A 3D-Printed SFE-Graded Alloy Mitigates Cryogenic Discontinuous Plastic Flow and Hydrogen Embrittlement

The lunar polar permanently shadowed regions, rich in water ice for hydrogen production, impose a trade-off in FCC alloys: lowering stacking-fault energy (SFE) enhances hydrogen embrittlement resistance but exacerbates cryogenic discontinuous plastic flow (DPF). To address this, we designed and fabricated via additive manufacturing a compositionally graded (CoCrMn)_{100 - 2 x}Fe_xNi_x alloy with a single-phase FCC structure. Guided by thermodynamic calculations and first-principles predictions, the gradient-structured build exhibits spatial SFE and microstructural gradients. Quasi-static tensile tests from 298 K down to 20 K reveal significant strengthening with retained high ductility, while DPF is strongly suppressed, showing only minor stress drops. Mechanistically, the graded architecture partitions deformation: high-SFE regions promote dislocation glide and cellular substructures, whereas low-SFE regions enable planar slip and deformation nanotwinning, delocalizing strain and suppressing avalanche-like dislocation activity. Under hydrogen charging at 298 K, embrittlement resistance is preserved via a dual mechanism combining deformation-induced nanotwins and a Mn concentration gradient. This synergy balances dislocation mobility and hydrogen trapping, offering a new paradigm for simultaneous improvement of cryoplasticity and hydrogen compatibility. Our work establishes a multidisciplinary design strategy for alloys targeting extreme hydrogen and cryogenic environments.