Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding

Journal Pre-proofs Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding Ke Xu, Zhongwu Liu, Hongya Yu, Xichun Zhong, Hui Zhang, Zhijian Liu PII: DOI: Reference:

S0304-8853(19)32886-0 https://doi.org/10.1016/j.jmmm.2019.166383 MAGMA 166383

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Journal of Magnetism and Magnetic Materials

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Please cite this article as: K. Xu, Z. Liu, H. Yu, X. Zhong, H. Zhang, Z. Liu, Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding, Journal of Magnetism and Magnetic Materials (2020), doi: https://doi.org/10.1016/j.jmmm.2019.166383

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Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding Ke Xu1, Zhongwu Liu1,2,*, Hongya Yu1, Xichun Zhong1, Hui Zhang1, Zhijian Liu3 1School

of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China 2Dongguan 3Guangdong

Hyper Tech Co. Ltd. Dongguan 523808, China

Institute of Iron and Steel, Guangzhou, 510641, China

Abstract: The plasma assisted ball milling technology is employed for the preparation of hard magnetic Sm2Fe17NX magnetic powders for the first time. Using conventional high-energy ball milling, Sm2Fe17 alloy powders can only be prepared from Sm2Fe17 alloy precursor but not from Sm and Fe metal precursor. However, by the plasma-assisted ball milling, Sm2Fe17 alloy powders with very fine grains can be directly obtained from the mixture of pure Sm and pure Fe fragments. It is also found that the Sm2Fe17 alloy has been partially nitrided by plasma assisted ball milling under nitrogen atmosphere. The precipitation of soft magnetic α-Fe phase and the oxidation of Sm2Fe17 particles can also be effectively inhibited by the plasma during milling. In addition, the nitriding effect of Nd-Fe alloy powders prepared by plasma-assisted ball milling is better than those prepared by conventional high-energy ball milling during the subsequent nitrding process, since the plasma field can increase the initial free energy of Sm2Fe17 powder and reduce its difference with the energy barrier. The present wok indicates that the nitriding efficiency of Sm2Fe17 alloy can be greatly improved by adding plasma field during the powdering. Key words: permanent magnets, Sm-Fe-N powder, plasma assisted ball milling, free energy, magnetic properties

*

Corresponding author, E-mail: [email protected]

1. Introduction Since Coey et al. [1] prepared the 2:17 type Sm2Fe17NX alloys by nitriding Sm2Fe17 alloy in 1990, Sm-Fe-N type permanent magnetic materials with high anisotropic field and high Curie temperature have attracted much attention

[2].

It was suggested that Sm2Fe17NX alloys

may become the next generation rare earth permanent magnet due to their excellent magnetic properties together with high corrosion resistance, oxidation resistance and heat resistance. Up to now, there are four approaches, including oxidation-reduction diffusion Hydrogenation-Disproportionation-Desorption-Recombination (HDDR) followed by nitriding

[6],

[5],

[3, 4],

melt quenching

and mechanical alloying by high energy ball milling [7], to prepare

Sm2Fe17NX alloys. Generally, melt quenching process has been suggested suitable for industrial production due to its simplicity

[8, 9].

Sm2Fe17Nx powders prepared by melt

quenching show uniform phase structure, composition as well as very fine grains [6]. However, it also involves some problems [10, 11]. In the process of melting Sm2Fe17 alloy, a large amount of samarium will be volatilized, and as a result, the composition of Sm2Fe17 alloy is difficult to precisely control

[11].

In addition, the nitriding effect of Sm2Fe17 ribbons obtained by

melt-spinning is unsatisfactory in the subsequent nitriding process

[12].

High-energy ball

milling method is another simple method for preparing Sm2Fe17 alloy powders, but it also has some shortcomings [13], including low working efficiency and easy oxidation of the Sm2Fe17 alloy powders during the transfer process. Once the Sm2Fe17 powder is oxidized, nitrogen atoms can hardly enter into the alloy and form Sm2Fe17NX phase during the nitriding process. To enhance the formation of the alloys in mechanical alloying, some researchers have proposed to add a physical energy field to the mechanical energy in traditional ball milling [14-16].

The combined effect can accelerate the refinement of powder and the processing of

mechanical alloying. Plasma assisted ball milling, which employ a plasma field during the milling, thus shows potential to improve the efficiency of ball milling. This new process can

also enhance the interaction between the powders with the reactive gases [17-19]. Up to now, the plasma assisted ball milling has been used for preparing various types of alloys, including MgB2, Bi2S3, Sb2S3 and LiFePO4, etc

[14].

However, the preparation of Sm-Fe-N alloys by

plasma assisted ball milling method has not been reported yet. In this work, we have managed to employ the novel process of plasma assisted ball milling to prepare hard magnetic alloys of Sm-Fe-N alloys. The preliminary results show that the assisted plasma can enhance the formation of Sm2Fe17 and Sm2Fe17Nx phases. 2. Experimental The strip cast Sm2Fe17 alloy or the mixture of Sm and Fe metal-fragments with atomic ratio of 2:17 were employed as the raw materials for preparing Sm2Fe17NX alloy powders after removing surface oxides. Both high-energy ball milling and plasma-assisted ball milling under N2 atmosphere are employed with same mass ratio of material to ball ( =1:100). Here, a specially designed facility named dielectric barrier discharge plasma assisted ball milling is employed for plasma-assisted ball milling, as shown in Fig.1. The details of this facility have been described elsewhere. [14] The current, voltage, motor speed, and time are set to 2 A, 150 V, 1300RPM, and 6h, respectively, during milling. These parameters have been optimized in the early stage based on a large number of experiments. As we know, it is difficult to ionize the reactive gas to get plasma when the current and voltage are too low, and the very high current and voltage will break through the shock rod[14]. To enhance the nitriding effect, the ball milled alloy powders were treated by isothermal nitriding at 480 ℃ for 8 hours in a tube furnace with a steady nitrogen flow.

Fig. 1 Schematic of the dielectric barrier discharge plasma assisted ball milling [14]

The magnetic properties of the samples were tested by a vibration sample magnetometer (VSM) in a Physical Properties Measurement System (PPMS-9, Quantum Design, USA) with a maximum magnetic field of 5T. The phase constitution was characterized by X-ray diffraction analyzer (X'Pert Pro, PANalytic, Netherlands) with radiation of Cu-Kα radiation (λ=1.5418 Å, 40 kV, 40 mA) in the 2θ range of 20°-90°. The surface composition was tested by X-ray photoelectron spectroscopy (Axis Ultra DLD, Kratos, UK) using monochrome Al-Kα X-ray source. 3. Results 3.1. Phase constitution Figure 2 shows the XRD patterns of the strip cast Sm2Fe17 alloy and the mixture of Sm + Fe metals after conventional high energy ball milling and plasma-assisted ball milling in nitrogen atmosphere. The diffraction peaks of Sm2Fe17 and -Fe phases can be detected in the sample of Sm2Fe17 alloy after high energy ball milling (Curve (a)). However, only the -Fe diffraction peaks have been found for the precursor of mixed metals after high energy ball milling in Curve (b). In addition, no recognizable Sm2Fe17Nx characteristic peaks can be observed in the XRD pattern of the obtained powders by conventional high energy ball milling. In contrast, the distinct Sm2Fe17Nx, Sm2Fe17 and -Fe peaks are observed in the powders prepared by plasma assisted ball milling for both Sm2Fe17 alloy and metal mixture

precursors, as shown in Curve (c) and (d), respectively. The results indicate that using Sm2Fe17 alloy as the precursor, the Sm2Fe17 phase still exists in the powders after conventional high energy ball milling or plasma-assisted ball milling. However, using the pure Sm and Fe metal mixture as the precursor, the Sm2Fe17 phase could not be prepared by conventional high energy ball milling, but it can be obtained by plasma-assisted ball milling. Based on the estimation from the X-ray diffraction line width using the Scherrer formula( D 

K )[22,23], the average grain sizes for all phases in the powders obtained by BCOS

traditional ball milling of Sm-Fe alloy, traditional ball milling of pure Sm and pure Fe metal mixture, plasma ball milling of Sm-Fe alloy, and plasma ball milling of pure Sm and pure Fe metal mixture are 57 nm, 64 nm, 36 nm and 39 nm respectively. It indicates that the fine Sm2Fe17NX crystalline grains can be obtained by plasma milling, which is helpful to improve the magnetic properties. In addition, it is worthy of noting that the alloy powders after plasma

Intensity (a.u.)

assisted milling have been partly nitrided to Sm2Fe17Nx.

(a)

Sm2Fe17+-Fe

(b)

-Fe

Sm2Fe17Nx+Sm2Fe17+-Fe

(c)

Sm2Fe17Nx+Sm2Fe17+-Fe

(d) 20

30

40

50

60

70

80

90

2-Theta(deg) Sm2Fe17Nx Sm2Fe17 -Fe

Fig. 2 XRD patterns of the Sm-Fe powders prepared from Sm2Fe17 alloy by conventional high energy ball milling (a), pure samarium and iron metals by high energy ball milling (b), Sm2Fe17 alloy by plasma assisted ball milling (c), and pure samarium and iron metals by plasma assisted ball milling (d)

Figure 3 shows the XRD patterns of the conventional high energy ball milled and plasma assisted ball milled Sm2Fe17 alloys after subsequent nitriding at 480℃ for 6 h in nitrogen atmosphere. Sm2Fe17N3 and α-Fe phases can be observed in Pattern (b) of plasma-assisted ball milled sample after nitriding. The content of α-Fe in plasma-assisted ball milled sample remains rather low, which is close to the content of α-Fe before nitriding (Pattern (c) in Fig.2). The nitrided samarium-iron alloy powder prepared by high energy ball milling presents Sm2Fe17, Sm2Fe17NX and α-Fe phases (Pattern (a)). Comparing the XRD Pattern (a) in Fig.2 and Pattern (a) in Fig.3, the volume fraction of α-Fe increases greatly after the nitriding process. The existence of soft magnetic phases such as Sm2Fe17 and α-Fe is generally considered not beneficial to the hard magnetic properties. In addition, based on Scherrer formula, it can be calculated that the grain sizes of Sm2Fe17NX phase in Fig.3 (a) and (b) are 96 nm and 52 nm, respectively. The metal powder obtained by plasma milling technology can still maintain fine grains after high temperature nitriding, which can effectively improve the magnetic properties of Sm2Fe17NX magnetic powder.

Sm2Fe17Nx+Sm2Fe17+-Fe

(b)

Sm2Fe17Nx+Sm2Fe17+-Fe

Intensity (a.u.)

(a)

20

30

40

50

60

70

80

90

2-Theta(deg) Sm2Fe17Nx Sm2Fe17 -Fe

Fig. 3 XRD pattern of the samples prepared from powders obtained by high energy ball milled Sm2Fe17 alloy (a) and plasma-assisted ball milled Sm2Fe17 alloy (b) after isothermal nitriding at 480℃

The XPS spectra of the nitrided samples after conventional high energy ball milling and plasma-assisted ball milling are shown in figures 4(a) and (b), respectively. The results show that, for the conventional high energy ball milled powders, there are samarium iron oxides on the surface, which should be the reason for the reduced nitriding effect. However, for the sample prepared by plasma-assisted ball milling, only nitride is detected on the surface of the sample and no O peak is found. Combined with Borsa's research on the effect of oxygen on nitriding process[20], it can be concluded that the plasma-assisted ball milling process can prevent the oxidation of alloy powder and help to form the Sm2Fe17Nx phase. 14000 O-Fe 1s

12000

O-Sm 1s

10000

531.95eV

529.5eV

6000

706.7eV

8000 7000

4000

6000

2000 0 525

(b)

Fe-N 2p

9000

8000

CPS

CPS

10000

11000

(a)

528

531

534

537

540

5000 700

Binding Energy(eV)

705

710

715

720

725

730

Binding Energy(eV)

Fig. 4 XPS spectra of Sm2Fe17 alloy surface by conventional high energy ball milling (a) and plasma assisted ball milling (b)

3.2. Magnetic properties Figures 5 (a) and (b) show the demagnetization curves and coercivity values, respectively of the magnetic powders prepared by different methods at room temperature using the Sm2Fe17 alloy as the milling precursor. The results suggest that the powder obtained by conventional high-energy ball milling is soft magnetic, since the hard magnetic phase, such as Sm2Fe17NX, was not obtained. After nitriding treatment, the coercivity increased to

only 50 kA/m. This is because not only the nitriding of Sm2Fe17 alloy powder is incomplete but also the existence of soft magnetic α-Fe phase and oxides except Sm2Fe17NX phase. On the contrary, the coercivity of the powder obtained by plasma-assisted ball milling is 26 kA/m, which should be attributed to the formation of a small amount of Sm2Fe17NX layer on the surface of the powder. After nitriding, its coercivity is significantly enhanced to 200 kA/m, which is 4 times higher than that of alloy powder obtained by high energy ball milling. The reason can be mainly attributed to the increased amount of hard magnetic Sm2Fe17NX phase and the elimination of soft magnetic phase, though the grain size may also have role on the effect of coercivity. Hence, the results indicate that the plasma-assisted ball milling can enhance the subsequent nitriding effect.

(b)

80

50 40 30

M (emu/g)

70 60

20

(a) -200 -150 -100

-50

0

H (kA/m)

50

Nitriding at 480℃ after Plasma ball milling

100

10

0 150

High energy ball milling

Plasma ball milling

Nitriding at 480℃ after high energy ball milling

200 150 100 50 0

Fig. 5 Demagnetization curves of magnetic powders prepared by different methods (a) and a comparison of the coercivity for the powders obtained by different ball milling methods (b) using Sm2Fe17 alloy as the precursor.

We have also checked the magnetic properties of the sample prepared using pure samarium and pure iron as the milling precursor. The coercivity of the powder after plasma-assisted ball milling is 23 kA/m. After nitriding, it is significantly enhanced to 192 kA/m. Since the conventional high energy ball milling cannot directly synthesize Sm2Fe17

H (kA/m)

90 High energy ball milling Nitriding at 480℃ after high energy ball milling Plasma assisted ball milling Nitriding at 480℃ after Plasma assisted ball milling

powder from pure samarium and pure iron, no nitrding treatment can be carried out for comparison. Nevertheless, the results further confirm that the plasma-assisted ball milling can not only promote the formation of Sm2Fe17 phase but also lead to partly nitriding effect during milling.

4. Discussion In this work, the conventional ball milling and plasma assisted ball milling were employed in the process for preparing Sm2Fe17Nx magnetic powders. Fig. 6 shows the energy levels of the reactions during nitriding process. The initial free energy of Sm2Fe17 alloy powder obtained by plasma-assisted ball milling is higher than that obtained by high energy ball milling. Since the reaction barrier is the same, the nitriding effect of alloy powder obtained by plasma-assisted ball milling is much better than that obtained by high energy ball milling [13,14]. In addition, the plasma-assisted ball milling can inhibit the volatilization of Sm in the process of Sm2Fe17 alloying, realize the partial nitriding during milling, and effectively inhibit the oxidation of Sm2Fe17.

Fig. 6 Free energy diagram of Sm2Fe17 alloy powders prepared by different methods during nitriding

Based on above results, the role of plasma field on the preparation of Sm2Fe17NX powders can be understood. Fig. 7 shows a schematic diagram of the changes of phase

constitution in different stages by using pure Sm and Fe metals as the starting materials. The plasma-assisted ball milling can synthesize the powders with Sm2Fe17 phase, but after the conventional high-energy ball milling, the powder remains separated Sm and Fe phases under the same milling parameters. The reason should be attributed to the added plasma field, which promoting the atomic diffusion and increases the initial free energy of Sm and Fe reaction, Sm2Fe17 can be synthesized rapidly when Sm and Fe are collided by alloy ball.

Fig. 7 Schematic diagram of conventional high energy ball milling and plasma assisted ball milling on pure Sm and Fe metals

Fig. 8 shows a schematic diagram of the phase changes of the alloy powder in different stages by using Sm2Fe17 alloy as the starting materials. By both conventional high-energy ball milling and plasma-assisted ball milling, Sm2Fe17 phase remains in the milled powders, but with the help of plasma, the Sm2Fe17NX phase can be formed on the surface of Sm2Fe17 powders. Furthermore, combining our results with Borsa's research on the effect of oxygen on nitriding process[20] and Torchane's research on nitriding kinetics[21], it can be assumed that an oxide layer is easy to form on the surface of Sm2Fe17 powder obtained by conventional high energy ball milling process, but it can be prevented by introducing the plasma field. Thus, the plasma assisted ball milling can effectively inhibit the oxidation of the powder and improve the nitriding effect.

Fig. 8 Schematic diagram of conventional high energy ball milling and plasma assisted ball milling on Sm2Fe17 alloy

It is worthy of noting that Sm2Fe17NX phase can be directly formed after plasma assisted ball milling. Therefore, it suggested that the powder consisting of pure Sm2Fe17NX phase may be obtained after optimizing the milling process and plasma field. In that case, this work provides a potential novel approach for one-step synthesis of hard magnetic Sm2Fe17NX powders. 5. Conclusion A plasma physical field was employed in ball milling to improve the preparation efficiency of Sm2Fe17NX powders. The phase constitution and magnetic properties of the powders prepared by conventional ball milling method and plasma assisted ball milling method followed by nitriding heat treatment using pure Sm and Fe metals or Sm-Fe alloy as the starting materials were studied. The results show that plasma-assisted ball milling can help to avoid the oxidation and partly nitride the surface of Sm2Fe17 alloy powders. It can also inhibit the precipitation of soft magnetic α-Fe phase and increase the initial free energy of nitriding process of Sm2Fe17 alloy powder. Because the energy barrier remains unchanged, the nitriding effect can be greatly improved and Sm2Fe17NX magnetic powders can be obtained. The conventional high-energy ball milling cannot prepare Sm2Fe17 alloy from pure Sm and pure Fe metals and it can only obtain Sm2Fe17 powder from Sm2Fe17 alloy. Moreover, the

grain size of the metal powder obtained by plasma milling technology is far smaller than that obtained by traditional ball milling, and the fine crystalline structure can still be maintained after high temperature nitriding. Based on the underlying mechanism, plasma assisted ball milling may be developed as a new approach for one-step synthesis of Sm2Fe17NX hard magnetic powders. Acknowledgements This work was partly supported by the Guangdong Iron and Steel Research Institute and the DongGuan Innovative Research Team Program (Grant no. 201536000200027). The authors also thank Professors Min Zhu and Liuzhang Ouyang for fruitful discussions. References [1] J. M. D. Coey, H. Sun, Improved magnetic properties by treatment of iron-based rare earth intermetallic compounds in anmonia, J. Magn. Magn. Mater. 87 (1990) 251-254. [2] A. Teresiak, M. Kubis, N. Mattern, M. Wolf, W. Gruner, K. H. Muller, Influence of nitrogenation on structure development and magnetic properties of mechanically alloyed and annealed Sm-Fe powders, J. Alloy. Compd. 292 (1999) 212-220. [3] A. Kawamoto, T. Ishikawa, S. Yasuda, K. Takeya, K. Ishizaka, T. Iseki. Sm-(Fe, Mn)-N Magnet Powder Made by Reduction and Diffusion Method, IEEE T. MAGN. 124 (2004) 881-886. [4] A. Kawamoto, T. Ishikawa, S. Yasuda, K. akeya, K. Ishizaka, T. Iseki, K. Ohmori, Sm2Fe17N3, magnet powder made by reduction and diffusion method, IEEE T. Magn. 35 (1999) 3322-3324. [5] J. Yang, S. Z. Zhou, M. C. Zhang, F. B Li, J. H. Zhao, R. Wang, Preparation and magnetic properties of Sm2Fe17NX compound, Mater. Lett. 12 (1991) 242-246. [6] M. Katter, J. Wecker, L. Schultz, Structural and hard magnetic properties of rapidly solidified Sm-Fe-N, J. Appl. Phys. 70 (1991) 3188-3196. [7] W. Liu, Q. Wang, X. K. Sun, X. G. Zhao, T. Zhao, Z. D. Zhang, Y. C. Chuang, Metastable Sm-Fe-N magnets prepared by mechanical alloying, J. Magn. Magn. Mater. 131 (1994) 413-416. [8] F. E. Pinkerton, C. D. Fuerst. High-coercivity samarium-iron-nitrogen from nitriding melt-spun ribbons[J]. J. Mater. Eng. Perform, 1993, 2(2):219-223. [9]J. E. Shield, B. B. Kappes, B. E. Meacham, K. W. Dennisc, M. J. Kramerc. Microstructures and phase formation in rapidly solidified Sm-Fe alloys[J]. J. Alloy. Compd, 2003, 351(1-2):0-113.

[10] Sugimoto, Satoshi, Achiha, Makoto, Nakamura, Hajime. Magnetic Properties of Sm-Fe-(C, N) Melt-Spun Ribbons with Low Sm Content[J]. Materials Transactions Jim, 35(12):917-922. [11] M. Katter, J. Wecker, C. Kuhrt, L. Schultz, R. Grössinger, Magnetic properties and thermal stability of Sm2Fe17NX with intermediate nitrogen concentrations, J. Magn. Magn. Mater. 117 (1992) 419-427. [12] J. M. D. Coey, P. A. I. Smith. Magnetic nitrides, J. Magn. Magn. Mater. 200 (1999) 405-424. [13] K. Y. Wang, Y. Z. Wang, L. Yin, L. Song, X. L. Rao, G. C. Liu, B. P. Hu, Sm2Fe17Ny powder with high coercivity prepared by high energy ball milling, Solid. State. Commun. 88 (1993) 521-523. [14] L. Z. Ouyang, Z. J. Cao, H. Wang, R. Z. Hu, M. Zhu, Application of dielectric barrier discharge plasma-assisted milling in energy storage materials-A review, J. Alloy. Compd. 691 (2017) 422-435. [15]Z. J. Cao, L. Z. Ouyang, Y. Y. Wu, H. Wang, J. W. Liu, F. Fang, D. L. Sun, Q. G Zhang, M. Zhu, Dual-tuning effects of In, Al, and Ti on the thermodynamics and kinetics of Mg85In5Al5Ti5 alloy synthesized by plasma milling, J. Alloy. Compd. 623 (2015) 354-358. [16] S. Wang, W. C. Wang, D. Z. Yang, Z. J. Liu, Direct synthesis of AlN nano powder by dielectric barrier discharge plasma assisted high-energy ball milling, J. Mater. Sci-Mater. El. 27 (2016) 8518-8523. [17] L. Yan, X. H. Zhu, Y. Qin, J. J. Xu, Y. Z. Gao, Plasma nitriding technology using dielectric barrier discharge at atmospheric pressure, 3rd International Conference on Surface Engineering, 2002. [18] Z. J. Liu, L. Y. Dai, D. Z. Yang, S. Wang, B. J. Zhang, W. C. Wang, T. H. Cheng, Synthesis of aluminum nitride powders from a plasma-assisted ball milled precursor through carbothermal reaction, Mater. Res. Bull. 61 (2015) 152-158. [19] L. Y. Dai. Behavior of Fe powder during high-energy ball milling cooperated with dielectric barrier discharge plasma, Acta Metall. Sin. 26 (2013) 63-68. [20] D. M. Borsa, D. O. Boerma, Phase identification of iron nitrides and iron Oxy-Nitrides with Mössbauer spectroscopy, Hyperfine Interact. 151 (2003) 31-48. [21] L. Torchane, P. Bilger, J. Dulcy, and M. Gantois, Control of iron nitride layers growth kinetics in the binary Fe-N system, Metall. Mater. Trans. A. 27A (1996) 1823-1835. [22] B. D. Cullity, S. R. Stock. Elements of X-Ray Diffraction[J]. Physics Today, 1959, 10(3): 97-99. [23] Uwe, Holzwarth, Neil, Gibson. The Scherrer equation versus the 'Debye-Scherrer equation'.[J].Nature nanotechnology,2011,6(9):534.

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Manuscript title: Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding

I have made substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work, and I have drafted the work or revised it critically for important intellectual content and I have approved the final version to be published, and I agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons who have made substantial contributions to the work reported in the manuscript, including those who provided editing and writing assistance but who are not authors, are named in the Acknowledgments section of the manuscript and have given their written permission to be named. If the manuscript does not include Acknowledgments, it is because the authors have not received substantial contributions from nonauthors.

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Highlights 

The technology is employed for the preparation of Sm2Fe17NX for the first time.



The Sm2Fe17 powder can be partially nitride by plasma assisted ball milling.



The precipitation of soft magnetic of Sm2Fe17 can be effectively inhibited.



Plasma field can increase the initial free energy of Sm2Fe17 powder.



The nitriding efficiency of Sm2Fe17 can be greatly improved by adding plasma field.