Processing and properties of PcBN composites fabricated by HPHT using PSN and Al as sintering additive

Abstract

Dense polycrystalline cubic boron nitride (PcBN) composites were fabricated by high-pressure and high-temperature (HPHT) sintering using polysilazane (PSN) and Al as sintering additive. After high-energy ball milling, the cBN fine particles were uniformly coated with PSN by ultrasonic treatment. After thermocuring and pyrolysis, the cBN–SiCN particles were mixed with Al. The PcBN composites were prepared after sintering at 1450 °C for 10 min with a pressure of 5 GPa. The refining effect of high-energy ball milling on the cBN particles was studied by scanning electron microscopy (SEM) and laser particle size analyzer. The oxidation of the cBN particles after milling was investigated by nitrogen–oxygen analyzer. The phase composition and microstructure of the sintered PcBN composites were investigated by X-ray diffractometer (XRD) and SEM. The main phases of the sintered PcBN composites are cBN, AlN, SiC and Si3N4. The conversion of cBN to hBN was inhibited by the formation of AlN. The mechanical properties of the sintered PcBN composites were improved by the appearance of SiC and Si3N4. The density and mechanical properties of the PcBN composites both increased with the content of the cBN particles increasing. The sintered sample with 60 wt% cBN, 30 wt% PSN and 10 wt% Al showed the best results: density of 99.7%, Vickers’ hardness of (25.2 ± 0.8) GPa and flexural strength of (602 ± 15) MPa.