Electric current-induced solid-state crack healing and life extension

This study demonstrates the complete closure of a crack and subsequent materials healing via a solid-state process upon application of high-density electric current pulses. This novel method leverages the simultaneous generation of a high-temperature field near the crack tip, a compressive stress zone induced by temperature gradients, and a significant electromagnetic force acting in Mode I, all arising from the flow of electric current around the crack. Finite element-based analysis is employed to optimize the process parameters, ensuring the dominance of the compressive stress field over the tensile electromagnetic force near the crack tip. Conjugate experiments demonstrate that fatigue-induced edge cracks in a metallic material (e.g., SS 316) can be fully healed by applying electric current pulses with extended pulse-width (e.g., 200 ms) and high densities (e.g., 10⁶⁻10⁸ A/m²). Detailed microstructural analysis of the healed region reveals micro-void-free complete bonding between the crack faces, characterized by a narrow strip (<100 μm width) featuring small, recrystallized grains. The observed boundary migration, entrapment of cavities inside grains, and partial alignment of dislocation substructures across the original crack confirm the solid-state diffusion bonding responsible for the materials healing. The yield strength, ductility and fatigue life of the “healed” material are commendable and can be significantly improved to mimic those of as-received material after solutionizing heat treatment. Overall, this study introduces a novel method for controlled crack closure and materials healing in in-service components, offering the potential to extend their operational life significantly.