uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 268) Show all publications
Levamaki, H., Tian, L.-Y., Vitos, L. & Ropo, M. (2019). An automated algorithm for reliable equation of state fitting of magnetic systems. Computational materials science, 156, 121-128
Open this publication in new window or tab >>An automated algorithm for reliable equation of state fitting of magnetic systems
2019 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 156, p. 121-128Article in journal (Refereed) Published
Abstract [en]

In computational physics and materials science ground-state properties are often extracted from an equation of state fit to energy-volume data. Magnetic systems often have multiple magnetic phases present in the energy-volume data, which poses a challenge for the fitting approach because the results are sensitive to the selection of included fitting points. This is because practically all popular equation of state fitting functions, such as Murnaghan and Birch-Murnaghan, assume just one phase and therefore cannot correctly fit magnetic energy-volume data that contains multiple phases. When fitting magnetic energy-volume data it is therefore important to select the range of fitting points in such a way that only points from the one relevant phase are included. We present a simple algorithm that makes the point selection automatically. Selecting fitting points automatically removes human bias and should also be useful for large-scale projects where selecting all fitting points by hand is not feasible.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Equation of state fitting, EOS
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-369378 (URN)10.1016/j.commatsci.2018.09.026 (DOI)000449375500015 ()
Available from: 2019-01-15 Created: 2019-01-15 Last updated: 2019-01-15Bibliographically approved
Xie, R., Li, W., Lu, S., Song, Y. & Vitos, L. (2019). Generalized stacking fault energy of carbon-alloyed paramagnetic gamma-Fe. Journal of Physics: Condensed Matter, 31(6), Article ID 065703.
Open this publication in new window or tab >>Generalized stacking fault energy of carbon-alloyed paramagnetic gamma-Fe
Show others...
2019 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 6, article id 065703Article in journal (Refereed) Published
Abstract [en]

Generalized stacking fault energy (GSFE) is an important parameter for understanding the underlying physics governing the deformation mechanisms in face-centred cubic (fcc) materials. In the present work, we study the long-standing question regarding the influence of C on the GSFE in austenitic steels at paramagnetic state. We calculate the GSFE in both gamma-Fe and Fe-C alloys using the exact muffin-tin orbitals method and the Vienna Ab initio Simulation Package. Our results show that the GSFE is increased by the presence of interstitial C, and the universal scaling law is used to verify the accuracy of the obtained stacking fault energies. The C-driven change of the GSFE is discussed considering the magnetic contributions. The effective energy barriers for stacking fault, twinning and slip formation are employed to disclose the C effect on the deformation modes, and we also demonstrate that the magnetic structures as a function of volume explain the effect of paramagnetism on the C-driven changes of the stacking fault energies as compared to the hypothetical non-magnetic case.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
C-alloyed gamma-Fe, GSFE, paramagnetism, ab initio
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-373304 (URN)10.1088/1361-648X/aaf2fa (DOI)000454553700001 ()30524044 (PubMedID)
Funder
VINNOVASwedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2019-01-16 Created: 2019-01-16 Last updated: 2019-01-16Bibliographically approved
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
Lizarraga, R., Holmstrom, E. & Vitos, L. (2018). Alloying effect of tungsten on the structural and magnetic properties of CoCrFeNiW high entropy alloys. PHYSICAL REVIEW MATERIALS, 2(9), Article ID 094407.
Open this publication in new window or tab >>Alloying effect of tungsten on the structural and magnetic properties of CoCrFeNiW high entropy alloys
2018 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 9, article id 094407Article in journal (Refereed) Published
Abstract [en]

The recent observation of the hexagonal-closed-packed (hcp) phase in CoCrFeNi-based multicomponent alloys has reopened the question of phase stability in these alloys. We investigate the alloying effect of tungsten on the crystal and magnetic structures of (CoCrFeNi)(1-x)W-x high entropy alloys using density functional theory by means of the exact muffin-tin orbital method. The body-centered-cubic (bcc), face-centered-cubic (fcc), and hcp phases are investigated in two magnetic states: ferrimagnetic and paramagnetic. Below 8 at. % W the ground state of (CoCrFeNi)(1-x)W-x is the ferrimagnetic hcp phase and above that, the ferrimagnetic bcc phase is stabilized. Our calculations show that the fcc and hcp phases are energetically very close in the whole range of studied W compositions and because CoCrFeNi and (CoCrFeNi)(0.93)W-0.07 are observed in the fcc phase at room temperature, the hcp-fcc structural phase transition is expected to occur at lower temperatures. The total magnetic moment in bcc is almost double the value calculated for the fcc and hcp structures, which is due to that Cr moments are nearly quenched in bcc but are coupled antiferromagnetically to Fe, Ni, and Co in both hcp and fcc. We calculated also the Curie temperature of these alloys using the mean-field approximation. The calculated value was found to be 155 K for fcc CoCrFeNi, in excellent agreement with experiments, and the addition of W decreases this value. Our results contribute to the development of these relatively unknown corrosion-resistant materials into industrial applications, such as cemented carbides.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-366727 (URN)10.1103/PhysRevMaterials.2.094407 (DOI)000445518700002 ()
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)
Available from: 2018-12-12 Created: 2018-12-12 Last updated: 2018-12-12Bibliographically approved
Yang, Z.-b., Sun, J., Lu, S. & Vitos, L. (2018). Assessing elastic property and solid-solution strengthening of binary Ni-Co, Ni-Cr, and ternary Ni-Co-Cr alloys from first-principles theory. Journal of Materials Research, 33(18), 2763-2774
Open this publication in new window or tab >>Assessing elastic property and solid-solution strengthening of binary Ni-Co, Ni-Cr, and ternary Ni-Co-Cr alloys from first-principles theory
2018 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 33, no 18, p. 2763-2774Article in journal (Refereed) Published
Abstract [en]

The elastic properties and solid-solution strengthening (SSS) of the binary Ni-Co and Ni-Cr, and ternary Ni-Co-Cr alloys were investigated by the first-principles method. The results show that both Co and Cr increase lattice parameters of the binary alloys linearly. However, nonlinearity is found in compositional dependence of lattice parameters in the ternary Ni-Co-Cr alloys, that is, Co increases but decreases the lattice parameter at low and high Cr concentrations, respectively. Co increases the bulk, shear, and Young's moduli (B, G, and E), while Cr increases B but decreases G and E in the binary alloys. In the ternary Ni-Co-Cr alloys, G and E have a similar compositional dependence to those in the binary alloys, except for B. Based on the Labusch model, the SSS parameter of Ni-Cr is larger than that of Ni-Co. The SSS effect increases significantly with Cr addition, especially at low Co concentrations in the ternary Ni-Co-Cr alloys. Meanwhile, it increases mildly with Co addition at low Cr concentrations but decreases with Co addition at high Cr concentrations.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2018
Keywords
alloy, elastic properties, simulation
National Category
Metallurgy and Metallic Materials Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-368758 (URN)10.1557/jmr.2018.174 (DOI)000446676400012 ()
Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2018-12-10Bibliographically 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
Show others...
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
Östlin, A., Vitos, L. & Chioncel, L. (2018). Correlated electronic structure with uncorrelated disorder. Physical Review B, 98(23), Article ID 235135.
Open this publication in new window or tab >>Correlated electronic structure with uncorrelated disorder
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 23, article id 235135Article in journal (Refereed) Published
Abstract [en]

We introduce a computational scheme for calculating the electronic structure of random alloys that includes electronic correlations within the framework of the combined density functional and dynamical mean-field theory. By making use of the particularly simple parametrization of the electron Green's function within the linearized muffin-tin orbitals method, we show that it is possible to greatly simplify the embedding of the self-energy. This in turn facilitates the implementation of the coherent potential approximation, which is used to model the substitutional disorder. The computational technique is tested on the Cu-Pd binary alloy system, and for disordered Mn-Ni interchange in the half-metallic NiMnSb.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-372923 (URN)10.1103/PhysRevB.98.235135 (DOI)000453462700003 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research German Research Foundation (DFG), FOR 1346 TRR80/F6The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2019-01-10Bibliographically 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
Show others...
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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

Search in DiVA

Show all publications