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Zhang, H., Sun, X., Lu, S., Dong, Z., Ding, X., Wang, Y. & Vitos, L. (2018). Elastic properties of AlxCrMnFeCoNi (0 <= x <= 5) high-entropy alloys from ab initio theory. Acta Materialia, 155, 12-22
Open this publication in new window or tab >>Elastic properties of AlxCrMnFeCoNi (0 <= x <= 5) high-entropy alloys from ab initio theory
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2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 155, p. 12-22Article in journal (Refereed) Published
Abstract [en]

Using ab initio calculations, we investigate the elastic properties of paramagnetic AlxCrMnFeCoNi (0 <= x <= 5) high -entropy alloys (HEAs) in both body-centered cubic (bcc) and face-centered cubic (fcc) structures. Comparison with available experimental data demonstrates that the employed approach describes accurately the elastic moduli. The predicted lattice constants increase monotonously with Al addition, whereas the elastic parameters exhibit complex composition dependences. The elastic anisotropy is unusually high for both phases. The brittle/ductile transitions formulated in terms of Cauchy pressure and Pugh ratio become consistent only when the strong elastic anisotropy is accounted for. The negative Cauchy pressure of CrMnFeCoNi is due to the relatively low bulk modulus and C-12 elastic constant, which in turn are consistent with the relatively low cohesive energy. The present findings in combination with the experimental data suggest anomalous metallic character for the HEAs system. 

National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-232868 (URN)10.1016/j.actamat.2018.05.050 (DOI)000439675000002 ()
Note

QC 20180810

Available from: 2018-08-10 Created: 2018-08-10 Last updated: 2018-08-10Bibliographically approved
Li, X., Irving, D. L. & Vitos, L. (2018). First-principles investigation of the micromechanical properties of fcc-hcp polymorphic high-entropy alloys. Scientific Reports, 8, Article ID 11196.
Open this publication in new window or tab >>First-principles investigation of the micromechanical properties of fcc-hcp polymorphic high-entropy alloys
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 11196Article in journal (Refereed) Published
Abstract [en]

High-entropy alloys offer a promising alternative in several high-technology applications concerning functional, safety and health aspects. Many of these new alloys compete with traditional structural materials in terms of mechanical characteristics. Understanding and controlling their properties are of the outmost importance in order to find the best single-or multiphase solutions for specific uses. Here, we employ first-principles alloy theory to address the micro-mechanical properties of five polymorphic high-entropy alloys in their face-centered cubic (fcc) and hexagonal close-packed (hcp) phases. Using the calculated elastic parameters, we analyze the mechanical stability, elastic anisotropy, and reveal a strong correlation between the polycrystalline moduli and the average valence electron concentration. We investigate the ideal shear strength of two selected alloys under shear loading and show that the hcp phase possesses more than two times larger intrinsic strength than that of the fcc phase. The derived half-width of the dislocation core predicts a smaller Peierls barrier in the fcc phase confirming its increased ductility compared to the hcp one. The present theoretical findings explain a series of important observations made on dual-phase alloys and provide an atomic-level knowledge for an intelligent design of further high-entropy materials.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-232883 (URN)10.1038/s41598-018-29588-z (DOI)000439686700019 ()30046064 (PubMedID)2-s2.0-85050698721 (Scopus ID)
Note

QC 20180809

Available from: 2018-08-09 Created: 2018-08-09 Last updated: 2018-08-09Bibliographically approved
Levamäki, H., Tian, L., Kokko, K. & Vitos, L. (2018). Gradient-level and nonlocal density functional descriptions of Cu-Au intermetallic compounds. European Physical Journal B: Condensed Matter Physics, 91(6), Article ID 128.
Open this publication in new window or tab >>Gradient-level and nonlocal density functional descriptions of Cu-Au intermetallic compounds
2018 (English)In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 91, no 6, article id 128Article in journal (Refereed) Published
Abstract [en]

We use three gradient level and two nonlocal density functional approximations to study the thermodynamic properties of Cu-Au compounds. It is found that a well-designed gradient level approximation (quasi non-uniform approximation, QNA) reproduces the experimental equilibrium volumes and the formation energies of L12 and L10 phases. On the other hand, QNA predicts a non-existent beta(2) phase, which can be remedied only when employing the nonlocal hybrid-level Heyd-Scuseria-Ernzerhof (HSE06) or Perdew-Burke-Ernzerhof (PBE0) approximations. Gradient-level approximations lead to similar electronic structures for the Cu-Au compounds whereas hybrids shift the d-band towards negative energies and account for the complex d-d hybridization more accurately.

Place, publisher, year, edition, pages
SPRINGER, 2018
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-232252 (URN)10.1140/epjb/o2018-90166-9 (DOI)000436369100003 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation VINNOVASwedish Energy Agency
Note

QC 20180720

Available from: 2018-07-20 Created: 2018-07-20 Last updated: 2018-07-20Bibliographically approved
Landa, A., Soederlind, P., Naumov, I. I., Klepeis, J. E. & Vitos, L. (2018). Kohn Anomaly and Phase Stability in Group VB Transition Metals. Computation, 6(2), Article ID 29.
Open this publication in new window or tab >>Kohn Anomaly and Phase Stability in Group VB Transition Metals
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2018 (English)In: Computation, E-ISSN 2079-3197, Vol. 6, no 2, article id 29Article, review/survey (Refereed) Published
Abstract [en]

In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being alpha-U and Cr. Whereas alpha-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals-materials with relatively high superconducting critical temperatures. This article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (xi 00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
Kohn anomaly, Fermi surface nesting, phonon softening
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-228420 (URN)10.3390/computation6020029 (DOI)000431867700003 ()
Note

QC 20180528

Available from: 2018-05-28 Created: 2018-05-28 Last updated: 2018-05-28Bibliographically approved
Levamaki, H., Nagy, A., Vilja, I., Kokko, K. & Vitos, L. (2018). Kullback-Leibler and relative Fisher information as descriptors of locality. International Journal of Quantum Chemistry, 118(12), Article ID e25557.
Open this publication in new window or tab >>Kullback-Leibler and relative Fisher information as descriptors of locality
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2018 (English)In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 118, no 12, article id e25557Article in journal (Refereed) Published
Abstract [en]

Kullback-Leibler and relative Fisher information functionals are applied in studying deviation from local density approximation. The reduced density gradient s and the local kinetic energy parameter alpha are key ingredients of these new locality descriptors. The relative Kullback-Leibler information density contains extra knowledge as it is negative where the given probability density is smaller than the reference density. The relative Fisher information incorporates the highest order deviations from the uniform electron gas approximation.

Place, publisher, year, edition, pages
WILEY, 2018
Keywords
density functional theory, descriptors of locality, Kullback-Leibler information, relative Fisher information
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-228414 (URN)10.1002/qua.25557 (DOI)000432000700004 ()2-s2.0-85037672111 (Scopus ID)
Note

QC 20180528

Available from: 2018-05-28 Created: 2018-05-28 Last updated: 2018-05-28Bibliographically approved
Choi, Y. W., Koo, Y. M., Kwon, S. K. & Vitos, L. (2018). Ordered Phases in Fe-Si Alloys: A First-Principles Study. Journal of the Korean Physical Society, 72(6), 737-740
Open this publication in new window or tab >>Ordered Phases in Fe-Si Alloys: A First-Principles Study
2018 (English)In: Journal of the Korean Physical Society, ISSN 0374-4884, E-ISSN 1976-8524, Vol. 72, no 6, p. 737-740Article in journal (Refereed) Published
Abstract [en]

It is known that the formation of ordered phases causes the brittleness of electrical steels. We employed first-principles method in order to examine the possibility of the ordered-phases formation in Fe-Si alloys. It is found that the D03-like ordered configuration is most stable among other atomic configurations in the ferromagnetic state. In the paramagnetic state, for low Si concentration, the stability of the ordered configurations is comparable to that of disordered ones. However, as Si content increases, the B2 ordered phase as well as the D03 phase becomes more stable than the disordered ones. 

Place, publisher, year, edition, pages
The Korean Physical Society, 2018
Keywords
Electrical steel, Embrittlement, First-principles calculations, Ordered phases
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-227410 (URN)10.3938/jkps.72.737 (DOI)000428268100016 ()2-s2.0-85044338814 (Scopus ID)
Note

Export Date: 9 May 2018; Article; Correspondence Address: Kwon, S.K.; Graduate Institute of Ferrous Technology, Pohang University of Science and TechnologySouth Korea; email: sekk@postech.ac.kr; Funding details: 2014-03374; Funding details: STINT, Swedish Foundation for International Cooperation in Research and Higher Education; Funding details: VR, Vetenskapsrådet; Funding details: Carl Tryggers Stiftelse för Vetenskaplig Forskning; Funding details: SSF, Stiftelsen för Strategisk Forskning; Funding details: OTKA 109570, OTKA, Országos Tudományos Kutatási Alapprogramok; Funding details: FASI, Federal Agency for Science and Innovation; Funding details: NRF-2017R1A2A1A18071775, NRF, National Research Foundation of Korea; Funding text: This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF-2017R1A2A1A18071775), the Swedish Research Council, the Swedish Foundation for Strategic Research, Sweden’s Innovation Agency (VIN-NOVA Grant No. 2014-03374), the Swedish Foundation for International Cooperation in Research and Higher Education, the Carl Tryggers Foundation, and the Hungarian Scientific Research Fund (OTKA 109570). QC 20180530

Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2018-05-30Bibliographically approved
Li, X., Schönecker, S., Li, W., Varga, L. K., Irving, D. L. & Vitos, L. (2018). Tensile and shear loading of four fcc high-entropy alloys: A first-principles study. Physical Review B, 97(9), Article ID 094102.
Open this publication in new window or tab >>Tensile and shear loading of four fcc high-entropy alloys: A first-principles study
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094102Article in journal (Refereed) Published
Abstract [en]

Ab initio density-functional calculations are used to investigate the response of four face-centered-cubic (fcc) high-entropy alloys (HEAs) to tensile and shear loading. The ideal tensile and shear strengths (ITS and ISS) of the HEAs are studied by employing first-principles alloy theory formulated within the exact muffin-tin orbital method in combination with the coherent-potential approximation. We benchmark the computational accuracy against literature data by studying the ITS under uniaxial [110] tensile loading and the ISS for the [11 (2) over tilde](111) shear deformation of pure fcc Ni and Al. For the HEAs, we uncover the alloying effect on the ITS and ISS. Under shear loading, relaxation reduces the ISS by similar to 50% for all considered HEAs. We demonstrate that the dimensionless tensile and shear strengths are significantly overestimated by adopting two widely used empirical models in comparison with our ab initio calculations. In addition, our predicted relationship between the dimensionless shear strength and shear instability are in line with the modified Frenkel model. Using the computed ISS, we derive the half-width of the dislocation core for the present HEAs. Employing the ratio of ITS to ISS, we discuss the intrinsic ductility of HEAs and compare it with a common empirical criterion. We observe a strong linear correlation between the shear instability and the ratio of ITS to ISS, whereas a weak positive correlation is found in the case of the empirical criterion.

Place, publisher, year, edition, pages
American Physical Society, 2018
Keywords
Ab-Initio, Theoretical Strength, Ideal Strength, Metals, Approximation, Dislocation, Crystals, Aluminum, Molybdenum, Simulation
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-224677 (URN)10.1103/PhysRevB.97.094102 (DOI)000426775200002 ()2-s2.0-85043990703 (Scopus ID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Note

QC 20180323

Available from: 2018-03-23 Created: 2018-03-23 Last updated: 2018-03-27Bibliographically approved
Lee, J.-Y. -., Punkkinen, M. P., Schönecker, S., Nabi, Z., Kádas, K., Zólyomi, V., . . . Kwon, S. K. (2018). The surface energy and stress of metals. Surface Science, 674, 51-68
Open this publication in new window or tab >>The surface energy and stress of metals
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2018 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 674, p. 51-68Article in journal (Refereed) Published
Abstract [en]

We investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Density-functional theory calculations, Metals, Surface energy, Surface relaxation, Surface stress
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-227516 (URN)10.1016/j.susc.2018.03.008 (DOI)000432759200009 ()2-s2.0-85045204083 (Scopus ID)
Funder
Swedish Energy AgencyThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)VINNOVA, 2014-03374Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-06-13Bibliographically approved
Huang, S., Vida, A., Heczel, A., Holmstrom, E. & Vitos, L. (2018). Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory (vol 69, pg 2107, 2017). JOM: The Member Journal of TMS, 70(6), 1037-1037
Open this publication in new window or tab >>Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory (vol 69, pg 2107, 2017)
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2018 (English)In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 70, no 6, p. 1037-1037Article in journal (Refereed) Published
Place, publisher, year, edition, pages
SPRINGER, 2018
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-230422 (URN)10.1007/s11837-018-2775-6 (DOI)000432755000040 ()2-s2.0-85041914187 (Scopus ID)
Note

QC 20180619

Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-06-19Bibliographically approved
Tian, L.-Y., Wang, G., Harris, J. S., Irving, D. L., Zhao, J. & Vitos, L. (2017). Alloying effect on the elastic properties of refractory high-entropy alloys. MATERIALS & DESIGN, 114, 243-252
Open this publication in new window or tab >>Alloying effect on the elastic properties of refractory high-entropy alloys
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2017 (English)In: MATERIALS & DESIGN, ISSN 0264-1275, Vol. 114, p. 243-252Article in journal (Refereed) Published
Abstract [en]

Ab initio total energy calculations are used to determine the elastic properties of TiZrVNb, TiZrNbMo and TiZrVNbMo high-entropy alloys in the body centered cubic (bcc) crystallographic phase. Calculations are performed using the Vienna Ab initio Simulation Package and the Exact Muffin-Tin Orbitals methods, and the compositional disorder is treated within the frameworks of the special quasi-random structures technique and the coherent potential approximation, respectively. Special emphasis is given to the effect of local lattice distortion and trends against composition. Significant distortion can be observed in the relaxed cells, which result in an overlap of the first and second nearest neighbor (NN) shells represented in the histograms. When going from the four-component alloys TiZrVNb and TiZrNbMo to the five-component TiZrVNbMo, the changes in the elastic parameters follow the expected trends, except that of C-44 which decreases upon adding equiatomic Mo to TiZrVNb despite of the large shear elastic constant of elemental Mo. Although the rule of mixtures turns out to be a useful tool to estimate the elastic properties of the present HEAs, to capture the more delicate alloying effects one needs to resort to ab initio results.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
High-entropy alloys, Lattice parameter, Elastic constant, Local lattice distortion, Alloying effect
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-200188 (URN)10.1016/j.matdes.2016.11.079 (DOI)000390650800031 ()2-s2.0-85006056575 (Scopus ID)
Note

QC 20170123

Available from: 2017-01-23 Created: 2017-01-23 Last updated: 2017-06-30Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

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