A method for hierarchical nitridation of an alloy

Abstract

The present invention belongs to the technical field of magnetic materials and discloses a method for hierarchical nitriding of an alloy. The method of the present invention includes the steps of: after the alloy is roughly crushed and screened, hydrogen is introduced for hydrogen treatment to obtain a hydrogen-treated alloy; the hydrogen-treated alloy is subjected to dehydrogenation treatment under vacuum conditions to obtain a dehydrogenated alloy; nitrogen is introduced into the dehydrogenated alloy for nitriding treatment, and the nitriding treatment is divided into N levels, N≥2, to obtain an interstitial nitrogen atom compound. The present invention performs hydrogen treatment on the alloy to make the sample more easily nitrided, divides the nitriding process into multiple heating stages, enables the sample to gradually increase the nitrogen content in different heating stages, greatly shortens the reaction time of nitriding, improves the quality of nitriding, and finally realizes efficient and uniform nitriding of the alloy. After the alloy powder is ball-milled for a short time, H cj reaches 10.37 kOe.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic materials, and in particular to a method for hierarchical nitridation of an alloy. Background Art

[0002] In 1990, researchers discovered the interstitial atom effect of Re2Fe 17 including Sm2Fe 17 alloy: by introducing small-sized elements such as H, C, and N into the unit cell of Sm2Fe 17 causes lattice expansion. Neutron diffraction structure analysis shows that these small-sized atoms will enter the interstitial sites 9e and 6h of the alloy unit cell, which will increase the Fe-Fe atomic spacing, thereby enhancing the interatomic exchange interaction between Fe-Fe, and significantly increasing the magnetocrystalline anisotropy and Curie temperature; among them, the introduction of N atoms has the most significant effect on the improvement of coercivity and Curie temperature. Therefore, Re-M-N interstitial nitrogen atom compounds represented by Sm2Fe 17 N x materials have received extensive attention.

[0003] For Sm2Fe 17 N x it has been shown by research that when the nitrogen content x = 3, the performance is optimal. The existing preparation methods of Sm2Fe 17 N x magnetic powder can generally be divided into two steps: First, prepare a Sm-Fe alloy; then perform nitridation treatment on the Sm-Fe alloy to obtain Sm-Fe-N magnetic powder.

[0004] The existing nitridation processes for Sm-Fe alloys include: nitrogen nitridation, ammonia nitridation, ammonia-hydrogen mixed gas nitridation, etc. However, the nitridation efficiency in a nitrogen atmosphere is low and the nitridation time is long; while the nitridation efficiency is high in an ammonia atmosphere or an ammonia-hydrogen mixed gas atmosphere, but the nitrogen content is difficult to control around 3. And, since the thermal stability of Sm2Fe 17 N x material depends on the nitrogen content x value, and the thermal stability is proportional to the x value within a certain range. If nitridation is always carried out at a relatively high temperature, some components with low nitrogen content may decompose at this temperature, that is, too high a temperature will pose a threat to the thermal stability of components with low nitrogen content. Therefore, achieving efficient and uniform nitridation of Sm-Fe alloy and enabling the nitrogen content to be controlled around 3 is the key to preparing Sm-Fe-N magnetic powder with excellent permanent magnetic properties. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for hierarchical nitridation of an alloy to solve the problems of low nitridation efficiency and difficult control of nitrogen content in the existing nitridation processes.

[0006] To achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for hierarchical nitridation of an alloy, comprising the following steps:

[0008] (1) After the alloy is roughly crushed and screened, hydrogen is introduced for hydrogen treatment to obtain a hydrogen-treated alloy;

[0009] (2) The hydrogen-treated alloy is subjected to dehydrogenation treatment under vacuum conditions to obtain a dehydrogenated alloy;

[0010] (3) Nitrogen is introduced into the dehydrogenated alloy for nitridation treatment. The nitridation treatment is divided into N levels, N≥2, to obtain an interstitial nitrogen atom compound;

[0011] Wherein, the alloy is a Re-M alloy, and Re is one or more of Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu; M is one or more of Fe, Co, Ti, Nb, V, Cr, Mn, Si, Mo, Ga, Ni, Cu, Zn, Zr, Hf, Ta, W.

[0012] Further, in the method for hierarchical nitridation of the alloy, the particle size of the alloy powder obtained after screening in step (1) is 10-200 mesh.

[0013] Further, in the method for hierarchical nitridation of the alloy, the temperature of the hydrogen treatment in step (1) is 200-300°C, the time of the hydrogen treatment in step (1) is 1-3 h, and the flow rate of hydrogen in the hydrogen treatment in step (1) is 100-250 mL / min.

[0014] Further, in the method for hierarchical nitridation of the alloy, the pressure P≤10 Pa under vacuum conditions in step (2), the temperature of the dehydrogenation treatment in step (2) is 200-300°C, and the time of the dehydrogenation treatment in step (2) is 10-90 min.

[0015] Further, in the method for hierarchical nitridation of the alloy, in the nitridation treatment in step (3), the temperature difference T≥20°C between adjacent levels.

[0016] Further, in the method for hierarchical nitridation of the alloy, the temperature of the nitridation treatment in step (3) is 300-550°C, the total time of the nitridation treatment in step (3) is 6-15 h, and the flow rate of nitrogen in the nitridation treatment in step (3) is 200-500 mL / min.

[0017] Further, in the method for hierarchical nitridation of the alloy, in the nitridation treatment in step (3), the time t of each level of nitridation treatment ≥0.5 h.

[0018] Further, in the stepwise nitriding method of the alloy, after the nitriding treatment in step (3), washing and drying treatments are further included, and the specific methods of the washing and drying treatments are as follows: after washing with any one of water, alcohol or acetic acid, drying is carried out at 20-100 °C for 1-3 h under vacuum conditions.

[0019] Further, in the stepwise nitriding method of the alloy, after obtaining the interstitial nitrogen atom compound in step (3), ball milling is carried out, the ball milling time is 1-60 min, and the mass ratio of the material:ball:solvent in the ball milling is 1:5-10:1-2.

[0020] It can be seen from the above technical solutions that, compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention designs a stepwise nitriding process under an N2 atmosphere. First, the alloy is subjected to hydrogen treatment to make the sample more easily nitrided; secondly, a nitriding atmosphere of high-purity N2 is selected, and the nitriding process is divided into multiple heating stages, so that the nitrogen content of the sample gradually increases in different heating stages. Based on this process, the alloy sample can always be maintained at a temperature suitable for thermal stability, greatly shortening the reaction time of conventional nitrogen nitriding, further improving the quality of nitriding, ensuring that the material reaches the best nitriding degree, obtaining high-quality interstitial atom compounds, and finally realizing the efficient and uniform nitriding of the alloy, with the nitrogen content x≈3;

[0022] (2) After the process optimization of stepwise nitriding, the finally prepared magnetic powder reaches 10.37 kOe after short-time ball milling. cj BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0024] Figure 1 XRD patterns of the Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Examples 1-3;

[0025] Figure 2 XRD patterns of the Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Comparative Example 1;

[0026] Figure 3 XRD patterns of the Sm2(Fe 0.9 Co 0.1 )​17 N x SEM image of the powder;

[0027] Figure 4 The Sm2(Fe 0.9 Co 0.1 ) 17 N x Particle size distribution diagram of the powder;

[0028] Figure 5 The Sm2(Fe 0.9 Co 0.1 ) 17 N x SEM image of the powder after grinding;

[0029] Figure 6 The Sm2(Fe 0.9 Co 0.1 ) 17 N x Particle size distribution diagram of the powder after grinding;

[0030] Figure 7 The Sm2(Fe 0.9 Co 0.1 ) 17 N x Demagnetization curve of the powder after grinding at 20 kOe. Detailed implementation method

[0031] The present invention provides a method for hierarchical nitriding of an alloy, comprising the following steps:

[0032] (1) After the alloy is roughly crushed and screened, hydrogen is introduced for hydrogen treatment to obtain a hydrogen-treated alloy;

[0033] (2) The hydrogen-treated alloy is subjected to dehydrogenation treatment under vacuum conditions to obtain a dehydrogenated alloy;

[0034] (3) Nitrogen is introduced into the dehydrogenated alloy for nitriding treatment. The nitriding treatment is divided into N levels, N≥2, to obtain an interstitial nitrogen atom compound;

[0035] Wherein, the alloy is a Re-M alloy, and Re is one or more of Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu; M is one or more of Fe, Co, Ti, Nb, V, Cr, Mn, Si, Mo, Ga, Ni, Cu, Zn, Zr, Hf, Ta, W.

[0036] The reason for the hydrogen treatment in the present invention is due to the interstitial N atom compound Re-M-N x (taking Sm2Fe17 N x For example), the raw material Sm2Fe 17 There is: Sm2Fe 17 +H2→Sm2Fe 17 H x , and for the alloy in which H atoms enter the lattice in advance, it is easier to infiltrate N atoms to achieve nitridation.

[0037] In the present invention, the Re is preferably one or more of Ce, Pr, Nd, Sm, Gd, Tb, Tm, further preferably one or more of Nd, Sm, Tm, and more preferably Sm.

[0038] In the present invention, the M is preferably one or more of Fe, Co, Ti, Cr, Si, Ni, Cu, further preferably one or more of Fe, Co, Cr, Si, and more preferably two of Fe and Co.

[0039] In the present invention, the particle size of the alloy powder obtained after sieving in step (1) is preferably 10-200 mesh, further preferably 20-80 mesh, and more preferably 20-40 mesh.

[0040] In the present invention, the temperature of the hydrogen treatment in step (1) is preferably 200-300 °C, further preferably 200-240 °C, and more preferably 200 °C.

[0041] In the present invention, the time of the hydrogen treatment in step (1) is preferably 1-3 h, further preferably 1-2 h, and more preferably 1 h.

[0042] In the present invention, the flow rate of hydrogen in the hydrogen treatment in step (1) is preferably 100-250 mL / min, further preferably 140-200 mL / min, and more preferably 150 mL / min.

[0043] In the present invention, the pressure P under vacuum conditions in step (2) is preferably ≤10 Pa.

[0044] In the present invention, the temperature of the dehydrogenation treatment in step (2) is preferably 200-300 °C, further preferably 200-250 °C, and more preferably 200 °C.

[0045] In the present invention, the time of the dehydrogenation treatment in step (2) is preferably 10-90 min, further preferably 40-70 min, and more preferably 60 min.

[0046] In the present invention, in the nitridation treatment in step (3), the temperature difference T between adjacent gradings is preferably ≥20 °C.

[0047] In the present invention, the temperature of the nitriding treatment in step (3) is preferably 300 to 550 °C, more preferably 380 to 500 °C.

[0048] In the present invention, the total time of the nitriding treatment in step (3) is preferably 6 to 15 h, more preferably 8 to 12 h, and even more preferably 10 h.

[0049] In the present invention, the flow rate of nitrogen in the nitriding treatment in step (3) is preferably 200 to 500 mL / min, more preferably 320 to 480 mL / min, and even more preferably 400 mL / min.

[0050] In the present invention, in the nitriding treatment in step (3), the time t of each stage of nitriding treatment is preferably ≥0.5 h, more preferably ≥0.8 h, and even more preferably ≥1 h.

[0051] In the present invention, in the nitriding treatment in step (3), the time of the first-stage nitriding treatment is preferably 2 to 6 h, more preferably 3 to 5 h, and even more preferably 4 h.

[0052] In the present invention, after the nitriding treatment in step (3), washing and drying treatments are further included.

[0053] In the present invention, the specific methods of the washing and drying treatments are preferably as follows: after washing with any one of water, alcohol or acetic acid solution, drying is carried out at 20 to 100 °C for 1 to 3 h under vacuum conditions; more preferably: after washing with any one of water or acetic acid solution, drying is carried out at 40 to 80 °C for 2 to 3 h under vacuum conditions; even more preferably: after washing with acetic acid solution, drying is carried out at 60 °C for 2 h under vacuum conditions.

[0054] Specifically in the examples of the present invention, the pH of the acetic acid solution is 5. The present invention has no special limitation on the pH of the acetic acid solution, and it can be determined according to the common knowledge in the art.

[0055] In the present invention, after obtaining the interstitial nitrogen atom compound in step (3), ball milling is further carried out. Specifically in the examples of the present invention, the ball milling is pendulum milling.

[0056] In the present invention, the time of the ball milling is preferably 1 to 60 min, more preferably 15 to 45 min, and even more preferably 20 min.

[0057] In the present invention, the mass ratio of the material:ball:solvent in the ball milling is preferably 1:5 to 10:1 to 2, more preferably 1:8 to 10:1.6 to 2, and even more preferably 1:10:2.

[0058] In the present invention, there is no special limitation on the solvent in the ball milling, and well-known organic solvents in the art can be used.

[0059] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0060] Example 1

[0061] This example provides a method for hierarchical nitridation of Sm2(Fe 0.9 Co 0.1 ) 17 alloy, including the following steps:

[0062] (1) After the alloy is roughly crushed and screened in a vacuum glove box, alloy powder with a particle size of 20 - 40 meshes is taken, placed in a vacuum furnace, and a hydrogen atmosphere of 150 mL / min is introduced. Hydrogen treatment is carried out at 200 °C for 1 h to obtain a hydrogen-treated alloy.

[0063] (2) The hydrogen-treated alloy is dehydrogenated in a vacuum environment maintained by a vacuum pump at a pressure below 10 Pa and a temperature of 200 °C for 60 min to obtain a dehydrogenated alloy.

[0064] (3) Nitrogen with a flow rate of 400 mL / min is introduced into the dehydrogenated alloy for nitridation treatment. The nitridation treatment is divided into two levels. The temperature of the first level is 400 °C and the time is 4 h. The temperature of the second level is 480 °C and the time is 2 h. After nitridation is completed, the sample is washed with acetic acid solution with pH = 5 to remove calcium and dried in a vacuum oven at 60 °C for 2 h to obtain an interstitial nitrogen atom compound. According to the naming rule of "NT_total nitridation time - first-level nitridation time + second-level nitridation time", the interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N x powder obtained in Example 1 is named NT6-42;

[0065] Among them, the Sm2(Fe 0.9 Co 0.1 ) 17 alloy is named Sm-Fe-Co.

[0066] Example 2

[0067] The difference from Example 1 is that: the nitridation treatment time of the first level is 4 h, and the nitridation treatment time of the second level is 4 h. Other conditions and processes are the same as those in Example 1. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N xThe powder is named NT8-44.

[0068] Example 3

[0069] It is different from Example 1 in that the first-stage nitriding treatment time is 4 h and the second-stage nitriding treatment time is 6 h. Other conditions and processes are the same as those in Example 1. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N x The powder is named NT10-46.

[0070] Comparative Example 1

[0071] This comparative example provides a nitriding method for Sm2(Fe 0.9 Co 0.1 ) 17 alloy, including the following steps:

[0072] After the alloy is roughly crushed and screened in a vacuum glove box, alloy powder with a mesh size of 20-40 is taken and placed in a vacuum furnace. Without hydrogen treatment and staged nitriding, nitrogen is directly introduced at a flow rate of 400 mL / min, and conventional nitriding treatment is carried out at 480 °C for 18 h to obtain an interstitial nitrogen atom compound. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N x The powder is named NoH-NT18.

[0073] Comparative Example 2

[0074] This comparative example provides a nitriding method for Sm2(Fe 0.9 Co 0.1 ) 17 alloy, including the following steps:

[0075] (1) After the alloy is roughly crushed and screened in a vacuum glove box, alloy powder with a mesh size of 20-40 is taken and placed in a vacuum furnace. A hydrogen atmosphere with a flow rate of 150 mL / min is introduced, and hydrogen treatment is carried out at 200 °C for 1 h to obtain a hydrogen-treated alloy;

[0076] (2) The hydrogen-treated alloy is dehydrogenated in a vacuum environment maintained by a vacuum pump at 10 Pa or less and 200 °C for 1 h to obtain a dehydrogenated alloy;

[0077] (3) The dehydrogenated alloy is introduced with nitrogen at a flow rate of 400 mL / min and subjected to conventional nitriding treatment at 480 °C for 6 h to obtain an interstitial nitrogen atom compound. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 Nx The powder is named NT-6.

[0078] Comparative Example 3

[0079] It is different from Comparative Example 2 in that the conventional nitriding treatment time is 8 h, and other conditions and processes are the same as those in Comparative Example 2. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N x The powder is named NT-8.

[0080] Comparative Example 4

[0081] It is different from Comparative Example 2 in that the conventional nitriding treatment time is 10 h, and other conditions and processes are the same as those in Comparative Example 2. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N x The powder is named NT-10.

[0082] Comparative Example 5

[0083] It is different from Comparative Example 2 in that the conventional nitriding treatment time is 12 h, and other conditions and processes are the same as those in Comparative Example 2. The interstitial nitrogen atom compound Sm2(Fe 0.9 Co 0.1 ) 17 N x The powder is named NT-12.

[0084] The interstitial nitrogen atom compounds Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Examples 1 to 3 and Comparative Example 1 were subjected to X-ray diffraction tests, and the results are as Figures 1 - 2 shown.

[0085] Figure 1 are the XRD patterns of the Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Examples 1 to 3. It can be seen from Figure 1 that the alloy powders have all achieved a certain degree of nitridation, and the main phase of Sm2(Fe 0.9 Co 0.1 ) 17 N x is obtained.

[0086] Figure 2 is the Sm2(Fe 0.9 Co0.1 ) 17 N x XRD pattern of the powder. In Comparative Example 1, the sample was not treated with hydrogen before nitridation and was directly nitrided in a nitrogen atmosphere at 480 °C for 18 h. As Figure 2 can be seen, Sm2(Fe 0.9 Co 0.1 ) 17 N x phase was formed in Comparative Example 1. However, obvious Fe-Co peaks also existed in the XRD pattern, and even the peak intensity of the Fe-Co peaks was relatively high and had become the main peak. The existence of the Fe-Co phase in Comparative Example 1 may be due to the presence of a certain oxide layer on the alloy sample before nitridation, the occurrence of oxidation reactions during nitridation, and the decomposition of the nitrided components during the long-term nitridation process. In the XRD pattern of the nitrided sample, the peak intensity of the Fe-Co phase can, to a certain extent, reflect the quality of the nitridation process. From Figure 1 , Figure 2 comparison, it can be known that the hierarchical nitridation scheme described in the present invention is better.

[0087] Table 1 summarizes the lattice parameter values, calculated nitrogen content x, and XRD peak intensity of the diffraction peaks of the Fe-Co phase of the Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Examples 1 to 3 and Comparative Examples 1 to 5. The lattice parameter values were calculated from the XRD results; the calculation of the nitrogen content x was based on the assumption that the expansion of the lattice during nitridation was all caused by the entry of nitrogen atoms, so x = (V NT -V RD ) / (3×V N ), where V NT , V RD are the unit cell volumes of the powder before and after nitridation, respectively, and the volume V N of the nitrogen atom was taken as In Table 1, a and c are the unit cell parameters of the powder, V is the unit cell volume, is the change value of the unit cell volume of the powder after nitridation, ΔV(%) is the percentage change in the unit cell volume of the powder after nitridation, x is the nitrogen content, and I Fe-Co is the XRD peak intensity of the diffraction peak of the Fe-Co phase.

[0088] Table 2 shows the magnetic property test results of the Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Example 1, Example 3, and Comparative Example 4. The test conditions were that after the powder was magnetized with a pulsed magnetic field, the demagnetization curve was measured under a 20 kOe magnetic field, where σ 20 is the magnetization intensity, σr is the remanent magnetization, and H cj is the intrinsic coercivity.

[0089] Table 1. Parameters of Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Examples 1 to 3 and Comparative Examples 1 to 5

[0090]

[0091]

[0092] Table 2. Magnetic properties of Sm2(Fe 0.9 Co 0.1 ) 17 N x powders obtained in Example 1, Example 3, and Comparative Example 4

[0093]

[0094] According to the data in Table 1, comparing Example 3 and Comparative Example 1, it can be seen that the optimized hierarchical nitriding process with hydrogen treatment achieved a nitriding degree higher than that of conventional nitriding for 18 h under nitriding for a total duration of 10 h, and the Fe-Co phase was greatly controlled.

[0095] According to the data in Table 1, considering the same total nitriding duration, comparing Example 1 and Comparative Example 2, Example 2 and Comparative Example 3, and Example 3 and Comparative Example 4, it can be found that: under the first-stage nitriding treatment for 4 h, the nitrogen content x value of the sample after final nitriding is relatively close to the value obtained by conventional nitriding after hydrogen treatment, and they are basically at the same level. However, the Fe-Co of the two-stage nitriding sample is greatly reduced compared with conventional nitriding, and the contribution to performance improvement is obvious. The specific magnetic property comparison between Example 3 and Comparative Example 4 is shown in Table 2. This shows that under the first-stage nitriding time of 4 h, during the first-stage nitriding process, the sample basically reached the maximum value of the nitriding degree at this temperature, achieving a good fit between the time setting and the nitriding progress.

[0096] Figure 3 、 Figure 4 is the SEM image and particle size distribution diagram of the Sm2(Fe 0.9 Co 0.1 ) 17 N x powder obtained in Example 3. It can be seen that the finally hierarchically nitrided sample is spherical-like with an average size of 4.66 μm. However, the performance of this sample obviously did not fully achieve that of Sm2(Fe 0.9 Co 0.1 ) 17 Nx The performance expression of the material. Therefore, further ball milling is selected to control the particle size and further grind the particles to improve the performance of the alloy powder.

[0097] Such as Figure 5 , Figure 6 For the Sm2(Fe 0.9 Co 0.1 ) 17 N x SEM image and particle size distribution diagram of the powder after high-energy swing milling for 20 min. Among them, the mass ratio of Sm2(Fe 0.9 Co 0.1 ) 17 N x powder: ball: cyclohexane solvent is 1:10:2. It can be seen that after 20 min of ball milling, the average size of the particles reaches 2.14 μm. For the Sm2(Fe 0.9 Co 0.1 ) 17 N x powder, the magnetic properties under a magnetic field of 20 kOe are measured, and the demagnetization curve obtained is as Figure 7 shown. It can be seen that for Sm2(Fe 0.9 Co 0.1 ) 17 N x powder, after short-time ball milling, H cj reaches 10.37 kOe.

[0098] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for hierarchical nitridation of an alloy, characterized in that, It includes the following steps: (1) After the alloy is roughly crushed and screened, hydrogen is introduced for hydrogen treatment to obtain a hydrogen-treated alloy; (2) The hydrogen-treated alloy is subjected to dehydrogenation treatment under vacuum conditions to obtain a dehydrogenated alloy; (3) Nitrogen is introduced into the dehydrogenated alloy for nitridation treatment. The nitridation treatment is divided into N levels, N≥2, to obtain an interstitial nitrogen atom compound; Among them, the alloy is a Re-M alloy, Re is one or more of Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu; M is one or more of Fe, Co, Ti, Nb, V, Cr, Mn, Si, Mo, Ga, Ni, Cu, Zn, Zr, Hf, Ta, W; The temperature of the hydrogen treatment in step (1) is 200-300°C, the time of the hydrogen treatment in step (1) is 1-3 h, and the flow rate of hydrogen in the hydrogen treatment in step (1) is 100-250 mL / min; The temperature of the dehydrogenation treatment in step (2) is 200-300°C, and the time of the dehydrogenation treatment in step (2) is 10-90 min; In the nitridation treatment in step (3), the flow rate of nitrogen is 200-500 mL / min, and the temperature difference T between adjacent stages is ≥20°C; After obtaining the interstitial nitrogen atom compound in step (3), ball milling is also carried out. The time of ball milling is 1-60 min, and the mass ratio of material:ball:solvent in ball milling is 1:5-10:1-2.

2. The hierarchical nitriding method of the alloy according to claim 1, characterized in that The particle size of the alloy powder obtained after screening in step (1) is 10-200 mesh.

3. The hierarchical nitriding method of the alloy according to claim 2, characterized in that The pressure P under vacuum conditions in step (2) is ≤10 Pa.

4. The stepwise nitriding method of the alloy according to claim 3, characterized in that, The temperature of the nitridation treatment in step (3) is 300-550°C, and the total time of the nitridation treatment in step (3) is 6-15 h.

5. The stepwise nitriding method of the alloy according to claim 3 or 4, characterized in that, In the nitridation treatment in step (3), the time t of each stage of nitridation treatment is ≥0.5 h.

6. The stepwise nitriding method of the alloy according to claim 5, characterized in that, After the nitridation treatment in step (3), washing and drying treatments are also included. The specific methods of washing and drying are as follows: After washing with any one of water, alcohol or acetic acid, it is dried at 20-100°C under vacuum conditions for 1-3 h.

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