Design of high strength Cu alloy interlayer for mechanical bonding Ti to steel and characterization of their tri-layered clad

• Cladding Ti/steel at low temperatures is difficult due to their high melting temp.
• We explore the possibility of low temperature cladding using Cu alloy interlayer.
• Good deformability, high strength and least reactivity with Ti/steel are required.
• Cu–8Ag initially soft, but strengthen rapidly with shear will be a good candidate.
• Hardness of Cu–8Ag interlayer after HPT joining was close to those of Ti and steel.

Cu–8 wt.% Ag alloy is proposed as a good interlayer alloy with good deformability, high strength, least reactivity and low melting temperature for low temperature joining of Ti and carbon steel. Titanium and carbon steel plates with a Cu–8Ag interlayer plate were joined by high pressure torsioning (HPT) at room temperature and the effect of post-HPT annealing on their mechanical performance was examined. The most pronounced increase of the Vickers microhardness (from 88 to 248 Hv) was observed in Cu–8Ag, suggesting Cu–Ag is the ideal bonding interlayer with a lower melting temperature, an initial excellent deformability and high strength after joining. With the increase of heat-treatment temperature, the tensile strength increased initially up to 350 °C and then decreased with increase of annealing temperature above 350 °C. The maximum strength after annealing at 250 °C is due to the combined effect of the precipitation strengthening of Cu–8Ag interlayer and static strain aging of both S20C and Ti. The stress–strain curves exhibited the step-wise fracture, with the first step resulting from the fracture of S20C plate and the next from co-fracture of Ti plate and Cu–Ag interlayer. The co-fracture of Cu–8Ag and Ti suggests that the bonding strength between two layers is fairly high even in the presence of intermetallic layer.