Very High Pressure Sintering of High Dense Form Boron Nitride using Wurtzite Type as Starting Materials

Abstract

Shock synthesized wurtzite type boron nitride (w-BN) powders with particle size of 0.1∼0.5 μm were treated in the temperature range between 1150°C and 1900°C at 6.7 GPa. The purpose of this study is to clarify the sintering process and the relation between microstructure and mechanical properties. A link type of cubic anvil very high pressure apparatus was used for very high pressure sintering. w-BN transformed to zinc blende phase (z-BN) above 1300°C. The apparent density and vicker's micro hardness of sintered compacts increased with increasing temperature of treatment up to 1600°C for 15 min. Any grain growth was not observed in the sintered compact treated below 1600°C.
The compact, obtaind at 6.7 GPa and 1600°C for 15 m in, consisted of 10 w t% w-BN and 90 wt% z-BN and had theoretical density and extremely high hardness above 8000 kg/mm2. Hardness and density decre ased with increasing temperature above 1600°C and grain growth was arisen. Plate-like grains whose plane corresponded to (111) of z-BN was observed in the compact obtained at 1900°C. It is seemed that a prefered orientation of w-BN powder to (002) relates to anisopropic grain growth of z-BN.