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Structural Determination of (Cr,Co)7C3
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
Sandvik Coromant R&D, Stockholm.
Sandvik Coromant R&D, Stockholm.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.ORCID iD: 0000-0001-5031-919X
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2013 (English)Conference paper (Refereed)
Abstract [en]

Chromium is one of the most well-known WC grain growth inhibitors in cemented carbides. It is thus vital to understand and to be able to thermodynamically model the prevailing phase equilibria in the WC-Co-Cr system. To do this it is important that the lower order systems, such as the Co-Cr-C system, are correctly described. Previous investigations have shown that the M7C3 (M=Cr,Co,W) phase is the first carbide to form when Cr is added in excess to the WC+fcc-Co/liquid+graphite phase field. However, the exact structure of this phase has not been investigated and there are many proposed structures already for the binary Cr7C3 carbide, ranging from trigonal, via hexagonal to orthorhombic symmetry. Recent investigations show that the hexagonal structure belonging to the P63mc space group is the stable structure at 0 K. In the present study the binary Cr7C3 carbide and a mixed M7C3 carbide are investigated. The structures of both carbides and preferential positions for Co atoms in the mixed carbide are determined by XRD measurements in combination with ab initio calculations and Rietveld refinement.

Place, publisher, year, edition, pages
2013. HM104/1-HM104/12 p.
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-126797OAI: diva2:642410
18th Plansee Seminar, 3 – 7 June, 2013 in Reutte, Austria

QC 20130902

Available from: 2013-08-21 Created: 2013-08-21 Last updated: 2015-12-08Bibliographically approved
In thesis
1. Experimental and theoretical study of carbides in the Co-Cr-C system: Structure, alloying and stability
Open this publication in new window or tab >>Experimental and theoretical study of carbides in the Co-Cr-C system: Structure, alloying and stability
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The research presented in this thesis explores the structure, alloying and stability of the carbides in the Co-Cr-C system by using the CALPHAD approach supported by experimental measurements and ab initio calculations.

WC-Co based cemented carbide materials consist of hard WC grains and a ductile Co-based binder. Cr is usually added to cemented carbides for the purpose of reducing grain growth during sintering or to increase corrosion resistance. The Co-Cr-C system is highly relevant for Cr-containing cemented carbides. For example, it determines the allowable C-content interval in the quaternary W-Co-Cr-C system with respect to the formation of unwanted Cr-based carbides.

The CALPHAD method is based on critical assessment of model parameters constituting phenomenological expressions of the Gibbs energy and its derivatives, e.g. enthalpy, entropy and heat capacity. A thermodynamic assessment based on the CALPHAD method relies heavily on the available experimental or ab initio calculated information.

The crystal structures of Cr23C6 and Cr3C2 have previously been accurately determined. However, various authors reported different crystal structures for the Cr7C3 carbide. A combined experimental and ab initio investigation of the crystal structure of Cr7C3 and M7C3 (M=Co,Cr) was thus performed. Furthermore, the stabilities of all end-member compounds of the mixed carbide at 0 K were

determined by ab initio calculations.

Available experimental information on phase equilibria with carbides in the Co-Cr-C system was found to be insufficient to describe all the features in the phase diagram. Therefore, the liquid + M23C6 + M7C3 and M7C3 + M3C2 + graphite equilibria (M=Co,Cr) were investigated experimentally with focus on the solubility of Co in the M23C6, M7C3 and M3C2 carbides.

Finally, a reassessment of the thermodynamic description of the Co-Cr-C system was performed, which resulted in a set of thermodynamic models and parameters that accurately describe all of the considered information.

Applied experimental methods and theoretical models are explained throughout the thesis. Important examples from the appended papers are also given.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. viii, 39 p.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
urn:nbn:se:kth:diva-141129 (URN)978-91-7595-008-2 (ISBN)
2014-03-07, Sal Kuben N111, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Swedish Research Council

QC 20140212

Available from: 2014-02-12 Created: 2014-02-07 Last updated: 2014-02-12Bibliographically approved

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