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Materials 2018, 11(2), 255;

On the Stability of c-BN-Reinforcing Particles in Ceramic Matrix Materials

Fraunhofer IKTS, Fraunhofer Institute for Ceramic Technologies and Systems, 01277 Dresden, Germany
Institute for Materials Science, Dresden University of Technology, 01062 Dresden, Germany
Author to whom correspondence should be addressed.
Received: 10 January 2018 / Revised: 29 January 2018 / Accepted: 1 February 2018 / Published: 7 February 2018
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Cubic boron nitride (c-BN) composites produced at high pressures and temperatures are widely used as cutting tool materials. The advent of new, effective pressure-assisted densification methods, such as spark plasma sintering (SPS), has stimulated attempts to produce these composites at low pressures. Under low-pressure conditions, however, transformation of c-BN to the soft hexagonal BN (h-BN) phase can occur, with a strong deterioration in hardness and wear. In the present work, the influence of secondary phases (B2O3, Si3N4, and oxide glasses) on the transformation of c-BN was studied in the temperature range between 1100 °C and 1575 °C. The different heat treated c-BN particles and c-BN composites were analyzed by SEM, X-ray diffraction, and Raman spectroscopy. The transformation mechanism was found to be kinetically controlled solution–diffusion–precipitation. Given a sufficiently low liquid phase viscosity, the transformation could be observed at temperatures as low as 1200 °C for the c-BN–glass composites. In contrast, no transformation was found at temperatures up to 1575 °C when no liquid oxide phase is present in the composite. The results were compared with previous studies concerning the c-BN stability and the c-BN phase diagram. View Full-Text
Keywords: cubic boron nitride; c-BN; composites; phase transformation; hexagonal boron nitride; microstructure cubic boron nitride; c-BN; composites; phase transformation; hexagonal boron nitride; microstructure

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Wolfrum, A.-K.; Matthey, B.; Michaelis, A.; Herrmann, M. On the Stability of c-BN-Reinforcing Particles in Ceramic Matrix Materials. Materials 2018, 11, 255.

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