Building habitats on the Moon is required for long-duration missions foreseen in the very near future. The availability of lunar regolith will allow to manufacture such in space habitats and reduce the cost of space missions. However, the Moon has specific environmental characteristics that are different compared to terrestrial habitats: meteoroids impacts, high cosmic radiation level and high temperature gradient, etc.

Functionally graded materials (FGM) are high-performance composite materials, featuring such advantages as localized tailoring of material properties, improved interfacial boundary compatibility, and enhanced thermomechanical behaviour. Much of the current in-situ resource utilization (ISRU) manufacturing research explores additive manufacturing (AM) of as-received regolith, with some consideration given to metal alloys extracted in-situ. This study combines these two aspects by investigating the feasibility of in-situ manufactured metallic-regolith FGMs.

In this study three regolith simulant powders were first characterized based on their similarity with the actual lunar regolith and then assessed further for their AM processability. Digital Light Processing (DLP), Spark Plasma Sintering (SPS) and laser scanning, were selected due to their compatibility with metallic-ceramic processing in a space environment. The chosen AM techniques were first assessed on their capability to effectively consolidate regolith alone, before progressing to AM of regolith directly onto metallic substrates.

The powder characterisation proved that all three simulants have composition and particle size distribution close to the ones of the actual lunar regolith. Powders are composed of plagioclase, pyroxene and iron titanium oxide. Dense regolith samples were successfully shaped with DLP and subsequently consolidated with Spark Plasma Sintering at 1050 °C under 80 MPa with crushed lunar regolith simulant. Optimized processing conditions based on the sintering temperature, initial powder particle size and different compositions in the lunar regolith powders were identified. The reduction of the particle size proved to be the most significant factor to obtain a good densification.

Additive manufacturing was then studied as a potential technique to manufacture functionally graded materials combining the properties of the lunar regolith and metals (Ti6Al4V and 316L). The combination of lunar regolith and Ti6Al4V was found as the most promising. The hardness profile showed a gradual transition between the two layers and the interface was found to be strong and without any cracking or delamination. Furthermore, interesting segregation effects at the interface regions were observed and investigated in this work.

Additionally, results from this study indicate that laser-based additive manufacturing techniques could be a feasible method for application of FGM coatings, which presents a topic for further study focused on wear, corrosion and thermal resistant in-situ resource coatings.

While the current study showed that it is feasible to AM FGMs from lunar regolith, further developments of a fully optimized method have the potential to produce tailored, high-performance materials in an off-earth manufacturing setting, for the production of aerospace, robotic, or architectural components.