The manufacturing of bi-metal structure has received much interest because it provides compensated properties for a single metal alloy, meeting the harsh requirements for components used in key industries like aerospace, defense, energy, etc. Additive manufacturing (AM) has been extensively applied in building multi-material structures because of its ability to vary material type and composition in a layer-by-layer mode. However, fusion-based AM technologies usually induce interfacial cracks and delamination resulted from the large mismatch of coefficient of thermal expansion (CTE) between dissimilar materials, while the solid-state AM methods generate a large number of pores at the interface, requiring post-fabrication heat treatment. In this study, we aim to build high-quality 17-4 PH stainless steel and nickel alloy bi-metal structure with material extrusion AM method, followed by debinding and sintering processes. The microstructure and mechanical properties of the bi-metal structure were thoroughly investigated. It was revealed that small pores were distributed in the whole part, and no brittle intermetallic phase but slightly larger pores were formed at the interface. The material transition zone was relatively small in thickness, exhibiting low bonding strength and low hardness but a ductile deformation behavior. The completion of this study provides a pioneering analysis of bimetal structures built by extrusion-based sintering-assisted AM, and shows a great promise for further adoption of this technology in a variety of industrial applications.
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