Insights into hydrogen-induced vacancy stability and creep in chemically complex alloys

TL;DR

This study uncovers the electronic-structure mechanisms by which hydrogen influences vacancy stability and creep behavior in various Fe-based alloys, highlighting differences between BCC and FCC structures.

Contribution

It introduces a comprehensive framework linking hydrogen-assisted vacancy stabilization to creep in complex Fe alloys using first-principles calculations and cluster dynamics.

Findings

H stabilizes vacancies at low content in BCC Fe

Higher chemical potentials are needed for vacancy stabilization in FCC Fe and Fe-Cr-Ni alloys

Plastic deformation is more affected by hydrogen in BCC Fe than in FCC alloys

Abstract

Hydrogen (H) content modifies the creep response of Fe-based alloys by altering thermodynamics of point-defects; here we identify the electronic-structure mechanism underlying this effect. Using spin-polarized first-principles calculations combined with a cluster dynamics formulation, we establish a general framework linking H-assisted vacancy stabilization to diffusion-mediated creep in BCC Fe, FCC Fe, and chemically complex FCC Fe-Cr-Ni alloys. H-vacancy binding analysis shows that H-stabilized vacancies form at low hydrogen content in BCC Fe but require much higher chemical potentials in FCC Fe and Fe-Cr-Ni alloys due to broader d-bands, electronic screening, and chemical disorder. Consequently, plastic deformation mediated by diffusive processes is expected to be far more strongly impacted in BCC Fe than in FCC alloys. These electronic-controlled trends determine steady-state vacancy populations and provide a symmetry-resolved microscopic basis for H-assisted creep in ferritic and austenitic steels.