DFT study of hydrogen and helium defects at the (112̄1) twin boundary in hcp scandium

We have investigated the grain boundary energy of ([Formula: see text]) twin boundaries, the formation energies of hydrogen (H) and helium (He) defects in tetrahedral (T) and octahedral (O) interstitial sites at the ([Formula: see text]) twin boundary in hcp scandium (Sc) by first-principles calculations based on density functional theory. It is found that the formation energies of the tetrahedral and octahedral interstices H, and tetrahedral interstice He increase significantly towards the ([Formula: see text]) twin boundary plane, while the formation energy of the octahedral interstice He atom near the ([Formula: see text]) twin boundary plane decreases. To analyze these results, we present the electronic densities of states (DOSs) of H, He and their nearest-neighbor Sc (NN-Sc) atoms in several tetrahedral and octahedral configurations. We have also calculated the formation energies of He-vacancy clusters (He[Formula: see text]V) in the Sc grain boundary, which indicates the stabilities of He[Formula: see text]V clusters depend on the variations of the relaxed vacancy volume near the ([Formula: see text]) twin boundary plane.

First-principles study of hydrogen diffusion in transition metal palladium

By adopting the first-principles total energy calculations based on density functional theory (DFT), the diffuse pattern and path of hydrogen in bulk palladium are investigated by calculating the system energy of hydrogen atom occupying different positions in palladium crystal lattice. The results indicate that the most stable position of hydrogen atom in palladium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. Hydrogen diffusion along the indirect octahedral–tetrahedral–octahedral (O–T–O) path is energetically most favorable in transition metal palladium, and the activation energy is 0.5245 eV.

Modeling of Orientation Dependence of Critical Resolved Shear Stress and Deformation Mechanisms on Yield Point of Austenitic Stainless Steels Hardened by Interstitial and Substitution Atoms

The proposed dislocation model describes the orientation dependence of the critical resolved shear stress (CRSS) and deformation mechanisms on the yield point in single crystals of austenitic stainless steel with nitrogen impurities. The model takes into account the following: the change of the interstitial atom position in the lattice from octahedral interstice to tetrahedral site owing to passage of a leading Shockley’s partial dislocation; the change in the separation width between two partial dislocation in external stress field; the relationship between the width of the extended dislocation and the elastic interaction of the extended dislocation with the impurity atoms.

Site preference of alloying elements in Fe3Al-based alloys

On the basis of the first principle interatomic potentials, the site preference of various alloying elements in Fe3Al were evaluated for Ti, Si, Ni, Mn, Mo, and Cr, respectively. The calculated results of the substitutional distribution were in good agreement with the experimental results. Moreover, the calculated results showed that H atoms in Fe3Al prefer to occupy the Fe-type octahedral interstice on the surface, which resulted in concentration of H atoms on the surface. Cr addition decreased the absorbability of Fe3Al-based alloys for H atoms and the force to drive H atoms segregating to surface. The concentration of H atoms on the surface can be decreased by Cr addition.