Effects of additive LiF on the synthesis of cBN in the system of Li 3N–hBN at HPHT

Abstract

High-quality cBN single crystals were successfully synthesized in the system of Li 3N–hBN with additive LiF at high pressure and high temperature (HPHT). The lowest synthetic conditions of cBN decreased to 4.6 GPa, 1320 °C by employing 3 wt.% LiF, and it didn't change anymore though more than 3 wt.% LiF had been added. The quality of cBN crystals improved markedly. The cBN crystals and other products were examined by X-Ray diffraction and scanning electron microscopy. The X-Ray analysis reveals that the “graphitization index” (GI) of hBN increased by adding 3 wt.% LiF into the system of Li 3N–hBN at HPHT. The SEM photographs show that different growth steps were formed on the cBN crystal surface in systems of Li 3N–hBN and Li 3N–LiF–hBN, respectively.