Effect of sintering temperature on the structure and properties of polycrystalline cubic boron nitride prepared by SPS

The polycrystalline cubic boron nitride (PcBN) with Si3N4–AlN–Al2O3–Y2O3 ceramic system as binding agents was prepared by spark plasma sintering (SPS). The starting materials Si3N4, AlN, Al2O3, Y2O3, and cBN in the ratio of 22:14:10:4:50 were heated to a sintering temperature between 1250 °C and 1450 °C at a heating rate of 300 °C/min, with a holding time of 5 min in nitrogen atmosphere. The microstructure, phase constitution, microhardness and fracture toughness of the prepared PcBN were then studied. It was shown that the Si3N4–AlN–Al2O3–Y2O3–cBN polycrystalline materials were densified in a very short sintering time resulting in materials with relative densities of more than 95%. When the sintering temperature increased, the microhardness and fracture toughness of prepared PcBN were also increased. The microhardness of PcBN prepared at 1250–1450 °C was between 28.0 ± 0.5 GPa and 48.0 ± 0.9 GPa, and its fracture toughness KIC was from 7.5 ± 0.2 MPa m1/2 to 11.5 ± 0.3 MPa m1/2. Microstructure study showed that the ceramic-binding agents bonded with cubic boron nitride particles firmly. Our work demonstrated that spark plasma sintering technology could become a novel method for the preparation of PcBN cutting materials.