Fabrication and Characterization of Wire Arc Additively Manufactured Ferritic-Austenitic Bimetallic Structure

Bimetallic parts are used in many industrial fields, such as pressure vessels, shipbuilding, aerospace, and automotive industries. Conventional bimetallic part production involves a combination of two different metals that are joined using welding and brazing operations. Additive manufacturing technologies offer a cost-effective and innovative manufacturing alternative for complex 3D-shaped parts that can have multi-material designs for better structural performance. However, the structural performance of bimetallic components is primarily influenced by the combination of the employed materials, the interface’s morphology, and interface bonding strength. This work investigated the microstructure and mechanical behavior of a bimetallic thick-walled structure as “WAAM Wall” fabricated by depositing low-alloyed metal-cored wire on the top of 316L stainless steel by robotic wire arc additive manufacturing (WAAM) process. The results showed that both low-carbon steel and austenitic stainless steel SS316L wires are suitable for manufacturing defect-free bimetallic WAAM components, which may widen the design flexibility to manufacture bi-metallic and or functionally graded WAAM components. However, detailed microstructural characterization indicated that martensitic microstructure containing chrome carbides was developed at the bimetallic interface due to an increase in Ni and Cr contents, resulting in a sudden increase of 95% in hardness and a sharp decrease of 70% in fracture toughness at the interface region compared to the SS 316L side. This high-hardness region also resulted in an increase of about 113% and 86% for yield and tensile strengths and a sharp reduction of 69% for elongation values in horizontal interface specimens compared to vertical interface specimens.