Al2O3-coated h-BN composite powders and as-prepared Si3N4-based self-lubricating ceramic cutting tool material

The surfaces of solid lubricant hexagonal boron nitride (h-BN) powders were coated with compacted and integrated Al(OH)3 by heterogeneous nucleation and then the h-BN@Al2O3 composite powders were prepared by calcination under vacuum at 1200 °C for 2 h, as determined by SEM, EDS and XRD. The Si3N4 self-lubricating ceramic cutting tool material with coated h-BN was prepared by vacuum hot pressing. Microstructure analysis showed that the h-BN@Al2O3 particles were dispersed homogeneously in the matrix and that the particles were tightly bound. Vickers hardness was 14.1 GPa, fracture toughness was 7.2 MPa·m1/2, and flexural strength was 732 MPa, as determined by mechanical property testing. The hardness, fracture toughness, and flexural strength of the material were increased by 27.0%, 5.9% and 22.2%, respectively, relative to the material to which uncoated h-BN was added. Cutting tests showed that the Si3N4/TiC/(h-BN@Al2O3) self-lubricating ceramic cutting tool had better antifriction property and wear resistance than the corresponding cutting tool.