용융염법을 이용한 다이아몬드 입자 표면의 금속 탄화물 코팅에 관한 연구

Abstract

Diamond has high hardness and thermal conductivity, and the diamond compacts are used as grinding wheels, cutting tools, and heat sinks of electronic devices. For diamond/metal composite fabrication, coating diamond particles with metal carbide provides improved wettability between the diamond particles and the matrix. In this study, diamond particles were coated with chromium (Cr) and titanium (Ti) using a molten salt method. Diamond and metal powders were heated at 600–950℃ in molten salts of lithium chloride (LiCl), potassium chloride (KCl), and sodium chloride (NaCl) to create a chromium carbide (here Cr7C3) or titanium carbide (TiC) coating on the diamond particles. Carbide formation was influenced by the diffusion rate and eutectic point of the molten salt mixture. The resulting Cr7C3 or TiC coating surface and microstructure were characterized by X-ray diffraction and scanning electron microscopy, respectively. Coating layer thickness was determined using particle size analysis and confirmed by energy dispersive spectroscopy results. A uniform Cr7C3 or TiC layer formed on the surface of the diamond particles at a relatively low temperature, at which the graphitization of diamond is avoided. In addition to the eutectic point, diamond particles can be coated with a chromium carbide layer with a similar coating thickness and shape using a LiCl-KCl-NaCl molten salt in various compositions. Compared with a mixture of LiCl, KCl, and calcium chloride (CaCl2), which had been used in our previous study, the LiCl-KCl-NaCl mixture increased the reaction rate and initiated coating at a much lower temperature. The coating of Cr on the diamond surface was much thicker than the titanium coating on the diamond surface, regardless of temperature. This indicates that the Cr coating on the diamond surface is much faster in coating reaction or diffusion rate than the Ti coating on the diamond surface. The differences between the two molten salt mixtures for coating diamond are discussed in terms of the diffusion parameters.