Nitrogen-doped high-entropy alloy powder and method for preparing same

Abstract

The application discloses nitrogen-doped high-entropy alloy powder and a preparation method thereof. In order to solve the problems of low gap nitrogen solid solubility, easy precipitation of brittle metal nitride and uneven composition in the existing physical nitriding technology, the application adopts anhydrous metal halide, alkali metal amide and alkali metal azide as a reaction precursor. In the process of closed heating reaction, the amide is melted to provide a continuous liquid phase mass transfer medium; the azide is decomposed to release alkali metal and local high-pressure nitrogen gas; the alkali metal drives the metal halide to co-reduction; in the initial stage of nucleation and growth, the multi-component metal atoms are combined with the amino free radicals and high-pressure nitrogen gas in the system to directly embed nitrogen atoms into the lattice gap position, and high-concentration in-situ solid solution doping is completed. The application avoids the diffusion resistance of gas molecules in the traditional gas-solid nitriding, and realizes the preparation of alloy powder with high purity, uniform phase and no precipitation of brittle metal nitride.

Description

Technical Field

[0001] This invention relates to the field of alloy material synthesis and preparation technology, specifically to a nitrogen-doped high-entropy alloy powder and its preparation method. Background Technology

[0002] High-entropy alloys are typically composed of multiple major metallic elements in equiatomic or near-equiatomic ratios, exhibiting excellent mechanical and physical properties. Introducing non-metallic elements such as nitrogen into the alloy matrix for interstitial doping can generate interstitial solid solution strengthening, further enhancing the alloy's yield strength and deformation plasticity. Therefore, nitrogen-doped high-entropy alloy powders have clear application needs in industrial fields such as powder metallurgy, additive manufacturing of structural components, and surface hardening coatings.

[0003] Currently, the technology for preparing nitrogen-doped high-entropy alloy powders mainly relies on gas-solid or gas-liquid physical interface reaction pathways. Common conventional processes include mechanical alloying methods involving high-energy ball milling under nitrogen or ammonia atmospheres, and molten gas atomization powder preparation methods using nitrogen-containing gas as the atomizing medium. These traditional methods typically use nitrogen molecules as the main nitrogen dopant source, and through prolonged high-temperature, high-pressure annealing or high-intensity mechanical collisions, promote the penetration and dissolution of gaseous nitrogen elements into the already formed metal alloy matrix.

[0004] However, existing technologies face fundamental limitations in achieving high-concentration and uniform interstitial nitrogen doping due to their physicochemical mechanisms. Because diatomic nitrogen molecules possess extremely high dissociation energies and low thermodynamic equilibrium solubility in dense metal solid solutions, traditional gas-solid nitriding processes encounter significant mass diffusion resistance. Gaseous nitrogen molecules struggle to penetrate deep into the metal lattice, hindering the effective increase of the actual interstitial nitrogen content in the powder. Furthermore, the high-temperature processing environment of traditional physical nitriding provides long-range diffusion conditions for metal atoms. Transition metals with a strong affinity for nitrogen readily undergo localized segregation, preferentially precipitating brittle metal nitride second phases. This localized precipitation not only consumes interstitial free nitrogen but also disrupts the overall homogeneous solid solution state of the alloy elements, making it difficult for existing nitriding processes to achieve high-concentration interstitial doping while maintaining a single-phase solid solution structure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a nitrogen-doped high-entropy alloy powder and its preparation method. This solves the problem that existing technologies, when preparing nitrogen-doped high-entropy alloy powder, are limited by the thermodynamic solubility limit and the gas molecule dissociation kinetic barrier, making it difficult to achieve high concentration and uniform nitrogen doping within the solid solution lattice. At the same time, conventional high-temperature nitriding or long-term physical ball milling processes easily lead to the segregation of strong nitride-forming elements and the precipitation of a second phase, and are also prone to introducing oxygen impurities and mechanical contamination.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a nitrogen-doped high-entropy alloy powder, employing the following technical solution: A nitrogen-doped high-entropy alloy powder is prepared by a reaction precursor containing the following components and molar ratios through closed co-reduction and in-situ nitriding: anhydrous metal halide; alkali metal amine, the number of moles added being 2.5 to 5.0 times the total number of moles of anhydrous metal halide; alkali metal azide, the number of moles added being 1.05 to 1.20 times the total number of theoretical electrons required to completely reduce the anhydrous metal halide to the elemental metal.

[0007] Preferably, the anhydrous metal halide is composed of anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride, and anhydrous vanadium chloride; and the molar ratio of anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride, and anhydrous vanadium chloride is (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2): (0.8 to 1.2).

[0008] Preferably, the alkali metal amine is sodium amine or potassium amine; the alkali metal azide is sodium azide or potassium azide.

[0009] Preferably, the macroscopic main phase of the nitrogen-doped high-entropy alloy powder is a face-centered cubic solid solution structure, and the mass fraction of nitrogen in the powder is 1.38 wt% to 2.23 wt%, and the mass fraction of oxygen is less than or equal to 0.22 wt%.

[0010] Secondly, the present invention provides a method for preparing nitrogen-doped high-entropy alloy powder, employing the following technical solution: A method for preparing nitrogen-doped high-entropy alloy powder includes the following steps: (1) Under an inert atmosphere, anhydrous metal halides, alkali metal azides and alkali metal amines are mechanically mixed to obtain a mixture of reaction precursors; (2) Place the reaction precursor mixture obtained in step (1) in a closed reaction vessel and keep it at a constant temperature at the first temperature for in-situ gas-phase purification; (3) Then the temperature is raised to the second temperature and kept at a constant temperature to allow the reaction precursor mixture to undergo a medium-temperature co-reduction and in-situ doping reaction; (4) After the reaction is completed, the product is cooled and depressurized, and then subjected to anhydrous quenching, washing and purification and vacuum drying to obtain the final nitrogen-doped high-entropy alloy powder.

[0011] Preferably, in step (1), the inert atmosphere is high-purity argon gas with a water and oxygen content of less than 0.1 ppm; the mechanical mixing is dry ball milling, the ball-to-material mass ratio is controlled at (5 to 10):1, the mixing speed is 150 to 300 rpm, and the mixing time is 2 to 6 hours.

[0012] Preferably, in step (2), the heating rate to the first temperature is 0.5 to 2.0 °C / min, the first temperature is 250 to 300 °C, and the constant temperature holding time is 1.0 to 3.0 hours.

[0013] Preferably, in step (3), the heating rate to the second temperature is 0.5 to 3.0 °C / min, the second temperature is 400 to 600 °C, and the constant temperature holding time is 4.0 to 10.0 hours; during the holding reaction, the self-generated gauge pressure in the sealed reactor is controlled at 5.0 MPa to 15.0 MPa.

[0014] Preferably, in step (4), the specific implementation of anhydrous quenching is as follows: the cooled mixed reaction product is placed in anhydrous ethanol cooled in an ice bath for stirring and soaking, the solid-liquid mass ratio is controlled to be 1:(10 to 20), and the soaking time is 1.0 to 2.0 hours.

[0015] Preferably, in step (4), the washing and purification process involves using ultrapure water to ultrasonically wash and centrifuge the quenched product until no white precipitate is formed when silver nitrate solution is added to the washing supernatant; the process parameters for vacuum drying are: absolute pressure less than 0.01 Pa, temperature of 60 to 80 °C, and drying time of 12 to 24 hours.

[0016] This invention provides a nitrogen-doped high-entropy alloy powder and its preparation method. It has the following beneficial effects: 1. This invention constructs a reaction system using anhydrous metal halides, alkali metal amides, and alkali metal azides. During the closed co-reduction process, the alkali metals released by the decomposition of alkali metal azides and high-pressure nitrogen drive the reduction of metal halides. Simultaneously, combined with the amino radicals provided by the alkali metal amides, nitrogen atoms are embedded into the interstitial positions of the crystal lattice in the initial stage of the assembly of multi-component metal atoms into nuclei. This avoids the resistance of gas molecules to diffusion inside the metal in traditional gas-solid nitriding, and achieves a high-concentration interstitial solid solution nitriding effect.

[0017] 2. This invention overcomes the steric hindrance between pure solid particles by introducing alkali metal amines into the system and utilizing their ability to melt and form a liquid phase medium in the intermediate temperature reaction range. This improves the diffusion and mass transfer rate of metal precursor ions and active nitrogen species. Furthermore, it absorbs and releases heat during the reduction reaction to maintain a uniform temperature field, ensuring that multi-component metal atoms nucleate synchronously in various micro-regions. This achieves the synthesis effect of consistent powder phase and high reaction yield under large-scale preparation conditions.

[0018] 3. This invention employs a two-stage stepped heating process. In the first temperature stage, the reducing gas released by the heated amine compound is used to purify the water and oxygen impurities on the surface of the raw material in the gas phase. Subsequently, in the second temperature stage, the self-generated high pressure generated by the closed system promotes the reaction equilibrium to shift towards the formation of a solid solution. At the same time, the medium temperature condition restricts the long-range diffusion of metal atoms. This reduces the content of interstitial oxygen impurities in the alloy powder while achieving a high-purity preparation effect that suppresses the precipitation of brittle metal nitrides. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see the appendix Figure 1 This invention provides a nitrogen-doped high-entropy alloy powder and its preparation method.

[0022] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Anhydrous ethanol, high-purity argon and ultrapure water, which are not specifically mentioned, are all commercially available analytical grade or higher conventional chemical products. Whether they are disclosed or not does not affect those skilled in the art to implement this scheme. Their specific structures and physicochemical parameters are omitted here.

[0023] In the core reaction precursors of this invention, sodium amide has the molecular formula NaNH2 (CAS number 7782-92-5), and sodium azide has the molecular formula NaN3 (CAS number 26628-22-8). Both are powders with a purity greater than or equal to 99.5%. The metal precursors used include anhydrous ferrous chloride (FeCl2, CAS number 7758-94-3), anhydrous cobalt chloride (CoCl2, CAS number 7646-79-9), anhydrous nickel chloride (NiCl2, CAS number 7718-54-9), anhydrous chromium chloride (CrCl3, CAS number 10025-73-7), and anhydrous vanadium chloride (VCl3, CAS number 7718-98-1). All of the above metal precursors are ultra-dry purity powders with a purity greater than or equal to 99.9%.

[0024] Preparation example: Preparation Example 1: This preparation example provides a dual-effect coupled nitrogen-containing molten salt reaction precursor mixture, comprising the following steps: (1) In a high-purity argon glove box with water and oxygen content of less than 0.1 ppm, anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride and anhydrous vanadium chloride were accurately weighed in a molar ratio of 1:1:1:1:1 as metal precursors.

[0025] (2) Calculate the total number of moles of electrons required for the above metal precursor to be completely reduced to the metal element, and accurately weigh sodium azide powder according to the weighing ratio of 1.10 times the theoretical stoichiometric ratio.

[0026] (3) Weigh out sodium amino powder precisely at a ratio of 3.5:1 to the total number of moles of the metal precursor.

[0027] (4) Transfer the weighed metal precursor, sodium azide and sodium amide to a ball mill jar with a polytetrafluoroethylene liner, add zirconium oxide grinding balls, control the ball-to-material mass ratio to be 8:1, and seal the ball mill jar in a glove box.

[0028] (5) Place the sealed ball mill jar on a planetary ball mill and dry mechanically mix at 200 rpm for 4 hours to collect a uniform mixture of nitrogen-containing molten salt reaction precursors with double-effect coupling.

[0029] Preparation Example 2: This preparation example provides a dual-effect coupled nitrogen-containing molten salt reaction precursor mixture, comprising the following steps: (1) In a high-purity argon glove box with water and oxygen content less than 0.1 ppm, anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride and anhydrous vanadium chloride were accurately weighed in a molar ratio of 0.8:1.2:0.8:1.2:1.0 as metal precursors.

[0030] (2) Calculate the total number of moles of electrons required for the above metal precursor to be completely reduced to the metal element, and accurately weigh sodium azide powder according to the weighing ratio of 1.05 times the theoretical stoichiometric ratio.

[0031] (3) Weigh out sodium amino powder precisely at a ratio of 2.5:1 to the total number of moles of the metal precursor.

[0032] (4) Transfer the weighed metal precursor, sodium azide and sodium amide to a ball mill jar with a polytetrafluoroethylene liner, add zirconium oxide grinding balls, control the ball-to-material mass ratio to be 5:1, and seal the ball mill jar in a glove box.

[0033] (5) Place the sealed ball mill jar on a planetary ball mill and dry mechanically mix at 150 rpm for 2 hours to collect a uniform mixture of nitrogen-containing molten salt reaction precursors with double-effect coupling.

[0034] Preparation Example 3: This preparation example provides a dual-effect coupled nitrogen-containing molten salt reaction precursor mixture, comprising the following steps: (1) In a high-purity argon glove box with water and oxygen content less than 0.1 ppm, anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride and anhydrous vanadium chloride were accurately weighed in a molar ratio of 1.2:0.8:1.2:0.8:1.0 as metal precursors.

[0035] (2) Calculate the total number of moles of electrons required for the above metal precursor to be completely reduced to the metal element, and accurately weigh sodium azide powder according to the weighing ratio of 1.20 times the theoretical stoichiometric ratio.

[0036] (3) Weigh out sodium amino powder precisely at a ratio of 5.0:1 to the total number of moles of the metal precursor.

[0037] (4) Transfer the weighed metal precursor, sodium azide and sodium amide to a ball mill jar with a polytetrafluoroethylene liner, add zirconium oxide grinding balls, control the ball-to-material mass ratio to be 10:1, and seal the ball mill jar in a glove box.

[0038] (5) Place the sealed ball mill jar on a planetary ball mill and dry mechanically mix at 300 rpm for 6 hours to collect a uniform mixture of nitrogen-containing molten salt reaction precursors with double-effect coupling.

[0039] Example: Example 1: This embodiment provides a method for preparing nitrogen-doped high-entropy alloy powder, including the following steps: (1) Loading and sealing: In a high-purity argon glove box with water and oxygen content of less than 0.1 ppm, the mixture of nitrogen-containing molten salt reaction precursors obtained in Preparation Example 1 was loaded into a Hastelloy high-pressure reactor with a pressure threshold of 25.0 MPa. The powder was compacted and the filling coefficient was controlled to be 20% of the effective volume of the reactor. Then the flange was tightened to seal the reactor tightly.

[0040] (2) In-situ gas-phase purification: The sealed reactor is placed in a heating furnace and slowly heated to 280°C at a heating rate of 1.0°C / min, and kept at this temperature for 2.0 hours. During this stage, sodium amide partially melts and generates trace amounts of self-generated hydrogen gas, which performs in-situ deep reduction and deoxygenation of the reactants.

[0041] (3) Medium-temperature co-reduction and in-situ doping: The reactor was heated to 500°C at a heating rate of 2.0°C / min and kept at a constant temperature for 6.0 hours. During this stage, sodium azide was decomposed in a controlled manner to release local high-pressure nitrogen gas and nascent metallic sodium, which drove the co-reduction of metal chloride and in-situ nitriding. The self-generated surface pressure inside the reactor climbed and stabilized at about 10.0 MPa.

[0042] (4) Anhydrous quenching: After the reaction is completed, stop heating and allow the reactor to cool naturally to room temperature. After venting the residual high-pressure gas in the reactor, open the reactor in the fume hood, scrape off the mixed reaction salt block, immerse it in anhydrous ethanol cooled in an ice bath, control the solid-liquid mass ratio to be 1:15, and slowly stir and soak for 1.5 hours to quench the residual trace active substances.

[0043] (5) Washing, purification and drying: The above ethanol suspension was filtered, and the filter cake was transferred to ultrapure water and treated with an ultrasonic cleaner at a frequency of 40 kHz for 20 minutes, followed by centrifugation at 6000 rpm. The ultrasonic washing and centrifugation process was repeated 4 times. Silver nitrate solution was added to the last supernatant to confirm that no white precipitate was formed. Finally, the filter cake was solvent-replaced with anhydrous ethanol and placed in a vacuum drying oven. It was vacuum dried for 18 hours under conditions of absolute pressure less than 0.01 Pa and temperature of 70 °C to obtain pure nitrogen-doped high-entropy alloy powder.

[0044] Example 2: This embodiment provides a method for preparing nitrogen-doped high-entropy alloy powder, including the following steps: (1) Loading and sealing: In a high-purity argon glove box with water and oxygen content of less than 0.1 ppm, the mixture of nitrogen-containing molten salt reaction precursors obtained in Preparation Example 2 was loaded into a Hastelloy high-pressure reactor with a pressure threshold of 25.0 MPa. The powder was compacted and the filling coefficient was controlled to be 15% of the effective volume of the reactor. Then the flange was tightened to seal the reactor tightly.

[0045] (2) In-situ gas phase purification: The sealed reaction vessel is placed in a heating furnace and slowly heated to 250°C at a heating rate of 0.5°C / min. The temperature is then maintained at this temperature for 1.0 hour to carry out in-situ gas phase purification.

[0046] (3) Medium-temperature co-reduction and in-situ doping: The reactor was heated to 400°C at a heating rate of 1.0°C / min and kept at a constant temperature for 10.0 hours. The reaction kinetics were relatively slow at this temperature. The holding time was extended to ensure complete co-reduction. The autogenous pressure inside the reactor increased and stabilized at about 5.0 MPa.

[0047] (4) Anhydrous quenching: After the reaction is completed, stop heating and allow the reactor to cool naturally to room temperature. After purging the residual gas in the reactor, take out the reaction product and immerse it in anhydrous ethanol cooled in an ice bath, controlling the solid-liquid mass ratio to be 1:10, and slowly stir and soak for 1.0 hour.

[0048] (5) Washing, purification and drying: After filtration, the filter cake was transferred to ultrapure water, sonicated at 40 kHz for 15 minutes, and centrifuged at 4000 rpm. The washing and centrifugation process was repeated 3 times until chloride ions were removed. After replacing the water with anhydrous ethanol, the powder was placed in a vacuum drying oven and vacuum dried for 24 hours under an absolute pressure of less than 0.01 Pa and a temperature of 60 °C to obtain nitrogen-doped high-entropy alloy powder.

[0049] Example 3: This embodiment provides a method for preparing nitrogen-doped high-entropy alloy powder, including the following steps: (1) Loading and sealing: In a high-purity argon glove box with water and oxygen content of less than 0.1 ppm, the mixture of nitrogen-containing molten salt reaction precursors obtained in Preparation Example 3 was loaded into a Hastelloy high-pressure reactor with a pressure threshold of 25.0 MPa. The powder was compacted and the filling coefficient was controlled to be 30% of the effective volume of the reactor. Then the flange was tightened to seal the reactor tightly.

[0050] (2) In-situ gas phase purification: The sealed reaction vessel is placed in a heating furnace and slowly heated to 300°C at a heating rate of 2.0°C / min. The temperature is then maintained at this temperature for 3.0 hours to carry out in-situ gas phase purification.

[0051] (3) Medium-temperature co-reduction and in-situ doping: The reactor was heated to 600°C at a heating rate of 3.0°C / min and kept at a constant temperature for 4.0 hours. The high loading rate and high temperature led to rapid and violent decomposition reaction, and the self-generated gauge pressure in the reactor climbed and stabilized at about 15.0 MPa.

[0052] (4) Anhydrous quenching: After the reaction is complete, allow it to cool naturally to room temperature. After venting the high-pressure gas, take out the product and immerse it in anhydrous ethanol cooled in an ice bath. Control the solid-liquid mass ratio to be 1:20 and stir slowly for 2.0 hours.

[0053] (5) Washing, purification and drying: After filtration, the filter cake was transferred to ultrapure water, sonicated at 40 kHz for 30 minutes, and centrifuged at 8000 rpm. The washing and centrifugation process was repeated 5 times until chloride ions were removed. After replacing the water with anhydrous ethanol, the powder was placed in a vacuum drying oven and vacuum dried for 12 hours under an absolute pressure of less than 0.01 Pa and a temperature of 80 °C to obtain nitrogen-doped high-entropy alloy powder.

[0054] Example 4: This embodiment provides a method for preparing nitrogen-doped high-entropy alloy powder, including the following steps: (1) Loading and sealing: In a high-purity argon glove box with water and oxygen content of less than 0.1 ppm, the mixture of nitrogen-containing molten salt reaction precursors obtained in Preparation Example 1 was loaded into a Hastelloy high-pressure reactor with a pressure threshold of 25.0 MPa. The powder was compacted and the filling coefficient was controlled to be 25% of the effective volume of the reactor. Then the flange was tightened to seal the reactor tightly.

[0055] (2) In-situ gas phase purification: The sealed reaction vessel is placed in a heating furnace and heated to 280°C at a very slow heating rate of 0.5°C / min. The temperature is then kept constant at this temperature for 2.5 hours to carry out in-situ deep purification.

[0056] (3) Medium-temperature co-reduction and in-situ doping: The reactor was heated to 550°C at an extremely slow heating rate of 0.5°C / min and kept at a constant temperature for 8.0 hours. The extremely slow heating rate created a gentle phase transition and co-reduction environment, and the self-generated surface pressure inside the reactor climbed and stabilized at about 12.0 MPa.

[0057] (4) Anhydrous quenching: After the reaction is complete, allow it to cool naturally to room temperature. Remove the air, take out the product and immerse it in anhydrous ethanol cooled in an ice bath, control the solid-liquid mass ratio to be 1:15, and stir slowly for 1.5 hours.

[0058] (5) Washing, purification and drying: After filtration, the filter cake was transferred to ultrapure water, sonicated at 40 kHz for 25 minutes, and centrifuged at 6000 rpm. The washing and centrifugation process was repeated 4 times until chloride ions were removed. After replacing the water with anhydrous ethanol, the powder was placed in a vacuum drying oven and vacuum dried for 16 hours under an absolute pressure of less than 0.01 Pa and a temperature of 75 °C to obtain nitrogen-doped high-entropy alloy powder.

[0059] Comparative example: Comparative Example 1: Compared with Example 1, the difference is that sodium azide was not added when preparing the precursor, but a block of metallic sodium that meets the theoretical stoichiometric ratio was used as a reducing agent; otherwise, they are the same.

[0060] Comparative Example 2: Compared with Example 1, the difference is that sodium amide was not added when preparing the precursor, and sodium azide was used as the reducing agent and the only nitrogen source, while the rest were the same.

[0061] Comparative Example 3: Compared with Example 1, the difference is that the in-situ gas phase purification step of holding at 280°C for 2.0 hours was omitted. Instead, the sealed reactor was directly heated to 500°C at a heating rate of 2.0°C / min and held at that temperature for 6.0 hours. All other aspects are the same.

[0062] Comparative Example 4: Compared with Example 1, the difference is that the above-mentioned precursor formulation of metal chloride and double-effect molten salt was not used for co-reduction synthesis. Instead, the equiatomic ratio iron-cobalt-nickel-chromium-vanadium high-entropy alloy powder prepared by vacuum atomization was placed in the reactor and annealed at a constant temperature of 500°C and 10.0 MPa for 6.0 hours. The remaining product washing, purification and drying steps were the same.

[0063] Test example: Test Example 1: The vacuum-dried powder sample was placed in the groove of the glass slide sample stage and compacted and smoothed with a glass plate. The crystalline phase was determined using X-ray diffraction with a Cu K radiation source. ,wavelength The aperture is 1.5406 Å, the tube voltage is 40 kV, and the tube current is 40 mA. Continuous scanning mode is used, and the scanning angle is... The sampling range was 20° to 90°, with a sampling step size of 0.02° and a scan rate of 5° / min. After acquiring the diffraction data, smoothing was performed and background baseline was subtracted, and the positions of the main diffraction peaks were read. Based on Bragg's equation and the interplanar spacing formula for face-centered cubic crystal systems, the lattice constant was calculated. .

[0064] Table 1: X-ray diffraction analysis data of products from each example and comparative example

[0065] According to X-ray diffraction data, the powder products of Examples 1 to 4 exhibit a face-centered cubic high-entropy solid solution structure. No byproduct residues were detected, indicating that the reduction reaction was complete and the water washing process removed the soluble salts. The lattice constant of the equiatomic ratio iron-cobalt-nickel-chromium-vanadium high-entropy alloy typically ranges from 3.57 Å to 3.58 Å. The lattice constants of the various examples increased to above 3.60 Å, indicating lattice expansion. The main diffraction peak shifted to a lower angle, indicating that nitrogen atoms entered the interstitial positions of the face-centered cubic lattice, causing lattice distortion and achieving interstitial nitrogen doping.

[0066] Comparative Example 1, without the addition of sodium azide, produced a product with a lattice constant of 3.585 Å. In the single sodium amide nitrogen-supplying system, the interstitial nitrogen solid solution content decreased. Comparative Example 2, without the addition of sodium amide, produced a multiphase mixture containing unreacted matter. The solid-phase decomposition system lacked a liquid medium, resulting in uneven component mixing, indicating that sodium amide provided the necessary liquid-phase environment for high-entropy phase nucleation. Comparative Example 4, using gas-solid nitriding, produced a metal nitride precipitate phase. Due to the high thermodynamic affinity of chromium and vanadium for nitrogen, nitrogen preferentially combines with specific elements during the gas-solid treatment, disrupting the solid solution state of the elements. In the liquid-phase co-reduction process of this scheme, metal nucleation and interstitial nitrogen atom insertion occur simultaneously. Limited by reaction kinetics, long-range diffusion and aggregation of metal atoms are hindered, suppressing the precipitation of the metal nitride second phase.

[0067] Test Example 2: The theoretical mass of the high-entropy alloy product was calculated based on the molar amounts of each anhydrous metal chloride. The total mass of the vacuum-dried powder was weighed using an analytical balance, and the reaction yield (actual mass / theoretical mass × 100%) was calculated. Samples were taken from five different locations in the same batch of powder, including the center and four edges of the container. X-ray diffraction tests were performed on the powder at each sampling point, using the same parameters as in Test Example 1. The integrated intensity of the strongest diffraction peak of the impurity phase in the spectrum was extracted, and its percentage relative to the integrated intensity of the main diffraction peak of the face-centered cubic solid solution was calculated.

[0068] Table 2: Reaction yield and impurity peak intensity percentage data for each example and comparative example

[0069] The yields of Examples 1 to 4 were above 82.1%, and the percentage of impurity peak intensity at all five sampling points was 0. The yield of Comparative Example 2 decreased to 31.7%, with impurity phase content ranging from 8.4% to 82.1% at different sampling points. The yield of Comparative Example 1 was 64.2%, and impurity phases were present.

[0070] Comparative Example 2 employed a solid-state reaction system, where the decomposition of sodium azide and the metal reduction reaction were limited by the contact area between solid particles. The low interfacial mass transfer rate and incomplete metal precursor conversion led to a decrease in yield. The exothermic reduction reaction created localized hotspots in the solid-state system, and temperature differences resulted in varying reaction progress and nucleation rates in different regions, leading to component segregation and unreacted residues.

[0071] In the example formulation, sodium amide melts in the intermediate temperature range, providing a liquid phase medium. The metal precursor, reducing agent decomposition products, and nitrogen atoms disperse and dissolve miscibly in the liquid phase environment. The liquid phase medium reduces steric hindrance, increases atomic diffusion rates, promotes precursor transformation, and improves overall yield. The heat capacity of the liquid phase absorbs the heat of reaction, regulating the temperature field. Under uniform mass and heat transfer conditions, multi-component metal atoms nucleate synchronously in each region, ensuring the consistency of the entire batch of powder phases.

[0072] Test Example 3: The mass fractions of nitrogen and oxygen in each group of powder products were determined using an oxygen, nitrogen, and hydrogen elemental analyzer. For each test, 15 to 20 milligrams of vacuum-dried powder were weighed and placed in a high-temperature degassed graphite crucible. Under a flow of 99.999% pure helium, the graphite crucible was pushed into a pulsed electrode furnace and heated to 2500°C to melt the powder. The oxygen in the powder reacted with the graphite to generate a mixture of carbon monoxide and carbon dioxide, and the oxygen release was measured using an infrared detector. The nitrogen in the powder was released as nitrogen molecules; after purification to remove interfering gases, the nitrogen release was measured using a thermal conductivity detector. Each group of samples was tested in triplicate.

[0073] Table 3: Test data of oxygen and nitrogen element mass fraction of powders in each example and comparative example

[0074] Elemental analysis data showed that the nitrogen content of the products in the examples ranged from 1.38 wt% to 2.23 wt%. Comparative Example 4, using a gas-solid nitriding process with gas-atomized powder, produced products with a nitrogen content between 0.21 wt% and 0.29 wt%. In the gas-solid reaction, nitrogen molecules face high diffusion resistance and low solid solubility in the dense metal phase. The co-reduction mechanism in the examples allowed free nitrogen atoms to participate in deposition during the initial stage of metal nucleation, increasing the nitrogen doping concentration.

[0075] In Comparative Example 1, without the addition of sodium azide, the nitrogen content of the product decreased to below 0.46 wt%. In the single sodium amide molten salt system, the lack of high-pressure nitrogen gas driven by the decomposition of sodium azide reduced the number of nitrogen atoms entering the interstitial spaces, indicating that the combined use of sodium azide and sodium amide has a direct effect on increasing the nitrogen doping level.

[0076] Comparative Example 2 was not subjected to elemental analysis because the product was a multiphase mixture and contained unreacted metal chlorides.

[0077] Comparative Example 3 eliminated the 280°C isothermal platform and directly heated to the reaction temperature, increasing the oxygen content of the product to between 0.82 wt% and 0.94 wt%. The oxygen mass fraction of the product in the examples remained below 0.22 wt%. The direct heating process caused moisture and oxides adsorbed on the surface of the metal precursor to enter the final crystal lattice or form inclusions. The isothermal platform in the examples utilized hydrogen released from the initial decomposition of sodium amide to establish a reducing atmosphere, performing gas-phase deoxygenation of the precursor before the main reduction reaction, reducing the surface oxygen content and controlling the oxygen impurity level of the powder.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A nitrogen-doped high-entropy alloy powder, characterized in that, Prepared by closed co-reduction and in-situ nitriding of a reaction precursor containing the following components and molar ratios: Anhydrous metal halides; Alkali metal amines, wherein the molar number of alkali metal amines added is 2.5 to 5.0 times the total molar number of the anhydrous metal halides; An alkali metal azide, wherein the number of moles of the alkali metal azide added is 1.05 to 1.20 times the total number of theoretical moles of electrons required to completely reduce the anhydrous metal halide to the elemental metal.

2. The nitrogen-doped high-entropy alloy powder according to claim 1, characterized in that, The anhydrous metal halide is composed of anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride, and anhydrous vanadium chloride; The molar ratio of anhydrous ferrous chloride, anhydrous cobalt chloride, anhydrous nickel chloride, anhydrous chromium chloride and anhydrous vanadium chloride is (0.8~1.2):(0.8~1.2):(0.8~1.2):(0.8~1.2):(0.8~1.2).

3. The nitrogen-doped high-entropy alloy powder according to claim 2, characterized in that, The alkali metal amine is sodium amine or potassium amine; the alkali metal azide is sodium azide or potassium azide.

4. The nitrogen-doped high-entropy alloy powder according to claim 3, characterized in that, The macroscopic main phase of the nitrogen-doped high-entropy alloy powder is a face-centered cubic solid solution structure, and the mass fraction of nitrogen in the powder is 1.38wt% to 2.23wt%, and the mass fraction of oxygen is less than or equal to 0.22wt%.

5. The method for preparing nitrogen-doped high-entropy alloy powder according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Under an inert atmosphere, anhydrous metal halides, alkali metal azides and alkali metal amines are mechanically mixed to obtain a mixture of reaction precursors; (2) Place the reaction precursor mixture obtained in step (1) in a closed reaction vessel and keep it at a constant temperature at the first temperature for in-situ gas-phase purification; (3) The temperature is then raised to the second temperature and kept constant to allow the reaction precursor mixture to undergo a medium-temperature co-reduction and in-situ doping reaction; (4) After the reaction is completed, the product is cooled and depressurized, and then subjected to anhydrous quenching, washing and purification and vacuum drying to obtain the final nitrogen-doped high-entropy alloy powder.

6. The method for preparing nitrogen-doped high-entropy alloy powder according to claim 5, characterized in that, In step (1), the inert atmosphere is high-purity argon gas with a water and oxygen content of less than 0.1 ppm; the mechanical mixing is dry ball milling, with the ball-to-material mass ratio controlled at (5-10):1, the mixing speed at 150-300 rpm, and the mixing time at 2-6 hours.

7. The method for preparing nitrogen-doped high-entropy alloy powder according to claim 5, characterized in that, In step (2), the heating rate to the first temperature is 0.5 to 2.0 °C / min, the first temperature is 250 to 300 °C, and the constant temperature holding time is 1.0 to 3.0 hours.

8. The method for preparing nitrogen-doped high-entropy alloy powder according to claim 5, characterized in that, In step (3), the heating rate to the second temperature is 0.5 to 3.0 °C / min, the second temperature is 400 to 600 °C, and the constant temperature holding time is 4.0 to 10.0 hours; During the heat preservation reaction, the autogenous gauge pressure inside the sealed reactor reaches 5.0 MPa to 15.0 MPa.

9. The method for preparing nitrogen-doped high-entropy alloy powder according to claim 5, characterized in that, In step (4), the specific implementation of the anhydrous quenching is as follows: the cooled mixed reaction product is placed in anhydrous ethanol cooled in an ice bath for stirring and soaking, the solid-liquid mass ratio is controlled to be 1:(10-20), and the soaking time is 1.0-2.0 hours.

10. The method for preparing nitrogen-doped high-entropy alloy powder according to claim 5, characterized in that, In step (4), the washing and purification process involves using ultrapure water to ultrasonically wash and centrifuge the quenched product until no white precipitate is formed when silver nitrate solution is added to the washing supernatant. The process parameters for vacuum drying are: absolute pressure less than 0.01 Pa, temperature of 60-80℃, and drying time of 12-24 hours.

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