Hydrogenation-induced microstructure changes in titanium

•Hydrogen induced microstructure changes in Ti studied by PL and DB spectroscopies.•Vacancies and vacancy clusters formed at concentration from 1.31 to 2.27at.%.•Cluster-hydrogen and vacancy-hydrogen complexes formed at concentration up to 32at.%. Microstructure changes of commercially pure titanium in a wide range of hydrogen concentrations from 0.8at.% to 32.0at.% were studied by means of positron lifetime spectroscopy and Doppler broadening spectroscopy. We have obtained new experimental data on the evolution of positron annihilation parameters τf, τd and their corresponding intensities If, Id, as well as relative changes of parameters S/S0 and W/W0 depending on the hydrogen concentration in commercially pure titanium after gas-phase hydrogenation at 873K. Results suggest that the hydrogenation of Ti samples up to concentrations of 1.31–2.27at.% and subsequent cooling to a room temperature leads to the formation of vacancies and vacancy clusters. Further increase of the hydrogen concentration up to 32.0at.% leads to the interaction of hydrogen with these defects and the formation of “cluster-hydrogen” and “vacancy-hydrogen” complexes.