Atomistic modelling of the diffusion of C in Fe-Cr alloys
Résumé
The diffusion of C in Fe-Cr solid solutions is modelled and compared to experimental data. Aset of binding energies and migration barriers for C diffusion in different local chemicalenvironments are first calculated using density functional theory. A pair interaction model isdeveloped in order to reproduce these data and predict the migration barriers in otherenvironments. The diffusion model is then implemented in a kinetic Monte Carlo method tosimulate tracer diffusion experiments, using a standard procedure, and internal frictionexperiments, using a novel method. Simulations of internal friction show a unique Snoek peakin the whole concentration range, between pure iron and pure chromium. The average migration barrier for C diffusion in Fe-Cr alloys is found to increase progressively with the Crconcentration, with a small rate below 6 percentCr. In Cr-rich alloys, the effective migration barrierfor C diffusion is found to be larger in tracer diffusion than in the internal friction simulations. We conclude that the effective migration barrier extracted from tracer diffusion is closely related to trapping effects of C atoms in Fe-rich local environments, whereas the migration barrier associated with internal friction is mainly controlled by the spectrum of migration barriers of the most frequent configurations, as it is clearly shown in the Cr-rich domain.