing Sm2Fe17 powder with a binder, pressing the mixture, and then debinding, sintering, and nitriding to obtain the magnet. However, traditional pressing processes are difficult to use for fabricating complex shapes, and the magnets exhibit poor density uniformity. Furthermore, the low nitrogen atom diffusion efficiency during nitriding limits the improvement in coercivity and energy product.

[0004] Samarium iron nitrogen (SmFe17Nx) materials, with their superior intrinsic magnetism, better oxidation resistance, higher Curie temperature, and lower material cost compared to neodymium iron boron (NdFeB), have become a strong competitor to bonded NdFeB magnetic powders, playing an irreplaceable role, especially in high-temperature applications. However, SmFe17Nx materials are unstable at high temperatures and prone to decomposition during sintering, so their current application is mainly focused on the preparation and bonding of magnets. This is primarily because Sm2Fe17Nx compounds readily undergo irreversible decomposition at temperatures exceeding 550℃, making it difficult to prepare dense magnets using traditional sintering processes. Therefore, Sm2Fe17Nx compounds are generally mixed with plastic binders such as PA6 and PA12 at 200-300℃, granulated, and then injection molded to produce injection-molded magnets. Due to the addition of a large amount of binder, the material density and magnetic properties of injection-molded magnets are still lower than those of sintered magnets.

[0005] With the continuous surge in the permanent magnet application market, product requirements are becoming increasingly demanding in terms of miniaturization, precision, and irregular shapes. The processing difficulty of these products is also constantly rising. Metal Injection Molding (MIM) is a process that utilizes high precision and the ability to manufacture complex shapes, while also offering high production efficiency, making it suitable for large-scale production. Therefore, MIM samarium iron nitrogen (SMM) has certain advantages in small, irregularly shaped products; however, achieving the required sintering density while ensuring the preservation of nitrogen (N) remains a subject of further research.

[0006] Patent CN108766755A discloses a method for preparing anisotropic sintered SmFeN permanent magnets. The method involves first pressing Sm2Fe17 into shape, and simultaneously orienting it during the pressing process. Then, sintering and nitriding processes are used to obtain sintered samarium iron nitrogen magnets. However, the pressing process is only suitable for producing single-orientation magnetic sheets or two-stage magnetic rings, which greatly limits the size and structure of the products.

[0007] Patent CN111667967B discloses a high-flowability samarium iron nitride flexible bonded permanent magnet for injection molding and its preparation method. By optimizing the organic additive formulation, the melt flowability of the samarium iron nitride bonded magnet is improved, which is convenient for molding devices with complex shapes and large aspect ratios. However, due to the inclusion of adhesive, the overall density of the magnet is relatively large, so the magnetic performance is not high, and the maximum magnetic energy product is only 11 MGOe. Summary of the Invention

[0008] This invention provides a samarium iron nitrogen magnet manufactured by MIM injection molding and its preparation process, in order to solve the technical problems mentioned in the background art.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, a process for fabricating high-performance sintered samarium iron nitride magnets by MIM injection molding includes:

[0011] S1: Sm2Fe is prepared by vacuum induction melting of Sm and Fe raw materials with a purity ≥99.5%. 17 The alloy, after being crushed and passed through a 200-400 mesh sieve, yields an initial powder with an average particle size of 50-80 μm. This powder, along with 1%-3% (by mass) Nb powder with a particle size ≤10 μm and 0.5%-1% (by mass) ZrO2 ball milling media, is placed in a planetary ball mill and ball-milled at 300-400 r / min for 8-12 h under an inert gas atmosphere, allowing the Nb element to be adsorbed onto Sm2Fe. 17 A preliminary mechanical mixing layer is formed on the powder surface; the addition of Nb can suppress excessive grain growth during sintering, and smaller grains will significantly improve the coercivity of the magnet; it lays an excellent substrate foundation for the subsequent nitriding process; the mechanical force of the ZrO2 ball milling media promotes the activation of the powder surface, increases the sphericity of the metal powder, and increases the adsorption capacity of the subsequent binder.

[0012] S2: The ball-milled mixed powder is annealed at 700-780℃ for 2-3 hours to promote the Nb element to transform into Sm2Fe. 17 Diffusion at grain boundaries and near-surface regions forms a stable Nb nano-modified layer, in which Nb elements diffuse into Sm2Fe. 17Grain boundaries and near-surface regions exhibit a gradient distribution, with the Nb nano-modified layer thickness ranging from 100 to 150 nm. The Nb nano-modified layer is applied in two steps: the first step is mechanical alloying, where Sm₂Fe is alloyed under inert gas protection. 17 Alloy powder and Nb powder are subjected to high-energy ball milling, which allows Nb particles to embed into Sm2Fe. 17 On the surface, a preliminary mechanical mixing layer is formed; the second step is heat treatment diffusion: the ball-milled mixed powder is annealed at 700–780℃ to promote the Nb atoms to migrate to Sm2Fe. 17 Diffusion at grain boundaries and near-surface regions forms a stable Nb nano-modified layer, which greatly improves coercivity and magnetic stability.

[0013] S3: A paraffin-polylactic acid-stearic acid ternary binder system with a mass ratio of 60:30:10 is used to bind the pretreated Sm2Fe 17 The powder and binder are mixed at a solid content of 65%-70% by volume and stirred at 120-150℃ and 50-80r / min for 3-5 hours to form a uniform feedstock. The feedstock is then injected into the mold through a screw injection molding machine at 180-220℃ and an injection pressure of 80-120MPa. After holding the pressure for 5-10 seconds, the molded part is cooled and demolded to obtain an injection-molded preform with a density ≥90%. During the injection molding process, a pulsed magnetic field is used to induce preferential grain orientation, with an orientation magnetic field strength of 1-2T. A gradient binder system is selected for the addition of additives. Polylactic acid is used as a biodegradable carrier and decomposes preferentially during the degreasing stage to form initial microporous channels. The low melting point of paraffin wax ensures the flowability of the feedstock, and stearic acid improves the interfacial compatibility between the powder and the binder, reducing molding defects.

[0014] S4: Solvent degreasing: The injection-molded preform is placed in n-heptane solvent and ultrasonically vibrated at 50-60℃ for 4-6 hours to remove 60%-70% of the paraffin components and form a connected pore network;

[0015] S5: Thermal Degreasing: The temperature is increased from room temperature to 400-500℃ at a rate of 5-8℃ / min, and held in a nitrogen atmosphere for 2-5 hours to completely decompose and volatilize the polylactic acid. The final degreased green body has a residual carbon content of ≤0.1%. A dual-medium synergistic degreasing process is employed: solvent degreasing forms preliminary channels, while gas can be discharged along preset channels during thermal degreasing, avoiding the bubbling and cracking problems of traditional single thermal degreasing. The dimensional shrinkage rate of the green body after degreasing is controlled at 1.5%-2%. This degreasing process facilitates the formation of fine micropores and channels within the matrix, promoting nitrogen penetration and improving the nitriding effect without causing large deformation and shrinkage of the product, thus affecting the overall dimensions.

[0016] S6: Place the degreased green body into a vacuum sintering furnace, heat it to 1000-1100℃ at 10℃ / min, hold it for 2-3 hours, then fill it with nitrogen or argon to a slight negative pressure, and then cool it to room temperature with a fan. During the sintering process, the Nb-modified layer on the surface of Sm2Fe17 powder forms a Nb-rich phase at the grain boundaries, so that the average grain size is controlled at 5-10μm and the grain boundaries are clear and uniform.

[0017] S7: Place the sintered green body into a high-pressure nitriding furnace and use a three-stage process:

[0018] Low-temperature adsorption section: temperature 450-500℃, ammonia pressure 0.5-1MPa, heat preservation for 0.5-3h, so that N atoms are physically adsorbed on the magnet surface and form an initial nitride layer;

[0019] Medium-temperature diffusion section: The temperature is raised to 550-600℃, the ammonia pressure is reduced to 0.2-0.3MPa, and the temperature is maintained for 0.5-3h. The concentration gradient is used to promote the diffusion of N atoms into the interior, while avoiding grain coarsening at high temperature.

[0020] High-temperature solution treatment section: Heat to 650-700℃, introduce a mixture of N2 and H2 gas at a volume ratio of 3:1, pressure 1-1.5MPa, and hold for 0.5-3 hours to allow N atoms to fully dissolve in Sm2Fe. 17 The crystal lattice forms a stable Sm2Fe17N3-x phase; a three-stage process is adopted: low-temperature adsorption stage, medium-temperature diffusion stage, and high-temperature solid solution stage, which increases the nitriding depth to 50-80μm and the nitrogen content is uniformly distributed (8%-10% N atom fraction on the surface and 6%-8% in the core).

[0021] S8: The nitrided magnet is ultrasonically cleaned to remove residual impurities on the surface. Then, a 5-10 μm thick Al2O3 protective layer is deposited using physical vapor deposition. Finally, it is processed to the required size by electrical discharge machining to obtain the final samarium iron nitride magnet.

[0022] Furthermore, the inert gas in S1 is argon or nitrogen.

[0023] Furthermore, the annealing temperature in S2 is 750°C, and the holding time is 2.5 hours.

[0024] Furthermore, the thickness of the Nb nano-modified layer in S2 is 130 nm.

[0025] Furthermore, in S6, Sm2Fe 17 The Nb-modified layer on the powder surface forms an Nb-rich phase at the grain boundaries, thereby controlling the average grain size to 8 μm.

[0026] Furthermore, the thickness of the Al2O3 protective layer in S8 is 8 μm.

[0027] Secondly, a samarium iron nitrogen magnet prepared using the aforementioned MIM injection molding process for high-performance sintered samarium iron nitrogen magnets.

[0028] The advantages of this invention over the prior art are as follows:

[0029] 1. The present invention can suppress excessive grain growth during sintering by adding Nb, and smaller grains will significantly improve the coercivity of the magnet; it lays a good foundation for the subsequent nitriding process; the mechanical force of ZrO2 ball milling media promotes powder surface activation, increases the sphericity of metal powder, and increases the adsorption capacity of subsequent binders.

[0030] 2. The present invention forms the Nb nano-modified layer in two steps. The first step is mechanical alloying: under the protection of an inert gas, Sm2Fe... 17 Alloy powder and Nb powder are subjected to high-energy ball milling, which allows Nb particles to embed into Sm2Fe. 17 On the surface, a preliminary mechanical mixing layer is formed; the second step is heat treatment diffusion: the ball-milled mixed powder is annealed at 700–780℃ to promote the Nb atoms to migrate to Sm2Fe. 17 Diffusion at grain boundaries and near-surface regions forms a stable Nb nano-modified layer. If only ball milling is used to form the Nb nano-modified layer, mechanical alloying only achieves physical embedding of Nb particles, without atomic-level diffusion, resulting in uneven Nb distribution, discontinuous modified layer, and limited improvement in coercivity. If only heat treatment is used to form the Nb nano-modified layer, the Nb diffusivity is low, and the improvement in coercivity is unsatisfactory. This invention uses a two-step process to form the Nb nano-modified layer, overcoming the technical problems of poor coercivity and magnetic instability in existing technologies, and greatly improving both coercivity and magnetic stability.

[0031] 3. The additives of this invention are selected from a gradient binder system. Polylactic acid, as a biodegradable carrier, decomposes preferentially during the degreasing stage to form initial microporous channels. The low melting point of paraffin ensures the flowability of the feed. Stearic acid improves the interfacial compatibility between the powder and the binder and reduces molding defects.

[0032] 4. This invention employs a dual-medium synergistic degreasing process: solvent degreasing forms preliminary channels, and during thermal degreasing, gas can be discharged along preset channels, avoiding the bubbling and cracking problems of traditional single thermal degreasing. The shrinkage rate of the green body after degreasing is controlled at 1.5%-2%. This degreasing process is conducive to the formation of fine micropores and channels inside the matrix, which is beneficial to nitrogen penetration and improves the nitriding effect, without causing large deformation and shrinkage of the product, thus affecting the overall size.

[0033] 5. Compared with traditional nitriding under a single temperature and pressure, where the diffusion depth of N atoms is only 5-10 μm, this invention, through segmented control, places the sintered green body into a high-pressure nitriding furnace and adopts a three-stage process: a low-temperature adsorption stage, a medium-temperature diffusion stage, and a high-temperature solid solution stage, thereby increasing the nitriding depth to 50-80 μm and achieving a uniform distribution of nitrogen content (8%-10% N atom fraction on the surface and 6%-8% in the core). Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is illustrative in nature and is in no way intended to limit the present invention or its application or use. 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.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0036] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as exemplary rather than limiting. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters below denote similar items; therefore, once an item is defined, further discussion of it is unnecessary.

[0037] Example 1:

[0038] A process for fabricating high-performance sintered samarium iron nitrogen magnets by MIM injection molding includes:

[0039] S1: Sm2Fe 17 Alloy powder pretreatment: Sm2Fe is prepared by vacuum induction melting of Sm and Fe raw materials with a purity ≥99.5%. 17The alloy was crushed and passed through a 250-mesh sieve to obtain an initial powder with an average particle size of 55 μm. This powder, along with 1% (by mass) Nb powder (average particle size = 8 μm) and 1% ZrO2 ball milling media, was placed in a planetary ball mill and ball-milled at 300 r / min for 10 h under argon protection, allowing Nb elements to adsorb onto Sm2Fe. 17 A preliminary mechanical mixing layer is formed on the powder surface; the addition of Nb can suppress excessive grain growth during sintering, and smaller grains will significantly improve the coercivity of the magnet; it lays an excellent substrate foundation for the subsequent nitriding process; the mechanical force of the ZrO2 ball milling media promotes the activation of the powder surface, increases the sphericity of the metal powder, and increases the adsorption capacity of the subsequent binder.

[0040] S2: The ball-milled mixed powder was annealed at 750℃ for 2.5 hours to promote the conversion of Nb to Sm2Fe. 17 Diffusion at grain boundaries and near-surface regions forms a stable Nb nano-modified layer, in which Nb elements diffuse into Sm2Fe. 17 Gradient distribution is observed at grain boundaries and near-surface regions; the Nb nano-modified layer thickness is 130 nm. The Nb nano-modified layer is applied in two steps. The first step is mechanical alloying: under inert gas protection, Sm2Fe... 17 Alloy powder and Nb powder are subjected to high-energy ball milling, which allows Nb particles to embed into Sm2Fe. 17 On the surface, a preliminary mechanical mixing layer is formed; the second step is heat treatment diffusion: the ball-milled mixed powder is annealed at 750℃ to promote Nb atoms to migrate to Sm2Fe. 17 Diffusion at grain boundaries and near-surface regions forms a stable Nb nano-modified layer, which greatly improves coercivity and magnetic stability.

[0041] S3: A paraffin-polylactic acid-stearic acid ternary binder system with a mass ratio of 60:30:10 is used to bind the pretreated Sm2Fe 17 The powder and binder are mixed at a solid content of 65% by volume and stirred at 150℃ and 80r / min for 3 hours to form a uniform feedstock. The feedstock is then injected into the mold at 195℃ and 120MPa by a screw injection molding machine. After holding the pressure for 10 seconds, the molded preform is cooled and demolded to obtain a density ≥90%. During the injection molding process, a pulsed magnetic field is used to induce preferential grain orientation, with an orientation magnetic field strength of 1.52T. A gradient binder system is selected for the addition of additives. Polylactic acid is used as a biodegradable carrier and decomposes preferentially during the degreasing stage to form initial microporous channels. The low melting point of paraffin wax ensures the flowability of the feedstock, and stearic acid improves the interfacial compatibility between the powder and the binder, reducing molding defects.

[0042] S4: Solvent degreasing: The injection-molded preform is placed in n-heptane solvent and ultrasonically vibrated at 50°C for 4 hours to remove 60% of the paraffin component and form a connected pore network;

[0043] S5: Thermal Degreasing: The temperature is increased from room temperature to 400℃ at a rate of 5℃ / min, and held in a nitrogen atmosphere for 2 hours to completely decompose and volatilize polylactic acid. The residual carbon content of the final degreased green body is ≤0.1%. A dual-medium synergistic degreasing process is adopted: solvent degreasing forms preliminary channels, and gas can be discharged along the preset channels during thermal degreasing, avoiding the bubbling and cracking problems of traditional single thermal degreasing. The shrinkage rate of the green body after degreasing is controlled at 1.5%-2%. This degreasing process is conducive to the formation of fine micropores and channels inside the matrix, which is conducive to nitrogen penetration and improves the nitriding effect, without causing large deformation and shrinkage of the product, thus affecting the overall size.

[0044] S6: Place the degreased green body into a vacuum sintering furnace, heat to 1100℃ at 10℃ / min, hold for 2 hours, then purge with nitrogen or argon to a slight negative pressure, and then cool to room temperature with a rapid fan. During sintering, Sm2Fe 17 The Nb-modified layer on the powder surface forms an Nb-rich phase at the grain boundaries, which controls the average grain size to 5-10 μm and results in clear and uniform grain boundaries.

[0045] S7: Place the sintered green body into a high-pressure nitriding furnace and use a three-stage process:

[0046] Low-temperature adsorption section: Temperature 450℃, ammonia pressure 1MPa, heat preservation for 1h, so that N atoms are physically adsorbed on the magnet surface and form an initial nitriding layer.

[0047] Medium-temperature diffusion section: The temperature is raised to 550℃, the ammonia pressure is reduced to 0.2MPa, and the temperature is maintained for 2 hours. The concentration gradient is used to promote the diffusion of N atoms into the interior, while avoiding grain coarsening at high temperature.

[0048] High-temperature solution treatment section: The temperature is raised to 650℃, and a mixture of N2 and H2 gas is introduced at a volume ratio of 3:1, with a pressure of 1MPa and held for 1 hour to allow N atoms to fully dissolve in the Sm2Fe17 lattice and form a stable Sm2Fe17N3-x phase. A three-stage process is adopted: low-temperature adsorption section, medium-temperature diffusion section, and high-temperature solution treatment section, which increases the nitriding depth to 50-80μm and ensures uniform nitrogen content distribution (8%-10% N atom fraction on the surface and 6%-8% in the core).

[0049] S8: The nitrided magnet is ultrasonically cleaned to remove residual impurities on the surface. Then, an 8μm thick Al2O3 protective layer is deposited using physical vapor deposition. Finally, it is machined to the required size by electrical discharge machining to obtain the final samarium iron nitride magnet.

[0050] Comparative Example 1:

[0051] This comparative example provides a preparation process for high-performance sintered samarium iron nitrogen magnets by MIM injection molding, including the following steps. The only difference between this comparative example and Example 1 is that Nb element is not added in S1 and step S2 is missing. All other steps are the same as in Example 1.

[0052] Comparative Example 2:

[0053] This comparative example provides a preparation process for high-performance sintered samarium iron nitrogen magnets by MIM injection molding, including the following steps. The only difference between this comparative example and Example 1 is that ball milling is performed in S1, and the rest are the same as in Example 1.

[0054] Comparative Example 3:

[0055] This comparative example provides a process for preparing high-performance sintered samarium iron nitrogen magnets by MIM injection molding, including the following steps. The only difference between this comparative example and Example 1 is the absence of step S2; all other steps are the same as in Example 1.

[0056] Comparative Example 4:

[0057] This comparative example provides a process for preparing high-performance sintered samarium iron nitrogen magnets by MIM injection molding, including the following steps. The only difference between this comparative example and Example 1 is that a single binder is used in step S3 and step S4 is missing. All other steps are the same as in Example 1.

[0058] Comparative Example 5:

[0059] This comparative example provides a process for preparing high-performance sintered samarium iron nitrogen magnets by MIM injection molding, including the following steps. The only difference between this comparative example and Example 1 is that a single temperature and pressure are used in step S7, while the rest are the same as in Example 1.

[0060] The comprehensive performance of the MIM samarium iron nitrogen magnets obtained in Example 1 and Comparative Examples 1-5 is shown in the table below:

[0061]

[0062] As demonstrated by Examples 1 and Comparative Examples 1-4 above, the samarium iron nitride magnets prepared using the MIM injection molding high-performance sintered samarium iron nitride magnet preparation process described in this invention have a remanence of 10.7 KGs, a coercivity of 15.2 KOe, and a magnetic energy product of 29 MGOe. The samarium iron nitride magnets exhibit excellent magnetic properties. Compared with Example 1, the addition of Nb significantly improved the coercivity and magnetic energy product of the samarium iron nitride magnets, resulting in superior magnetic properties. Comparative Examples 2 and 3 show that, in forming the Nb nano-modified layer, if only ball milling is used in Comparative Example 2, mechanical alloying only achieves the physical embedding of Nb particles without atomic-level diffusion, resulting in uneven Nb distribution, discontinuous modified layer, and limited improvement in coercivity (only 8.5 KOe). In Comparative Example 3, if only heat treatment is used to form the Nb nano-modified layer, the Nb diffusivity is low, and the improvement in coercivity is not ideal (only 10.2 KOe). This invention uses a two-step method to form the Nb nano-modified layer, overcoming the technical problems of poor coercivity and magnetic instability in the prior art, and greatly improving coercivity and magnetic stability.

[0063] A process for preparing high-performance sintered samarium iron nitrogen magnets by MIM injection molding in this invention: In Sm2Fe 17 Nb element is added, and an Nb nano-modified layer is formed through high-energy ball milling and heat treatment. Then, a degreased preform is obtained using a paraffin-polylactic acid-stearic acid ternary binder system with a mass ratio of 60:30:10 and gradient degreasing. After sintering the degreased preform, a three-stage nitriding process is used, followed by ultrasonic cleaning and other treatments to obtain a highly magnetic samarium iron nitride magnet. This invention provides a MIM injection molding process for high-performance sintered samarium iron nitride magnets. From the formation of the Nb nano-modified layer, gradient binder, gradient degreasing, vacuum sintering, and the three-stage nitriding process, each step is interconnected. Only by employing this MIM injection molding process can a highly magnetic samarium iron nitride magnet be prepared.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A preparation process of MIM injection molded high-performance sintered samarium iron-nitrogen magnet, characterized in that: S1: Sm and Fe raw materials with purity ≥99.5% are prepared by vacuum induction melting to produce Sm2Fe 17 alloy, crushed and passed through a 200-400 mesh sieve to obtain an initial powder with an average particle size of 50-80 μm, the powder is placed together with Nb powder with a mass fraction of 1%-3% and a particle size of ≤10 μm and ZrO2 ball milling medium with a mass fraction of 0.5%-1% in a planetary ball mill, and the Nb element is adsorbed on the surface of the Sm2Fe 17 powder under the protection of inert gas at 300-400 r / min for 8-12 h to form a preliminary mechanical mixing layer; S2: the mixed powder after ball milling is annealed at 700-780℃ for 2-3 hours to promote the diffusion of Nb element to Sm2Fe 17 grain boundary and near surface area, forming a stable Nb nano-modified layer, in which the Nb element is distributed in Sm2Fe 17 grain boundary and near surface area in a gradient distribution, and the thickness of the Nb nano-modified layer is 100-150nm; S3: Using paraffin wax-poly lactic acid-stearic acid ternary binder system with mass ratio of 60:30:10, the pretreated Sm2Fe 17 The powder and the binder are mixed with solid phase content of 65%-70% by volume fraction, stirred at 120-150°C and 50-80r / min for 3-5h to form a uniform feed, injected into a mold through a screw injection molding machine at 180-220°C and an injection pressure of 80-120MPa, kept for 5-10s, and then cooled and demolded to obtain an injection molded body with a density of ≥90%, and meanwhile, a pulse magnetic field is used to induce grain preferred orientation during the injection molding process, and the orientation magnetic field strength is 1-2T. S4: solvent debinding: placing the injection molded body in n-heptane solvent, ultrasonic oscillation at 50-60℃ for 4-6h, removing 60%-70% of paraffin components to form a connected pore network; S5: thermal debinding: heating from room temperature to 400-500℃ at a rate of 5-8℃ / min, and keeping in nitrogen atmosphere for 2-5h to completely decompose and volatilize polylactic acid, with the final debinding body having a carbon content of ≤0.1%; S6: Put the defatted blank into the vacuum sintering furnace, and heat up to 1000-1100℃ at 10℃ / min, keep for 2-3h, then fill in nitrogen or argon to micro negative pressure, and then cool to room temperature quickly by air blower. During the sintering process, Sm2Fe 17 The Nb modified layer on the surface of the powder forms Nb-rich phase at the grain boundary, so that the average grain size is controlled at 5-10μm, and the grain boundary is clear and uniform; S7: placing the sintered body into a high-pressure nitriding furnace, and adopting a three-stage process: low-temperature adsorption stage: temperature 450-500℃, ammonia gas pressure 0.5-1MPa, and keeping for 0.5-3h to make N atoms physically adsorbed on the surface of the magnet and form an initial nitrided layer; medium-temperature diffusion stage: heating to 550-600℃, ammonia gas pressure reduced to 0.2-0.3MPa, and keeping for 0.5-3h to promote the diffusion of N atoms to the inside by using the concentration gradient, while avoiding grain coarsening at high temperature; High temperature solid solution section: heating to 650-700℃, according to the volume ratio 3:1, N2 and H2 mixed gas is passed in, pressure 1-1.5MPa, heat preservation 0.5-3h, make N atom fully solid solution in Sm2Fe 17 Lattice, forming stable Sm2Fe 17 N 3-x Phase; S8: ultrasonic cleaning the magnet after nitriding to remove surface residual impurities, then coating a 5-10μm thick Al2O3 protective layer by physical vapor deposition, and finally processing to the required size by electric spark cutting to obtain the final samarium iron-nitrogen magnet.

2. The process for producing a MIM injection molded high performance sintered samarium iron nitride magnet according to claim 1, characterized by, Wherein, the inert gas in S1 is argon or nitrogen.

3. The process for producing a MIM injection molded high performance sintered samarium iron nitride magnet according to claim 1, characterized by, Wherein, the annealing temperature in S2 is 750℃, and the holding time is 2.5h.

4. The process for producing a MIM injection molded high performance sintered samarium iron nitride magnet according to claim 1, characterized by, Wherein, the thickness of the Nb nano-modified layer in S2 is 130nm.

5. The process for producing a MIM injection molded high performance sintered samarium iron nitride magnet according to claim 1, characterized by, Wherein, The S6 Sm2Fe 17 The Nb-modified layer on the powder surface forms a Nb-rich phase at the grain boundaries, allowing the average grain size to be controlled to 8 μm.

6. The process for producing a MIM injection molded high performance sintered samarium iron nitride magnet according to claim 1, wherein Wherein, the thickness of the Al2O3 protective layer in S8 is 8μm.

7. A samarium iron-nitrogen magnet prepared by the preparation process of MIM injection molded high-performance sintered samarium iron-nitrogen magnet according to any one of claims 1-6.

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