Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Ferritic Fe and Fe-Cr alloys are basic structural materials of present and future nuclear fission and fusion reactors. The formation of the micro- and nanostructure of these alloys and the structural evolution under irradiation is essentially influenced by the interaction between solutes, vacancies and self-interstitials. These processes take place in different alloys such as reactor-pressure-vessel and oxide-dispersion-strengthened steels. The understanding of the nanostructure of those materials and of its radiation-induced evolution is indispensable for nuclear reactor safety. First-principle calculations based on the Density Functional Theory (DFT) are a very useful method to get atomistic insights into the interactions between solutes, vacancies and self-interstitials in bcc Fe. Traditionally, formation and binding energies of these species are investigated at T=0 and these data are further used in calculations on larger length and time scales such as in kinetic Monte Carlo simulations and Rate Theory.
The main objective of present work is the determination of the temperature-dependent free formation and binding energy of selected point defects and their clusters in bcc Fe. For this purpose DFT is used to obtain the corresponding vibrational free energies within the framework of the harmonic approximation. The substitutional solutes Cu, Y and Ti, the interstitial solute atom O, the vacancy as well as small clusters consisting of solute atoms and vacancies are considered. The results are compared with theoretical data obtained by other authors and discussed in relation to experimental solubility data. It is found that the free energies show a significant dependence on temperature. This must be taken into account in multiscale simulations that use DFT input data.