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Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys
Accepted Manuscript Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys G. Dirras, D. Tingaud, D. Ueda, A. Hocini, K. Ameyama PII: DOI: Reference:
S0167-577X(17)31053-4 http://dx.doi.org/10.1016/j.matlet.2017.07.027 MLBLUE 22869
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
7 April 2017 6 June 2017 2 July 2017
Please cite this article as: G. Dirras, D. Tingaud, D. Ueda, A. Hocini, K. Ameyama, Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet.2017.07.027
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys G. Dirrasa,*, D. Tingauda, D. Uedab, A. Hocinia, K. Ameyamab a
Université Paris 13, Sorbonne Paris-Cité, 99 avenue Jean-Baptiste Clément, 93430,
Villetaneuse, France b
Department of Mechanical Engineering, Ritsumeikan University, Kustasu-Shiga,
Japan (*)
Corresponding author: E-mail: [email protected] —Tel: +33149403488
Abstract Ti-25Nb-25Zr -titanium alloys with both Traditional (IP) and harmonic structure designed (HS) were submitted to monotonic simple shear tests. The HS alloy exhibited superior flow stress and strength. Yet, the strain to failure was very close for both materials as was the strain hardening rate evolution. 11 twin boundaries dominate the post-mortem microstructure of IP. Conversely, complete twinning inhibition was the main feature for HS alloy. Dynamic Hall-Petch-like effect and high density of geometrically necessary dislocation boundaries due to plastic incompatibility between the core and the ultrafine-grained shell of HS alloy, respectively, are invoked for the observed mechanical behaviors. Keywords: Metals and alloys; microstructure; mechanical behavior; simple shear; titanium; harmonic structure 1. Introduction -titanium alloys have attracted attention due to their excellent properties. [1]. In such typical application, both strength and forming capability (ductility) are needed
1
simultaneously. Nonetheless, from a classical metallurgical point of view, these properties are seen as antinomies. Many research groups have been involved in the quest for the design of high strength and ductile materials [2-4]. Regarding -titanium alloys, extensive efforts to increase their tensile strength have been carried out [5]. For example, it was reported that the combination of both twinning and slip, enhance the uniform elongation while maintaining high strength [5,6]. Chemical-based formulation approaches have been used to design -titanium alloys which exhibited both transformation-induced plasticity (TRIP) and twin-induced plasticity (TWIP) effects [7,8]. Recently the concept of harmonic structure (HS) has been introduced [9]. A superior combination of strength and ductility in comparison to conventionally-designed materials have been achieved, which was attributed to the 3D network of ultra-finegrained (u-f-g) polycrystalline shell that surrounds coarse-grained (CG) multicrystalline cores, a peculiarity of HS. In this letter, we compare, for the first time, the mechanical behavior under simple shear tests at room temperature and the underlying deformation mechanisms of HS and traditional β-titanium Ti-25Nb-25Zr microstructures to shed light on the changes potentially introduced by the new HS design approach. 2. Materials and procedure Plasma Rotating Electrode Process (PREP) was used to prepare Ti-25Nb-25Zr powder whose chemical composition is as follows (%wt.): Zr (25.22) Nb (24.92) Fe (0.08) C (0.03) N (0.01) H (0.01) O (0.08) Ti (balance). The average particle size particle size was about 163μm. Conventional alloy samples were prepared from the as-PREP powder. For HS alloy further processing was carried out. A planetary ball mill apparatus (SUJ2 5mm balls; rotation speed: 150 rpm; Ar atmosphere; RT; Ball-to-powder ratio:
2
9:2) was used for 72ks. Prior to the milling process, the same Ti-25Nb-25Zr powder was milled to make a Ti-25Nb-25Zr coating layer on the surface of both vial and balls, in order to avoid contamination caused by the milling media. It should be noted that during the milling the powder particles are not disintegrated. Sintering was achieved by Spark Plasma Sintering (SPS) under pressure of 100 MPa at 1073K for 30min. The mechanical behavior was studied by simple shear tests performed by an MTS M20 testing machine equipped with a shearing device having a load capacity of 100kN at a constant strain rate of 10-3s-1. The sample geometry was 20mm in diameter and 1mm in thickness with 1521mm3 sheared volume. More details about the shear tests have been given elsewhere [10]. EBSD investigations were carried out using a Zeiss Supra 40VP FEG scanning electron microscope. Step size between the neighboring measurement positions of 0.05μm was used. The data were further processed by OIM™ software version 5. 3. Results and discussion Figure 1 compares the mechanical behavior of the two alloys. It can be seen that the HS alloy exhibits enhanced mechanical properties. Its yield shear stress ( strength (
= 445MPa) are higher than that of IP material (
=220MPa) and
= 150MPa and
= 430MPa). The inset in Fig. 1 illustrates this behavior for a selected strain range. It is interesting to note that mechanical properties enhancement which occurs by virtue of the specific design is not accompanied ductility loss as classically observed. Yet, the same trend has been systematically reported after tensile test on several HS materials so far produced [11-13]. It has also to be noted that the IP alloy actually displays slightly higher hardening behavior (
= 280 MPa) than the HSD one (
= 225
MPa). The strain hardening rate (SHR) evolutions are presented in Fig.1. The SHR of IP
3
is higher than that of the HS counterpart, particularly at lower strain. Its decrease upon straining is smooth compared to that of the HS alloy for which a sharp decrease is observed which is a characteristic of u-f-g materials, meaning that in the HS alloy, the u-f-g shell probably deforms first and protects the core from yielding. A Steady-state hardening stage is subsequently observed for both alloys starting at 10% and 15% of strain for HS and IP, respectively. Such high SHR values has been reported by Brodzek et al [8] in β -metastable Ti-Cr-Sn system and was attributed to a complex interplay between TWIP, TRIP and dislocations effects. Figure 2 show post-mortem EBSD analysis of the deformed samples, in terms of inverse pole figure (IPF) maps and Kernel Average Misorientation (KAM) parameter for the first neighbors which is the average misorientation angle between the current pixel orientation and its five first neighbors. For the HS material, the IPF map (Fig.2a) shows fluctuating orientation, mainly at the u-f-g shell and CG core interfaces. Lenticular-like and slip bands are also seen in the CG core. Fig.2b shows the gradient of local misorientation as measured by the KAM parameter. Slightly higher local orientation values are observed within or at the vicinity of the shell regions, meaning qualitatively that a higher dislocation density, mainly GNDs arranged in LAGBs are stored there. Fig.2c and 2d show the case of IP alloy. The IPF maps (Fig.2c) displays a fundamentally different picture. Here the striking feature is the presence of high density of mechanical twins, in line with fundamental deformation mechanism of β-titanium alloys [14-15]. The high density of twin boundaries (TBs) subdivides dynamically the microstructure into small domains as secondary twins formed inside larger ones. Interestingly, the KAM map shows a strong localized a gradient of misorientation, which in addition is higher (red color) than for the HS alloy. These higher levels are
4
found within the twins, at twin boundaries and at twin/twin interaction, while other areas surrounded by TBs remains un-deformed (blue color). A possible reason why the cores in HS do not undergo twinning may be related to the fact that due to a constraint resulting from the HS specificity (CG cores separated by harder UFG shells), local (near shell facets) plastic accommodation necessitates pronounced plastic strain gradients. However, to implement the latter, a limited number of twinning systems may prove to be insufficient. Nevertheless, it may happen that a much richer variety of slip systems are suitable. Which is probably the case here. Figure 3 shows the distribution of misorientaion across the boundary for the two alloys. While both LAGBS and 11 TBs characterize the IP alloy, the HS counterpart displays mainly a high fraction GNDs that are arranged in LAGBs. This is a consequence of plastic incompatibility accommodation resulting from the grain size gradient between the core and the shell. Deformation twinning has been reported to results in an extra strain hardening. Indeed, large elongation through the significant strain hardening due to the dynamic grain refinement by twinning have been reported in [14]. Yet, despite complete twinning inhibition, the strengthening response by virtue of HS concept appears also to be very efficient yet not at the ductility expense. 4. Conclusion The simple shear response of Ti-25Zr-25Nb β-titanium alloys having a traditional polycrystalline microstructure and harmonic structure has been investigated. The HSD material deformed by conventional plasticity and showed high flow stress and strength without ductility loss. These effects occur by virtue of grain-size difference between the shell and the core that lead to large strain incompatibility accommodated by a high
5
density of GNDs. Dynamic grain refinement via intensive twinning during simple shear loading of the conventional Ti-25Zr-25Nb β-titanium counterpart induced slightly higher SHR values. Nevertheless, the strengthening response by virtue of HS design concept appears to be very efficient. Acknowledgment This work was supported by the French national research Agency, in the framework of ANR 14-CE07-0003 "HighS-Ti" program.
Figure captions Figure 1. True stress and strain hardening rate evolutions as function of true shear strain. Figure 2. (a, c) IPF and (b, d) KAM maps illustrating the deformation characteristics of the two alloys. For the KAM, The misorientation level increases from blue (zero) to orange colors. See text for details. Figure 3. Distribution of the misorientation across boundaries in both alloys: 11 TBs and LAGBs dominate in the conventional alloy, while mainly LAGBs are revealed in HS alloy.
6
References [1] M. Geetha, A.K. Singh, R. Asokomani, A.K. Gogia, Ti based biomaterials, the ultimate choice for orthopaedic implants—a review, Prog. Mater. Sci. 54 (2009) 397425. [2] Y.T. Zhu, X.Z. Liao, X.L. Wu, Deformation twinning in nanocrystalline materials, Prog. Mater. Sci. 57 (2012) 1-62. [3] L. Lu, Y. Shen, X. Chen, L. Qian, K. Lu, Ultrahigh Strength and High Electrical Conductivity in Copper, Science 304 (2004) 422-426. [4] T. Sadat, G. Dirras, D. Tingaud, M. Ota, T. Chauveau, D. Faurie, S.K. Vajpai, K. Ameyama, Bulk Ni–W alloys with a composite-like microstructure processed by spark plasma sintering: Microstructure and mechanical properties, Mater. Des. 89 (2015) 1181-1190. [5] T. Furuhara, Role of defects on microstructure development of beta titanium alloys, T. Met. Mater. 6 (2000) 221-224. [6] X.H. Min, K. Tsuzaki, S. Emura, K. Tsuchiya, Heterogeneous twin formation and its effect on tensile properties in Ti–Mo based β titanium alloys, Mater. Sci. Eng. A 554 (2012) 53-60. [7] M. Marteleur, F. Sun, T. Gloriant, P. Vermaut, P.J. Jacques, F. Prima, On the design of new β-metastable titanium alloys with improved work hardening rate thanks to simultaneous TRIP and TWIP effects, Scr. Mater. 66 (2012) 749-752. [8] C. Brozek, F. Sun, P. Vermaut, Y. Millet, A. Lenain, D. Embury, P.J. Jacques, F. Prima, A β-titanium alloy with extra high strain-hardening rate: Design and mechanical properties, Scr. Mater. 114 (2016) 60-64.
7
[9] S. K. Vajpai, C. Sawangrat, O. Yamaguchi, O. P. Ciuca , K. Ameyama, Effect of bimodal harmonic structure design on the deformation behaviour and mechanical properties of Co-Cr-Mo alloy , Mater. Sci. Eng. C 58 (2016) 1008–1015. [10]. G. Dirras, S. Bouvier, J. Gubicza, B. Hasni, T. Szilágyi, Mechanical characteristics under monotonic and cyclic simple shear of spark plasma sintered ultrafine-grained nickel, Mater. Sci. Eng. A 526 (2009) 201-210. [11] Z. Zhang, S.K. Vajpai, D. Orlov, K. Ameyama, improvement of mechanical properties in SUS304L steel through, the control of bimodal microstructure characteristics, Mater. Sci. Eng. A 598 (2014) 106-113. [12] S.K. Vajpai, M. Ota, T. Watanabe, R. Maeda, T. Sekiguchi, T. Kusaka, Kei Ameyama, The development of high performance Ti-6Al-4V alloy via a unique microstructural design with bimodal grain size distribution. Metall. Mater. Trans. A 46 (2015) 903–914. [13] S.K. Vajpai, M. Ota, Z. Zhang, K. Ameyama, Three-dimensionally gradient harmonic structure design: an integrated approach for high performance structural materials, Mater. Lett. 4 (2016) 191-197. [14] X. Min, X. Chen, S. Emura, K. Tsuchiya, Mechanism of twinning-induced plasticity in β-type Ti–15Mo alloy, Scripta Mater. 69 (2013) 393-396. [15] L. Qu, Y. Yang, Y.F. Lu, L. Feng, J.H. Ju, P. Ge, W. Zhou, D. Han and D.H. Ping, A detwinning process of {332}<113> twins in beta titanium alloys, Scr. Mater. 69 (2013) 389-392.
8
9
10
11
Highlights β Ti-25Nb-25Zr alloys with traditional and harmonic structures evaluated by simple shear tests Traditional microstructure involves intense {332} <113> mechanical twinning Complete inhibition of twinning revealed in the Harmonic structure Dynamic Hall-Petch and shell-shielding effects explain the observed behaviors
12
Graphical abstract
13
S0167-577X(17)31053-4 http://dx.doi.org/10.1016/j.matlet.2017.07.027 MLBLUE 22869
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
7 April 2017 6 June 2017 2 July 2017
Please cite this article as: G. Dirras, D. Tingaud, D. Ueda, A. Hocini, K. Ameyama, Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys, Materials Letters (2017), doi: http://dx.doi.org/10.1016/j.matlet.2017.07.027
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
Dynamic Hall-Petch versus grain-size gradient effects on the mechanical behavior under simple shear loading of β-titanium Ti-25Nb-25Zr alloys G. Dirrasa,*, D. Tingauda, D. Uedab, A. Hocinia, K. Ameyamab a
Université Paris 13, Sorbonne Paris-Cité, 99 avenue Jean-Baptiste Clément, 93430,
Villetaneuse, France b
Department of Mechanical Engineering, Ritsumeikan University, Kustasu-Shiga,
Japan (*)
Corresponding author: E-mail: [email protected] —Tel: +33149403488
Abstract Ti-25Nb-25Zr -titanium alloys with both Traditional (IP) and harmonic structure designed (HS) were submitted to monotonic simple shear tests. The HS alloy exhibited superior flow stress and strength. Yet, the strain to failure was very close for both materials as was the strain hardening rate evolution. 11 twin boundaries dominate the post-mortem microstructure of IP. Conversely, complete twinning inhibition was the main feature for HS alloy. Dynamic Hall-Petch-like effect and high density of geometrically necessary dislocation boundaries due to plastic incompatibility between the core and the ultrafine-grained shell of HS alloy, respectively, are invoked for the observed mechanical behaviors. Keywords: Metals and alloys; microstructure; mechanical behavior; simple shear; titanium; harmonic structure 1. Introduction -titanium alloys have attracted attention due to their excellent properties. [1]. In such typical application, both strength and forming capability (ductility) are needed
1
simultaneously. Nonetheless, from a classical metallurgical point of view, these properties are seen as antinomies. Many research groups have been involved in the quest for the design of high strength and ductile materials [2-4]. Regarding -titanium alloys, extensive efforts to increase their tensile strength have been carried out [5]. For example, it was reported that the combination of both twinning and slip, enhance the uniform elongation while maintaining high strength [5,6]. Chemical-based formulation approaches have been used to design -titanium alloys which exhibited both transformation-induced plasticity (TRIP) and twin-induced plasticity (TWIP) effects [7,8]. Recently the concept of harmonic structure (HS) has been introduced [9]. A superior combination of strength and ductility in comparison to conventionally-designed materials have been achieved, which was attributed to the 3D network of ultra-finegrained (u-f-g) polycrystalline shell that surrounds coarse-grained (CG) multicrystalline cores, a peculiarity of HS. In this letter, we compare, for the first time, the mechanical behavior under simple shear tests at room temperature and the underlying deformation mechanisms of HS and traditional β-titanium Ti-25Nb-25Zr microstructures to shed light on the changes potentially introduced by the new HS design approach. 2. Materials and procedure Plasma Rotating Electrode Process (PREP) was used to prepare Ti-25Nb-25Zr powder whose chemical composition is as follows (%wt.): Zr (25.22) Nb (24.92) Fe (0.08) C (0.03) N (0.01) H (0.01) O (0.08) Ti (balance). The average particle size particle size was about 163μm. Conventional alloy samples were prepared from the as-PREP powder. For HS alloy further processing was carried out. A planetary ball mill apparatus (SUJ2 5mm balls; rotation speed: 150 rpm; Ar atmosphere; RT; Ball-to-powder ratio:
2
9:2) was used for 72ks. Prior to the milling process, the same Ti-25Nb-25Zr powder was milled to make a Ti-25Nb-25Zr coating layer on the surface of both vial and balls, in order to avoid contamination caused by the milling media. It should be noted that during the milling the powder particles are not disintegrated. Sintering was achieved by Spark Plasma Sintering (SPS) under pressure of 100 MPa at 1073K for 30min. The mechanical behavior was studied by simple shear tests performed by an MTS M20 testing machine equipped with a shearing device having a load capacity of 100kN at a constant strain rate of 10-3s-1. The sample geometry was 20mm in diameter and 1mm in thickness with 1521mm3 sheared volume. More details about the shear tests have been given elsewhere [10]. EBSD investigations were carried out using a Zeiss Supra 40VP FEG scanning electron microscope. Step size between the neighboring measurement positions of 0.05μm was used. The data were further processed by OIM™ software version 5. 3. Results and discussion Figure 1 compares the mechanical behavior of the two alloys. It can be seen that the HS alloy exhibits enhanced mechanical properties. Its yield shear stress ( strength (
= 445MPa) are higher than that of IP material (
=220MPa) and
= 150MPa and
= 430MPa). The inset in Fig. 1 illustrates this behavior for a selected strain range. It is interesting to note that mechanical properties enhancement which occurs by virtue of the specific design is not accompanied ductility loss as classically observed. Yet, the same trend has been systematically reported after tensile test on several HS materials so far produced [11-13]. It has also to be noted that the IP alloy actually displays slightly higher hardening behavior (
= 280 MPa) than the HSD one (
= 225
MPa). The strain hardening rate (SHR) evolutions are presented in Fig.1. The SHR of IP
3
is higher than that of the HS counterpart, particularly at lower strain. Its decrease upon straining is smooth compared to that of the HS alloy for which a sharp decrease is observed which is a characteristic of u-f-g materials, meaning that in the HS alloy, the u-f-g shell probably deforms first and protects the core from yielding. A Steady-state hardening stage is subsequently observed for both alloys starting at 10% and 15% of strain for HS and IP, respectively. Such high SHR values has been reported by Brodzek et al [8] in β -metastable Ti-Cr-Sn system and was attributed to a complex interplay between TWIP, TRIP and dislocations effects. Figure 2 show post-mortem EBSD analysis of the deformed samples, in terms of inverse pole figure (IPF) maps and Kernel Average Misorientation (KAM) parameter for the first neighbors which is the average misorientation angle between the current pixel orientation and its five first neighbors. For the HS material, the IPF map (Fig.2a) shows fluctuating orientation, mainly at the u-f-g shell and CG core interfaces. Lenticular-like and slip bands are also seen in the CG core. Fig.2b shows the gradient of local misorientation as measured by the KAM parameter. Slightly higher local orientation values are observed within or at the vicinity of the shell regions, meaning qualitatively that a higher dislocation density, mainly GNDs arranged in LAGBs are stored there. Fig.2c and 2d show the case of IP alloy. The IPF maps (Fig.2c) displays a fundamentally different picture. Here the striking feature is the presence of high density of mechanical twins, in line with fundamental deformation mechanism of β-titanium alloys [14-15]. The high density of twin boundaries (TBs) subdivides dynamically the microstructure into small domains as secondary twins formed inside larger ones. Interestingly, the KAM map shows a strong localized a gradient of misorientation, which in addition is higher (red color) than for the HS alloy. These higher levels are
4
found within the twins, at twin boundaries and at twin/twin interaction, while other areas surrounded by TBs remains un-deformed (blue color). A possible reason why the cores in HS do not undergo twinning may be related to the fact that due to a constraint resulting from the HS specificity (CG cores separated by harder UFG shells), local (near shell facets) plastic accommodation necessitates pronounced plastic strain gradients. However, to implement the latter, a limited number of twinning systems may prove to be insufficient. Nevertheless, it may happen that a much richer variety of slip systems are suitable. Which is probably the case here. Figure 3 shows the distribution of misorientaion across the boundary for the two alloys. While both LAGBS and 11 TBs characterize the IP alloy, the HS counterpart displays mainly a high fraction GNDs that are arranged in LAGBs. This is a consequence of plastic incompatibility accommodation resulting from the grain size gradient between the core and the shell. Deformation twinning has been reported to results in an extra strain hardening. Indeed, large elongation through the significant strain hardening due to the dynamic grain refinement by twinning have been reported in [14]. Yet, despite complete twinning inhibition, the strengthening response by virtue of HS concept appears also to be very efficient yet not at the ductility expense. 4. Conclusion The simple shear response of Ti-25Zr-25Nb β-titanium alloys having a traditional polycrystalline microstructure and harmonic structure has been investigated. The HSD material deformed by conventional plasticity and showed high flow stress and strength without ductility loss. These effects occur by virtue of grain-size difference between the shell and the core that lead to large strain incompatibility accommodated by a high
5
density of GNDs. Dynamic grain refinement via intensive twinning during simple shear loading of the conventional Ti-25Zr-25Nb β-titanium counterpart induced slightly higher SHR values. Nevertheless, the strengthening response by virtue of HS design concept appears to be very efficient. Acknowledgment This work was supported by the French national research Agency, in the framework of ANR 14-CE07-0003 "HighS-Ti" program.
Figure captions Figure 1. True stress and strain hardening rate evolutions as function of true shear strain. Figure 2. (a, c) IPF and (b, d) KAM maps illustrating the deformation characteristics of the two alloys. For the KAM, The misorientation level increases from blue (zero) to orange colors. See text for details. Figure 3. Distribution of the misorientation across boundaries in both alloys: 11 TBs and LAGBs dominate in the conventional alloy, while mainly LAGBs are revealed in HS alloy.
6
References [1] M. Geetha, A.K. Singh, R. Asokomani, A.K. Gogia, Ti based biomaterials, the ultimate choice for orthopaedic implants—a review, Prog. Mater. Sci. 54 (2009) 397425. [2] Y.T. Zhu, X.Z. Liao, X.L. Wu, Deformation twinning in nanocrystalline materials, Prog. Mater. Sci. 57 (2012) 1-62. [3] L. Lu, Y. Shen, X. Chen, L. Qian, K. Lu, Ultrahigh Strength and High Electrical Conductivity in Copper, Science 304 (2004) 422-426. [4] T. Sadat, G. Dirras, D. Tingaud, M. Ota, T. Chauveau, D. Faurie, S.K. Vajpai, K. Ameyama, Bulk Ni–W alloys with a composite-like microstructure processed by spark plasma sintering: Microstructure and mechanical properties, Mater. Des. 89 (2015) 1181-1190. [5] T. Furuhara, Role of defects on microstructure development of beta titanium alloys, T. Met. Mater. 6 (2000) 221-224. [6] X.H. Min, K. Tsuzaki, S. Emura, K. Tsuchiya, Heterogeneous twin formation and its effect on tensile properties in Ti–Mo based β titanium alloys, Mater. Sci. Eng. A 554 (2012) 53-60. [7] M. Marteleur, F. Sun, T. Gloriant, P. Vermaut, P.J. Jacques, F. Prima, On the design of new β-metastable titanium alloys with improved work hardening rate thanks to simultaneous TRIP and TWIP effects, Scr. Mater. 66 (2012) 749-752. [8] C. Brozek, F. Sun, P. Vermaut, Y. Millet, A. Lenain, D. Embury, P.J. Jacques, F. Prima, A β-titanium alloy with extra high strain-hardening rate: Design and mechanical properties, Scr. Mater. 114 (2016) 60-64.
7
[9] S. K. Vajpai, C. Sawangrat, O. Yamaguchi, O. P. Ciuca , K. Ameyama, Effect of bimodal harmonic structure design on the deformation behaviour and mechanical properties of Co-Cr-Mo alloy , Mater. Sci. Eng. C 58 (2016) 1008–1015. [10]. G. Dirras, S. Bouvier, J. Gubicza, B. Hasni, T. Szilágyi, Mechanical characteristics under monotonic and cyclic simple shear of spark plasma sintered ultrafine-grained nickel, Mater. Sci. Eng. A 526 (2009) 201-210. [11] Z. Zhang, S.K. Vajpai, D. Orlov, K. Ameyama, improvement of mechanical properties in SUS304L steel through, the control of bimodal microstructure characteristics, Mater. Sci. Eng. A 598 (2014) 106-113. [12] S.K. Vajpai, M. Ota, T. Watanabe, R. Maeda, T. Sekiguchi, T. Kusaka, Kei Ameyama, The development of high performance Ti-6Al-4V alloy via a unique microstructural design with bimodal grain size distribution. Metall. Mater. Trans. A 46 (2015) 903–914. [13] S.K. Vajpai, M. Ota, Z. Zhang, K. Ameyama, Three-dimensionally gradient harmonic structure design: an integrated approach for high performance structural materials, Mater. Lett. 4 (2016) 191-197. [14] X. Min, X. Chen, S. Emura, K. Tsuchiya, Mechanism of twinning-induced plasticity in β-type Ti–15Mo alloy, Scripta Mater. 69 (2013) 393-396. [15] L. Qu, Y. Yang, Y.F. Lu, L. Feng, J.H. Ju, P. Ge, W. Zhou, D. Han and D.H. Ping, A detwinning process of {332}<113> twins in beta titanium alloys, Scr. Mater. 69 (2013) 389-392.
8
9
10
11
Highlights β Ti-25Nb-25Zr alloys with traditional and harmonic structures evaluated by simple shear tests Traditional microstructure involves intense {332} <113> mechanical twinning Complete inhibition of twinning revealed in the Harmonic structure Dynamic Hall-Petch and shell-shielding effects explain the observed behaviors
12
Graphical abstract
13