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An improved thermodynamic modeling of the Fe-Cr system down to zero kelvin coupled with key experiments
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-5031-919X
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0003-3598-2465
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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.

Place, publisher, year, edition, pages
2011. Vol. 35, no 3, 355-366 p.
Keyword [en]
Phase separation, Stainless steels, Atom probe, Ab initio calculations, Heat capacity, Magnetic
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-41795DOI: 10.1016/j.calphad.2011.05.002ISI: 000294939900012ScopusID: 2-s2.0-80051747296OAI: diva2:445235
QC 20111003Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2012-06-12Bibliographically approved
In thesis
1. Thermodynamic and Kinetic Investigation of the Fe-Cr-Ni System Driven by Engineering Applications
Open this publication in new window or tab >>Thermodynamic and Kinetic Investigation of the Fe-Cr-Ni System Driven by Engineering Applications
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.
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
urn:nbn:se:kth:diva-96707 (URN)978-91-7501-394-7 (ISBN)
Public defence
2012-08-28, sal B2, Brinellvägen 23, MSE, KTH, Stockholm, 10:00 (English)
StandUpSwedish e‐Science Research Center

QC 20120612

Available from: 2012-06-12 Created: 2012-06-10 Last updated: 2013-04-18Bibliographically approved

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