It was pointed out that very little was known concerning diffusion processes in the present materials, either with regard to the bulk diffusion of the components or with regard to grain boundary or 2/ interphase boundary diffusion. Therefore, an investigation was made here of diffusion phenomena in the Ti-Al system and measurements were made of the self-diffusion of 44Ti in the ordered 2-phase, Ti3Al, which existed (D019 structure) within an homogeneity range of about 22 to 39at%Al (table 5). The Ti tracer experiments were complemented by interdiffusion experiments in the 2-phase, in order to estimate the diffusivity of the Al component via the Darken equation. It was found that the Ti self-diffusion was almost independent of the Al concentration in the hyperstoichiometric 2 phase. The absolute values of the Ti diffusivity were relatively low. It was concluded that diffusion proceeded via a vacancy mechanism, and that no constitutional vacancies but Al antisite defects formed. The chemical diffusivity was higher than the self-diffusivity, and this was attributed to the fact that the thermodynamic factor was larger than unity in the 2 phase. The Al self-diffusion coefficient was deduced to be lower than the self-diffusivity, by a factor of 2 or 3, at temperatures ranging from 1273 to 1173K.

J.Rüsing, C.Herzig: Scripta Metallurgica et Materialia, 1995, 33[4], 561-6

Table 5

Diffusion of 44Ti in Ti-Al Intermetallic Phases