Even tiny cracks can cause bridges to collapse, pipelines to rupture, and fuselages to detach from airplanes due to hard-to-detect corrosion in tiny cracks, scratches, and dents. A new coating strategy for metal self-heals within seconds when scratched, scraped, or cracked. The novel material could prevent tiny defects from turning into localized corrosion, which can cause major structures to fail.
When damaged by scratches and cracks, the material system readily flows and reconnects to rapidly heal. The material was demonstrated to heal repeatedly, even after scratching the exact same spot nearly 200 consecutive times.
While a few self-healing coatings already exist, those systems typically work for nanometer- to micron-sized damages. To develop a coating that can heal larger scratches in the millimeter-scale, researchers looked to fluids such as oils, which are self-healing. But common oils flow too readily, so the system needed contradicting properties: fluidic enough to flow automatically but not so fluidic that it drips off the metal’s surface.
A network of lightweight particles — in this case, graphene capsules — was created to thicken the oil. The network fixes the oil coating, keeping it from dripping. But when the network is damaged by a crack or scratch, it releases the oil to flow readily and reconnect. The material can be made with any hollow, lightweight particle — not just graphene.
The coating not only sticks but sticks well, even underwater and in harsh chemical environments such as acid baths. It could be painted onto bridges and boats that are naturally submerged underwater as well as metal structures near leaked or spilled highly corrosive fluids.
The coating can also withstand strong turbulence and stick to sharp corners without budging. When brushed onto a surface from underwater, the coating goes on evenly without trapping tiny bubbles of air or moisture that often lead to pinholes and corrosion.