Effect of hydrogen concentration on various properties of gamma TiAl

Theoretical study on hydrogen solubility and diffusivity in the γ-TiAl L10 structure

“…For some (unacceptable) jumps, results indicate a high migration energy ranging from [0.96e1.14] eV. One of these values could correspond to the value found by Wang [17], which is 0.9 eV.…”

“…Regarding tetrahedral sites, there are three different positions: 4n, 4m and 4i sites. It can be noted that, contrary to what Chen [15] and Wang [17] concluded, there are more than two octahedral sites and one tetrahedral site. The insertion of interstitial elements in the TiAl-L1 0 system is thus more complex than expected.…”

“…The other positions on faces (2e) and edges (1b and 2f) of the super-cell box are less stable, at least 400 meV higher in energy than the 1c position. Wang's results [17] indicate that O 1 is more stable than O 2 (0.350 eV) and T (0.209 eV). As far as position is concerned, we can say that our results are in good agreement with Wang's.…”

“…The main difficulty is to describe how H atoms can diffuse in an energy landscape such as the one generated by the TiAl crystal. Wang [17] studied the diffusion of H in TiAl. As explained previously, it is difficult to determine the exact position from his simulations.…”

“…Authors show that H insertion should happen in octahedral sites, but they do not indicate and describe which insertion sites. In terms of diffusivity data, Wang [17] only studied a few migration mechanisms but didn't compute diffusion coefficient values.…”