First-principles study of hydrogen diffusion in alpha Ti

Understanding the diffusion mechanism of hydrogen in titanium can give fundamental knowledge to reveal the mechanisms of thermohydrogen processing of titanium alloys. The diffusion characteristics of hydrogen along the C axis and in the basal plane of α-Ti were studied using the first-principles total-energy pseudo-potential method. For hydrogen diffusion in the basal plane, our calculations show that the indirect octahedral-tetrahedral-octahedral mechanism is energetically more favorable than the direct octahedral-octahedral mechanism and the calculated activation energy of 0.514 eV is in good agreement with the experimental data. For hydrogen diffusion along the C axis, the direct octahedral-octahedral mechanism is most favored and the calculated activation energy is 0.694 eV. The results indicate that there are different mechanisms and anisotropy for hydrogen diffusion along the C axis and in the basal plane of α-Ti.