Development and kinetic analysis of cobalt gradient formation in WC-Co composites

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Title Development and kinetic analysis of cobalt gradient formation in WC-Co composites
Publication Type dissertation
School or College College of Mines & Earth Sciences
Department Metallurgical Engineering
Author Guo, Jun
Date 2011-08
Description Functionally graded cemented tungsten carbide (FG WC-Co) is one of the main research directions in the field of WC-Co over decades. Although it has long been recognized that FG WC-Co could outperform conventional homogeneous WC-Co owing to its potentially superior combinations of mechanical properties, until recently there has been a lack of effective and economical methods to make such materials. The lack of the technology has prevented the manufacturing and industrial applications of FG WC-Co from becoming a reality. This dissertation is a comprehensive study of an innovative atmosphere heat treatment process for producing FG WC-Co with a surface cobalt compositional gradient. The process exploited a triple phase field in W-C-Co phase diagram among three phases (solid WC, solid Co, and liquid Co) and the dependence of the migration of liquid Co on temperature and carbon content. WC-Co with a graded surface cobalt composition can be achieved by controlling the diffusion of carbon transported from atmosphere during sintering or during postsintering heat treatment. The feasibility of the process was validated by the successful preparations of FG WC-Co via both carburization and decarburization process following conventional liquid phase sintering. A study of the carburization process was undertaken to further understand and quantitatively modeled this process. The effects of key processing parameters (including heat treating temperature, atmosphere, and time) and key materials variables (involving Co content, WC grain size, and addition of grain growth inhibitors) on the formation of Co gradients were examined. Moreover, a carbon-diffusion controlled kinetic model was developed for simulating the formation of the gradient during the process. The parameters involved in this model were determined by thermodynamic calculations and regression-fit of simulation results with experimental data. In summary, this research first demonstrated the principle of the approach. Second, a model was developed to predict the gradients produced by the carbon-controlled atmosphere heat treatment process, which is useful for manufacturing WC-Co with designed gradients. FG WC-Co materials produced using this method are expected to exhibit superior performance in many applications and to have a profound impact on the manufacturing industries that use tungsten carbide tools.
Type Text
Publisher University of Utah
Subject Tungsten carbide-cobalt alloys; Cobalt gradient formation; WC-Co composites; FG WC-Co
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Jun Guo 2011
Format application/pdf
Format Medium application/pdf
Format Extent 3,796,783 bytes
Identifier us-etd3,49045
Source Original housed in Marriott Library Special Collections, TN7.5 2011 .G86
ARK ark:/87278/s6st84js
Setname ir_etd
ID 194350
Reference URL https://collections.lib.utah.edu/ark:/87278/s6st84js
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