Hydrogen solubility in hcp titanium with the account of vacancy complexes and hydrides: A DFT study

[Display omitted] •Vibrational free energies of hydrogen solid solution and titanium hydrides are calculated.•Solubility of hydrogen in titanium is predicted.•The influence of hydrogen on concentration of H-vacancy complexes is estimated. The saturation solubility of hydrogen with respect to titanium hydrides, and the concentration of H-vacancy complexes in α-Ti are predicted on the basis of a thermodynamic model and ab initio calculated free energies. The presence of hydrogen increases the vacancy complex concentration by several orders of magnitude, with most of these complexes containing three H atoms. We show also that the solubility of hydrogen within the titanium is strongly influenced by the temperature-dependent free energy terms, and that by including these terms in the thermodynamic model it is possible to obtain good agreement with experiment.