Strong machinable ceramic nano-composites with in-situ synthesized BN

A series of ceramic composites containing Si3N4, SiC, ZrO2, Al2O3 and nano-sized h-BN was prepared. Boric acid and urea were ball-milled with these ceramic powders and then in-situ reduced into nano-sized BN coated on the surface of ceramic particles. The reaction processes and the microstructure characteristics of BN nanocomposite powders were analyzed by SEM, TEM, XRD and IR methods. t-BN first appeared as semifinished product during reduction and then turned into h-BN after reheated at higher temperature. Finally hot-pressing was applied to prepare ceramic composites. A drill test was also undertaken to evaluate the machinability. The results showed that all these materials containing more than 20wt% BN exhibit a combination of high strength and excellent machinability, which can be attributed to nano-sized h-BN particles dispersed in ceramic grain boundaries uniformly.