Segregation, precipitation, and phase separation in Fe-Cr systems isinvestigated. Monte Carlo simulations using semiempirical interatomicpotential, first-principles total energy calculations, and experimentalspectroscopy are used. In order to obtain a general picture of the relation ofthe atomic interactions and properties of Fe-Cr alloys in bulk, surface, andinterface regions several complementary methods has to be used. Using ExactMuffin-Tin Orbitals method the effective chemical potential as a function of Crcontent (0-15 at.% Cr) is calculated for a surface, second atomic layer andbulk. At ~10 at.% Cr in the alloy the reversal of the driving force of a Cratom to occupy either bulk or surface sites is obtained. The Cr containingsurfaces are expected when the Cr content exceeds ~10 at.%. The second atomiclayer forms about 0.3 eV barrier for the migration of Cr atoms between bulk andsurface atomic layer. To get information on Fe-Cr in larger scales we usesemiempirical methods. Using combined Monte Carlo molecular dynamicssimulations, based on semiempirical potential, the precipitation of Cr intoisolated pockets in bulk Fe-Cr and the upper limit of the solubility of Cr intoFe layers in Fe/Cr layer system is studied. The theoretical predictions aretested using spectroscopic measurements. Hard X-ray photoelectron spectroscopyand Auger electron spectroscopy investigations were carried out to explore Crsegregation and precipitation in Fe/Cr double layer and Fe_0.95Cr_0.05 andFe_0.85Cr_0.15 alloys. Initial oxidation of Fe-Cr was investigatedexperimentally at 10^-8 Torr pressure of the spectrometers showing intenseCr_2O_3 signal. Cr segregation and the formation of Cr rich precipitates weretraced by analysing the experimental spectral intensities with respect toannealing time, Cr content, and kinetic energy of the exited electron.
展开▼
