Repairing large cracks and reversing fatigue damage in structural metals

Self-healing materials represent a paradigm shift from traditional materials development, enabling intrinsic repair of functionality (such as strength) after a catastrophic failure as opposed to part replacement. Several healing mechanisms have been demonstrated in polymeric and ceramic materials, but few in metallic systems. This study demonstrates a novel liquid-assisted self-healing metal-matrix composite (MMC) designed to be capable of over 90% strength recovery after a healing cycle. The aluminum (Al)-based matrix is reinforced with continuous nickel-titanium (NiTi) shape-memory alloy (SMA) reinforcements. Using a tailored heat treatment for healing, a paired effect of crack closure from the SMA reinforcement and partial liquefaction of the matrix occurs. These effects result in a compressive force across the crack surface, and, coupled with increased diffusion rates from the liquefied matrix, produces consolidation and healing in the composite structure. This work provides experimental and computational evidence for the healing mechanism under both tensile and fatigue conditions.