Investigation On The Static HTHP Synthesis Technology Of Cubic Boron Nitride

At present, China has joined in the ranks of the major cBN production country. However, compared with the international advanced countries, the level of cBN production technology in China remains to be further improved. High quality cBN single crystals can not be produced in high volume, and the yield, grade, transparency and strength of the cBN produced are low, which could not meet the demand of industy development. The main reason lies in the low level assembly structure, the backward cBN synthesis technology and the poor catalyst systems. Among these, the catalyst and the technological factors are the focus of attention. In order to enhance our cBN competitiveness in the international market, we should fully study the catalyst systems and raw materials and research the synthesis technology of cBN single crystal, so as to improve and obtain cBN single crystals with high quality.In this paper, with hBN as raw materials, and Li3N, Ca3N2, Mg3N2as a catalyst respectively, static high pressure and high temperature (HTHP) technology was adopted to produce cBN single crystals. In the synthetic experiment, the ratio of hBN and catalyst was adjusted, parameters of synthesis process was optimized to obtain the optimal conditions for the synthesis of cBN single crystals with large grains and high quality. The paper aimed to to provide effective conditions to explore the synthesis and growth mechanisms of cBN single crystals under high pressure and high temperature, and lay experimental basis to better guide the practical production. The main results of this paper are as follows:The cBN single crystals are produced under high temperature and high pressure, with Li3N as catalyst and high purity hBN as raw material. The effects of the addition amount of Li3N catalyst, Li3N size and the synthesis process parameters on the synthesis results of cBN single crystal are explored. The performances of yield and conversion rate, particle size distribution and static strength of the cBN single crystals are measured, and the surface morphology is observed after synthesis. Finally, we arrived at the conclusions that, the synthesis result is better with the Li3N catalyst additon of10%, and the optimal cBN single crystals were obtained at the technology conditions of1470℃and4.90GPa in10minutes, with the step pressure of4.05GPa and pause time of100～120seconds.The cBN single crystals are produced under high temperature and high pressure, with Ca3N2as catalyst and high purity hBN as raw material. In the C3sN2-hBN system, the effects of the synthesis process parameters on the synthesis results of cBN single crystal are explored. The performances of yield and conversion rate, particle size distribution and static strength of the cBN single crystals are measured, and the surface morphology is observed after synthesis. Finally, we arrived at the conclusions that, with Ca3N2addition amount of10%, the optimal cBN single crystals were obtained at the technology conditions of1460℃and4.80GPa in10minutes, with the step pressure of3.75GPa and pause time of80～120seconds.The cBN single crystals are produced under high temperature and high pressure, with Mg3N2as catalyst and high purity hBN as raw material. In the Mg3N2-hBN system, the effects of the synthesis process parameters on the synthesis results of cBN single crystal are explored. The performances of yield and conversion rate, particle size distribution and static strength of the cBN single crystals are measured, and the surface morphology is observed after synthesis. Finally, we arrived at the conclusions that, with Mg3N2addition amount of10%, the optimal cBN single crystals were obtained at the technology conditions of1400℃and4.75GPa in10minutes, with the step pressure of3.65GPa and pause time of80-120seconds.At optimal technology conditions, cBN single crystals synthesized with Li3N have the highest yield, conversion rate and largest grain size, which are amber colour, high transparent, perfectly grew, with regular shape, dense and smooth crystal surface, low impurity content and few growth defects, and therefore the catalyst is especially suitable for producing of high quality cBN single crystals of large size in industry. The cBN single crystals synthesized with Ca3N2have the lower yield, conversion rate and smaller grain size than that of Li3N, which are light yellow, high transparent, perfectly grew, with regular shape, dense and smooth crystal surface, low impurity content and few growth defects, and in addition to the low price which reduces production cost, the catalyst is especially suitable for producing of high quality cBN single crystals of small size in industry. The cBN single crystals synthesized with Mg3N2have the lowest yield, conversion rate and smallest grain size, which are black and opacity, imperfectly grew, with irregular shape, loose and rough crystal surface, and growth defects of growth steps, holes, scratch and rupture angle. However, for the cheap price which greatly reduces the production cost, the catalyst is suitable to produce of low grade cBN single crystals of small size and microsize in industry.