An Investigation of the Mechanical Properties and Fracture Characteristic of Hot-Pressed Boron Nitride Ceramics

The overall mechanical characterization of hot-pressed hexagonal boron nitride (h-BN) based ceramics was performed. Hardness, flexure strength and fracture toughness (KIC) measurements were carried out using Vickers indentations, 3-point bending tests and SEVNB method, respectively. The fracture characteristics of hot-pressed h-BN ceramics were investigated by analyzing fracture surfaces using scanning electron microscope (SEM). The hardness, ranged from HV = 0.20GPa to HV = 0.25GPa, which was higher in the surfaces parallel to the hot-press direction due to the perpendicular alignment of the basal planes of the h-BN platelets to the hotpress direction. The fracture toughness and flexure strength values were determined to be 2.6 MPa.m1/2 and 0.14 GPa, respectively. A single KIC value was obtained since a slight variation of the fracture toughness was observed with the orientation of h-BN. The microstructural observations of h-BN grains indicated completely brittle fracture with intergranular voids and microcracks revealing a mixed mode of fracture.