Chromium carbide coating of diamond particles using low temperature molten salt mixture

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) using a molten salt method. Diamond and Cr powders were heated at 600–950 °C in molten salts of lithium chloride (LiCl), potassium chloride (KCl), and sodium chloride (NaCl) to create a chromium carbide (here Cr7C3) coating on the diamond particles. Carbide formation was influenced by the diffusion rate and eutectic point of the molten salt mixture. The resulting Cr7C3 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 layer formed on the surface of the diamond particles at a relatively low temperature, at which the graphitization of diamond is avoided. 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 differences between the two molten salt mixtures for coating diamond are discussed in terms of the diffusion parameters.