A novel Ni–Co–Al multi-principal filler wire for inhibiting Fe–Ti intermetallic compounds in welding CP-Ti/Q345 bimetallic sheets

In this work, a novel Ni–Co–Al multi-principal wire was used as only one type of filler material to finish the joining of TA1/Q345 bimetallic sheets by in situ preparation of high-entropy materials in the weld zone (WZ). The results indicated that a good weld formation could be achieved by using the Ni–Co–Al wire. The thermodynamic environment with high mixing entropy (ΔS mix) and low mixing Gibbs free energy (ΔG mix) in the WZ could be created by the Ni–Co–Al wire and the elements introduced from base metals. It could efficiently inhibit the formation of Fe–Ti IMCs and promote the solid-solution structures of FCC and BCC in the WZ. Fe–Ti IMCs were only presented in the transition zones on the TA1 flyer layer as well as a narrow region of the WZ within ∼30 μm away from the Q345/WZ interface, where the ΔG mix was higher than the ΔG of Fe–Ti IMCs.