First-Principles Estimation of Hydrogen Occupancy around Lattice Defects in Al

Abstract

Estimations of the fundamental relationship between hydrogen and lattice defects are important for understanding hydrogen embrittlement mechanisms and for predicting the amount of penetrating hydrogen. In this paper, hydrogen-trap energy around the lattice defects (e.g., atomic vacancy, stacking fault, grain boundaries, and free surfaces) within the Al lattice are calculated using first-principles calculations based on Generalized Gradient Approximation (GGA) and Ultra-Soft (US) pseudo potential. The hydrogen-trap energies obtained are 0.30 eV at the atomic vacancy, 0.002 eV at the stacking fault, 0.02 eV at the Σ3{111} Symmetrical Tilt Grain Boundary (STGB), 0.19 eV at the Σ3{112} STGB, and 0.45-0.60 eV at the free surfaces. Moreover, the hydrogen occupancies at the hydrogen-trap sites around the lattice defects are evaluated for several hydrogen gaseous environments using the obtained hydrogen-trap energies. Hydrogen occupancies around the lattice defects are extremely low under the pure hydrogen gaseous conditions. However, according to experimental data, hydrogen concentration can become higher for Al structures due to the hydrogen atoms generated by the surface oxidation process under a moist environment or other reasons. In such cases, the vacancy has a strong interaction with the hydrogen atoms.