Material- and geometry-driven thermal behavior of additively manufactured lattice structures: A comparative study of Invar 36 and Inconel 718

Dimensional stability under thermal stress is a critical requirement for high-value components used in aerospace, metrology and high-precision systems, where small thermally induced distortions seriously compromise performance. This work analyzes the thermal expansion behavior of additively manufactured lattice structures produced by Powder Bed Fusion–Laser Beam (PBF-LB), considering two materials with contrasting thermal responses: Invar 36 and Inconel 718. While Invar 36 is widely recognized for its near-zero coefficient of thermal expansion (CTE), Inconel 718 exhibits a conventional thermoelastic behavior, enabling a systematic comparison between material-driven and geometry-driven effects. A total of 32 specimens were designed, combining solid and lattice configurations with linear and rounded architectures, different numbers of solid external walls, and both as-built and machined conditions. Thermal expansion was experimentally characterized over the temperature range from − 170 °C to 400 °C, while the CTE was evaluated over selected temperature intervals to provide a robust comparison between materials and lattice configurations. The results show that the global thermal response is primarily governed by the material selection, with Invar 36 exhibiting a strongly temperature-dependent behavior associated with the progressive disappearance of the Invar effect, whereas Inconel 718 displays a stable and nearly linear response. An idealized finite element model (FEM) showed that the nominal lattice geometry alone does not modify global elongation, whereas the experimental specimens exhibited small configuration-dependent deviations. For the investigated strut-based lattices, lattice architecture and wall number had a secondary influence, whereas machining systematically reduced the thermal strain of Invar 36 lattices but not of Inconel 718. These findings indicate that such lattice structures can be implemented without significantly compromising dimensional stability, particularly when the material response is properly considered.