Development of IN718–Ti6Al4V functionally continuous gradient material by dual wire WAAM-TIG and its tribo-mechanical characteristics

Abstract

This study aimed to fabricate IN718 and Ti6Al4V-based functionally continuous gradient materials ( FCGMs) to tailor the simultaneous integration and resultant tribo-mechanical response for high-performance applications. A dual-wire WAAM-TIG (tungsten inert gas-based wire arc additive manufacturing) technology was employed to in-situ control the mass flow rate of these two alloys. This would also help to fabricate near-net-shape products cost-effectively, as wire feedstock was utilised, requiring minimal post-processing. It enabled the successful fabrication of IN718–Ti6Al4V-based FCGMs with varying gradients (20%–10% Ti6Al4V) despite their distinct thermophysical properties. The EDS analysis showed the absence of abrupt interfaces and clustering of governing elements, indicating sound metallurgical bonding. The XRD results revealed the formation of Ti-rich intermetallic phases (NiTi, Ni3Ti, Fe2Ti) and a gradual transition to γ-Ni dominant matrix from higher to lower Ti-regions. This phase evolution governed the microstructural transformation from refined dendritic/intermetallic-rich structures to comparatively coarser Ni-based grains. Inevitably, the Ti-rich region exhibited higher hardness (about 3 times) and ∼35% ultimate tensile strength than IN718, attributed to intermetallic strengthening and finer microstructure. However, the elongations increased from 21% to 33% in the 20% to 10% Ti6Al4V regions, showing good ductility when compared with IN718 (38%). The scratch analysis also showed significant improvement, ∼60% higher fracture toughness, indicating superior resistance to localised deformation. Similarly, tribological analysis demonstrated a ∼30% reduction in the coefficient of friction and specific wear rate, with dominant adhesive wear with some traces of abrasion, specifically in the Ti-rich regions. © 2026 Elsevier Ltd.