Grain boundary-specific effects of Mn concentration on hydrogen trapping and embrittlement in bcc Fe: A spin-polarised DFT study
Year: 2026
Type: article
Abstract: Hydrogen embrittlement limits the performance of ferritic steels in liquid-hydrogen environments, where hydrogen-enhanced decohesion (HEDE) dominates due to reduced hydrogen mobility. Using spin-polarised density functional theory, we quantify how manganese (Mn) modifies hydrogen solution, segregation, and cohesion at two representative bcc Fe grain boundaries: the high-angle Σ5(013)[100] (Σ5) and the coherent-twin Σ3(1-12)[110] (Σ3). At Σ5, Mn induces a coverage-dependent reversal in hydrogen energetics: low coverage weakens intrinsic trapping, intermediate coverage deepens traps beyond those of pure Fe, and full coverage eliminates deep traps and renders hydrogen (H) insertion thermodynamically unfavourable. Charge-density-difference maps reveal corresponding transitions from diffuse to strongly localised Mn–H–Fe interactions, followed by electronic passivation at full Mn coverage. At Σ3, Mn monotonically suppresses H trapping without producing intermediate stabilisation regimes. Magnetic effects are restricted to Mn located at the GB plane. In all cases, Mn increases intrinsic cohesion, and at Σ5 high Mn coverage partially restores cohesion in the presence of H. These results reconcile conflicting literature reports and show that Mn is neither universally embrittling nor beneficial; its effect depends on boundary structure, concentration, and site occupancy. High Mn coverage suppresses H trapping and improves GB resistance, while intermediate coverage deepens traps and reduces cohesion at boundaries.
Source: Materials & Design
Language: English
Subfield: Metals and Alloys
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,650
OpenAlex ID: W7213291086