Despite the great potential offered by additive manufacturing to produce structures with complex shapes, one of its current major limitations is the impossibility to in situ fabricate multi-materials assemblies and/or architectured structures. The Belgian company Aerosint developed a printing head capable of printing two or three materials simultaneously by Laser Powder Bed Fusion (LPBF). However, the fabrication of multi-materials parts also brings about new challenges. Indeed, depending on the co-deposited materials, the solidification mechanisms occurring at the interfaces will be completely different, depending on whether the materials are reactive, miscible, or immiscible. Mixing at the interface can become very complex, especially in reactive and immiscible cases. Currently, multi-material additive manufacturing is an innovative technology of high interest where guidelines for processing parameters and compositions are missing. In this study, we propose a procedure to efficiently characterize such interfaces using a combination of modelling tools (COMSOL and Thermo-Calc) and state-of-the-art experimental characterization methods, comparing as-built LPBF and electron beam welded (EBW) specimens.