Integrated laser additive manufacturing of high-strength steel and Ti6Al4V: Experimental investigations and thermodynamic calculations

This work focuses on the challenging task of joining high-strength steels and titanium alloys, which are extensively utilized in the defense and aerospace industries. The study presented the fabrication of bimetals comprising high-strength steel (HSS)and Ti6Al4V (TC4) using laser-directed energy deposition (LDED) technology. The research elucidated the interface bonding mechanism of LDEDed HSS/TC4 bimetals and analyzed various bonding strategies for achieving superior properties of steel/titanium joints based on thermodynamic calculations. Due to the limited compatibility between Fe and Ti, a large amount of Fe-Ti intermetallics, especially Fe2Ti, were formed at the interface of LDEDed HSS/TC4 bimetals. The presence of Fe2Ti intermetallics caused a significant enhancement in interfacial hardness, ultimately leading to the fracture of tensile specimens during the wire cutting. Thermodynamic calculations indicated that utilizing a composition gradient processing strategy does not yield a high-quality metallurgical bonding interface between HSS and TC4. Interlayer engineering is an effective building strategy to obtain high-performance LDEDed HSS/TC4 bimetals. Moreover, these compatible interlayers should ensure a reasonable match of thermophysical properties and have a certain thickness. The findings provide valuable insights into bonding and failure behavior, building strategies, and potential future directions for joining high-strength steels and titanium alloys.