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Levämäki, H., Tian, 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, 2019
Keywords
EOS, Equation of state fitting, Ground state, Magnetism, Automated algorithms, Computational physics, Equation of state, Fitting functions, Ground state properties, Large-scale projects, Magnetic energies, SIMPLE algorithm, Equations of state
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-236337 (URN)10.1016/j.commatsci.2018.09.026 (DOI)000449375500015 ()2-s2.0-85053772857 (Scopus ID)
Note

QC 20181109

Available from: 2018-11-09 Created: 2018-11-09 Last updated: 2018-11-28Bibliographically approved
Al-Zoubi, N., Schönecker, S., Li, X., Li, W., Johansson, B. & Vitos, L. (2019). Elastic properties of 4d transition metal alloys: Values and trends. Computational materials science, 159, 273-280
Open this publication in new window or tab >>Elastic properties of 4d transition metal alloys: Values and trends
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2019 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 159, p. 273-280Article in journal (Refereed) Published
Abstract [en]

Using the Exact Muffin-Tin Orbitals method within the Perdew-Burke-Ernzerhof exchange-correlation approximation for solids and solid surfaces (PBEso1), we study the single crystal elastic constants of 4d transition metals (atomic number Z between 39 and 47) and their binary alloys in the body centered cubic (bcc) and face centered cubic (fcc) structures. Alloys between the first neighbors Z(Z + 1) and between the second neighbors Z(Z + 2) are considered. The lattice constants, bulk moduli and elastic constants are found in good agreement with the available experimental and theoretical data. It is shown that the correlation between the relative tetragonal shear elastic constant C-fcc'-2C(bcc)' and the structural energy difference between the fcc and bcc lattices Delta E is superior to the previously considered models. For a given crystal structure, the equiatomic Z(Z + 2) alloys turn out to have similar structural and elastic properties as the pure elements with atomic number (Z + 1). Furthermore, alloys with composition Z(1-x)(Z + 2)(x) possess similar properties as Z(1-2x)(Z + 1)(2x). The present theoretical data on the structural and the elastic properties of 4d transition metal alloys provides consistent input for coarse scale modeling of material properties.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Exact muffin-tin orbital method, 4d transition metals, Binary alloys, Elastic constants, First-principles, Structural properties, EGAN RA, 1968, JOURNAL OF PHYSICS PART C SOLID STATE PHYSICS, V1, P763 glas D., 1975, Physical Metallurgy of Zirconium, tos L, 2001, PHYSICAL REVIEW B, V64, dersen O. K., 1998, Tight-Binding Approach to Computational Materials ScienceMRS Symposia Proceedings No. 491, Y GK, 1982, JOURNAL DE PHYSIQUE, V43, P327
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-244490 (URN)10.1016/j.commatsci.2018.12.027 (DOI)000457856900027 ()2-s2.0-85058676887 (Scopus ID)
Note

QC 20190327

Available from: 2019-03-27 Created: 2019-03-27 Last updated: 2019-04-04Bibliographically approved
Li, X., Schönecker, S., Li, X., Hao, S., Zhao, J., Johansson, B. & Vitos, L. (2019). First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys. PHYSICAL REVIEW MATERIALS, 3(3), Article ID 034401.
Open this publication in new window or tab >>First-principles study of crystal-face specificity in surface properties of Fe-rich Fe-Cr alloys
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2019 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 3, article id 034401Article in journal (Refereed) Published
Abstract [en]

A density-functional theory investigation of the (100) and (110) surfaces of the body-centered cubic (bcc) Fe1-xbCrxb binary alloys, x(b) <= 15 at.%, is reported. The energies and segregation energies of these surfaces were calculated for chemically homogeneous concentration profiles and for Cr surface contents deviating from the nominal one of the bulk. The implications of these results for the surface alloy phase diagram are discussed. The surface chemistry of Fe-Cr(100) is characterized by a transition from Cr depletion to Cr enrichment in a critical bulk Cr composition window of 6 < x(b) < 9 at.%. In contrast, such threshold behavior of the surface Cr content is absent for Fe-Cr(110) and a nearly homogeneous Cr concentration profile is energetically favorable. The strongly suppressed surface-layer relaxation at both surfaces is shown to be of magnetic origin. The compressive, magnetic contribution to the surface relaxation stress is found to correlate well with the surface magnetic moment squared at both surface terminations. The stability of the Cr surface magnetic moments against bulk Cr content is clarified based on the surface electronic structure.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-247823 (URN)10.1103/PhysRevMaterials.3.034401 (DOI)000460683400001 ()
Note

QC 20190327

Available from: 2019-03-27 Created: 2019-03-27 Last updated: 2019-03-27Bibliographically approved
Ren, G.-d., Dai, C.-r., Mei, W., Sun, J., Lu, S. & Vitos, L. (2019). Formation and temporal evolution of modulated structure in high Nb-containing lamellar gamma-TiAl alloy. Acta Materialia, 165, 215-227
Open this publication in new window or tab >>Formation and temporal evolution of modulated structure in high Nb-containing lamellar gamma-TiAl alloy
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2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 165, p. 215-227Article in journal (Refereed) Published
Abstract [en]

The formation and temporal evolution of the modulated structure in a lamellar gamma-based Ti-45Al-8.5Nb alloy have been investigated by transmission electron microscopy (TEM) in combination with first-principles theory in this work. The results show that the Nb-rich O phase as a constituent of the modulated structure is thermodynamically stable below 650 degrees C in the alpha(2) lamellae. The morphology of the O phase variants changes from thin plate-like shape with a low volume fraction at initial annealing to rectangle/square shape with a high volume fraction after a prolonged annealing, and the retransformed alpha(2), named as alpha(2-II) hereafter, emerges at intersections of the variants with two orthogonal habit planes due to their elastic interactions. The partitioning coefficient of Nb between the O phase and alpha(2) is about 2 at 600 degrees C. The diffusion coefficient of Nb derived from growth kinetics of the O phase is about (1.3 +/- 0.2) x 10(-22) m(2)s(-1) in the alpha(2) lamellae. Significant precipitation hardening effect of the O phase has been revealed for the alpha(2) lamellae and gamma/(alpha(2)+O) lamellar microstructure, which is supposed to be attributed to refining the alpha(2) lamellae associated with elastic strain energy from the alpha(2) -> O phase transformation and introducing the interface between the modulated lamella and adjacent gamma phase. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Titanium aluminides, Orthorhombic phase, Microstructural evolution, Diffusion, Nano-indentation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-244506 (URN)10.1016/j.actamat.2018.11.041 (DOI)000457665100020 ()2-s2.0-85057440485 (Scopus ID)
Note

QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-04Bibliographically 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
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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
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-241183 (URN)10.1088/1361-648X/aaf2fa (DOI)000454553700001 ()30524044 (PubMedID)2-s2.0-85059403568 (Scopus ID)
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-03-04Bibliographically approved
Xie, R., Lizárraga, R., Linder, D., Hou, Z., Ström, V., Lattemann, M., . . . Vitos, L. (2019). Quantum mechanics basis of quality control in hard metals. Acta Materialia, 169, 1-8
Open this publication in new window or tab >>Quantum mechanics basis of quality control in hard metals
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2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 169, p. 1-8Article in journal (Refereed) Published
Abstract [en]

Non-destructive and reliable quality control methods are a key aspect to designing, developing and manufacturing new materials for industrial applications and new technologies. The measurement of the magnetic saturation is one of such methods and it is conventionally employed in the cemented carbides industry. We present a general quantum mechanics based relation between the magnetic saturation and the components of the binder phase of cemented carbides, which can be directly employed as a quality control. To illustrate our results, we calculate the magnetic saturation of a binder phase, 85Ni15Fe binary alloy, using ab-initio methods and compare the theoretical predictions to the magnetic saturation measurements. We also analyse interface and segregation effects on the magnetic saturation by studying the electronic structure of the binder phase. The excellent agreement between calculations and measurements demonstrates the applicability of our method to any binder phase. Since the magnetic saturation is employed to ensure the quality of cemented carbides, the present method allows us to explore new materials for alternative binder phases efficiently.

Place, publisher, year, edition, pages
Acta Materialia Inc, 2019
Keywords
Ab-initio calculations, Binder phase, Hard metal, Magnetic saturation
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-246425 (URN)10.1016/j.actamat.2019.02.036 (DOI)2-s2.0-85062451846 (Scopus ID)
Note

QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved
Zhao, W., Li, W., Li, X., Gong, S., Vitos, L. & Sun, Z. (2019). Thermo-mechanical properties of Ni-Mo solid solutions: A first-principles study. Computational materials science, 158, 140-148
Open this publication in new window or tab >>Thermo-mechanical properties of Ni-Mo solid solutions: A first-principles study
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2019 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 158, p. 140-148Article in journal (Refereed) Published
Abstract [en]

The mechanical strength of Ni-based single-crystal superalloys under service condition is related to the thermo-mechanical properties of the disordered γ matrix. Here we use density functional theory and quasi-harmonic approximation to determine the temperature-dependent bulk moduli and generalized stacking fault energies (GSFEs) of Ni-Mo solid solutions. We show that the increasing temperatures between 1000 K and 1400 K cause evident reductions in the bulk moduli and planar fault energies of Ni-Mo alloys. Furthermore, their negative slopes versus temperature are gradually diminished with increasing Mo concentration except that of the unstable stacking fault energy. Adopting recent theoretical models for twinning based on GSFE, increasing temperature enhances the twinnability of low-Mo alloys but has limited influences in the case of high-Mo alloys. The composition-dependent thermal expansion, the thermal electronic excitation and the magnetic transition are shown to be the main factors rendering the complex variations in the elastic properties and twinning behavior of Ni-Mo solid solution with temperature.

Place, publisher, year, edition, pages
Elsevier B.V., 2019
Keywords
Bulk modulus, First-principles calculations, Solid solution, Stacking fault energy, Superalloys, Twinning, Binary alloys, Calculations, Density functional theory, Elastic moduli, Mechanical properties, Molybdenum alloys, Nickel alloys, Single crystals, Stacking faults, Thermal expansion, First-principles calculation, First-principles study, Generalized stacking fault energies, Harmonic approximation, Increasing temperatures, Ni-based single crystal superalloy, Stacking fault energies, Thermomechanical properties, Solid solutions
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-248185 (URN)10.1016/j.commatsci.2018.11.027 (DOI)000456022400017 ()2-s2.0-85056748712 (Scopus ID)
Note

QC 20190412

Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-12Bibliographically 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 Press, 2018
Keywords
Steels, Transition metal carbides, Heterophase interface, Interfacial energy, ab initio calculation
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-234584 (URN)10.1016/j.actamat.2018.06.030 (DOI)000442062800003 ()2-s2.0-85048928839 (Scopus ID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Research CouncilSwedish Foundation for Strategic Research
Note

QC 20180914

Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-09-14Bibliographically 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
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235876 (URN)10.1103/PhysRevMaterials.2.094407 (DOI)000445518700002 ()2-s2.0-85059639691 (Scopus ID)
Note

QC 20181009

Available from: 2018-10-09 Created: 2018-10-09 Last updated: 2019-03-18Bibliographically 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 University Press, 2018
Keywords
alloy, elastic properties, simulation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-237124 (URN)10.1557/jmr.2018.174 (DOI)000446676400012 ()2-s2.0-85048827607 (Scopus ID)
Note

QC 20181121

Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2018-11-21Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

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