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Theoretical Investigations of High-Entropy Alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

High-entropy alloys (HEAs) are composed of multi-principal elements with equal or near-equal concentrations, which open up a vast compositional space for alloy design. Based on first-principle theory, we focus on the fundamental characteristics of the reported HEAs, as well as on the optimization and prediction of alternative HEAs with promising technological applications.

The ab initio calculations presented in the thesis confirm and predict the relatively structural stability of different HEAs, and discuss the composition and temperature-induced phase transformations. The elastic behavior of several HEAs are evaluated through the single-crystal and polycrystalline elastic moduli by making use of a series of phenomenological models. The competition between dislocation full slip, twinning, and martensitic transformation during plastic deformation of HEAs with face-centered cubic phase are analyzed by studying the generalized stacking fault energy. The magnetic moments and magnetic exchange interactions for selected HEAs are calculated, and then applied in the Heisenberg Hamiltonian model in connection with Monte-Carlo simulations to get further insight into the magnetic characteristics including Curie point. The Debye-Grüneisen model is used to estimate the temperature variation of the thermal expansion coefficient.

This work provides specific theoretical points of view to try to understand the intrinsic physical mechanisms behind the observed complex behavior in multi-component systems, and reveals some opportunities for designing and optimizing the properties of materials

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 35
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-218162ISBN: 978-91-7729-544-0 (print)OAI: oai:DiVA.org:kth-218162DiVA, id: diva2:1159786
Presentation
2017-11-15, konferensrummet, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20171127

Available from: 2017-11-27 Created: 2017-11-23 Last updated: 2017-11-27Bibliographically approved
List of papers
1. Temperature dependent stacking fault energy of FeCrCoNiMn high entropy alloy
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2015 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 108, p. 44-47Article in journal (Refereed) Published
Abstract [en]

The stacking fault energy (SFE) of paramagnetic FeCrCoNiMn high entropy alloy is investigated as a function of temperature via ab initio calculations. We divide the SFE into three major contributions: chemical, magnetic and strain parts. Structural energies, local magnetic moments and elastic moduli are used to estimate the effect of temperature on each term. The present results explain the recently reported twinning observed below room-temperature and predict the occurrence of the hexagonal phase at cryogenic conditions.

Keywords
High-entropy alloy, Stacking fault energy, Twinning, First-principles calculation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-173754 (URN)10.1016/j.scriptamat.2015.05.041 (DOI)000360250700011 ()2-s2.0-84939776873 (Scopus ID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA
Note

QC 20150923

Available from: 2015-09-23 Created: 2015-09-18 Last updated: 2018-06-01Bibliographically approved
2. Phase stability and magnetic behavior of FeCrCoNiGe high-entropy alloy
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 25Article in journal (Refereed) Published
Abstract [en]

We report an alternative FeCrCoNiGe magnetic material based on FeCrCoNi high-entropy alloy with Curie point far below the room temperature. Investigations are done using first-principles calculations and key experimental measurements. Results show that the equimolar FeCrCoNiGe system is decomposed into a mixture of face-centered cubic and body-centered cubic solid solution phases. The increased stability of the ferromagnetic order in the as-cast FeCrCoNiGe composite, with measured Curie temperature of 640 K, is explained using the exchange interactions.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-181815 (URN)10.1063/1.4938398 (DOI)000368442100017 ()2-s2.0-84952683248 (Scopus ID)
Funder
Swedish Research CouncilVINNOVA, 2014-03374
Note

QC 20160209. QC 20160216

Available from: 2016-02-09 Created: 2016-02-05 Last updated: 2017-11-30Bibliographically approved
3. Mechanism of magnetic transition in FeCrCoNi-based high entropy alloys
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2016 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 103, p. 71-74Article in journal (Refereed) Published
Abstract [en]

First-principles alloy theory and Monte-Carlo simulations are performed to investigate the magnetic properties of FeCrCoNiAlx high entropy alloys. Results show that face-centered-cubic (fcc) and body-centered-cubic (bcc) structures possess significantly different magnetic behaviors uncovering that the alloy's Curie temperature is controlled by the stability of the Al-induced single phase or fcc-bcc dual-phase. We show that the appearance of the bcc phase with increasing Al content brings about the observed transition from the paramagnetic state for FeCrCoNi to the ferromagnetic state for FeCrCoNiAl at room-temperature. Similar mechanism is predicted to give rise to room-temperature ferromagnetism in FeCrCoNiGa high entropy alloy.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
First-principles calculation, High-entropy alloy, Magnetic transition, Monte-Carlo simulation, Aluminum, Calculations, Crystal structure, Entropy, Ferromagnetism, Intelligent systems, Magnetism, Stainless steel, Body-centered cubic (bcc) structure, Face-centered cubic, Ferromagnetic state, High entropy alloys, Magnetic transitions, Paramagnetic state, Room temperature ferromagnetism, Monte Carlo methods
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-186897 (URN)10.1016/j.matdes.2016.04.053 (DOI)000376892300008 ()2-s2.0-84964558121 (Scopus ID)
Note

QC 20160518

Available from: 2016-05-18 Created: 2016-05-16 Last updated: 2018-06-01Bibliographically approved
4. Thermal expansion in FeCrCoNiGa high-entropy alloy from theory and experiment
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2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, no 24, article id 241902Article in journal (Refereed) Published
Abstract [en]

First-principle alloy theory and key experimental techniques are applied to determine the thermal expansion of FeCrCoNiGa high-entropy alloy. The magnetic transition, observed at 649 K, is accompanied by a significant increase in the thermal expansion coefficient. The phase stability is analyzed as a function of temperature via the calculated free energies accounting for the structural, magnetic, electronic, vibrational and configurational contributions. The single- and polycrystal elastic modulus for the ferro- and paramagnetic states of the face-centered and body-centered cubic phases are presented. By combining the measured and theoretically predicted temperature-dependent lattice parameters, we reveal the structural and magnetic origin of the observed anomalous thermal expansion behavior.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-209983 (URN)10.1063/1.4985724 (DOI)000403678300010 ()2-s2.0-85020521759 (Scopus ID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA, 2014-03374Carl Tryggers foundation
Note

QC 20170628

Available from: 2017-06-28 Created: 2017-06-28 Last updated: 2018-06-01Bibliographically approved
5. Mechanical performance of FeCrCoMnAlx high-entropy alloys from first-principle
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(English)Manuscript (preprint) (Other academic)
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-218287 (URN)
Note

QC 20171127

Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2017-11-27Bibliographically approved
6. Thermal expansion, elastic and magnetic properties of FeCoNiCu-based high-entropy alloys using first-principle theory
Open this publication in new window or tab >>Thermal expansion, elastic and magnetic properties of FeCoNiCu-based high-entropy alloys using first-principle theory
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(English)Manuscript (preprint) (Other academic)
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-218288 (URN)
Note

QC 20171127

Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2017-11-27Bibliographically approved

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