Fabrication of Machinable Silicon Carbide-Boron Nitride Ceramic Nanocomposites
SiC/BN nanocomposite powders with the microstructure of micrometer-sized SiC particles coated with nanometer-sized BN particles were prepared via a chemical reaction, which used a mixture of boric acid (H3BO3) and urea (CO(NH2)2) as reactants coated on the surface of the SiC particles to react under a nitrogen-gas atmosphere. The results of XRD, TEM, and SAED studies showed that the coating layer (BN) was composed mostly of amorphous and nanometer-sized BN particles at the reaction temperature of 850°C. When the nanocomposite powders were hot-pressed at 1850°C, machinable SiC/BN ceramic nanocomposites with fine grain size and homogeneous microstructure were fabricated. The composite that contained 20 wt% BN exhibited high strength (the three-point bending strength was 588.4 ± 26.8 MPa) and excellent machinability.
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