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

Abstract

Reaction diffusion in Ti/Al and Ti-5 mol%O/Al diffusion couples has been investigated by electron-probe microanalysis. Only one intermetallic compound TiAl3 was observed as an intermediate phase in a temperature range from 773 to 903 K in both the diffusion couples. Si, an impurity element in aluminum, was concentrated in TiAl3. The growth of the intermediate layer 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 the rate constant, k2, for layer growth can be described with the following equation in the temperature range from 773 to 903 K in the Ti/Al diffusion couples. kTiAl(3)2 = 3.5 exp [-(237±15)kJ mol-1/RT]m2 s-1 In the case of the oxygen doped diffusion couples, the layer growth of TiAl3 was significantly suppressed and the activation energy was 263±7 kJ mol-1 for temperatures from 773 to 873 K. The suppression is explained by aluminum oxide formed between aluminum and TiAl3. The Kirkendall marker was shifted toward the aluminum side, which suggests that diffusion of Al is faster than that of Ti in the intermediate phase.