Scale-Up, Mechanical Evaluation, and Hardware Demonstration of the NASA HR-2 Superalloy Fabricated by Laser Powder Bed Fusion for Hydrogen-Sensitive Liquid Rocket Engine Applications

NASA Hydrogen Resistant-2 (HR-2) is a γ′-strengthened Ni-Fe-based superalloy developed for additive manufacturing of liquid rocket engine (LRE) components exposed to hydrogen environments. This study advances laser powder bed fusion (L-PBF) HR-2 from laboratory-scale material development toward system-relevant hardware demonstration through process scale-up, heat-treatment optimization, fatigue evaluation, hydrogen-environment testing, and fabrication of representative RS-25 turbomachinery components. L-PBF HR-2 demonstrated robust printability with low porosity and a stable processing window, while optimized heat treatment achieved the 95-ksi yield-strength requirement. HR-2 also exhibited excellent cryogenic tensile performance, with simultaneous increases in strength and ductility in liquid hydrogen. Tensile testing in 5-ksi gaseous hydrogen resulted in only minor changes in strength and no significant loss of ductility, confirming strong resistance to hydrogen environment embrittlement. High-cycle fatigue testing showed favorable fatigue resistance, with crack initiation primarily controlled by crystallographic slip rather than manufacturing defects. Process scale-up from the EOS M100 to the EOS M290 enabled successful fabrication of representative RS-25 hardware, including a lift-off seal housing, single-piece rotor, and mixer. The lift-off seal demonstrated reliable fabrication of small unsupported internal channels (~2.8 mm diameter) with excellent densification and dimensional fidelity. Overall, the results demonstrate that L-PBF HR-2 combines robust manufacturability, high mechanical performance, excellent hydrogen resistance, and the capability to produce complex, production-scale LRE hardware, providing a strong foundation for further qualification and implementation in hydrogen-sensitive propulsion applications.