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Electronic origin of the anomalous stability of Fe rich bcc Fe-Cr alloys
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
2006 (English)In: Phys. Rev. B, Vol. 73, no 10, 104416Article in journal (Refereed) Published
Abstract [en]

The binary Fe-Cr alloy is a system with a miscibility gap. The decomposition occurs either via the nucleation and growth mechanism or as spinodal decomposition, depending on the Cr content. However, at low chromium concentrations the alloys are anomalously stable. This is shown to be true only for the ferromagnetic body centered cubic (bcc) phase. The stability stems from the negative mixing enthalpy at low concentrations of chromium. We show that the effect has an electronic origin, that is, it is directly related to variations of the electronic structure in the alloy with concentration. We also demonstrate that the variation in the state density of the majority channel at the Fermi level in the concentration interval below 20 at. % Cr indicates increasing tendency of the system towards the spinodal decomposition in the system. Moreover, in the equimolar concentration region, significant deviations of the spin up band from its canonical shape are observed, which destabilize the bcc phase.

Place, publisher, year, edition, pages
2006. Vol. 73, no 10, 104416
National Category
Condensed Matter Physics
URN: urn:nbn:se:uu:diva-93593DOI: 10.1103/PhysRevB.73.104416ISI: 000236467200064OAI: oai:DiVA.org:uu-93593DiVA: diva2:167119
Available from: 2005-10-13 Created: 2005-10-13 Last updated: 2016-08-11Bibliographically approved
In thesis
1. Modelling of Formation and Evolution of Defects and Precipitates in Fe-Cr Alloys of Reactor Relevance
Open this publication in new window or tab >>Modelling of Formation and Evolution of Defects and Precipitates in Fe-Cr Alloys of Reactor Relevance
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fe-Cr alloys form the basis of many industrially important steels. Due to their excellent resistance to radiation induced swelling, ferritic steels are expected to be used for critical structural components in advanced nuclear systems, such as fast breeder reactors, accelerator driven systems and fusion reactors. In this thesis project, theoretical modelling of bulk properties of Fe-Cr alloys has been performed for a wide range of phenomena. Electronic structure calculations, based on density functional theory, have been used to determine equilibrium properties for different magnetic states of the alloy. Ferromagnetic alloys of low Cr concentration (<10% Cr) are anomalously stable, which is related to the variation in sign of the mixing enthalpy which was predicted for the first time in this work. This finding is in agreement with experimental evidence of long range ordering in Fe-Cr alloys with low Cr concentration, as well as the observed phase separation for compositions with higher Cr content.

The character of the interaction of point defects with solute Cr atoms in an iron matrix was investigated ab initio. It was found that due to magnetic interactions, interstitial defects are bound by Cr atoms in bulk iron. Vacancies, on the other hand, interact only weakly with Cr. These results may offer qualitative explanations to the observed concentration dependence of radiation induced swelling in Fe-Cr model alloys.

The ab initio predictions inspired an effort to develop an interatomic alloy potential capable of reproducing both the thermodynamic bulk behaviour of the alloy, such as the mixing enthalpy, and the point defect interactions, in order to perform large scale atomistic and stochastic simulations on scales out of reach for density functional theory. A two-band extension of the embedded atom method of interatomic potentials was developed in order to model ferromagnetic Fe-Cr alloys of arbitrary composition. Kinetic Monte-Carlo simulations of thermal aging, using this two-band potential, reproduce the experimentally measured formation and evolution of solute precipitation as a function of concentration for temperatures relevant to structural materials in nuclear reactors.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. viii+54 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 103
Nuclear physics, Kärnfysik
National Category
Subatomic Physics
urn:nbn:se:uu:diva-6014 (URN)91-554-6365-7 (ISBN)
Public defence
2005-11-04, Siegbahnsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Available from: 2005-10-13 Created: 2005-10-13Bibliographically approved

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