Microstructural evolution and formation mechanism of FCC titanium hydride in Ti–6Al–4V–xH alloys

The microstructural evolution and phase transformations in the hydrogenated (0–0.5 wt.%) Ti6Al4V alloy were studied to reveal the influence of hydrogen on the characteristics of titanium alloys. The crystallographic, microstructural and formation mechanism for hydride behavior were investigated. Conclusive evidences for the face-centered cubic (FCC) δ hydride phase formation were found in the Ti6Al4V alloy by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The δ hydrides could precipitate not only from the α phase, but also from the β phase. The formation mechanisms of the δ hydrides formed in both phases were established. The equilibrium phase transformation sequence for the hydrogenated Ti6Al4V alloy during cooling was presented.