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Thermodynamic and Kinetic Investigation of the Fe-Cr-Ni System Driven by Engineering Applications
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work is a thermodynamic and kinetic study of the Fe-Cr-Ni system as the core of stainless steels. The Fe-Cr, Fe-Ni and Cr-Ni systems were studied intensively using both computational and experimental techniques, including CALPHAD (CALculation of PHAse Diagrams), phase field simulation, ab initio modeling, calorimetry, and atom probe tomography. The purpose of this thesis is to reveal the complexity of the phase transformations in the Fe-Cr-Ni system via the integrated techniques. Due to the importance of the binary Fe-Cr system, it was fully reassessed using the CALPHAD technique by incorporating an updated description of the lattice stability for Fe down to zero kelvin. The improved thermodynamic description was later adopted in a phase field simulation for studying the spinodal decomposition in a series of Fe-Cr binary alloys. Using atom probe tomography and phase field simulation, a new approach to analyze the composition amplitude of the spinodal decomposition was proposed by constructing an amplitude density spectrum. The magnetic phase diagram of the Fe-Ni system was reconstructed according to the results from both ab initio calculations and reported experiments. Based on the Inden-Hillert-Jarl magnetic model, the thermodynamic reassessment of the Fe-Ni system demonstrated the importance of magnetism in thermodynamic and kinetic investigations. Following this, the current magnetic model adopted in the CALPHAD community was further improved. Case studies were performed showing the advantages of the improved magnetic model. Additionally, the phase equilibria of the Fe-Cr-Ni ternary were discussed briefly showing the need of thermodynamic and kinetic studies at low temperatures. The “low temperature CALPHAD” concept was proposed and elucidated in this work showing the importance of low temperature thermodynamics and kinetics for designing the new generation of stainless steels.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , v, 63 p.
Keyword [en]
phase transformation, magnetism, spinodal decomposition, stainless steel, low temperature CALPHAD, phase field, ab initio, atom probe tomography, calorimetry
National Category
Metallurgy and Metallic Materials
Research subject
SRA - E-Science (SeRC); SRA - Energy
Identifiers
URN: urn:nbn:se:kth:diva-96707ISBN: 978-91-7501-394-7 (print)OAI: oai:DiVA.org:kth-96707DiVA: diva2:532627
Public defence
2012-08-28, sal B2, Brinellvägen 23, MSE, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Hero-m
Funder
StandUpSwedish e‐Science Research Center
Note

QC 20120612

Available from: 2012-06-12 Created: 2012-06-10 Last updated: 2013-04-18Bibliographically approved
List of papers
1. Phase Equilibria and Thermodynamic Properties in the Fe-Cr System
Open this publication in new window or tab >>Phase Equilibria and Thermodynamic Properties in the Fe-Cr System
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2010 (English)In: Critical reviews in solid state and materials sciences, ISSN 1040-8436, E-ISSN 1547-6561, Vol. 35, no 2, 125-152 p.Article, review/survey (Refereed) Published
Abstract [en]

Phase equilibria and thermodynamic properties in the Fe-Cr system have been reviewed comprehensively based on experimental information and available computer simulations in different scales. The evaluated phase equilibria show significant differences from the currently accepted thermodynamic description by CALPHAD (calculation of phase diagram) approach. The thermodynamic properties of the Fe-Cr system, such as heat capacity, enthalpy, and activity, have been evaluated in reported experiments. The experiments on phase separation in the Fe-Cr system have also been critically reviewed with a focus on spinodal decomposition. The reported data are concentrated in the temperature range from 673 to 823 K. In addition, there is a transition region between spinodal decomposition and nucleation regimes within the composition limit from 24 to 36.3 at.% Cr and the temperature range between 700 and 830 K. In view of the importance of magnetism in the Fe-Cr system, some inadequacies of the currently used thermodynamic description are pointed out in addition to some problems with the current magnetic model. Remaining issues on the thermodynamics of the Fe-Cr system have been elaborated for future refinement of the thermodynamic description of the Fe-Cr system. According to the present review, the melting temperature of Cr is recommended to be about 2136 K, which is 44 K lower than the value adopted in the research community on thermodynamics, such as the Scientific Group Thermodata Europe.

Keyword
phase diagram, CALPHAD, ab initio, irradiation, melting temperature, spinodal decomposition
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27514 (URN)10.1080/10408431003788472 (DOI)000278705100003 ()2-s2.0-77953569969 (Scopus ID)
Note
QC 20110112Available from: 2011-01-12 Created: 2010-12-13 Last updated: 2017-12-11Bibliographically approved
2. An improved thermodynamic modeling of the Fe-Cr system down to zero kelvin coupled with key experiments
Open this publication in new window or tab >>An improved thermodynamic modeling of the Fe-Cr system down to zero kelvin coupled with key experiments
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2011 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 35, no 3, 355-366 p.Article in journal (Refereed) Published
Abstract [en]

A thermodynamic modeling of the Fe-Cr system down to 0 K is performed on the basis of our recent comprehensive review of this binary system [W. Xiong, M. Selleby, Q. Chen, J. Odqvist, Y. Du, Evaluation of phase equilibria and thermochemical properties in the Fe-Cr system, Crit. Rev. Solid State Mater. Sci. 35 (2010) 125-152]. The model predicts a sign change for the magnetic ordering energy of mixing rather than the enthalpy of mixing in the bcc phase at 0 K. Designed key experiments are performed not only to check the validity of the present modeling but also to assist in understanding the mechanism for spinodal decomposition of the Fe-Cr alloy. Heat capacities and Curie temperatures of several Fe-rich alloys are determined between 320 and 1093 K by employing differential scanning calorimetry. The measured heat capacities are found to be in remarkable agreement with the prediction based on the present modeling. Microstructural patterns and frequency distribution diagrams of Cr are studied in alloys containing 26.65, 31.95, and 37.76 at.% Cr by using atom probe tomography. The observed phase separation results correspond well with our model-predicted boundary for the spinodal decomposition. Interestingly, a horn on the Cr-rich spinodal boundary is predicted below 200 K for the first time. This work demonstrates a way to bridge the ab initio calculations and CALPHAD approach. (C) 2011 Elsevier Ltd. All rights reserved.

Keyword
Phase separation, Stainless steels, Atom probe, Ab initio calculations, Heat capacity, Magnetic
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-41795 (URN)10.1016/j.calphad.2011.05.002 (DOI)000294939900012 ()2-s2.0-80051747296 (Scopus ID)
Note
QC 20111003Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2017-12-08Bibliographically approved
3. Magnetic phase diagram of the Fe-Ni system
Open this publication in new window or tab >>Magnetic phase diagram of the Fe-Ni system
2011 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 2, 521-530 p.Article in journal (Refereed) Published
Abstract [en]

Magnetic phase diagrams of body-centered cubic and face-centered cubic Fe-Ni alloys were constructed using available experimental data and ab initio calculations. The results show that significant improvements in the "standard" diagrams (handbooks and CALPHAD databases) are required. The present work demonstrates that the CALPHAD magnetic model is not sophisticated enough to describe the Fe-Ni system. In addition, a new thermodynamic description of the lattice stability for pure Ni is urgently needed, since the recommended magnetic properties for CALPHAD modeling are distinct from the experimental and ab initio results. This work indicates that the construction of magnetic phase diagrams is indispensable during the phase transformation study of magnetic systems. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2011
Keyword
Invar alloy, Magnetic properties, Thermodynamics, Steels, Martensitic phase transformation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-29381 (URN)10.1016/j.actamat.2010.09.055 (DOI)000285486300011 ()2-s2.0-78449258198 (Scopus ID)
Note

QC 20110201

Available from: 2011-02-01 Created: 2011-02-01 Last updated: 2017-12-11Bibliographically approved
4. An improved magnetic model for thermodynamic modeling
Open this publication in new window or tab >>An improved magnetic model for thermodynamic modeling
2012 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 39, 11-20 p.Article in journal (Refereed) Published
Abstract [en]

The standard magnetic model in the current CALPHAD modeling is based on the Inden-Hillert-Jarl model and an empirical constraint due to Weiss and Tauer that can be used to connect ferromagnetism and antiferromagnetism. In this work, we demonstrate that many artifacts can be produced by using the current approach when modeling systems with elements of different forms of magnetism. We then propose several simple measures to improve the standard magnetic model so that a physically and numerically correct and more accurate description for the Gibbs energy of magnetic ordering can be obtained in normal situations. Especially, we have assumed that each magnetic phase always possesses both ferromagnetic and antiferromagnetic states, with one of them stable and the other non-stable. The concept of 'effective magnetic moment' has also been introduced as a measure of the maximum magnetic entropy. A case study on the Al-Cr-Fe system has been performed at 0 K showing the importance of reasonable description of the magnetic phase diagrams. It has been stressed that the extended magnetic model in this work can be further employed for bridging atomistic and phenomenological modeling for multi-scale simulation.

Keyword
Magnetic ordering, Phase diagram, Ab initio, Fe-Ni, Fe-Rh, Al-Cr-Fe
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-96784 (URN)10.1016/j.calphad.2012.07.002 (DOI)000311926800002 ()2-s2.0-84865427906 (Scopus ID)
Funder
Vinnova
Note

QC 20130109. Updated from manuscript to article in journal.

Available from: 2012-06-12 Created: 2012-06-12 Last updated: 2017-12-07Bibliographically approved
5. Investigation of Spinodal Decomposition in Fe-Cr Alloys: CALPHAD Modeling and Phase Field Simulation
Open this publication in new window or tab >>Investigation of Spinodal Decomposition in Fe-Cr Alloys: CALPHAD Modeling and Phase Field Simulation
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2011 (English)In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 172-174, 1060-1065 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Switzerland: Trans Tech Publications, 2011
Keyword
magnetic transition, ab initio, enthalpy of mixing, atomic mobility, Cahn-Hilliard equation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-49606 (URN)10.4028/www.scientific.net/SSP.172-174.1060 (DOI)000303359700164 ()2-s2.0-79960921235 (Scopus ID)
Projects
Hero-m
Note

QC 20111208

Available from: 2011-12-08 Created: 2011-11-28 Last updated: 2017-12-08Bibliographically approved
6. An Effective Method to Estimate Composition Amplitude of Spinodal Decomposition for Atom Probe Tomography Validated by Phase Field Simulations
Open this publication in new window or tab >>An Effective Method to Estimate Composition Amplitude of Spinodal Decomposition for Atom Probe Tomography Validated by Phase Field Simulations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Reasonable evaluation of composition amplitude in spinodal decomposition is a challenge to microanalysis of atom probe tomography, especially at early stages when phase separation is not prominent. This impedes quantitative analysis of spinodal structure in atom probe tomography as well as comparison with simulated results from phase field simulations. We hereby report an effective method to estimate the composition amplitude by constructing an amplitude density spectrum. This method can sensitively determine the composition amplitude at early stages. In particular, it substantially bridges experimental and simulation techniques comprising both discrete and continuum data in the study of spinodal decomposition. Moreover, it was found that the commonly adopted Langer-Bar-on-Miller method for atom probe analysis underestimates the composition amplitude of spinodal decomposition. Case studies have been performed on the Fe-Cr binary alloys.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-96789 (URN)
Note
QS 2012Available from: 2012-06-12 Created: 2012-06-12 Last updated: 2012-06-12Bibliographically approved

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  • en-US
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