Nano and Heterogeneous Materials Center, School of Materials Science and Engineering, Nanjing Universityof Science and Technology, Nanjing 210094, China
Cite this article:
ZHAO Yonghao, MAO Qingzhong. Toughening of Nanostructured Metals. Acta Metall Sin, 2022, 58(11): 1385-1398.
Metallic structural materials have a wide range of industrial applications (including in the aviation, aerospace, navigation, military industry, nuclear power, chemical industry, construction, and bridge-building fields) due to their unique properties (such as heat resistance and high strength and toughness). At present, there are development opportunities for metallic structural materials, but these materials are also facing challenges due to the gradual substitution of carbon fiber composites and the increasing shortage of metal mineral resources. China's metallic structural material industry is facing development roadblocks and opportunities. Nanostructured metals and alloys have a wide range of potential industrial applications in the field of aviation, aerospace, navigation, military industry with requirements for energy conservation and weight reduction due to their high strength, but their low fracture elongation is a major limitation. The low ductility of nanostructured metals is caused by their low strain hardening rate; the strain hardening rate is caused by the difficulty of dislocation accumulation. This is because the small grain size limits dislocation propagation and reaction. After more than 20 years of research, the low ductility of nanostructured metals has been improved by tailoring the metal microstructures, such as by introducing nano-precipitation, twin boundaries, multi-scale grain distribution, twinning, or phase transformation, nano-gradient structure, and heterogeneous structure, or by lowering dislocation density, etc. These toughening schemes improve the dislocation accumulation capacity and strain hardening rate of nanostructured metals, and ultimately improve their toughness. The tensile properties of nanostructured metals are closely related to their microstructures and deformation temperature, strain rate, tensile sample size, and loading state.
Fund: National Key Research and Development Program of China(2021YFA1200203);National Natural Science Foundation of China(51971112);Fundamental Research Funds for the Central Universities(30919011405)
About author: ZHAO Yonghao, professor, Tel: (025)84315304, E-mail: yhzhao@njust.edu.cn
Fig.1 Comparison of fracture toughness-strength of metallic, ceramic and organic polymer materials[1] (PP—polypropylene, PE—polyethylene, PC—polycarbonate, PS—polystyrene, PET—poly(ethylene terephthalare), PTFE—poly tetra fluoroethylene)
Fig.2 Proportion of composite and metallic structural materials used in the U.S. Boeing 787 airliner
Fig.3 Relationship between metal strength and dislocation density
Fig.4 Schematic of tensile curves of ceramics, metals, and organic polymers and the relationship between static toughness and strength, fracture elongation, and work hardening rate (PMCs—polymer matrix composites; ε—strain, σ—stress)
Fig.5 Tensile curves of coarse-grained copper (CG Cu) and annealed nano/ultrafine-grained copper (Insets show the corresponding dislocation accumulation)[48]
Fig.6 Dependence of the strengthening effect on the radii of precipitates
Fig.7 Tensile curves of CG solid solution, liquid nitrogen rolling (NS), and low-temperature aging (NS + P) 7075 aluminum alloys (a), dislocation accumulation near the precipitated phase after tension (b-d), and nano-precipitated phase before tension (e-g)[56] (The inset shows dimension of the tensile sample with a thickness of 1 mm)
Fig.8 Tensile curves of equal channel angular pressing (ECAP) and subsequent liquid nitrogen drawing and rolling (ECAP + D + R) of ultrafine grained (UFG) copper (a), nano deformation twins introduced by liquid nitrogen deformation (b), and interaction of twin boundaries and dislocations (c)[82] (Inset in Fig.8a shows dimension of tensile sample with a thickness of 0.1 mm, b—Burgers vector)
Fig.9 Microstructures (a, b) and tensile curves (c) of high-purity and dense bi/multi-modal nickel (Bi-Ni/multi-Ni) and review of yield strength-tensile ductility of nickel (d)[87] (The twins in Figs.9a and b are indicated by black arrows; the inset in Fig.9c shows the picture of the fractured tensile specimens; ED—electro-deposition, HPT—high pressure torsion)
Fig.10 Tensile curves (a) and X-ray diffraction spectra (b) of ultrafine grained Fe-Mn alloy[89]
Fig.11 Gradient nano-grained (GNG) structured copper prepared by surface mechanical grinding treatment[95] (a) schematic of the tensile bar sample of which the gauge section was processed by means of surface mechanical grinding treatment (SMGT) (b, c) schematics of the cross-sectional microstructure of the gauge consisting of a gradient nano-grained layer (dark blue) and a deformed coarse grained layer (blue) on a coarse grained core (light blue) (d) a typical cross-sectional SEM image of a SMGT Cu sample (e) a cross-sectional bright-field TEM image of microstructures 3 mm below the treated surface (The arrow indicates the processing direction, and the inset shows the electron diffraction pattern) (f) a transversal grain size distribution from TEM measurements in the top 5-mm-deep layer (g) variation of average transversal grain (subgrain or cell) sizes along depth from the surface (Error bars represent the standard deviation of grain-size measurements)
Fig.12 Tensile engineering stress-strain (σe-εe) curves (a), strain hardening curves (b-d), and complex stress states (e, f) of nano-gradient stainless steel[96] (GS—gradient-structured, NS—nanostructured; Θ—strain hardening rate, εT—true strain, σT—true stress, H—microhardness, ΔH—H increment; inset in Fig.12b shows transient response on the σT-εT curve of the GS-CG sample between two inflection points marked by "×" corresponding to the Θ-up-turn on its Θ-εT curve)
Fig.13 Effects of thickness (T) and length (L) of ultrafine grained Cu tensile samples on tensile curves and deformation mechanisms (W—width of gauge, PEEQ—equivalent plastic strain)[109]
1
Gludovatz B, Hohenwarter A, Catoor D, et al. A fracture-resistant high-entropy alloy for cryogenic applications [J]. Science, 2014, 345: 1153
doi: 10.1126/science.1254581
pmid: 25190791
Suryanarayana C, Koch C C. Nanocrystalline materials-current research and future directions [J]. Hyperfine Interact., 2000, 130: 5
4
Valiev R Z, Langdon T G. Principles of equal-channel angular pressing as a processing tool for grain refinement [J]. Prog. Mater. Sci., 2006, 51: 881
doi: 10.1016/j.pmatsci.2006.02.003
5
Lin Y J, Wen H M, Li Y, et al. Erratum to: Stress-induced grain growth in an ultra-fine grained Al alloy [J]. Metall. Mater. Trans., 2014, 45B: 1948
6
Valiev R Z, Islamgaliev R K, Alexandrov I V. Bulk nanostructured materials from severe plastic deformation [J]. Prog. Mater. Sci., 2000, 45: 103
doi: 10.1016/S0079-6425(99)00007-9
7
Zhilyaev A P, Langdon T G. Using high-pressure torsion for metal processing: Fundamentals and applications [J]. Prog. Mater. Sci., 2008, 53: 893
doi: 10.1016/j.pmatsci.2008.03.002
8
Saito Y, Utsunomiya H, Tsuji N, et al. Novel ultra-high straining process for bulk materials—Development of the accumulative roll-bonding (ARB) process [J]. Acta Mater., 1999, 47: 579
doi: 10.1016/S1359-6454(98)00365-6
9
Li Y S, Tao N R, Lu K. Microstructural evolution and nanostructure formation in copper during dynamic plastic deformation at cryogenic temperatures [J]. Acta Mater., 2008, 56: 230
doi: 10.1016/j.actamat.2007.09.020
10
Lu K, Lu J. Surface nanocrystallization (SNC) of metallic materials-presentation of the concept behind a new approach [J]. J. Mater. Sci. Technol., 1999, 15: 193
11
Tao N R, Wang Z B, Tong W P, et al. An investigation of surface nanocrystallization mechanism in Fe induced by surface mechanical attrition treatment [J]. Acta Mater., 2002, 50: 4603
doi: 10.1016/S1359-6454(02)00310-5
12
Liu X C, Zhang H W, Lu K. Strain-induced ultrahard and ultrastable nanolaminated structure in nickel [J]. Science, 2013, 342: 337
doi: 10.1126/science.1242578
pmid: 24136963
13
Mao Q Z, Liu Y F, Zhao Y H. A review on mechanical properties and microstructure of ultrafine grained metals and alloys processed by rotary swaging [J]. J. Alloys Compd., 2022, 896: 163122
doi: 10.1016/j.jallcom.2021.163122
14
Meyers M A, Mishra A, Benson D J. Mechanical properties of nanocrystalline materials [J]. Prog. Mater. Sci., 2006, 51: 427
doi: 10.1016/j.pmatsci.2005.08.003
15
Koch C C. Optimization of strength and ductility in nanocrystalline and ultrafine grained metals [J]. Scr. Mater., 2003, 49: 657
doi: 10.1016/S1359-6462(03)00394-4
16
Ma E. Instabilities and ductility of nanocrystalline and ultrafine-grained metals [J]. Scr. Mater., 2003, 49: 663
doi: 10.1016/S1359-6462(03)00396-8
17
Koch C C, Youssef K M, Scattergood R O, et al. Breakthroughs in optimization of mechanical properties of nanostructured metals and alloys [J]. Adv. Eng. Mater., 2005, 7: 787
doi: 10.1002/adem.200500094
18
Ma E. Eight routes to improve the tensile ductility of bulk nanostructured metals and alloys [J]. JOM, 2006, 58(4): 49
doi: 10.1007/s11837-006-0215-5
19
Koch C C. Structural nanocrystalline materials: An overview [J]. J. Mater. Sci., 2007, 42: 1403
doi: 10.1007/s10853-006-0609-3
20
Zhao Y H, Zhu Y T, Lavernia E J. Strategies for improving tensile ductility of bulk nanostructured materials [J]. Adv. Eng. Mater., 2010, 12: 769
doi: 10.1002/adem.200900335
21
Ovid'ko I A, Valiev R Z, Zhu Y T. Review on superior strength and enhanced ductility of metallic nanomaterials [J]. Prog. Mater. Sci., 2018, 94: 462
doi: 10.1016/j.pmatsci.2018.02.002
22
Darling K A, VanLeeuwen B K, Koch C C, et al. Thermal stability of nanocrystalline Fe-Zr alloys [J]. Mater. Sci. Eng., 2010, A527: 3572
23
Atwater M A, Scattergood R O, Koch C C. The stabilization of nanocrystalline copper by zirconium [J]. Mater. Sci. Eng., 2013, A559: 250
24
Fu H L, Zhou X, Xue H T, et al. Breaking the purity-stability dilemma in pure Cu with grain boundary relaxation [J]. Mater. Today, 2022, 55: 66
doi: 10.1016/j.mattod.2022.03.002
25
Chauhan M, Mohamed F A. Investigation of low temperature thermal stability in bulk nanocrystalline Ni [J]. Mater. Sci. Eng., 2006, A427: 7
26
Tao J M, Zhu X K, Scattergood R O, et al. The thermal stability of high-energy ball-milled nanostructured Cu [J]. Mater. Des., 2013, 50: 22
doi: 10.1016/j.matdes.2013.02.083
27
Liang N N, Liu J Z, Lin S C, et al. A multiscale architectured CuCrZr alloy with high strength, electrical conductivity and thermal stability [J]. J. Alloys Compd., 2018, 735: 1389
doi: 10.1016/j.jallcom.2017.11.309
28
Liang N N, Zhao Y H, Li Y, et al. Influence of microstructure on thermal stability of ultrafine-grained Cu processed by equal channel angular pressing [J]. J. Mater. Sci., 2018, 53: 13173
doi: 10.1007/s10853-018-2548-1
29
Tang L L, Zhao Y H, Islamgaliev R K, et al. Microstructure and thermal stability of nanocrystalline Mg-Gd-Y-Zr alloy processed by high pressure torsion [J]. J. Alloys Compd., 2017, 721: 577
doi: 10.1016/j.jallcom.2017.05.164
30
Zhang Y S, Zhang W, Wang X, et al. Microstructure and mechanical property evolutions of bulk core-shell structured Ti-N alloys during annealing [J]. J. Alloys Compd., 2017, 710: 418
doi: 10.1016/j.jallcom.2017.03.254
31
Liang N N, Xu R R, Wu G Z, et al. High thermal stability of nanocrystalline FeNi2CoMo0.2V0.5 high-entropy alloy by twin boundary and sluggish diffusion [J]. Mater. Sci. Eng., 2022, A848: 143399
32
Liu X R, Wei D J, Zhuang L M, et al. Fabrication of high-strength graphene nanosheets/Cu composites by accumulative roll bonding [J]. Mater. Sci. Eng., 2015, A642: 1
33
Liu X R, Zhuang L M, Zhao Y H. Microstructure and mechanical properties of ultrafine-grained copper by accumulative roll bonding and subsequent annealing [J]. Materials, 2020, 13: 5171
doi: 10.3390/ma13225171
34
Xu R R, Liang N N, Zhuang L M, et al. Microstructure and mechanical behaviors of Al/Cu laminated composites fabricated by accumulative roll bonding and intermediate annealing [J]. Mater. Sci. Eng., 2022, A832: 142510
35
Wan Y C, Tang B, Gao Y H, et al. Bulk nanocrystalline high-strength magnesium alloys prepared via rotary swaging [J]. Acta Mater., 2020, 200: 274
doi: 10.1016/j.actamat.2020.09.024
36
Mao Q Z, Zhang Y S, Liu J Z, et al. Breaking material property trade-offs via macrodesign of microstructure [J]. Nano Lett., 2021, 21: 3191
doi: 10.1021/acs.nanolett.1c00451
37
Mao Q Z, Zhang Y S, Guo Y Z, et al. Enhanced electrical conductivity and mechanical properties in thermally stable fine-grained copper wire [J]. Commun. Mater., 2021, 2: 46
doi: 10.1038/s43246-021-00150-1
38
Mao Q Z, Chen X, Li J S, et al. Nano-gradient materials prepared by rotary swaging [J]. Nanomaterials, 2021, 11: 2223
doi: 10.3390/nano11092223
39
Yang Y, Chen X, Nie J F, et al. Achieving ultra-strong magnesium-lithium alloys by low-strain rotary swaging [J]. Mater. Res. Lett., 2021, 9: 255
doi: 10.1080/21663831.2021.1891150
40
Mao Q Z, Wang L, Nie J F, et al. Enhancing strength and electrical conductivity of Cu-Cr composite wire by two-stage rotary swaging and aging treatments [J]. Composites, 2022, 231B: 109567
41
Chen Y Y, Nie J F, Wang F, et al. Revealing hetero-deformation induced (HDI) stress strengthening effect in laminated Al-(TiB2 +TiC)p/6063 composites prepared by accumulative roll bonding [J]. J. Alloys Compd., 2020, 815: 152285
doi: 10.1016/j.jallcom.2019.152285
42
Nie J F, Liu M X, Wang F, et al. Fabrication of Al/Mg/Al composites via accumulative roll bonding and their mechanical properties [J]. Materials, 2016, 9: 951
doi: 10.3390/ma9110951
43
Yang Y, Nie J F, Mao Q Z, et al. Improving the combination of electrical conductivity and tensile strength of Al 1070 by rotary swaging deformation [J]. Results Phys., 2019, 13: 102236
doi: 10.1016/j.rinp.2019.102236
44
Lu F H, Nie J F, Ma X, et al. Simultaneously improving the tensile strength and ductility of the AlNp/Al composites by the particle's hierarchical structure with bimodal distribution and nano-network [J]. Mater. Sci. Eng., 2020, A770: 138519
45
Chen X, Liu C M, Wan Y C, et al. Grain refinement mechanisms in gradient nanostructured AZ31B Mg alloy prepared via rotary swaging [J]. Metall. Mater. Trans., 2021, 52A: 4053
46
Nie J F, Lu F H, Huang Z W, et al. Improving the high-temperature ductility of Al composites by tailoring the nanoparticle network [J]. Materialia, 2020, 9: 100523
doi: 10.1016/j.mtla.2019.100523
47
Sanders P G, Youngdahl C J, Weertman J R. The strength of nanocrystalline metals with and without flaws [J]. Mater. Sci. Eng., 1997, A234-236: 77
48
Zhao Y H, Topping T, Li Y, et al. Strength and ductility of Bi-modal Cu [J]. Adv. Eng. Mater., 2011, 13: 865
doi: 10.1002/adem.201100019
Budrov Z, Van Swygenhoven H, Derlet P M, et al. Plastic deformation with reversible peak broadening in nanocrystalline nickel [J]. Science, 2004, 304: 273
pmid: 15073373
51
Yamakov V, Wolf D, Phillpot S R, et al. Deformation-mechanism map for nanocrystalline metals by molecular-dynamics simulation [J]. Nat. Mater., 2004, 3: 43
pmid: 14704784
52
Van Swygenhoven H, Derlet P M, Frøseth A G. Stacking fault energies and slip in nanocrystalline metals [J]. Nat. Mater., 2004, 3: 399
pmid: 15156199
53
Wei Q, Cheng S, Ramesh K T, et al. Effect of nanocrystalline and ultrafine grain sizes on the strain rate sensitivity and activation volume: fcc versus bcc metals [J]. Mater. Sci. Eng., 2004, A381: 71
54
Kelly A, Nicholson R B. Strengthening Methods in Crystals [M]. Amsterdam: Elsevier, 1971: 1
55
Luan B F, Wu G H, Hansen N, et al. High strength Al2O3p/6061 Al composites: Effect of particles, subgrains and precipitates [J]. Mater. Sci. Technol., 2007, 23: 233
doi: 10.1179/174328407X154365
56
Zhao Y H, Liao X Z, Cheng S, et al. Simultaneously increasing the ductility and strength of nanostructured alloys [J]. Adv. Mater., 2006, 18: 2280
doi: 10.1002/adma.200600310
57
Shanmugasundaram T, Murty B S, Sarma V S. Development of ultrafine grained high strength Al-Cu alloy by cryorolling [J]. Scr. Mater., 2006, 54: 2013
doi: 10.1016/j.scriptamat.2006.03.012
58
Cheng S, Zhao Y H, Zhu Y T, et al. Optimizing the strength and ductility of fine structured 2024 Al alloy by nano-precipitation [J]. Acta Mater., 2007, 55: 5822
doi: 10.1016/j.actamat.2007.06.043
59
Takata N, Ohtake Y, Kita K, et al. Increasing the ductility of ultrafine-grained copper alloy by introducing fine precipitates [J]. Scr. Mater., 2009, 60: 590
doi: 10.1016/j.scriptamat.2008.12.018
60
Hu C M, Lai C M, Du X H, et al. Enhanced tensile plasticity in ultrafine-grained metallic composite fabricated by friction stir process [J]. Scr. Mater., 2008, 59: 1163
doi: 10.1016/j.scriptamat.2008.06.040
61
Kuwabara T, Kurishita H, Hasegawa M. Development of an ultra-fine grained V-1.7 mass% Y alloy dispersed with yttrium compounds having superior ductility and high strength [J]. Mater. Sci. Eng., 2006, A417: 16
62
Kim W J, Sa Y K. Micro-extrusion of ECAP processed magnesium alloy for production of high strength magnesium micro-gears [J]. Scr. Mater., 2006, 54: 1391
doi: 10.1016/j.scriptamat.2005.11.066
63
Hassan S F, Gupta M. Enhancing physical and mechanical properties of Mg using nanosized Al2O3 particulates as reinforcement [J]. Metall. Mater. Trans., 2005, 36A: 2253
64
Song R, Ponge D, Raabe D. Improvement of the work hardening rate of ultrafine grained steels through second phase particles [J]. Scr. Mater., 2005, 52: 1075
doi: 10.1016/j.scriptamat.2005.02.016
65
Liu G, Zhang G J, Jiang F, et al. Nanostructured high-strength molybdenum alloys with unprecedented tensile ductility [J]. Nat. Mater., 2013, 12: 344
doi: 10.1038/nmat3544
pmid: 23353630
66
Zhao Y H. In situ thermomechanical processing to avoid grain boundary precipitation and strength-ductility loss of age hardening alloys [J]. Trans. Nonferrous Met. Soc. China, 2021, 31: 1205
doi: 10.1016/S1003-6326(21)65572-3
67
Yang T, Zhao Y L, Tong Y, et al. Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys [J]. Science, 2018, 362: 933
doi: 10.1126/science.aas8815
pmid: 30467166
68
Lei Z F, Liu X J, Wu Y, et al. Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes [J]. Nature, 2018, 563: 546
doi: 10.1038/s41586-018-0685-y
69
Jin Z H, Gumbsch P, Albe K, et al. Interactions between non-screw lattice dislocations and coherent twin boundaries in face-centered cubic metals [J]. Acta Mater., 2008, 56: 1126
doi: 10.1016/j.actamat.2007.11.020
70
You Z S, Li X Y, Gui L J, et al. Plastic anisotropy and associated deformation mechanisms in nanotwinned metals [J]. Acta Mater., 2013, 61: 217
doi: 10.1016/j.actamat.2012.09.052
71
Cheng S, Zhao Y H, Wang Y M, et al. Structure modulation driven by cyclic deformation in nanocrystalline NiFe [J]. Phys. Rev. Lett., 2010, 104: 255501
doi: 10.1103/PhysRevLett.104.255501
72
Gu L, Liang N N, Chen Y Y, et al. Achieving maximum strength-ductility combination in fine-grained Cu-Zn alloy via detwinning and twinning deformation mechanisms [J]. J. Alloys Compd., 2022, 906: 164401
doi: 10.1016/j.jallcom.2022.164401
73
Shi S J, Dai L J, Zhao Y H. Ternary relation among stacking fault energy, grain size and twin nucleation size in nanocrystalline and ultrafine grained CuAl alloys [J]. J. Alloys Compd., 2022, 896: 162953
doi: 10.1016/j.jallcom.2021.162953
74
Jiang W, Gao X Z, Cao Y, et al. Charpy impact behavior and deformation mechanisms of Cr26Mn20Fe20Co20Ni14 high-entropy alloy at ambient and cryogenic temperatures [J]. Mater. Sci. Eng., 2022, A837: 142735
75
Gao X Z, Dai L J, Zhao Y H. Twin boundary-dislocation interactions in nanocrystalline Cu-30% Zn alloys prepared by high pressure torsion [J]. J. Mater. Res. Technol., 2020, 9: 11958
doi: 10.1016/j.jmrt.2020.08.060
76
Li Y S, Dai L J, Cao Y, et al. Grain size effect on deformation twin thickness in a nanocrystalline metal with low stacking-fault energy [J]. J. Mater. Res., 2019, 34: 2398
doi: 10.1557/jmr.2019.194
77
Gao X Z, Lu Y P, Liu J Z, et al. Extraordinary ductility and strain hardening of Cr26Mn20Fe20Co20Ni14 TWIP high-entropy alloy by cooperative planar slipping and twinning [J]. Materialia, 2019, 8: 100485
doi: 10.1016/j.mtla.2019.100485
78
Jiang W, Gao X Z, Guo Y Z, et al. Dynamic impact behavior and deformation mechanisms of Cr26Mn20Fe20Co20Ni14 high-entropy alloy [J]. Mater. Sci. Eng., 2021, A824: 141858
79
Lu L, Shen Y F, Chen X H, et al. Ultrahigh strength and high electrical conductivity in copper [J]. Science, 2004, 304: 422
pmid: 15031435
80
Andrews P V, West M B, Robeson C R. The effect of grain boundaries on the electrical resistivity of polycrystalline copper and aluminium [J]. Philos. Mag., 1969, 19: 887
81
Callister W D. Materials Science and Engineering: An Introduction [M]. 7th Ed., New York: John Wiley & Sons, Inc., 2007: 674
82
Zhao Y H, Bingert J F, Liao X Z, et al. Simultaneously increasing the ductility and strength of ultra-fine-grained pure copper [J]. Adv. Mater., 2006, 18: 2949
doi: 10.1002/adma.200601472
83
Whang S H. Nanostructured Metals and Alloys [M]. Oxford: Woodhead Publishing, 2011: 375
84
Legros M, Elliott B R, Rittner M N, et al. Microsample tensile testing of nanocrystalline metals [J]. Philos. Mag., 2000, 80A: 1017
85
Tellkamp V L, Lavernia E J, Melmed A. Mechanical behavior and microstructure of a thermally stable bulk nanostructured Al alloy [J]. Metall. Mater. Trans., 2001, 32A: 2335
86
Wang Y M, Chen M W, Zhou F H, et al. High tensile ductility in a nanostructured metal [J]. Nature, 2002, 419: 912
doi: 10.1038/nature01133
87
Zhao Y H, Topping T, Bingert J F, et al. High tensile ductility and strength in bulk nanostructured nickel [J]. Adv. Mater., 2008, 20: 3028
doi: 10.1002/adma.200800214
88
Bouaziz O, Allain S, Scott C P, et al. High manganese austenitic twinning induced plasticity steels: A review of the microstructure properties relationships [J]. Curr. Opin. Solid State Mater. Sci., 2011, 15: 141
doi: 10.1016/j.cossms.2011.04.002
89
Cheng S, Choo H, Zhao Y H, et al. High ductility of ultrafine-grained steel via phase transformation [J]. J. Mater. Res., 2008, 23: 1578
doi: 10.1557/JMR.2008.0213
90
Wang Y M, Ott R T, Hamza A V, et al. Achieving large uniform tensile ductility in nanocrystalline metals [J]. Phys. Rev. Lett., 2010, 105: 215502
doi: 10.1103/PhysRevLett.105.215502
91
Zhao Y H, Zhu Y T, Liao X Z, et al. Tailoring stacking fault energy for high ductility and high strength in ultrafine grained Cu and its alloy [J]. Appl. Phys. Lett., 2006, 89: 121906
doi: 10.1063/1.2356310
92
Zhao Y H, Bingert J F, Topping T D, et al. Mechanical behavior, deformation mechanism and microstructure evolutions of ultrafine-grained Al during recovery via annealing [J]. Mater. Sci. Eng., 2020, A772: 138706
93
Zhao Y H, Bingert J F, Zhu Y T, et al. Tougher ultrafine grain Cu via high-angle grain boundaries and low dislocation density [J]. Appl. Phys. Lett., 2008, 92: 081903
94
Meng A, Chen X, Nie J F, et al. Microstructure evolution and mechanical properties of commercial pure titanium subjected to rotary swaging [J]. J. Alloys Compd., 2021, 859: 158222
doi: 10.1016/j.jallcom.2020.158222
95
Fang T H, Li W L, Tao N R, et al. Revealing extraordinary intrinsic tensile plasticity in gradient nano-grained copper [J]. Science, 2011, 331: 1587
doi: 10.1126/science.1200177
pmid: 21330487
96
Wu X L, Jiang P, Chen L, et al. Extraordinary strain hardening by gradient structure [J]. Proc. Natl. Acad. Sci. USA, 2014, 111: 7197
doi: 10.1073/pnas.1324069111
97
Wu X L, Yang M X, Yuan F P, et al. Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility [J]. Proc. Natl. Acad. Sci. USA, 2015, 112: 14501
doi: 10.1073/pnas.1517193112
98
Ma X L, Huang C X, Moering J, et al. Mechanical properties of copper/bronze laminates: role of interfaces [J]. Acta Mater., 2016, 116: 43
doi: 10.1016/j.actamat.2016.06.023
99
Zhang Y S, Zhao Y H, Zhang W, et al. Core-shell structured titanium-nitrogen alloys with high strength, high thermal stability and good plasticity [J]. Sci. Rep., 2017, 7: 40039
doi: 10.1038/srep40039
pmid: 28059150
100
Wu X L, Zhu Y T. Heterogeneous materials: A new class of materials with unprecedented mechanical properties [J]. Mater. Res. Lett., 2017, 5: 527
doi: 10.1080/21663831.2017.1343208
101
Yang M X, Pan Y, Yuan F P, et al. Back stress strengthening and strain hardening in gradient structure [J]. Mater. Res. Lett., 2016, 4: 145
doi: 10.1080/21663831.2016.1153004
102
Zhu Y T, Wu X L. Perspective on hetero-deformation induced (HDI) hardening and back stress [J]. Mater. Res. Lett., 2019, 7: 393
doi: 10.1080/21663831.2019.1616331
103
Wang Y M, Ma E, Valiev R Z, et al. Tough nanostructured metals at cryogenic temperatures [J]. Adv. Mater., 2004, 16: 328
doi: 10.1002/adma.200305679
104
Wang Y M, Ma E. Three strategies to achieve uniform tensile deformation in a nanostructured metal [J]. Acta Mater., 2004, 52: 1699
doi: 10.1016/j.actamat.2003.12.022
105
Yu C Y, Kao P W, Chang C P. Transition of tensile deformation behaviors in ultrafine-grained aluminum [J]. Acta Mater., 2005, 53: 4019
doi: 10.1016/j.actamat.2005.05.005
106
Jia D, Wang Y M, Ramesh K T, et al. Deformation behavior and plastic instabilities of ultrafine-grained titanium [J]. Appl. Phys. Lett., 2001, 79: 611
doi: 10.1063/1.1384000
107
Stolyarov V V, Valiev R Z, Zhu Y T. Enhanced low-temperature impact toughness of nanostructured Ti [J]. Appl. Phys. Lett., 2006, 88: 041905
108
Cheng S, Zhao Y H, Guo Y Z, et al. High plasticity and substantial deformation in nanocrystalline NiFe alloys under dynamic loading [J]. Adv. Mater., 2009, 21: 5001
doi: 10.1002/adma.200901991
pmid: 25378188
109
Zhao Y H, Guo Y Z, Wei Q, et al. Influence of specimen dimensions on the tensile behavior of ultrafine-grained Cu [J]. Scr. Mater., 2008, 59: 627
doi: 10.1016/j.scriptamat.2008.05.031
110
Zhao Y H, Guo Y Z, Wei Q, et al. Influence of specimen dimensions and strain measurement methods on tensile stress-strain curves [J]. Mater. Sci. Eng., 2009, A525: 68
111
Zhao Y H, Gu Y L, Guo Y Z. Plasticity and deformation mechanisms of ultrafine-grained Ti in necking region revealed by digital image correlation technique [J]. Nanomaterials, 2021, 11: 574
doi: 10.3390/nano11030574
112
Zhao Y H, Gu Y L. Deformation mechanisms and plasticity of ultrafine-grained Al under complex stress state revealed by digital image correlation technique [J]. Nanotechnol. Rev., 2021, 10: 73
doi: 10.1515/ntrev-2021-0007
