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Ab initio study of Cr interactions with point defects in bcc Fe
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Neutron Research.
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 1, 014110- p.Article in journal (Refereed) Published
Abstract [en]

The properties of Cr in alpha Fe have been investigated by ab initio calculations based on density functional theory. The intrinsic point defect formation energies were found to be larger in model bcc Cr as compared to those in ferromagnetic bcc Fe. The interactions of Cr with point defects (vacancy and self-interstitials) have been characterized. Single Cr atoms interact weakly with vacancies but significantly with self-interstitial atoms (SIA). Mixed interstitials of any interstitial symmetry are bound. Configurations where two Cr atoms are in nearest-neighbor position are generally unfavorable in bcc Fe except when they are a part of a < 111 > interstitial complex. Mixed < 110 > interstitials do not have as strong directional stability as pure Fe interstitials have. The effects on the results using the atom description scheme of either the ultrasoft pseudopotential (USPP) or the projector augmented wave (PAW) formalisms are connected to the differences in local magnetic moments that the two methods predict. As expected for the Fe-Cr system, the results obtained using the PAW method are more reliable than the ones obtained with USPP.

Place, publisher, year, edition, pages
2007. Vol. 75, no 1, 014110- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-93595DOI: 10.1103/PhysRevB.75.014110ISI: 000243894600044OAI: oai:DiVA.org:uu-93595DiVA: diva2:167121
Available from: 2005-10-13 Created: 2005-10-13 Last updated: 2017-12-14Bibliographically 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 103
Keyword
Nuclear physics, Kärnfysik
National Category
Subatomic Physics
Identifiers
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
Opponent
Supervisors
Available from: 2005-10-13 Created: 2005-10-13Bibliographically approved

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