In this paper, pure polycrystalline cubic boron nitride (cBN) without additives was synthesized by a direct sintering method at 7.3 GPa and 2100 °C using industrial cBN powders with different particle sizes. High-pressure experiments without heating verified that the actual pressure of the cBN particles in the cavity was lower than that of the fine-grained samples during the sintering of coarse-grained samples. The best hardness (4900 HV2) and density (3.342 g/cm²) of sintered bodies were obtained when using fine-grained (2–4 μm) particles. The fracture modes of fine-grained and coarse-grained sintered bodies were investigated using scanning electron microscopy, and the microstructures of intra-grain and grain boundaries were systematically studied using high-resolution transmission electron microscopy. It was concluded that the main fracture mode of the fine-grained sample was transgranular fracture, while that of the coarse-grained sample was intergranular fracture. Moreover, a large number of dislocations and high-density twins were generated in the cBN grains under high temperature and high pressure, which improved the hardness of samples and caused transgranular fracture in fine-grained (2–4 μm) samples. This study of the fracture mode of industrial pure polycrystalline cBN is important to enable its use as a high-precision machining tool material.

在本文中，使用不同粒径的工业cBN粉末，通过直接烧结法在7.3 GPa和2100°C下合成了不含添加剂的纯多晶立方氮化硼（cBN）。在不加热的情况下进行的高压实验证明，在烧结粗粒样品的过程中，空腔中cBN颗粒的实际压力低于细粒样品的实际压力。最佳硬度（4900 HV2）和密度（3.342 g / cm ²当使用细颗粒（2-4μm）时，获得的烧结体为）。利用扫描电子显微镜研究了细晶粒和粗晶粒烧结体的断裂模式，并利用高分辨率透射电子显微镜系统地研究了晶粒内和晶界的微观结构。可以得出结论，细颗粒样品的主要断裂模式是穿晶断裂，而粗颗粒样品的主要断裂模式是晶间断裂。此外，在高温高压下，cBN晶粒中产生了大量的位错和高密度孪晶，这提高了样品的硬度并导致了细晶粒（2-4μm）样品的经晶断裂。