A SiO 2 nanolayer, 1.0-2.8 mass% in content, was coated on cubic boron nitride (cBN) powder by rotary chemical vapor deposition (RCVD). The morphology of the SiO 2 nanolayer changed from isolated islands to a continuous layer with increasing supply rate of the precursor, tetraethyl orthosilicate. The effect of the SiO 2 coating on the sinterability and mechanical properties of cBN for machine-tool applications was evaluated. The SiO 2-coated cBN (cBN/SiO 2) powder was mixed with Al 2O 3 and consolidated by spark plasma sintering (SPS) at 1473-1873 K. The phase transformation temperature of cBN to hexagonal BN (hBN) in Al 2O 3-cBN/SiO 2 was 1773 K, 100 K higher than that in Al 2O 3-cBN composites. The highest density of the Al 2O 3-cBN/SiO 2 composites was 99.5% at 30 vol% cBN/SiO 2 content, at which the microhardness and fracture toughness were 28 GPa and 4.1 MPa·m 1/2, respectively. This indicates that RCVD-deposited SiO 2 is a promising sintering aid for cBN and Al 2O 3-cBN/SiO 2 sintered bodies produced by SPS may be applicable as cutting tools.
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