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

The diffusion coefficient of hydrogen in some gamma based titanium aluminid e alloys was determined at room temperature using sn electrochemical techni que. A cast Ti-48Al-2Cr alloy as well as Ti-46.5Al-4(Cr,Nb,Ta,B) sheet mate rial with primary annealed ans designed fully lamellar microstructures were subjected to cathodic hydrogen charging at room temperature in the galvano static mode. The potential variation with time was monitored from which dat a the values of the diffusion coefficient of hydrogen, D were calculated fr om well known error function/infinite series solutions to Fick's second law . Very good correlation was obtained with respect to theoretical calculatio ns. The diffusion coefficients appear to be in close agreement with those f or the cast alloy calculated from microhardness measurements. The value of D can be overestimated for thick specimens. Results show that neither the m icrostructure in terms of grain/ lamellar colony size, nor the charging cur rent density, appear to have a significant effect on the value of D. Lattic e diffusion appears to be rate controlling. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.