Abstract
Properties of polycrystalline materials strongly depend on their microstructural features such as the grain size distribution, the boundary condition and so on. In this paper, we provide our works concerning microstructural features and some properties of high-purity polycrystalline cBN synthesized from hBN by the direct conversion method. A fine-grained (<0.5 μm) and homogeneous high-purity polycrystalline cBN (>99.9%) with the highest mechanical properties can be obtained by controlling temperature conditions within 2200-2400°C at 7.7 GPa. Many cBN grains rapidly become larger at temperatures above these conditions, and a considerably inhomogeneous microstructure which causes the deterioration of mechanical properties is formed.
