Tailoring interlayer microstructural morphology characteristics for enhanced mechanical performance in laser welded titanium-steel dissimilar joints

Due to their exceptional properties, dissimilar metallic joints composed of titanium alloys and steel find numerous industrial applications. Steel possesses high strength, whereas titanium is frequently used for lightweight applications due to its exceptional strength-to-weight ratio. The joint’s versatility and low weight contribute to its widespread use in numerous engineering sectors, including the automotive and aerospace industries. The process of joining steel with titanium is challenging due to various obstacles, including the reactivity of titanium, the formation of intermetallic layers, and mismatches in thermal expansion, among others. However, the most significant issue is the presence of brittle and rigid intermetallic layers, which can be mitigated by inserting interlayers between titanium and steel. Interlayers facilitate the bonding process between the two materials above, enhancing their mechanical properties by acting as an intermediary between them. Therefore, the performance and longevity of the welded joint are contingent upon the appropriate selection and configuration of the interlayer. The present paper addresses the effect of interlayers, such as chemical composition, thickness, and fabrication method, on the mechanical properties of dissimilar junctions, including fatigue resistance, hardness, and ductility. With an increase in Cu interlayer thickness up to 500 μm, joint strength improves, but hardness reduces due to reductions in Cu/Fe and Ti/Cu phases. Pure vanadium interlayer above 35 wt.% develops brittleness along the Ti/V interface, which is responsible for joint failure. Ni interlayer increases the weld strength by reducing TiFe 2 and TiCr 2 brittle phases. But above 45 wt.% it develops gas holes. Compared to the Cu interlayer, the Cu-Nb composite interlayer provides better weld strength.