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First step to a genomic CALPHAD database for cemented carbides: C-Co-Cr alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. (Unit of structure)
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

CALPHAD (CALculation of PHAse Diagrams) denotes the methodology used to assess thermodynamic data based on experiments as well as on first principles calculations. Essential for this method is the coupling of phase diagram and thermodynamic properties. It has been widely and successfully applied for decades in the field of materials science and engineering. Nevertheless, some shortcomings of the existing thermodynamic databases call for updated descriptions with improved thermodynamic modeling from unary, binary to ternary and higher-order systems. This thesis attempts to pioneer the development of a new generation of CALPHAD databases taking C-Co-Cr alloys with subsystems, unaries and binaries, as example. The present modeling and assessment work not only validate the new models applied in the development of the next, the 3rd, generation database, but also result in improved descriptions in a wider temperature range.In this 3rd generation database, thermodynamic descriptions are valid from 0 K up to high temperatures above liquidus. The Einstein model, rather than the polynomial basis functions used in the previous 2nd generation database, is applied to model the harmonic lattice vibration contribution to the heat capacity of condensed phases at low temperatures. In addition, terms describing the electronic excitations and anharmonic lattice vibrations, as well as the magnetic contribution, are added. A generalized two-state model is employed for the liquid phase to describe the gradual transition from the liquid to amorphous state. A revised magnetic model is adopted accounting for both the ferromagnetic and anti-ferromagnetic states explicitly. A newly suggested method to avoid violating the 3rd law of thermodynamics is adopted for e.g. stoichiometric phases. However, there is still some concern as Nernst’s heat theorem which states that 𝑑𝐶𝑃/𝑑𝑇 is zero at 0 K is not obeyed. All solution phases are modelled within the framework of the compound energy formalism (CEF).The task of the thesis is to construct an updated self-consistent thermodynamic description of the C-Co-Cr system for the third generation CALPHAD databases. The improvement is significant from a modeling point of view when compared to the second generation database. A good agreement between the calculated thermodynamic properties and the experimental data is achieved. The reliability of the extrapolations of unary and binary systems into higher order systems is demonstrated.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 47
Keywords [en]
CALPHAD, Einstein model, two-state model, compound energy formalism, thermodynamic description, C-Co-Cr
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-207812ISBN: 978-91-7729-447-4 (print)OAI: oai:DiVA.org:kth-207812DiVA, id: diva2:1098618
Public defence
2017-06-09, Sal B2, Brinellvägen 23, 10:00
Opponent
Supervisors
Note

QC 20170529

Available from: 2017-05-29 Created: 2017-05-24 Last updated: 2017-05-30Bibliographically approved
List of papers
1. Thermodynamic re-assessment of the Co-Cr system supported by first-principles calculations
Open this publication in new window or tab >>Thermodynamic re-assessment of the Co-Cr system supported by first-principles calculations
2016 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 52, p. 1-7Article in journal (Refereed) Published
Abstract [en]

The phase equilibria and thermochemical properties of the Co-Cr system was re-assessed using the Calphad method with the aid of ab initio calculations. Four solution phases, liquid, bcc, fcc and hcp phases are modeled using the substitutional solution model. The sigma phase, as an intermetallic compound with certain homogeneous composition range, is modeled by a full five sublattices partitioned CEF model. The formation enthalpies of all end-members are obtained from ab initio calculations. The calculated results fit the experimental data reasonably well which indicates that this ab initio aided model is a proper description for the sigma phase.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Ab initio, Calphad, Co-Cr, Compound energy formalism (CEF), Partitioned CEF, Sigma phase, Thermodynamic modeling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-180914 (URN)10.1016/j.calphad.2015.10.013 (DOI)000371558300001 ()2-s2.0-84946831910 (Scopus ID)
Funder
VINNOVA, 2012-02892
Note

QC 20160128

Available from: 2016-01-28 Created: 2016-01-25 Last updated: 2017-11-30Bibliographically approved
2. Thermodynamic evaluation of pure Co for the third generation of thermodynamic databases
Open this publication in new window or tab >>Thermodynamic evaluation of pure Co for the third generation of thermodynamic databases
Show others...
2016 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951Article in journal (Refereed) Published
Abstract [en]

An updated thermodynamic description of pure Co was obtained by applying new models for the third generation of Calphad databases. In these models, different contributions to the heat capacity, especially the vibrational part, were treated separately, each with a clear physical meaning. More importantly, the phase stabilities of the various allotropes are now physically well defined. Thus, the derived thermodynamic properties vary more reasonably and smoothly from 0K and up. Calculated thermodynamic properties were compared with experimental data and good agreement was obtained. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
CALPHAD method, Cobalt, Thermodynamic database, Thermodynamic modeling
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-195142 (URN)10.1002/pssb.201600231 (DOI)000394614300003 ()2-s2.0-84990062915 (Scopus ID)
Note

Correspondence Address: Li, Z.email: zhoul@kth.se. QC 20161108

Available from: 2016-11-08 Created: 2016-11-02 Last updated: 2017-11-29Bibliographically approved
3. A new thermodynamic description of stable Cr-carbides for the third generation of thermodynamic databases
Open this publication in new window or tab >>A new thermodynamic description of stable Cr-carbides for the third generation of thermodynamic databases
(English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669Article in journal (Other academic) Submitted
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-207769 (URN)
Note

QC 20170529

Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-29Bibliographically approved
4. Binary cases of the third generation of thermodynamic databases: Co-Cr, Co-C, Cr-C systems
Open this publication in new window or tab >>Binary cases of the third generation of thermodynamic databases: Co-Cr, Co-C, Cr-C systems
(English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-207770 (URN)
Note

QC 20170529

Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-29Bibliographically approved
5. Thermodynamic evaluation of the Co-Cr-C system within the framework of the third generation of thermodynamic databases
Open this publication in new window or tab >>Thermodynamic evaluation of the Co-Cr-C system within the framework of the third generation of thermodynamic databases
(English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-207771 (URN)
Note

QC 20170529

Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-29Bibliographically approved

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