Additive Manufacturing (AM) enables the fabrication of complex geometries that are difficult or impossible to accomplish using conventional manufacturing techniques. The emergence of Multi-material AM (MMAM) further extends these capabilities by integrating different materials within the same part. This opens up the opportunities for the design of mechanical metamaterials with tunable thermal expansion, which is of critical importance in high-precision applications, such as space systems and optical benches. The coefficient of thermal expansion (CTE) of these metamaterials can be tuned by combining two different materials within a specific lattice structure. In this thesis, the design, simulation, fabrication, and characterization of tunable CTE metamaterials, composed of Invar and Inconel 718, produced via bi-metallic laser-based powder bed fusion (PBF-LB) were investigated. The work was carried out within the framework of the SeRANIS project, which seeks to enable adaptive thermally stable structures for next-generation satellite systems. Firstly, a study was conducted to determine an optimal laser scanning strategy to be applied on vertical interfaces between the two materials. The quality of the interfaces was analyzed for the presence of defects and material intermixing, characterized by energy dispersive X-ray spectroscopy (EDS). Using optimized scanning strategies, metamaterials with tunable CTE based on triangular-shaped unit cells were printed. The samples included unit cells with different geometric parameters, matrices of combined unit cells and an actuator intended for a satellite experiment. The samples’ CTE were measured either by dilatometry or digital image correlation (DIC) and these values were compared with the finite element method (FEM) simulations used to predict the metamaterials’ CTE. Lastly, the structural integrity of the printed metamaterials was analyzed through tensile testing and thermal cycling to evaluate suitability for space applications. This thesis demonstrated the successful fabrication of Invar-Inconel 718 metamaterials with predictable and adjustable CTE. The optimized single scan strategy led to defect-free, metallurgically sound interfaces, showing that, in MMAM, process optimization must consider not only suitable parameters for each individual material, but also ideal scanning strategies at their interfaces. The triangular negative CTE metamaterials exhibited an experimentally measured CTE in close agreement with FEM simulations. The results indicated that metamaterial CTE can be tuned through geometric design, with the hinge stiffness identified as a key parameter, and material assignment within the lattice structure. By mitigating bulging effects, larger unit cell arrays provided a more representative metamaterial behavior than isolated unit cells. The integration of additional geometries for the satellite actuator did not significantly alter the thermal response. By combining positive and negative CTE unit cells, an overall CTE could be varied over a large range of values. Tensile tests confirmed that fracture occurred consistently in the weaker material (Invar), validating the interface strength. Thermally cycled samples did not fail or exhibit plastic deformation. Overall, this thesis establishes a design and manufacturing framework for tunable CTE metamaterials, reliable for space applications, with predictable thermal expansion behavior. Future possible directions for material selection, distribution, and geometric optimization were identified to further enhance the performance of these metamaterials.     «

Additive Manufacturing (AM) enables the fabrication of complex geometries that are difficult or impossible to accomplish using conventional manufacturing techniques. The emergence of Multi-material AM (MMAM) further extends these capabilities by integrating different materials within the same part. This opens up the opportunities for the design of mechanical metamaterials with tunable thermal expansion, which is of critical importance in high-precision applications, such as space systems and opt...     »