Strong interface bonding in copper/steel composites enabled by high cooling rates during twin-wire arc-directed energy deposition

Here, a copper/steel composite structure with superior mechanical properties was prepared using the twin-wire arc-directed energy deposition technique. Microstructural analysis shows that during the transition from steel to copper, liquid copper infiltrated into the steel substrate, forming a transition zone approximately 300 μm wide at the interface. While most of the copper was distributed along the grain boundaries, a fraction precipitated within the steel grains with 9R or FCC structures due to the rapid cooling rate. In contrast to the coarse grains in the pure copper and pure steel regions, the transition zone exhibited fine equiaxed grains with an average size of approximately 27 μm. Numerical simulations revealed that the refined microstructure was attributed to the copper significantly reducing the undercooling required for grain nucleation, as well as high cooling rate at the interface and copper at the grain boundaries inhibiting grain growth. Furthermore, cracks appeared in the transition and steel zones due to the differing thermophysical properties of both materials and the infiltration of copper. Tensile strength of the bimetallic structure perpendicular to the interface reached 380 MPa, with fracture occurring in the copper zone, indicating strong interfacial bonding.