Ductility of Nanocrystalline Metals: Intrinsic or Extrinsic


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While the super-high strength of various nanocrystalline metals (NC metals, grain size d<100 nm) has drawn great attention in the past few decades, the poor ductility has become a seemingly insurmountable obstacle for the wide application of such metals. Other limiting factors include, in particular, the high cost associated with delivering such materials. Recent efforts from various groups have brought forth strong hope that the ductility of NC metals can be greatly improved by the application of “microstructure engineering”. However, the testing methods used to evaluate the mechanical properties, especially at small scales, have invited concerns. A natural question arises as to whether the reported allegedly good ductility of many NC metals is intrinsic or extrinsic. This article attempts to critically evaluate such issues. We will examine the experimental results in conjunction with some finite element modeling on the stress state and strain measurement of specimens during mechanical testing. Factors such as sample geometry and loading mode will be critically assessed. We point out that while intrinsic ductility may be possessed by some NC metals, careful attention should be paid to how strain measurement is made.



Materials Science Forum (Volumes 633-634)

Edited by:

Yonghao Zhao and Xiaozhou Liao




Y.Z. Guo et al., "Ductility of Nanocrystalline Metals: Intrinsic or Extrinsic", Materials Science Forum, Vols. 633-634, pp. 151-164, 2010

Online since:

November 2009




[1] Hall EO. The deformation and ageing of mild steel: III. Discussion of results. Proceedings of the Physical Society B, London 1951; 64: 747.

[2] Petch NJ. The cleavage strength of polycrystals. Journal of Iron and Steel Institute 1953; 174: 25.

[3] Courtney TH. Mechanical Behavior of Materials: Waveland Press, Inc., (2000).

[4] Meyers MA, Mishra A, Benson DJ. Mechanical properties of nanocrystalline materials. Progress in Materials Science 2006; 51: 427.

DOI: https://doi.org/10.1016/j.pmatsci.2005.08.003

[5] Ma E. Instabilities and ductility of nanocrystalline and ultrafine-grained metals. Scripta Materialia 2003; 49: 663.

DOI: https://doi.org/10.1016/s1359-6462(03)00396-8

[6] Ma E. Controlling plastic instability. Nature Materials 2003; 2: 7.

[7] Ma E. Eight routes to improve the tensile ductility of bulk nanostructured metals and alloys. JOM 2006: 49.

DOI: https://doi.org/10.1007/s11837-006-0215-5

[8] Zhao YH, Liao XZ, Cheng S, Ma E, Zhu YT. Simultaneous increasing the ductility and strength of nanostructured alloys. Advanced Materials 2006; 18: 2280.

DOI: https://doi.org/10.1002/adma.200600310

[9] Kecskes LJ, Cho KC, Dowding RJ, Schuster BE, Valiev RZ, Wei Q. Grain size engineering of bcc refractory metals: top-down and bottom-up-application to tungsten. Materials Science and Engineering A 2007; 467: 33.

DOI: https://doi.org/10.1016/j.msea.2007.02.099

[10] Wang YM, Chen MW, Zhou FH, Ma E. High tensile ductility in a nanostructured metal. Nature 2002; 419: 912.

DOI: https://doi.org/10.1038/nature01133

[11] Wang YM, Ma E. Three strategies to achieve uniform tensile deformation in a nanostructured metal. Acta Materialia 2004; 52: 1699.

DOI: https://doi.org/10.1016/j.actamat.2003.12.022

[12] Ye RQ, Han BQ, Lavernia EJ. Simulation of deformation and failure process in bimodal Al alloys. Metallurgical and Materials Transactions A 2005; 36: 1833.

DOI: https://doi.org/10.1007/s11661-005-0047-x

[13] Lee ZH, Witkin D, Lavernia EJ, Nutt SR. Bimodal structureed bulk nanocrystalline Al7. 5Mg alloy. In: Ovid'ko IA, al. e, editors. Mater Res Soc Symp, vol. 791. Boston, MA: MRS, 2004. p. Q1. 6. 1.

DOI: https://doi.org/10.1557/proc-791-q1.6

[14] Zhang H, Ye J, Joshi SP, Schoenung JM, Chin ESC, Ramesh KT. Rate-dependent behavior of hierarchical Al matrix composites. Scripta Materialia 2008; 59: 1139.

DOI: https://doi.org/10.1016/j.scriptamat.2008.07.036

[15] Valiev RZ, Alexandrov IV, Zhu YT, Lowe TC. Paradox of strength and ductility in metals processed by severe plastic deformation. Journal of Materials research 2002; 17: 5.

[16] Wei Q, Zhang H, Schuster BE, Ramesh KT, Valiev RZ, Kecskes LJ, Dowding RJ. Microstructure and mechanical properties of super-strong nanocrystalline tungsten processed by high-pressure torsion. Acta Materialia 2006; 54: 4079.

DOI: https://doi.org/10.1016/j.actamat.2006.05.005

[17] Lu L, Chen X, Huang X, Lu K. Revealing the Maximum Strength in Nanotwinned Copper. Science 2009; 323: 607.

DOI: https://doi.org/10.1126/science.1167641

[18] Lu L, Schwaiger R, Shan ZW, Dao M, Lu K, Suresh S. Nano-sized twins induce high rate sensitivity of flow stress in pure copper. Acta Materialia 2005; 53: 2169.

DOI: https://doi.org/10.1016/j.actamat.2005.01.031

[19] Lu L, Shen YF, Chen XH, Qian LH, Lu K. Ultrahigh strength and high electrical conductivity in copper. Science 2004; 304: 422.

[20] Ma E, Wang YM, Lu QH, Sui ML, Lu L, Lu K. Strain hardening and large tensile elongation in ultrahigh-strength nano-twinned copper. Applied physics letters 2004; 85: 4932.

DOI: https://doi.org/10.1063/1.1814431

[21] Zhao YH, Guo YZ, Wei Q, Dangelewicz AM, Xu C, Zhu YT, Langdon TG, Zhou YZ, Lavernia EJ. Influence of specimen dimensions on the tensile behavior of ultrafine-grained Cu. Scripta Materialia 2008; 59: 627.

DOI: https://doi.org/10.1016/j.scriptamat.2008.05.031

[22] Koch CC. Nanostructured materials: processing, properties and potential applications. Norwich: Noyes Publications, (2002).

[23] Koch CC, Ovid'ko IA, Seal S, Veprek S. Structural Nanocrystalline Materials-fundamentals and applications. Cambridge: Cambridge University Press, (2007).

[24] Zhilyaev AP, Langdon TG. Using high-pressure torsion for metal processing: fundamentals and applications. Progress in Materials Science 2008; 53: 893.

DOI: https://doi.org/10.1016/j.pmatsci.2008.03.002

[25] Valiev RZ, Islamgaliev RK, Alexandrov IV. Bulk nanostructured materials from severe plastic deformation. Progress in Materials Science 2000; 45: 103.

DOI: https://doi.org/10.1016/s0079-6425(99)00007-9

[26] Valiev RZ, Langdon TG. Principles of equal-channel angular pressing as a processing tool for grain refinement. Progress in Materials Science 2006; 51: 881.

DOI: https://doi.org/10.1016/j.pmatsci.2006.02.003

[27] Gleiter H. Nanostructured Materials. Progress in Materials Science 1989; 33: 223.

[28] Youssef KM, Scattergood RO, Murty KL, Horton JA, Koch CC. Ultrahigh strength and high ductility of bulk nanocrystalline copper. Applied physics letters 2005; 87: 091904.

DOI: https://doi.org/10.1063/1.2034122

[29] Youssef KM, Scattergood RO, Murty KL, Koch CC. Ultratough nanocrystalline copper with a narrow grain size distribution. Applied physics letters 2004; 85: 929.

DOI: https://doi.org/10.1063/1.1779342

[30] Keeler SP, Backofen WA. Plastic Instability and Fracture in Sheets Stretched over Rigid Punches. Trans ASM 1963; 56: 25.

[31] Cheng S, Ma E, Wang YM, Kecskes LJ, Youssef KM, Koch CC, Trociewitz UP, Han K. Tensile properties of in situ consolidated nanocrystalline Cu. Acta Materialia 2005; 53: 1521.

DOI: https://doi.org/10.1016/j.actamat.2004.12.005

[32] Ghosh AK, Backofen WA. Strain hardening and instability in biaxially stretched sheets. Metallurgical Transactions 1973; 4: 1113.

DOI: https://doi.org/10.1007/bf02645615

[33] Dieter GE. Mechanical Metallurgy. New York: McGraw-Hill, (1986).

[34] Li H, Ebrahimi F. Ductile to brittle transition in nanocrystalline metals. Advanced Materials 2005; 17: (1969).

[35] Li H, Ebrahimi F. Tensile behavior of a nanocrystalline Ni-Fe alloys. Acta Materialia 2006; 54: 2877.

DOI: https://doi.org/10.1016/j.actamat.2006.02.033

[36] Li HQ, Ebrahimi F. Transition of deformation and fracture behavior in nanostructured facecentered cubic metals. Applied physics letters 2004; 84: 4307.

[37] Li HQ, Ebrahimi F, Choo H, Liaw PK. Grain size dependence of tensile behavior in nanocrystalline Ni-Fe alloys. Journal of Materials Science 2006; 41: 7636.

DOI: https://doi.org/10.1007/s10853-006-0856-3

[38] Ghosh AK. Strain localization in the diffuse neck in sheet metal. Metallurgical Transactions 1974; 5: 1607.

[39] Hart EW. Theory of the tensile test. Acta Metallurgica 1967; 15: 351.

[40] Wei Q. Strain rate effects in the ultrafine grain and nanocrystalline regimes-its influence on some constitutive behavior. Journal of materials science 2007; 42: 1709.

DOI: https://doi.org/10.1007/s10853-006-0700-9

[41] Wei Q, Cheng S, Ramesh KT, Ma E. Effect of nanocrystalline and ultrafine grain sizes on the strain rate sensitivity and activation volume: fcc versus bcc metals. Materials science and engineering A 2004; 381: 71.

DOI: https://doi.org/10.1016/j.msea.2004.03.064

[42] Asaro RJ, Suresh S. Mechanistic models for the activation volumes and rate sensitivity in metals with nanocrystalline grains and nano-scale twins. Acta Materialia 2005; 53: 3369.

DOI: https://doi.org/10.1016/j.actamat.2005.03.047

[43] Lin IH, Hirth JP, Hart EW. Plastic instability in uniaxial tension tests. Acta Metallurgica 1981; 29: 819.

DOI: https://doi.org/10.1016/0001-6160(81)90124-3

[44] Lu L, Li SX, Lu K. An abnormal strain rate effect on tensile behavior in nanocrystalline copper. Scripta Materialia 2001; 45: 1163.

DOI: https://doi.org/10.1016/s1359-6462(01)01138-1

[45] Cheng S, Zhao YH, Zhu YT, Ma E. Optimizing the strength and ductility of fine structured 2024 Al alloy by nano-precipitation. Acta Materialia 2007; 55: 5822.

DOI: https://doi.org/10.1016/j.actamat.2007.06.043

[46] Malow TR, Koch CC, Miraglia PQ, Murty KL. Compressive mechanical behavior of nanocrystalline Fe investigated with an automated ball indentation technique. Materials Science and Engineering A 1998; 252: 36.

DOI: https://doi.org/10.1016/s0921-5093(98)00661-3

[47] Carsley JE, Milligan WW, Hackney SA, Aifantis EC. Glasslike behavior in a nanostructured Fe/Cu alloy. Metallurgical and Materials Transactions A 1995; 26: 2479.

DOI: https://doi.org/10.1007/bf02671262

[48] Wei Q, Jia D, Ramesh KT, Ma E. Evolution and microstructure of shear bands in nanostructured Fe. Applied physics letters 2002; 81: 1240.

DOI: https://doi.org/10.1063/1.1501158

[49] Jia D, Ramesh KT, Ma E. Effects of nanocrystalline and ultrafine grain sizes on constitutive behavior and shear bands in iron. Acta materialia 2003; 51: 3495.

DOI: https://doi.org/10.1016/s1359-6454(03)00169-1

[50] Wei Q, Jiao T, Ramesh KT, Ma E, Kecskes LJ, Magness L, Dowding RJ, Kazykhanov VU, Valiev RZ. Mechanical behavior and dynamic failure of high-strength ultrafine grained tungsten under uniaxial compression. Acta Materialia 2006; 54: 77.

DOI: https://doi.org/10.1016/j.actamat.2005.08.031

[51] Wei Q, Schuster BE, Mathaudhu SN, Hartwig KT, Kecskes LJ, Dowding RJ, Ramesh KT. Dynamic behavior of body-centered cubic metals with ultrafine grained and nanocrystalline microstructures. Materials Science and Engineering A 2008; 493: 58.

DOI: https://doi.org/10.1016/j.msea.2007.05.126

[52] Wei Q, Jiao T, Ramesh KT, Ma E. Nano-structured vanadium: processing and mechanical properties under quasi-static and dynamic compression. Scripta materialia 2004; 50: 359.

DOI: https://doi.org/10.1016/j.scriptamat.2003.10.010

[53] Cheng S, Milligan WW, Wang XL, Choo H, Liaw PK. Compressive and tensile deformation behavior of consolidated Fe. Materials Science and Engineering A 2008; 493: 226.

DOI: https://doi.org/10.1016/j.msea.2007.08.088

[54] Jia D, Wang YM, Ramesh KT, Ma E, Zhu YT, Valiev RZ. Deformation behavior and plastic instabilities of ultrafine-grained titanium. Applied physics letters 2001; 79: 611.

DOI: https://doi.org/10.1063/1.1384000

[55] Wang YM, Ma E. On the origin of ultrahigh cryogenic strength of nanocrystalline metals. Applied physics letters 2004; 85: 2750.

[56] Sharpe WN, Yuan B, Edwards RL. A new technique for measuring the mechanical properties of thin films. Journal of Microelectromechanical Systems 1997; 6: 193.

[57] Hemker KJ, Sharpe WN. Microscale characterization of mechanical properties. Annual Review of Materials Research 2007; 37: 93.

[58] Vendroux G, Knauss WG. Submicron Deformation Field Measurements: Part 2. Improved Digital Image Correlation. Experimental Mechanics 1998; 38: 86.

DOI: https://doi.org/10.1007/bf02321649