Determination of the diffusion coefficient of hydrogen in gamma titanium aluminides during electrolytic charging Original Research Article

The diffusion coefficient of hydrogen in some gamma based titanium aluminide alloys was determined at room temperature using an electrochemical technique. A cast Ti–48Al–2Cr alloy as well as Ti–46.5Al–4(Cr,Nb,Ta,B) sheet material with primary annealed and designed fully lamellar microstructures were subjected to cathodic hydrogen charging at room temperature in the galvanostatic mode. The potential variation with time was monitored from which data the values of the diffusion coefficient of hydrogen, D were calculated from well known error function/infinite series solutions to Fick’s second law. Very good correlation was obtained with respect to theoretical calculations. The diffusion coefficients appear to be in close agreement with those for the cast alloy calculated from microhardness measurements. The value of D can be overestimated for thick specimens. Results show that neither the microstructure in terms of grain/lamellar colony size, nor the charging current density, appear to have a significant effect on the value of D. Lattice diffusion appears to be rate controlling.