Influence of interactions between hydrogen and (101¯2) twin boundary on hydrogen embrittlement in α-Ti

Ti and Ti alloys are used in several areas thanks to their good mechanical properties, however, the large affinity of hydrogen during industrial application would limit their service life. This study serves as a comprehensive investigation of the embrittlement effects induced by additional hydrogen in detail by means of first-principles calculations with the Pseudopotential Plane-wave method within the framework of the Rice-Wang thermodynamic model. The existence of the twin boundary markedly influences segregation energy, the activation barriers for diffusion between sites, and intergranular embrittlement. We demonstrate that segregation energy and the barriers in the region near the boundary are consistently lower than in bulk, indicating that the sites located at the boundary are more attractive to hydrogen than bulk. Further, the intergranular strength of a Ti grain boundary is reduced with hydrogen segregation. An analysis in terms of the relaxed atomic and electronic structures and bonding characters shows that the weakening effect of hydrogen is due to the breaking of the interfacial Ti-Ti bonds, which significantly decrease twin boundary adhesion and its resistance to cracking.