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Thermodynamic and kinetic properties of Fe-Cr and TiC-ZrC alloys from Density Functional Theory
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. KTH, School of Industrial Engineering and Management (ITM), Centres, VinnExcellence Centre for Hierarch. Eng. of Industrial Materials, HERO-M.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The complete and accurate thermodynamic and kinetic description of any systemis crucialfor understanding and predicting its properties. A particular interest is in systemsthat are used for some practical applications and have to be constantly improved usingmodification of their composition and structure. This task can be quite accuratelysolved at a fundamental level by density functional theory methods. Thesemethods areapplied to two practically important systems Fe-Cr and TiC-ZrC.The elastic properties of pure iron and substitutionally disordered Fe-Cr alloy are investigatedas a function of temperature and concentration using first-principles electronicstructurecalculations by the exact muffin-tin orbitals method. The temperature effectson the elastic properties are included via the electronic, magnetic, and lattice expansioncontributions. It is shown that the degree of magnetic order in both pure iron andFe90Cr10 alloy mainly determines the dramatic change of the elastic anisotropy of thesematerials at elevated temperatures. A peculiarity in the concentration dependence ofthe elastic constants in Fe-rich alloys is demonstrated and related to a change in theFermi surface topology.A thermodynamic model for the magnetic alloys is developed from first principles andapplied to the calculation of bcc Fe-Cr phase diagram. Various contributions to the freeenergy (magnetic, electronic, and phonon) are estimated and included in the model. Inparticular, it is found that magnetic short range order effects are important just abovethe Curie temperature. The model is applied for calculating phase equilibria in disorderedbcc Fe-Cr alloys. Model calculations reproduce a feature known as a Nishizawahorn for the Fe-rich high-temperature part of the phase diagram.The investigation of the TiC-ZrC system includes a detailed study of the defect formationenergies and migration barriers of point defects and defect complexes involvedin the diffusion process. It is found, using ab initio atomistic simulations of vacancymediateddiffusion processes in TiC and ZrC, that a special self-diffusion mechanism isoperative for metal atom diffusion in sub-stoichiometric carbides. It involves a noveltype of a stable point defect, a metal vacancy ”dressed” in a shell of carbon vacancies.It is shown that this vacancy cluster is strongly bound and can propagate through thelattice without dissociating.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , viii, 62 p.
Keyword [en]
ab initio, first principles, point defects, vacancy clusters, alloys, steels, iron, carbides, diffusion, phase diagram, density functional theory, elastic constants, elastic properties, thermodynamic modelling
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-96285ISBN: 978-91-7501-340-4 (print)OAI: oai:DiVA.org:kth-96285DiVA: diva2:530156
Public defence
2012-06-12, F2, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
HERO-M
Note

QC 20120604

Available from: 2012-06-04 Created: 2012-06-01 Last updated: 2013-04-02Bibliographically approved
List of papers
1. First-principles study of elastic properties of Cr- and Fe-rich Fe-Cr alloys
Open this publication in new window or tab >>First-principles study of elastic properties of Cr- and Fe-rich Fe-Cr alloys
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 2, 024106Article in journal (Refereed) Published
Abstract [en]

Elastic properties of substitutionally disordered Cr- and Fe-rich Fe-Cr alloys are derived from first-principles calculations using the exact muffin-tin orbitals method and the coherent potential approximation. A peculiarity in the concentration dependence of elastic constants in Fe-rich alloys is demonstrated and related to a change in the Fermi surface topology. Our calculations predict high values for the elastic constants of Cr-rich Fe-Cr alloys, but at the same time show that these alloys could be rather brittle according to the Pugh criterion (the ratio between shear and bulk moduli is calculated to be greater than 0.5).

Place, publisher, year, edition, pages
American Physical Society, 2011
Keyword
GENERALIZED GRADIENT APPROXIMATION, INITIO MOLECULAR-DYNAMICS, AUGMENTED-WAVE METHOD, ELECTRONIC-STRUCTURE, TRANSITION-METALS, THERMAL-EXPANSION, CORRELATION HOLE, CHROMIUM-ALLOYS, SINGLE-CRYSTALS, SOLID-SOLUTIONS
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-36888 (URN)10.1103/PhysRevB.84.024106 (DOI)000292384100005 ()2-s2.0-79961182340 (Scopus ID)
Funder
Swedish Research CouncilEU, European Research Council
Note

QC 20110720

Available from: 2011-07-20 Created: 2011-07-18 Last updated: 2017-12-08Bibliographically approved
2. Effect of temperature on the elastic anisotropy of pure Fe and Fe0.9Cr0.1 random alloy
Open this publication in new window or tab >>Effect of temperature on the elastic anisotropy of pure Fe and Fe0.9Cr0.1 random alloy
2011 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 20, 205504Article in journal (Refereed) Published
Abstract [en]

The elastic properties of pure iron and substitutionally disordered 10 at. % Cr Fe-Cr alloy areinvestigated as a function of temperature using first-principles electronic-structure calculations bythe exact muffin-tin orbitals method. The temperature effects on the elastic properties are includedvia the electronic, magnetic, and lattice expansion contributions. We show that the degree ofmagnetic order in both pure iron and Fe90Cr10 alloy mainly determines the dramatic change of theelastic anisotropy of these materials at elevated temperatures. The effect of lattice expansion isfound to be secondary but also very important for quantitative modeling.

Place, publisher, year, edition, pages
American Physical Society, 2011
Keyword
first principles, Fe-Cr, elastic properties, ab initio
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-49607 (URN)10.1103/PhysRevLett.107.205504 (DOI)000297133700008 ()2-s2.0-81055148207 (Scopus ID)
Projects
The Hero-m center (Hierarchic Engineering of Industrial Materials)
Funder
Swedish Research Council, 90399101
Note

QC 20111201

Available from: 2011-11-28 Created: 2011-11-28 Last updated: 2017-12-08Bibliographically approved
3. First-principles based thermodynamic model of phase equilibria in bcc Fe-Cr alloys
Open this publication in new window or tab >>First-principles based thermodynamic model of phase equilibria in bcc Fe-Cr alloys
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 17, 174111- p.Article in journal (Refereed) Published
Abstract [en]

A first-principles based thermodynamic model for magnetic alloys is applied to the calculation of the Fe-Cr phase diagram restricted by the bcc structure. The model includes magnetic, electronic, phonon, and local atomic relaxations contributions to the free-energy derived from ab initio calculations. Atomic short-range-order effects are found to be relatively small and they have been neglected in the calculations, assuming that alloys are in the completely random state. In contrast, we have taken into consideration magnetic short-range-order effects, which are found to be very important in particular above the Curie temperature. The calculated phase diagram is in reasonable agreement with the latest CALPHAD assessment. Our calculations reproduce a feature known as a Nishizawa horn for the Fe-rich high-temperature part of the phase diagram.

Keyword
Generalized Gradient Approximation, High-Temperature Calorimeter, Initio Molecular-Dynamics, Total-Energy Calculations, Augmented-Wave Method, Iron-Chromium Alloys, Miscibility Gap, Electronic-Structure, Magnetic-Properties, Finite-Temperature
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-96420 (URN)10.1103/PhysRevB.86.174111 (DOI)000311138600001 ()2-s2.0-84870014447 (Scopus ID)
Funder
VinnovaSwedish Research CouncilEU, European Research Council, 228074
Note

QC 20121217. Updated from submitted to published.

Available from: 2012-06-04 Created: 2012-06-04 Last updated: 2017-12-07Bibliographically approved
4. Ab-initio calculations of kinetic properties in ZrC and TiC carbides
Open this publication in new window or tab >>Ab-initio calculations of kinetic properties in ZrC and TiC carbides
2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).

Series
Solid State Phenomena, ISSN 1012-0394
Keyword
first principles, TiC, ZrC, carbides, self-diffusion, ab initio, point defects
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-49624 (URN)10.4028/www.scientific.net/SSP.172-174.990 (DOI)000303359700154 ()2-s2.0-79960924975 (Scopus ID)
Conference
International Conference on Solid-Solid Phase Transformations in Inorganic Materials (PTM 2010)
Projects
The Hero-m center (Hierarchic Engineering of Industrial Materials)
Note

QC 20111230

Available from: 2011-11-28 Created: 2011-11-28 Last updated: 2012-08-30Bibliographically approved
5. Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides
Open this publication in new window or tab >>Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 5, 054203- p.Article in journal (Refereed) Published
Abstract [en]

We find, using ab initio atomistic simulations of vacancy-mediated diffusion processes in TiC and ZrC, that a multivacancy self-diffusion mechanism is operative for metal-atom diffusion in substoichiometric carbides. It involves a special type of a stable point defect, a metal vacancy "dressed" in a shell of carbon vacancies. We show that this vacancy cluster is strongly bound and can propagate through the lattice without dissociating.

Keyword
Functional Perturbation-Theory, Ab-Initio Calculations, Augmented-Wave Method, Titanium Carbide, Neutron-Diffraction, Carbon Vacancies, Point-Defects, Disorder, Order, Transition
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-96422 (URN)10.1103/PhysRevB.87.054203 (DOI)000315373500003 ()2-s2.0-84874548645 (Scopus ID)
Funder
VinnovaSwedish Research CouncilEU, European Research Council, 228074
Note

QC 20130402. Updated from submitted to published.

Available from: 2012-06-04 Created: 2012-06-04 Last updated: 2017-12-07Bibliographically approved
6. Multi-length scale modeling of martensitic transformations in stainless steels
Open this publication in new window or tab >>Multi-length scale modeling of martensitic transformations in stainless steels
Show others...
2012 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 19, 6508-6517 p.Article in journal (Refereed) Published
Abstract [en]

In the present work a multi-length scale model is developed to study both the athermal and stress-assisted martensitic transformations in a single crystal of 301 type stainless steel. The microstructure evolution is simulated using elastoplastic phase-field simulations in three dimensions. The input data for the simulations is acquired from a combination of computational techniques and experimental works. The driving force for the transformation is calculated by using the CALPHAD technique and the elastic constants of the body-centered cubic phase are calculated by using ab initio method. The other input data is acquired from experimental works. The simulated microstructures resemble a lath-type martensitic microstructure, which is in good agreement with the experimental results obtained for a stainless steel of similar composition. The martensite habit plane predicted by the model is in accordance with experimental results. The Magee effect, i.e. formation of favorable martensite variants depending on the loading conditions, is observed in the simulations. The results also indicate that anisotropic loading conditions give rise to a significant anisotropy in the martensitic microstructure.

Keyword
phase-field simulations, ab initio, multi-length scale model, martensitic transformation, microstructure
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-95306 (URN)10.1016/j.actamat.2012.08.012 (DOI)000311188400007 ()2-s2.0-84867582531 (Scopus ID)
Projects
hero-m
Funder
Vinnova
Note

QC 20121119. Updated from accepted to published.

Available from: 2012-05-21 Created: 2012-05-21 Last updated: 2017-12-07Bibliographically approved

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