Collaborative Research: Strengthening Metallic Nanofoams Through Ligament Scale Materials Design

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Nanoscale metal foams exhibit several remarkable properties. The most common nanostructured foams are currently made of pure metals, and they demonstrate exceptional performance in areas such as catalysis, batteries, and optics. These metal foams are, however, often fragile and difficult to integrate into engineering applications. The ability to mechanically strengthen foams to create robust materials has heretofore been limited in pure metals. This award supports research aimed at creating a new class of materials - composite nano foams - which display the same remarkable properties as pure metal foams, but with significantly enhanced structural integrity. The new materials designed through this work will allow researchers and engineers to exploit unique properties without suffering failure during mechanical handling or service. The fundamental knowledge gained from this research may be used in designing and manufacturing catalysts with low cost and high strength, fuel cells with higher capacity and faster charging times, biomedical implants with high fatigue resistance, and lighter and stronger hydrogen storage units. A team of researchers at two universities, Clarkson and Purdue, will carry out this work, exposing students at both schools to the increasingly common long-distance collaborations needed for advancing research. The research team will couple computational methods of materials engineering at the atomistic and mesoscopic scales (molecular dynamics and finite element analysis) to experimental methods of manufacturing and characterizing composite nanostructured foams. The working hypothesis is that coating individual foam ligaments with nanostructure multilayers will result in the formation of stronger foams. To create these materials, copper and nickel will be electroplated to form core-shell layers on templates of paper-like mats of eletrospun polymers, which will be oxidized and then subsequently reduced to form nanoscale copper metal wires. Pulsed-laser thermoelastic excitation will be used to determine the dispersion and vibrational resonance to obtain the foam's bulk elastic properties. These results will be compared directly to finite element simulations of the composite to isolate the effects of geometry and ligament properties. Foam strength will be predicted based on molecular dynamics simulations of the ligaments, which will provide information to feed into the finite element models, and finally compared to experimental studies of the yield strength using nanoindentation with a flat punch geometry. The intellectual significance of this work will be the development of a new class of materials guided by computational materials engineering, and the development of novel techniques for manufacturing and testing nanoscale metallic foams.