Quantitative Evaluation of Interdiffusion in Fe2Al5 during Reactive Diffusion in the Binary FeAl System

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 temperatures of T=823-913 K, and then a compound layer of Fe2Al5 was observed to form at the interface. The observation indicates that there exists the parabolic relationship between the mean thickness of the Fe2Al5 layer and the annealing time. The parabolic relationship means that the growth of the Fe2Al5 layer is 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× 10^-16, 1.18× 10^-14 and 2.92× 10^-14 m^2/s at T=823, 873 and 913 K, respectively. Expressing the temperature dependence of D as D=D0 exp(-Q/RT), values of D0=2.34× 10^2 m^2/s and Q=276 kJ/mol were obtained by the least-squares method.