Mobility and retention of implanted hydrogen in Ti225 titanium alloy

The behaviours of implanted hydrogen in Ti225 alloy was investigated in this work. Hydrogen ion beam implantation was used to load hydrogen into the sample. Resonant nuclear reaction analysis (NRA) and elastic recoil detection analysis (ERDA) were applied to obtain the depth profiles of hydrogen versus implantation dose. Two kinds of hydrogen have been found in the samples, one is as quasi-mobile and another is chemically bonded hydrogen. Three hydrogen precipitation stages, which relate to the different chemical states of hydrogen, are determined. Using X-ray diffraction (XRD), the hydride phase transformation from solid solution in titanium to titanium hydride (TiH1) and then titanium dihydride (TiH2) tetragonal structure has been observed. The change is dose dependent in the implantation dose range between 2×1016 and 6×1017 H/cm2. The phase transformation from TiH1 to TiH2 occurs at an implantation dose greater than 1×1017 H/cm2 but finishes at a dose of 6×1017H/cm2 with the saturation of hydrogen concentration at approximately 23 at.%. The inhomogeneous planar distribution of the hydrogen was also observed using both scanning micro-probe ERDA and scanning electron microscopy (SEM).