Using Al/Fe/Al diffusion couples prepared by a diffusion bonding technique, the reactive diffusion in the binary Fe–Al system was experimentally examined in a previous study. The diffusion couple was isothermally annealed at 823 to 913K, and then a compound layer of Fe2Al5 was observed to form at the interface. The observation indicated that there exists the parabolic relationship between the mean thickness of the Fe2Al5 layer and the annealing time. The parabolic relationship meant  that the growth of the Fe2Al5 layer was controlled by volume diffusion. A mathematical model for the reactive diffusion controlled by volume diffusion was used in order to analyze numerically the growth rate of the Fe2Al5 layer. Through the analysis, the interdiffusion coefficient D of Fe2Al5 was evaluated to be 5.93 x 10-16, 1.18 x 10-14 and 2.92 x 10-14m2/s at T = 823, 873 and 913K, respectively. The temperature dependence was found to be described by:

D (m2/s) = 2.34 x 102 exp[-276(kJ/mol)/RT]

using the least-squares method.

Quantitative Evaluation of Interdiffusion in Al5Fe2 during Reactive Diffusion in the Binary Fe–Al System. M.Kajihara: Materials Transactions, 2006, 47[6], 1480-4