Influence of Cu/Ni interlayers on rotary friction welded dissimilar SS321-Ti6Al4V joints

Joining of stainless steel (SS) and Ti alloys offers lightweight, cost-efficient, and versatile part design options across various industries. This work incorporates Cu and Ni interlayers and compares the evolution of temperature, force, and microstructure, with and without interlayers. With these interlayers, SS321 underwent dynamic recrystallization-driven grain refinement, whereas SS321 grains coarsen without interlayers. Ti6Al4V consistently undergoes grain refinement. Interlayers impact elemental diffusion and intermetallic formation, replacing Fe-Ti intermetallics with Ni-Ti and Cu-Ti intermetallics in the interlayered joints. Additionally, in this study, interlayers reduce peak welding temperatures, resulting in higher forces for improved contact and enhanced joint strength. Joint strength increases by 30% with the Cu interlayer and 64% with the Ni interlayer. Tensile tests reveal brittle failures with intermetallics at the fracture sites. Notably, the Ni interlayer leads to failure at the Ti6Al4V-Ni interface, instead of SS321-Ti6Al4V interface.