Preparation of diboride coatings by electrophoretic deposition in nanoparticle-containing molten inorganic salts

•A novel method of producing diboride coatings was proposed via EPD in molten salts.•At 980 °C a dense TiB2 coating (>40 GPa hardness) was prepared by EPD in molten salts.•A ZrB2 coating with a nanocrystal structure was prepared by EPD in molten chlorides. Electrophoretic deposition is a type of significant method for preparing coatings and films, which has been widely investigated in aqueous and organic suspensions. However, electrophoretic deposition in molten inorganic salts containing nanoparticles, have not been reported in the literature. Here we report the possibility of electrophoretic deposition of nanoparticles in molten inorganic salts. In two types of molten systems (fluorides (980 °C) and chlorides (710 °C)), the electrophoretic deposition of diboride nanoparticles (e.g., TiB2 and ZrB2) on different cathode substrates under cell voltages of 1.2–1.5 V (below the decomposition voltage of the electrolytes), has been successfully demonstrated, resulting in a compact TiB2 coating with hardness of 43.7 ± 2.8 GPa and a ZrB2 coating with a nanocrystal structure. Besides diboride nanoparticles, this proposed process should be applicable for a wider range of nanoparticles to produce more types of coatings and films.