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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
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
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
Huang, S., Li, X., Huang, H., Holmstrom, E. & Vitos, L. (2018). Mechanical performance of FeCrCoMnAlx high-entropy alloys from first-principle. Materials Chemistry and Physics, 210, 37-42
Open this publication in new window or tab >>Mechanical performance of FeCrCoMnAlx high-entropy alloys from first-principle
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2018 (English)In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 210, p. 37-42Article in journal (Refereed) Published
Abstract [en]

The elastic parameters and ideal tensile strength in the 10011 direction for the body-centered cubic solid solution phase of FeCrCoMnAlx (0.6 <= x <= 1.5) high-entropy alloys are determined using first-principle alloy theory. Based on the estimated theoretical Curie temperatures, all alloys considered here are predicted to order ferromagnetically at room temperature. The mechanical behaviors are analyzed through the single-crystal and polycrystalline elastic moduli, Pugh ratio, and Debye temperature by making use of a series of phenomenological models. High ideal tensile strength is found for the equiatomic FeCrCoMnAl system, and the intrinsic strength increases with decreasing Al content.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
High-entropy alloys, Mechanical performance, First-principle calculations
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-352577 (URN)10.1016/j.matchemphys.2017.08.061 (DOI)000429762200006 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA, 2014-03374
Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2018-08-07Bibliographically 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 D0(3)-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 D0(3) phase becomes more stable than the disordered ones.

Place, publisher, year, edition, pages
KOREAN PHYSICAL SOC, 2018
Keywords
First-principles calculations, Electrical steel, Embrittlement, Ordered phases
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-354525 (URN)10.3938/jkps.72.737 (DOI)000428268100016 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA, 2014-03374]The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2018-07-24Bibliographically approved
Li, X., Schonecker, 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
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-350286 (URN)10.1103/PhysRevB.97.094102 (DOI)000426775200002 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2018-05-09 Created: 2018-05-09 Last updated: 2018-05-09Bibliographically approved
Lee, J.-Y. -., Punkkinen, M. P., Schönecker, S., Nabi, Z., Kádas, K., Zolyomi, 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 (gamma), and surface stress (tau) 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 gamma of simple metals decreases as the atomic number increases in a given group, while the surface stress tau has its minimum in the middle. The transition metal series show parabolic trends for both gamma and tau 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 gamma and tau 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 tau for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing gamma 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 SCIENCE BV, 2018
Keywords
Surface relaxation, Surface energy, Surface stress, Density-functional theory calculations, Metals
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-356604 (URN)10.1016/j.susc.2018.03.008 (DOI)000432759200009 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research VINNOVA, 2014-03374Swedish Energy AgencyThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2018-08-03 Created: 2018-08-03 Last updated: 2018-08-03Bibliographically approved
Li, X., Li, X., Schonecker, S., Li, R., Zhao, J. & Vitos, L. (2018). Understanding the mechanical properties of reduced activation steels. Materials & design, 146, 260-272
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.

Keywords
Reduced activation ferritic/martensitic steels, Elastic properties, Ductility
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-351615 (URN)10.1016/j.matdes.2018.03.009 (DOI)000428802500026 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-13Bibliographically approved
Tian, L.-Y., Lizarraga, R., Larsson, H., Holmstrom, E. & Vitos, L. (2017). A first principles study of the stacking fault energies for fcc Co-based binary alloys. Acta Materialia, 136, 215-223
Open this publication in new window or tab >>A first principles study of the stacking fault energies for fcc Co-based binary alloys
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2017 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 136, p. 215-223Article in journal (Refereed) Published
Abstract [en]

The stacking fault energy is closely related to structural phase transformations and can help to understand plastic deformation mechanisms in materials. Here we perform first principles calculations of the stacking fault energy in the face centered cubic (fcc) Cobalt-based binary alloys Co1-x M-x, where M = Cr, Fe, Ni, Mo, Ru, Rh, Pd and W. We investigate the concentration range between 0 and 30 at.% of the alloying element. The results are discussed in connection to the phase transition between the low temperature hexagonal close packed (hcp) and the fcc structures observed in Co and its alloys. By analyzing the stacking fault energies, we show that alloying Co with Cr, Ru, and Rh promotes the hcp phase formation while Fe, Ni and Pd favor the fcc phase instead. The effect of Mo and W on the phase transition differs from the other elements, that is, for concentrations below 10% the intrinsic stacking fault energy is lower than that for pure fcc Co and the energy barrier is higher, whereas above 10% the situation reverses. We carry out also thermodynamic calculations using the ThermoCalc software. The trends of the ab initio stacking fault energy are found to agree well with those of the molar Gibbs energy differences and the phase transition temperature in the binary phase diagrams and give a solid support for the phase stability of these alloys.

Keywords
First principles calculations, Stacking fault energies, Cobalt-based alloys, Thermodynamic calculations
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-333947 (URN)10.1016/j.actamat.2017.07.010 (DOI)000407665300019 ()
Available from: 2017-12-13 Created: 2017-12-13 Last updated: 2017-12-13Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

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