Dislocation glide and mechanical twinning in a ductile VNbTi medium entropy alloy

doi:10.1016/j.jmst.2021.09.016

Abstract

Abstract:

An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported. The screw dislocation glide, deformation twinning, and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%. The {112}<111> twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission. Dislocations dominate subsequent tensile deformation, and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations (e.g., debris, dipoles, and loops) and dense dislocation networks. The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration. The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium- and high-entropy alloys.

Key words: Medium-entropy alloy, Mechanical twinning, Screw dislocation, Multiplanar slip, Tensile deformation

Mingxu Wu, Shubin Wang, Fei Xiao, Guoliang Zhu, Chao Yang, Da Shu, Baode Sun. Dislocation glide and mechanical twinning in a ductile VNbTi medium entropy alloy[J]. J. Mater. Sci. Technol., 2022, 110: 210-215.

Figures/Tables 6

Fig. 1. Tensile properties and microstructure of the equiatomic VNbTi alloy: (a) engineering stress-strain curve with an inset showing the zoom-in image of yielding stage, (b) corresponding true stress-strain curve (the inset picture shows the schematic view of the tensile specimen), (c) XRD patterns of as-cast and deformed specimens, (d, e) fractographs of the fractured specimen, (f) inverse pole figure (IPF) of the as-cast specimen.

Fig. 2. TEM images of VNbTi alloy at microplastic region: (a) screw dislocations at low magnification (the inset shows the SAED), (b, c) magnified images of (a).

Fig. 3. Deformation bands in the equimolar VNbTi alloy: (a) inverse pole figure (IPF) of twins, (b) kernel average misorientation (KAM) map of (a), (c) IPF of kink bands, (d) KAM image of (c), (e) misorientation angle of twinning and kinking, (f, g) pole figures of twins and kink bands, respectively.

Fig. 4. EBSD band contrast (BC) and IPF images of equimolar VNbTi MEA at different tensile stages: BC images of (a) 1%-strained specimen, (c) 5%-strained specimen, (e) 10%-strained specimen, (g) 15%-strained specimen and (i) fractured specimen; (b), (d), (f), (h) and (j) are there corresponding IPF images.

Fig. 5. Deformation substructure of equiatomic VNbTi alloy: (a) twinning-kinking mixed microstructure, (b) magnified image of (a), (c) twins, ω phase and dislocation cross-slip, (d, e) multiplanar dislocation slip dislocation kink and debris, (f) dislocation bands, (g) dislocations and twins in low magnification, (h) magnified image of (g) showing ω phase along twin boundaries, (i) magnified image of (g) showing dislocation jogs, dipoles and loops. (a-e) and (f-i) are obtained in 1%-strained and tensile fractured VNbTi specimens, respectively. The SAEDs are shown in the insets.

Fig. 6. Schematic view of dislocation glide and twinning behavior.

References 24

[1]	O.N. Senkov, G.B. Wilks, J.M. Scott, D.B. Miracle, Intermetallics 19 (2011) 698-706. DOI URL
[2]	L. Lilensten, J.P. Couzinié, L. Perrière, A. Hocini, C. Keller, G. Dirras, I. Guillot, Acta Mater. 142 (2018) 131-141. DOI URL
[3]	J.P. Couzinié, L. Lilensten, Y. Champion, G. Dirras, L. Perrière, I. Guillot, Mater. Sci. Eng. A 645 (2015) 255-263. DOI URL
[4]	L. Wang, C. Fu, Y. Wu, R. Li, X. Hui, Y. Wang, Scr. Mater. 162 (2019) 112-117. DOI URL
[5]	G. Dirras, J. Gubicza, A. Heczel, L. Lilensten, J.P. Couzinié, L. Perrière, I. Guillot, A. Hocini, Mater. Charact. 108 (2015) 1-7. DOI URL
[6]	S. Wang, M. Wu, D. Shu, G. Zhu, D. Wang, B. Sun, Acta Mater. 201 (2020) 517-527. DOI URL
[7]	X. Zhang, W. Wang, J. Wu, S. Wang, J. Sun, J.Y. Chung, S.J. Pennycook, Mater. Sci. Eng. A 809 (2021) 140931.
[8]	W. Xi, W. Sun, G.D. Han, Mater. Charact. 103 (2015) 170-174. DOI URL
[9]	G. Dirras, H. Couque, L. Lilensten, A. Heczel, D. Tingaud, J.P. Couzinié, L. Per- rière, J. Gubicza, I. Guillot, Mater. Charact. 111 (2016) 106-113. DOI URL
[10]	S. Wang, M. Wu, D. Shu, B. Sun, Mater. Lett. 264 (2020) 127369.
[11]	E.M. Savitskii, G.S. Burkhanov, Physical Metallurgy of Refractory Metals and Al- loys, Consultants Bureau, New York, 1970.
[12]	T. Shimomura, T. Kainuma, R. Watanabe ,J. Less Common Met. 57 (1978) 147-159. DOI URL
[13]	L. Patriarca, W. Abuzaid, H. Sehitoglu, H.J. Maier, Y. Chumlyakov, Mater. Char- act. 75 (2013) 165-175.
[14]	P. Gumbsch, H.J. Gao, Science 283 (1999) 965-968. PMID
[15]	V.M. Finkel, I.N. Voronov, A.M. Savelev, A. I. Eliseenko, Phys. Met. Metallogr. 29 (1970) 131-140.
[16]	A. Vinogradov, D. Orlov, A. Danyuk, Y. Estrin, Acta Mater. 61 (2013) 2044-2056. DOI URL
[17]	F. Maresca, W.A. Curtin, Acta Mater. 182 (2020) 144-162. DOI URL
[18]	F. Wang, G.H. Balbus, S. Xu, Y. Su, J. Shin, P.F. Rottmann, K.E. Knipling, J.C. Stinville, L.H. Mills, O.N. Senkov, I.J. Beyerlein, T.M. Pollock, D.S. Gianola, Science 370 (2020) 95-101. DOI URL
[19]	D. Hull, D.J. Bacon, Introduction to Dislocations,5th ed., Elsevier, 2011.
[20]	D. Caillard, Acta Mater. 61 (2013) 2808-2827. DOI URL
[21]	M. Marteleur, H. Idrissi, B. Amin-Ahmadi, F. Prima, D. Schryvers, P.J. Jacques, Materialia 7 (2019) 100418.
[22]	Y. Zheng, W. Zeng, Y. Wang, S. Zhang, Mater. Sci. Eng. A 702 (2017) 218-224. DOI URL
[23]	S. Liu, D. Kent, N. Doan, M. Dargusch, G. Wang, Bioact. Mater. 4 (2019) 8-16.
[24]	Y. Jia, L. Zhang, P. Li, X. Ma, L. Xu, S. Wu, Y. Jia, G. Wang, Front. Mater. 7 (2020) 1-11. DOI URL