Fractography of fracture surface of CrMnFeCoNi high-entropy alloy after electron-beam processing

In the past decade the attention of scientists in the field of physical materials science is attracted to studying the high-entropy alloys. By the technology of wire-arc additive manufacturing (WAAM) a high-entropy alloy (HEA) of a nonequiatomic composition was obtained. Deformation curves obtained under uniaxial tension at a rate of 1.2 mm/min at room temperature using Instron 3369 unit were analyzed in two states: initial/after fabrication and after electron-beam processing (EBP). EBP was conducted to detect its influence on structural-phase states and mechanical properties. The EBP leads to a decrease in strength and plastic properties of the HEA. By means of scanning electron microscope LEO EVO 50, analysis of structure of fracture surface and the near-surface zone was performed. Dependences of the ultimate strength and relative elongation to failure on EBT parameters were revealed, and it was shown that values of strength and plasticity decrease nonmonotonically with an increase in electron beam energy density in the range E_S = 10 – 30 J/cm² at constant values of duration, frequency, and number of pulses. Along with a pit character of the fracture a presence of micropores and microlayering was detected. Investigation of the HEA’s fracture surface after EBP except for areas with a ductile fracture mechanism revealed the regions with a band (lamellar) structure. At E_S = 10 J/cm², the area of such structure is 25 %; it increases nonmonotonically to 65 % at E_S = 30 J/cm². The diameter of pits of detachment in fracture bands varies in the limits of 0.1 – 0.2 μm, which is considerably less than that in the remainder of the HEA samples. After EBP the thickness of the molten layer varies in the limits of 0.8 – 5.0 μm and grows with an increase in the energy density of electron beam. EBT leads to generation of crystallization cells, the sizes of which change within the range 310 – 800 nm as E_S increases from 15 to 30 J/cm². It is suggested that the defects being formed in surface layers in ЕВР may be the reason for decreasing the HEA’s maximum values of strength and plasticity.

1. George E.P., Curtin W.A., Tasan C.C. High entropy alloys: A focused review of mechanical properties and deformation mechanisms. Acta Materialia. 2020, vol. 188, pp. 435–474. https://doi.org/10.1016/j.actamat.2019.12.015

2. Shivam V., Basu J., Pandey V.K., Shadangi Y., Mukhopadhyay N.K. Alloying behaviour, thermal stability and phase evolution in quinary AlCoCrFeNi high entropy alloy. Advanced Powder Technology. 2018, vol. 29, no. 9, pp. 2221–2230. https://doi.org/10.1016/j.apt.2018.06.006

3. Ganesh U.L., Raghavendra H. Review on the transition from conventional to multi-component-based nano-high-entropy alloys-NHEAs. Journal of Thermal Analysis and Calorimetry. 2020, vol.  139, pp. 207–216. https://doi.org/10.1007/s10973-019-08360-z

4. Alshataif Y.A., Sivasankaran S., Al-Mufadi F.A., Alaboodi A.S., Ammar H.R. Manufacturing methods, microstructural and mecha­nical properties evolutions of high-entropy alloy: A review. Metals and Materials International. 2019, vol. 26, pp. 1099–1133. https://doi.org/10.1007/s12540-019-00565-z

5. Cheng K.-C., Chen J.-H., Stadler S., Chen S.-H. Properties of ato­mized AlCoCrFeNi high-entropy alloy powders and their phase-adjustable coatings prepared via plasma spray process. Applied Surface Science. 2019, vol. 478, pp. 478–486. https://doi.org/10.1016/j.apsusc.2019.01.203

6. Joseph J., Hodgson P., Jarvis T., Wu X., Stanford N., Fabijanic D.M. Effect of hot isostatic pressing on the microstructure and mechanical properties of additive manufactured AlxCoCrFeNi high entropy alloys. Materials Science and Engineering: A. 2018, vol. 733,

7. pp.  59–70. https://doi.org/10.1016/j.msea.2018.07.036

8. Jian R., Wang L., Zhou S., Zhu Y., Liang Y.-J., Wang B., Xue Y. Achieving fine-grain tungsten heavy alloys by selecting a high entropy alloy matrix with low W grain growth rate. Materials Letters. 2020, vol. 278, article 128405. https://doi.org/10.1016/j.matlet.2020.128405

9. Hou L., Hui J., Yao Y., Chen J., Liu J. Effects of Boron Content on microstructure and mechanical properties of AlFeCoNiBx high entropy alloy prepared by vacuum arc melting. Vacuum. 2019, vol.  164, pp. 212–218. https://doi.org/10.1016/j.vacuum.2019.03.019

10. Wu H., Huang S., Zhao C., Zhu H., Xie Z., Tu C., Li X. Microstructures and mechanical properties of in-situ FeCrNiCu high entropy alloy matrix composites reinforced with NbC particles. Intermetallics. 2020, vol. 127, article 106983. https://doi.org/10.1016/j.intermet.2020.106983

11. Xu Y., Li C., Huang Z., Chen Y., Zhu L. Microstructure evolution and mechanical properties of FeCoCrNiCuTi0.8 high-entropy alloy prepared by directional solidification. Entropy. 2020, vol. 22, no. 7, article 786. https://doi.org/10.3390/e22070786

12. Liu Y., Zhang Y., Zhang H., Wang N., Chen X., Zhang H., Li Y. Microstructure and mechanical properties of refractory HfMo0.5NbTiV0.5Six high entropy composites. Journal of Alloys and Compounds. 2017, vol. 694, pp. 869–876. https://doi.org/10.1016/j.jallcom.2016.10.014

13. Zhang Y., Han T., Xiao M., Shen Y. Effect of Nb content on microstructure and properties of laser cladding FeNiCoCrTi0.5Nbx high-entropy alloy coating. Optik. 2019, vol. 198, article 163316. https://doi.org/10.1016/j.ijleo.2019.163316

14. Tabachnikova E.D., Shapovalov Yu.O., Smirnov S.N., Gorban  V.F., Krapivka N.A., Firstov S.A. Low-temperature mechanical properties and thermally activated plasticity parameters of the CrMnFeCoNi2Cu high entropy alloy. Low Temperature Physics. 2020, vol.  46, article 958. https://doi.org/10.1063/10.0001720

15. Nadutov V.M., Volosevich P.Yu., Proshak A.V., Panarin V.E., Sva­vil’nyi N.E. Structure of ion-plasma coatings from AlFeNiCoCuCr high-entropy alloy. Metallofizika i noveishie tekhnologii. 2017, vol.  39, no. 11, pp. 1525–1545. (In Russ.).

16. Rempel’ A.A., Gel’chinskii B.R. High-entropy alloys: preparation, properties and practical application. Izvestiya. Ferrous Metallurgy. 2020, vol. 63, no. 3-4, pp. 248–253. (In Russ.). https://doi.org/10.17073/0368-0797-2020-3-4-248-253

17. Rogachev A.S. Structure, stability, and properties of high-entropy alloys. Physics of Metals and Metallography. 2020, vol. 121, no. 8, pp. 733–764. https://doi.org/10.1134/S0031918X20080098

18. Bashev V.F., Kushnerev A.I. Structure and properties of cast and splat-quenched high-entropy Al–Cu–Fe–Ni–Si alloys. Physics of Metals and Metallography. 2017, vol. 118, no. 1, pp. 39–47. https://doi.org/10.1134/S0031918X16100033

19. Shaysultanov D.G., Stepanov N.D., Salishchev G.A., Tikhonovs­kii   M.A. Effect of heat treatment on the structure and hardness of high-entropy alloys CoCrFeNiMnVx (x = 0.25, 0.5, 0.75, 1). Physics of Metals and Metallography. 2017, vol. 118, no. 6, pp. 579–590. https://doi.org/10.1134/S0031918X17060084

20. Miracle D.B., Senkov O.N. A critical review of high entropy alloys and related concepts. Acta Materialia. 2017, vol. 122, pp. 448–511. https://doi.org/10.1016/j.actamat.2016.08.081

21. Zhang W., Liaw P.K., Zhang Y. Science and technology in high-entropy alloys. Science China Materials. 2018, vol. 61, no. 1, pp.  2–22. https://doi.org/10.1007/s40843-017-9195-8

22. Osintsev K.A., Gromov V.E., Konovalov S.V., Ivanov Yu.F., Panchenko I.A. High-entropy alloys: Structure, mechanical properties, deformation mechanisms and application. Izvestiya. Ferrous Metallurgy. 2021, vol. 64, no. 4, pp. 249–258. (In Russ.). https://doi.org/10.17073/0368-0797-2021-4-249-258

23. Gromov V.Е., Konovalov S.V., Ivanov Yu.F., Osintsev K.A. Structure and Properties of High-Entropy Alloys. Springer, Advanced Structured Materials, 2021, vol. 107, 110 p. https://doi.org/10.1007/978-3-030-78364-8

24. Ivanov Yu.F., Gromov V.E., Konovalov S.V., Shlyarova Yu.A. Evolution of the structure of AlCoCrFeNi high-entropy alloy irradiated by a pulsed electron beam. Zhurnal tekhnicheskoi fiziki. 2021, vol.  91, no. 12, pp. 1971–1974. (In Russ.). https://doi.org/10.21883/JTF.2021.12.51762.205-21

25. Ivanov Yu.F., Gromov V.Е., Zagulyaev D.V., Konovalov S.V., Shlia­rova Yu.A., Semin A.P. Prospects for the application of surface treatment of alloys by electron beams in state-of-the-art technologies. Progress in Physics of Metals. 2020, vol. 21, no. 3, pp. 345–362. https://doi.org/10.15407/ufm.21.03.345

26. Gromov V.E., Ivanov Yu.F., Vorobiev S.E., Konovalov S.V. Fatigue of Steels Modified by High Intensity Electron Beams. Cambridge CISP Ltd, 2015, 272 p.

27. GOST 1497 – 84. Metals. Tensile test methods. Moscow: Standartinform, 2005, 24 p. (In Russ.).

28. Koval’ N.N., Ivanov Yu.F. Nanostructuring of the surface of cermet and ceramic materials during pulsed electron-beam processing. Izvestiya vuzov. Fizika. 2008, no. 5, pp. 60–70. (In Russ.).