Mechanical properties of bulk single crystalline nanoporous gold investigated by millimetre-scale tension and compression testing

Briot, N.; Kennerknecht, Tobias; Eberl, C.; Balk, T. John

doi:10.1080/14786435.2013.868944

Cited by 98 publications

(48 citation statements)

References 53 publications

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“…More importantly, however, tensile and bending tests on micron-or millimeter-sized NPG samples so far invariably revealed an overall brittle failure at the specimen level. 5,15,17 This was first apparent in the study on fracture behavior in three-point bending tests by Li et al, 1 and the brittleness in bending was later confirmed by Biener et al 17 Balk and coworkers 15,16 tested small volumes in tension, Figure 11 Flow stress, σ M , in the metal versus ligament size, L. Closed symbols, flow stress in the metal phase of the composite samples (for composite types indicated by labels), as obtained by evaluating data from Figure 5 with Equation (7). Open symbols, data from Jin, H.J.…”

Section: Discussionmentioning

confidence: 86%

“…Yet, whereas micro-scale and, more recently, macroscale nanoporous metal samples show excellent deformability in compression, 5,14 tension and bending studies so far have invariably indicated macroscopically brittle failure. 1,5,[15][16][17] This seems to prevent hopes of applying nanoporousmetal-based materials in technology. The brittle behavior has been linked to a tension-compression asymmetry of the mechanical behavior of porous bodies: while densification of the network implies strain hardening in compression, density loss in tension results in work softening.…”

Section: Introductionmentioning

confidence: 99%

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Nanoporous-gold-based composites: toward tensile ductility

et al. 2015

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We report on mechanical tests on interpenetrating-phase nanocomposite materials made by vacuum impregnation of nanoscale metal networks with a polymer. The metal component is nanoporous gold made by dealloying, whereas two epoxy resins and polyurethane are explored as the polymer component. The composites are strong and deformable in compression. Although previous observations invariably indicate tensile brittleness for nanoporous gold, composite samples made from cm-sized nanoporous samples enable macroscopic tensile and four-point bending tests that show ductility. This implies that the high strength of individual metal objects such as nanowires can now be incorporated into a strong and ductile material from which macroscopic things can be formed. In fact, a rule-of-mixture-type analysis of the stresses carried by the metal phase suggests quantitative agreement with data reported from separate experiments on small-scale gold nanostructures. NPG Asia Materials (2015) 7, e187; doi:10.1038/am.2015.58; published online 12 June 2015 INTRODUCTION Nanoporous metals made by dealloying 1-3 take the form of monolithic bodies consisting of an interconnected network of nanoscale 'ligaments' in a polycrystalline microstructure with typically 10 to 100 μm grain size. 4,5 The material is under study as a model material for clarifying the deformation mechanisms and mechanical properties of small-scale metal bodies such as nanowires or nanopillars. [5][6][7][8][9][10] In principle, nanoporous gold (NPG) offers the opportunity of incorporating the extremely high strength that has been reported for individual metal nanostructures, such as nanowires, 6,11-13 into a design strategy for a material that is amenable to the shaping of technologically relevant macroscopic bodies. Yet, whereas micro-scale and, more recently, macroscale nanoporous metal samples show excellent deformability in compression, 5,14 tension and bending studies so far have invariably indicated macroscopically brittle failure. 1,5,[15][16][17] This seems to prevent hopes of applying nanoporousmetal-based materials in technology. The brittle behavior has been linked to a tension-compression asymmetry of the mechanical behavior of porous bodies: while densification of the network implies strain hardening in compression, density loss in tension results in work softening. 18 This latter behavior implies a plastic instability with shear localization and brittle failure in tension. A materials design strategy that prevents the density change under load impregnates is impregnating the pore space with a ductile but lightweight phase, such as a polymer. Compression tests with mm-sized composite samples from NPG and bisphenol-F epoxy confirmed that the impregnation suppresses the density change along with the compressive strain hardening. 18 The compression tests also revealed that the large

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Section: Discussionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Nanoporous-gold-based composites: toward tensile ductility

et al. 2015

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“…Stress-strain behavior of NPG-empirical findings Several studies have investigated the dependency of the yield and flow behavior [2,7,11,13,16,21,23] as well as the stiffness [32,33] of NPG on L. Compression tests on highly deformable macroscopic samples are particularly meaningful, since they also afford an inspection of the variation of plastic and elastic properties as the microstructure changes during compression. Figure 3 illustrates this for a set of NPG samples with L = 20, 40, 150 nm.…”

Section: Microstructurementioning

confidence: 99%

“…Several of these studies even either report or even presuppose agreement, [2,5,7,12,13,16] while others discuss corrections. [22,23,36,37] Thus, even though it is now widely realized that the Gibson-Ashby scaling relations are not designed for network structures such as NPG, these relations remain indispensable as a starting point for discussing scaling in that material.…”

Section: Scaling Lawsmentioning

confidence: 99%

“…After initial studies of NPG used small-scale testing schemes, [2,[12][13][14][15][16][17][18] it is now possible to make cm-size samples that can be subjected conventional macroscopic compression [7,11,[19][20][21][22] or even tension [11,23,24] tests. The large strain that is reached in compression affords testing protocols comprising, for example, strainrate jumps [7] or load-unload segments.…”

Section: Introductionmentioning

confidence: 99%

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Nanoporous Gold—Testing Macro-scale Samples to Probe Small-scale Mechanical Behavior

Mameka¹,

Wang

Markmann

et al. 2015

Materials Research Letters

122

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Nanoporous gold made by dealloying exemplifies how the exciting mechanical properties of nanoscale objects can be exploited in designing materials from which macroscopic things can be formed. The homogeneous microstructure and the possibility of adjusting the ligament size, L, between few and few hundred nm, along with the high deformability and reproducible mechanical behavior predestine the material for model studies of small-scale plasticity using reliable macroscopic testing schemes on mm-or cm-size samples. Such experiments tend to agree with the Gibson-Ashby scaling relation for strength versus solid fraction, while suggesting an essentially L −1 scaling of the local strength of the ligaments. By contrast, the elastic compliance is dramatically enhanced compared to the Gibson-Ashby relation for the stiffness. Contrary to intuition, the anomalously compliant behavior of the nanomaterial goes along with a trend for more stiffness at smaller L. This article discusses surface excess elasticity, nonlinear elastic behavior and specifically shear instability of the bulk, network connectivity, and the surface chemistry as relevant issues which deserve further study.

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Size Effects in the Mechanical Properties of Bulk Bicontinuous Ta/Cu Nanocomposites Made by Liquid Metal Dealloying

et al. 2015

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Control of microstructural length scales is central to the design and fabrication of strong and tough metals. [1][2][3] Most strengthening strategies in metals, such as precipitation hardening, grain refinement, and work hardening, uniformly control the intrinsic microstructure and generally work to inhibit dislocation motion. These methods increase the stress required to move dislocations but they also tend to lower ductility. As the physical dimensions are reduced below that of a material's internal microstructural obstacles, a number of interesting size effects come into play. For example, the strength of metallic thin films scales with the inverse of the film thickness, [4] dislocation-free whiskers are many times stronger than conventional wires, [5] the hardness of metals increases with decreasing indentation size, [6] and the compressive strength of micropillars is much greater than that measured in the bulk. [7][8][9][10] There is general recognition that dislocation activity is different in reduced volumes where interactions with free surfaces can lead to dislocation starvation, source truncation, or pileup. [11][12][13][14] Although the exact origin of size-dependent strengthening is still debated and may vary from system to system, experimental observations of smaller-is-stronger show promising new metallic materials. It is compelling to consider how to translate these kinds of mechanical responses into bulk materials.One class of bulk-nanostructured materials that exhibit size effects on their mechanical properties are dealloyed metals, for which nanoporous gold (NPG) is a model system due to its ease of fabrication. [15][16][17][18][19] NPG is made via electrochemical dealloying, immersing a Ag-rich Ag-Au parent alloy in acid, selectively dissolving away the silver atoms while leaving the gold atoms behind to diffuse along the metal/electrolyte interface, self-organizing into a porous structure with welldefined length scales (e.g., average ligament or pore diameter). [20][21][22] Dealloyed metals are porous at scales smaller than the parent alloy grain size and the dealloyed phase is a complex, 3D network of interconnected beams without any crystal defects that did not exist prior to dealloying. Indentation and micropillar compression tests show that with smaller feature size, the strength of individual NPG ligaments approach the theoretical strength of gold, but testing of bulk samples generally results in brittle failure, a feature common to most nanoporous metals (NPMs). [23,24] Weissmuller recently showed that if the pores of nanoporous gold are impregnated with a polymer, then the mechanical properties of the composite are greatly improved compared to the porous component alone, having both good strength and high plastic strain in compression. [25] The challenge with electrochemically dealloyed materials is that they tend to be precious metals, whose low melting points make it difficult to make strong materials for structural applications. Kato introduced a possible solution by developing a new ...

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Mechanical properties of bulk single crystalline nanoporous gold investigated by millimetre-scale tension and compression testing

Cited by 98 publications

References 53 publications

Nanoporous-gold-based composites: toward tensile ductility

Nanoporous-gold-based composites: toward tensile ductility

Nanoporous Gold—Testing Macro-scale Samples to Probe Small-scale Mechanical Behavior

Size Effects in the Mechanical Properties of Bulk Bicontinuous Ta/Cu Nanocomposites Made by Liquid Metal Dealloying

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