Synthesis of Super-Hard Materials by Direct Conversion Sintering under High Pressure and High Temperature and Their Mechanical Properties
Hitoshi SUMIYA
Abstract:Single-phase (binderless) super-hard polycrystalline cBN and polycrystalline diamond have been successfully synthesized by direct conversion sintering from high-purity hBN and graphite, respectively, under static high pressure and at high temperature. The polycrystalline cBN synthesized at †7.7 GPa and 2200-2400Ž consists of homogeneous fine grains of <0.5 ƒÊm. The polycrystalline diamond synthesized at †15 GPa and 2200-2400Ž reveals a homogeneous fine structure comprised of very small diamond grains of several tens of nanometers. The polycrystalline cBN and polycrystalline diamond have considerably higher hardnesses than those of their single crystals. The transverse rupture strengths (TRSs) are much higher than those of conventional polycrystalline cBN and diamond containing binder and show a positive temperature dependence above 800-1000Ž where the TRSs of conventional polycrystals are rather deteriorated. The fine microstructure without any secondary phases and excellent mechanical properties of the polycrystalline cBN and diamond thus fabricated are promising for next-generation high-precision and high-efficiency cutting tools. Key Words:Diamond, cubic Boron Nitride, High pressure, Direct conversion, Polycrystalline, Binder-less, Super hard