Hydrogen redistribution in titanium due to bending stress studied by micro ERDA

The influence of bending stress on the hydrogen behaviour in titanium was investigated by elastic recoil detection analysis with a heavy ion microbeam (micro ERDA) and X-ray diffraction (XRD). The samples were made by hydrogen ion implantation into polished pure titanium sheets. Three-dimensional hydrogen distributions were obtained by scanning the microbeam over the sample using the depth information of ERDA. Inhomogeneous hydrogen distributions in the titanium were observed which vary with the depth. With mechanical bending of the samples the inhomogeneities increased in varied grade. The surface hydrogen loaded by surface polishing is stable, whereas the implanted hydrogen located inside of the sample is mobile under bending. These different hydrogen behaviours are relevant to the chemical states of hydrogen. Different titanium hydrides are formed by the different loading methods. An relatively unknown titanium dihydride phase (TiH2(x)) with a tetragonal texture was identified by XRD in the depth region of implanted hydrogen. It is less stable than the normal titanium-dihydride phase (TiH2(d)) observed in the surface region. The change of hydrogen distribution is related to the dehydrogenation of the TiH2(x) and TiH(g) under bending.