Concentration dependence of the ternary interdiffusivities in the Fe-Cr-Al System at 1100 ºC: experimental and simulation studies

Interdiffusion experiments were carried out on model alloys Fe-(6-32)Cr-(1.2-29)Al (wt%) at 1100°C using diffusion couples in which the concentration of one of the three elements Fe, Cr and Al was each time maintained constant. Based on the resulting concentration profiles the interdiffusivity matrices required for the description of ternary diffusion were determined. For the calculation of the ternary diffusivities, a numerical approach after Dayananda and Sohn was used, in which the four ternary interdiffusion coefficients are determined over a selected composition range from a single diffusion couple experiment. The experimentally determined coefficients were then used in a finite-difference diffusion model (ODIN) to simulate the concentration profiles across the experimental couples. The results reveal that the cross-term effects are much higher in the couples with constant Fe content than in couples with constant Cr content, which in turn show more significant interactions than the couples with constant Al content. The main-term interdiffusion coefficients for Cr, D∼ CrCr Fe, are up to two times larger than that for Al, D∼ AlAl Fe, for the couples with constant Cr content. In opposition, the D∼ AlAl Fe are 2 to 11 times larger than the D∼ CrCr Fe for the couples with constant Fe content, and up to 5 times for the couples with constant Al content. Good agreement was obtained between the measured and the simulated profiles. © 2005 Science Reviews.