基于PcBN应用的立方氮化硼触媒法高压高温合成

Catalytic Process Synthesis of Cubic Boron Nitride by High Pressure and High Temperature as Used for PcBN

聚晶立方氮化硼(PcBN)具有优异的高硬度、耐热和耐磨等多种物理性能,已经成为重要的刀具材料,应用领域广阔。立方氮化硼(cBN)是硬度仅次于金刚石的超硬材料,利用cBN的超硬特性,可以制成聚晶立方氮化硼。以六方氮化硼(hBN)为原料,经静态触媒法超高压高温反应,可以得到PcBN特殊要求的cBN。研究了hBN预处理后的粒度和结晶度,合成cBN的二阶升压工艺中暂停时间及台阶压力,诱导剂的添加等工艺变化对cBN合成的影响。采用N2气氛热压烧结法对hBN进行预处理,明显改变了hBN的结晶度,但是其粒度变化不大。对于粒度相近的hBN,其结晶度的变化对cBN合成结果影响更显著。采用较低结晶度的hBN合成cBN时转化率较高,cBN晶体的粒度相对较小,正是合成PcBN的理想原料。合成cBN时,台阶压力高,cBN成核较多;台阶压力低,成核少;台阶压力低时,晶粒较大,晶形明显变好。随着暂停时间的延长,cBN的成核率降低,产量减少,粒度明显增大,晶形完整率提高。通过添加B、Si或Ce等晶形诱导剂,可以调整cBN晶体的颜色、晶形和杂质含量等。为了得到用于制备PcBN的高质量cBN,控制合成工艺条件为:台阶压力4.0GPa,终态压力4.6GPa,暂停时间15s,合成温度1 390℃。

As one kind of important materials used for preparing cutting tools,polycrystalline cubic boron nitride（PcBN）behave many good properties,such as,heat resistant,high hardness,abrasion resistant,etc,so it is used in a variety of fields.Cubic boron nitride（cBN）has very high hardness only lower than that of diamond which has the best hardness in the world,so cBN can be synthesized by the approach of static high pressure and high temperature with the addition of catalytic agent in Hexagon boron nitride（hBN）.We studied the effects of the size and crystallinity degree of hBN after pretreatment,reaction time and pressure in the two stage pressure rise for synthesizing cBN,and the influence of addition of crystal inducing agent on the result of obtained cBN.The pretreatment and sintering of hBN presursor in N2 may significantly change the crystallinity degree of hBN,but has no apparent influence on size.For the same size hBN,its crystallinity degree has much more effects on the synthesis of cBN.The relatively lower crystallinity degree of hBN is suitable for preparing cBN crystals with higher conversion and lower grain size,which are ideal raw materials for synthesizing PcBN.The crystal nucleus grains are increased with the increase of reaction pressure,however,the size of crystal grains are increased with the decrease of reaction pressure.Moreover,the crystal nucleus grains and conversion are decreased with the increase of reaction time,and the size of cBN crystal and the shape integrity of cBN are increased.The color,crystalline form and impurity content of cBN can be controlled by adjusting the addition of crystal inducing agents,such as B,Si and Ce.In order to obtain high quality cBN for special use of PcBN,some parameters of synthesizing cBN should be preferably determined,that is,reaction pressure of 4.0 GPa,final pressure of 4.6 GPa,reaction time of 15 sand temperature of 1 390 ℃.