Effect of hydrogen on surface energy of fcc Fe alloys: A first-principles study

Aiming at revealing hydrogen (H) – materials interactions, the present theoretical work investigates the effect of H on the (111) surface energy (γ_s, and in actual fact the fracture free energy was studied herein) of Fe-rich fcc binary alloys Fe₃₅X and Fe₂₇X₉ and ternary alloy Fe₂₇Cr₉Ni₃, where X represents 31 alloying elements including Al, Co, Cr, Cu, Mn, Mo, Ni, V, W, and Zn. These γ_s values were predicted by density functional theory (DFT) based first-principles calculations using the nonmagnetic (NM, the present focus), ferromagnetic (FM), and antiferromagnetic (AFM) configurations. Correlation analysis reveals that the volume of X (V₀^X) is a predominant descriptor to model γ_s with γ_s∝1/V₀^X with the goodness-of-fit R² = 0.943 for the case of NM Fe₃₅X. It is found that hydrogen adsorption decreases γ_s, i.e., increasing H-coverage on the surface of fcc Fe alloys decreases γ_s nearly linearly for most alloys. We further found that γ_s increases initially and then decreases with increasing volume for each alloy, implying that for Fe alloys with less H-coverage, γ_s decreases with increasing temperature.