Mechanical response of nanoporous metals: A story of size, surface stress, and severed struts

Nanoporous metals made by dealloying are macroscopic network architectures that can contain approximate to 10(15) nanoscale struts or ligaments per sample. Their mechanical performance is critical to their applications as functional or lightweight high-strength materials. Testing nanoporous metals at the macroscopic scale offers opportunities for unraveling the properties of nanoscale solids in general. The central questions in this area include whether the macroscopic strength and elastic modulus of nanoporous metals can be correlated with the properties of nanoscale ligaments by the classical Gibson-Ashby equations, whether the dealloying-made network structure differs from the conventional foam metals, how network connectivity influences mechanical response, and how ligament size and surface properties affect the elastic and plastic response of nanoscale solids and that of nanoporous metals, particularly the tension-compression asymmetry in strength. This article reviews the fundamental observations of the mechanical response of nanoporous metals with a focus on gold and the emerging understanding of the aforementioned issues.