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Influence of nitrogen Gas pressure on the miscibility Gap in the Ti-Zr carbonitride system
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0003-4556-032X
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-7656-9733
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-4521-6089
2012 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 32, 11-15 p.Article in journal (Refereed) Published
Abstract [en]

The microstructure of cemented carbides with a gradient structure at the surface consists of WC, cubic carbonitrides and a binder phase. The carbonitrides can, for example, consist of Ti(C,N)-Zr(C,N) where it is reasonable to believe that there is a miscibility gap with Ti-rich and Zr-rich carbonitrides. In the present work, the effect of the N-2-gas pressure on the equilibrium composition of the miscibility gap in the (Ti,Zr)(C,N) system has been investigated. In the study, the carbonitride system is in equilibrium with: WC, liquid binder, graphite and, N-2-gas of different pressures. Both Fe and Co are used as binder phase to study the effect of the binder phase. The results verify that there is a miscibility gap in the carbonitride system and that the region of the miscibility gap will change when N is introduced. There is a critical N-2-gas pressure lower than 0.1 bar and above that pressure the compositions of the carbonitride are rather constant as a result of the formation of a surface rim.

Place, publisher, year, edition, pages
2012. Vol. 32, 11-15 p.
Keyword [en]
Cemented carbides, TiC, ZrC, Miscibility gap
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-95088DOI: 10.1016/j.ijrmhm.2011.12.014ISI: 000302841400003Scopus ID: 2-s2.0-84858336869OAI: oai:DiVA.org:kth-95088DiVA: diva2:527701
Note
QC 20120522Available from: 2012-05-22 Created: 2012-05-14 Last updated: 2013-11-18Bibliographically approved
In thesis
1. Aspects of Structural Evolution in Cemented Carbide – Carbide Size, Shape and Stability
Open this publication in new window or tab >>Aspects of Structural Evolution in Cemented Carbide – Carbide Size, Shape and Stability
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cemented carbide is a composite material used in applications like cutting tools and rock drilling inserts. The material commonly consists of WC grains embedded in a Co-rich binder phase and the material properties strongly depend on the WC grain size. Hence, to tailor the properties it is important to understand the fundamental mechanisms of grain coarsening. At the same time, the higher demands on material properties today also require new solutions. In the present work, some different aspects of structural evolutions in cemented carbides have been investigated.

The first part of the work considers WC grain coarsening by means of size, size distribution and shape. Some efforts of the work have been to evaluate the effects of C-activity and initial WC powder size and distribution on the coarsening behavior in the material using different characterization techniques, e.g. scanning electron microscopy, and electron backscattered diffraction. Additionally, two earlier developed models are used and evaluated with the experimental data. The results indicate that the C-activity will affect size, size distribution and shape of the WC grains. It was also observed that the initial WC powder size and size distribution will have a large influence on the WC grain coarsening. The statistical shape was found to fit a spherical approximation but for individual grains both faceted and non-faceted shapes was observed. Steps and planar defects were observed supporting that the nucleation of new atomic layers is the main rate limiting mechanism for grain coarsening.

The second part of this work considers the carbide phase stability in the (Ti,Zr)C system. The phase stability was investigated after synthesizing and aging a mixed (Ti,Zr)C using X-ray diffraction and different types of electron microscopy techniques. A decomposed lamellar structure was found with a composition variation of approximately 10% between the 50-75 nm thick lamellas. The experimental investigations were supported by computational work and the results were in good agreement. Additionally, two cemented carbide related systems were studied. A miscibility gap was found in the two investigated systems, (Ti,Zr,W)(C,N)-Co or Fe-graphite, and the effect of N2-gas pressure was investigated suggesting a critical N2-gas pressure below 0.1 bar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xii, 72 p.
Keyword
Cemented carbide, (Ti, Zr)C, Coarsening, Phase separation, C-activity, initial WC powder size, electron backscattered diffraction, microscopy, X-ray diffraction
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-133933 (URN)978-91-7501-944-4 (ISBN)
Public defence
2013-12-13, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
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Note

QC 20131118

Available from: 2013-11-18 Created: 2013-11-13 Last updated: 2013-11-18Bibliographically approved

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Borgh, IdaBorgenstam, Annika

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