Diamond Coated WC Tools for Machining Wood and Particle Board
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Diamond Coated WC Tools for Machining Wood and Particle Board Raghuveer S. Makala, S.N. Yoganand, K. Jagannadham, R.L. Lemaster1, J. Bailey2 Department of Materials Science and Engineering, 1 Department of Wood and Paper Science, 2 Department of Mechanical Engineering, North Carolina State University, Raleigh, NC-27695-7907. ABSTRACT Diamond coating was provided to improve the performance of WC-Co tools used in machining wood and particle board. Microwave plasma chemical vapor deposition was used to deposit diamond using a gas mixture with CH4: H2 in the ratio 0.5: 100 at a temperature of 9000C. The microwave energy was set at 900W and a pressure of 35Torr was maintained in the chamber. An essential factor that determines the life of polycrystalline diamond coated tools is poor film adhesion. To counter this problem, we have developed a process that includes etching away cobalt from surface regions, treatment with H2 plasma and use of TiN/ TiC intermediate and embedding layers. The TiN/ TiC layers were deposited by reactive magnetron sputtering. These layers embed diamond crystallites and improve adhesion, and in addition act as good diffusion barriers for Co. The diamond coated and uncoated tools have been characterized in the as deposited conditions and after prescribed wear by machining particle board using SEM and Xray mapping. It was also found that the limited contact area with diamond on the cutting edge affects the adhesion of the coating. Improvement in contact area by providing a larger radius to the cutting edge is discussed.
INTRODUCTION Polycrystalline diamond coatings are useful in a wide variety of wear resistant applications because of their excellent properties. In the present study we deposited CVD diamond coatings to enhance the life and performance of WC-Co tools (sintered WC with cobalt as the binder) used in machining wood and particle board [1]. The hard and brittle carbide grains dispersed in a soft and ductile cobalt binder provide hardness to resist wear and toughness to the tool cutting edge [2]. However, without a hard coating such as diamond, the cemented WC tools are found to wear rapidly when machining particle board. Successful development of diamond coated tools with better adhesion and improved wear resistance has significant benefits in machining particle board such as reduced down time and less defective machined surfaces and as a result, reduced wastage. An important factor that determines the life of the diamond-coated tools is the adhesion of the diamond layers. The catalytic effect of cobalt binder in WC favors the formation of sp2 carbon (non-diamond) phases during the early stages of deposition, that is considered responsible for weak interfacial strength [3,4]. Various approaches to avoid the detrimental effect of cobalt on the growth of diamond films and its resulting weak adhesion strength to the substrate have been proposed earlier [5]. In the present study, we present different procedures of surface treatment and modifications to the cutting edge of the tools that we h
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