Hydrogen–Dislocation Interactions at Cryogenic Temperatures: Serrated Yielding and Embrittlement Resistance in High-Strength Austenitic Alloys

Comprehensive studies of hydrogen embrittlement in high-strength austenitic alloys under cryogenic conditions are scarce, leaving the combined effect of hydrogen charging and extreme temperatures largely unexplored. Given the demands of cryogenic applications such as hydrogen storage and transport, understanding material behavior under these conditions is crucial. Here, we present the first systematic study of hydrogen's effect at liquid helium temperature (4.2 K) on the mechanical properties of precipitation hardened austenitic alloys, specifically the nickel-based Alloy 718 and austenitic stainless steel A286. Both materials were subjected to pressurized hydrogen charging at 473 K followed by slow strain rate tensile testing at room temperature and at 4.2 K. Hydrogen charging caused significant ductility loss at room temperature in both alloys. In contrast, testing at 4.2 K resulted in increased strength and no evidence of hydrogen embrittlement. Notably, materials pre-charged with hydrogen and tested at 4.2 K exhibited higher stress drop amplitudes and increased strain accumulation during serration events, suggesting persistent hydrogen-dislocation interactions and possible enhanced dislocation pinning by obstacles such as Lomer-Cottrell locks. These results indicate that while hydrogen influences plasticity mechanisms at cryogenic temperatures, embrittlement is suppressed, providing new insight into the safe development of austenitic alloys in cryogenic hydrogen environments.