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Microstructure, grain size distribution and grain shape in WC-Co alloys sintered at different carbon activities
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.
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2014 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0958-0611, Vol. 43, 205-211 p.Article in journal (Refereed) Published
Abstract [en]

The properties of cemented carbides strongly depend on the WC grain size and it is thus crucial to control coarsening of WC during processing. The aim of this work was to study the effect of sintering at different carbon activities on the final microstructure, as well as the coarsening behavior of the WC grains, including the size distribution and the shape of WC grains. These aspects were investigated for five WC-Co alloys sintered at 1410 C for 1 h at different carbon activities in the liquid, in the range from the graphite equilibrium (carbon activity of 1) to the eta (M6C) phase equilibrium (carbon activity of 0.33). The grain size distribution was experimentally evaluated for the different alloys using EBSD (electron backscatter diffraction). In addition, the shape of the WC grains was evaluated for the different alloys. It was found that the average WC grain size increased and the grain size distribution became slightly wider with increasing carbon activity. Comparing the two three-phase (WC-Co-eta and WC-Co-graphite) alloys a shape change of the WC grains was observed with larger grains having more planar surfaces and more triangular shape for the WC-Co-graphite alloy. It was indicated that in alloys with a relatively low volume fraction of the binder phase the WC grain shape is significantly affected by impingements. Moreover, after 1 h of sintering the WC grains are at a non-equilibrium state with regards to grain morphology.

Place, publisher, year, edition, pages
2014. Vol. 43, 205-211 p.
Keyword [en]
Carbon activity, Cemented carbide, Coarsening, Electron backscatter diffraction (EBSD), WC shape
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-133936DOI: 10.1016/j.ijrmhm.2013.12.007ISI: 000333789700032ScopusID: 2-s2.0-84891399234OAI: diva2:663964

QC 20140203. Updated from submitted to published.

Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2014-05-05Bibliographically 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.
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
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)

QC 20131118

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

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