Mechanical properties of meteoritic Fe–Ni alloys for in-situ extraterrestrial structures

A critical requirement for outposts and settlements on the Moon and Mars is the use of in-situ resources to create pressurized, human-rated habitats with low mass (i.e., high tensile strength), high reliability (i.e., high toughness) and easy processability. This study assesses the capability of binary Fe–Ni alloys - with Ni content of 5–11 wt%, typical of M-type asteroids and iron meteorites - to meet these requirements. We measure the hardness and tensile properties of these Fe–Ni alloys at 21 °C in the as-cast state (representative of melted and cast meteorite material), with grain sizes of ∼90 μm. As the Ni concentration increases from 5 to 11 wt%, strength increases near linearly: from 260 to 440 MPa for the yield stress, and from 340 to 560 MPa for the ultimate tensile strength. Ductility however decreases, also near-linearly, from 20 to 3%. The yield stress of Fe-(5,7,9)Ni alloys, measured between −89 and 21 °C (relevant to the Moon and Mars), increases steeply with decreasing temperature. The temperature-dependence of the yield stress for these alloys - as well as pure Fe, Fe-1.4Ni and Fe-2.9 Ni alloys from literature - is fitted to an Arrhenius-like model, allowing to extrapolate yield stress values of Fe–Ni alloys for the full range of Lunar and Martian temperatures. A pressurized habitat consisting of flat plates of Fe–Ni alloy welded into a half cylinder (Quonset hut, with 5 m radius and 10 m length) is modeled via finite element analysis to determine the plate thickness (and thus alloy mass). For the above ∼400 m3 habitat with a 1 bar atm on the Moon or Mars, the thickness of the Fe–7Ni plates can be as low as 10 mm to prevent plastic deformation of the alloy. This plate thickness corresponds to 20–30 iron-nickel meteorites with ∼½ ton mass, as observed to exist on Mars by NASA rovers. This confirms the feasibility of using Fe–Ni meteorites - after in-situ collection, melting and casting – to create metallic sheets which can be welded into pressurized structures, at low energy and infrastructure costs.