Metallurgical and microstructural assessment of DSS 2507/inconel 625 dissimilar metal wall fabricated by T-WAAM

Twin-wire arc additive manufacturing (T-WAAM) enables the simultaneous co deposition of dissimilar alloys; however, the mechanistic interplay among the solidification thermal history, phase stability, and crystallographic texture in the DSS-2507/IN-625 system remains unresolved. This study presents the GMAW-based T-WAAM fabrication of a DSS-2507/IN-625 dissimilar wall and delivers a comprehensive, position-resolved multitechnique characterisation spanning XPS, optical microscopy, FESEM-EDS, XRD, and EBSD across the top, middle, and bottom build regions. A key novelty lies in the sequential coupling of XRD-derived lattice parameters 3.64 Å (Ni-FCC) and 3.66 Å (Fe-FCC), refined by Nelson–Riley extrapolation as crystallographic reference inputs to EBSD phase indexing, enabling unambiguous discrimination of overlapping Fe-rich and Ni-rich FCC Kikuchi patterns and accurate phase fraction quantification. XPS confirmed the chemical stability of Ni, Fe, Cr, Mo, and Nb across all regions. Microstructural analysis revealed a gradient from columnar-dendritic morphology at the top to equiaxed cellular grains at the middle and coarser columnar structures at the bottom. FESEM-EDS revealed preferential interdendritic enrichment of Ni (∼35 wt.%) and Nb. EBSD phase maps revealed Ni-FCC dominance (53–55%) at the top and an increasing Fe-FCC contribution near the substrate, with a consistent ∼45° preferred grain orientation and a pronounced {111}, {101}, and {001} FCC texture shaped by directional solidification.