Interfacial microstructures in stainless steel and zirconium dissimilar induction kinetic weld joints

Induction kinetic welding (IKW) is an emerging solid-state technology that has been optimized and applied to dissimilar joining of a Zircaloy-4 alloy tube to a 304 L stainless steel plug. A groove profile is applied to the tangential edge of the stainless-steel plug to increase the contact area, thereby promoting mechanical interlocking and metallurgical diffusion bonding, while optimized processing parameters enhance the circular dissimilar bonding between the plug and the tube. The dissimilar joint fractures in the Zircaloy-4 tube base metal (far from the weld line) during tensile loading indicate a joining efficiency of 100%. The metallurgical bond at the zirconium-steel interface was studied using various advanced material characterization techniques, including electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) phase analysis, which indicate that a β‑zirconium phase formed at the interface due to elemental diffusion of zirconium and nickel. A mixture of fragmented α‑zirconium and austenite forms a micro-scale interaction region across the weldment by tangential deformation and diffusion. Nanoscale examination of the interfacial bonding layer using ion-beam scanning transmission electron microscopy (FIB/STEM) revealed a wavy interface formed by a combination of shearing and diffusion between the zirconium and the stainless-steel plug, thereby suppressing the formation of a thick intermetallic layer. Elemental diffusion of nickel and its accumulation at the boundary of the interface, as well as the formation of ordered chromium-rich (and slightly Mn-rich) nanoscale Zr 3 Fe intermetallic features and zirconium-rich nanoparticles, were observed adjacent to the wavy joint interface. This is formed by diffusive tangential shear deformation, which appears to be the key metallurgical bonding feature of a hard interfacial layer.