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Thermodynamic and kinetic investigation of systems related to lightweight steels
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lightweight steels have attracted considerable interest for automobile applications due to the weight reduction without loss of high strength and with retained excellent plasticity. In austenitic Fe-Mn-Al-C steels, the nano-precipitation of the κ-carbide within the austenitic matrix significantly contributes to the increase in yield strength. In the present work, the precipitation strengthening simulation has been carried out within the framework of the ICME approach. Thermodynamic assessments of the quaternary Fe-Mn-Al-C system as well as its sub-ternary systems were performed with the CALPHAD method. All available information on phase equilibria and thermochemical properties were critically evaluated and used to optimize the thermodynamic model parameters. By means of the partitioning model, the κ-carbide was described using a five-sublattice model (four substitutional and one interstitial sublattice), which can reflect the ordering between metallic elements and reproduce the wide homogeneity range of the κ-carbide. Based on the present thermodynamic description, a thermodynamic database for lightweight steels was created. Using the database, the phase equilibria evolution in lightweight steels can be satisfactorily predicted, as well as the partition of alloying elements. In order to accelerate the development of a kinetic database for multicomponent systems, a high-throughput optimization method was adopted to optimize the diffusion mobilities. This method may largely reduce the necessary diffusion-couple experiments in multicomponent systems. Based on the developed thermodynamic and kinetic databases for lightweight steels, the precipitation of the κ-carbide was simulated using TC-PRISMA. The volume fraction and particle size were reasonably reproduced. Finally, the precipitation strengthening contribution to the yield strength was predicted. The calculation results show that the anti-phase boundary effect is predominant in the precipitation strengthening. Overall, the relationship between the composition, processing parameters, microstructure and mechanical properties are established in the thesis.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. , p. 74
Series
TRITA-ITM-AVL ; 2018:34
Keywords [en]
Fe-Mn-Al-C, CALPHAD, MGI, ICME, Precipitation strengthening, Lightweight steels.
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-228401ISBN: 978-91-7729-840-3 (print)OAI: oai:DiVA.org:kth-228401DiVA, id: diva2:1209708
Public defence
2018-09-21, rum 4301, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180524

Available from: 2018-05-24 Created: 2018-05-23 Last updated: 2022-06-26Bibliographically approved
List of papers
1. Thermodynamic assessment of the Al-C-Fe system
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2017 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 58, p. 34-49Article in journal (Refereed) Published
Abstract [en]

The Al-C-Fe system was assessed in the framework of the CALPHAD approach. Through the critical review of thermochemical properties of liquid Al-Fe alloys, the binary Al-Fe description was revised to agree better with the experimental data. The partitioning model based on the Compound Energy Formalism (CEF) was utilized to describe the disordered and ordered bcc, fcc and κ phases. Moreover, ab initio calculations were performed to determine the enthalpies of formation of the ordered structures based on the bcc and fcc lattices in the binary Al-Fe and for the end-members of the κ phase in the ternary Al-C-Fe system. In order to simplify the database, the present work also employed a two-sublattice model to describe the B2 ordered phase in the Al-Fe system, which can be applied easily to diffusion simulations. Comprehensive comparison between the model-predicted and experimental data confirms that the present evaluation describe the Al-C-Fe system satisfactorily, especially the κ phase.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Ab initio, Al-C-Fe, Al-Fe, CALPHAD, Partitioning model, κ carbide
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-209500 (URN)10.1016/j.calphad.2017.05.003 (DOI)000410869300005 ()2-s2.0-85019406320 (Scopus ID)
Note

QC 20170621

Available from: 2017-06-21 Created: 2017-06-21 Last updated: 2024-03-18Bibliographically approved
2. Thermodynamic modeling of the Al-C-Mn system supported by ab initio calculations
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2018 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, p. 222-230Article in journal (Refereed) Published
Abstract [en]

A CALPHAD-type thermodynamic assessment of the Al-C-Mn system was carried out in the present work. Special attention was paid to the ternary κ-phase with the aid of ab initio calculations. The enthalpies of formation at 0 K of all end-members of the κ phase were derived from the ab initio calculations and utilized in the present optimization. The κ phase was modeled as an ordered form of the fcc structure for the substitutional sub-lattices, employing the following formula within the framework of compound energy formalism: (Al,Mn)0.25(Al,Mn)0.25(Al,Mn)0.25(Al,Mn)0.25(C,Va)0.25. With the present optimized model parameters, the wide homogeneity range of the κ phase was reproduced satisfactorily. Comparison between the predicted and measured phase equilibria as well as the ab initio calculation results validates the present optimized model parameters.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
Al-C-Mn, kappa phase, partitioning model, ab initio, CALPHAD
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-228395 (URN)10.1016/j.calphad.2018.01.007 (DOI)000428000100024 ()2-s2.0-85043301506 (Scopus ID)
Note

QC 20180524

Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2024-03-18Bibliographically approved
3. Thermodynamic investigation of the Al-Fe-Mn system over the whole composition and wide temperature ranges
Open this publication in new window or tab >>Thermodynamic investigation of the Al-Fe-Mn system over the whole composition and wide temperature ranges
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2018 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 742, p. 1046-1057Article in journal (Refereed) Published
Abstract [en]

The Al-Fe-Mn system is a core system for both aluminum alloys and lightweight steels. In the present work its phase relations were studied over the entire composition range between RT and well above the melting temperature using the CALPHAD method. For the first time the stable gamma 1 phase and the meta-stable 4 phase were successfully introduced into the description of the Al-Mn binary system. The wide solubility ranges of the third element in the binary intermetallic compounds, such as Al6Mn, Al13Fe4, gamma 1 and gamma 2, were reproduced satisfactorily. The ternary phases, i.e. phi, zeta and D3, were reasonably well described using compound energy models. Moreover, the phase equilibria between the bcc, fcc and beta-Mn phases in the Fe-Mn rich part were well predicted using the present description.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
Al-Mn, Al-Fe-Mn, Thermodynamic modeling, gamma 1, phi, CALPHAD
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-226187 (URN)10.1016/j.jallcom.2018.01.291 (DOI)000427505800124 ()2-s2.0-85041585703 (Scopus ID)
Note

QC 20180518

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2024-03-18Bibliographically approved
4. Computational materials design for lightweight steels with ICME approach: thermodynamics and precipitation strengthening simulation
Open this publication in new window or tab >>Computational materials design for lightweight steels with ICME approach: thermodynamics and precipitation strengthening simulation
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-228399 (URN)
Note

QC 20180524

Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2022-12-06Bibliographically approved
5. Experimental Investigation and Computer Simulation of Diffusion in Fe˗Mo and Fe˗Mn˗Mo Alloys with Different Optimization Methods
Open this publication in new window or tab >>Experimental Investigation and Computer Simulation of Diffusion in Fe˗Mo and Fe˗Mn˗Mo Alloys with Different Optimization Methods
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2017 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48, p. 536-550Article in journal (Refereed) Published
Abstract [en]

In order to simulate the diffusional phase transformations involving the fcc and bcc phases for microalloyed steels, the diffusion mobilities for fcc and bcc Fe˗Mo and Fe˗Mn˗Mo alloys were experimentally investigated and critically assessed. The diffusion-couple technique was employed to extract the interdiffusion coefficients in Fe˗Mo and Fe˗Mn˗Mo alloys with the Sauer-Freise and Whittle-Green methods. Based on the present experimental interdiffsivities, the mobility parameters for the fcc and bcc phases in the Fe˗Mo and Fe˗Mn˗Mo systems were optimized using the traditional method. Simultaneously, a direct method was developed and utilized to directly fit mobilities to the diffusion profiles rather than the diffusivities in the present work. The satisfactory description of the diffusion behavior in the Fe˗Mo and Fe˗Mn˗Mo systems has confirmed the reliability of the direct method. Particularly, the two sets of diffusion mobilities obtained with both methods could simulate the diffusion phenomenon between the fcc and bcc phases in the Fe˗Mo and Fe˗Mn˗Mo systems successfully.

Keywords
Diffusion mobility, Direct method, Diffusion couple, Fe˗Mo, Fe˗Mn˗Mo, Fcc and bcc
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-228398 (URN)10.1007/s11661-016-3822-y (DOI)000391492200049 ()2-s2.0-84991758453 (Scopus ID)
Note

QC 20180524

Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2024-03-18Bibliographically approved

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