Wolfrum Anne-Kathrin, Matthey Björn, Michaelis Alexander, Herrmann Mathias
Fraunhofer IKTS, Fraunhofer Institute for Ceramic Technologies and Systems, 01277 Dresden, Germany.
Institute for Materials Science, Dresden University of Technology, 01062 Dresden, Germany.
Materials (Basel). 2018 Feb 7;11(2):255. doi: 10.3390/ma11020255.
Cubic boron nitride (c-BN) composites produced at high pressures and temperatures are widely used as cutting tool materials. The advent of new, effective pressure-assisted densification methods, such as spark plasma sintering (SPS), has stimulated attempts to produce these composites at low pressures. Under low-pressure conditions, however, transformation of c-BN to the soft hexagonal BN (h-BN) phase can occur, with a strong deterioration in hardness and wear. In the present work, the influence of secondary phases (B₂O₃, Si₃N₄, and oxide glasses) on the transformation of c-BN was studied in the temperature range between 1100 °C and 1575 °C. The different heat treated c-BN particles and c-BN composites were analyzed by SEM, X-ray diffraction, and Raman spectroscopy. The transformation mechanism was found to be kinetically controlled solution-diffusion-precipitation. Given a sufficiently low liquid phase viscosity, the transformation could be observed at temperatures as low as 1200 °C for the c-BN-glass composites. In contrast, no transformation was found at temperatures up to 1575 °C when no liquid oxide phase is present in the composite. The results were compared with previous studies concerning the c-BN stability and the c-BN phase diagram.
在高压和高温下制备的立方氮化硼（c-BN）复合材料被广泛用作切削刀具材料。新型有效压力辅助致密化方法的出现，如放电等离子烧结（SPS），激发了人们在低压下制备这些复合材料的尝试。然而，在低压条件下，c-BN会转变为软质的六方氮化硼（h-BN）相，导致硬度和耐磨性大幅下降。在本研究中，研究了第二相（B₂O₃、Si₃N₄和氧化物玻璃）在1100℃至1575℃温度范围内对c-BN转变的影响。通过扫描电子显微镜（SEM）、X射线衍射和拉曼光谱对不同热处理的c-BN颗粒和c-BN复合材料进行了分析。发现转变机制为动力学控制的溶解-扩散-沉淀。在液相粘度足够低的情况下，对于c-BN-玻璃复合材料，在低至1200℃的温度下就能观察到转变。相比之下，当复合材料中不存在液态氧化物相时，在高达1575℃的温度下都未发现转变。将结果与先前关于c-BN稳定性和c-BN相图的研究进行了比较。
