Influence of tantalum interlayer thickness on Ti–Fe intermetallic formation and mechanical behaviour of Ti–6Al–4V/SS304 welds

Dissimilar welding of titanium alloys to stainless steels offers the potential to combine lightweight, corrosion-resistant titanium with the toughness and cost-effectiveness of steel, yet the formation of brittle Ti-Fe intermetallic compounds (IMCs) at the interface has long prevented its reliable applications. This study examines the role of tantalum interlayer thickness in controlling intermetallic phases evolution and enhancing the mechanical response in pulsed gas tungsten arc welded (P-GTAW) Ti-6Al-4V/SS304 joints. Composite interlayer consisting of Tantalum (Ta) foils of 0.1, 0.3, and 0.5 mm thickness combined with Cu filler was introduced at the interface, and the resulting welds were evaluated through ultimate tensile strength (UTS), microhardness, and detailed microstructural characterization using scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) supported by fractography analysis. The results demonstrate that increasing interlayer thickness progressively suppressed the formation of Ti-Fe IMCs, refined the fusion zone grain structure, and promoted the development of Cu and Ta based phases. The joints with thickest Ta foil (0.5 mm) depicted high maximum strength (297 MPa), improving by 75% compared to the thinnest interlayer and microhardness profiles becoming smoother across the fusion boundary. These findings confirm that interlayering is an effective method to mitigate brittle phase formation in dissimilar Ti-SS welds. The improvements demonstrated underscore tantalum's potential for aerospace and structural applications are required, where both high strength and reliability are required.