Achieving metallurgical and mechanical compatibility in dissimilar Fe-Cr-Ni alloys via compositionally graded interfaces fabricated by underwater laser dual-wire directed energy deposition

Ensuring reliable in-service repair of pressurized water reactor (PWR) components demands metallic cladding that can withstand simultaneous high-temperature loading and aggressive aqueous corrosion. Conventional direct underwater deposition of Ni-based alloys onto duplex stainless steels is widely reported to be challenged by interfacial cracking and performance degradation induced by dilution of Ni/Cr element. In this work, a local-dry underwater laser-wire directed energy deposition (LD-ULDED) strategy incorporating dual-wire co-feeding is developed to fabricate compositionally graded Fe-Cr-Ni alloy cladding for dissimilar-metal repair. By actively regulating the feeding ratio between Fe-based (ER2209) and Ni-based (ERNiCrFe-7A) wires, a continuous chemical gradient is established, enabling a transition in phase constitution, solidification morphology, and mechanical response. Microstructural characterization reveals a progressive evolution from ferrite-austenite duplex structures to homogeneous austenitic dendrites, which promotes metallurgical bonding and mechanical continuity across graded interlayers. High-temperature (350 ℃) tensile testing demonstrates a non-monotonic, layer-dependent mechanical response along the compositional gradient. The 75% IN690 layer exhibits the lowest tensile strength and mixed fracture characteristics due to M₂₃C₆ precipitation, grain-boundary migration, and localized strain concentration, whereas the fully Ni-rich layer achieves the highest ductility (46.1%) with a more uniform strain distribution. Electrochemical testing in boric acid-NaCl solution further shows that the 25% IN690 layer provides the most favorable corrosion resistance, benefiting from a balanced Fe-Cr-Ni chemistry and refined dual-phase microstructure. These results indicate that the dual-wire LD-ULDED strategy establishes a crack-free compositionally graded Fe-Cr-Ni cladding with spatially differentiated mechanical and corrosion responses, while also identifying a property-sensitive intermediate composition window in the present gradient path.