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  • 1.
    Gorbatov, Oleg I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Razumov, I. K.
    Gornostyrev, Yu N.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Role of magnetism in Cu precipitation in alpha-Fe2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 17, p. 174113-Article in journal (Refereed)
    Abstract [en]

    The temperature-dependent solubility of Cu in alpha-Fe and initial stages of Cu precipitation are investigated in first-principles calculations and statistical thermodynamic and kinetic modeling based on ab initio effective interactions. We demonstrate that the weakening of the phase separation tendency with increasing temperature, especially close to the magnetic phase transition, is related to the strong dependence of the "chemical" interactions on the global magnetic state. At the same time, our calculations demonstrate that the vibrational contribution obtained in the quasiharmonic approximation is relatively small for temperatures near the Curie point. The results of Monte Carlo simulations of Cu solubility and clustering are in good agreement with experimental data.

  • 2.
    Grönhagen, Karin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Razumowski, Vsevolod
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ödqvist, J.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Phase-field coupled with CALPHAD database and ab-initio modeling of diffusion barriers and prefactors for simulating spinodal decomposition in ZrC-TiC carbidesManuscript (preprint) (Other academic)
  • 3.
    Rahaman, Moshiour
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Razumovskiy, Vsevolod
    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.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Temperature dependence of stacking-fault and anti-phase boundary energies in Al3Sc from ab initio calculations2013In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 93, no 25, p. 3423-3441Article in journal (Refereed)
    Abstract [en]

    Temperature dependence of intrinsic stacking-fault energies (SFE) and anti-phase boundary energies (APBE) of AlSc is investigated in first-principles calculations using the axial Ising model and supercell approach. The temperature effect has been taken into consideration by including the one-electron thermal excitations in the electronic structure calculations, and vibrational free energy in the harmonic approximation as well as by using temperature dependent lattice constant. The latter has been determined within the Debye-Gruneisen model, which reproduces well the experimental data. The APBE and SFE are found to be reduced by about 10% in the temperature interval from 0 to 1000 K. It is shown that the inclusion of the free energy of lattice vibrations in the harmonic approximation increases the SFE further by about 4%. We also find a substantial contribution from local lattice relaxations in the case of APBE for the (111) plane and SFE leading to their reduction by about 30%.

  • 4. Razumovskii, I. M.
    et al.
    Bykov, Y. G.
    Beresnev, A. G.
    Poklad, V. A.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Effect of the Particle Size of γ’ Phase on the Mechanical Properties of Ni base Superalloy2011In: Euro Superalloys 2010, Trans Tech Publications Inc., 2011, Vol. 278, p. 96-101Conference paper (Refereed)
    Abstract [en]

    The effect of gamma’ particle size upon the mechanical properties of Ni base superalloy EP741NP obtained by powder metallurgy was investigated. The particle size of gamma’ phase in gamma-gamma’ microstructure was varied by changing the cooling rate V from the temperature of the solid solution treatment at 1200 C (V = 80, 200 and 400 C \ min.). After solid solution treatment billets were subjected to aging in the standard mode. It was established that as V increases from 80 to 200 C \ min., the average particle’s size of gamma’ phase decreases from 0.54 microns to 0.22 microns in the aged state. This improves the characteristics of creep and low cycle fatigue at 650C: time to rupture under load 1000 MPa increased from 132 hours to 416 hours and low cycle fatigue increased from 42,215 to 82,016 cycles.

  • 5. Razumovskii, I. M.
    et al.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Logunov, A. V.
    Larionov, V. N.
    Ospennikova, O. G.
    Poklad, V. A.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    New generation of Ni-based superalloys designed on the basis of first-principles calculations2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 497, no 1-2, p. 18-24Article in journal (Refereed)
    Abstract [en]

    A new approach to the design of Ni-based single crystal superalloys is proposed. It is based on a concept that under given structural conditions, the creep-rupture characteristics of superalloys are mainly determined by interatomic bonding given by the cohesive energy. In order to characterize the individual contribution of each alloying element to the strength properties at high temperature, we introduce a parameter, X, which is the partial molar cohesive energy of an alloy component. This parameter is then obtained in the total energy first-principles calculations for a usual set of alloying elements. We demonstrate that creep-rupture characteristics of alloys indeed correlate with the total gain partial molar cohesive energy due to alloying and find that W, Ta, and Re have the highest values of X, and should therefore play the major role in providing high-temperature strength of superalloys. Based on this finding, we design three new superalloys with a high content of W and show that they have superior creep-rupture properties compared not only with their counterparts with the lower content of W, but also with the best Ru-bearing Ni-based superalloys.

  • 6.
    Razumovskiy, Vsevolod
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology. KTH, School of Industrial Engineering and Management (ITM), Centres, VinnExcellence Centre for Hierarch. Eng. of Industrial Materials, HERO-M.
    Thermodynamic and kinetic properties of Fe-Cr and TiC-ZrC alloys from Density Functional Theory2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The complete and accurate thermodynamic and kinetic description of any systemis crucialfor understanding and predicting its properties. A particular interest is in systemsthat are used for some practical applications and have to be constantly improved usingmodification of their composition and structure. This task can be quite accuratelysolved at a fundamental level by density functional theory methods. Thesemethods areapplied to two practically important systems Fe-Cr and TiC-ZrC.The elastic properties of pure iron and substitutionally disordered Fe-Cr alloy are investigatedas a function of temperature and concentration using first-principles electronicstructurecalculations by the exact muffin-tin orbitals method. The temperature effectson the elastic properties are included via the electronic, magnetic, and lattice expansioncontributions. It is shown that the degree of magnetic order in both pure iron andFe90Cr10 alloy mainly determines the dramatic change of the elastic anisotropy of thesematerials at elevated temperatures. A peculiarity in the concentration dependence ofthe elastic constants in Fe-rich alloys is demonstrated and related to a change in theFermi surface topology.A thermodynamic model for the magnetic alloys is developed from first principles andapplied to the calculation of bcc Fe-Cr phase diagram. Various contributions to the freeenergy (magnetic, electronic, and phonon) are estimated and included in the model. Inparticular, it is found that magnetic short range order effects are important just abovethe Curie temperature. The model is applied for calculating phase equilibria in disorderedbcc Fe-Cr alloys. Model calculations reproduce a feature known as a Nishizawahorn for the Fe-rich high-temperature part of the phase diagram.The investigation of the TiC-ZrC system includes a detailed study of the defect formationenergies and migration barriers of point defects and defect complexes involvedin the diffusion process. It is found, using ab initio atomistic simulations of vacancymediateddiffusion processes in TiC and ZrC, that a special self-diffusion mechanism isoperative for metal atom diffusion in sub-stoichiometric carbides. It involves a noveltype of a stable point defect, a metal vacancy ”dressed” in a shell of carbon vacancies.It is shown that this vacancy cluster is strongly bound and can propagate through thelattice without dissociating.

  • 7.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Isaev, E. I.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio calculations of elastic properties of Pt-Sc alloys2008In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 16, no 8, p. 982-986Article in journal (Refereed)
    Abstract [en]

    Elastic properties of substitutionally disordered Pt-rich Pt-Sc alloys and L1(2)-ordered Pt3Sc compound are derived from the first-principles calculations based on the exact muffin-tin orbitals (EMTO) method. We demonstrate that these alloys should exhibit a ductile behavior, which combined with relatively high melting temperature and strong cohesive properties make them a very promising candidate for high-temperature applications.

  • 8.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Isaev, Eyvaz I.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    New Pt-Based Superalloy System Designed from First Principles2009In: Advanced Intermetallic-Based Alloys For Extreme Environment And Energy Applications / [ed] Palm M; Bewlay BP; He YH; Takeyama M; Wiezorek JMK, 2009, Vol. 1128, p. 233-238Conference paper (Refereed)
    Abstract [en]

    Pt-Sc alloys with the gamma-gamma' microstructure are proposed as a basis for a new generation of Pt-based superalloys for ultrahigh-temperature applications. This alloy system was identified on the basis of first-principles calculations. Here we discuss the prospects of the Pt-Sc alloy system on the basis of calculated elastic properties, phonon spectra, and defect formation energies.

  • 9.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab-initio calculations of kinetic properties in ZrC and TiC carbides2011Conference paper (Refereed)
    Abstract [en]

    Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).

  • 10.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben Forschung GmbH, Austria.
    Lozovoi, A. Y.
    Razumovskii, I. M.
    First-principles-aided design of a new Ni-base superalloy: Influence of transition metal alloying elements on grain boundary and bulk cohesion (vol 82, pg 369, 2015) ERRATUM2016In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 106, p. 401-402Article in journal (Refereed)
  • 11.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben Forschung GmbH, Austria.
    Lozovoi, A. Y.
    Razurnovskii, I. M.
    First-principles-aided design of a new Ni-base superalloy: Influence of transition metal alloying elements on grain boundary and bulk cohesion2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 82, p. 369-377Article in journal (Refereed)
    Abstract [en]

    A new approach to the design of Ni-base polycrystalline superalloys is proposed. In this approach, we assume that the creep rupture characteristics of a superalloy are mostly determined by the strength of interatomic bonding at grain boundaries (GBs) and in the bulk of gamma matrix. The ideal work of separation, W-sep, of a GB is used as a fundamental thermodynamic quantity that controls the mechanical strength of an interface, whereas the partial cohesive energy, chi, of an alloy component serves to characterize its contribution into the strength of the bulk. Using the Sigma 5 (2 1 0)[1 0] symmetric tilt GB as a representative high-angle GB in Ni, we calculate W-sep, chi, and GB segregation energies, E-seg for the complete set of 4d and 5d transition metal impurities, to which we add B (a typical microalloying addition), S and Bi (notoriously known as harmful impurities in Ni-base superalloys). The purpose of the analysis is to identify the elements that demonstrate a high tendency to segregate to GBs, have positive (preferably high) partial cohesive energies in the bulk, and have positive impact on W-sep of GBs. We refer to these elements as low-alloying additions. Our study reveals Zr, Hf, Nb, Ta and B as the most promising low-alloying additions. Our next step is to introduce the elements found in the first step into a new powder metallurgy (P/M) Ni-base superalloy. The results of the subsequent testing confirm that the newly created P/M superalloy indeed demonstrates superior mechanical properties at high temperatures compared to the existing Russian P/M alloy EP741NP.

  • 12.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lozovoi, A. Yu.
    Razumovskii, I. M.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Analysis of the Alloying System in Ni-Base Superalloys Based on Ab Initio Study of Impurity Segregation to Ni Grain Boundary2011In: EURO SUPERALLOYS 2010 / [ed] Heilmaier, M, Trans Tech Publications Inc., 2011, Vol. 278, p. 192-197Conference paper (Refereed)
    Abstract [en]

    A new approach to the design of Ni-based polycrystalline superalloys is proposed. It is based on a concept that under given structural conditions, the performance of superalloys is determined by the strength of interatomic bonding both in the bulk and at grain boundaries of material. We characterize the former by the cohesive energy of the bulk alloy, whereas for the latter we employ the work of separation of a representative high angle grain boundary. On the basis of our first principle calculations we suggest Hf and Zr as “minor alloying additions” to Ni-based alloys. Re, on the other hand, appears to be of little importance in polycrystalline alloys.

  • 13.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. National University of Science and Technology MISIS, Moscow, Russian Federation .
    Razumovskii, I. M.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Butrim, V. N.
    Vekilov, Yu. Kh.
    The influence of alloying elements on grain boundary and bulk cohesion in aluminum all: Ab initio study2012In: Thermec 2011 Supplement, Trans Tech Publications Inc., 2012, Vol. 409, p. 417-422Conference paper (Refereed)
    Abstract [en]

    The effect of B, Si, P, Cr, Ni, Zr and Mg on cohesive properties of Al and the specialgrain boundary (GB) Σ5 (210)[100], as well as their segregation behavior at the GB and the (210)surface are studied by first principles method. The analysis of these parameters allows us to singleout Ni as the best and phosphorus as the worst interatomic bond strengthening alloying elements.

  • 14.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Effect of temperature on the elastic anisotropy of pure Fe and Fe0.9Cr0.1 random alloy2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 20, article id 205504Article in journal (Refereed)
    Abstract [en]

    The elastic properties of pure iron and substitutionally disordered 10 at. % Cr Fe-Cr alloy areinvestigated as a function of temperature using first-principles electronic-structure calculations bythe exact muffin-tin orbitals method. The temperature effects on the elastic properties are includedvia the electronic, magnetic, and lattice expansion contributions. We show that the degree ofmagnetic order in both pure iron and Fe90Cr10 alloy mainly determines the dramatic change of theelastic anisotropy of these materials at elevated temperatures. The effect of lattice expansion isfound to be secondary but also very important for quantitative modeling.

  • 15.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    First-principles study of elastic properties of Cr- and Fe-rich Fe-Cr alloys2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 2, article id 024106Article in journal (Refereed)
    Abstract [en]

    Elastic properties of substitutionally disordered Cr- and Fe-rich Fe-Cr alloys are derived from first-principles calculations using the exact muffin-tin orbitals method and the coherent potential approximation. A peculiarity in the concentration dependence of elastic constants in Fe-rich alloys is demonstrated and related to a change in the Fermi surface topology. Our calculations predict high values for the elastic constants of Cr-rich Fe-Cr alloys, but at the same time show that these alloys could be rather brittle according to the Pugh criterion (the ratio between shear and bulk moduli is calculated to be greater than 0.5).

  • 16.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Vacancy-cluster mechanism of metal-atom diffusion in substoichiometric carbides2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 5, p. 054203-Article in journal (Refereed)
    Abstract [en]

    We find, using ab initio atomistic simulations of vacancy-mediated diffusion processes in TiC and ZrC, that a multivacancy self-diffusion mechanism is operative for metal-atom diffusion in substoichiometric carbides. It involves a special type of a stable point defect, a metal vacancy "dressed" in a shell of carbon vacancies. We show that this vacancy cluster is strongly bound and can propagate through the lattice without dissociating.

  • 17.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Razumovskii, I. M.
    Lozovoi, A. Y.
    Butrim, V. N.
    Vekilov, Yu. Kh.
    The effect of alloying elements on grain boundary and bulk cohesion in aluminum alloys: An ab initio study2011In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 65, no 10, p. 926-929Article in journal (Refereed)
    Abstract [en]

    The effect of B, Si, P, Cr, Ni, Zr and Mg impurities on cohesive properties of Al and its special grain boundary (GB) Sigma 5 (2 1 0) [1 0 0], as well as their segregation behavior at the GB and (2 1 0) surface are studied from first principles. Our analysis determines Ni to be the best and P the worst alloying elements in regard to the overall resistance to decohesion of Al alloys.

  • 18.
    Razumovskiy, Vsevolod I.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Vekilov, Yu. Kh.
    Razumovskii, I. M.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Butrim, V. N.
    Mironenko, V. N.
    Effect of Alloying Elements and Impurities on Interface properties in Aluminum Alloys2011In: Physics of the solid state, ISSN 1063-7834, E-ISSN 1090-6460, Vol. 53, no 11, p. 2189-2193Article in journal (Refereed)
    Abstract [en]

    The segregation energies of B, Si, P, Cr, Ni, Zr, and Mg on the special grain boundary (GB) Σ5 (210)[100] and on the open (210) surface of aluminum have been determined and the GB splitting energy has been calculated by the density functional theory methods. It has been shown that all elements listed above enrich the GB; for B, Si, P, Cr, Ni and Zr, Mg, interstitial and substitutional sites are preferred, respectively. The effect of alloying elements on the GB binding has been estimated using the parameter η equal to the change in the fracture work of the aluminum GB when adding alloying element atoms. From the viewpoint of strengthening the GB binding forces, Zr, Cr, Ni, and Mg are efficient, Si and B are neutral and phosphorus weakens GBs.

  • 19.
    Razumovskiy, Vsevolod
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Mat Ctr Leoben Forsch GmbH, A-8700 Leoben, Austria.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Dilner, David
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Korzhavyi, Pavel
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Effect of carbon vacancies on thermodynamic properties of TiC-ZrC mixed carbides2014In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 46, p. 87-91Article in journal (Refereed)
    Abstract [en]

    Thermodynamic properties of a TiZrC mixed carbide system are investigated by first-principles methods within density functional theory. Carbon vacancies are found to have a significant contribution to the thermodynamics of TiZrC mixed carbides. The temperature effect on the thermodynamic properties of the system is calculated taking into consideration the corresponding electronic and vibrational thermal excitations.

  • 20.
    Ruban, Andrei V.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles based thermodynamic model of phase equilibria in bcc Fe-Cr alloys2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 17, p. 174111-Article in journal (Refereed)
    Abstract [en]

    A first-principles based thermodynamic model for magnetic alloys is applied to the calculation of the Fe-Cr phase diagram restricted by the bcc structure. The model includes magnetic, electronic, phonon, and local atomic relaxations contributions to the free-energy derived from ab initio calculations. Atomic short-range-order effects are found to be relatively small and they have been neglected in the calculations, assuming that alloys are in the completely random state. In contrast, we have taken into consideration magnetic short-range-order effects, which are found to be very important in particular above the Curie temperature. The calculated phase diagram is in reasonable agreement with the latest CALPHAD assessment. Our calculations reproduce a feature known as a Nishizawa horn for the Fe-rich high-temperature part of the phase diagram.

  • 21.
    Ruban, Andrei V.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Razumovskiy, Vsevolod I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Spin-wave method for the total energy of paramagnetic state2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 17, p. 174407-Article in journal (Refereed)
    Abstract [en]

    Spin-wave formalism provides a convenient alternative way of modeling the high-temperature paramagnetic state for a certain type of magnets within the framework of Hamiltonian-type electronic-structure methods. For Heisenberg systems, it is formally equivalent to the so-called disordered local moment approach, which is usually used in the methods based on the coherent potential approximation within the Green's function or multiple-scattering techniques. In this paper, we demonstrate that the spin-wave method has certain advantages when it comes to the calculation of forces and relaxations. It also allows one to take magnetic short-range-order effects into consideration. As examples of the application of the spin-wave method, we calculate the energy of the paramagnetic state in fcc Co and bcc Fe, the vacancy formation energy, elastic constants, and phonon spectrum in bcc paramagnetic Fe. We demonstrate that magnetic short-range-order effects play a crucial role in the mechanical stabilization of the bcc Fe at high temperature in the paramagnetic state.

  • 22.
    Yeddu, Hemantha Kumar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Razumovskiy, Vsevolod. I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Korzhavyi, Pavel. A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ruban, Andrei. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Multi-length scale modeling of martensitic transformations in stainless steels2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 19, p. 6508-6517Article in journal (Refereed)
    Abstract [en]

    In the present work a multi-length scale model is developed to study both the athermal and stress-assisted martensitic transformations in a single crystal of 301 type stainless steel. The microstructure evolution is simulated using elastoplastic phase-field simulations in three dimensions. The input data for the simulations is acquired from a combination of computational techniques and experimental works. The driving force for the transformation is calculated by using the CALPHAD technique and the elastic constants of the body-centered cubic phase are calculated by using ab initio method. The other input data is acquired from experimental works. The simulated microstructures resemble a lath-type martensitic microstructure, which is in good agreement with the experimental results obtained for a stainless steel of similar composition. The martensite habit plane predicted by the model is in accordance with experimental results. The Magee effect, i.e. formation of favorable martensite variants depending on the loading conditions, is observed in the simulations. The results also indicate that anisotropic loading conditions give rise to a significant anisotropy in the martensitic microstructure.

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