Diffusion in the titanium-aluminum system. II. Interdiffusion in the composition range between 25 and 100 at.% titanium

Interdiffusion phenomena have been investigated m the Ti-Al system in the region from 25 to 100 at.% Ti at temperatures between 700 and 1200°C. The phase diagram of the Ti-Al system has been constructed using data from concentration-penetration curves recorded for various types of diffusion couples. In the composition range 25 at.% Al, the phase diagram is found to agree with that proposed by Blackburn. In the Al-rich part of the diagram a phase Ti2Al5 was found which is probably the same as the compound Ti5Al11 reported by Schubert et al. The growth of the various diffusion layers is non-parabolic; the reason is supposed to be the influence of grain boundary diffusion. The latter decreases steadily with increasing annealing time as a result of grain growth in the layer. Ti is the most mobile element in the Ti3Al phase at temperatures between 768–865°C, whereas in the Al-richer compounds Al is the most mobile element at temperatures between 784–972°C