Nanoporous (NP) metals are three-dimensional (3D) structures with characteristic length-scale of its constituents (ligaments, junctions, and pores) in the range from a few to hundreds of nanometers. Such materials are of great interest for many applications, including catalysis, biological material analogues, and the next generation interconnect materials in electronics packaging. Investigations targeting understanding of the mechanical properties of such materials have tried to separate effects of the geometrical arrangement of the 3D network from those due to the nanostructure (abundance of surfaces, presence of grains, and other defects). Traditionally, this has been achieved by assuming that the network is geometrically similar to that of a macroscopic, low-density metal foam.
The goal of this work is to attack the problem using a comprehensive approach that involves isolating the prominent geometry and size scale effects and examining their specific contributions individually for a range of relative densities. Specifically, 3D printed models printed and tested in compression at the macroscale replicate the geometrical arrangement of the nanoporous 3D network independently of any size effects. The relative modulus and relative compressive yield strength for the 3D printed structures with same arrangement as the nanoporous solid exhibit different scalings with density compared to stochastic macroscale foams. The deformation mechanism in stochastic macroscale foams is isolated in the ligaments and switches from bending to compression dominated behavior as the relative density increases. In contrast, due to the presence of enlarged junctions, the deformation mode for the 3D printed nanoporous structures remains bending dominated even at high relative densities. Nanoscale experiments and molecular dynamics (MD) simulations provide a glimpse into the relative modulus and strength scalings and reveal a more nuanced dependence, with unexpected enhancement in both the relative modulus and relative strength.
Obtaining a clear understanding of the contribution of geometrical structure on the properties of nanoporous metals will significantly advance our understanding of how to tailor NP metal microstructure such as grains, interfaces, and surfaces to enhance the physical properties of the material. Thus, the findings reported here could inform future studies to maximize the versatility and potential of nanoporous metal structures.Ph.D
