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Kinking in a refractory TiZrHfNb0.7 medium-entropy alloy
Journal Pre-proofs Kinking in a refractory TiZrHfNb0.7 medium-entropy alloy Shubin Wang, Mingxu Wu, Da Shu, Baode Sun PII: DOI: Reference:
S0167-577X(20)30074-4 https://doi.org/10.1016/j.matlet.2020.127369 MLBLUE 127369
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
29 August 2019 10 December 2019 15 January 2020
Please cite this article as: S. Wang, M. Wu, D. Shu, B. Sun, Kinking in a refractory TiZrHfNb0.7 medium-entropy alloy, Materials Letters (2020), doi: https://doi.org/10.1016/j.matlet.2020.127369
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Elsevier B.V. All rights reserved.
Kinking in a refractory TiZrHfNb0.7 medium-entropy alloy
Shubin Wang a, Mingxu Wu a, Da Shu a , Baode Sun a, b
a. Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China b. State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China
Abstract As a type of cooperative deformation like twinning, kinking can improve the deformability of materials by stress relaxation and crystal reorientation. In this work, kinking with <011> lattice rotation axis was identified in a refractory TiZrHfNb0.7 medium-entropy alloy (MEA). Through intragranular misorientation axis (IGMA) analysis, the {112} <111> dislocation slip was determined. The formation of intensive band structure in 70% cold rolled alloy was attributed to continuous nucleation and propagation of kink bands in coarse grains. Keywords: Medium-entropy alloy, Cold rolling, Kinking, Microstructure, Metals and alloys 1. Introduction Refractory high-entropy alloys (RHEAs) usually display much higher yield strength
Corresponding author: [email protected] 1
up to very high temperatures, which makes them promising candidates for hightemperature structural materials [1, 2]. However, many RHEAs suffer from a lack of ductility and exhibit a poor strain hardening around the room temperature [2]. The notable exceptions are the Senkov TiZrHfNbTa [3] and its derivatives TiZrHfNb [4] and Hf0.5Nb0.5Ta0.5Ti1.5Zr [5] alloys, which exhibit excellent room-temperature tensile ductility. The heavily cold rolling ability of the TiZrHfNbTa alloy has opened the door for structure-properties control by thermomechanical processing [6]. The screw dislocation with a Burgers vector 𝒃=a/2<111> governed the plastic deformation of TiZrHfNbTa alloy [7]. The heterogeneous deformed microstructures contain localized bands with high density of dislocation defects and dislocation-free soft zones [8, 9]. At the grain-size scale, interestingly, lamellas that arise at grain boundaries and spread into the interior of grains have been found in deformed TiZrHfNbTa alloys both under quasi-static [3, 10] and dynamic condition [11]. Recently, this deformation feature also appeared in the high-pressure torsion (HPT) processed TiZrHfNbTa [12] and TiZrHfNb [13] alloys or tensile deformed Ti40Zr25Nb25Ta10 [14] MEA. These lamellas were considered to be mechanical twins [12], micro-sized shear bands [14] or possibly kink bands [9, 11]. However, the exact nature of these lamellas has not been clarified yet. Kinking is a locally crystallographic bend with an arbitrary rotating degree about an axis that lies in the slip plane and normal to the slip direction, in contrast to a fixed misorientation of twinning. [15]. As a secondary deformation process, it can effectively accommodate dislocation slip against stress concentration and improve the 2
deformability of materials [16]. Kinking is prevalent in materials showing high plastic anisotropy like hcp structured Zn single crystal [17] and ductile Ti3SiC2 ceramics [18]. Recently, kinking deformation has been found in β titanium alloys [16, 19]. In this study, kink band deformation was crystallographically confirmed in a TiZrHfNb0.7 mediumentropy alloy (MEA). In addition, the relevant dislocation slip mode and intensive band structure evolution were discussed.
2. Material and methods The TiZrHfNb0.7 alloy ingot was melted in a water-cooled copper crucible under argon atmosphere using high-frequency electromagnetic induction heating. Plates with a dimension of 50 mm 15 mm 8 mm were cut from the as-cast ingot and then coldrolled with total thickness reduction of 20% and 70%, respectively. The crystal structures and microstructures after deformation were characterized by X-ray diffraction (XRD) using Cu-Kα radiation, optical microscope and electron backscattered diffraction (EBSD). Samples for EBSD analysis were mechanically and electrochemically polished with a solution of 10% HClO4 and 90% CH4O at -35 °C and 20 V for 20 s. EBSD analyses were performed using HKL Channel 5 software. Samples for optical observation were etched in 5% HNO3 + 10% HF + 85% H2O solution.
3. Results and discussion The X-ray diffraction results are shown in Fig. 1. Although the content of Nb is reduced relative to equiatomic TiZrHfNb alloy, all the as-cast and cold-rolled 3
TiZrHfNb0.7 alloys remain body-centered cubic (BCC) single phase. These results are consistent with that in TiZrHfNb0.6 alloy [20] where the BCC is stable even after compression.
Fig. 1. X-ray diffraction patterns of the as-cast and cold-rolled refractory TiZrHfNb0.7 alloy
After 20% cold rolling, the nearly paralleled band structure is arranged throughout a grain in Fig. 2(a). The corresponding local misorientation map was derived in Fig. 2(b) to qualitatively reflect the local plastic strain around the bands. The deformation strain is significantly larger at the band-matrix interface, especially at the band tip region. To quantitatively evaluate the crystal orientation difference between bands and matrix, the misorientation profile in Fig. 2(c) was created along the white line. These arbitrary misorientation angles in the range of 15° to 25° exclude the possibility of twinning.
4
Fig. 2. 20% cold rolled TiZrHfNb0.7 alloy: (a) inverse pole figure map; (b) local misorientation map; (c) misorientation profile (relative to the first point) along the line inset in (a); (d) {011}, {112} and {541} pole figures of the rectangular subset in (a).
According to the intragranular misorientation axis (IGMA) analysis method [21] based on the theory of dislocation slip-induced lattice rotation, the lattice rotation axis 𝑻 during kinking can be expressed as 𝑻 = γ𝒃 × 𝒏, where γ, 𝒃 and 𝒏 are the plastic shear gradient, Burgers vector and slip plane normal vector of the specific slip system, respectively. In other words, the rotation axis lies in the slip plane and is perpendicular to the Burgers vector. In BCC alloy, the Burgers vector 𝒃 of the perfect slip dislocation is of type 1/2<111>, while the slip planes 𝒏 can have three types of {110}, {112} and {123}. The possible rotation axis 𝑻 corresponding to these three slip modes can be deduced to be <112>, <011> and <541>. Therefore, if the structure in Fig. 2(a) is a 5
deformation kink band, the invariant crystal plane during deformation should belong to one of the {112}, {011} and {541}. Fig. 2(d) lists the {011}, {112} and {541} pole figures of the rectangular area in Fig. 2(a). An evident pole focus is exhibited in {011} pole figure, along with the rest of {011} poles, all {112} and all {541} poles rotated around this focused {011} pole. This crystallography confirms the occurrence of kink bands in Fig. 2(a) with the lattice rotation axis (𝑻) of <011> corresponding to the activation of {112} <111> slip mode during kinking process.
Fig. 3. 70% cold rolled TiZrHfNb0.7 alloy: (a) optical microstructure showing dense kink bands; (b) inverse pole figure map; (c) misorientation profile (relative to the first point) along the line inset in (b); (d) frequency distribution of the misorientation in the entire area of (b); (e) {011}, {112} and {541} pole figures of the rectangular subset in (b). 6
After 70% cold rolling, interestingly, intensive band structure formed in a stretched coarse grain in Fig. 3(a). The misorientation angles (Fig. 3(c)) along the line in Fig.3 (b) is around 20° to 30°. The statistical misorientation distribution was calculated in Fig. 3(d). Except for subgrains and low-angle boundaries, many highangle boundaries ranging from 10° to 40° represent the band-matrix misorientation angle. As shown in Fig. 3(e), a {011} focused pole emerges, with the rest of {011} poles, all {112} and all {541} poles rotated around this pole. This result once again confirms the <011> lattice rotation axis during kink band deformation.
Fig. 4. Schematic illustration of the kink band deformation in TiZrHfNb0.7 alloy
The kink formation for TiZrHfNb0.7 alloy during cold rolling was illustrated in Fig. 4. According to Hess and Barnett [22], the generation of dislocation pairs with opposite sign contributes to the nucleation of kink bands. Then, these dislocations with [111] shear direction are aligned as a wall perpendicular to the (211) slip plane to relax 7
the long-range stress field caused by the randomly accumulated dislocations. During plastic deformation, the increasingly aligned dislocations promoted progressive rotation of the kink band. The bands initiate at stress concentration region and then propagate across the entire grain. With further deformation, the bands tend to be locked up and this strain is accommodated either by broadening of existing kink band or initiating a new kink band, which can phenomenologically explain the intensive kink bands in Fig. 3(a, b). For TiZrHfNbTa alloy and its derivatives [3, 10-13], consistent with Fig. 2(a), these lamellas all arise from grain boundaries and propagate within a single grain. In other words, the occurrence of kinking within grains with specific crystallographic orientation. This characteristic excludes the possibility of the shear band which is a noncrystallographic deformation mode and it can penetrate multiple grains. The misorientation angles among the band-matrix interface are in the range of 10°~50° for TiZrHfNbTa alloy both under dynamic compression and HPT, which is much lower than that of the twin (50.5° for {332}<113> twin and 60° for {112}<111> twin) of BCC alloy. However, this arbitrary rotating degree is exactly a characteristic of kink deformation. So here we speculate that these bands or lamellar structures observed in TiZrHfNbTa [3, 11], TiZrHfNb [13] and Ti40Zr25Nb25Ta10 [14] high-entropy alloys are also likely to be deformation kinking rather than shear band or twinning.
4. Conclusions Kinking was identified in both 20% and 70% cold-rolled TiZrHfNb0.7 alloy. Using 8
intragranular misorientation axis (IGMA) analysis method, the <011> lattice rotation axis and {112} <111> dislocation slip mode were confirmed. The intensive band structure can be interpreted by considering the nucleation and propagation of kink bands during deformation. This kinking is likely to exist widely in TiZrHfNbTa and its derived high-entropy alloys.
Acknowledgements This work was supported by the National Key R&D Program of China (No. 2016YFB0701405), the National Natural Science Foundation of China (No. 51821001) and the Shanghai Science and Technology Committee (No. 16DZ2260602).
References [1] J.P. Couzinié, G. Dirras, Mater. Charact. 147 (2019) 533-544. [2] O.N. Senkov, D.B. Miracle, K.J. Chaput, J.-P. Couzinie, J. Mater. Res. 33(19) (2018) 30923128. [3] G. Dirras, L. Lilensten, P. Djemia, M. Laurent-Brocq, D. Tingaud, J.P. Couzinie, L. Perriere, T. Chauveau, I. Guillot, Mater. Sci. Eng. A 654 (2016) 30-38. [4] Y.D. Wu, Y.H. Cai, T. Wang, J.J. Si, J. Zhu, Y.D. Wang, X.D. Hui, Mater. Lett. 130 (2014) 277-280. [5] S. Sheikh, S. Shafeie, Q. Hu, J. Ahlström, C. Persson, J. Veselý, J. Zýka, U. Klement, S. Guo, J. Appl. Phys. 120(16) (2016) 164902. [6] E.P. George, D. Raabe, R.O. Ritchie, Nat. Rev. Mater. (2019). 9
[7] J.P. Couzinie, L. Lilensten, Y. Champion, G. Dirras, L. Perriere, I. Guillot, Mat. Sci. Eng. A 645 (2015) 255-263. [8] L. Lilensten, J.P. Couzinié, L. Perrière, A. Hocini, C. Keller, G. Dirras, I. Guillot, Acta Mater. 142 (2018) 131-141. [9] J.P. Couzinié, G. Dirras, Mater. Charact. 147 (2019) 533-544. [10] O.N. Senkov, J.M. Scott, S.V. Senkova, F. Meisenkothen, D.B. Miracle, C.F. Woodward, J. Mater. Sci. 47(9) (2012) 4062-4074. [11] G. Dirras, H. Couque, L. Lilensten, A. Heczel, D. Tingaud, J.P. Couzinie, L. Perriere, J. Gubicza, I. Guillot, Mater. Charact. 111 (2016) 106-113. [12] J. Čížek, P. Haušild, M. Cieslar, O. Melikhova, T. Vlasák, M. Janeček, R. Král, P. Harcuba, F. Lukáč, J. Zýka, J. Málek, J. Moon, H.S. Kim, J. Alloy. Compd. 768 (2018) 924-937. [13] J. Gubicza, A. Heczel, M. Kawasaki, J.-K. Han, Y. Zhao, Y. Xue, S. Huang, J.L. Lábár, J. Alloy. Compd. 788 (2019) 318-328. [14] V.T. Nguyen, M. Qian, Z. Shi, T. Song, L. Huang, J. Zou, Mat. Sci. Eng. A 742 (2019) 762772. [15] A.G. Crocker, J.S. Abell, Philos. Mag. 33(2) (2006) 305-310. [16] Y. Yang, S.Q. Wu, G.P. Li, Y.L. Li, Y.F. Lu, K. Yang, P. Ge, Acta Mater. 58(7) (2010) 27782787. [17] E. Orowan, Nature 149(3788) (1942) 643-644. [18] M.W. Barsoum, T. Zhen, S.R. Kalidindi, M. Radovic, A. Murugaiah, Nat. Mater. 2(2) (2003) 107-111. [19] Y. Zheng, W. Zeng, Y. Wang, S. Zhang, Mat. Sci. Eng. A 702 (2017) 218-224. 10
[20] L. Zhang, H. Fu, S. Ge, Z. Zhu, H. Li, H. Zhang, A. Wang, H. Zhang, Mater. Charact. 142 (2018) 443-448. [21] M. Yamasaki, K. Hagihara, S.-i. Inoue, J.P. Hadorn, Y. Kawamura, Acta Mater. 61(6) (2013) 2065-2076. [22] Hess JB, Barrett CS. Met. Trans. 185 (1949) 599-606.
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Shubin Wang: Conceptualization, Methodology, Formal analysis, Investigation, Writing-Original Draft. Mingxu Wu: Investigation, Writing-Original Draft. Da Shu: Conceptualization, Formal analysis, Writing-Original Draft, Writing - Review & Editing, Supervision, Project administration. Baode Sun: Project administration, Funding acquisition.
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Highlights 1. Kinking has been crystallographically confirmed in deformed TiZrHfNb0.7 alloy.
2. The initiation and propagation of kinking contribute to intensive band structure.
3. Kinking would exist widely in TiZrHfNbTa and its derived high-entropy alloys.
14
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
15
S0167-577X(20)30074-4 https://doi.org/10.1016/j.matlet.2020.127369 MLBLUE 127369
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
29 August 2019 10 December 2019 15 January 2020
Please cite this article as: S. Wang, M. Wu, D. Shu, B. Sun, Kinking in a refractory TiZrHfNb0.7 medium-entropy alloy, Materials Letters (2020), doi: https://doi.org/10.1016/j.matlet.2020.127369
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Elsevier B.V. All rights reserved.
Kinking in a refractory TiZrHfNb0.7 medium-entropy alloy
Shubin Wang a, Mingxu Wu a, Da Shu a , Baode Sun a, b
a. Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China b. State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China
Abstract As a type of cooperative deformation like twinning, kinking can improve the deformability of materials by stress relaxation and crystal reorientation. In this work, kinking with <011> lattice rotation axis was identified in a refractory TiZrHfNb0.7 medium-entropy alloy (MEA). Through intragranular misorientation axis (IGMA) analysis, the {112} <111> dislocation slip was determined. The formation of intensive band structure in 70% cold rolled alloy was attributed to continuous nucleation and propagation of kink bands in coarse grains. Keywords: Medium-entropy alloy, Cold rolling, Kinking, Microstructure, Metals and alloys 1. Introduction Refractory high-entropy alloys (RHEAs) usually display much higher yield strength
Corresponding author: [email protected] 1
up to very high temperatures, which makes them promising candidates for hightemperature structural materials [1, 2]. However, many RHEAs suffer from a lack of ductility and exhibit a poor strain hardening around the room temperature [2]. The notable exceptions are the Senkov TiZrHfNbTa [3] and its derivatives TiZrHfNb [4] and Hf0.5Nb0.5Ta0.5Ti1.5Zr [5] alloys, which exhibit excellent room-temperature tensile ductility. The heavily cold rolling ability of the TiZrHfNbTa alloy has opened the door for structure-properties control by thermomechanical processing [6]. The screw dislocation with a Burgers vector 𝒃=a/2<111> governed the plastic deformation of TiZrHfNbTa alloy [7]. The heterogeneous deformed microstructures contain localized bands with high density of dislocation defects and dislocation-free soft zones [8, 9]. At the grain-size scale, interestingly, lamellas that arise at grain boundaries and spread into the interior of grains have been found in deformed TiZrHfNbTa alloys both under quasi-static [3, 10] and dynamic condition [11]. Recently, this deformation feature also appeared in the high-pressure torsion (HPT) processed TiZrHfNbTa [12] and TiZrHfNb [13] alloys or tensile deformed Ti40Zr25Nb25Ta10 [14] MEA. These lamellas were considered to be mechanical twins [12], micro-sized shear bands [14] or possibly kink bands [9, 11]. However, the exact nature of these lamellas has not been clarified yet. Kinking is a locally crystallographic bend with an arbitrary rotating degree about an axis that lies in the slip plane and normal to the slip direction, in contrast to a fixed misorientation of twinning. [15]. As a secondary deformation process, it can effectively accommodate dislocation slip against stress concentration and improve the 2
deformability of materials [16]. Kinking is prevalent in materials showing high plastic anisotropy like hcp structured Zn single crystal [17] and ductile Ti3SiC2 ceramics [18]. Recently, kinking deformation has been found in β titanium alloys [16, 19]. In this study, kink band deformation was crystallographically confirmed in a TiZrHfNb0.7 mediumentropy alloy (MEA). In addition, the relevant dislocation slip mode and intensive band structure evolution were discussed.
2. Material and methods The TiZrHfNb0.7 alloy ingot was melted in a water-cooled copper crucible under argon atmosphere using high-frequency electromagnetic induction heating. Plates with a dimension of 50 mm 15 mm 8 mm were cut from the as-cast ingot and then coldrolled with total thickness reduction of 20% and 70%, respectively. The crystal structures and microstructures after deformation were characterized by X-ray diffraction (XRD) using Cu-Kα radiation, optical microscope and electron backscattered diffraction (EBSD). Samples for EBSD analysis were mechanically and electrochemically polished with a solution of 10% HClO4 and 90% CH4O at -35 °C and 20 V for 20 s. EBSD analyses were performed using HKL Channel 5 software. Samples for optical observation were etched in 5% HNO3 + 10% HF + 85% H2O solution.
3. Results and discussion The X-ray diffraction results are shown in Fig. 1. Although the content of Nb is reduced relative to equiatomic TiZrHfNb alloy, all the as-cast and cold-rolled 3
TiZrHfNb0.7 alloys remain body-centered cubic (BCC) single phase. These results are consistent with that in TiZrHfNb0.6 alloy [20] where the BCC is stable even after compression.
Fig. 1. X-ray diffraction patterns of the as-cast and cold-rolled refractory TiZrHfNb0.7 alloy
After 20% cold rolling, the nearly paralleled band structure is arranged throughout a grain in Fig. 2(a). The corresponding local misorientation map was derived in Fig. 2(b) to qualitatively reflect the local plastic strain around the bands. The deformation strain is significantly larger at the band-matrix interface, especially at the band tip region. To quantitatively evaluate the crystal orientation difference between bands and matrix, the misorientation profile in Fig. 2(c) was created along the white line. These arbitrary misorientation angles in the range of 15° to 25° exclude the possibility of twinning.
4
Fig. 2. 20% cold rolled TiZrHfNb0.7 alloy: (a) inverse pole figure map; (b) local misorientation map; (c) misorientation profile (relative to the first point) along the line inset in (a); (d) {011}, {112} and {541} pole figures of the rectangular subset in (a).
According to the intragranular misorientation axis (IGMA) analysis method [21] based on the theory of dislocation slip-induced lattice rotation, the lattice rotation axis 𝑻 during kinking can be expressed as 𝑻 = γ𝒃 × 𝒏, where γ, 𝒃 and 𝒏 are the plastic shear gradient, Burgers vector and slip plane normal vector of the specific slip system, respectively. In other words, the rotation axis lies in the slip plane and is perpendicular to the Burgers vector. In BCC alloy, the Burgers vector 𝒃 of the perfect slip dislocation is of type 1/2<111>, while the slip planes 𝒏 can have three types of {110}, {112} and {123}. The possible rotation axis 𝑻 corresponding to these three slip modes can be deduced to be <112>, <011> and <541>. Therefore, if the structure in Fig. 2(a) is a 5
deformation kink band, the invariant crystal plane during deformation should belong to one of the {112}, {011} and {541}. Fig. 2(d) lists the {011}, {112} and {541} pole figures of the rectangular area in Fig. 2(a). An evident pole focus is exhibited in {011} pole figure, along with the rest of {011} poles, all {112} and all {541} poles rotated around this focused {011} pole. This crystallography confirms the occurrence of kink bands in Fig. 2(a) with the lattice rotation axis (𝑻) of <011> corresponding to the activation of {112} <111> slip mode during kinking process.
Fig. 3. 70% cold rolled TiZrHfNb0.7 alloy: (a) optical microstructure showing dense kink bands; (b) inverse pole figure map; (c) misorientation profile (relative to the first point) along the line inset in (b); (d) frequency distribution of the misorientation in the entire area of (b); (e) {011}, {112} and {541} pole figures of the rectangular subset in (b). 6
After 70% cold rolling, interestingly, intensive band structure formed in a stretched coarse grain in Fig. 3(a). The misorientation angles (Fig. 3(c)) along the line in Fig.3 (b) is around 20° to 30°. The statistical misorientation distribution was calculated in Fig. 3(d). Except for subgrains and low-angle boundaries, many highangle boundaries ranging from 10° to 40° represent the band-matrix misorientation angle. As shown in Fig. 3(e), a {011} focused pole emerges, with the rest of {011} poles, all {112} and all {541} poles rotated around this pole. This result once again confirms the <011> lattice rotation axis during kink band deformation.
Fig. 4. Schematic illustration of the kink band deformation in TiZrHfNb0.7 alloy
The kink formation for TiZrHfNb0.7 alloy during cold rolling was illustrated in Fig. 4. According to Hess and Barnett [22], the generation of dislocation pairs with opposite sign contributes to the nucleation of kink bands. Then, these dislocations with [111] shear direction are aligned as a wall perpendicular to the (211) slip plane to relax 7
the long-range stress field caused by the randomly accumulated dislocations. During plastic deformation, the increasingly aligned dislocations promoted progressive rotation of the kink band. The bands initiate at stress concentration region and then propagate across the entire grain. With further deformation, the bands tend to be locked up and this strain is accommodated either by broadening of existing kink band or initiating a new kink band, which can phenomenologically explain the intensive kink bands in Fig. 3(a, b). For TiZrHfNbTa alloy and its derivatives [3, 10-13], consistent with Fig. 2(a), these lamellas all arise from grain boundaries and propagate within a single grain. In other words, the occurrence of kinking within grains with specific crystallographic orientation. This characteristic excludes the possibility of the shear band which is a noncrystallographic deformation mode and it can penetrate multiple grains. The misorientation angles among the band-matrix interface are in the range of 10°~50° for TiZrHfNbTa alloy both under dynamic compression and HPT, which is much lower than that of the twin (50.5° for {332}<113> twin and 60° for {112}<111> twin) of BCC alloy. However, this arbitrary rotating degree is exactly a characteristic of kink deformation. So here we speculate that these bands or lamellar structures observed in TiZrHfNbTa [3, 11], TiZrHfNb [13] and Ti40Zr25Nb25Ta10 [14] high-entropy alloys are also likely to be deformation kinking rather than shear band or twinning.
4. Conclusions Kinking was identified in both 20% and 70% cold-rolled TiZrHfNb0.7 alloy. Using 8
intragranular misorientation axis (IGMA) analysis method, the <011> lattice rotation axis and {112} <111> dislocation slip mode were confirmed. The intensive band structure can be interpreted by considering the nucleation and propagation of kink bands during deformation. This kinking is likely to exist widely in TiZrHfNbTa and its derived high-entropy alloys.
Acknowledgements This work was supported by the National Key R&D Program of China (No. 2016YFB0701405), the National Natural Science Foundation of China (No. 51821001) and the Shanghai Science and Technology Committee (No. 16DZ2260602).
References [1] J.P. Couzinié, G. Dirras, Mater. Charact. 147 (2019) 533-544. [2] O.N. Senkov, D.B. Miracle, K.J. Chaput, J.-P. Couzinie, J. Mater. Res. 33(19) (2018) 30923128. [3] G. Dirras, L. Lilensten, P. Djemia, M. Laurent-Brocq, D. Tingaud, J.P. Couzinie, L. Perriere, T. Chauveau, I. Guillot, Mater. Sci. Eng. A 654 (2016) 30-38. [4] Y.D. Wu, Y.H. Cai, T. Wang, J.J. Si, J. Zhu, Y.D. Wang, X.D. Hui, Mater. Lett. 130 (2014) 277-280. [5] S. Sheikh, S. Shafeie, Q. Hu, J. Ahlström, C. Persson, J. Veselý, J. Zýka, U. Klement, S. Guo, J. Appl. Phys. 120(16) (2016) 164902. [6] E.P. George, D. Raabe, R.O. Ritchie, Nat. Rev. Mater. (2019). 9
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Shubin Wang: Conceptualization, Methodology, Formal analysis, Investigation, Writing-Original Draft. Mingxu Wu: Investigation, Writing-Original Draft. Da Shu: Conceptualization, Formal analysis, Writing-Original Draft, Writing - Review & Editing, Supervision, Project administration. Baode Sun: Project administration, Funding acquisition.
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Highlights 1. Kinking has been crystallographically confirmed in deformed TiZrHfNb0.7 alloy.
2. The initiation and propagation of kinking contribute to intensive band structure.
3. Kinking would exist widely in TiZrHfNbTa and its derived high-entropy alloys.
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Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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