Hydriding behaviour of FeTi and FeTi 1.15: Ease of activation and skipping of β region

Abstract

High pressure hydrogen absorption studies have been carried out on FeTi and FeTi 1.15. P-C-T absorption isotherms, X-ray diffraction and Mössbauer studies on virgin FeTi, subjected to a few activation cycles, clearly indicate the predominant conversion of the α to the γ phase. The role of post-activation annealing treatment and the variation of plateau pressure in the subsequent hydriding cycles, without any further heat treatment, are discussed in relation to β-phase stabilization. From the comparison of the hydriding behaviour of FeTi with FeTi 1.15, it can be seen that the difficulties associated with the activation of virgin pure FeTi can be related to its tendency for β-phase skipping. It is also shown that the ease of activation of FeTi 1.15 is not related to the weakening of Fe-Ti bonding, as suggested earlier, but arises because of the presence of an oxygen stabilized ternary phase which helps to lower the plateau pressure and facilitates the α to β conversion.