Host Atom Diffusion in Ternary Fe-Cr-Al Alloys
Résumé
In the Fe-rich corner of the Fe-Cr-Al ternary phase diagram, both interdiffusion experiments [1048 K to 1573 K (775 degrees C to 1300 degrees C)] and Fe-58 tracer diffusion experiments [873 K to 1123 K (600 degrees C to 850 degrees C)] were performed along the Fe50Cr50-Fe50Al50 section. For the evaluation of the interdiffusion data, a theoretical model was used which directly yields the individual self-diffusion coefficients of the three constituents and the shift of the original interface of the diffusion couple through inverse modeling. The driving chemical potential gradients were derived using a phenomenological Gibbs energy function which was based on thoroughly assessed thermodynamic data. From the comparison of the individual self-diffusivities of Fe as obtained from interdiffusion profiles and independent Fe-58 tracer diffusivities, the influence of the B2-A2 order-disorder transition becomes obvious, resulting in a slightly higher activation enthalpy for the bcc-B2 phase and a significantly lower activation entropy for this phase.