Size Effects on the Mechanical Behavior of Nanoporous Au

Abstract

Recent nanomechanical tests on submicron metal columns and wires have revealed a dramatic increase in yield strength with decreasing sample size. Here, we demonstrate that nanoporous metal foams can be envisioned as a three-dimensional network of ultrahigh-strength nanowires, thus bringing together two seemingly conflicting properties: high strength and high porosity. Specifically, we characterized the size-dependent mechanical properties of nanoporous gold using a combination of nanoindentation, column microcompression, and molecular dynamics simulations. We find that nanoporous gold can be as strong as bulk Au, despite being a highly porous material, and that the ligaments in nanoporous gold approach the theoretical yield strength of Au.

Deformation Behavior of Nanoporous Metals

“…Furthermore, nanoindentation can be easily applied to thin-films and irregularly shaped samples as long as the surface roughness is low. Other, experimentally more complex methods are pillar micro-compression tests [36,37] and film or beam bending tests. [16,35,38,39] Examples of nanoindentation and beam deflection tests are shown in Figure 5.…”

“…In this context, np Au can be envisioned as a three-dimensional network of defect-free, ultra-high strength Au nanowires. [37] Length-scale effects in plasticity can also be studied theoretically using molecular dynamics (MD) simulations. [48,49] Preliminary molecular dynamics (MD) results show indeed that it is difficult to incorporate stable dislocation sources (such as a Frank-Read source) in nm-sized ligaments.…”

Refinement of Nanoporous Copper: A Summary of Micro-Alloying of Au-Group and Pt-Group Elements

“…For instance, the yield strength of nanometer-sized ligaments of nanoporous gold increased from ³880 MPa to 4.6 GPa with the decrease in the pore size from 50 to 10 nm. 8) On the other hand, it has been shown that the microstructure of the starting materials plays a critical role in the formation of the final nanoporous structures. 1,2,913) The characteristics of the casting structures, the intermetallics, and the phase segregations typical of the crystalline alloys, such as AlCu, 1,2,10) NiCuMn, 9) NiMn, 11) TiCu 12,13) alloys are reflected in the final porous structures.…”

Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression

“…Recent experiments have shown that the fitted exponent coefficients are 2 and 1.5 for modulus and yield strength, respectively, for low density open-cell foam materials, 6,8,12,15 which is similar from the Gibson-Ashby's scaling law. However, when the relative density is high, they have the following relations based on GibsonAshby's scaling law:…”

“…[4][5][6] Extensive experimental, theoretical and MD efforts have been devoted to investigate the mechanical properties of nanoporous metals under moderate conditions. [6][7][8][9][10][11][12][13][14][15][16][17][18] These studies have shown that the mechanical properties of nanoporous metals, such as the effective elastic modulus and the yield strength, are closely related to the relative density and the ligament size. A number of models 15,18,19 have been proposed to capture the scaling laws and the deformation mechanisms at the nanoscale due to the large surface-to-volume ratio for nanoporous metals, while the Gibson-Ashby model 7 has been widely used for porous metals with microstructural sizes on the order of micrometers and above.…”