Evaluation of CVD-Deposited SiO2 as a Sintering Aid for Cubic Boron Nitride Consolidated with Alumina by Spark Plasma Sintering

Authors


Author to whom correspondence should be addressed. e-mail: turong@imr.tohoku.ac.jp

Abstract

A SiO2 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 SiO2 nanolayer changed from isolated islands to a continuous layer with increasing supply rate of the precursor, tetraethyl orthosilicate. The effect of the SiO2 coating on the sinterability and mechanical properties of cBN for machine-tool applications was evaluated. The SiO2-coated cBN (cBN/SiO2) powder was mixed with Al2O3 and consolidated by spark plasma sintering (SPS) at 1473–1873 K. The phase transformation temperature of cBN to hexagonal BN (hBN) in Al2O3–cBN/SiO2 was 1773 K, 100 K higher than that in Al2O3–cBN composites. The highest density of the Al2O3–cBN/SiO2 composites was 99.5% at 30 vol% cBN/SiO2 content, at which the microhardness and fracture toughness were 28 GPa and 4.1 MPa·m1/2, respectively. This indicates that RCVD-deposited SiO2 is a promising sintering aid for cBN and Al2O3–cBN/SiO2 sintered bodies produced by SPS may be applicable as cutting tools.

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