Microstructures and mechanical properties of 316LSi/IN625 FGMs manufactured by CMT-WAAM

In this study, functionally graded materials (FGMs) composed of nickel-based high temperature alloy, Inconel 625 (IN625) and austenitic stainless steel 316LSi were prepared using cold metal transfer (CMT)-based arc additive manufacturing (WAAM). The prepared 316LSi/IN625 FGMs exhibited dense structures without any signs of solidification cracking at the interface (IF). The microstructural observations showed abrupt transition across the IF, characterized by discontinuous dendritic. Elemental diffusion at the IF was confirmed by energy dispersive X-ray spectroscopy (EDS), indicating a diffusion layer of approximately 100 μm with no significant compositional changes. The 316LSi layer primarily consisted of austenitic matrix with minor δ-ferrite, whereas the IN625 layer exhibited precipitated phases on the austenitic matrix. The yield strength (YS) and ultimate tensile strength (UTS) of prepared FGMs were 514.24 and 680.32 MPa, respectively. All IF samples fractured on the 316LSi region, indicating ductile fracture due to lower UTS compared with IN625. Microhardness testing showed a gradual increase from 188.5 HV on the 316LSi side to 224.6 HV on the IN625 side along the building direction. This work demonstrates that CMT-WAAM is a promising approach for defect-free FGMs reliable interfacial bonding and desired mechanical properties.