Effect of temperature and pressure on hydrides and microstructure in grade 2 titanium subjected to hydrogen gas

The formation of hydrides plays a key role in hydrogen embrittlement of titanium and is strongly influenced by the material's composition, microstructure, and the mode of hydrogen charging. In the present study, experimental investigations were conducted on a single-phase α-titanium alloy (Grade 2) subjected to gaseous hydrogen charging at temperatures ranging from 300 to 500°C, under pressures of 3 or 30 bar for 6 hours. A wide range of hydrogen concentration was obtained, with overall homogeneous hydrides distribution through samples thickness, permitting to characterize hydrides features under severe conditions preceding hydrogen embrittlement. Although temperature is the main parameter governing the hydrogen content, the influence of pressure was also clearly observed. Both δ and γ hydrides were identified under all charging conditions. The evolution of lattice parameters were determined from X-ray diffraction (XRD) measurements, extending available literature data up to approximately 7500 wppm. From SEM-EBSD investigations, the effect of grain orientation on hydride nature and morphology was detailed, and the main observed ORs between hydrides and matrix were found to differ from those known at low hydrogen concentration. • A wide range of overall hydrogen concentrations achieved through simultaneous gas hydrogen charging under pressure and temperature • Identification of δ, γ and ε hydrides as a function of hydrogen concentration • Evidence of the influence of crystal orientation and grain boundaries on hydride distribution • Effect of hydrogen on lattice parameters up to 7500 wppm