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Analysis of WC grain growth during sintering using electron backscatter diffraction and image analysis
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
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2008 (English)In: International Journal of Refratory metals and Hard Materials, ISSN 0263-4368, Vol. 26, no 5, 449-455 p.Article in journal (Refereed) Published
Abstract [en]

The WC carbide grain size is important for the technological properties of cemented carbide cutting tools. in the present work the WC carbide grain size distribution is determined after milling and sintering for 0.25, 1 and 8 h at 1430 degrees C. The WC grain size distribution, both for the powder after milling and the sintered specimens, is determined by two different methods, i.e. image analysis on scanning electron microscopy (SEM) images and electron backscatter diffraction (EBSD). It should be noted that in this work the 2D grain size distribution is considered. The EBSD analysis clearly shows that the special 12 boundaries are present in the powder and that their fraction decreases during sintering and particularly during the early stages. When the 12 boundaries are omitted in the EBSD analysis the results of the grain size measurements for the two methods agree quite well.

Place, publisher, year, edition, pages
2008. Vol. 26, no 5, 449-455 p.
Keyword [en]
carbides, grain size, image analysis, Sigma 2 boundaries, cemented carbides, co alloys, boundaries
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-17683DOI: 10.1016/j.ijrmhm.2007.10.004ISI: 000257611900010Scopus ID: 2-s2.0-44649122750OAI: oai:DiVA.org:kth-17683DiVA: diva2:335728
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-04-26Bibliographically approved
In thesis
1. WC grain growth during sintering of cemented carbides: Experiments and simulations
Open this publication in new window or tab >>WC grain growth during sintering of cemented carbides: Experiments and simulations
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cemented carbides are composite materials consisting of a hard carbide and a ductile binder. They are powdermetallurgically manufactured, where liquid-phase sintering is one of the main steps. The most common cemented carbide consists of WC and Co and it is widely used for cutting tools. Two of the most important factors controlling the mechanical properties are the WC grain size and the grain size distribution and thus it is of great interest to understand the grain growth behavior.

In this thesis the grain growth during sintering at 1430 °C is studied both experimentally and through computer simulations. The grain growth behavior in cemented carbides cannot be explained from the classical LSW-theory. The WC grains have a faceted shape necessitating growth by 2-D nucleation of new atomic layers or surface defects. A new model based on 2-D nucleation, long-range diffusion and interface friction is formulated.

Three powders having different average sizes are studied and both experiments and simulations show that a fine-grained powder may grow past a coarse-grained powder, indicating that abnormal grain growth has taken place in the fine-grained powder. Fine-grained powders with various fractions of large grains are also studied and it is seen that a faster growth is obtained with increasing fraction of large grains and that an initially slightly bimodal powder can approach the logaritmic normal distribution after long sintering times.

The grain size measurements are performed on 2-D sections using image analysis on SEM images or EBSD analysis. Since the growth model is based on 3-D size distributions the 2-D size distributions have to be transformed to 3-D, and a new method, Inverse Saltykov, is proposed. The 2-D size distribution is first represented with kernel estimators and the 3-D size distribution is optimized in an iterative manner. In this way both negative values in the 3-D size distribution and modifications of the raw data are avoided.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vii, 42 p.
Keyword
Cemented carbide, Grain growth, Abnormal grain growth, Image analysis, Modeling, 3-D grain size distribution, Inverse Saltykov
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-32430 (URN)978-91-7415-915-8 (ISBN)
Public defence
2011-05-16, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110426Available from: 2011-04-26 Created: 2011-04-14 Last updated: 2011-04-26Bibliographically approved

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