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August 30, 2019 01:00 pm

Engineers Develop Bone-Like Metal Foam That Can Be 'Healed' At Room Temperature

An anonymous reader quotes a report from Phys.Org: Now, for the first time, Penn Engineers have developed a way to repair metal at room temperature. They call their technique "healing" because of its similarity to the way bones heal, recruiting raw material and energy from an external source. The study was conducted by James Pikul, assistant professor in the Department of Mechanical Engineering and Applied Mechanics and Zakaria Hsain, a graduate student in his lab. Beyond the energy costs associated with the current process of repairing metal by melting it to a more pliable form, there are some metal components where such a repair strategy is not even an option. For example, melting removes the intricate internal structure of metallic foams, which are metals made with internal pockets of air. This arrangement of struts and gaps reduces the material's weight while maintaining its overall strength. To heal metal foams, which generally have better structural properties than polymers, Pikul and Hsain started by finding a way for them to "sense" where they had been damaged. Rather than encapsulating additional chemicals used in repair, the researchers realized that they could use the breaking of a polymer layer as a kind of chemical signal. Pikul and Hsain used chemical vapor deposition to evenly coat each strut of the nickel foam with a layer of Parylene D, a chemically inert and stretchy polymer. Because this material's damage tolerance is slightly lower than that of nickel, it breaks first as the sample is damaged, revealing the metal underneath. The researchers could then use electroplating to build new nickel struts only on the exposed nickel where they were needed. "Pikul and Hsain healed three types of damage in their experiments on centimeter-scale samples of their polymer-coated nickel foam: samples with cracks, samples that had been pulled apart until they were connected by just a few struts, and samples that had been cleaved in two," the report adds. "Healing the damage took about four hours, and because electroplating acts on all of the exposed nickel at once, the time it takes to heal damage is independent of the sample's size." The study was published in the journal Advanced Functional Materials.

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