Cubic boron nitride (cBN) has long been used to create superhard tool materials [1, 2] due to its high hardness (up to 60 GPa) and chemical inertness with respect to many steels, which makes it valuable for cutting tools [3]. The most commercially known cBN-bonding systems are cBN-Al, cBN-TiC (TiCN), and cBN-Co&Al.

The main problem in high-speed machining of parts for these cutting materials is chemical wear, where temperatures in the cutting zone can reach up to 1000-1100 °C, leading to a decrease in strength and an increase in ductility of cubic boron nitride composites. One solution to this problem is to add inert components to the structure bonds, such as refractory carbides, borides, and nitrides of p- and d-elements. For cutting tools based on cubic boron nitride, the best wear resistance and service life for high-speed turning of Inconel 718 is achieved at a cBN content of 45-60% with ceramic bonds of Ti (C,N) or TiN.

Within the framework of the project "Development of the Center for Collective Use of the Institute of Materials Science of the National Academy of Sciences of Ukraine" (2023.05/0007, National Research Foundation of Ukraine), the structure and properties of superhard composite materials BL with a cBN content of 60 %, obtained in the cBN(Al)-SiB₄-WC system under high pressure and temperature, were investigated. The experiments were carried out  using the high-pressure apparatus "toroid-30".After reaching a pressure of 7.7 GPa, the composite material was sintered in the temperature range of 1600-2300 °C (time heater for 1 min). As a result, ceramic inserts, which were then ground with diamond wheels to achieve dimensions of d = 9.52 mm and h = 3.18 mm, in accordance with ISO 1832-2017 for cutting inserts - RNGN 090300T.

According to the X-ray phase analysis, the phase composition of the cBN(Al)-SiB₄-WC system composites does not change significantly with sintering temperature. The main phase is cubic boron nitride (cBN), whose lattice period varies depending on the sintering conditions. At high temperatures, rhombohedral silicon boride SiB₄ decomposes, and as a result of its interaction with tungsten carbide WC, two new phases are formed: hexagonal tungsten boride W₂B₅ (a = 0.2993(2) nm, c = 1.395(1) nm) and tetragonal tungsten silicide WSi₂ (a = 0.3208(1) nm, c = 0.7841(3) nm). An excess of boron and carbon forms micron-sized clusters of B-C compounds. Aluminum, when added in small quantities, oxidizes to α-Al₂O₃, which prevents the oxidation of other components. Thus, the material is a ceramic-matrix composite consisting of cBN, W₂B₅, WSi₂, as well as B-C and α-Al₂O₃ compounds. Electron microscopy of the obtained material at a sintering temperature of 2000 °C showed that a homogeneous porous structure was formed. The density and Young's modulus of the ceramic increase with sintering temperature and reach their maximum values at 2000 °C. A further increase in temperature leads to annealing of defects, recrystallization of the structure, and partial graphitization of cBN, which worsens the material's characteristics. The materials obtained at 1800-2000 °C have the best physical and technical characteristics and are suitable for the manufacture of cutting inserts.

Thus, ceramic-matrix composites of the cBN(Al)-SiB₄-WC system form high-strength, porous materials with high physical and mechanical characteristics. Compounds of tungsten boride and silicide, as well as aluminum oxide, provide oxidation resistance, which makes them suitable for processing high-alloy steels at high temperatures.