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- Asp Grönhagen, Klara, 1973-
(author)
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Phase-field modeling of surface-energy driven processes
- 2009
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Asp Grönhagen, Klara, et al.
(author)
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Phase-field modelling of spinodal decomposition in TiAlN including the effect of metal vacancies
- 2015
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In: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 95, s. 42-45
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Journal article (peer-reviewed)abstract
- Using a CALPHAD approach together with a Cahn-Hilliard model, we describe the microstructure evolution in cubic Ti1-xAlxN including vacancies on the metal sublattice. Our results show that vacancy content has a pronounced effect on the decomposition kinetics. Furthermore, vacancies show a strong tendency to segregate to the coherent AlN-TiN interface regions. We illustrate how vacancies anneal to grain boundaries, and finally, we compare our prediction to experimental differential scanning calorimetry data and attribute the second peak in the thermogram to vacancy depletion.
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| 3. |
- Asp Grönhagen, Klara, et al.
(author)
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Phase-field simulation of sintering and related phenomena : A vacancy diffusion approach
- 2006
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In: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 54, s. 1241-1248
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Knutsson, Axel, et al.
(author)
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Surface directed spinodal decomposition at TiAlN / TiN interfaces
- 2013
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In: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:11, s. 114305-1-114305-8
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Journal article (peer-reviewed)abstract
- In contrast to the monolithic c-Ti1-xAlxN, the isostructural spinodal decomposition to c-AlN and c-TiN of the c-Ti1-xAlxN/TiN multilayers have the same onset temperature regardless of composition (x=0.50 and 0.66). The onset is also located at a lower temperature compared to the monoliths with the same Al-content, revealed by differential scanning calorimetry. Zcontrast STEM imaging shows a decomposed structure of the multilayers at a temperature where it is not present in the monoliths. Atom probe tomography reveal the formation of an AlN-rich layer followed by a TiN-rich area parallel to the interface in the decomposed Ti0.34Al0.66N/TiN coating, consistent with surface directed spinodal decomposition. Phase field simulations predict such behavior and show that the surface directed spinodal decomposition is affected by in the internal interfaces, as deposited elemental fluctuations, coherency stresses and alloy composition.
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| 5. |
- Xiong, Wei, 1983-, et al.
(author)
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Investigation of Spinodal Decomposition in Fe-Cr Alloys : CALPHAD Modeling and Phase Field Simulation
- 2011
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In: Solid State Phenomena. - Switzerland : Trans Tech Publications. - 1012-0394 .- 1662-9779. ; 172-174, s. 1060-1065
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Journal article (peer-reviewed)abstract
- 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.
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