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MEAM Ph.D. Thesis Defense: “Room-temperature Electrochemical Healing of Structural Metals”
September 29, 2022 at 10:00 AM - 11:00 AM
For over 6,000 years, repairing high-strength metallic materials has required high temperatures and large energy inputs. Likewise, recent innovations in self-healing and repairable metals have remained limited by the need for heating, the small size of repairable cracks, and the low strength and constrained chemical composition of healed metals. While welding remains the most widely used approach to repair metals, the increasing ubiquity of digital manufacturing and “unweldable” alloys call for radically different approaches. This thesis pioneers a new approach for repairing structural metals at room-temperature, termed “electrochemical healing”. First, by mimicking the transport-mediated healing of bone, selective nickel electrodeposition enables rapid, effective, low-energy, and room-temperature healing of a cellular metal. A polymer coating restricts electrodeposition only at fracture or high stress sites, and a statistical method quantifies and predicts the probability of a target recovery of tensile strength based on energy input. This thesis extends room-temperature healing to low-carbon steel, a widely used structural metal, by elucidating how ion transport and electrolyte chemistry influence growth morphology and strength in fractured steel wires repaired with nickel electrodeposition. Pulsed electroplating and electrolyte chemistry selection improve nickel adhesion and enable fully fractured steel wires to recover up to 69% of their pristine strength. Finally, this thesis presents a framework for effective room temperature electrochemical healing based on a quantitative model that links geometric, mechanical, and electrochemical parameters to the recovery of tensile strength in repaired metals. This framework enables full recovery of tensile strength in a variety of structural metals, including “unweldable” alloys and a 3D-printed difficult-to-weld funicular shellular structure, as well as over 100% recovery of toughness in an aluminum alloy. The model reveals scaling relationships for the energetic, financial, and time costs of repairing metals that facilitate the practical adoption of electrochemical healing. Room-temperature electrochemical healing could open exciting possibilities for the scalable, autonomous, repeatable, and prophylactic repair of metals in structures and robots, enable cellular materials that respond to environmental stimulus with growth and morphogenesis, and advance the life cycle sustainability of structural metals.
Ph.D. Candidate, Department of Mechanical Engineering & Applied Mechanics, University of Pennsylvania
Advisor: James Pikul