PSI - Issue 68

D.M. Tshwane et al. / Procedia Structural Integrity 68 (2025) 39–46 D.M. Tshwane et al. / Structural Integrity Procedia 00 (2025) 000–000

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1. Introduction The titanium alloy material remains the most promising material for various applications such as gas turbines, energy, chemical, and biomedical industries due to its unique and remarkable strength-to-weight ratio (Banerjee and Williams, 2013). However, effects of corrosion and hydrogen embrittlement (HE) remain crucial and key factors in material failure and limitation (Wang et al., 2023). The HE of the material is the result of the hydrogen atoms' interaction with the surface, quickly penetrating the matrix and building up near the fracture tip. The primary cause of the stress corrosion crack of the alloy is HE, which significantly reduces the components of the useful life of the titanium alloy (Gutelmacher and Eliezer, 2005). This significantly reduces the service life of titanium-composite components. A great deal of work has gone into characterizing and comprehending reaction mechanisms between titanium alloy and HE (Wang et al., 2023). These mechanisms were generally indirectly inferred from the experimentally characterized fracture surface. Hydrogen is the lightest element in nature, making it difficult to examine its atomic processes directly, and moreover, it is difficult to capture the static distribution of solute hydrogen and hydrides through experiments (Chang et al., 2018). On the other hand, titanium has a strong affinity for hydrogen and can absorb it in large amounts, needless to say high hydrogen concentrations lead to the formation of titanium hydrides. Essentially, titanium hydrides occur when there is a high content of hydrogen (Gutelmacher and Eliezer, 2004). The TiAl 6 V 4 alloy's response to hydrogen penetration and embrittlement varies depending on its microstructural condition (Deconinck et al., 2023). The production of brittle hydride causes the TiAl 6 V 4 alloy's tensile characteristics to deteriorate, including loss of ductility and a decrease in the critical stress intensity factor (Wu et al., 2023). Previously, first-principle density functional theory (DFT) calculations were conducted to better understand the behaviour of hydrogen when interacting with titanium alloys (Olsson et al., 2016; Hu et al., 2002). The increasing hydrogen coverage mostly reduces the interaction distance of the interplanar potential, indicating hydrogen-induced bond weakening in the material. In addition, it was reported that hydrides with a higher hydrogen concentration have higher unstable stacking fault energies on densely packed planes. In addition, it was demonstrated that the hydride surface energy depends sensitively on the H coverage, with the lowest values observed for surfaces completely coated with H. Olsson et al . (2016) reported that the H coverage has a significant impact on the (001) surface energy and deduced that hydrogen transport to the separation zone may also have an impact on the decohesion process (Olsson et al., 2016). In another study, Xie et al . (2014) examined the adsorption locations and adsorption energies of H 2 molecules on the Fe (110) surface at hydrogen coverage levels ranging from 0.125 to 1.0 monolayer. The study reported that the hydrogen adsorption process on the Fe (110) surface is mostly unaffected by coverage. Kresse (2000) examined the parallels and discrepancies between hydrogen adsorption and dissociation on the surfaces of Ni (111), (100) and (110) to understand the function of hydrogen on Ni metal, and it was found that the top site is the most preferable. First-principles calculations on the interaction between hydrogen and surface play a critical role in gaining valuable insights on titanium embrittlement mechanisms. Using DFT method, Wang et al . (2023) demonstrated that H atoms are more likely to adsorb on the titanium surface and subsequently accumulate below it, and H atoms also require energy to diffuse into bulk and to desorb to generate H 2 . As the H coverage increases, the surface energy falls, reducing the work of the titanium fracture. Again, first-principles calculations were used to examine hydrogen adsorption on the surfaces of HCP Ti (0001), FCC Al (111), and ꝩ-TiAl (100) (Wang and Gong, 2014). The study compared the adsorption energy of hydrogen and the diffusion energy barrier between different sites to determine the most energy efficient adsorption site and optimal diffusion channel. The interaction between the H and the TiAl surface was greater and required less heat to generate hydrogen, compared to the interaction between the H and the bulk TiAl (Wang and Gong, 2014). To the best of our knowledge, there are no reported studies of H 2 adsorption on the TiAl 2 V surface, specifically to elucidate hydrogen embrittlement mechanisms. Furthermore, there are limited studies on the effect of Van der Waals (vdW) forces on H 2 molecule adsorption on alloys. Consequently, there are no studies on the effect of vdW on H 2 adsorption on TiAl 2 V. Among the few reports based on single atom alloys, the details of the adsorption and dissociation of H 2 molecules on the low Miller index Cu surfaces (111), (100), and (110) as well as two distinct surface of Cu nanorows were reported by Álvarez-Falcón et al. (2016). The study revealed that the Van der Waals forces play an important role in characterizing H 2 molecule adsorption on Cu alloys. In this current work, the first-principle density functional theory is employed to investigate the interface of Ti 2 AlV surface with the hydrogen molecule to elucidate