Investigation of the hydrogen adsorption properties on titanium metal under vacuum conditions

Abstract

The lightweight nature and exceptional temperature resistance of titanium (Ti) render it a highly favored material for spacecraft applications. However, Ti is susceptible to various corrosion phenomena, particularly hydrogen embrittlement, which can significantly impact the functionality and lifespan of spacecraft. As experimental methods encounter challenges when investigating the internal mechanism of rapid-onset hydrogen embrittlement, we employ a molecular dynamics approach to explore the adsorption, diffusion, and dissociation behavior of hydrogen atoms and molecules (H/H₂) on Ti metal surfaces and oxidation products. The adsorption energies of the four bound forms, H-Ti, H-TiO₂, H₂-Ti, and H₂-TiO₂, during adsorption are 7.577 eV (hcp), 0.608 eV (bridge), nearly 0 eV, and 0.1127 eV (bridge), with maximum energy barriers for diffusion/dissociation of 1.045 eV, 2.694 eV, 0.3735 eV, and 2.612 eV, respectively. Thus, Ti metal readily undergoes chemical adsorption with hydrogen atoms while promoting dissociation of molecular hydrogen on its surface. Consequently, hydrogen adsorption onto the Ti metal surface and subsequent entry of hydrogen atoms into its bulk structure are enhanced, ultimately increasing susceptibility to hydrogen embrittlement. However, adsorption is limited once Ti metal oxidizes to form a protective surface layer of TiO₂ due to reduced reactivity at the oxide–metal interface.