Theoretical study of the insertion and diffusivity of hydrogen in the Ti3Al-D019 system: Comparison with Ti-hcp and TiAl-L10 systems

Abstract

Using first-principles calculations, the insertion and diffusivity of hydrogen in the Ti 3 Al-D0 19 system are presented and discussed. After a brief description of the properties of Ti 3 Al, the different sites of insertion are identified and discussed. The octahedral configuration surrounded by Ti atoms only (2a Wyckoff position) is found to be the preferred insertion site for H atoms. The second octahedral and the two tetrahedral sites are found significantly less stable than 2a sites. Phonon, electronic and elastic properties were computed to analyze the interactions between hydrogen and the metal. Results show that hydrogen atoms interact little with the metal. The insertion into a 2a site minimizes the elastic deformation and electronic transfer of surrounding atoms. The diffusion coefficient of hydrogen is then calculated and discussed by using DFT simulations, kinetic Monte-Carlo simulations and a multi-site approach. These results are compared with those of H diffusion into the Ti-hcp and TiAl-L1 0 systems.

Electrons Meet Alloy Development: A γ‐TiAl‐Based Alloy Showcase

“…They could show that all these species diffuse faster in the basal plane of γ‐TiAl than across the tetragonal axis direction. Qualitatively, the same result was obtained also from Connétable [ 102 ] who, in addition to γ‐TiAl, also studied H diffusion in hexagonal ‐TiAl and hcp Ti. Interestingly, the hexagonal structures exhibit faster diffusion along the hexagonal axis rather than in the basal plane.…”

“…All those results were shown qualitatively and also quantitatively to agree with experiments. [ 101,102 ] Zhao et al [ 103 ] showed that Nb increases migration barriers for bulk diffusion of O in γ‐TiAl and, hence, Nb improves poor oxidation resistance of the γ phase. For a comprehensive review on diffusion in the Ti−Al system, the reader is referred to publications of Mishin et al [ 104 ] or a more recent modeling‐based review of Xing et al [ 105 ]…”

“…All those results were shown qualitatively and also quantitatively to agree with experiments. [101,102] Zhao et al [103] showed that Nb increases migration barriers for bulk diffusion of O in γ-TiAl and, hence, Nb improves poor Figure 10. Polycrystalline elastic moduli (Young's, E, shear, G, and bulk, B) calculated using the VoightÀReussÀHill averaging method for γ-TiAl as a function of Zr content.…”