Interpreting the ductility of nanocrystalline metals<sup>1</sup>

Sharon, John Anthony; Padilla, Henry A.; Boyce, Brad Lee

doi:10.1557/jmr.2013.139

Cited by 48 publications

(26 citation statements)

References 88 publications

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“…Fig. 6d provides a recent compilation by Sharon et al [167] of elongation at fracture versus microstructure length scale showing the same expected trend for a range of metals. It is essential to realize that the use of the elongation to failure e engf as a ductility index mixes both the resistance to necking, e u , and the resistance to damage accumulation, which is better quantified by the true fracture strain e f ; see Section 1.…”

Section: Fracture Of Bulk Ufg and Nanostructured Metalssupporting

confidence: 76%

“…The voids grow until final impingement with the plastic flow localized in the intervoid ligament, reminiscent of the void coalescence process observed in CG metals, but here at the scale of a single crystalline ligament. The true fracture strain resulting from this mechanism can be quite large as recently shown by Sharon et al [167] for thick electrodeposited NiFe alloy layers exhibiting 75% area reduction at fracture and clear dimples. These films can be considered as being bulk NC systems as the grain size was around 30 nm involving thus hundreds of grains over the thickness.…”

Section: Single Phasementioning

confidence: 79%

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Failure of metals III: Fracture and fatigue of nanostructured metallic materials

2016

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a b s t r a c tPushing the internal or external dimensions of metallic alloys down to the nanometer scale gives rise to strong materials, though most often at the expense of a low ductility and a low resistance to cracking, with negative impact on the transfer to engineering applications. These characteristics are observed, with some exceptions, in bulk ultra-fine grained and nanocrystalline metals, nano-twinned metals, thin metallic coatings on substrates and freestanding thin metallic films and nanowires. This overview encompasses all these systems to reveal commonalities in the origins of the lack of ductility and fracture resistance, in factors governing fatigue resistance, and in ways to improve properties. After surveying the various processing methods and key deformation mechanisms, we systematically address the current state of the art in terms of plastic localization, damage, static and fatigue cracking, for three classes of systems: (1) bulk ultra-fine grained and nanocrystalline metals, (2) thin metallic films on substrates, and (3) 1D and 2D freestanding micro and nanoscale systems. In doing so, we aim to favour cross-fertilization between progress made in the fields of mechanics of thin films, nanomechanics, fundamental researches in bulk nanocrystalline metals and metallurgy to impart enhanced resistance to fracture and fatigue in high-strength nanostructured systems. This involves exploiting intrinsic mechanisms, e.g. to enhance hardening and rate-sensitivity so as to delay necking, or improve grain-boundary cohesion to resist intergranular cracks or voids. Extrinsic methods can also be utilized such as by hybridizing the metal with another material to delocalize the deformation -as practiced in stretchable electronics. Fatigue crack initiation is in principle improved by a fine structure, but at the expense of larger fatigue crack growth rates. Extrinsic toughening through hybridization allows arresting or bridging cracks. The content and discussions are based on experimental, theoretical and simulation results from the recent literature, and focus is laid on linking microstructure and physical mechanisms to the overall mechanical behavior.

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Section: Fracture Of Bulk Ufg and Nanostructured Metalssupporting

confidence: 76%

Section: Single Phasementioning

confidence: 79%

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

2016

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“…Unfortunately, this information is not generally available and therefore it is necessary to use an alternative approach. It is also worth noting that, although not directly relevant to the present research, a comparison of different specimen dimensions was also developed recently for tensile specimens prepared from thin films [38]. Table 2 shows that as-annealed vanadium, when cut to the dimensions of the HPT tensile samples but not processed by HPT, has a UTS of ~260 MPa and an elongation to failure of ~79%.…”

Section: A Comparison Of Properties After Hpt Ecap and Ecap With Crymentioning

confidence: 90%

Achieving superior grain refinement and mechanical properties in vanadium through high-pressure torsion and subsequent short-term annealing

Huang¹,

Lemang²,

Zhang³

et al. 2016

Materials Science and Engineering: A

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Commercial purity vanadium with an initial grain size of ~27 m and a Vickers microhardness of Hv  85 was processed by high-pressure torsion (HPT) under a pressure of 6.0 GPa at room temperature through 1/2 to 10 turns. After processing through 10 turns, some samples were immediately subjected to a short-term annealing (15 min) at different temperatures from 773 to 1173 K. The microstructures developed in HPT and in HPT plus post-HPT annealing were characterized by electron backscatter diffraction (EBSD).Processing by HPT for 10 turns gave a refined grain size of ~410 nm and an increased hardness of Hv  240. Post-HPT annealing demonstrated that the ultrafine grained vanadium has good thermal stability up to at least 873 K. Tensile testing at room temperature gave an ultimate tensile strength of ~920 MPa after 10 turns of HPT with an elongation of ~29%.These results show HPT processing produces superior mechanical properties in vanadium by comparison with processing by ECAP or ECAP plus cryorolling.

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“…This fracture angle value is similar to the observation in Refs. [25,26], which is a typical fracture angle value for the nanostructured foils such as Al, Cu and Ni-Fe after tensile test. The annealed aluminium sample shows a high ductility, and there are large and deep dimples on the fracture surface, as shown in Fig.…”

Section: Figures 4a To 4ementioning

confidence: 99%

“…[25] From volume conservation, the final cross-sectional area (A final ) can be converted into a true fracture strain, as shown in Eq. (1) [25] ,…”

Section: Figures 4a To 4ementioning

confidence: 99%

High Strength and Ductility of Ultrathin Laminate Foils Using Accumulative Roll Bonding and Asymmetric Rolling

Tieu

Hadi

et al. 2014

Metall Mater Trans A

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As product miniaturization is becoming widely popular, many microparts are being produced by microforming of sheets/foils, whose strength needs to be able to maintain structural stability of the microcomponents. In addition, their strength and ductility of foils generally reduce with a reduction in the thickness due to the size effect. In this paper, we report the fabrication of an aluminum laminate foil using a combined process of accumulative roll bonding (ARB) and asymmetric rolling (AR). It was found that this improves both strength and ductility. TEM results show that the laminate structures produced by ARB develop an inhomogeneous microstructure with nanoscale grains and abnormal coarsening in some grains during AR processing. Both these effects result in an improved ductility and strength. Using these rolled products, micro-cups of very small wall thickness/cup diameter ratio (1/200) have been successfully fabricated by micro-deep drawing without the need for annealing. KeywordsAluminum alloy; Nanostructure; Abnormal grain growth; Rolling; Deep drawing; Ultrathin laminate foil Disciplines Engineering | Science and Technology Studies Publication DetailsYu, H., Tieu, A. Kiet., Hadi, S., Lu, C., Godbole, A. & Kong, C. (2015). High strength and ductility of ultrathin laminate foils using accumulative roll bonding and asymmetric rolling. Metallurgical Abstract: As product miniaturization is becoming widely popular, many microparts are being produced by microforming of sheets/foils, whose strength needs to be able to maintain structural stability of the micro components. In addition, their strength and ductility of foils generally reduces with a reduction in the thickness due to the size effect. In this paper, we report the fabrication of an aluminum laminate foil using a combined process of Accumulative Roll Bonding (ARB) and Asymmetric Rolling (AR). It was found that this improves both strength and ductility. TEM results show that the laminate structures produced by ARB develop an inhomogeneous microstructure with nanoscale grains and abnormal coarsening in some grains during AR processing. Both these effects result in an improved ductility and strength. Using these rolled products, micro-cups of very small wall thickness/cup diameter ratio (1/200) have been successfully fabricated by micro deep drawing without the need for annealing.

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Interpreting the ductility of nanocrystalline metals¹

Abstract: Abstract

Cited by 48 publications

References 88 publications

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Achieving superior grain refinement and mechanical properties in vanadium through high-pressure torsion and subsequent short-term annealing

High Strength and Ductility of Ultrathin Laminate Foils Using Accumulative Roll Bonding and Asymmetric Rolling

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Interpreting the ductility of nanocrystalline metals1

Abstract: Abstract

Cited by 48 publications

References 88 publications

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

Achieving superior grain refinement and mechanical properties in vanadium through high-pressure torsion and subsequent short-term annealing

High Strength and Ductility of Ultrathin Laminate Foils Using Accumulative Roll Bonding and Asymmetric Rolling

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Interpreting the ductility of nanocrystalline metals¹