Arc welding of titanium alloy to stainless steel with Cu foil as interlayer and Ni-based alloy as filler metal

An innovative weld with high tensile strength was fabricated for gas tungsten arc welding of TC4 titanium alloy and 304 stainless steel with Cu foil as interlayer and Ni-based alloy as filler metal simultaneously. Due to the high longitudinal residual stress, transverse cracks easily generated in the weld seam with pure Cu wire as filler metal. With the newly designed weld, the longitudinal residual stress in the weld seam was much lower than the fracture strength of Ni-based deposited metal, hence the transverse cracking of the joint was remarkably inhibited. The Cu foil enfolded at the end face of titanium alloy sheet effectively reduced the dissolution of titanium alloy, suppressing the formation of Ti-based brittle compounds in the interfacial zone. The Ti-side interface consisted of β-Ti, Ti2Ni, TiNi, TiNi3, (Cr,Mo), Ti(Fe,Cr,Ni)2, (Cr,Fe,Ni) solid solution, and Ni–Fe–Cr–Ti phases, resulting in high microhardness of Ti-side interface up to 855 HV0.1. At the weld toe, TixCuy phases with lower microhardness and brittleness are formed between the unmelted Cu foil and titanium alloy substrate, reducing the cracking sensitivity of Ti-side interface. The tensile strength of the corresponded TC4/304SS joint reached 485 MPa, and all joints fractured at the Ti-side interface that consisted of β-Ti and Ti2Ni phases.