Structural features of HfTaTiNbZr high-entropy alloy fabricated by high energy ball milling

The paper shows the possibility of obtaining the HfTaTiNbZr high-entropy alloy (HEA) of equimolar concentration from powder components using the method of high-energy ball milling (HEBM) and spark plasma sintering (SPS). Initial powders were processed for 20, 40, 60 and 90 min in a high-energy planetary ball mill. The surface morphology, microstructure, and phase composition studies of HEA samples showed that an HfTaTiNbZr multicomponent powder mixture undergoes significant structural changes during the HEBM process. It was found based on the X-ray phase analysis data that mill processing for 20 min leads to the formation of a solid solution based on Hf (Fm3m) with an FCC structure. Subsequent HEBM for 40 min contributes to the appearance of a solid solution based on Ta (Im3m) with a BCC structure. After 60 min of processing, the peaks of Hf and Ta based solid solutions on the X-ray diffraction pattern completely merge to form one common asymmetric peak within the ~35+51° angle range. It was found that the HfTaTiNbZr HEA with a BCC structure is formed after 90 min of HEBM. According to scanning electron microscopy (SEM), the material has a homogeneous structure, and EDX results showed that the initial elements of Ti, Hf, Ta, Nb, Zr are uniformly distributed in the material volume. Powders obtained after 90 min HEBM were sintered at t = 1150 and 1350 °C for 10 min. The X-ray phase analysis, SEM and EDX results of high-entropy alloys consolidated by the SPS at t = 1350 °С showed that the material mostly consists of one phase with a BCC structure and a small amount of Hf₂Fe and ZrO. The hardness of the sintered HEA (10.7 GPa) exceeded the hardness of the material consolidated from initial element mixture (6.2 GPa) by 1.8 times. Densities of samples sintered at t = 1350 °С from the initial and HEA powders were 9.49 g/cm³ (95.8 %) and 9.87 g/cm³ (99.7 %), respectively.

1. Cantor B, Chang I.T.H., Knight P., Vincent A.J.B. Microstructural development in equiatomic multicomponent alloys. Mater. Sci. Eng. A. 2004. Vol. 375—377. P. 213— 218. doi 10.1016/j.msea.2003.10.257.

2. Yeh J.-W, Chen S.-K, Lin S.-J, Gan J.-Y, Chin T.-S, Shun T.-T, Tsau C.-H, Chang S.-Y. Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes. Adv. Eng. Mater. 2004. Vol. 6. P. 299—303. doi10.1002/adem.200300567.

3. Senkov O.N., Miracle D.B., Chaput K.J. Development and exploration of refractory high entropy alloys: A review. J. Mater. Res. 2018. Vol. 33. No. 19. P. 3092—3128.

4. Ye Y.F., Wang Q, Lu J., Liu C.T., Yang Y High-entropy alloy: Challenges and prospects. Mater. Today. 2016. Vol. 19. Iss. 6. P. 349-362.

5. Yeh J.-W, ChenS.-K, Gan J.-W, LinS.-J, Chin T.-S, Shun T.-T, Tsau C.-H, Chang S.-Y. Formation of simple crystal structures in Cu-Co-Ni-Cr-Al-Fe-Ti-V alloys with multi-principal metallic elements. Metall. Mater. Trans. A. 2004. Vol. 35. P. 2533-2536. doi10.1007/s11661-006-0234-4.

6. Guo S, Liu C.T. Phase stability in high entropy alloys: Formation of solid solution or amorphous phase. Prog. Natur. Sci. Mater. Int. 2011. Vol. 21. P. 433-446.

7. Guo S, Ng C., Lu J, Li C.T. Effect of valence electron concentration on stability of FCC or BCC phase in high entropy alloys. J. Appl. Phys. 2011. Vol. 109. No. 103505.

8. Zhang Y., Zuo T.T., TangZ., GaoM.C.,DahmenK.A., LiawP.K., Lu Z.P. Microstructures and properties of high-entropy alloys. Prog. Mater. Sci. 2014. Vol. 61. P. 1-93.

9. Gali A., George E.P. Tensile properties of high- and medium-entropy alloys. Intermetallics. 2013. Vol. 39. P. 74-78.

10. Otto F., Dlouhy A., Somsen Ch., Bei H., Eggeler G., George E.P. The influence of temperature and microstructure on tensile properties of a CoCrFeMnNi high-entropy alloy. Acta Mater. 2013. Vol. 61. P. 5743-5755.

11. Kilmametov A., Kulagin R., Mazilkin A., Seils S., Boll T, Heilmaier M., Hahn H. High-pressure torsion driven mechanical alloying of CoCrFeMnNi high entropy alloy. Scripta Mater. 2019. Vol. 158. P. 29-33.

12. Zhu C., Lu Z.P., Nieh T.G. Incipient plasticity and dislocation nucleation of FeCoCrNiMn high-entropy alloy. Acta Mater. 2013. Vol. 61. P. 2993-3001.

13. GludovatzB., Honenwarter A., CatoorD., ChangE.H., George E.P., Ritchie R.O. A fracture-resistant high-entropy alloy for cryogenic applications. Science. 2014. Vol. 345. P. 1153-1158.

14. Zhang Z.J., Mao M.M., Wang J., Gludovatz B., Zhang Z., Mao S.X., George E.P., Yu Q., Ritchie R.O. Nanoscale origins of the damage tolerance of the high-entropy alloy CrMnFeCoNi. Nat. Commun. 2015. Vol. 6. No. 10143. P. 1-6. DOI: 10.1038/ncomms10143.

15. Prusa F., Senkova A., Kucera V, Capek J., Vojtech D. Properties of high-strength ultrafine-grained CoCrFeNiMn high-entropy alloy prepared by short-term mechanical alloying and spark plasma sintering. Mater. Sci. Eng. A. 2018. Vol. 734. P. 341-352.

16. SunS.J., Tian Y.Z., LinH.R.,DongX.G., WangY.H., ZhangZ.J., Zhang Z.F. Enhanced strength and ductility of bulk CoCrFeMnNi high entropy alloy having fully recrystallized ultrafine-grained structure. Mater. Design. 2017. Vol. 133. P. 122-127.

17. Shahmir H., He J., Lu Z., Kawasaki M., Langdona T.G. Evidence for superplasticity in a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion. Mater. Sci. Eng. A. 2017. Vol. 685. P. 342-348.

18. Senkov O.N., Scott J.M., Senkova S.V, Miracle D.B., Woodward C.F. Microstructure and room temperature properties of a high-entropy TaNbHfZrTi alloy. J. Alloys Compd. 2011. Vol. 509. P. 6043-6048.

19. Senkov O.N., Wilks G.B., Miracle D.B., Chuang C.P, Liaw P.K. Refractory high-entropy alloys. Intermetallics. 2010. Vol. 18. P. 758-1765.

20. He J.Y., Zhu C., Zhou D.Q., Liu W.H., Nieh T.G., Lu Z.P. Steady state flow of the FeCoNiCrMn high entropy alloy at elevated temperatures. Intermetallics. Vol. 55. P. 9-14.

21. Pickering E.J., Minoz-Moreno R., Stone H.J., Jones N.G. Precipitation in the equiatomic high-entropy alloy CrMnFeCoNi. Scripta Mater. 2016 Vol. 113. P. 106-109.

22. Otto F., Dlouhy A., Pradeep K.G., Kubenova M., Raabec D., Eggeler G., Georgea E.P. Decomposition of the singlephase high-entropy alloy CrMnFeCoNi after prolonged anneals at intermediate temperatures. Acta Mater. 2016. Vol. 112. P. 40-52.

23. Salishchev G.A., Tikhonovsky M.A., Shaysultanov D.G., Stepanov N.D., Kuznetsov A.V, Kolodiy I.V, Tortika A.S., Senkov O.N. Effect of Mn and V on structure and mechanical properties of high-entropy alloys based on CoCrFeNi system. J. Alloys Compd. 2014. Vol. 591. P. 11-21.

24. Gludovatz B., George E.P., Ritchie R.O. Processing, microstructure and mechanical properties of the CrMnFeCoNi high-entropy alloy. J. Metals. 2015. Vol. 67. No.10. P. 22622270. DOI: 10.1007/s11837-015-1589-z.

25. He F., Wang Z., Wu Q., Li J., Wang J., Liu C.T. Phase separation of metastable CoCrFeNi high entropy alloy at intermediate temperatures. Scripta Mater. 2017. Vol. 126. P. 15-19.

26. Vaidya M., Muralikrishna G.M., Murty B.S. High-entropy alloys by mechanical alloying: A review. J. Mater. Res. 2019. Vol. 34. P. 664-686.

27. RogachevA.S., VadchenkoS.G., KochetovN.A., RouvimovS., Kovalev D.Yu, Shchukin A.S., Moskovskikh D.O., Nepapu-shevA.A., Mukasyan A.S. Structure and properties of equiatomic CoCrFeNiMn alloy fabricated by high-energy ball milling and spark plasma sintering. J. Alloys Compd. 2019. Vol. 805. P. 1237-1245.

28. Wu YD., Cai Y.H., Wang J'., Si J.J., Zhu J., Wang Y.D., HuiX.D. A refractory Hf25Nb25Ti25Zr25 high-entropy alloy with excellent structural stability and tensile properties. Mater. Lett. 2014 Vol. 130. P. 277-280.

29. Singh A.K., Subramaniam A. On the formation of disordered solid solutions in multi-component alloys. J. Alloys Compd. 2004 Vol. 587. P. 113-119.

30. Idbenali M., Selhaoui N., Bouirden L., Servant C. Thermodynamic assessment of the Fe-Hf binary system. J. Alloys Compd. 2008. Vol. 456. P. 151-158.