Multiscale probing of interfacial architecture and evolutionary mechanisms in AISI 410L/NS163 electron beam welds during aging

• Aging treatment significantly enhances the compatibility of the AISI 410L/NS163 heterogeneous interfaces. • Stress-to-thermodynamic synergistic mechanism drives transition in carbide precipitation. • Interface-specific evolution involves dual control of dislocation adjustment and epitaxial stability. • Synergistic dislocation redistribution and stress release promote improvement in interfacial performance. The microstructure of dissimilar metal welded joints has consistently been a major cause of the strength-ductility trade-off. This study systematically investigates the interfacial structure evolution of an electron beam welded joint between AISI 410L ferritic stainless steel and NS163 Co-based superalloy during aging at 600 °C using multi-scale characterization techniques. The crystallographic mismatch between the base metals and weld metal leads to distinct interfacial evolution behavior. We proposed a synergistic mechanism between precipitation-induced diffusion blocking and thermodynamic evolution, driving the contraction of the transition zone during aging. HRTEM confirms that aging significantly reduces the interfacial lattice mismatch, with the fusion boundary decreasing from 7.62 % to 1.32 %, and the phase boundary markedly decreasing from 21.43 % to 6.62 %, effectively alleviating stress concentration at the interface. After aging, the micropillar compressive yield strength increases by approximately 20 %, and plastic compatibility is enhanced, leading to a significant improvement in the weld quality. This study provides a theoretical basis for optimizing the thermal stability of dissimilar metal welded joints.