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On high temperature oxidation resistance: Towards the materials genome of high temperature alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The efficiency of a heat engine increases with increasing service temperature. This leads to a demand for material that can withstand aggressive environments and sometimes also high load at higher and higher temperature. That is the rationale for the work of this thesis. It is divided into two parts, both addressing model alloy systems for components used in oxidizing high temperature environments. In the first part the phase equilibria and phase diagrams of Ni-Ru and Al-Ni-Ru are investigated from a thermodynamic point of view using the well known Calphad method. In particular, the debated existance of a miscibility gap between the aluminides NiAl and RuAl is considered. This led to a combined ab initio/Calphad approach and it is suggested that there is a miscibility gapat low temperature. In the second part, first of its kind diffusion simulations in oxides are performed in the technologically important Fe-O and Cr-O systems. In the simulations, the moving phase boundary problem is solved with use of temperature and composition dependent diffusion coefficients, that are evaluated for complex oxide phases modeled with up to four sublattices. This type of simulations attracts a lot of interest and it looks very promising for future extension to higher order systems.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , vii, 32 p.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-154227ISBN: 978-91-7595-313-7 (print)OAI: oai:DiVA.org:kth-154227DiVA: diva2:756022
Public defence
2014-11-14, B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141222

Available from: 2014-10-22 Created: 2014-10-15 Last updated: 2014-10-23Bibliographically approved
List of papers
1. Thermodynamic assessment of the Ni-Ru system
Open this publication in new window or tab >>Thermodynamic assessment of the Ni-Ru system
2004 (English)In: Journal of phase equilibria (Print), ISSN 1054-9714, E-ISSN 1544-1032, Vol. 25, no 3, 252-254 p.Article in journal (Refereed) Published
Abstract [en]

The Ni-Ru system is assessed using the CALPHAD technique. The only available experimental information for this system concerns phase equilibria, whereas no thermochemical information has been found. The THERMO-CALC software is applied to obtain Gibbs energy (G) functions for the individual phases. The phase diagram calculated from the new G functions is in excellent agreement with the experimental diagram, and all the thermodynamic parameters are given in the Appendix. In addition, tentative activity diagrams and the metastable miscibility gaps in fcc and hcp phases are calculated from the new thermodynamic description.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-44836 (URN)10.1361/15477030419504 (DOI)000222115100005 ()2-s2.0-3042590293 (Scopus ID)
Note

QC 20111026

Available from: 2011-10-26 Created: 2011-10-25 Last updated: 2017-12-08Bibliographically approved
2. Thermodynamic reassessment of the Ni-Ru system and assessment of the Al-Ni-Ru system at 1273-1523 K using ab initio calculations
Open this publication in new window or tab >>Thermodynamic reassessment of the Ni-Ru system and assessment of the Al-Ni-Ru system at 1273-1523 K using ab initio calculations
2008 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 56, no 15, 4062-4069 p.Article in journal (Refereed) Published
Abstract [en]

The Ni-Ru and Al-Ni-Ru systems are assessed with a combined CALPHAD and ab initio approach. Particular attention is paid to the possible existence of a miscibility gap in the B2 phase. Both face-centered cubic and body-centered cubic ordering are analyzed within the compound energy formalism. Ab initio calculations for the B2 phase show a similar trend as calorimetric measurements but the magnitude is much smaller. It is found that the calorimetric measurements cannot be reconciled with any reasonable phase diagram, whereas the ab initio results can. From the parameters obtained, isothermal sections in reasonable agreement with experimental phase diagrams are calculated. We have concluded that there is no miscibility gap in the B2 phase at 1273 K and higher temperatures.

Keyword
thermodynamics, CALPHAD, intermetallics, ab initio electron theory, enthalpy of formation, total-energy calculations, augmented-wave method, basis-set, phase, approximation, metals, exchange, alloys
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-17840 (URN)10.1016/j.actamat.2008.04.028 (DOI)000259409300034 ()2-s2.0-48449083486 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Modeling of diffusion in wustite and simulation of oxidation of iron at 600°C
Open this publication in new window or tab >>Modeling of diffusion in wustite and simulation of oxidation of iron at 600°C
2008 (English)In: 6th European Stainless Steel Conference / [ed] Pentti Karjalainen and Staffan Hertzman, Helsinki: Jernkontoret , 2008, 273-278 p.Conference paper, Published paper (Refereed)
Abstract [en]

A long missing feature in the diffusion simulation software DICTRA has been the diffusion in oxides. Recently, this capability was implemented and in this report we present some results of the current achievements.DICTRA can now treat diffusion in basically any oxide, provided that there is diffusion data available and that the necessary mobilities have been assessed. The first system to be addressed was the important Fe-O system. It contains three different oxides, from the simple wustite to the complex magnetite, which has the spinel structure. The current  approach was successful and the work was continued with the Cr-O system and the technically important Fe-Cr-O. We will present the diffusion models and the results of the assessment, as well as successful simulations of oxidation where layers of oxides grow on top of an Fe or Fe-Cr substrate.

Place, publisher, year, edition, pages
Helsinki: Jernkontoret, 2008
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-154224 (URN)91-974131-9-4 (ISBN)
Conference
European Stainless Steel Conference Science and Market Helsinki, Finland, June 10–13, 2008
Note

QC 20141022

Available from: 2014-10-15 Created: 2014-10-15 Last updated: 2014-10-22Bibliographically approved
4. Modeling of iron diffusion in the iron oxides magnetite and hematite with variable stoichiometry
Open this publication in new window or tab >>Modeling of iron diffusion in the iron oxides magnetite and hematite with variable stoichiometry
2011 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 1, 53-60 p.Article in journal (Refereed) Published
Abstract [en]

The vacancy model of diffusion is applied to magnetite and hematite, and mathematical expressions for the iron flux in the lattice-fixed frame of reference, as a function of the defect structure, are presented The defect structures, i e the vacancy content on the different type of sites, and the thermodynamic factors are calculated from the available Calphad type of thermodynamic descriptions for the oxides Expressions for Fe tracer diffusion coefficients are derived and the relations between mobility and tracer diffusivity are given The mobilities are fitted by a least-squares optimization to experimental data on tracer diffusion from the literature For magnetite, an excellent representation of the experimental tracer data is achieved together with a satisfactory description of the sparse chemical diffusion data available For hematite, the experimental scatter is very large and anomalous large frequency factors and activation energies have been reported In the present report a compromise is suggested.

Keyword
Lattice defects, Thermodynamics, Bulk diffusion, Kinetics, Binary oxides
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27694 (URN)10.1016/j.actamat.2010.08.032 (DOI)000284789200006 ()2-s2.0-78049529140 (Scopus ID)
Note

QC 20101221

Available from: 2010-12-21 Created: 2010-12-20 Last updated: 2017-12-11Bibliographically approved
5. High temperature oxidation of chromium: Kinetic modeling and microstructural investigation
Open this publication in new window or tab >>High temperature oxidation of chromium: Kinetic modeling and microstructural investigation
Show others...
2013 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 240, 41-50 p.Article in journal (Refereed) Published
Abstract [en]

Using CALPHAD methods, Cr2O3 growth on pure Cr is modeled using DICTRA and the vacancy model for diffusion. The results are compared with thermobalance and TEM experiments at 625 and 700 degrees C in O-2. The experimental scatter is significant, leading to a compromise suggestion. With the experimental conditions from the furnace exposures in this work, optimized mobilities are validated with a series of oxidation simulations. Despite the complex microstructure and initial growth rate variations, it is possible to reproduce the experimental oxide thicknesses with good accuracy, allowing for extension to multicomponent systems.

Keyword
High temperature corrosion, Stainless steel, SEM, TEM, Kinetic parameters
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-124286 (URN)10.1016/j.ssi.2013.02.017 (DOI)000319242600006 ()2-s2.0-84876242848 (Scopus ID)
Funder
Swedish Foundation for Strategic Research
Note

QC 20130702

Available from: 2013-07-02 Created: 2013-06-28 Last updated: 2017-12-06Bibliographically approved

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