Multi-material structures have gained significant attention for their ability to combine properties of different alloys, making them promising for technical applications and potential replacements for conventional single-alloy components. The advancement of Additive Manufacturing (AM) has enabled the fabrication of such structures through hybrid method-combining AM with casting or welding-or directly using AM to create bimetallic or functionally graded materials. Both approaches face challenges, particularly due to the differing thermophysical properties and phase transformations at interfaces, which often result in cracking.

This thesis explores two fabrication strategies: integrating Laser Powder Bed Fusion (LPBF) with casting techniques (induction melting and squeeze casting), and direct fabrication of multi-material structures using LPBF with intermediate alloy compositions. The study focuses on four material systems: 316L stainless steel/Inconel 718 with CuCrZr copper alloy, and 316L stainless steel/Ti6Al4V titanium alloy with aluminum alloys (AlSi10Mg and AlMg3).

The first part of the research examines Cu-matrix composites. 316L-CuCrZr and Inconel 718-CuCrZr structures are created by combining LPBF (for 316L and Inconel 718) with induction melting (for CuCrZr). The goal is to fabricate crack-free CuCrZr-based composites, embedding 316L in lattice form and Inconel 718 as grid structures. The 316L-CuCrZr interface exhibits interdiffusion phenomena leading to austenite-to-ferrite phase transformation, with texture and strain analyzed after each processing step using Bragg Edge Imaging. Compression testing evaluates the strengthening effect of the 316L lattice. In Inconel 718-CuCrZr composites, interdiffusion results in Mo, Cr, and Nb-rich precipitates at the interface, significantly increasing hardness, as confirmed by nano-indentation mapping.

The second part investigates aluminum-based composites reinforced with 316L and Ti6Al4V using LPBF. The aluminum component is fabricated through induction melting (AlSi10Mg) or squeeze casting (AlMg3). For induction melting, parametric optimization enables crack-free Ti6Al4V-AlSi10Mg composites with controlled interface width. However, in 316L-AlSi10Mg composites, ternary Al-Fe-Si intermetallics form regardless of processing parameters, causing cracking. With squeeze casting, minimizing the interface width between 316L and AlMg3 (below 10 µm) avoids cracking, although Fe-Al intermetallics still appear.

The final section explores LPBF-based 316L-CuCrZr bimetallic and functionally graded structures using varied compositional steps. The work emphasizes texture evolution, crack susceptibility, and ferrite formation in different 316L/CuCrZr ratios using Bragg Edge Imaging, Polarization Contrast Neutron Imaging, and electron microscopy (EBSD, EDS). A thermodynamic model is developed to explain ferrite (BCC) formation when mixing 316L and CuCrZr, particularly in ratios from 40:60 to 10:90 wt.% 316L:CuCrZr. In-situ synchrotron diffraction tracks the austenite-ferrite transformation during heating (up to 1000 °C) in 316L-CuCrZr mixtures. Additionally, real-time monitoring using airborne acoustic set-up analyzes melt-pool dynamics through laser back-reflections, with data trained via Convolutional Neural Networks.