dsorption, dissociation, penetration, and diffusion of N₂ molecules on Ti surface and in Ti bulk as well as the nitridation mechanism were investigated via first-principles calculations. The reaction process was divided into four steps and the mechanism for the determined reaction path was analyzed. We investigated the diffusion energy barrier in the reaction path of each step using the climbing image nudged elastic band (CI-NEB) method, and the entire reaction path was calculated as the minimum energy path (MEP). The calculated adsorption energies of N atoms and N₂ molecules show that nitrogen atoms and molecules are most stable at the HCP site on the α-Ti (0001) surface. Charge transfer provided theoretical support for N₂ dissociation. We calculated the diffusion energy barrier to the penetration from the HCP site on the α-Ti (0001) surface to the O site, which the N atom prefers to occupy. The diffusion coefficient is the highest when the diffusion path is from one O site, through the adjacent H site, to the next layer of O sites, while the energy barrier to diffusion is the highest, compared to those of other steps. Finally, we determined the rate-determining steps of the reaction pathway for the entire nitridation process. This study provides fundamental insight into the nitridation mechanism for N₂ molecules in titanium alloys.
 

第一性原理计算,渗氮,钛合金