Hydrogen diffusion coefficients in the titanium alloys IMI 834, Ti 10-2-3, Ti21S, and alloy C

The diffusion coefficients of hydrogen were determined for three beta titanium alloys, which differ in the stability of the beta phase, and, for comparison, for one near-alpha titanium alloy in the temperature range from 40 degrees C to 500 degrees C. For this purpose, a step hydrogen concentration profile was produced by charging one side of rods of these materials with hydrogen by means of an electrochemical technique. After subsequent diffusion annealing, the hydrogen concentration profiles were determined analyzing small discs cut from these rods. The corresponding diffusion coefficient was calculated by adapting its value in such a way that a numerical diffusion simulation yields the experimentally determined profile. In all cases studied, the hydrogen diffusion coefficient was found to be independent of the hydrogen concentration and showed an Arrhenius-type temperature dependence. Hydrogen diffusion in alpha titanium was slower as compared to the beta titanium alloys under investigation. Furthermore, the diffusion coefficient of the metastable beta titianium alloys is only slightly affected by the prior heat treatment that determines the morphology and volume fraction of the precipitated alpha phase.