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  • 1.
    Barkar, Thomas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of concentration dependent gradient energy coefficient on spinodal decomposition in the Fe-Cr system2018In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 143, p. 446-453Article in journal (Refereed)
    Abstract [en]

    The Cahn–Hilliard equation is solved with thermodynamic and kinetic input, using the Thermo-Calc and DICTRA software packages rather than simpler models e.g. regular solution. A concentration dependent expression for the gradient energy coefficient is introduced and its effect on simulated decomposition is discussed. Simulations were carried out in 2D and 3D using the FiPy software package modified for non-linear problems.

  • 2.
    Barkar, Thomas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Phase field modeling of spinodal decomposition in Fe-Cr based alloys2015In: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, International Conference on Solid-Solid Phase Transformations in Inorganic Materials , 2015, p. 827-828Conference paper (Refereed)
  • 3.
    Borgenstam, Annika
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Engstrom, A.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Metallurgy.
    DICTRA, a tool for simulation of diffusional transformations in alloys2000In: Journal of phase equilibria (Print), ISSN 1054-9714, E-ISSN 1544-1032, Vol. 21, no 3, p. 269-280Article in journal (Refereed)
    Abstract [en]

    In the present paper, a general survey of the diffusion-controlled transformations (DICTRA) software is given. DICTRA is an engineering tool for diffusion simulations in multicomponent alloys. The simulations are based on multicomponent diffusion and thermodynamic data, both obtained by analyzing and assessing experimental information. This allows for many different cases to be studied as soon as the underlying data are available. DICTRA is not a complete simulation tool because only geometries that can be transformed into one space variable can be treated, but many well posed problems of practical interest may be solved. The program contains several different models, which are discussed in the present paper. Each model has its own applications and several examples from recent simulations are given in order to demonstrate the usage of the particular models.

  • 4. Chen, Q
    et al.
    Engstrom, A
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Strandlund, Henrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermo-Calc program interfaces and their applications - Direct insertion of thermodynamic and kinetic data into modeling of materials processing, structure, and property2005In: PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5 / [ed] Zhong, ZY; Saka, H; Kim, TH; Holm, EA; Han, YF; Xie, XS, ZURICH-UETIKON: TRANS TECH PUBLICATIONS LTD , 2005, Vol. 475-479, p. 3145-3148Conference paper (Refereed)
    Abstract [en]

    Thermodynamic and kinetic data are generally essential for quantitative modeling of materials processing, structure, and property. Thermo-Calc program interfaces, including TQ, TC-API, and TC MATLAB Toolbox, provides a hierarchy of APIs for application programmers to access thermodynamic and kinetic data via the kernel of Thermo-Calc and DICTRA, the most widely used software and database system for multi-component phase equilibrium and phase transformation calculations. With these program interfaces, variation of thermodynamic and kinetic properties can be directly obtained in real time as the local temperature, pressure, or composition changes. The structure and usage of the Thermo-Calc program interfaces will be introduced in this article. Successful application examples will be illustrated.

  • 5. Crusius, Sabine
    et al.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Knoop, Usula
    Inden, Gerhard
    KTH, Superseded Departments, Physics.
    Ågren, John
    On the growth of ferrite allotriomorphs in fe-c alloys1992In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 83, no 10, p. 729-738Article in journal (Refereed)
    Abstract [en]

    Different geometrical models of allotriomorphic growth of ferrite in undercooled austenite are investigated by means of numerical and analytical treatments of diffusional growth under local equilibrium. The results obtained by the numerical method are compared with analytical solutions for those cases where such solutions may be derived. An excellent agreement is obtained. The numerical method is subsequently applied to simulate the experiments by Aaronson et al. and some more recent experiments by Hougardy et al.. taking into account the concentration dependence of the diffusivity of C in austenite and the most recent thermodynamic assessment of the ferrite/austenite equilibrium. Taking into account the experimental uncertainties we conclude that the growth of allotriomorphic ferrite must be essentially controlled by long-range carbon diffusion in austenite.

  • 6. Crusius, Sabine
    et al.
    Inden, Gerhard
    KTH, Superseded Departments, Physics.
    Knoop, Ursula
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    On the numerical treatment of moving boundary problems1992In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 83, no 9, p. 673-678Article in journal (Refereed)
    Abstract [en]

    Some numerical methods for solving a Stefan problem are discussed and compared with the exact solution. The growth of a planar particle from a supersaturated solution (or solidification from a supercooled liquid) is considered. It is found that the Murray-Landis method, based on a finite difference technique to solve the diffusion equation on a contracting grid, yields a poor accuracy for high supersaturations. The enthalpy method, also based on the finite difference technique and an interpolation formula for obtaining the interface position, shows a satisfactory performance at high supersaturations but a less satisfactory one at low supersaturations. It is demonstrated that the poor accuracy of the Murray-Landis method depends on the application of a less accurate flux-balance equation for finite time increments and the procedure for displacing the grid points. A modification of the Murray-Landis method is developed and is found to have superior numerical performance.

  • 7. Engström, Anders
    et al.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    COMPUTER-SIMULATION OF DIFFUSION IN MULTIPHASE SYSTEMS1994In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 25, no 6, p. 1127-1134Article in journal (Refereed)
    Abstract [en]

    A general model to treat multicomponent diffusion in multiphase dispersions is presented. The model is based on multicomponent diffusion data and basic thermodynamic data and contains no adjustable parameters. No restriction is placed on the number of components or phases that take part in the calculations, as long as the necessary thermodynamic and kinetic data are available. The new model is implemented into the DICTRA software, which makes use of THERMO-CALC to handle the thermodynamics. The model is applied to carburization of Ni alloys and heat treatment of welded joints between dissimilar materials. In both cases, the diffusion is accompanied by carbide formation or dissolution. A good agreement between experiments and calculations is found, despite the fact that no adjustable parameters are needed.

  • 8.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Dynamic Coupling of Computational Fluid Dynamics and Thermodynamics Software: Applied on a Top Blown Converter2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, no 2, p. 147-153Article in journal (Refereed)
    Abstract [en]

    A novel modeling approach is presented where a computational fluid dynamics software is coupled to thermodynamic databases to obtain dynamic simulations of metallurgical process phenomena. The modeling approach has been used on a fundamental model of a top-blown converter. Reactions between gas-steel, gas-slag, steel-slag and gas-steel-slag have been considered. The results show that the mass transport in the surface area is totally controlled by convection. Also, that a large amount of CO produced during the decarburization might slow down the rate of decarburization in droplets ejected from the bath. For the present simulation conditions reflecting laboratory experiments, it was also seen that the amount of slag (FeO and/or SiO2) created is close to zero, i.e. only gas (CO+CO2) is created as the oxygen jet hits the steel bath. It was also illustrated how an extrapolation of the decarburization rate, sampled from a few seconds of simulation, could be done to get a rough estimate of the carbon content at a later stage in the process as long as the carbon content is relatively high. The overall conclusion is that it is possible to make a dynamic coupling of the Thermo-Calc databases and a CFD software to make dynamic simulations of metallurgical processes such as a top-blown converter.

  • 9.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Dynamic Modeling of Steel, Slag and Gas Reactions during Initial Blowing in a Top-Blown Converter2008In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Article in journal (Other academic)
    Abstract [en]

    A dynamic modeling approach is presented where a computational fluid dynamics software is coupled to a thermodynamics software to obtain simulations of reactions between steel, slag and gas in a top-blown converter. For each simulation the transport of momentum, energy and mass of species as well as the thermodynamic equilibrium in each cell containing at least two phases was treated. The overall conclusion is that the present calculation procedure is successful for dynamic simulations of interaction between an oxygen gas jet with a melt and a slag. The predicted rate of decarburization was found to agree well with experimental data from laboratory trials. In addition, four cases where simulated for which the temperature, the dissolved carbon content and the dissolved oxygen content were varied. The most important findings from these comparisons were that: i) a higher initial oxygen concentration in the melt yields a larger decarburization rate, ii) carbon content also plays a big role for the desiliconization where a low carbon content is required for desiliconization to take place, iii) decarburization and desiliconization is largely influenced by the temperature at which reactions take place, where low temperature favors desiliconization and iv) the region affected by a lower carbon/silicon concentration (hot-spot region) directly below the jet was approximately 10 mm for the current setup.

  • 10.
    Ersson, Mikael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Dynamic modelling of steel, slag and gas during initial blowing in a top-blown converter2011In: Steel Grips - Journal of Steel and Related Materials, ISSN 1611-4442, E-ISSN 1866-8453, no 9, p. 41-47Article in journal (Refereed)
    Abstract [en]

    A coupling between computational fluid dynamics (CFD) and thermodynamics has recently been done. In the current model improvement, a more realistic model was developed, where the numbers of gas species and slag phases were increased. For each simulation the transport of momentum, energy and mass of species as well as the thermodynamic equilibrium in each cell containing at least two phases was treated. Read how this calculation procedure can handle dynamic simulations of interaction between an oxygen gas jet, a melt and a slag. How is the agreement between the predicted rate of decarburization and experimental data? Which findings were achieved from the simulation of four cases varying the temperature, the dissolved carbon content and the dissolved oxygen content?

  • 11. Hallstedt, Bengt
    et al.
    Dupin, Nathalie
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Lukas, Hans Leo
    Schuster, Julius C.
    Solak, Nuri
    Thermodynamic models for crystalline phases. Composition dependent models for volume, bulk modulus and thermal expansion2007In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 31, no 1, p. 28-37Article in journal (Refereed)
    Abstract [en]

    The thermodynamic modelling of solid (crystalline) phases forms a central topic within the Calphad approach and a variety of aspects have been discussed at previous Ringberg workshops. At the present Ringberg workshop, modelling of volume and its temperature, pressure and composition dependence formed a major part of the discussions. In addition, modelling of the heat capacity above the (equilibrium) melting temperature, sublattice modelling of complex phases, modelling of ordering and interstitial solutions in the bcc lattice and the effect of magnetism were addressed.

  • 12. Hallström, Samuel
    et al.
    Halvarsson, Mats
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jonsson, Torbjorn
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    High temperature oxidation of chromium: Kinetic modeling and microstructural investigation2013In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 240, p. 41-50Article in journal (Refereed)
    Abstract [en]

    Using CALPHAD methods, Cr2O3 growth on pure Cr is modeled using DICTRA and the vacancy model for diffusion. The results are compared with thermobalance and TEM experiments at 625 and 700 degrees C in O-2. The experimental scatter is significant, leading to a compromise suggestion. With the experimental conditions from the furnace exposures in this work, optimized mobilities are validated with a series of oxidation simulations. Despite the complex microstructure and initial growth rate variations, it is possible to reproduce the experimental oxide thicknesses with good accuracy, allowing for extension to multicomponent systems.

  • 13.
    Hallström, Samuel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Modeling of diffusion in wustite and simulation of oxidation of iron at 600°C2008In: 6th European Stainless Steel Conference / [ed] Pentti Karjalainen and Staffan Hertzman, Helsinki: Jernkontoret , 2008, p. 273-278Conference paper (Refereed)
    Abstract [en]

    A long missing feature in the diffusion simulation software DICTRA has been the diffusion in oxides. Recently, this capability was implemented and in this report we present some results of the current achievements.DICTRA can now treat diffusion in basically any oxide, provided that there is diffusion data available and that the necessary mobilities have been assessed. The first system to be addressed was the important Fe-O system. It contains three different oxides, from the simple wustite to the complex magnetite, which has the spinel structure. The current  approach was successful and the work was continued with the Cr-O system and the technically important Fe-Cr-O. We will present the diffusion models and the results of the assessment, as well as successful simulations of oxidation where layers of oxides grow on top of an Fe or Fe-Cr substrate.

  • 14.
    Hallström, Samuel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Modeling of iron diffusion in the iron oxides magnetite and hematite with variable stoichiometry2011In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 1, p. 53-60Article in journal (Refereed)
    Abstract [en]

    The vacancy model of diffusion is applied to magnetite and hematite, and mathematical expressions for the iron flux in the lattice-fixed frame of reference, as a function of the defect structure, are presented The defect structures, i e the vacancy content on the different type of sites, and the thermodynamic factors are calculated from the available Calphad type of thermodynamic descriptions for the oxides Expressions for Fe tracer diffusion coefficients are derived and the relations between mobility and tracer diffusivity are given The mobilities are fitted by a least-squares optimization to experimental data on tracer diffusion from the literature For magnetite, an excellent representation of the experimental tracer data is achieved together with a satisfactory description of the sparse chemical diffusion data available For hematite, the experimental scatter is very large and anomalous large frequency factors and activation energies have been reported In the present report a compromise is suggested.

  • 15. Hammerschmidt, T.
    et al.
    Abrikosov, I. A.
    Alfe, D.
    Fries, S. G.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jacobs, M. H. G.
    Kossmann, J.
    Lu, X-G
    Paul, G.
    Including the effects of pressure and stress in thermodynamic functions2014In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 1, p. 81-96Article in journal (Refereed)
    Abstract [en]

    Most applications of thermodynamic databases to materials design are limited to ambient pressure. The consideration of elastic contributions to thermodynamic stability is highly desirable but not straight-forward to realise. We present examples of existing physical models for pressure-dependent thermodynamic functions and discuss the requirements for future implementations given the existing results of experiments and first-principles calculations. We briefly summarize the calculation of elastic constants and point out examples of nonlinear variation with pressure, temperature and chemical composition that would need to be accounted for in thermodynamic databases. This is particularly the case if a system melts from different phases at different pressures. Similar relations exist between pressure and magnetism and hence set the need to also include magnetic effects in thermodynamic databases for finite pressure. We present examples to illustrate that the effect of magnetism on stability is strongly coupled to pressure, temperature, and external fields. As a further complication we discuss dynamical instabilities that may appear at finite pressure. While imaginary phonon frequencies may render a structure unstable and destroy a crystal lattice, the anharmonic effects may stabilize it again at finite temperature. Finally, we also outline a possible implementation scheme for strain effects in thermodynamic databases.

  • 16.
    Hillert, Mats
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Comments on kinetics model of isothermal pearlite formation in a 0.4C-1.6Mn steel2004In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 50, no 1, p. 171-173Article in journal (Refereed)
    Abstract [en]

    A recent attempt to use the volume fraction of isothermally formed pearlite to decide how Mn partitions between ferrite and cementite is criticized. An alternative method is proposed.

  • 17.
    Hillert, Mats
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Comments on Reply to comments on kinetics model of isothermal pearlite formation in a 0.4C-1.6Mn steel2004In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 51, no 1, p. 77-78Article in journal (Refereed)
    Abstract [en]

    A recent statement that the correction of a serious error in a thermodynamic calculation was not relevant to the interpretation is shown to be caused by the use of an incorrect equation instead of the lever rule.

  • 18.
    Hillert, Mats
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Melting of a peritectic phase2004In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 50, no 7, p. 1055-1059Article in journal (Refereed)
    Abstract [en]

    The reverse of a peritectic reaction belongs to the class of eutectic and eutectoid reactions and the same theory is now applied after modification for the fact that the predominating diffusion occurs within one of the growing phases, here the liquid one. The complications caused by the metastable congruent melting point are examined.

  • 19.
    Hillert, Mats
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mobility of alpha/gamma phase interfaces in Fe alloys2006In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 54, no 7, p. 1259-1263Article in journal (Refereed)
    Abstract [en]

    Information on the mobility of alpha/gamma phase interfaces in Fe alloys has been scarce and one has long relied on an evaluation for alpha/alpha grain boundaries. New and old information is now reviewed. There are strong indications that the mobility is much lower than for alpha/alpha grain boundaries.

  • 20.
    Hillert, Mats
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Schalin, M.
    Computer simulation of cooling curves for solidification2000In: Materials transactions, JIM, ISSN 0916-1821, Vol. 41, no 8, p. 1098-1103Article in journal (Refereed)
    Abstract [en]

    The method of simulating cooling curves for solidifying alloys is examined. Usually, a simulation program only results in a curve showing the fraction solidified material as a function of temperature. In order to predict the cooling curve, i.e. temperature as a function of time, it is necessary to use a simulation program that also evaluates the changes of enthalpy during solidification and takes into account the possible variation of the rate of heat extraction with temperature or with a temperature difference between a crucible and a furnace. By comparing predicted cooling curves obtained in that way with experiments it was investigated how to take into account the heat capacity of the crucible. Two simulation programs were used; one based on the Gulliver-Scheil approximations and the other taking back diffusion into account, using a finite difference technique. In both cases the enthalpy was evaluated continuously during cooling.

  • 21.
    Hillert, Mats
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Diffusion in interstitial compounds with thermal and stoichiometric defects2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 5Article in journal (Refereed)
    Abstract [en]

    The ordinary flux equation for diffusion, which considers the composition gradient as the driving force, is seldom of much use in studying closely stoichiometric phases. Depending on the defect structure it would instead be profitable to use an appropriate function of the activity. Such functions will now be derived and it will be shown how the operating defect mechanism of diffusion can be identified from information on the variation of the activity inside a phase during diffusion. However, it is usually very difficult to measure the activity profile inside a phase. It will be shown how it can be obtained by combining results from several experiments. The method will be used to analyze experimental information on the formation of surface layers of Fe4N and Fe3C.

  • 22.
    Hillert, Mats
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Metallurgy.
    Diffusion-controlled lengthening of Widmanstatten plates2003In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 51, no 7, p. 2089-2095Article in journal (Refereed)
    Abstract [en]

    Various treatments of the diffusion-controlled lengthening of plates during precipitation from a supersaturated solid solution are compared numerically. Serious doubts are raised about the validity of Trivedi's treatment which has been generally accepted. A recent treatment based directly on Ivantsov's solution gives results in between those of Trivedi's equation and Zener's equation, as modified by Hillert.

  • 23. Hillert, Mats
    et al.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    Escape of carbon from ferrite plates in austenite1993In: ACTA METALL MATER, ISSN 0956-7151, Vol. 41, no 7, p. 1951-1957Article in journal (Refereed)
    Abstract [en]

    A newly developed computer program for the simulation of diffusional transformations has been applied to study the escape of carbon from a plate of ferrite assuming that the plate initially formed by a partitionless reaction from an Fe-C austenite. Thereafter the ferrite austenite interface was assumed to be immobile and local equilibrium was assumed for carbon but not for iron. The process first follows a parabolic rate law and is there controlled by the rate of diffusion in ferrite. Later stages are not parabolic and are controlled by the diffusivity in austenite. Its concentration dependence was taken into account. It was found that the rate could be estimated analytically using the maximum value rather than the average value.

  • 24.
    Hillert, Mats
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Metallurgy.
    Role of carbon and alloying elements in the formation of bainitic ferrite2004In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 35A, no 12, p. 3693-3700Article in journal (Refereed)
    Abstract [en]

    One approach to the prediction of the carbon content of austenite, remaining after the precipitation of bainitic ferrite, is based on the assumption that bainitic ferrite during growth inherits the carbon content of the parent austenite. An alternative approach is based on the assumption that bainitic ferrite grows with a low carbon content and there is no major difference between Widmanstatten ferrite and bainitic ferrite. The two approaches are now compared using information from alloyed steels with considerable amounts of Si, where the formation of cementite is retarded. The former approach does not account for the effect of Mn and fails severely at low alloy contents. The latter approach seems more promising but is not without difficulties. In particular, in order to explain the effects of Cr and Mo, it seems necessary to introduce a kinetic effect, presumably caused by solute drag.

  • 25.
    Huyan, Fei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    Borgenstam, Annika
    A Thermodynamic-Based Model to Predict the Fraction of Martensite in Steels2016In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47A, no 9, p. 4404-4410Article in journal (Refereed)
    Abstract [en]

    A thermodynamic-based model to predict the fraction of martensite in steels with undercooling has been developed. The model utilizes the thermodynamic driving force to describe the transformation curve and it is able to predict the fraction of athermal martensite at quenching to different temperatures for low alloy steels. The only model parameter is a linear function of the martensite start temperature (M (s)), and the model predicts that a steel with a higher M (s) has a lower difference between the martensite start and finish temperatures. When the present model is combined with a previously developed thermodynamic-based model for M (s), the model predictions of the full martensite transformation curve with undercooling are in close agreement with literature data.

  • 26.
    Huyan, Fei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yan, Jia-Yi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    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.
    Simulation of the Growth of Austenite from As-Quenched Martensite in Medium Mn Steels2018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 4, p. 1053-1060Article in journal (Refereed)
    Abstract [en]

    As part of an ongoing development of third-generation advanced high-strength steels with acceptable cost, austenite reversion treatment of medium Mn steels becomes attractive because it can give rise to a microstructure of fine mixture of ferrite and austenite, leading to both high strength and large elongation. The growth of austenite during intercritical annealing is crucial for the final properties, primarily because it determines the fraction, composition, and phase stability of austenite. In the present work, the growth of austenite from as-quenched lath martensite in medium Mn steels has been simulated using the DICTRA software package. Cementite is added into the simulations based on experimental observations. Two types of systems (cells) are used, representing, respectively, (1) austenite and cementite forming apart from each other, and (2) austenite forming on the cementite/martensite interface. An interfacial dissipation energy has also been added to take into account a finite interface mobility. The simulations using the first type of setup with an addition of interfacial dissipation energy are able to reproduce the observed austenite growth in medium Mn steels reasonably well.

  • 27.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Computer simulation of diffusion controlled transformations in multicomponent alloys1997Doctoral thesis, comprehensive summary (Other scientific)
  • 28.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Dissolution of complex carbides in austenitic stainless steels1997Report (Other academic)
  • 29.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Multicomponent diffusion simulation2011In: Fundamentals of Thermodynamic Modelling of Materials, EDP Sciences, 2011, Vol. 14, p. 04002-Conference paper (Refereed)
  • 30.
    Höglund, Lars
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Ågren, John
    KTH, Superseded Departments, Metallurgy.
    Analysis of the Kirkendall effect, marker migration and pore formation2001In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 49, no 8, p. 1311-1317Article in journal (Refereed)
    Abstract [en]

    Some aspects of Kirkendall and lattice plane migration are studied by means of numerical simulations. The simulations are performed using individual mobilities assessed in this work and thermodynamic data available in literature. The simulations show that the position and stability of the Kirkendall plane as well as a number of other interesting features can be predicted using numerical simulation software in combination with assessed thermodynamic and kinetic data.

  • 31.
    Höglund, Lars
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Simulation of Carbon Diffusion in Steel Driven by a Temperature Gradient2010In: Journal of Phase Equilibria and Diffusion, ISSN 1547-7037, Vol. 31, no 3, p. 212-215Article in journal (Refereed)
    Abstract [en]

    The basis of thermomigration in multicomponent alloys is summarized, and the general equations are given and implemented in the DICTRA software. Experimental information from Okafor et al. is analyzed with the new simulations and it is concluded that steady- state conditions was not established during their experiment. A heat of transport Q(C)* = -44000 J/mol, almost four times larger than the value given by Okafor et al., was found to give a satisfactory representation of the experimental information.

  • 32.
    Kolmskog, Peter
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thermodynamic Analysis of the Critical Condition for Acicular FerriteArticle in journal (Other academic)
  • 33.
    Larsson, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. Thermocalc Software, SE-11364 Stockholm, Sweden.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. Thermocalc Software, SE-11364 Stockholm, Sweden.
    A scheme for more efficient usage of CALPHAD data in simulations2015In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 50, p. 1-5Article in journal (Refereed)
    Abstract [en]

    A method is suggested that allows thermodynamic data to be dynamically stored and retrieved. The purpose of the method is to reduce computer simulation time when Calphad type databases are being used. Some test simulations are presented and these indicate that simulations can be made to run 5-40 times faster without any significant loss of accuracy.

  • 34.
    Larsson, Henrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Multiphase diffusion simulations in 1D using the DICTRA homogenization model2009In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 33, no 3, p. 495-501Article in journal (Refereed)
    Abstract [en]

    A model for multiphase simulations in 1D previously reported in [H. Larsson, A. Engstrom, Acta Mater. 54 (2006) 2431] has been further developed and incorporated in the DICTRA software. The model is based on the assumption of local equilibrium and locally averaged kinetic properties, which computationally transforms the problem into a single-phase diffusion process. The applicability of the model is discussed and example simulations are presented.

  • 35.
    Leach, Lindsay
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kolmskog, Peter
    Sandv Min & Rock Technol, Sandv Ind Area, 6480 RTDRB, S-81181 Sandviken, Sweden..
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hillert, Mats
    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.
    Critical Driving Forces for Formation of Bainite2018In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, no 10, p. 4509-4520Article in journal (Refereed)
    Abstract [en]

    An empirical equation for predicting bainite start temperatures of steels was recently derived by starting from binary Fe-C alloys and continuing with ternary Fe-C-M alloys. This result is now illustrated with a family of B-S lines in a T,C diagram for a series of constant Mn contents. The critical driving force for the formation of ferrite is calculated for diffusionless or diffusional processes, and these quantities are used as dependent variables with carbon content or temperature as independent variables. Negative critical driving forces are predicted for a diffusionless process in binary Fe-C alloys, showing that this process cannot apply to the formation of bainite. The critical driving force for a diffusional process increases strongly with decreasing temperature and increasing carbon content. Mn and Ni, contrary to Cr, Mo and Si, have remarkably small effects on this critical driving force. The results are discussed by imagining that the magnitude of the critical driving force is governed by the height of an energy barrier that must be surmounted during growth. It is modeled as completely determined by the alloy composition. It is represented with an equation evaluated by fitting to the recent empirical equation and describing the carbon dependence of the barrier.

  • 36.
    Leach, Lindsay
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kolmskog, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hillert, Mats
    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.
    Use of Fe-C Information as Reference for Alloying Effects on B-S2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 10, p. 4531-4540Article in journal (Refereed)
    Abstract [en]

    Many empirical equations of the variation of the critical temperature with alloy content of the start of bainite formation in steels are available. They are often obtained by regression analysis of measured values for a large number of alloyed steels, usually with several alloying elements. However, such equations differ considerably, especially when applied to pure Fe-C alloys, which results in large differences between reported effects of individual alloying elements since they have not been based on the Fe-C system as a reference. Apparently, for the first time, an empirical equation is now derived by starting with information from Fe-C alloys and low alloy steels and then adding the effect of each alloying element separately, using information from ternary Fe-C-M alloys. Sets of information from the same alloy content but different carbon contents proved particularly useful. Lines connecting such points are regarded as B-S lines for the respective alloy content and the effect of alloying elements was evaluated from their distance from the B-S line for Fe-C alloys. Only under this condition can coefficients for alloying elements be expected to represent the physical effect of the elements. The resulting equation was tested with about 600 experimental B-S temperatures.

  • 37.
    Leach, Lindsay
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    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.
    Diffusion-Controlled Lengthening Rates of Bainitic Ferrite a Part of the Steel Genome2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 6, p. 2613-2618Article in journal (Refereed)
    Abstract [en]

    As a step in the further development of models and databases to support design of new steels, i.e., the steel genome, the growth of bainitic ferrite plates is accounted for by a thermodynamic and kinetic approach. The thermodynamic aspects are represented by CALPHAD databases and a Gibbs energy barrier for growth B-m. Experimental information on ferrite-plate growth rates for a number of Fe-C alloys, some of high-purity, are analyzed in terms of a modified Zener-Hillert model and the barrier as well as some kinetic parameters are evaluated. It is found that the barrier varies in a smooth way with carbon content and lengthening rate. In order to improve the agreement with the experimental information it was necessary to adjust the diffusion coefficient of carbon in austenite at low temperatures. It is concluded that the representation of the experimental data is satisfactory.

  • 38.
    Leach, Lindsay
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    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.
    Representing lengthening rate of bainitic ferrite - a part of the steel genomeManuscript (preprint) (Other academic)
    Abstract [en]

    As a step in the further development of models and databases to support design of new steels, i.e. the steel genome, the growth of bainitic ferrite plates is accounted for by a thermodynamic and kinetic approach. The thermodynamic aspects are represented by CALPHAD databases and a Gibbs energy barrier for growth Bm. Experimental information on ferrite-plate growth rates for a number of Fe-C alloys, some of high-purity, are analyzed in terms of a modified Zener-Hillert model and the barrier as well as some kinetic parameters are evaluated. It is found that the barrier varies in a smooth way with carbon content and lengthening rate. In order to improve the agreement with the experimental information it was necessary to adjust the diffusion coefficient of carbon in austenite at low temperatures. It is concluded that the representation of the experimental data is satisfactory.

  • 39. LIU, ZI-KUI
    et al.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Jonsson, Björn
    Ågren, John
    AN EXPERIMENTAL AND THEORETICAL-STUDY OF CEMENTITE DISSOLUTION IN AN FE-CR-C ALLOY1991In: MET TRANS A-PHYS MET MATER SC, ISSN 0360-2133, Vol. 22, no 8, p. 1745-1752Article in journal (Refereed)
    Abstract [en]

    The dissolution of cementite at 910-degrees-C in an Fe-2.06Cr-3.91C (at. pct) alloy is investigated experimentally. The Cr concentration profiles in austenite and cementite are measured by means of the scanning transmission electron microscopy/energy dispersive spectrometry (STEM/EDS) technique at different dissolution times. The measurements show the Cr enrichment in the cementite during the dissolution process. The measurements suggest that the main part of the reaction for this alloy is controlled by Cr diffusion in the cementite or in the austenite matrix. This observation is in agreement with predictions of the local equilibrium hypothesis. The carbide fraction and average particle diameter are evaluated as functions of dissolution time. The Cr enrichment of the cementite results in a supersaturation and a possible decomposition of the cementite. Microstructural evidence for such a decomposition is found by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A new program package called DICTRA,[11] which is suitable for the simulation of diffusional reactions in multicomponent alloys, has been applied to the present case. The simulation is compared with the experimental data, and a good agreement between the two is found.

  • 40.
    Malik, Amer
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Outokumpu Stainless Research Foundation.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Phase-Field Modeling of Sigma-Phase Precipitation in 25Cr7Ni4Mo Duplex Stainless Steel2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 10, p. 4914-4928Article in journal (Refereed)
    Abstract [en]

    Phase-field modeling is used to simulate the formation of sigma phase in a model alloy mimicking a commercial super duplex stainless steel (SDSS) alloy, in order to study precipitation and growth of sigma phase under linear continuous cooling. The so-called Warren-Boettinger-McFadden (WBM) model is used to build the basis of the multiphase and multicomponent phase-field model. The thermodynamic inconsistency at the multiple junctions associated with the multiphase formulation of the WBM model is resolved by means of a numerical Cut-off algorithm. To make realistic simulations, all the kinetic and the thermodynamic quantities are derived from the CALPHAD databases at each numerical time step, using Thermo-Calc and TQ-Interface. The credibility of the phase-field model is verified by comparing the results from the phase-field simulations with the corresponding DICTRA simulations and also with the empirical data. 2D phase-field simulations are performed for three different cooling rates in two different initial microstructures. A simple model for the nucleation of sigma phase is also implemented in the first case. Simulation results show that the precipitation of sigma phase is characterized by the accumulation of Cr and Mo at the austenite-ferrite and the ferrite-ferrite boundaries. Moreover, it is observed that a slow cooling rate promotes the growth of sigma phase, while a higher cooling rate restricts it, eventually preserving the duplex structure in the SDSS alloy. Results from the phase-field simulations are also compared quantitatively with the experiments, performed on a commercial 2507 SDSS alloy. It is found that overall, the predicted morphological features of the transformation and the composition profiles show good conformity with the empirical data.

  • 41. Ratke, L.
    et al.
    Brueck, S.
    Mathiesen, R.
    Ludwig, A.
    Gruber-Pretzler, M.
    Tonn, B.
    Gzovskyy, K.
    Granasy, L.
    Tegze, G.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Arnberg, L.
    Gust, E.
    Anger, G.
    Lauer, M.
    Garen, R.
    Reifenhaeuser, B.
    Lead-free bearing alloys for engine applications results of the ESA-MAP project MONOPHAS2007In: Transactions of the Indian Institute of Metals, ISSN 0019-493X, Vol. 60, no 2-3, p. 103-111Article in journal (Refereed)
    Abstract [en]

    Recent developments to reduce fuel consumption, emission and air pollution, size and weight of engines for automotive, truck, ship propulsion and electrical power generation lead to temperature and load conditions within engines that cannot be provided by conventional bearings. Therefore a European project has been established to develop a technically usable aluminium based lead free bearing material with sufficient hardness, wear and friction properties and good corrosion resistance to be produced with semi-continuous casting process. The paper describes the scientific challenges, approaches to tackle the solidification and casting problems and presents some illustrative research results.

  • 42. Shi, P
    et al.
    Engström, A
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermo-Calc and DICTRA enhance materials design and processing2005In: PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5 / [ed] hong, ZY; Saka, H; Kim, TH; Holm, EA; Han, YF; Xie, XS, ZURICH-UETIKON: TRANS TECH PUBLICATIONS LTD , 2005, Vol. 475-479, p. 3339-3346Conference paper (Refereed)
    Abstract [en]

    The Thermo-Calc and DICTRA software/database/interface packages are aimed at providing materials scientists and engineers with comprehensive assisting tools in their daily work of materials design and processing. During their long-history development, a wide range of comprehensive thermodynamic and kinetic models, powerful computation techniques, internally consistent databases and flexible application programming interfaces have been implemented. There are many successful applications that have significantly enhanced materials design and processing.

  • 43. Shi, Ping-Fang
    et al.
    Engström, Anders
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Qing, Chen
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Computational thermodynamics and kinetics in materials modelling and simulations2007In: Journal of Iron and Steel Research International, ISSN 1006-706X, E-ISSN 2210-3988, Vol. 14, p. 210-215Article in journal (Refereed)
  • 44. Tong, M.
    et al.
    Liu, J.
    Xie, Yu.
    Dong, H. B.
    Davidchack, R. L.
    Dantzig, J.
    Ceresoli, D.
    Marzari, N.
    Cocks, A.
    Zhao, C.
    Richardson, I.
    Kidess, A.
    Kleijn, C.
    Hoglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Wen, S. W.
    Barnett, R.
    Browne, D. J.
    An integrated framework for multi-scale multi-physics numerical modelling of interface evolution in welding2012In: IOP Conf. Ser. Mater. Sci. Eng., 2012, no 1Conference paper (Refereed)
    Abstract [en]

    The project Modelling of Interface evolution in advanced Welding (MIntWeld) is a 4-year international research project funded by the European Commission under their FP7 programme. Its main target is to develop a numerical toolbox which can be used to predict the evolution of interfaces during welding. There are various interfaces involving multiple phenomena and different spatial scales, which can be simulated using corresponding numerical modelling methods respectively. The modelling methods include quantum dynamics, molecular dynamics, phase field, phase field crystal, computational fluid dynamics, phase transformation and heat transfer, thermodynamics, continuum mechanics and life and defects prediction. Although each modelling method is based on different physical theories and involves different scales, they are not isolated. Therefore, this project aims to design a common framework which couples each model with the upstream and/or downstream model at the relevant neighbouring length scales. The data exchange framework which underpins the coupling of the models is described, and typical examples addressing the solution to the challenges faced, such as those of data interpolation between one discretisation of the computational domain and another, are discussed. Initial successes from the model-linking efforts of the authors are also presented.

  • 45.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, M.
    Barkar, Thomas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Initial clustering - A key factor for phase separation kinetics in Fe-Cr-based alloys2014In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 75, p. 62-65Article in journal (Refereed)
    Abstract [en]

    Clustering of alloying elements in solution-treated Fe-Cr-based alloys is of considerable importance for their microstructure stability upon aging. The clustering of Cr after solution treatment in three stainless steel alloy categories has been studied by atom probe tomography. Furthermore, phase-field simulations are applied to examine the effect of initial clustering on phase separation evolution. It is concluded that the clustering of Cr found in solution-treated ferritic and duplex alloys plays a critical role in the nanostructure evolution during aging.

  • 46. Zhu, Z.
    et al.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Larsson, H.
    Reed, R. C.
    Isolation of optimal compositions of single crystal superalloys by mapping of a material's genome2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 90, p. 330-343Article in journal (Refereed)
    Abstract [en]

    The multicomponent composition space pertinent to the single crystal nickel-based superalloys is mapped and searched, using computational modelling. A resolution of 0.1 wt.% for the alloying elements is assumed, consistent with manufacturing practice. Databases are constructed of alloy compositions which are predicted to be of promising microstructural architecture: e.g. equal fractions of the γ and γ′ phases. These may be regarded as maps - one might term them genomes - of this class of structural alloy. By combining the databases with additional composition-dependent property models, it is demonstrated that compositions can be identified which - subject to the accuracy and limitations of the sub-models - are likely to prove optimal, e.g. on the basis of their creep resistance, density and cost. The methods circumvent the need for the traditional empirically-driven approaches to alloy design.

  • 47.
    Ågren, John
    et al.
    KTH, Superseded Departments, Metallurgy.
    Hayes, F. H.
    Höglund, Lars
    KTH, Superseded Departments, Materials Science and Engineering.
    Kattner, U. R.
    Legendre, B.
    Schmid-Fetzer, R.
    Applications of computational thermodynamics2002In: Zeitschrift für Metallkunde, ISSN 0044-3093, Vol. 93, no 2, p. 128-142Article in journal (Refereed)
    Abstract [en]

    The major tools used in applying computational thermodynamics to various problems in materials science are briefly presented and several practical examples are given as illustrations. Solutions to industrial problems, pertaining to the processing of and microstructure development in several different materials, are shown with answers given in graphical form. Solutions to kinetic problems linked with diffusion are also treated. The last section is devoted to the problem of interfacing between thermodynamic computations and applications oriented software.

1 - 47 of 47
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