TiB2-ZrB2-SiC composite ceramic coating with the formation of solid-phase (TixZr1-x)B-2 deposited by atmospheric plasma spraying as a barrier to molten cryolite-based salt

TiB2, ZrB2, and SiC powders with particles measuring several micrometers were first agglomerated and then deposited onto the substrate of a porous carbon block as a barrier to molten cryolite-based salt. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy were conducted to investigate the fine microstructure of the obtained ceramic coating and to elucidate the evolution of agglomerated powder from sprayed particles in plasma jet to splats on a substrate. Results indicated that a highly dense ceramic coating consisting of a solid solution (TixZr1-x)B-2, residual TiB2, and ZrB2 was obtained. The compactness of the coating and the formation of a solid solution phase was mainly caused by a SiC-rich liquid phase, as determined from a boride and silicon carbide pseudodiagram. After being submerged in molten cryolite-based salt for 8 h, the ceramic coating was firmly bonded to a carbon block. No molten slat permeated the ceramic coating.