Dual-interfacial alloying mechanism in Ti-steel laminated metal composite fabricated by wire-arc directed energy deposition using a Cu-Ni interlayer

Ti-steel laminated metal composites have been widely used in shipbuilding and the chemical industry due to the superior corrosion resistance of Ti and the favorable mechanical properties of stainless steel. In this paper, Ti-steel laminated metal composites without Ti-Fe IMCs have been fabricated by directed energy deposition-arc method using a Cu-Ni transition interlayer. Based on the analysis of microstructure analysis, the cross-sectional microstructure can be divided into 304SS / Cu-Ni interface containing (Fe, Cr) and (Cu) solid solution, Cu-Ni deposition layer containing (Fe, Cr) and (Cu) solid solution, and TA2/Cu-Ni interface containing Ti ₂FeCu and Ti-Cu IMCs. Besides, the Cu-Ni deposition layer contains a small content of recrystallized grains with {100}<100> texture and a large content of deformed grains with{100}<110> texture due to the impact of arc and droplets during continuous depositions. Furthermore, the peak hardness is decreased to 518 Hv and the mean value of compressive shear strength is enhanced to 195.27 MPa, which can be attributed to the elimination of interfacial Ti-Fe IMCs, defect-free microstructure, and residual stress relief. Based on polarization curves and electrochemical impedance spectroscopy, the corrosion resistance reduction of the cross-section is due to the formation of a mass of primary battery systems. Furthermore, based on the thermodynamics calculation of Fe-Cu-Ni, Ti-Fe-Cu, and Ti-Ni-Cu ternary systems, the alloying mechanism is that Ti-based IMCs with lower Gibbs free energy will be formed instead of brittle Ti-Fe IMCs, resulting in the elimination of Ti-Fe IMCs and the formation of less brittle phases at both 304SS / Cu-Ni interface and TA2 / Cu-Ni interface.