Abstract:When metallic alloys are exposed to a corrosive environment, porous nanoscale morphologies spontaneously form that can adversely affect the mechanical integrity of engineered structures. This form of stress-corrosion cracking is responsible for the well-known 'season cracking' of brass and stainless steel components in nuclear power generating stations. One explanation for this is that a high-speed crack is nucleated within the porous layer, which subsequently injects into non-porous parent-phase material. We … Show more
“…The observation indicates that the surface plays a vital role in controlling the flow stress and, thereby, the strength in nanoscale plasticity. The recent reports from the groups of Jin on electrochemically controlled creep rate [20] and of K. Sieradzki on the impact of adsorbate coverage on fracture toughness [24] of NPG further emphasize this finding. Modulating the surface behavior electrochemically therefore provides new opportunities, as yet to be exploited in depth, for exploring the mechanisms that govern small-scale mechanical behavior.…”
Section: Role Of Surface Statementioning
confidence: 77%
“…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.…”
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.
“…The observation indicates that the surface plays a vital role in controlling the flow stress and, thereby, the strength in nanoscale plasticity. The recent reports from the groups of Jin on electrochemically controlled creep rate [20] and of K. Sieradzki on the impact of adsorbate coverage on fracture toughness [24] of NPG further emphasize this finding. Modulating the surface behavior electrochemically therefore provides new opportunities, as yet to be exploited in depth, for exploring the mechanisms that govern small-scale mechanical behavior.…”
Section: Role Of Surface Statementioning
confidence: 77%
“…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.…”
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.
“…Recent work has shown that nanoporous gold can support cracking at a velocity of 200 m/s, which is about 50% of the limiting crack velocity in this material (i.e., the Rayleigh wave velocity). 10 Our current understanding of ambienttemperature electrochemical dealloying of alloys such as Ag-Au, Cu-Au, and Ni-Pt is based on the notion that connected preexisting atomicscale paths of the more electrochemically reactive component (Ag in the case of Ag-Au alloys) must exist in the alloy for selective dissolution to occur to depths greater than a few tens of nanometers. [11][12][13] Today, this general mechanism of dealloying is referred to as percolation dissolution.…”
Section: Dealloying-from Corrosion Science To the Physics Of Dealloyimentioning
“…(3), (13-16), (23) and (25). results (Balk et al, 2009;Lührs et al, 2016;Sun et al, 2015) and A was determined as a function of φ and ν E by numerically solving Eqs.…”
a b s t r a c tIn this work the relationship between the structural disorder and the macroscopic mechanical behavior of nanoporous gold under uniaxial compression was investigated, using the finite element method. A recently proposed model based on a microstructure consisting of four-coordinated spherical nodes interconnected by cylindrical struts, whose node positions are randomly displaced from the lattice points of a diamond cubic lattice, was extended. This was done by including the increased density as result of the introduced structural disorder. Scaling equations for the elastic Poisson's ratio, the Young's modulus and the yield strength were determined as functions of the structural disorder and the solid fraction. The extended model was applied to identify the elastic-plastic behavior of the solid phase of nanoporous gold. It was found, that the elastic Poisson's ratio provides a robust basis for the calibration of the structural disorder. Based on this approach, a systematic study of the size effect on the yield strength was performed and the results were compared to experimental data provided in literature. An excellent agreement with recently published results for polymer infiltrated samples of nanoporous gold with varying ligament size was found.
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