Reaction diffusion in Ti/Al and Ti-5mol%O/Al diffusion couples was investigated by means of electron-probe micro-analysis. Only Al3Ti was observed, as an intermediate layer, in both couples at 773 to 903K. The Si, which was an impurity element in Al, was concentrated in the Al3Ti. The growth of the intermediate layer was diffusion-limited, with an estimated activation energy of 237kJ/mol. In the case of O-doped diffusion couples, the layer growth of Al3Ti was appreciably suppressed and the activation energy was equal to 263kJ/mol at 773 to 873K. This suppression was attributed to the presence of Al2O3 which formed between the Al and the Al3Ti. Kirkendall markers shifted towards the Al side; thus suggesting that the diffusion of Al was faster than that of Ti in the intermediate layer.

K.Nonaka, H.Fujii, H.Nakajima: Materials Transactions, 2001, 42[8], 1731-40