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Materials for advanced energy technology from quantum-mechanical modeling
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.ORCID iD: 0000-0002-5904-1910
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis addresses promising material solutions for fusion reactors from a theoretical point of view. We focus on two specific systems: W-based alloys used as plasma-facing materials and reduced activation ferritic/martensitic (RAFM, Ferich) steels used as structural materials of breeding-blanket. We aim to systematically investigate the alloying effects on the micro-mechanical properties of these body-centered cubic (bcc) solid solutions. The all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA) is the main tool for our theoretical studies. The knowledge of the elastic parameters and their solute-induced changes is important for alloy design and for a multi-scale modeling approach to the mechanical properties. We also explore the planar faults in the present Fe-based alloys.In part one, the effect of neutron transmutation elements on the elastic properties of the W-based alloys are calculated. Under intensive radiation, W transforms to Re/Os and thus there is a certain degree of Re/Os doping in the base alloy. Both Re and Os solute atoms shrink the lattice constant, which lead to increasing bulk modulus as the amount of Re or Os increases. The polycrystalline shear and Young’s moduli of W1−xyRexOsy (0 ≤ xy ≤0.06) enhance with the addition of Re but decrease with increasing Os level. From the variations of the Cauchy pressure, Poisson’s ratio, Pugh ratio B/G, and the ratio of cleavage energy to shear modulus for the dominant slip system, we conclude that the intrinsic ductility of the alloy increases with increasing Re and Os content. We use the energy difference between the face-centered cubic (fcc) and bcc structures to estimate the alloying effect on the ideal tensile strength in the [001] direction.In part two, we choose three RAFM steels: CLAM/CLF-1, F82H, and EUROFER97 and investigate the micro-mechanical properties of the main alloy phases at low temperature (0 K). Being the main building blocks of the RAFM steels, first the lattice parameters, elastic properties, surface energy and unstable stacking fault energy of ferromagnetic α-Fe and Fe91Cr9 are calculated for reference. For quantitative understanding, we present a detailed analysis of the calculated individual alloying effects of V, Cr, Mn, and W on the elastic properties of Fe91Cr9. A linear superposition of these individual rates on the elastic properties of RAFM steels is shown to reproduce well the values from ab initio calculations. The composition dependence of the elastic constants is decomposed into electronic and volumetric contributions and they are analyzed separately. Finally, the intrinsic ductility is evaluated through Rice’s phenomenological theory by using the ratio of surface and unstable stacking fault energies. The results are consistent with those obtained by the common empirical criteria.In part three, the temperature dependence (T ≤ 1120 K) of the isothermal singlecrystal and polycrystalline elastic parameters of α-Fe and CLAM are reported by using a first-principles based modeling approach. The effect of temperature on the strongly temperature-dependent elastic constants C11 T and CT' is reproduced, as well as that on derived isotropic elastic moduli. Weak changes in C12 T and C44 T with temperature are obtained. The approach is applied to predict the temperature effect on the elastic parameters of three RAFM steels. Contributions due to loss of longrange magnetic order and the combined effect of volume expansion and entropy are found to be important in determining the temperature dependence of the elastic parameters in all the materials investigated.In part four, the (100) and (110) surface energies and surface segregation energies of Fe1−xbCrxb binary alloys, xb ≤ 15 at.%, are computed. These alloys form the basic building blocks of RAFM steels and thus their surface properties are of fundamental importance for the modeling the mechanical behavior. The implications of these results for the surface alloy phase diagram are discussed. The surface chemistry of Fe-Cr(100) is characterized by a transition from Cr depletion to Cr enrichment in a critical bulk Cr composition window of 6 < xb < 9 at.%. In contrast, a nearly homogeneous Cr concentration profile is energetically favorable in Fe-Cr(110) surface. The strongly suppressed surface-layer relaxation at both surfaces is shown to be of magnetic origin. The compressive, magnetic contribution to the surface relaxation stress is found to correlate well with the surface magnetic moment squared at both surface terminations. The surface electronic structures are used to explain the stability of the Cr surface magnetic moments against bulk Cr content.

Abstract [sv]

Denna avhandling behandlar lovande materiallösningar för fusionreaktorer ur teoretisk synvinkel. Vi fokuserar på två specifika system: W-baserade legeringar som kan användas som plasma-vända material och reducerad aktiverings ferritisk/martensisk(RAFM) stål som kan användas som strukturmaterial till ett täcke för tritiumalstring (breeding blanket). Vi syftar till att systematiskt undersöka legeringseffekterna på de mikromekaniska egenskaperna hos dessa rymdcentrerade kubiska (bcc) fasta lösningar. Den all-elektron exakt muffin-tin orbital (EMTO) metoden i kombination med den koherent potential approximationen (CPA) är de viktigaste verktygen för våra teoretiska studier. Kunskapen i de elastiska parametrarna och deras lösningsinducerade förändringar är viktiga för legeringsdesign och multi-skala modellering approach för de mekaniska egenskaperna. Vi undersöker också planfel i de aktuella legeringarna.I del ett beräknar vi vilken effekt neutron-transmutationselement har på de elastiska egenskaperna hos de W-baserade legeringarna. I del två undersöker vi de mikromekaniska egenskaperna hos den huvudsakliga legeringsfaser av tre RAFM stål: CLAM/CLF-1, F82H och EUROFER97. I del tre redogör vi temperaturberoende (T ≤ 1120 K) på de isotermiska elastiska parametrarna för α -Fe och CLAM med användning av en första princips baserad modelleringsmetod. I del fyra beräknar vi ytegenskaperna i(100) och (110) riktningar för Fe1-xbCrxbinära legeringar , xb ≤ 15 at.%.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2020. , p. 69
Series
TRITA-ITM-AVL ; 18
National Category
Other Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-273057ISBN: 978-91-7873-492-4 (print)OAI: oai:DiVA.org:kth-273057DiVA, id: diva2:1429744
Public defence
2020-06-03, https://kth-se.zoom.us/webinar/register/WN_eJweiFa5T-ik_eYrkrR-gg, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2020-05-12 Created: 2020-05-12 Last updated: 2020-05-27Bibliographically approved
List of papers
1. Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys: effects of transmutation of W
Open this publication in new window or tab >>Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys: effects of transmutation of W
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2016 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 29, article id 295501Article in journal (Refereed) Published
Abstract [en]

To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-yRexOsy (0 <= x, y <= 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young's modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C-11, the other elastic parameters including C-12, C-44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W-Re-Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch-Nabarro model for solid-solution hardening predicts larger strengthening effects in W1-yOsy than in W1-xRex. A strong correlation between C' and the fcc-bcc structural energy difference for W1-x-yRexOsy is revealed demonstrating that canonical band structure dictates the alloying effect on C'. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
disordered W-Re-Os alloys, elastic properties, ductility, solid-solution hardening
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-189354 (URN)10.1088/0953-8984/28/29/295501 (DOI)000377504100007 ()2-s2.0-84975057100 (Scopus ID)
Note

QC 20160708

Available from: 2016-07-08 Created: 2016-07-04 Last updated: 2020-05-12Bibliographically approved
2. Understanding the mechanical properties of reduced activation steels
Open this publication in new window or tab >>Understanding the mechanical properties of reduced activation steels
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2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 146, p. 260-272Article in journal (Refereed) Published
Abstract [en]

Reduced activation ferritic/martensitic (RAFM) steels are structural materials with potential application in Generation-IV fission and fusion reactors. We use density-functional theory to scrutinize the micro-mechanical properties of the main alloy phases of three RAFM steels based on the body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters and elastic properties of ferromagnetic alpha-Fe and Fe91Cr9, which are the main building blocks of the RAFM steels, and present a detailed analysis of the calculated alloying effects of V, Cr, Mn, and W on the mechanical properties of Fe91Cr9. The composition dependence of the elastic parameters is decomposed into electronic and volumetric contributions and studied for alloying levels that cover the typical intervals in RAFM steels. A linear superposition of the individual solute effects on the properties of Fe91Cr9 is shown to provide an excellent approximation for the ab initio values obtained for the RAFM steels. The intrinsic ductility is evaluated through Rice's phenomenological theory using the surface and unstable stacking fault energies, and the predictions are contrasted with those obtained by empirical criteria. Alloying with V or W is found to enhance the ductility, whereas additional Cr or Mn turns the RAFM base alloys more brittle.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Reduced activation ferritic/martensitic steels, Elastic properties, Ductility
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-226182 (URN)10.1016/j.matdes.2018.03.009 (DOI)000428802500026 ()2-s2.0-85056372795 (Scopus ID)
Note

QC 20180516

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2020-05-12Bibliographically approved
3. The influence of temperature on the elastic properties of α-Fe and body-centeredcubic reduced activation steels
Open this publication in new window or tab >>The influence of temperature on the elastic properties of α-Fe and body-centeredcubic reduced activation steels
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(English)In: Article in journal (Other academic) Submitted
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-273278 (URN)
Note

QC 20200523

Available from: 2020-05-12 Created: 2020-05-12 Last updated: 2020-05-23Bibliographically approved
4. First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys
Open this publication in new window or tab >>First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys
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2019 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 3, article id 034401Article in journal (Refereed) Published
Abstract [en]

A density-functional theory investigation of the (100) and (110) surfaces of the body-centered cubic (bcc) Fe1-xbCrxb binary alloys, x(b) <= 15 at.%, is reported. The energies and segregation energies of these surfaces were calculated for chemically homogeneous concentration profiles and for Cr surface contents deviating from the nominal one of the bulk. The implications of these results for the surface alloy phase diagram are discussed. The surface chemistry of Fe-Cr(100) is characterized by a transition from Cr depletion to Cr enrichment in a critical bulk Cr composition window of 6 < x(b) < 9 at.%. In contrast, such threshold behavior of the surface Cr content is absent for Fe-Cr(110) and a nearly homogeneous Cr concentration profile is energetically favorable. The strongly suppressed surface-layer relaxation at both surfaces is shown to be of magnetic origin. The compressive, magnetic contribution to the surface relaxation stress is found to correlate well with the surface magnetic moment squared at both surface terminations. The stability of the Cr surface magnetic moments against bulk Cr content is clarified based on the surface electronic structure.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-247823 (URN)10.1103/PhysRevMaterials.3.034401 (DOI)000460683400001 ()2-s2.0-85062963048 (Scopus ID)
Note

QC 20190327

Available from: 2019-03-27 Created: 2019-03-27 Last updated: 2020-05-12Bibliographically approved

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