Very high pressure sintering of cBN fine particles coated with TiN–TiB₂ layer formed by disproportionation reaction in molten salts

Sintering of a fine cubic boron nitride (cBN) particle with a grain size of less than 2 μm was successfully carried out under 5.5 GPa pressure at 1720 K for 30 min. TiN–TiB₂-coated cBN particles were used as the starting powder without adding any other binding materials. The coating was carried out by dipping the cBN particles in molten salts. The obtained cBN sintered compact shows a smooth microstructure with a well-controlled grain boundary; TiN–TiB₂ is distributed over the cBN-grain boundary in the shape of a net mesh similar to tiled floors. The Vickers microhardness of the obtained compact was found to be higher than that of commercially available typical cBN-cutting tools.