Multi-material additive manufacturing offers new opportunities for locally tailoring mechanical and functional properties within a single component. In this work, a bi-material combining stainless steels 316L and 17-4 PH was fabricated using Wire and Laser Additive Manufacturing (WLAM). Although these alloys share similar chemical compositions, their distinct crystallographic structures result in markedly different mechanical properties. Comprehensive analyses of the interface were conducted, including hardness measurements, microstructural characterization and chemical composition profiling. Results revealed three distinct hardness zones, with an intermediate layer, approximately one layer thick, exhibiting a markedly lower hardness, even lower than that of 316L. Microstructural analysis indicated that this transition zone consisted of roughly 30% austenite and 70% of a mixture of martensite and ferrite, with local chemical compositions differing from those of the base materials. Thus, despite the predominance of martensitic phase, the combination of local compositional variations and thermal history could explain the observed softening behaviour at the interface. Additionally, a precipitation heat treatment (H900), typically used to harden 17-4 PH, was applied to the bi-material. The treatment hardened the 17-4 PH region, but not the intermediate layer at the interface, despite the presence of copper.

Keywords: WLAM; multi-materials; Interface; Stainless Steel