Design strategies for bi-metallic additive manufacturing in the context of wire and arc directed energy deposition

Abstract

While the recent research in manufacturing bi-metallic structures using wire and arc directed energy deposition focuses on feasibility studies to understand material compatibility, the study presented here encircles a larger design framework, integrating deposition process, intermediate surface conditions, and mutual deposition (hatching) direction. The investigation addresses the issues associated with manufacturing actual bi-metallic structures and shades light on the intrinsic mechanism responsible for process-induced anisotropy and resulting interfacial strength. Interfacial shear tests of the candidate bi-metallic pair of low-carbon steel-316L stainless steel reveal that the intermediate machining before deposition of the second material, if deposited with low dilution and low heat input has a limited effect on the final build quality. The deposition direction influences the isotropy, i.e., strength improves when the shear force acts transversely to the deposition direction of the second material. Interlocking promoted by favorable deposition direction, as revealed by fractography, combined with metallurgical bonding, enhances the interfacial strength. Despite element migration and hardness spike in the interface up to 500 HV due to martensitic needles, a defect-free bi-metallic structure was possible with shear strengths over 400 MPa. The investigation contributes to the fundamental understanding of the approaches suitable for the deposition of sound bi-metallic structures.