Enhanced hydrogen embrittlement resistance of FeCoNiCrMn multi-principal element alloys via local chemical ordering and grain boundary segregation

Hydrogen embrittlement (HE), a persistent challenge for high-strength metallic materials, imposes severe limitations on their applications in hydrogen containing environments. Recent studies have revealed that FeCoNiCrMn multi-principal element alloys (MPEAs) exhibit exceptional HE resistance, offering transformative potential for next-generation structural materials. However, the atomic-scale mechanisms governing hydrogen-defect interactions in compositionally complex alloys remain elusive due to experimental limitations in tracking H atoms. To bridge this critical gap, we developed a deep-learning interatomic potential specifically tailored for FeCoNiCrMn-H systems, which enables large-scale molecular dynamics simulations that simultaneously resolve hydrogen migration, chemical ordering, and defect evolution at atomic resolution. The simulation results reveal a multi-mechanistic synergy driven by complex interactions between deformation twinning, local chemical ordered (LCO) structures, dislocations, and grain boundaries (GBs). Specifically, it is shown that H atoms can reduce stacking fault energy and thus promote deformation twinning. Meanwhile, LCO structures dynamically trap H atoms, forming LCOH complexes which exhibit a stronger dislocation pinning effect than the LCO structures alone. Moreover, Cr enrichment and Fe depletion at the GBs are found to increase GB fracture energy and reduce HE sensitivity. Collectively, these mechanisms contribute to the enhanced HE resistance of FeCoNiCrMn alloys. Our findings provide insights into the fundamental mechanisms underlying the exceptional HE resistance of FeCoNiCrMn alloys, and theoretical frameworks for designing MPEAs with superior mechanical properties to extend service life.