2012 年 22 巻 2 号 p. 121-128
Single-phase super-hard polycrystalline cBN and diamond have been synthesized by direct conversion sintering from hBN and graphite, respectively, under static high pressure and high temperature. The polycrystalline cBN and diamond consist of fine grains of several tens or hundreds nano-meters, having high hardnesses which are higher than those of their single crystals. They also have high transverse rupture strengths (TRSs) which are much higher than those of conventional sintered compacts containing binder materials. The fine microstructure features without any secondary phases and surpassing mechanical properties of the single-phase super-hard polycrystalline cBN and diamond are promising for applications in next-generation high-precision and high-efficiency cutting tools.