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  • 1.
    Asp Grönhagen, Klara
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Phase-field modeling of surface-energy driven processes2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Surface energy plays a major role in many phenomena that are important in technological and industrial processes, for example in wetting, grain growth and sintering. In this thesis, such surface-energy driven processes are studied by means of the phase-field method. The phase-field method is often used to model mesoscale microstructural evolution in materials. It is a diffuse interface method, i.e., it considers the surface or phase boundary between two bulk phases to have a non-zero width with a gradual variation in physical properties such as energy density, composition and crystalline structure.

    Neck formation and coarsening are two important diffusion-controlled features in solid-state sintering and are studied using our multiphase phase-field method. Inclusion of Navier-Stokes equation with surface-tension forces and convective phase-field equations into the model, enables simulation of reactive wetting and liquid-phase sintering. Analysis of a spreading liquid on a surface is investigated and is shown to follow the dynamics of a known hydrodynamic theory. Analysis of important capillary phenomena with wetting and motion of two particles connected by a liquid bridge are studied in view of important parameters such as contact angles and volume ratios between the liquid and solid particles.

    The interaction between solute atoms and migrating grain boundaries affects the rate of recrystallization and grain growth. The phenomena is studied using a phase-field method with a concentration dependent double-well potential over the phase boundary. We will show that with a simple phase-field model it is possible to model the dynamics of grain-boundary segregation to a stationary boundary as well as solute drag on a moving boundary.

    Another important issue in phase-field modeling has been to develop an effective coupling of the phase-field and CALPHAD methods. Such coulping makes use of CALPHAD's thermodynamic information with Gibbs energy function in the phase-field method. With the appropriate thermodynamic and kinetic information from CALPHAD databases, the phase-field method can predict mictrostructural evolution in multicomponent multiphase alloys. A phase-field model coupled with a TQ-interface available from Thermo-Calc is developed to study spinodal decomposition in FeCr, FeCrNi and TiC-ZrC alloys.

  • 2.
    Asp Grönhagen, Klara
    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.
    Phase-field simulation of sintering and related phenomena: A vacancy diffusion approach2006In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 54, 1241-1248 p.Article in journal (Refereed)
    Abstract [en]

    A phase-field model of sintering and related phenomena in a two-phase system and in a multi-phase system is presented. We consider diffusion of vacancies as the atomic mechanism for redistribution of material and we will use the familiar model of thermal vacancies in a crystal as our energy formulation. The solid material will thus be characterized by a low vacancy content and the surroundings by a very high vacancy content and a very low content of atoms. The surface of the solid body will be characterized by a continuous variation in vacancy content. The temporal development of particles during solid state sintering with effects such as wetting is shown in various simulations.

  • 3.
    Asp, Klara
    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.
    Phase-field simulaton of sintering based on vacancy diffusion effect of anisotropy2005In: Solid-Solid Phase Transformations in Inorganic Material 2005, Vol 2 / [ed] Howe, JM; Laughlin, DE; Lee, JK; Dahmen, U; Soffa, WA, 2005, 741-746 p.Conference paper (Refereed)
    Abstract [en]

    Recently the present authors presented a Phase-field model of sintering in a multiphase system. In the present contribution the major features of the model are summarized. The model is based on diffusion of vacancies as the atomic mechanism for redistribution of material. The solid material is characterized by a low vacancy content and the surroundings by a very high vacancy content and a very low content of atoms. The surface of the solid body is characterized by a continuous variation in vacancy content. The temporal development of particles during solid state sintering with effects such as wetting has been shown previously and here we discuss the effect of a highly anisotropic interfacial energy on the morphological evolution of the particles.

  • 4.
    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)
  • 5.
    Grönhagen, Klara
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, Johan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Grain-boundary segregation and dynamic solute drag theory: A phase-field approach2007In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, 955-960 p.Article in journal (Refereed)
    Abstract [en]

    We propose a model based on a phase-field approach to study grain-boundary segregation and solute drag. We will show that it is possible to model the dynamics of grain-boundary segregation to a stationary boundary as well as solute drag on a moving boundary with the same phase-field model. We shall achieve this by introducing a concentration dependency in the height of the double-well potential in the Gibbs-energy expression. As the model then will be able to treat the build-up of a concentration spike in the boundary as well as its disappearance we shall term this treatment dynamic solute-drag theory.

  • 6.
    Grönhagen, Klara
    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.
    Spinodal decomposition in FeCr and FeCr-based alloys : A phase-field approach coupled with CALPHAD databaseManuscript (preprint) (Other academic)
  • 7.
    Villanueva, Walter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Grönhagen, Klara
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Multicomponent and multiphase modeling and simulation of reactive wetting2008In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 77, no 5, 056313- p.Article in journal (Refereed)
    Abstract [en]

    A multicomponent and multiphase model with fluid motion is developed. The model is used to study reactive wetting in the case where concentration change of the spreading liquid and the substrate occurs. With the introduction of a Gibbs energy functional, the governing equations are derived, consisting of convective concentration and phase-field equations which are coupled to the Navier-Stokes equations with surface tension forces. The solid substrate is modeled hydrodynamically with a very high viscosity. Arbitrary phase diagrams, surface energies, and typical dimensionless numbers are some input parameters into the model. An axisymmetric model with an adaptive finite element method is utilized. Numerical simulations were done revealing two stages in the wetting process. First, the convection-dominated stage where rapid spreading occurs. The dynamics of the wetting is found to match with a known hydrodynamic theory for spreading liquids. Second, the diffusion-dominated stage where we observed depression of the substrate-liquid interface and elevation of the contact line region.

  • 8.
    Villanueva, Walter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Grönhagen, Klara
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Multicomponent and multiphase simulation of liquid-phase sintering2009In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, no 2, 512-520 p.Article in journal (Refereed)
    Abstract [en]

    Numerical simulation of liquid-phase sintering using a multicomponent and multiphase model is presented. The model consists of convective concentration and phase-field equations coupled with the Navier-Stokes equations with surface tension forces. The governing equations are nondimensionalized and an adaptive finite element method is utilized. An idealized phase diagram, surface energies, and typical dimensionless parameters are some input into the model. Important dynamics in liquid-phase sintering such as rapid wetting and motion of particles due to capillary forces are studied. Some factors that are known to significantly affect the dynamics of the sintering process such as contact angles and volume ratios are also investigated. In addition, numerical results on the motion of particles due to capillary forces were compared with an existing analytical model. Good agreement between numerical and analytical results is obtained within the validity of the analytical model.

  • 9.
    Xiong, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Grönhagen, Klara Asp
    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.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Chen, Qing
    Thermo-Calc Software AB.
    Investigation of Spinodal Decomposition in Fe-Cr Alloys: CALPHAD Modeling and Phase Field Simulation2011In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 172-174, 1060-1065 p.Article in journal (Refereed)
    Abstract [en]

    This work is dedicated to simulate the spinodal decomposition of Fe-Cr bcc (body centered cubic) alloys using the phase field method coupled with CALPHAD modeling. Thermodynamic descriptions have been revised after a comprehensive review of information on the Fe-Cr system. The present work demonstrates that it is impossible to reconcile the ab initio enthalpy of mixing at the ground state with the experimental one at 1529 K using the state-of-the-art CALPHAD models.

    While the phase field simulation results show typical microstructure of spinodal decomposition, large differences have been found on kinetics among experimental results and simulations using different thermodynamic inputs. It was found that magnetism plays a key role on the description of Gibbs energy and mobility which are the inputs to phase field simulation. This work calls for an accurate determination of the atomic mobility data at low temperatures.

1 - 9 of 9
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