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Yang, Y., Zhang, H., Sun, Q., Hu, Q.-M., Ding, X., Wang, Y. & Vitos, L. (2020). Ab initio study of the elastic properties of body-centered cubic Ti-Mo-based alloys. Computational materials science, 172, Article ID 109320.
Open this publication in new window or tab >>Ab initio study of the elastic properties of body-centered cubic Ti-Mo-based alloys
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2020 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 172, article id 109320Article in journal (Refereed) Published
Abstract [en]

Using ab initio alloy theory, we systemically investigate the effect of alloying elements on the elastic properties of body-centered cubic (bcc) Ti1-x-yMoxMy (0.05 <= x <= 0.2; 0 <= y <= 0.4; M = Mg, Mn, Ni, Zr, Nb, and W) alloys. The theoretical single-crystal and polycrystalline elastic moduli of Ti1-xMox (0.05 <= x <= 0.2) agree well with the available experimental values and previous theoretical data. The lattice parameters of Ti-Mo-M ternary alloys significantly increase (decrease) with increasing Mg and Zr (Mn and Ni) contents, while remain almost constant for Nb and W additions. It is found that Mg is a promising alloying element that could decrease the Young's modulus of bcc Ti-Mo alloys, but its content should be as small as possible since the stability of the beta phase decreases with increasing Mg concentration. On the other hand, Mn, Ni, Nb, Zr, and W enhance the Young's modulus and the stability of the beta phase.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Ti alloys, Elastic properties, Alloy design, Single-crystal Young's modulus, EMTO-CPA, First-principles calculations
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-266237 (URN)10.1016/j.commatsci.2019.109320 (DOI)000500937400002 ()2-s2.0-85073111138 (Scopus ID)
Note

QC 20200103

Available from: 2020-01-03 Created: 2020-01-03 Last updated: 2020-01-30Bibliographically approved
Oestlin, A., Zhang, Y., Terletska, H., Beiuseanu, F., Popescu, V., Byczuk, K., . . . Chioncel, L. (2020). Ab initio typical medium theory of substitutional disorder. Physical Review B, 101(1), Article ID 014210.
Open this publication in new window or tab >>Ab initio typical medium theory of substitutional disorder
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2020 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 1, article id 014210Article in journal (Refereed) Published
Abstract [en]

By merging single-site typical medium theory with density-functional theory, we introduce a self-consistent framework for electronic-structure calculations of materials with substitutional disorder which takes into account Anderson localization. The scheme and details of the implementation are presented and applied to the hypothetical alloy LicBe1-c, and the results are compared with those obtained with the coherent potential approximation. Furthermore, we demonstrate that Anderson localization suppresses ferromagnetic order for a very low concentration of (i) carbon impurities substituting oxygen in MgO1-cCc and (ii) manganese impurities substituting magnesium in Mg1-cMncO for the low-spin magnetic configuration.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-267744 (URN)10.1103/PhysRevB.101.014210 (DOI)000510144200002 ()
Note

QC 20200218

Available from: 2020-02-18 Created: 2020-02-18 Last updated: 2020-02-18Bibliographically approved
Sun, X., Zhang, H., Li, W., Ding, X., Wang, Y. & Vitos, L. (2020). Generalized stacking fault energy of al-doped CrMnFeCoNi high-entropy alloy. Nanomaterials, 10(1), Article ID 59.
Open this publication in new window or tab >>Generalized stacking fault energy of al-doped CrMnFeCoNi high-entropy alloy
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2020 (English)In: Nanomaterials, ISSN 2079-4991, Vol. 10, no 1, article id 59Article in journal (Refereed) Published
Abstract [en]

Using first-principles methods, we investigate the effect of Al on the generalized stacking fault energy of face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy as a function of temperature. Upon Al addition or temperature increase, the intrinsic and extrinsic stacking fault energies increase, whereas the unstable stacking fault and unstable twinning fault energies decrease monotonously. The thermodynamic expression for the intrinsic stacking fault energy in combination with the theoretical Gibbs energy difference between the hexagonal close packed (hcp) and fcc lattices allows one to determine the so-called hcp-fcc interfacial energy. The results show that the interfacial energy is small and only weakly dependent on temperature and Al content. Two parameters are adopted to measure the nano-twinning ability of the present high-entropy alloys (HEAs). Both measures indicate that the twinability decreases with increasing temperature or Al content. The present study provides systematic theoretical plasticity parameters for modeling and designing high entropy alloys with specific mechanical properties.

Place, publisher, year, edition, pages
MDPI AG, 2020
Keywords
First-principles, Generalized stacking fault energy, High-entropy alloys, Interfacial energy
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-267999 (URN)10.3390/nano10010059 (DOI)000516825600059 ()2-s2.0-85077398336 (Scopus ID)
Note

QC 20200329

Available from: 2020-03-29 Created: 2020-03-29 Last updated: 2020-03-29Bibliographically approved
Li, X., Wei, D., Vitos, L. & Lizarrága, R. (2020). Micro-mechanical properties of new alternative binders for cemented carbides: CoCrFeNiWx high-entropy alloys. Journal of Alloys and Compounds, 820, Article ID 153141.
Open this publication in new window or tab >>Micro-mechanical properties of new alternative binders for cemented carbides: CoCrFeNiWx high-entropy alloys
2020 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 820, article id 153141Article in journal (Refereed) Published
Abstract [en]

High-entropy alloys are a new type of materials with excellent properties that offer a great variety of possibilities due to the large degree of freedom in element composition. In particular, CoCrFeNiW alloys have recently attracted a lot of attention due to their potential use in solving the long-standing problem of substituting cobalt in the cemented carbide industry. The lack of experimental and theoretical studies on these multi-components alloys hinders their optimal development. In this work, we aim at filling in this gap by studying their mechanical properties employing first-principles alloy theory and experimental techniques. By using the calculated elastic parameters, we analyzed the mechanical stability, elastic anisotropy, Debye temperature, and derived polycrystalline moduli. Moreover, we fabricated CoCrFeNi and (CoCrFeNi)0.96W0.04 and analyzed them by means of X-ray diffraction and electron backscatter diffraction. The hardness and the Young's modulus were measured. The Young's moduli and the lattice parameters were compared to first principles calculations and good agreement was obtained. Hardness increases with the increment of W composition.

Place, publisher, year, edition, pages
Elsevier Ltd, 2020
Keywords
Elastic anisotropy, First principles calculations, High entropy alloys, Micromechanical properties, Anisotropy, Binders, Calculations, Carbide tools, Carbides, Chemical industry, Chromium alloys, Cobalt compounds, Degrees of freedom (mechanics), Elastic moduli, Entropy, Hardness, High-entropy alloys, Iron alloys, Mechanical stability, Tungsten alloys, Cemented carbide industry, Electron back scatter diffraction, Element compositions, Experimental techniques, First-principles calculation, Micromechanical property, Optimal development, Cobalt alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-267935 (URN)10.1016/j.jallcom.2019.153141 (DOI)000507854700096 ()2-s2.0-85076246544 (Scopus ID)
Note

QC 20200402

Available from: 2020-04-02 Created: 2020-04-02 Last updated: 2020-04-02Bibliographically approved
Choi, Y. W., Dong, Z., Li, W., Schönecker, S., Kim, H., Kwon, S. K. & Vitos, L. (2020). Predicting the stacking fault energy of austenitic Fe-Mn-Al (Si) alloys. Materials & design, 187, Article ID 108392.
Open this publication in new window or tab >>Predicting the stacking fault energy of austenitic Fe-Mn-Al (Si) alloys
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2020 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 187, article id 108392Article in journal (Refereed) Published
Abstract [en]

Aluminum and silicon are common alloying elements for tuning the stacking fault energy (SFE) of high Mn steels. Today the theoretical investigations on the Fe-Mn-Al/Si systems using Density Functional Theory (DFT) are very scarce. In the present study, we employ a state-of-the-art longitudinal spin fluctuations (LSFs) model in combination with DFT for describing the magnetic effects in Fe-Mn based alloys at finite temperature. We find that the traditional DFT-floating spin results fail to explain the experimental trends. However, the DFT-LSFs approach properly captures the Al-induced increase and Si-induced decrease of the SFE of the base alloy in line with the room-temperature observations. This finding highlights the importance of LSFs in describing the Al/Si effects on the SEE of Fe-Mn based alloys. We point out that the effects of the non-magnetic Al and Si additions on the SEE are in fact determined by the magnetic state of the host matrix. In addition, we estimate the role of carbon addition in the alloying effects of Al and Si. The present results provide a convenient pathway to access the important mechanical parameters for designing advanced high-strength alloys.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2020
Keywords
Stacking-fault energy, Austenitic steel, first-principles calculation, Magnetism, Longitudinal spin fluctuation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-267147 (URN)10.1016/j.matdes.2019.108392 (DOI)000506652800021 ()2-s2.0-85075802901 (Scopus ID)
Note

QC 20200217

Available from: 2020-02-17 Created: 2020-02-17 Last updated: 2020-02-17Bibliographically approved
Dong, Z., Li, W., Chai, G. & Vitos, L. (2020). Strong temperature – Dependence of Ni -alloying influence on the stacking fault energy in austenitic stainless steel. Scripta Materialia, 178, 438-441
Open this publication in new window or tab >>Strong temperature – Dependence of Ni -alloying influence on the stacking fault energy in austenitic stainless steel
2020 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 178, p. 438-441Article in journal (Refereed) Published
Abstract [en]

Using ab initio alloy theory, we calculate the impact of Ni on the stacking fault energy in austenitic stainless steel as a function of temperature. We show that the influence of Ni strongly couples with temperature. While a positive effect on the stacking fault energy is obtained at ambient temperature, the opposite negative effect is disclosed at elevated temperatures. An important rationale behind is demonstrated to be the variation of magneto-volume coupling induced by Ni alloying. The alloy influence on the finite temperature evolution of Ni impact is evaluated for elements Cr, Mo and N.

Place, publisher, year, edition, pages
Acta Materialia Inc, 2020
Keywords
Ab initio calculation, Alloying, Austenitic stainless steel, Stacking fault energy, Temperature
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-267790 (URN)10.1016/j.scriptamat.2019.12.013 (DOI)000510947200088 ()2-s2.0-85076714087 (Scopus ID)
Note

QC 20200305

Available from: 2020-03-05 Created: 2020-03-05 Last updated: 2020-03-05Bibliographically approved
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: 2020-01-30Bibliographically approved
Tian, L., Levämäki, H., Kuisma, M., Kokko, K., Nagy, A. & Vitos, L. (2019). Density functional theory description of random Cu-Au alloys. Physical Review B, 99(6), Article ID 064202.
Open this publication in new window or tab >>Density functional theory description of random Cu-Au alloys
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2019 (English)In: Physical Review B, Vol. 99, no 6, article id 064202Article in journal (Refereed) Published
Abstract [en]

Density functional alloy theory is used to accurately describe the three core effects controlling the thermodynamics of random Cu-Au alloys. These three core effects are exchange correlation (XC), local lattice relaxations (LLRs), and short-range order (SRO). Within the real-space grid-based projector augmented-wave (GPAW) method based on density functional theory (DFT), we adopt the quasinonuniform XC approximation (QNA), and take into account the LLR and the SRO effects. Our approach allows us to study the importance of all three core effects in a unified way within one DFT code. The results demonstrate the importance of the LLR term and show that going from the classical gradient level approximations to QNA leads to accurate formation energies at various degrees of ordering. The order-disorder transition temperatures for the 25%, 50%, and 75% alloys reach quantitative agreement with the experimental values only when also the SRO effects are considered.

Place, publisher, year, edition, pages
American Physical Society, 2019
Keywords
Binary alloys, Copper alloys, Gold alloys, Lunar surface analysis, Thermodynamics, Density functionals, Exchange correlations, Experimental values, Formation energies, Local lattice, Projector augmented waves, Quantitative agreement, Short-range order, Density functional theory
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-252070 (URN)10.1103/PhysRevB.99.064202 (DOI)000459222700003 ()2-s2.0-85061991346 (Scopus ID)
Note

QC 20190731

Available from: 2019-07-31 Created: 2019-07-31 Last updated: 2020-01-30Bibliographically approved
Tian, L.-Y., Levämäki, H., Eriksson, O., Kokko, K., Nagy, A., Delczeg-Czirjak, E. K. & Vitos, L. (2019). Density Functional Theory description of the order-disorder transformation in Fe-Ni. Scientific Reports, 9, Article ID 8172.
Open this publication in new window or tab >>Density Functional Theory description of the order-disorder transformation in Fe-Ni
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8172Article in journal (Refereed) Published
Abstract [en]

The thermodynamic ordering transformation of tetragonal FeNi system is investigated by the Exact Muffin-Tin Orbitals (EMTO) method. The tetragonal distortion of the unit cell is taken into account and the free energy is calculated as a function of long-range order and includes the configurational, vibrational, electronic and magnetic contributions. We find that both configurational and vibrational effects are important and that the vibrational effect lowers the predicted transformation temperature by about 480 K compared to the value obtained merely from the configurational free energy. The predicted temperature is in excellent agreement with the experimental value when all contributions are taken into account. We also perform spin dynamics calculations for the magnetic transition temperature and find it to be in agreement with the experiments. The present research opens new opportunities for quantum-mechanical engineering of the chemical and magnetic ordering in tetrataenite.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-254082 (URN)10.1038/s41598-019-44506-7 (DOI)000469912700013 ()31160612 (PubMedID)2-s2.0-85066778812 (Scopus ID)
Note

QC 20190624

Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2020-01-30Bibliographically approved
Molnár, D. S., Sun, X., Lu, S., Li, W., Engberg, G. & Vitos, L. (2019). Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel. Materials Science & Engineering: A, 759, 490-497
Open this publication in new window or tab >>Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel
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2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, p. 490-497Article in journal (Refereed) Published
Abstract [en]

The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Deformation twinning, microstructure, first principles, stacking fault energy, stainless steel
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-252728 (URN)10.1016/j.msea.2019.05.079 (DOI)000472813900052 ()2-s2.0-85066090205 (Scopus ID)
Funder
Vinnova, 2014-03374
Note

QC 20190731

Available from: 2019-06-04 Created: 2019-06-04 Last updated: 2020-03-09Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

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