Coating of chromium and titanium carbide on diamond particles in molten LiCl-KCl-NaCl

摘要

Diamond particles were coated with chromium (Cr) or titanium (Ti) using a molten salt synthesis (MSS) approach involving lithium chloride (LiCl), potassium chloride (KCl), and sodium chloride (NaCl). Diamond and metal powders were heated at 700-900 degrees C in the MSS to create chromium carbide (Cr7C3) or titanium carbide (TiC) coatings on the diamond particles. Carbide formation was influenced by the dissolved metal content and the diffusion rate. The thickness and morphology of the Cr coating layer was not significantly affected by the molar ratio of the LiCl-KCl-NaCl mixture, however, in terms of the coating atmosphere, it is most valuable using the eutectic LiCl-KCl-NaCl mixture having the molar ratio of 55:33:12 and the lowest melting point. The resulting Cr7C3 and TiC coated surfaces and microstructures were characterized by X-ray diffraction and scanning electron microscopy, respectively. A uniform Cr7C3 and TiC layer formed on the surface of the diamond particles at a relatively low temperature, at which the graphitization of diamond was avoided. The coating layer thickness estimated by particle size analysis increased linearly with coating temperature. The thickness of the Cr- and Ti-coated layers ranged from 1 to 10 and 0.5-1.5 mu m, respectively, which indicated that the TiC coating formed at a much slower rate than the Cr7C3 coating. (C) 2020 Elsevier B.V. All rights reserved.