Effect of oxygen in titanium on reaction diffusion between Ti and Al

Reaction diffusion in Ti/Al and Ti-5 mol%O/Al diffusion Couples has been in vestigated by electron-probe microanalysis. Only one intermetallic compound TiAl3 was observed as an intermediate layer in the temperature ran, from 7 73 to 903 K in both the diffusion couples. Si, which is an impurity element in aluminum, was concentrated in TiAl3. The growth of the intermediate lay er turned out to be diffusion limited; the activation energy was estimated to be 237 +/- 15 kJ . mol(-1) and the temperature dependence of square of t he rate constant, k(2), for layer growth can be described with the followin g equation in the temperature range from 773 to 903 K in the Ti/Al diffusio n couples. k(TiAl3)(2) = 3.5 exp[-(237 +/- 15) kJ . mol(-1)/RT]m(2)s(-1) in the case of the oxygen doped diffusion couples, the layer growth of TiAl 3 was significantly suppressed and the activation energy was 263 +/- 7 kJ . mol(-1) for temperatures from 773 to 873 K. The suppression is explained b y aluminum oxide formed between aluminum and TiAl3, The Kirkendall marker s hifted toward the aluminum side, which suggests that diffusion of Al is fas ter than that of Ti in the intermediate layer.