Cobalt diffusion in different microstructured WC-Co substrates during diamond chemical vapor deposition
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Basic and Applied Research: Section I
Cobalt Diffusion in Different Microstructured WC-Co Substrates during Diamond Chemical Vapor Deposition G. Cabral, N. Ali, E. Titus, and J. Gracio
(Submitted July 18, 2005) Our investigation on diamond deposition using cemented tungsten carbide (WC-Co) has shown that diamond particles deposit at different rates onto micrograin and coarse-grain WC-Co substrates. Diamond deposition was carried out using a parallel-plate plasma-enhanced chemical vapor deposition system, which utilized the bias-enhanced growth (BEG) process. BEG was performed at four different times: 15, 20, 25, and 30 min. The resultant diamond-based deposits were characterized for morphology, microstructure, and crystallinity using scanning electron microscopy. It was found that diamond nucleation initiated at the grain boundaries of the substrates. The present article discusses the possible reasons that can potentially explain our key findings. In particular, the CO diffusion from the bulk material through the grain boundaries and onto the substrate surface using a theoretical approach.
1. Introduction Cemented WC-Co hard metals containing WC grains in the submicron (i.e., 0.5-0.8 m) to ultrafine (i.e., 0.2-0.5 m) range and also containing 6 to 16 mass% of cobalt (Co) generally find use in micromachining applications, dental burs, surgical tools, microdrills, and punches used in the pharmaceutical industry.[1] The performance of such hardmetals during service and their lifetime is not ideal for many of the applications. Improvements in such areas can be achieved by the application of an ultrahard coating onto the component. Diamond films display an extraordinary combination of properties that enable them to be used in many different applications.[2-6] The task of direct diamond deposition onto grades of cemented WC-Co, consisting of submicron or ultrafine grains of WC and/or high content of Co (i.e., >8 wt.%) becomes an even more difficult endeavor. Because diamond deposition onto cemented WC-Co consisting of fine-sized WC grains and content with a high percentage of Co is difficult, relatively less work has been done on these grades of material.[7-9] However, many articles can be found in the open literature reporting diamond deposition onto coarse-grain WC-Co substrates with Co contents of
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