Molecular dynamics insights into the healing mechanism and mechanical recovery of fractured nanoporous gold via cold welding

Abstract

Cold welding is a solid-state joining process that achieves atomic bonding without external heat input. It emerges as a critical technology for nanoscale systems, offering unique advantages in connecting, repairing, and regenerating functional nanodevices. Nanoporous metals (NPMs) hold exceptional promise for advanced applications, yet their intrinsic crack-induced mechanical vulnerabilities limit practical deployment. This study pioneers a room-temperature healing strategy for fractured nanoporous gold (NPG) through mechanically-assisted cold welding. By leveraging compressive contact to activate surface diffusion-mediated atomic bonding at nanoscale ligament junctions, we achieve structural restoration with mechanical recovery efficacy dependent on processing parameters (holding time, temperature, and compressive strain) and architectural features (ligament size and relative density). Four distinct ligament healing modes, head-to-head, side-to-side, side-to-head, and unsuccessful connections, are observed. During the tension test of the healed material, it is found that substantial dislocation source depletion from prior deformation suppresses dislocation activity. Crucially, the healed architecture undergoes a paradigm shift in deformation mechanics: dominant ligament axial elongation replaces the characteristic bending mode of original structures, accompanied by altered mechanical scaling laws. The methodology demonstrates exceptional repeatability, with multi-cycle fracture-healing tests showing <8% variation in ultimate strength after five cycles. This study provides a viable pathway for repairing nanoscale metallic architectures, offering transformative implications for durable NPM-based device engineering.