Oscillating Laser Welding of TC4-304SS Dissimilar Joints: Regulating Microstructure and Mechanical Properties via Cu, Mo, and Nb Interlayers

This study investigated the use of oscillating laser welding with Cu, Mo, and Nb interlayers to mitigate the issue of brittle intermetallic compound (IMC) formation in titanium-steel dissimilar welding for TC4/304SS lap joints. This study systematically examined the influence of interlayer type on joining mechanisms, microstructure, and mechanical properties. Results indicated that direct welding produced Ti-Fe IMCs (TiFe phase) through fusion, resulting in a thick brittle layer. The Cu interlayer facilitated fusion welding while promoting the formation of TiFe₂ and TiCu₄ phases. Mo and Nb interlayers, through fusion-brazing and brazing mechanisms, respectively, inhibited Ti-Fe IMCs by generating Fe-Mo/Nb IMCs and (Ti, Mo/Nb) solid solutions. Mechanical testing indicated that Mo-interlayer joints exhibited the highest shear strength at 1129.53 N, representing a 31% increase relative to direct joining. This was followed by Nb at 1004.4 N, Cu at 871.6 N, and direct welding at 859.13 N. Fracture transitioned from brittle IMC layers in Cu and direct welding to interfaces between interlayers and TC4 in Mo and Nb systems. This study presents Mo/Nb interlayers as the most effective choice for high-strength Ti-steel joints, providing insights for the selection of interlayers in engineering applications.