Influence of Microwave and Conventional Annealing Processes in Improving an Electrodeposited Nickel Interlayer Character
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DIAMOND deposition on tungsten carbide with cobalt binder (WC-Co) faces major problems. The high process temperature and cobalt binder favor the reaction toward graphitic phase, and hence lower the nucleation and growth of diamond.[1,2] There is also a problem related to residual stresses due to the large mismatch in the coefficient of thermal expansion between diamond and tungsten carbide. These issues make the surface pretreatment using intermediate interlayer between tungsten carbide and diamond is necessary.[3–6] The use of electroplated nickel interlayer on tungsten carbide for diamond deposition is of interest in this study. Nickel material can promote nucleation and growth of heteroepitaxial diamond crystals from the small lattice mismatch with diamond.[7,8] However, application of nickel as an interlayer on tungsten carbide for diamond deposition is not yet fully explored. This could be due to high solubility of nickel for carbon, ABDELKARIM HASSAN, Postdoctoral Fellowship Award Recipient, is with Universiti Teknologi Malaysia, Johor Bahru, Malaysia, and also Senior Lecturer with the Faculty of Engineering and Technical Studies, University of Alimam Almahdi, Kosti, Sudan. Contact e-mail: [email protected] MOHD YUSOF NOORDIN, Dean and Professor, SUDIN IZMAN, Professor, and KURNIAWAN DENNI, Senior Lecturer, are with the Faculty of Mechanical Engineering, Universiti Teknologi Malaysia. Manuscript submitted March 21, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
which delays diamond nucleation and promotes graphite formation. However, earlier reports demonstrated that the solubility of nickel for carbon could be reduced by enriching its surface with carbon prior to diamond deposition inside the CVD reactor.[9–11] Although the reported techniques were useful and diamond nucleation and growth on bulk nickel was significantly improved, they are not suitable for treating the electroplated nickel interlayer on tungsten carbide. Interlayers deposited by electroplating process usually suffer from weak adhesion to the substrate due to the low processing temperature. Hence, they require being heat-treated for a long time to enable solid-state diffusion process to take place between the interlayer and substrate materials. Conversely, annealing inside the CVD reactor is a short period process and immediately followed by the subsequent diamond depositions.[9] Thus, the time required undergoing the interdiffusion between the nickel and tungsten carbide is not sufficient for improving the interlayer adhesion strength. Moreover, the rapid diffusion of carbon in nickel during the subsequent diamond deposition stage is expected to reduce the diffusion of substrate elements toward the interlayer and consequently will lead to slight interlayer adhesion improvement. Our previous study showed that although the diffusion of carbon from charcoal powder in nickel is less rapid, it could significantly reduce the diffusion of the substrate elements in nickel coating, and, therefore, did not much improve the nickel interlayer adhesion.[12
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