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 TiAl 3 was observed as an intermediate layer in the temperature range from 773 to 903 K in both the diffusion couples. Si, which is an impurity element in aluminum, was concentrated in TiAl 3 . 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, k 2 , 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. k 2 TiAl3 = 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 by aluminum oxide formed between aluminum and TiAl 3 . The Kirkendall marker shifted toward the aluminum side, which suggests that diffusion of Al is faster than that of Ti in the intermediate layer.