Enabling effective electrochemical healing of structural steel

Abstract

Low-carbon steel is a widely used structural metal that, when fractured, can be repaired with high temperature processes. There are many applications, however, that would benefit from a room-temperature repair process which maintains the steel microstructure and prevents nearby materials and electronics from overheating. This work seeks to enable effective room-temperature healing of steel by understanding how ion transport and electrolyte chemistry influence growth morphology and strength in fractured steel struts repaired with nickel electrodeposition. Experiments and simulations show that pulsed electroplating mitigates diffusion-limited growth to enable smooth and dense nickel deposits that have 4× higher adhesion to steel than nickel deposited by potentiostatic electroplating. By combining pulsed electroplating and electrolyte chemistry selection, fully fractured steel wires could be repaired to achieve up to 69% of their pristine wire strength. Finally, a simple geometric model highlights the advantageous energy and time requirements of electrochemical healing across length scales.

Electrochemical Healing of Fractured Metals

“…We describe this process as electrochemical healing because of its similarity to bone healing, where healing matter is transported to the fracture site through an immersed electrolyte and strength is restored through the growth and connection of matter from opposite fracture surfaces. [40] As an improvement over earlier approaches in which metal was only plated at the cross-section of a fractured strut, [40,41] we exposed the non-fractured surface of the metal to plating (Figure 2a). A pair of Ni 200 (>99% nickel alloy) half-dogbone samples prepared by waterjet cutting simulated a fractured dogbone sample (Figures 2a and Figure S2A, Supporting Information).…”

“…By enabling fast room-temperature diffusion of metal ions in an aqueous medium (10 −9 m 2 s −1 ), electrochemical healing represents a fundamentally different approach to repair fractured structural metals. [40][41][42] Coating a metal structure with a passivating coating ensures that metal ions are only reduced at fracture sites, thus resulting in efficient targeted healing (Bottom insets of Figure 1c). Using this approach, electrochemical plating of nickel has shown promise, by enabling 100% recovery of tensile strength in fractured cellular nickel (or nickel foam), with minimal energy use (≈10 2 J per mm of crack length) compared to many high-temperature healing techniques (up to 10 9 J mm −1 ).…”

“…[40] However, prior attempts to repair bulk metals using nickel plating failed to recover 100% of pristine tensile strength due to poor nickel-metal adhesion or defects caused by diffusion-limited plating. [41][42][43][44] To become a credible alternative to welding, electrochemical healing should ideally employ a simple process with a single electrolyte chemistry to effectively repair a wide variety of structural metals beyond nickel (including complex 3D printed structures and "unweldable" al-loys) within a quantitative predictive framework. Prior work on the electrochemical joining of metal parts achieved high adhesion of plated nickel to other metals, but required multi-step processes with acid pre-treatments and plating in different electrolyte chemistries, and did not present a model that predicted or provided understanding of how to achieve optimal mechanical properties of the joined parts.…”

Low energy repair of co-continuous metal-ceramic composites using electrodeposition

“…In this process, desired metal structures were coated with a polymer layer, and after fracture, they were submerged into an electrolyte bath to deposit metal at cracked regions to heal the samples. 11,12 Metal-ceramic composites are advanced composites that consist of a metallic matrix reinforced with materials including ceramic materials most commonly alumina and silicon carbide in continuous fiber, short fiber, whisker, and micro-platelets forms, as well as carbon fibers. 13,14 Because of high specific strength, stiffness, and elastic modulus, in addition to remarkable fracture toughness, metal-ceramic composites are used in aircraft structures such as landing gears, high-performance and light-weight structural composites, engine components, wear-resistance parts, and cutting tools for advanced manufacturing of aerospace parts.…”

“…In this process, desired metal structures were coated with a polymer layer, and after fracture, they were submerged into an electrolyte bath to deposit metal at cracked regions to heal the samples. 11,12…”