Exploration on the Effect of Pretreatment Conditions on Hydrogen-Induced Defects in Pure Titanium by Positron Annihilation Spectroscopy

Electrolytic hydrogen charging experiments on cold-deformed and well-annealed (annealing at 700 °C for 2 h) pure titanium samples were carried out, respectively. Positron annihilation spectroscopy and X-ray diffraction were used to characterize all experimental samples to explore the formation of vacancy defects and the storage form of hydrogen in pure titanium after charging. Results showed that hydrides formed in well-annealed samples after electrolytic hydrogen charging, but a new phase in the cold-deformed samples was not observed. The annealed samples formed vacancy-type defects in the process of electrolytic hydrogen charging, and the excess hydrogen atoms were easily trapped by vacancies to form a hydrogen vacancy complex (HmVn). The defects formed in the cold-deformed hindered the diffusion of hydrogen atoms and inhibited the formation of vacancies. Compared with the well-annealed electrolytic hydrogen charging samples, the S parameters of the deformed electrolytic hydrogen charging samples hardly changed. The coincidence Doppler broadening spectrum results showed that wide peaks related to hydrogen vacancy complexes were found in electrolytic hydrogen charging samples. The formation of hydride in titanium affected the positron annihilation environment in the low-momentum region. The hydride-related peak was observed only in the electrolytic hydrogen-charged samples after being well annealed.