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Three-dimensional phase-field modeling of martensitic microstructure evolution in steels
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-4521-6089
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.ORCID iD: 0000-0003-3336-1462
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2012 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 4, 1538-1547 p.Article in journal (Refereed) Published
Abstract [en]

In the present work a 3-D elastoplastic phase-field (PF) model is developed, based on the PF microelasticity theory proposed by A.G.Khachaturyan and by including plastic deformation as well as anisotropic elastic properties, for modeling the martensitic transformation (MT) by using the finite-element method. PF simulations in 3D are performed by considering different cases of MT occurring in an elastic material, with and without dilatation, and in an elastic perfectly plastic material with dilatation having isotropic as well as anisotropic elastic properties. As input data for the simulations the thermodynamic parameters corresponding to anFe–0.3%C alloy as well as the physical parameters corresponding to steels acquired from experimental results are considered. The simulation results clearly show auto-catalysis and morphological mirror image formation, which are some of the typical characteristics of a martensitic microstructure. The results indicate that elastic strain energy, anisotropic elastic properties, plasticity and the external clamping conditions affect MT as well as the microstructure.

Place, publisher, year, edition, pages
Elsevier, 2012. Vol. 60, no 4, 1538-1547 p.
Keyword [en]
Phase-field models, Martensitic phase transformation, Microstructure, Steels
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-62804DOI: 10.1016/j.actamat.2011.11.039ISI: 000301989500010Scopus ID: 2-s2.0-84856194252OAI: oai:DiVA.org:kth-62804DiVA: diva2:481181
Funder
Swedish e‐Science Research Center
Note

QC 20120424

Available from: 2012-01-20 Created: 2012-01-20 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Martensitic Transformations in Steels: A 3D Phase-field Study
Open this publication in new window or tab >>Martensitic Transformations in Steels: A 3D Phase-field Study
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Martensite is considered to be the backbone of the high strength of many commercial steels. Martensite is formed by a rapid diffusionless phase transformation, which has been the subject of extensive research studies for more than a century. Despite such extensive studies, martensitic transformation is still considered to be intriguing due to its complex nature. Phase-field method, a computational technique used to simulate phase transformations, could be an aid in understanding the transformation. Moreover, due to the growing interest in the field of “Integrated computational materials engineering (ICME)”, the possibilities to couple the phase-field method with other computational techniques need to be explored. In the present work a three dimensional elastoplastic phase-field model, based on the works of Khachaturyan et al. and Yamanaka et al., is developed to study the athermal and the stress-assisted martensitic transformations occurring in single crystal and polycrystalline steels. The material parameters corresponding to the carbon steels and stainless steels are considered as input data for the simulations. The input data for the simulations is acquired from computational as well as from experimental works. Thus an attempt is made to create a multi-length scale model by coupling the ab-initio method, phase-field method, CALPHAD method, as well as experimental works. The model is used to simulate the microstructure evolution as well as to study various physical concepts associated with the martensitic transformation. The simulation results depict several experimentally observed aspects associated with the martensitic transformation, such as twinned microstructure and autocatalysis. The results indicate that plastic deformation and autocatalysis play a significant role in the martensitic microstructure evolution. The results indicate that the phase-field simulations can be used as tools to study some of the physical concepts associated with martensitic transformation, e.g. embryo potency, driving forces, plastic deformation as well as some aspects of crystallography. The results obtained are in agreement with the experimental results. The effect of stress-states on the stress-assisted martensitic microstructure evolution is studied by performing different simulations under different loading conditions. The results indicate that the microstructure is significantly affected by the loading conditions. The simulations are also used to study several important aspects, such as TRIP effect and Magee effect. The model is also used to predict some of the practically important parameters such as Ms temperature as well as the volume fraction of martensite formed. The results also indicate that it is feasible to build physically based multi-length scale model to study the martensitic transformation. Finally, it is concluded that the phase-field method can be used as a qualitative aid in understanding the complex, yet intriguing, martensitic transformations.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 56 p.
Keyword
Phase-field method, Martensitic transformations, Plastic de formation, Multi-length scale modeling, Microstructure, Stress states, Steels
National Category
Materials Engineering Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-95316 (URN)978-91-7501-388-6 (ISBN)
Public defence
2012-06-15, B2, Materialvetenskap, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Hero-m
Note
QC 20120525Available from: 2012-05-25 Created: 2012-05-22 Last updated: 2012-08-07Bibliographically approved
2. Phase change with stress effects and flow
Open this publication in new window or tab >>Phase change with stress effects and flow
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis two kinds of phase change i.e., solid state phase transformation in steels and solid-to-liquid phase transformation in paraffin, have been modeled and numerically simulated. The solid state phase transformation is modeled using the phase field theory while the solid-to-liquid phase transformation is modeled using the Stokes equation and exploiting the viscous nature of the paraffin, by treating it as a liquid in both states.The theoretical base of the solid state, diffusionless phase transformation or the martensitic transformation comes from the Khachaturyan's phase field microelasticity theory. The time evolution of the variable describing the phase transformation is computed using the time dependent Ginzburg-Landau equation. Plasticity is also incorporated into the model by solving another time dependent equation. Simulations are performed both in 2D and 3D, for a single crystal and a polycrystal. Although the model is valid for most iron-carbon alloys, in this research an Fe-0.3\%C alloy is chosen.In order to simulate martensitic transformation in a polycrystal, it is necessary to include the effect of the grain boundary to correctly capture the morphology of the microstructure. One of the important achievements of this research is the incorporation of the grain boundary effect in the Khachaturyan's phase field model. The developed model is also employed to analyze the effect of external stresses on the martensitic transformation, both in 2D and 3D. Results obtained from the numerical simulations show good qualitative agreement with the empirical observations found in the literature.The microactuators are generally used as a micropump or microvalve in various miniaturized industrial and engineering applications. The phase transformation in a paraffin based thermohydraulic membrane microactuator is modeled by treating paraffin as a highly viscous liquid, instead of a solid, below its melting point.  The fluid-solid interaction between paraffin and the enclosing membrane is governed by the ALE technique. The thing which sets apart the presented model from the previous models, is the use of geometry independent and realistic thermal and mechanical properties. Numerical results obtained by treating paraffin as a liquid in both states show better conformity with the experiments, performed on a similar microactuator. The developed model is further employed to analyze the time response of the system, for different input powers and geometries of the microactuator.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 58 p.
Series
Trita-MEK, ISSN 0348-467X ; 2013:04
Keyword
Martensitic transformation, phase-field method, polycrystal, stress-effects, microactuator, finite-element simulations.
National Category
Materials Engineering Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-118451 (URN)978-91-7501-655-9 (ISBN)
Public defence
2013-03-13, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130219

Available from: 2013-02-19 Created: 2013-02-18 Last updated: 2013-02-19Bibliographically approved

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