Interfacial integrity in multi-metal additive manufacturing: challenges, mechanisms, and processing strategies

Multi-metal additive manufacturing (MM-AM) enables the fabrication of components with spatially tailored properties; however, achieving robust structural integrity at dissimilar metal interfaces remains a central technical challenge. This review critically examines interfacial design and processing strategies in MM-AM, with a particular focus on laser powder bed fusion (L-PBF) and laser directed energy deposition (L-DED). An operational diagram is introduced to systematically categorize the key factors governing metallurgical bonding in MM, including thermal expansion mismatch, phase incompatibility, and solidification behavior. Using this diagram, the review synthesizes current understanding of interfacial integrity mechanisms in bi-metallic systems. Process-driven mitigation strategies are then evaluated and classified into two primary approaches: the use of compositionally compatible interlayers and hybrid additive manufacturing (H-AM) strategies incorporating additional thermal, mechanical, or thermo-mechanical treatments during MM-AM. These approaches are critically assessed for their effectiveness in suppressing defect formation, including brittle intermetallic compounds and the accumulation of residual stress. Finally, an engineering-oriented framework is proposed to guide material selection and process design, providing a foundation for the scalable fabrication of structurally integrated multi-metal components.