Hydride Precipitation in Vanadium Studied by the Internal Friction Technique at High Frequency

The presence of hydrogen in the metals of group Va, niobium tantalum and vanadium gives rise to an abrupt increase of the curve of elastic energy dissipation vs temperature when the coexistence curve betwe.ep the solid solution(~-phase and the precipitated E-phase is crossed on first cooling. This inflection in the Q- curve is often followed by a maximum which was generically called the "precipitation peak" (1-5). The phenomenology of the peak presents complex features which are not yet satisfactorily understood. In addition, remarkable differences in its behaviour constantly appear whenever results from the three different metals or from different frequencies are compared. The origin of the precipitation peak is not understood at present and two main mechanisms have been proposed; the interaction between hydrogen (deuterium) and the dislocations generated by the misfitting precipitates (3-5), and the damping connected with the anisotropic growth or dissolution of precipitates (6,7). The present investigation concerning the V-H system aimed at clarifying the influence of vibration frequency on the phenomenology associated with precipitation. Attention has also been devoted to the consequences of mechanical deformation on specimens undergoing precipitation.