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A series of ceramic composites containing Si 3 N 4 , SiC, ZrO 2 , Al 2 O 3 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.

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