Electro-healing cracks in nickel

Healing cracks in metallic materials is challenging due to limited atomic mobility in solid state around ambient temperature. In this paper, we developed a novel crack-healing approach by means of an electrochemical process in which metallic ions in electrolyte are used as a healing agent. Pure Ni sheets with a through-thickness crack were taken as an example. Cracks with sizes in the micrometer range or larger are successfully healed by electro-healing. The electro-healing process starts with the vertical epitaxial growth of healing crystals from the original crack surfaces followed by lateral growth of healing crystals that bond with each other at atomistic level. Tensile tests exhibited that the healed samples have a comparable tensile strength as the virgin sample and some tensile ductility can be achieved for the sample of 100 μm thick. Post-fracture analysis indicated that part of the crack propagated along the substrate instead of healing crystals. The healing efficiency, ranging from 96% to 33% with an increasing sample thickness, is related to the fraction of fully-healed region and the strength difference between the substrate and the healing crystals.