ABSTRACT
Different from the monocrystalline cubic boron nitride (CBN) tools, the polycrystalline CBN abrasive tools mainly work in the extreme conditions (e.g., high temperature, impact load environment, etc.). In addition, the polycrystalline CBN grains overcome the drawback of anisotropy due to their unique microstructure. The wear mechanism and behaviour of a brazed polycrystalline CBN grinding wheel can be different; in this case, the grinding performance and life time of the polycrystalline CBN grinding wheel need further study. Therefore, it is necessary to investigate the crack propagation and fracture toughness of polycrystalline CBN abrasive materials as well as the influencing factors. In this chapter, the influences of grain size, the bonding strength of the grain boundary, and grain boundary stiffness on the fracture toughness of polycrystalline CBN abrasive materials under tensile loading were analysed. The stresses effects on wear and crack propagation were also deeply studied based on finite element simulation. The energy dissipations due to fractures of various microstructures as well as the length of cracks and the percentage of transgranular fracture were calculated. The relationship between fracture toughness and crack characteristics was studied in detail. The wear phenomenon of the polycrystalline CBN grinding wheel was also discussed.
