Tailoring the Coefficient of Thermal Expansion of Selective Laser Melting Invar 36 via Post-processing Heat Treatments

The thermal and mechanical behavior of SLM-fabricated Invar 36 was investigated as a function of process parameters and post-processing heat treatments commonly applied in aerospace applications. Density exhibits a non-monotonic dependence on volumetric energy density (VED), reaching a maximum at 52.08 J mm−3, with deviations leading to increased porosity. Yield strength, ultimate tensile strength, and elongation at break are largely insensitive to process parameters, although elongation shows a weak maximum near the optimal VED. The coefficient of thermal expansion (CTE) increases by over an order of magnitude from 20 to 350 °C. One heat treatment was found to optimize CTE, producing nearly identical behavior to the as-built specimens, while the other two treatments result in systematically higher CTE, on average 65% larger, leading to an accumulated thermal strain over the same temperature range about 15% higher. Hardness decreases under all heat treatments, reflecting stress relief and microstructural recovery. These results provide guidance for controlling density, thermal expansion, and mechanical performance of SLM Invar components for thermally demanding applications.