Deposition of Adherent Diamond Coating on WC-Co Substrate
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0890-Y01-02.1
Deposition of Adherent Diamond Coating on WC-Co Substrate Zhenqing Xu1, 2, Leonid Lev3, Michael Lukitsch3, and Ashok Kumar1, 2 1 Department of Mechanical Engineering, University of South Florida, Tampa, FL, 33620, USA 2 Nanomaterials and Nanomanufacturing Research Center, University of South Florida, Tampa, FL, 33620, USA 3 General Motors Corporation, Warren, MI 48090, USA ABSTRACT High quality well-adhered microcrystalline diamond coatings have been produced by the microwave plasma enhanced chemical vapor deposition (MPECVD) technique on cemented carbide substrates. A multi-interlayer system Cr/CrN/Cr was deposited on the WC-Co substrate before diamond deposition to work as a diffusion barrier. The coated substrate was peened with friable diamond powder to roughen the surface resulting in high nucleation density. Adherent diamond film has been successfully deposited on the substrate at temperature around 700ºC with 1.0 % CH4 in Hydrogen plasma. The surface morphology and film structure has been studied by Scanning Electron Microscopy (SEM) and X-Ray diffraction technique. The adhesion of the diamond film has been evaluated by Rockwell indentation tests. INTRODUCTION Cemented carbide is a material made by "cementing" tungsten carbide (WC) grains in a cobalt matrix1. The cemented tungsten carbide cutting tools are used widely in, machining, mining and stone cutting industry. However, cemented carbide tools are found to wear rapidly when used to machine some particular materials such as green ceramics, abrasive composites or high silicon aluminum. Diamond coating has been proposed to improve the wear resistance of cemented carbide tools. Successful development of diamond coatings for WC-Co cutting tools will significantly improve their performance. These coatings will reduce machine down-time, increase cutting productivity and improve the quality of machined surface. Poor adhesion of the diamond coating is the main technical barriers for commercialization of diamond-coated tools [1-4]. During high temperature deposition of diamond coating, Co leaching from WC-Co substrate catalyzes the formation of sp2-bonded (non-diamond) carbon, instead of sp3 –bonded diamond [5]. This results in the formation of a weak graphite layer at the interface between the diamond coating and the substrate. Various approaches have been reported to avoid or reduce the formation of this graphite layer [6-10]. In our study, a thin Cr/CrN/Cr multi-interlayer system has been pre-deposited to work as a diffusion barrier between the substrate and the diamond coating. Also, the substrate was peened by a friable diamond powder. This roughened the substrate and imbedded the particles of the diamond powder into it, providing the anchors for the deposited coating and improving its adhesion. 1
Some other carbides, besides tungsten carbide may be used in cemented carbide tools. Also, other compositions of the matrix, in addition to cobalt, can be used.
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EXPERIMENTAL Cemented carbide coupon samples (WC-6%Co) were cleaned by a
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