A combined experimental and theoretical study was made of self-diffusion in γ-phase material. The Ti self-diffusion coefficient was measured, at temperatures of 1184 to 1691K, by using a 44Ti radiotracer and serial sectioning. The diffusion coefficients exhibited a non-Arrhenius behavior, with a significant upward deviation at temperatures above 1470K. The results for Ti self-diffusion below 1470K could be described by:

D (m2/s) = 1.5 x 10-6 exp[-250(kJ/mol)/RT]

By combining these with published interdiffusion data, and using the Darken-Manning equation, it was deduced that Al self-diffusivity could be described by:

D (m2/s) = 2.1 x 10-2 exp[-360(kJ/mol)/RT]

Several diffusion mechanisms were considered. These included the migration of Ti and Al on their own sub-lattices via single vacancy jumps, 3-jump vacancy cycles and an anti-structural bridge mechanism.

C.Herzig, T.Przeorski, Y.Mishin: Intermetallics, 1999, 7[3-4], 389-404

Table 293

Interdiffusion in Ti3Al