Joining modes and IMC characteristics modulation in TC4/stainless steel dissimilar joints via energy-regulated interrupted pulsed arc welding with Cu interlayer assistance

Energy-regulated interrupted pulsed arc welding(IPAW) with Cu interlayer assistance was employed to modulate the intermetallic compound (IMC) characteristics and mechanical properties of joints between TC4 titanium alloy (TC4) and 304 stainless steel (304SS). Energy regulation enabled the formation of three distinct joining modes by precisely controlling the melting states of dissimilar base metals: brazing joints, welding-brazing joints, and fusion joints. The brazing joints, featuring a 60 μm-thick Ti-Cu IMC layer at TC4/Cu interface, exhibited the highest shear strength of approximately 110.05 MPa, due to the suppression of Ti-Fe atomic mixing. The welding-brazing joints featured a bimodal microstructure, characterized by upper interfacial regions composed of Fe(s,s) and Cu(s,s), while the lower regions contained a 64 μm-thick Ti-Cu IMC layer, which demonstrated a shear strength of 77.68 MPa. Fusion joints primarily consisted of Ti-Fe phases and Ti-Cu phases. The presence of the brittle TiFe 2 phase resulted in the lowest shear strength of only 52.98 MPa. An increase in pulsed current, a decrease in interrupted time,or a reduction in welding speed resulted in a transition from brazing to full fusion welding modes. Prolonging the pulsed time sequentially transformed the joint mode from brazing to fusion-brazing, and ultimately to full fusion welding. The shear strength of the joints initially increased and subsequently decreased with increasing heat input, correlating with intermetallic layer evolution and brittle phase formation. The mechanisms of joint formation across different joining modes, as well as the evolution of IMCs and their effects on joint performance, were thoroughly analyzed.