Abstract
Metallic materials for aerospace and liquid hydrogen technologies need to maintain high strength and ductility under cryogenic conditions. However, conventional strengthening strategies typically increase defect density and promote strain localization, resulting in a strength-ductility trade-off. This limitation becomes more critical at ultralow temperatures, where it facilitates discontinuous plastic flow and abrupt stress drops, substantially increasing the risk of premature failure. Here, a Co_(36)Ni_(46)Mo_(11)Al_7 medium-entropy is devel- oped, exhibiting an exceptional combination of tensile strength (2.1 GPa), high ductility (48%), and remarkably low stress drops of ≈99 MPa at 4.2 K. This bal- ance is enabled by two key mechanisms: enhanced lattice friction through com- positional tuning and the introduction of coherent L1_2 nanoprecipitates. These features effectively impede dislocation motion while promoting Hirth lock formation, thereby suppressing strain localization. Crucially, cryogenic loading- unloading-reloading tests, rarely performed at 4.2 K, reveal low back stress, directly indicating minimal dislocation accumulation despite the high strength. The findings highlight how dislocation-precipitate interactions can decouple strength from back stress accumulation, enabling a rare combination of ultra- high strength and suppressed discontinuous plastic flow. This approach estab- lishes a robust alloy design strategy for overcoming the long-standing conflict between strength, ductility, and mechanical stability in cryogenic environments.
NETL
NSTL
Wiley