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Chang-Eun Kim1 Raheleh Rahimi1 Ioannis Mastorakos2 David Bahr1

1, Purdue University, West Lafayette, Indiana, United States
2, Clarkson University, Potsdam, New York, United States

Metallic foam structures can be fabricated using a wide range of techniques; at the nanoscale de-alloying forms nm-sized ligament/pore foams in noble metals, while gas foaming at the meso-scale enables bulk material formation in engineering alloys. Capturing both length scales, nm-level porosity to sub-mm porosity, is challenging, and compositions accessible via these particular techniques are often mutually exclusive. This presentation addresses a new model of metal foam creating, using electrospun polymer fibers containing soluble metal acetate. Using a combination of oxidation and thermal reduction on electrospun fibers allows for multiple length scales of structural feature control, with meso-scale pores dominated by the fiber diameter and spacing, and ligament scale porosity and roughness dominated by thermal processing and diffusive processes. We demonstrate the fabrication of Cu-Ni alloys as a model solid solution structure, and create and characterize the architecture and microstructure of these materials between pure Cu and 50/50 Cu-Ni; any composition in this range is accessible using simple wet chemistry of the polymeric precursor used for electrospinning. The pyrolyzation of the polymer controls the larger length scale, and the initial oxidation step creates a mixed oxide structure for the alloy systems. Subsequent reduction causes homogenization of the resulting ligaments. The alloy foams, with porous ligaments with dimensions on the order of 200 nm, and pores on the order of 50 nm, exhibit a strength four times that of the pure copper films with 400 nm ligament dimensions. The increase in strength is attributed to both solid solution strengthening and also fractionally impacted by the length scale of the ligaments.

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