Bimetallic 17-4 PH/316 L stainless steel: Interfacial diffusion and mechanical response in multi-material MEX

Multi-material additive manufacturing enables the integration of distinct alloys with contrasting mechanical and microstructural properties, such as stainless steels 17–4 PH and AISI 316 L that are widely used in aerospace and tooling, within a single build; however, their combined performance in hybrid configurations remains underexplored. Here, we address key challenges related to densification, interfacial behavior and mechanical property control of metallic multi-material additive manufacturing structures. Near-full densification (98–99 %) was achieved with strong interfacial bonding and minimal deformation. Microstructural analysis revealed solid-state diffusion of Ni and Mo from 316 L into 17–4 PH, resulting in a chemically and structurally graded interface that affects local phase composition and fracture mechanics. Mechanical testing under tensile and flexural loading demonstrated that configurations with 17–4 PH as face material and 316 L as the core provided higher stiffness and strength while maintaining ductility, with flexural property metrics more than double to those of monolithic 316 L cores. Fractographic analysis confirmed that fractures initiated within the more brittle 17–4 PH material and often thereafter propagated along the interface, identifying it as a mechanically weaker zone serving as a crack pathway. These results highlight the potential hybrid stainless steel structures to achieve combined mechanical responses suitable for advanced engineering applications in a single manufacturing step, enabling the design of cost-efficient, multifunctional components for structural applications requiring hybrid mechanical behavior.