Most of the materials found in nature present a positive coefficient of thermal expansion (CTE), meaning they expand as the temperature rises. However, components that are subjected to high temperature variations and still require high dimensional accuracy, such as earth observation satellites, would benefit from the use of materials with extremely low or even negative CTE. Some metamaterials proposed in the literature should be able to achieve negative values of thermal expansion by combining two materials with high CTE difference in a specific lattice structure. Due to their complex geometry, AM is the most suitable process to fabricate such metamaterials. Negative-CTE metamaterials have been simulated in the literature and works on polymer AM have corroborated the simulation results. However, AM of these complex structures using two different metallic materials, which would present higher stiffness than polymers, and broaden the applications for these metamaterials, hasn’t been widely investigated. Due to recent advances in the AM field, there are now technologies that allow a 3D metal multi-material Laser-Powder Bed Fusion process, which was used in this research.

In this work, additively manufactured negative-CTE metamaterials made out of two different material combinations were studied: (1) Invar + 316L stainless steel and (2) Invar + Inconel 718. The specimens were printed in an L-PBF machine equipped with a multi-material recoater by Aerosint, which enables the simultaneous deposition of two different materials during the L-PBF process. Different scanning strategies were studied in order to improve the quality of the interface between the materials. The CTE of the metamaterials was then evaluated by dilatometry and the results were compared with FEM simulations.