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Lu, S., Ågren, J. & Vitos, L. (2018). Ab initio study of energetics and structures of heterophase interfaces: From coherent to semicoherent interfaces. Acta Materialia, 156, 20-30
Open this publication in new window or tab >>Ab initio study of energetics and structures of heterophase interfaces: From coherent to semicoherent interfaces
2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 156, p. 20-30Article in journal (Refereed) Published
Abstract [en]

Density functional theory calculations have been performed to study the structures and energetics of coherent and semicoherent TiC/Fe interfaces. A systematic method for determining the interfacial energy of the semicoherent interface with misfit dislocation network has been developed. The obtained interfacial energies are used to evaluate the aspect ratio for the plate-like precipitate and a quantitative agreement with the experimental results is reached. Based on the obtained interfacial energies and atomic structure details, we propose two scenarios for heterogeneous nucleation on an edge dislocation, shedding light on the thermodynamics of precipitate nucleation and growth. The present method can be easily applied to any heterophase interfaces between metals and oxides/carbides/nitrides.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2018
Keywords
Steels, Transition metal carbides, Heterophase interface, Interfacial energy, ab initio calculation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-362477 (URN)10.1016/j.actamat.2018.06.030 (DOI)000442062800003 ()
Funder
VINNOVASwedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2018-10-10 Created: 2018-10-10 Last updated: 2018-10-10Bibliographically approved
Huang, S., Vida, Á., Heczel, A., Holmström, E. & Vitos, L. (2018). Correction to: Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory. JOM: The Member Journal of TMS, 70(6), 1037-1037
Open this publication in new window or tab >>Correction to: Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory
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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
National Category
Metallurgy and Metallic Materials Materials Engineering
Identifiers
urn:nbn:se:uu:diva-359372 (URN)10.1007/s11837-018-2775-6 (DOI)000432755000040 ()
Note

WoS title: Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory (vol 69, pg 2107, 2017)

Correction to: JOM, vol. 69, issue 11, pages 2107-2112. DOI: 10.1007/s11837-017-2565-6

Available from: 2018-09-04 Created: 2018-09-04 Last updated: 2018-09-04Bibliographically approved
Huang, H., Li, X., Dong, Z., Li, W., Huang, S., Meng, D., . . . Vitos, L. (2018). Critical stress for twinning nucleation in CrCoNi-based medium and high entropy alloys. Acta Materialia, 149, 388-396
Open this publication in new window or tab >>Critical stress for twinning nucleation in CrCoNi-based medium and high entropy alloys
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2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 149, p. 388-396Article in journal (Refereed) Published
Abstract [en]

The CrCoNi-based medium and high entropy alloys (MHEAs) have drawn much attention due to their exceptional mechanical properties at cryogenic temperatures. The twinning critical resolved shear stress (CRSS) is a fundamental parameter for evaluating the strength-ductility properties of MHEAs. Here we construct and apply an extended twinning nucleation Peierls-Nabarro (P-N) model to predict the twinning CRSSes of face-centered cubic (FCC) CrCoNi-based MHEAs. The order of the twinning CRSSes of the selected alloys is CrCoNi > CrCoNiMn > CrCoNiFe > CrCoNiFeMn and the values are 291, 277, 274 and 236 MPa, respectively. These theoretical predictions agree very well with the experimental twinning CRSSes of CrCoNi and CrCoNiFeMn accounting for 260 +/- 30 and 235 +/- 10 MPa, respectively and are perfectly consistent with the strength-ductility properties including yield stress, ultimate tensile stress and uniform elongation for fracture of the FCC CrCoNi-based MHEAs obtained at cryogenic temperatures. The present method offers a first-principle quantum-mechanical tool for optimizing and designing new MHEAs with exceptional mechanical properties.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2018
Keywords
Critical resolved shear stress (CRSS), Medium and high entropy alloys (MHEAs), Twinning nucleation, Density functional theory
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-356197 (URN)10.1016/j.actamat.2018.02.037 (DOI)000430895000034 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA, 2014-03374The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-07-30Bibliographically 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.

National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-362004 (URN)10.1038/s41598-018-29588-z (DOI)000439686700019 ()30046064 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2018-10-05Bibliographically approved
Levamaki, 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
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-360011 (URN)10.1140/epjb/e2018-90166-9 (DOI)000436369100003 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVASwedish Energy AgencyCarl Tryggers foundation The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2018-09-13 Created: 2018-09-13 Last updated: 2018-09-13Bibliographically approved
Landa, A., Söderlind, 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 α-U and Cr. Whereas α-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 (ξ00) 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.

Keywords
Kohn anomaly, Fermi surface nesting, phonon softening
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-358101 (URN)10.3390/computation6020029 (DOI)000431867700003 ()
Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-08-24Bibliographically 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.

Keywords
density functional theory, descriptors of locality, Kullback-Leibler information, relative Fisher information
National Category
Theoretical Chemistry Signal Processing
Identifiers
urn:nbn:se:uu:diva-356849 (URN)10.1002/qua.25557 (DOI)000432000700004 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2018-08-15Bibliographically approved
Schonecker, S., Li, X., Richter, M. & Vitos, L. (2018). Lattice dynamics and metastability of fcc metals in the hcp structure and the crucial role of spin-orbit coupling in platinum. Physical Review B, 97(22), Article ID 224305.
Open this publication in new window or tab >>Lattice dynamics and metastability of fcc metals in the hcp structure and the crucial role of spin-orbit coupling in platinum
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 22, article id 224305Article in journal (Refereed) Published
Abstract [en]

We investigate the lattice dynamical properties of Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au in the nonequilibrium hcp structure by means of density-functional simulations, wherein spin-orbit coupling (SOC) was considered for Ir, Pt, and Au. The determined dynamical properties reveal that all eight elements possess a metastable hcp phase at zero temperature and pressure. The hcp Ni, Cu, Rh, Pd, and Au previously observed in nanostructures support this finding. We make evident that the inclusion of SOC is mandatory for an accurate description of the phonon dispersion relations and dynamical stability of hcp Pt. The underlying sensitivity of the interatomic force constants is ascribed to a SOC-induced splitting of degenerate band states accompanied by a pronounced reduction of electronic density of states at the Fermi level. To give further insight into the importance of SOC in Pt, we (i) focus on phase stability and examine a lattice transformation related to optical phonons in the hcp phase and (ii) focus on the generalized stacking fault energy (GSFE) of the fcc phase pertinent to crystal plasticity. We show that the intrinsic stable and unstable fault energies of the GSFE scale as in other common fcc metals, provided that the spin-orbit interaction is taken into account.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-358384 (URN)10.1103/PhysRevB.97.224305 (DOI)000434929500002 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA, 201403374Swedish Energy AgencyCarl Tryggers foundation The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2018-08-29Bibliographically approved
Ji, Z.-W., Lu, S., Hu, Q.-m., Kim, D., Yang, R. & Vitos, L. (2018). Mapping deformation mechanisms in lamellar titanium aluminide. Acta Materialia, 144, 835-843
Open this publication in new window or tab >>Mapping deformation mechanisms in lamellar titanium aluminide
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2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 144, p. 835-843Article in journal (Refereed) Published
Abstract [en]

Breakdown of Schmid's law is a long-standing problem for exploring the orientation-dependent deformation mechanism in intermetallics. The lack of atomic-level understanding of the selection rules for the plastic deformation modes has seriously limited designing strong and ductile intermetallics for high-temperature applications. Here we put forward a transparent model solely based on first principles simulations for mapping the deformation modes in gamma-TiAl polysynthetic twinned alloys. The model bridges intrinsic energy barriers and different deformation mechanisms and beautifully resolves the complexity of the observed orientation-dependent deformation mechanisms. Using the model, one can elegantly reveal the atomic-level mechanisms behind the unique channeled flow phenomenon in lamellar TiAl alloys.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2018
Keywords
Stacking fault, Twinning, Slip, First principles
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-347091 (URN)10.1016/j.actamat.2017.11.028 (DOI)000424067100076 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation VINNOVA
Available from: 2018-03-26 Created: 2018-03-26 Last updated: 2018-03-26Bibliographically approved
Huang, S., Holmstrom, E., Eriksson, O. & Vitos, L. (2018). Mapping the magnetic transition temperatures for medium- and high-entropy alloys. Intermetallics (Barking), 95, 80-84
Open this publication in new window or tab >>Mapping the magnetic transition temperatures for medium- and high-entropy alloys
2018 (English)In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 95, p. 80-84Article in journal (Refereed) Published
Abstract [en]

Tailorable magnetic state near room temperature is very promising for several technological, including magnetocaloric applications. Here using first-principle alloy theory, we determine the Curie temperature (T-C) of a number of equiatomic medium- and high-entropy alloys with solid solution phases. All calculations are performed at the computed lattice parameters, which are in line with the available experimental data. Theory predicts a large crystal structure dependence of T-C, which explains the experimental observations under specified conditions. The sensitivity of the magnetic state to the crystal lattice is reflected by the magnetic exchange interactions entering the Heisenberg Hamiltonian. The analysis of the effect of composition on T-C allows researchers to explore chemistry-dependent trends and design new multi-component alloys with pre-assigned magnetic properties.

Keywords
Curie temperature, High-entropy alloys, First-principle calculations, Monte-Carlo simulations
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-351640 (URN)10.1016/j.intermet.2018.01.016 (DOI)000428975100010 ()
Funder
Swedish Research CouncilVINNOVA, 2014-03374Swedish Foundation for Strategic Research Carl Tryggers foundation The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Energy Agency
Available from: 2018-06-07 Created: 2018-06-07 Last updated: 2018-06-07Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

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