The formation of intermetallics in Ti/steel dissimilar joints welded by Cu-Nb composite filler

Cu-Nb flux-cored wires with different Nb contents (5 at. %, 20 at. % and 30 at. %) were designed to butt join explosion-welded Ti/steel bimetallic plate. The lower Nb content in Cu5Nb filler results in the formation of extensive Cu-Ti compounds. Brittle Fe2Nb intermetallics form when the Nb content increases to similar to 30 at. %. The joints welded by Cu20Nb filler are crack free. Simple models are developed to explain the possible phase evolution mechanisms in the welded joint with Cu20Nb filler. The brittle intermetallics (Fe2Ti, Fe2Nb and FeTi) are dispersed and are surrounded by soft Cu phase, which significantly improve the cracking resistance of the weld metals. Cracks emerge and propagate along the regions rich in alpha-Fe + Fe2Nb, CuTi2 phases during the three-point bending tests. The tensile strength of the butt joints is similar to 334 MPa. Fractography of the tensile samples is corresponding well to the microstructures. (C) 2020 Elsevier B.V. All rights reserved.