Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Elastic Properties of Iron Alloys from First-Principles Theory
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Accurate description of materials requires the most advanced atomic-scale techniques from both experimental and theoretical areas. In spite of numerous available techniques, however, the experimental study of the atomic-scale properties and phenomena even in simple solids is rather difficult. Iron and its alloys (including steels) are among the most important engineering materials due to their excellent mechanical properties. In these systems, the above challenges become more complex due to the interplay between the structural, chemical, andmagnetic effects. On the other hand, advanced computational methods based on density functional theory (DFT) ensure a proper platform for studying the fundamental properties of materials from first-principles theory. The present thesis belongs to the latter category. We use advanced theoretical tools to give a systematic description of Fe and a series of Fe-rich alloys in the ferromagnetic (FM) body-centered-cubic (bcc), paramagnetic (PM) bcc, and PM face-centered-cubic (fcc) structures. For solving the basic DFT equations for steel alloys, we adopt the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA) and the disordered local magnetic moment (DLM) model.

We start by assessing our theoretical tools in the case of Fe. For the FM state, we find that there is a magnetic transition close to the ground state volume of bcc Fe, which is explained by the peculiarmagnetic band structure. We conclude that the common equation of state functions can not capture the physics of this magnetic transition, leading to serious underestimation of theoretical bulk modulus of Fe. When the above effect is properly taken into account, theory is shown to reproduce the low-temperature experimental bulk properties (equation of state and elastic parameters) of FM bcc Fe within ∼ 1% for the volume and ∼7% for the elastic constants.

Using the EMTO-CPA-DLM picture, in contrast to previous theoretical predictions, we demonstrate that the competing high-temperature cubic phases of PM Fe correspond to two distinct total energy minima in the tetragonal (Bain) configurational space. Both fcc and bcc lattices are dynamically stable, and at static conditions the fcc structure is found to be the thermodynamically stable phase. When the thermal expansion is taken into account, our theoretical bulk properties calculated for PM Fe agree well with the available experimental data. Increasing temperature is predicted to stabilize the bcc (δ) phase against the fcc (γ) one because of the shallow energy minimum around the bcc structure.

The calculated composition-dependent equilibriumlattice constants, single-crystal elastic constants Cij(c) (here c stands for the amount of alloying additions), and polycrystalline elastic parameters of FM bcc Fe show good agreement with former theoretical and available experimental data, implying that the employed theoretical approach is suitable to calculate the elastic properties of FM Fe alloys. For FM bcc Fe alloys, all impurities considered in this thesis (Al, Si, V, Cr, Mn, Co, Ni, and Rh) enlarge the equilibrium lattice parameter and accordingly decrease the C11(c), C12(c), and C′(c) elastic constants. However, a peculiar phenomenon appears for C44(c). Namely, in spite of increasing volume, Al, Si, V, Cr, and Mn are found to increase C44(c), whereas the alloying effects of Co, Ni, and Rh are small. The anomalous alloying effect in C44(c) isshown to originate from the particular electronic structure of FM bcc Fe. The complex composition dependence of C44(c) is reflected in the polycrystalline properties of FM Fe as well.

Unlike for FM bcc Fe, both positive and negative alloying effects appear for the theoretical equilibrium lattice parameters, single-crystal and polycrystalline elastic properties of PM bcc and fcc Fe. For many elastic parameters and binary systems considered in this thesis, alloying element induces opposite effects in fcc and bcc phases. In other words, the alloying effects on the elastic properties of PM Fe-based alloys show strong structure dependence. While neither the volume nor the electronic effect can explain the calculated trends of C′(c), we find that there is a general correlation between alloying effects on the lattice stability and C′(c). With a few exceptions, alloying elements have much larger effects on FM bcc Fe than on PM fcc Fe. A slightly larger alloying effect appears on PM fcc Fe compared to PM bcc Fe.

According to the calculated fundamental properties, we also estimate the relative hardness of Fe alloys via two phenomenological solid-solution strengthening mechanisms. In those caseswhere experimental data are available, the predicted solid-solution strengthening effects are in line with the observations. The metastable Mg-doped Fe alloys surpass all rival binaries in density and solid-solution strengthening effects. The Fe-Cr and Fe-Cr-Ni alloys containing a few percent of Mg are also predicted to possess unusually high solid-solution hardening and low density compared to the host alloys. These attributes make theMg-bearing stainless steels very promising candidates for many applications, such as the high-strength and light-weight designs desired by for example the automotive industry.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 74 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-48182ISBN: 978-91-7501-116-5 (print)OAI: oai:DiVA.org:kth-48182DiVA: diva2:456943
Public defence
2011-12-02, Sal B2, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111123Available from: 2011-11-23 Created: 2011-11-16 Last updated: 2012-03-12Bibliographically approved
List of papers
1. Static equation of state of bcc iron
Open this publication in new window or tab >>Static equation of state of bcc iron
Show others...
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 13, 132409- p.Article in journal (Refereed) Published
Abstract [en]

Body-centered-cubic (bcc) iron is one of the most investigated solid-state systems. Using four different density-functional methods, we show that there is a magnetic transition close to the ground-state volume of bcc Fe, which originates from the particular magnetic band structure. The common equation of state functions, used to determine the basic ground-state physical quantities from the calculated total energies, cannot capture the physics of this magnetic transition leading to serious underestimation of the Fe bulk modulus. Ignorance of the magnetic transition found here is reflected by large scatter of the published theoretical bulk moduli of ferromagnetic bcc Fe. Due to the low performance of the exchange-correlation functionals, most of the erroneous results are accidentally in good agreement with the experimental values. The present finding is of fundamental importance, especially taking into account that bcc Fe is frequently used as a test system in assessing the performance of exchange-correlation approximations or total-energy methods.

National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-26211 (URN)10.1103/PhysRevB.82.132409 (DOI)000283573500003 ()2-s2.0-78049368897 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20110224

Available from: 2011-02-24 Created: 2010-11-21 Last updated: 2017-12-11Bibliographically approved
2. Density-functional study of paramagnetic iron
Open this publication in new window or tab >>Density-functional study of paramagnetic iron
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 14, 140411- p.Article in journal (Refereed) Published
Abstract [en]

By using density-functional theory in combination with the coherent-potential approximation and the disordered local magnetic moment picture, we demonstrate that the competing high-temperature cubic phases of paramagnetic Fe correspond to two distinct total energy minima in the tetragonal (Bain) configurational space. Both the face-centered-cubic (fcc) and the body-centered-cubic (bcc) lattices are dynamically stable, and at static conditions the fcc structure is found to be the thermodynamically stable phase. The theoretical bcc and fcc bulk parameters are in agreement with the experimental data. Due to the shallow energy minimum around the bcc structure, increasing temperature is predicted to stabilize the bcc (δ) phase against the fcc (γ) one.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-48806 (URN)10.1103/PhysRevB.84.140411 (DOI)000296667600003 ()2-s2.0-80155128879 (Scopus ID)
Funder
Swedish Research CouncilEU, European Research Council
Note
QC 20111123Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
3. Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys
Open this publication in new window or tab >>Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 22Article in journal (Refereed) Published
Abstract [en]

Using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation, we have calculated the elastic parameters of ferromagnetic Fe1-mMgm (0 < m < 0.1) and Fe1-cCrc (0 < c < 0.2) random alloys in the body-centered cubic (bcc) crystallographic phase. Results obtained for Fe1-cCrc demonstrate that the employed theoretical approach accurately describes the experimentally observed composition dependence of the polycrystalline elastic moduli of Fe-rich alloys encompassing maximum similar to 10% Cr. The elastic parameters of Fe-Cr alloys are found to exhibit anomalous composition dependence around 5% Cr. The immiscibility between Fe and Mg at ambient conditions is well reproduced by the present theory. The calculated lattice parameter for the Fe-Mg regular solid solution increases by similar to 1.95% when 10% Mg is introduced in Fe, which corresponds approximately to 11% decrease in the average alloy density, in perfect agreement with the experimental finding. At the same time, we find that all of the elastic parameters of bcc Fe-Mg alloys decrease almost linearly with increasing Mg content. The present results show a much stronger alloying effect for Mg on the elastic properties of alpha-Fe than that for Cr. Our results call for further experimental studies on the mechanical properties of the Fe-Mg system.

Keyword
ab initio calculations, elastic moduli, ferromagnetic materials, iron, alloys, lattice constants, linear muffin-tin orbital method, magnesium, alloys, solubility, generalized gradient approximation, coherent-potential approximation, mechanical-properties, transition-metals, solid-solutions, alpha-iron, constants, system, energy, base
Identifiers
urn:nbn:se:kth:diva-18575 (URN)10.1103/PhysRevB.79.224201 (DOI)000267699300045 ()2-s2.0-67649967729 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Single-crystal elastic constants of ferromagnetic bcc Fe-based random alloys from first-principles theory
Open this publication in new window or tab >>Single-crystal elastic constants of ferromagnetic bcc Fe-based random alloys from first-principles theory
Show others...
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 18, 184105- p.Article in journal (Refereed) Published
Abstract [en]

The elastic properties of ferromagnetic Fe1-xMx (M=Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 <= x <= 0.1) random alloys in the body-centered-cubic (bcc) crystallographic phase have been studied using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The theoretical lattice parameters and the single-crystal elastic constants agree well with the available experimental data. The most significant alloying effects are found for Al, Si, and Ni additions. All elements enlarge the lattice parameter and decrease the C-11, C-12, and C' elastic constants and the bulk modulus of bcc Fe. At the same time, C-44 is found to increase with Al, Si, V, Cr, or Mn and remain nearly constant with Co, Ni, and Rh. Accordingly, the elastic anisotropy of bcc Fe increases with all alloying elements considered here. The calculated alloying effects on the single-crystal elastic constants are shown to originate from volume effects in combination with the peculiar electronic structure of bcc Fe.

Keyword
TOTAL-ENERGY CALCULATIONS, COHERENT-POTENTIAL APPROXIMATION, INITIO MOLECULAR-DYNAMICS, AUGMENTED-WAVE METHOD, IRON-NICKEL ALLOYS, AB-INITIO, MAGNETIC-PROPERTIES, ELECTRONIC-STRUCTURE, ALUMINUM-ALLOYS, SOLID-SOLUTIONS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-27530 (URN)10.1103/PhysRevB.81.184105 (DOI)000278141800028 ()2-s2.0-77955441751 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20101217

Available from: 2010-12-17 Created: 2010-12-13 Last updated: 2017-12-11Bibliographically approved
5. Theoretical elastic moduli of ferromagnetic bcc Fe alloys
Open this publication in new window or tab >>Theoretical elastic moduli of ferromagnetic bcc Fe alloys
2010 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 27, 275402- p.Article in journal (Refereed) Published
Abstract [en]

The polycrystalline elastic parameters of ferromagnetic Fe1-xMx (M = Al, Si, V, Cr, Mn, Co, Ni, Rh; 0 <= x <= 0.1) random alloys in the body centered cubic (bcc) crystallographic phase have been calculated using first-principles alloy theory in combination with statistical averaging methods. With a few exceptions, the agreement between the calculated and the available experimental data for the polycrystalline aggregates is satisfactory. All additions considered here decrease the bulk modulus (B) and Poisson's ratio (nu) of bcc Fe. The complex composition dependence of the C-44 single-crystal elastic constant is reflected in the polycrystalline shear modulus (G), Young's modulus (E), and Debye temperature (Theta). The polycrystalline anisotropy of bcc Fe is increased by all additions, and Al, Si, Ni, and Rh yield the largest alloying effects.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-27263 (URN)10.1088/0953-8984/22/27/275402 (DOI)000279003800008 ()2-s2.0-77953769654 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20101217Available from: 2010-12-17 Created: 2010-12-09 Last updated: 2017-12-11Bibliographically approved
6. Alloying effects on the elastic parameters of ferromagnetic and paramagnetic Fe from first-principles theory
Open this publication in new window or tab >>Alloying effects on the elastic parameters of ferromagnetic and paramagnetic Fe from first-principles theory
2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 7, 073707- p.Article in journal (Refereed) Published
Abstract [en]

The elastic properties of paramagnetic face-centered-cubic (fcc) Fe(1-x)M(x) (M = Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 <= x <= 0.1) random alloys are investigated using the exact muffin-tin orbitals density functional method in combination with the coherent-potential approximation. We find that the theoretical lattice parameter of fcc Fe is strongly enlarged by Al, V, and Rh and slightly reduced by Si, Cr, and Co, while it remains nearly constant with Mn and Ni. Both positive and negative alloying effects appear for the elastic constants C(ij)(x) of fcc Fe. These findings are in contrast to those obtained for ferromagnetic body-centered-cubic (bcc) Fe alloys, where all alloying elements considered here are predicted to enlarge the lattice parameter and decrease the C(11)(x) and C(12)(x) elastic constants of bcc Fe. With some exceptions, alloying has much larger effects on ferromagnetic bcc alloys than on paramagnetic fcc ones. Based on the theoretical elastic parameters of the paramagnetic fcc and ferromagnetic bcc phases, simple parameterizations in terms of chemical composition of the equilibrium lattice constants, single-crystal elastic constants, and polycrystalline elastic moduli of Fe-based alloys are presented.

Keyword
coherent-potential approximation, initio molecular-dynamics, total-energy calculations, wave basis-set, lattice-dynamics, single-crystals, iron, constants, metals, model
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-46855 (URN)10.1063/1.3644907 (DOI)000295883000055 ()2-s2.0-80054969961 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20111107Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2017-12-08Bibliographically approved
7. Elastic parameters of paramagnetic iron-based alloys from first-principles calculations
Open this publication in new window or tab >>Elastic parameters of paramagnetic iron-based alloys from first-principles calculations
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 5, 054107- p.Article in journal (Refereed) Published
Abstract [en]

The elastic properties of paramagnetic (PM) Fe1-xMx (M = Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 <= x <= 0.1) solid solutions in the body-centered-cubic (bcc) and face-centered-cubic (fcc) structures are investigated using the exact muffin-tin orbital density functional method in combination with the coherent-potential approximation and disordered local-magnetic-moment model. All impurities considered here enlarge or leave nearly constant the equilibrium volume of PM Fe but at the same time produce both positive and negative changes in the elastic parameters. Some of the alloying elements induce opposite effects on shear elastic parameters C' and C-44 of PM bcc and fcc Fe, which is discussed. With a few exceptions, we find that the alloying effects on PM bcc Fe are smaller than on PM fcc Fe. The trends in the tetragonal elastic constant C' show a general correlation with the trends obtained for the bcc-fcc lattice energy difference.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-48808 (URN)10.1103/PhysRevB.85.054107 (DOI)000300237800002 ()2-s2.0-84863272548 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20120312

Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
8. First-principles study of solid-solution hardening in steel alloys
Open this publication in new window or tab >>First-principles study of solid-solution hardening in steel alloys
2012 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, 269-272 p.Article in journal (Refereed) Published
Abstract [en]

Materials with excellent mechanical properties, such as light mass combined with remarkable hardness and toughness, are technologically important not least for automotive and other transport applications. Solid solution strengthening, due to dislocation pinning by impurities, is an effective route to enhance the intrinsic hardness of alloys. In the present work, we use advanced quantum theory to reveal the mechanical characteristics of iron alloys within and beyond their thermodynamic stability fields. Among the considered alloying elements, magnesium strongly reduces the density of the host alloys and significantly enhances the hardness. Our findings suggest that stainless steel grades containing a few percent of magnesium are promising engineering materials for high-strength and light-weight designs.

Keyword
Steel alloys, Hardness, Density functional theory, Iron alloys
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-48809 (URN)10.1016/j.commatsci.2011.12.020 (DOI)000300728600036 ()2-s2.0-84862778860 (Scopus ID)
Funder
Swedish Research CouncilEU, European Research Council
Note
QC 20120328Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
9. Mechanical properties and magnetism: stainless steel alloys from first-principles theory
Open this publication in new window or tab >>Mechanical properties and magnetism: stainless steel alloys from first-principles theory
Show others...
2011 (English)In: 2010 MRS Fall Meeting, 2011, 68-79 p.Conference paper, Published paper (Refereed)
Abstract [en]

Stainless steels are among the most important engineering materials, finding their principal scope in industry, specifically in cutlery, food production, storage, architecture, medical equipment, etc. Austenitic stainless steels form the largest sub-category of stainless steels having as the main building blocks the paramagnetic substitutional disordered Fe-Cr-Ni-based alloys. Because of that, austenitic steels represent the primary choice for non-magnetic engineering materials. The presence of the chemical and magnetic disorder hindered any previous attempt to calculate the fundamental electronic, structural and mechanical properties of austenitic stainless steels from first-principles theories. Our ability to reach an ab initio atomistic level approach in this exciting field has become possible by the Exact Muffin-Tin Orbitals (EMTO) method. This method, in combination with the coherent potential approximation, has proved an accurate tool in the description of the concentrated random alloys. Using the EMTO method, we presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we will discuss the role of magnetism on the stacking fault energies and elastic properties of paramagnetic Fe-based alloys.

Series
Materials Research Society Symposium Proceedings, ISSN 0272-9172 ; 1296
Keyword
magnetic properties, elastic properties, steel
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-31081 (URN)10.1557/opl.2011.1448 (DOI)2-s2.0-84859142705 (Scopus ID)978-161839509-2 (ISBN)
Conference
2010 MRS Fall Meeting; Boston, MA
Note

QC 20110308

Available from: 2011-03-08 Created: 2011-03-08 Last updated: 2014-09-04Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Zhang, Hualei
By organisation
Applied Material Physics
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 614 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf