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Thermodynamic analysis of the W-Co-Cr system supported by ab initio calculations and verified with quaternary data
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics. Sandvik Coromant R&D, Stockholm, Sweden.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-5031-919X
2015 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 50, 59-67 p.Article in journal (Refereed) Published
Abstract [en]

The present work aims at assessing the W-Co-Cr system with focus on including the ternary R-phase in the thermodynamic description. Enthalpies of formation at 0 K of all considered R-phase end-members are calculated using density functional theory and used in the assessment due to the scarceness of the experimental information. The resulting assessment is verified by comparing with recent experimental data in the W-Co-Cr-C quaternary system.

Place, publisher, year, edition, pages
2015. Vol. 50, 59-67 p.
Keyword [en]
W-Co-Cr, W-Co-Cr-C, Phase diagrams, Thermodynamics, Ab initio, DFT
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-172665DOI: 10.1016/j.calphad.2015.04.012ISI: 000358467900006ScopusID: 2-s2.0-84929323392OAI: diva2:850365
Swedish Research Council

QC 20150901

Available from: 2015-09-01 Created: 2015-08-27 Last updated: 2015-10-29Bibliographically approved
In thesis
1. Equilibrium aspects of Cr-alloyed cemented carbides
Open this publication in new window or tab >>Equilibrium aspects of Cr-alloyed cemented carbides
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In view of the extensive use of Cr as a grain growth inhibitor in WC-Co cemented carbides this thesis comprises a combined experimental and ab initio study of a number of critical issues pertaining to phase equilibria of the subsystems to the W-Co-Cr-C system.

To be able to predict which of the stable Cr-carbides forms above the solubility limits of Cr and C in the fcc phase the respective solubility of Co in Cr23C6, Cr7C3 and Cr3C2 are investigated experimentally. Furthermore, the site occupancies of Co in Cr7C3 are investigated by neutron diffraction as a first step towards a more realistic model for this phase.

The energetics of the ternary intermetallic R-phase and the unstable Co3C2 end-member compound are investigated by density functional theory. For Co3C2, the quasi-harmonic vibrational Gibbs energy is also calculated.

By subsequent CALPHAD assessment an improved thermodynamic description is developed and its agreement with experiment is investigated. The resulting thermodynamic description allows for improved accuracy in predicting the formation of carbide phases as a function of C content and Co/Cr ratio as well as liquidus and solidus temperatures.

Remaining issues may be attributed to the thermodynamic description of the W-Cr-C system and the stability of the Cr-based carbides in the Cr-C system. In the case of the Cr-based carbides, severe experimental scatter prevents an accurate determination of the stability of either of them. As a first attempt to resolve the situation, a state of the art ab initio approach is applied to calculate the finite temperature thermodynamic properties of Cr3C2, benchmarked with reported heat capacity and relative thermal expansion measurements.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. vii, 57 p.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-175856 (URN)978-91-7595-712-8 (ISBN)
Public defence
2015-11-25, sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Swedish Research Council, 621-2011-3569

QC 20151029

Available from: 2015-10-29 Created: 2015-10-23 Last updated: 2015-10-29Bibliographically approved

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