Full domain power-modulated galvanometer-scanned laser welding of zirconium alloys/nickel-based superalloys dissimilar joints: microstructural evolution and strength enhancement

Abstract

Dissimilar joining of zirconium alloys to nickel-based superalloys presents critical challenges in nuclear fuel assembly applications, where interfacial brittle intermetallic compounds (IMCs) and thermal stress concentration fundamentally limit the structural integrity of Zr/Ni joints. This study developed an innovative full domain power-modulated (FDPM) galvanometer-scanned laser welding technique with multiscale thermal management to address these critical issues in Zr-N36/IN718 joints. Through a series of experiments with dynamic heat input redistribution, temperature gradient optimization, and multi-stage residual stress mitigation, a quantitative correlation between thermal process and joint strengthening mechanism is established. Results indicate that reducing heat input by 42 % effectively alleviates excessive Ni/Cr/Fe elemental diffusion, decreasing IMCs layer thickness from 39 μm to 17 μm. The thermal management strategy (300 W preheating +360 W in-situ heat treatment) results in a 23.5 % reduction in small-angle grain boundaries (55.4–31.9 %) and 30 % decrease in kernel average misorientation (KAM) indicating substantial residual stress release. The joint tensile strength is enhanced from 23.73 MPa to 103 MPa, with the fracture mode transitioning from intergranular brittle to ductile dimple-dominated failure. Microstructural analysis demonstrates a γ-(Ni, Cr, Fe) matrix reinforced by nano-Ni₃Nb precipitates in the fusion zone, while gradient-distributed NiZr₂ and σ-FeCr phases at the reaction layer effectively mitigate thermal expansion mismatch.