Microstructural evolution and mechanical properties of bimetallic Inconel 718–SS308 fabricated by CMT-WAAM

This study investigates the microstructural evolution and mechanical properties of a bimetallic Inconel 718–SS308 wall fabricated using Cold Metal Transfer Wire Arc Additive Manufacturing (CMT-WAAM), with particular emphasis on the less-explored SS308/Inconel 718 transition zone. Microstructural examination revealed epitaxial grain growth and columnar dendritic structures across the interface, supported by a graded Fe–Ni diffusion profile. Electron backscatter diffraction analysis confirmed a dominant ⟨001⟩ crystallographic texture and a high fraction of high-angle grain boundaries, indicating a sound metallurgical bonding. Microhardness measurements revealed a smooth gradient from SS308 (200–240 HV) to Inconel 718 (360–400 HV), with a peak hardness of approximately 405 HV near the interface owing to solid-solution strengthening. Tensile testing demonstrated higher strength in the Inconel 718 region (ultimate tensile strength of 628 ± 15 MPa and yield strength of 495 ± 12 MPa), whereas the SS308 region exhibited superior ductility (elongation of 28.5 ± 1.5%). Fractures consistently occurred in the SS308 region. Overall, the results confirm that CMT-WAAM enables the fabrication of well-bonded Inconel 718–SS308 bimetallic structures with functionally graded properties suitable for repair and multimaterial applications.