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  • 1.
    Kadas, Krisztina
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermo-physical properties of iron-magnesium alloys2011In: Magnesium Alloys - Design, Processing and Properties / [ed] Frank Czerwinski, InTech, 2011, p. 69-94Chapter in book (Other academic)
  • 2. Laukkanen, P.
    et al.
    Punkkinen, Marko Patrick John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Puustinen, J.
    Levämäki, H.
    Tuominen, M.
    Schulte, K.
    Dahl, J.
    Lang, J.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kuzmin, M.
    Palotas, K.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Guina, M.
    Kokko, K.
    Formation and destabilization of Ga interstitials in GaAsN: Experiment and theory2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 19, p. 195205-Article in journal (Refereed)
    Abstract [en]

    Using first-principles total energy calculations we have found complex defects induced by N incorporation in GaAsN. The formation energy of the Ga interstitial atom is very significantly decreased due to local effects within the defect complex. The stability of the Ga interstitials is further increased at surfaces. The present results suggest that the energetically favorable Ga interstitial atoms are much more abundant in GaAsN than the previously considered N defects, which have relatively large formation energies. Our synchrotron radiation core-level photoemission measurements support the computational results. The formation of harmful Ga interstitials should be reduced by incorporating large group IV B atoms in GaAsN.

  • 3.
    Li, Xiaoqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhao, Jijun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic properties of vanadium-based alloys from first-principles theory2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 1, p. 014105-Article in journal (Refereed)
    Abstract [en]

    The effect of Cr and Ti on the fundamental mechanical properties of V-Cr-Ti alloys has been investigated using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The static lattice constant and elastic parameters have been calculated for the body-centered-cubic V1-x-yCrxTiy (0 <= x,y <= 0.1) random solid solution as a function of composition. Our theoretical predictions are in good agreement with the available experimental data. Alloys along the equicomposition region are found to exhibit the largest shear and Young's modulus as a result of the opposite alloying effects obtained for the two cubic shear elastic constants. The classical solid-solution hardening (SSH) model predicts larger strengthening effect in V1-yTiy than in V1-xCrx. By considering a phenomenological expression for the ductile-brittle transition temperature (DBTT) in terms of Peierls stress and SSH, it is shown that the present theoretical results can account for the variations of DBTT with composition.

  • 4. Punkkinen, M. P. J.
    et al.
    Lahti, A.
    Laukkanen, P.
    Kuzmin, M.
    Tuominen, M.
    Yasir, M.
    Dahl, J.
    Mäkelä, J.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China.
    Vitos, Levents
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Kokko, K.
    Thermodynamics of the pseudobinary GaAs1-xBix (0 ≤ x ≤ 1) alloys studied by different exchange-correlation functionals, special quasi-random structures and Monte Carlo simulations2015In: Computational Condensed Matter, ISSN 2352-2143, Vol. 5, p. 7-13Article in journal (Refereed)
    Abstract [en]

    GaAs<inf>1-x</inf>Bi<inf>x</inf> alloys have useful properties for many optoelectronic applications. Although the crystal growth by molecular beam epitaxy is influenced by kinetics, it is also important to understand the thermodynamics of the alloys. The Gibbs formation energies and the immiscibility curve of the totally disordered GaAs<inf>1-x</inf>Bi<inf>x</inf> (0 ≤ x ≤ 1) are determined using special quasi-random structures (SQS) of different sizes, different exchange-correlation functionals and Monte Carlo simulations. The local density approximation gives slightly larger mixing enthalpies and smaller Bi solubilities than the generalized gradient approximation for the GaAs<inf>1-x</inf>Bi<inf>x</inf> alloys, if the semiconducting GaAs and metallic Ga and Bi are reference states. The 64 and 512 atom SQS give similar mixing enthalpies, except at x = 0.5, where as eight atom SQS overestimate the mixing enthalpy significantly. The disordered alloys are more stable than the most stable ordered phases except at very low temperatures. The spinodal transformation temperature corresponds approximately to the latest experimental results, if the separated systems can conform to their own lattice constants. The spinodal transformation temperature is decreased very significantly, if the decomposing phases are constrained to maintain lattice coherence with the substrate. The strain energies of the alloys and decomposing phases are large also at the surfaces.

  • 5.
    Punkkinen, Marko P. J.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Laukkanen, P.
    Lång, J.
    Kuzmin, M.
    Dahl, J.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Pessa, M.
    Guina, M.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kokko, K.
    Structure of ordered oxide on InAs(100) surface2012In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 606, no 23-24, p. 1837-1841Article in journal (Refereed)
    Abstract [en]

    It was recently found that oxygen induces ordered reconstructions on several III-V surfaces. The most oxygen-rich reconstruction shows (3x1) periodicity. Based on first-principles investigations, a detailed atomic model is presented for this reconstruction. The uncommon periodicity is attributed to the highly stable In - O - In trilayer below surface which also leads to stabilizing additional bonds within the surface layer. The strain induced by the trilayer is more effectively accommodated within the (3 x 1) reconstruction than within the competing (2 x 1) reconstruction due to smaller number of dimers. It is proposed that the experimentally found semiconductivity is reached by substitutional atoms within the surface layer. Suitable substitution preserves the magnitude of the bulk band gap.

  • 6.
    Punkkinen, Marko Patrick John
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kokko, K.
    Levämäki, H.
    Ropo, M.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delczeg, Lorand
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delczeg-Czirjak, Erna Krisztina
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Adhesion of the iron-chromium oxide interface from first-principles theory2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 49, p. 495501-Article in journal (Refereed)
    Abstract [en]

    We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.

  • 7.
    Vitos, Levente
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden; Research Institute for Solid State Physics and Optics, Hungary.
    Zhang, Hulei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Al-Zoubi, Noura
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilsson, Jan-Olof
    Hertzman, Staffan
    Nilson, Börje
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Stainless steel alloys from first-principles theory2011In: 7th European Stainless Steel Conference: Science and Market, Proceedings, Associazione Italiana di Metallurgia , 2011Conference paper (Refereed)
    Abstract [en]

    Gaining an accurate description of materials obviously requires the most advanced atomic-scale techniques from both experimental and theoretical areas. In spite of the vast number of available techniques, however, the experimental study of the atomic-scale properties and phenomena even in simple solids is rather difficult. In steels the challenges become more complex due to the interplay between the structural, chemical and magnetic effects. On the other hand, advanced computational methods based on density functional theory ensure a proper platform for studying the fundamental properties of steel materials from first-principles. Our group at the Royal Institute of Technology in Stockholm has an international position in developing and applying computational codes for such applications. Using our ab initio tools, we have presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we review the most important developments within the ab initio quantum-mechanics-aided steel design with special emphasis on the role of magnetism on the fundamental properties of alloy steels.

  • 8.
    Vitos, Levente
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, Hulei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Al-Zoubi, Noura
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilsson, Jan-Olof
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilson, G.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Stainless Steel Alloys from First-principles Theory2012In: La Metallurgia Italiana, ISSN 0026-0843, no 5, p. 19-27Article in journal (Refereed)
    Abstract [en]

    Gaining an accurate description of materials obviously requires the most advanced atomic-scale techniques from both experimental and theoretical areas. In spite of the vast number of available techniques, however; the experimental study of the atomic-scale properties and phenomena even in simple solids is rather difficult. In steels the challenges become more complex due to the interplay between the structural, chemical and magnetic effects. On the other hand, advanced computational methods based on density functional theory ensure a proper platform for studying the fundamental properties of steel materials from first-principles. Our group at the Royal Institute of Technology in Stockholm has an international position in developing and applying computational codes for such applications. Using our ab initio tools, we have presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we review the most important developments within the ab initio quantum-mechanics-aided steel design with special emphasis on the role of magnetism on the fundamental properties of alloy steels.

  • 9.
    Vitos, Levente
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, Hulei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Al-Zoubi, Noura
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilsson, Jan-Olof
    AB Sandvik Materials Technolgy, Sweden.
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Mechanical properties and magnetism: stainless steel alloys from first-principles theory2011In: 2010 MRS Fall Meeting, 2011, p. 68-79Conference 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.

  • 10.
    Xiong, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Zhang, Hualei
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Vitos, Levente
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Magnetic phase diagram of the Fe-Ni system2011In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 2, p. 521-530Article in journal (Refereed)
    Abstract [en]

    Magnetic phase diagrams of body-centered cubic and face-centered cubic Fe-Ni alloys were constructed using available experimental data and ab initio calculations. The results show that significant improvements in the "standard" diagrams (handbooks and CALPHAD databases) are required. The present work demonstrates that the CALPHAD magnetic model is not sophisticated enough to describe the Fe-Ni system. In addition, a new thermodynamic description of the lattice stability for pure Ni is urgently needed, since the recommended magnetic properties for CALPHAD modeling are distinct from the experimental and ab initio results. This work indicates that the construction of magnetic phase diagrams is indispensable during the phase transformation study of magnetic systems. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 11.
    Zhang, Huaeli
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Punkkinen, Marko Patrick John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic parameters of paramagnetic iron-based alloys from first-principles calculations2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 5, p. 054107-Article in journal (Refereed)
    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.

  • 12.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM).
    Elastic properties of ferromagnetic BCC Fe alloys form first-principles theory2010Licentiate thesis, comprehensive summary (Other academic)
  • 13.
    Zhang, Hualei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic Properties of Iron Alloys from First-Principles Theory2011Doctoral 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.

  • 14.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Al-Zoubi, Noura
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Alloying effects on the elastic parameters of ferromagnetic and paramagnetic Fe from first-principles theory2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 7, p. 073707-Article in journal (Refereed)
    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.

  • 15.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles study of solid-solution hardening in steel alloys2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, p. 269-272Article in journal (Refereed)
    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.

  • 16.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 22Article in journal (Refereed)
    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.

  • 17.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Density-functional study of paramagnetic iron2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 14, p. 140411-Article in journal (Refereed)
    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.

  • 18.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Xiaoqing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Jesperson, Henrik
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Anomalous elastic hardening in Fe-Co alloys at high temperature2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 18, p. 184107-Article in journal (Refereed)
    Abstract [en]

    The elastic moduli of Fe1-cCoc (c <= 0.2) alloys are found to decrease strongly with increasing temperature, but show very weak alloying effects for both low-temperature ferromagnetic and high-temperature paramagnetic states. For temperatures slightly below and around the Curie temperature of Fe, Co addition significantly increases the elastic moduli. The variation of the tetragonal shear elastic constant upon 20% Co addition increases from a small negative value to more than 135% as the temperature rises from 0 to 1200 K. The expected elastic softening in the case of Al doping is not confirmed. Both anomalous trends are ascribed to the interplay between intrinsic chemical effects, magnetism, and temperature.

  • 19.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Punkkinen, Marko Patrick John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hu, Qing-Miao
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Static equation of state of bcc iron2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 13, p. 132409-Article in journal (Refereed)
    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.

  • 20.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Center of Microstructure Science, Frontier Institute of Science and Technology, State Key Laboratory for Mechanical Behavior of Materials, Xi'An Jiaotong University, Xi'an, China.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhou, Minna
    Punkkinen, Marko P. J.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Dept Phys & Mat Sci, Div Mat Theory, SE-75120 Uppsala, Sweden.
    Vitos, Levente
    Ab initio determination of the elastic properties of ferromagnetic body-centered cubic Fe-Mn-Al alloys2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 118, no 10, article id 103904Article in journal (Refereed)
    Abstract [en]

    The elastic properties of ferromagnetic Fe1-x-yMnyAlx (0 <= x <= 0.5, y = 0, 0.1, and 0.2) random solid solutions in the body-centered cubic (bcc) crystallographic phase have been investigated using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation. Comparison with the experimental data demonstrates that the employed theoretical approach accurately captures the observed composition dependence of the lattice parameter. The predicted elastic parameters follow complex composition dependence. The C-11, C-12, and C' = (C-11 - C-12)/2 single-crystal elastic constants, the bulk (B), shear (G), and Young's (E) moduli, and the Cauchy pressure (C-12 - C-44) mainly decrease with increasing Al content, whereas the Zener anisotropy ratio (C-44/C') strongly increases with x. C-44 exhibits a non-linear x dependence. The Poisson (v) and Pugh (B/G) ratios first decrease with x but show non-monotonous behavior in high-Al alloys. In terms of the Pugh criterion, these trends suggest an increased brittleness in Al-containing alloys. Manganese has a complex non-monotonous effect on B/G in low-Al alloys (below similar to 15 at. % Al) but enhances the brittleness of the bcc solid solution in large-Al regime. The peculiar Mn alloying effect is explained in terms of magneto-volume mechanisms.

  • 21.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Punkkinen, Marko P. J.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Theoretical elastic moduli of ferromagnetic bcc Fe alloys2010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 27, p. 275402-Article in journal (Refereed)
    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.

  • 22.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Punkkinen, Marko Patrick John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Hertzman, Staffan
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Single-crystal elastic constants of ferromagnetic bcc Fe-based random alloys from first-principles theory2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 18, p. 184105-Article in journal (Refereed)
    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.

  • 23.
    Zhang, Hualei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Wang, Guisheng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Punkkinen, Marko P. J.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Hertzman, Staffan
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Elastic anomalies in Fe-Cr alloys2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 19, p. 195501-Article in journal (Refereed)
    Abstract [en]

    Using ab initio alloy theory, we determine the elastic parameters of ferromagnetic and paramagnetic Fe1-cCrc (0 <= c <= 1) alloys in the body centered cubic crystallographic phase. Comparison with the experimental data demonstrates that the employed theoretical approach accurately describes the observed composition dependence of the polycrystalline elastic moduli. The predicted single-crystal elastic constants follow complex anomalous trends, which are shown to originate from the interplay between magnetic and chemical effects. The nonmonotonic composition dependence of the elastic parameters has marked implications on the micro-mechanical properties of ferrite stainless steels.

1 - 23 of 23
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