A new Ti/H phase transformation in the H2+ titanium alloy studied by x-ray diffraction, nuclear reaction analysis, elastic recoil detection analysis and scanning electron microscopy

The titanium hydrogenation process in the H2+ implanted Ti225 titanium alloy has been studied in this work. The Ti/H phase transformation from hydrogen solid solution (hcp) to gamma phase titanium hydride (TiH(γ)) with a primitive tetragonal structure and then to a titanium dihydride (TiH2(x)) with a body centred tetragonal structure has been characterized by x-ray diffraction, nuclear reaction analysis and elastic recoil detection analysis. This process is very different from the usual hydrogenation mechanism, in which the delta phase titanium dihydride (TiH2(δ)) with a face centred cubic structure is always involved. Both of the TiH(γ) and TiH2(x) are rare phases, which are formed under extreme conditions. The TiH(γ) was considered to be a metastable phase in low hydrogen concentration titanium, and the TiH2(x) phase has not yet been notated in the present Ti/H phase list. The characteristics of the TiH2(x) are unclear, but it is very stable at room temperature and exists as a mixture state with the titanium. A saturated fraction of the hydride to titanium phase has been obtained as about 15% (H/Ti ∼ 0.3) in a H2+ implanted sample