Superhard ceramic materials on the base of cBN cubic boron nitride are widely used now in the creation of cutting tools for high-speed (300-500 m/min) metalworking of stainless and chrome steels. Here thermobaric HPHT sintering of three powder mixtures of cBN-ZrC-Al, cBN-HfC-Al and cBN-TaC-Al systems was carried out using a high-pressure toroidal apparatus (p - 7.7 GPa, T - 1900-2200 °C, time - 45 s). The initial mixtures are the micropowders with a grain size of 1-7 µm and cBN:MeC:Al ratio of 60:35:5 (vol. %). The superhard ceramics obtained by this way were machined and subsequently manufactured into high-quality cutting inserts of Æ 9.52 mm of RNGN 090300T type.
The X-ray diffraction study of the ceramic materials obtained has revealed that the interaction between the components of the initial mixture lead to formation of the additional ZrB2, HfB2, TaB2 and AlN phases. Moreover, as a result of the calculations, carried out to clarify the crystal structure of the MeC carbides, it was shown that the aluminum atoms from  the charge participates in the formation of the substitution solid solutions on the base of MeC carbides under certain HPHT sintering condition. At the same time the nitrogen atoms, released at cBN decomposition, while migrating through the sample, are embedded in the crystal lattices of these carbides. The Young's modulus of the sintered ceramics is in the range of 500-650 GPa, Vickers hardness reaches 35-40 GPa, and porosity does not exceed 0.1 %. The microstructure is 90 % bimodal (cBN + carbide). During high-speed (300 m/min) machining of AISI 316L chrome steel, the linear wear of the cutting edge (VBmax) for ceramics sintered in the cBN-ZrC-Al system was 65 μm, for cBN-TaC-Al - 140 μm and for cBN-HfC-Al - 70 μm, which is a high indicator considering the generally accepted operating limit of the parameter VBmax=300 μm. The results obtained have shown that ceramics fabricated by the HPHT sintering of the cBN-ZrC-Al, cBN-HfC-Al and cBN-TaC-Al powder mixtures are the advanced materials suitable for high-speed metalworking of alloyed steels.
Acknolegements: Authors are grateful to the grant of the Ministry of Education and Science of Ukraine “Development of new superhard materials on the basis of cubic boron for working elements of cutting tools of new generation” (2023-2024), project NATO SPS G5773 “Advanced Material Engineering to Address Emerging Security Challenges”, and grant of the National Academy of Sciences of Ukraine “III-5-23 (0786) “Study of regularities and optimization of sintering parameters of composite materials based on refractory borides and carbides, their physical and mechanical properties in order to obtain products of complex shape for high-temperature equipment with an operating temperature of up to 2000 o?” (2023-2025) for financial support.