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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3. Results and discussion 3.1. Adsorption energy

The impact of hydrogen on the Ti 2 AlV (110) surface was examined through adsorption at various surface sites, namely, the top (Ti, Al, and V atoms), the bridge that connects two atoms, and hollow sites, which have been selected as potential adsorption locations. The H atom is positioned at multiple locations on the surface, and geometry optimization was used to determine adsorption stability. Once adsorption stability is achieved, the adsorption energy, which is a crucial element that leads to the determination of the interaction strength is calculated using Eq. 1. Fig. 2 (a) presents hydrogen adsorption on the Ti 2 AlV (110) surface at different adsorption sites (top, bridge, and hollow) obtained employing DFT and DFT-D . The dispersion term (long-range van der Waals interactions) was considered because it has been observed to have a significant influence on the estimations of adsorption energies (Grimme et al., 2011) . The current results revealed that every adsorption energy was found to be negative, suggesting an exothermic mechanism and spontaneous reaction. A stronger interaction between the adsorbent and the substrate is indicated by a higher negative value of the adsorption energy. More importantly, the effect of Van der Waals forces and dispersion correction was observed for all the adsorption sites, with all the adsorption energies strength for !) "* # +,) > !) "* # + . The calculated adsorption energy of H on the surface ranges from -3,623 to -5,110 eV and -3,963 to -5,289 eV for DFT and DFT-D, respectively. This suggests that standard DFT underestimates the adsorption energy while the DFT-D increases the accuracy of the calculated adsorption energy. The average adsorption energy difference between the DFT and DFT-D is approximately 0,036 eV. Additionally, it was discovered that the estimated adsorption energies differ with the adsorption surface sites, with Ti-V bridge site having the highest adsorption energy !) "* # + = -5,110 eV and !) "* # +,) = -5,289 eV and the hollow site showing the lowest adsorption energy strength of !) "* # + = -3,623 eV while for !) "* # +,) = -3,963 eV. This suggests that HE on the Ti 2 AlV (110) surface will occur mainly via the Ti-V bridge site, while the hollow site shows weak adsorption. Furthermore, when adsorption on top of different atoms was compared, it was discovered that the Al element is more resistant to H adsorption than the Ti atom. This further suggests that relatively high energy will be required to remove or detach a hydrogen atom from the Ti 2 AlV surface when adherent to Ti and V atoms, and less energy is needed to remove it from the Al site. This is consistent with previous report by Wang and Gong (2014) on the investigation of H adsorption on TiAl surfaces. According to Gutelmacher and Eliezer (2004), Ti has a great affinity for hydrogen, allowing it to absorb a large amount of the H atom.

(a)

(b)

Fig. 2. (a) Depiction of hydrogen adsorption on Ti2AlV (110) surface at different adsorption sites, i.e., top (Ti, Al and V), bridge (Al-V, Ti-Ti and Ti-V) and hollow sites and (b) depicts the coverage adsorption per hydrogen atom on the Ti2AlV (110) surface.