1, Brookhaven National Laboratory, Upton, New York, United States
2, Tohoku University, Sendai, , Japan
3, Argonne National Laboratory, Argonne, Illinois, United States
4, Zeiss Group, Pleasanton, California, United States
Nanoporous materials —also known as nanofoams— fabricated by dealloying methods exhibit unique properties and a bi-continuous network, leading to various applications as functional materials. A dealloying method utilizing a metal as a dealloying agent instead of an aqueous solution has led to an alternative route for fabricating nanoporous metals, for example, iron-based and titanium-based alloys. This opens new opportunities for material design, while preserving the unique bi-continuous morphology. It is, however, critical to establish the correlation between the processes, morphology (2D & 3D) and chemical heterogeneity of these new nanoporous metallic materials for suitable applications.
We utilized full-field nano-tomography via transmission X-ray microscopy to study the evolution of the morphology of nano-/meso-porous iron-based alloys by liquid metal dealloying. The 3D morphology of the materials was quantified as a function of processing conditions, including precursor compositions, dealloying temperature and time. A systematic trend of spontaneous coarsening as a result of prolonged dealloying time and increased temperature was observed; the precursor compositions significantly impact not just the porosity of the nanoporous materials, but also the surface shape of the nanofoams. A gradient of the ligament size and compositional change along the dealloying direction were also observed. In addition, spectroscopic imaging at synchrotron sources is a powerful technique for spatially resolving chemical and elemental distributions in these materials. X-ray fluorescence microscopy provides additional elemental and chemical information of the nano-porous materials. We also drew comparison between the structures fabricated by the liquid metal dealloying with the aqueous solution dealloying to shed light on the dealloying mechanism for future material design.