Mechanical properties of high purity polycrystalline cBN synthesized by direct conversion sintering method

Mechanical properties of high purity polycrystalline cBN sintered bodies synthesized by the direct conversion method under high pressure and high temperature have been investigated by hardness and transverse rupture strength (TRS) measurement in the temperature range of 20-1200 degrees C. It was confirmed that the hardness and TRS of the polycrystalline cBN depends strongly on the cBN grain size and the amount of residual (compressed) hBN in the sintered body. The fine-grained (< 0.5 mu m) and high purity (cBN > 99.9%) polycrystalline sintered body synthesized at 7.7 GPa, 2200-2400 degrees C has highest hardness and TRS at any temperature. The TRS of the sintered body shows a positive temperature dependence up to 1200 degrees C. The high hardness and high TRS at high temperature of the fine-grained high purity polycrystalline cBN suggest that the sintered body has high potential in cutting tool uses. (C) 2000 Kluwer Academic Publishers.