Effect of TiO2 on hydrogen trapping and diffusion at grain boundaries in Cr2O3-based coatings: experimental and first-principles studies

The lifespan of pipelines exposed to hydrogen environments over an extended period can be significantly reduced due to hydrogen embrittlement, and there is a potential risk of hydrogen-induced cracking. Currently, the most effective method is to incorporate a hydrogen permeation barrier layer on the inner surface of the pipelines. Therefore, this paper employs plasma spraying technology to prepare Cr₂O₃ and Cr₂O₃–10%TiO₂ hydrogen permeation barrier coatings and combines first-principles calculations based on density functional theory to explore in depth the synergistic effects of Cr₂O₃ and TiO₂ on hydrogen permeation resistance. Experimental results indicate that the doping of TiO₂ not only significantly enhances the surface smoothness of the coating but also effectively reduces pore defects. This improvement directly prolongs the time required for hydrogen atoms to penetrate the coating and decreases the hydrogen permeation current density, thereby greatly enhancing the hydrogen barrier performance of the coating. Furthermore, first-principles calculations reveal that the hydrogen permeation resistance mechanism of the composite coating primarily relies on two core aspects: on the one hand, its dense crystalline structure and stable chemical bond structure effectively hinder the adsorption process of hydrogen atoms on the coating surface, slowing down the permeation rate of hydrogen atoms. On the other hand, once hydrogen atoms successfully penetrate the interior of the hydrogen permeation barrier layer, they are trapped by interstitial sites and vacancies within the coating, effectively preventing further diffusion of the hydrogen atoms.