Hydrogen behavior in Ti surface nitridation: Hydrogen as an active component catalyzes the nitridation reaction

Abstract

Typically, H₂ is introduced into the nitriding atmosphere to enhance the efficiency of metal surface nitridation. However, the role of hydrogen as an active species in catalyzing the reaction is still uncertain. Here, we present the nitridation mechanism of pure titanium(Ti) surface (hexagonal, α phase) with and without H atoms(H) based on first-principles calculations of surface nitrogen adsorption, dissociation and penetration. First, the adsorption characteristics of N atoms(N) and N₂ molecules(N₂) and the system energy indicate that FCC and HCP are favorable adsorption sites. In contrast, the adsorption stability of N on H-containing surfaces shows higher trend. Second, the minimum energy path (MEP) study results based on the climb image nudged elastic band (CI-NEB) method show that H increases the efficiency of dissociation and penetration processes. A linear relationship exists between hydrogen concentration and the N penetration energy barrier. In addition, electronic structure calculations theoretically support H regulation of surface nitridation efficiency. The nearby H reduces the energy barrier for the dissociation of N₂ and the penetration of N by enhancing the interaction between N and surrounding Ti. This study provides theoretical support and new insights into the microscopic mechanism of H regulating the nitridation reaction of the Ti surface.