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.

Electrochemical mechanical polishing (ECMP) has emerged as a promising alternative to conventional chemical mechanical polishing (CMP), particularly for addressing challenges in planarizing ruthenium (Ru)—a critical barrier-layer material in advanced copper interconnects. This study systematically investigates the triboelectrochemical behavior and underlying mechanisms of ruthenium during ECMP, with a focus on the effects of mechanical power (induced by load and rotational speed) and applied potential. Through open-circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS), we demonstrate that mechanical energy input significantly enhances electrochemical reactions, with rotational speed exerting a more pronounced influence than applied load. Notably, the corrosion potential increases with load at constant speed, while the friction coefficient rises as rotational speed decreases. EIS analyses further reveal that higher rotational speeds promote the formation and growth of a thicker passive oxide film on ruthenium surfaces. These insights provide a theoretical foundation for optimizing ECMP processes toward high-efficiency, high-selectivity, and low-damage planarization of Ru-based interconnect structures.