Effect of Chlorine Salts on TiC Coating Morphology and Bonding Strength of Diamond Surface in Molten Salt Reaction

Abstract

To obtain a high-quality TiC coating on the diamond (D) surface and improve the interfacial properties of metal matrix composites, the optimized molten salt method is used to prepare TiC coatings on the D surface. The effects of NaCl, KCl, and NaCl–KCl molten salts on the uniformity, surface morphology, composition, and bonding ability of TiC coatings are investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction, and cold–hot cycling experiments. The results show that the boiling and pickling processes after the molten salt reaction can effectively remove the residual chloride salts and Ti powders to obtain clean TiC-coated D. The TiC particles of the coating surfaces prepared by NaCl and KCl molten salts are finer and more uniform, which is due to their higher melting points and shorter real reaction time compared with NaCl–KCl mixed salts. The TiC coating prepared by KCl has the best bonding ability and can withstand 50 times as many cold–hot cycles due to its uniform fine deposition particles and appropriate thickness. And, during cold–hot cycles, it can be found that the TiC coating cracking and shedding occur primarily at the edges and corners of the D with internal thermal stress concentration.