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

Direct link
BETA
Alternative names
Publications (10 of 283) 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
Tian, L.-Y., Levamaki, 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
Show others...
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
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387732 (URN)10.1038/s41598-019-44506-7 (DOI)000469912700013 ()31160612 (PubMedID)
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Molnar, D., 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
Show others...
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 SCIENCE SA, 2019
Keywords
Deformation twinning, Microstructure, First principles, Stacking fault energy, Stainless steel
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-390825 (URN)10.1016/j.msea.2019.05.079 (DOI)000472813900052 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Swedish Energy AgencyVinnova, 2014-03374
Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
Al-Zoubi, N., Schonecker, 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
Show others...
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
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-378523 (URN)10.1016/j.commatsci.2018.12.027 (DOI)000457856900027 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2019-03-25 Created: 2019-03-25 Last updated: 2019-03-25Bibliographically approved
Molnar, D., Engberg, G., Li, W., Lu, S., Hedstrom, P., Kwon, S. K. & Vitos, L. (2019). Experimental study of the gamma-surface of austenitic stainless steels. Acta Materialia, 173, 34-43
Open this publication in new window or tab >>Experimental study of the gamma-surface of austenitic stainless steels
Show others...
2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, p. 34-43Article in journal (Refereed) Published
Abstract [en]

We introduce a theory-guided experimental approach to study the gamma-surface of austenitic stainless steels. The gamma-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Stacking fault energy, Twinning, Electron backscatter diffraction, Plasticity, First-principles
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-390923 (URN)10.1016/j.actamat.2019.04.057 (DOI)000472812300005 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Swedish Energy AgencyCarl Tryggers foundation Vinnova, 2014-03374
Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-15Bibliographically approved
Dong, Z. & Vitos, L. (2019). Finite temperature magnetic properties of CrxCoyNi100-x-y medium entropy alloys from first principles. Scripta Materialia, 171, 78-82
Open this publication in new window or tab >>Finite temperature magnetic properties of CrxCoyNi100-x-y medium entropy alloys from first principles
2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 171, p. 78-82Article in journal (Refereed) Published
Abstract [en]

The magnetic structure of polymorphic Cr-Co-Ni medium entropy alloys is investigated as a function of temperature and chemical composition by ab initio calculations. Besides the thermal lattice expansion, the longitudinal spin fluctuations (LSFs) are accounted for in determining the magnetic state at finite temperature. We show that sizable local magnetic moments persist on all alloy components in the paramagnetic state for both face-centered cubic and hexagonal close-packed structures, and each alloy species exhibits particular temperature and concentration dependencies. The crucial role of LSFs for the finite temperature magnetic state and its impact on the temperature dependent elastic parameters are demonstrated.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Medium entropy alloy, Magnetism, Spin fluctuations, Chemical fluctuations, Ab initio calculation
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-393322 (URN)10.1016/j.scriptamat.2019.06.019 (DOI)000479026100016 ()
Funder
Swedish Research Council, 2015-5335Swedish Research Council, 2017-06474Swedish Foundation for Strategic Research , S14-0038Swedish Foundation for Strategic Research , SM16-0036Carl Tryggers foundation
Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically approved
Li, X., Schonecker, 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
Show others...
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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-379928 (URN)10.1103/PhysRevMaterials.3.034401 (DOI)000460683400001 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-03-28Bibliographically 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
Show others...
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. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. 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:uu:diva-378527 (URN)10.1016/j.actamat.2018.11.041 (DOI)000457665100020 ()
Available from: 2019-03-25 Created: 2019-03-25 Last updated: 2019-03-25Bibliographically 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
Dong, Z., Schonecker, S., Chen, D., Li, W., Lu, S. & Vitos, L. (2019). Influence of Mn content on the intrinsic energy barriers of paramagnetic FeMn alloys from longitudinal spin fluctuation theory. International journal of plasticity, 119, 123-139
Open this publication in new window or tab >>Influence of Mn content on the intrinsic energy barriers of paramagnetic FeMn alloys from longitudinal spin fluctuation theory
Show others...
2019 (English)In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 119, p. 123-139Article in journal (Refereed) Published
Abstract [en]

First-principles calculations were performed to investigate the influence of Mn content on the intrinsic energy barriers (IEBs) of paramagnetic FeMn alloys with face-centered cubic (fcc) structure. The IEBs were derived from the free energies accounting for longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the quantitative description of IEBs and their alloying dependencies at finite temperature. The unstable stacking and unstable twinning fault energies of the fcc phase slightly decrease with Mn content, whereas the intrinsic stacking fault energy (γfccisf) is predicted to monotonically increase. This latter finding contradicts the experimentally reported, local minimum of γisf in the fcc/hexagonal close-packed (hcp) coexistence region. The partitioning of Mn during the fcc/hcp phase transition is proposed to reconcile theory and experiment. Both temperature and impurities ([C] and Cr) hardly influence the monotonic concentration dependence of γfccisf but considerably alter the magnitude. The fcc/hcp interfacial energy is nearly independent of Mn concentration in contrast to the parabolic dependence predicted in thermodynamic modeling. In contrast to the fcc phase, the estimated intrinsic stacking fault energy of the ideal hcp structure monotonically decreases with Mn content and temperature. A high twinnability is predicted at 450 K within the stability field of the paramagnetic fcc Fe-Mn alloys.

Keywords
Manganese, Stacking fault energy, Paramagnetism, Longitudinal spin fluctuations, TWIP steels
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-388752 (URN)10.1016/j.ijplas.2019.02.020 (DOI)000471088600007 ()
Funder
Swedish Research Council, 2015-5335Swedish Research Council, 2017-06474Swedish Foundation for Strategic Research , S14-0038Swedish Foundation for Strategic Research , SM16-0036The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), CH2015-6292Carl Tryggers foundation Swedish National Infrastructure for Computing (SNIC)
Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

Search in DiVA

Show all publications