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Binary cases of the third generation of thermodynamic databases: Co-Cr, Co-C, Cr-C systems
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. (Unit of structure)
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Annan materialteknik
Identifikatorer
URN: urn:nbn:se:kth:diva-207770OAI: oai:DiVA.org:kth-207770DiVA, id: diva2:1098165
Anmärkning

QC 20170529

Tillgänglig från: 2017-05-23 Skapad: 2017-05-23 Senast uppdaterad: 2017-05-29Bibliografiskt granskad
Ingår i avhandling
1. First step to a genomic CALPHAD database for cemented carbides: C-Co-Cr alloys
Öppna denna publikation i ny flik eller fönster >>First step to a genomic CALPHAD database for cemented carbides: C-Co-Cr alloys
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
KTH Royal Institute of Technology, 2017. s. 47
Nyckelord
CALPHAD, Einstein model, two-state model, compound energy formalism, thermodynamic description, C-Co-Cr
Nationell ämneskategori
Materialteknik
Forskningsämne
Teknisk materialvetenskap
Identifikatorer
urn:nbn:se:kth:diva-207812 (URN)978-91-7729-447-4 (ISBN)
Disputation
2017-06-09, Sal B2, Brinellvägen 23, 10:00
Opponent
Handledare
Anmärkning

QC 20170529

Tillgänglig från: 2017-05-29 Skapad: 2017-05-24 Senast uppdaterad: 2017-05-30Bibliografiskt granskad

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Li, ZhouSelleby, Malin

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Li, ZhouSelleby, Malin
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Materialvetenskap
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Totalt: 47 träffar
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