Microstructural Integrity and Mechanical Synergy at the ER2205–Inconel 718 Interface in Functionally Graded Wire Arc Additively Manufactured Bimetallic Structures

This study investigates the microstructural and mechanical behaviour of an ER2205–Inconel 718 bimetallic wall fabricated by gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) technique. Twenty layers were deposited to build a well-bonded interface between ER2205 and Inconel 718. Optical microscopy, field-emission scanning electron microscopy, and electron backscatter diffraction analyses indicate a continuous interface with a narrow remelting zone and controlled dilution. ER2205 exhibited a stable duplex microstructure of ferrite and austenite, while Inconel 718 solidified with columnar dendritic morphology and revealed Nb and Mo rich interdendritic segregation. Grain size analysis indicated a broad distribution with maximum grains fall within 10–60 µm range and a peak near 90 µm due to combined thermal effects across the interface. XRD revealed γ-Ni, γ-NiFe, and α-Fe as major phases with a minor Cr₃C₂ peak, suggest limited diffusion without the formation of intermetallics. Microhardness measurements revealed a smooth transition across the wall with hardness increases from ER2205 to Inconel 718 and intermediate values at the interface. Tensile results revealed at ER2205 side ultimate tensile strength (UTS) of 667 MPa, yield strength (YS) of 239 MPa, and maximum elongation of 34%. The results indicate that WAAM enables the successful fabrication of ER2205–Inconel 718 bimetallic structures with strong bonding and reliable property transitions suitable for high-temperature and corrosive service environments.