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Understanding the mechanical properties of reduced activation steels
Dalian Univ Technol, Minist Educ, Key Lab Mat Modificat Laser Electron & Ion Beams, Dalian 116024, Peoples R China.;KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.ORCID iD: 0000-0001-9317-6205
Changzhou Vocat Inst Mechatron Technol, Inst Mold Technol, Changzhou 213164, Peoples R China..
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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. Vol. 146, p. 260-272
Keywords [en]
Reduced activation ferritic/martensitic steels, Elastic properties, Ductility
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-226182DOI: 10.1016/j.matdes.2018.03.009ISI: 000428802500026Scopus ID: 2-s2.0-85056372795OAI: oai:DiVA.org:kth-226182DiVA, id: diva2:1206161
Note

QC 20180516

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-12-05Bibliographically approved
In thesis
1. First-principles study of materials for advanced energy technology
Open this publication in new window or tab >>First-principles study of materials for advanced energy technology
2018 (English)Licentiate 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) 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) are the main tools 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 alloys by studying the surface and unstable stacking fault energies. In part one, the effect of neutron transmutation elements on the elastic properties of the W-based alloys are calculated. 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−x−yRexOsy (0 ≤ x, y ≤0.06) enhance with the addition of Re but decrease with increasing Os. From the variations of the Cauchy pressure, Poisson 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. The classical Labusch-Nabarro model for solid-solution hardening predicts that strengthening effects in W1−yOsy is larger than those in W1−xRex. 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. Within a simple empirical equation, we find that the melting temperature of W-Re-Os alloy decrease with Re and Os addition. In part two, we investigate the micro-mechanical properties of the main alloy phases of three reduced activation ferritic/martensitic (RAFM) steels: CLAM/CLF-1, F82H, and EUROFER97. 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 analyzed. 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.

Place, publisher, year, edition, pages
Kungliga Tekniska högskolan, 2018. p. 39
Series
TRITA-ITM-AVL ; 2018:48
National Category
Other Mechanical Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-234895 (URN)978-91-7729-907-3 (ISBN)
Presentation
2018-10-04, N111, Brinellvägen 23, KTH, Stockholm., 10:00 (English)
Opponent
Supervisors
Note

QC 20180912

Available from: 2018-09-12 Created: 2018-09-12 Last updated: 2018-09-18Bibliographically approved

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Li, XiaoqingSchönecker, StephanVitos, Levente

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