Rumiantseva Y. The development of wear-resistant cBN-based composite materials, reinforced by the refractory compounds whiskers, for cutting tools

The dissertation is devoted to the establishment of regularities of influence of chemical composition, morphology of additives and production technology on structure formation and properties of cutting materials with low cBN content. The paper considers the scientific and technical principles of cBN-based composites formation (BL group) as working elements of a wear-resistant cutting tool for high-speed processing of high-alloy iron-based alloys. The interactions of components during sintering under high pressure of composites based on cBN and structural features of polycrystalline materials based on cBN (PsBN) are considered. The advantages of new connections (TaN, NbN) in comparison with those traditionally used for the production of instrumental materials based on cBN of the BL group (TiC, TiN) was showed. The main mechanisms of tool wear based on cubic boron nitride analyzed and it showed that chemical and oxidative wear of the cutting tool prevails in the conditions of high-speed turning. The influence of the whisker’s chemical nature on the phase composition and composites properties showed. It is shown that if the sintering parameters are optimized, the addition of microfibers to samples with TaN bond leads to an increase in both hardness (from 20–25 GPa for non-reinforced to 25–40 GPa for reinforced) and crack resistance (from 2.0–2, 2 to 3.6–4.0 MPa • m1/2 for an indenter load of 24.5 N). For the first time, the presence of self-reinforcement mechanisms in the cBN – TaN – Al – SiCw and cBN – TaN – Al – Si3N4w systems was established. For the first time, the influence of additive morphology on oxidation resistance, electrical conductivity and efficiency of a cBN-based cutting tool with NbN bond sintered at the optimal sintering temperature (2000 ° C) shown, and their relationship was revealed. It is shown that obtained cBN-based samples with NbN binder have high values of hardness, crack resistance, modulus of elasticity (E = 587 - 670 GPa, HV = 23 - 28 GPa, K1C = 5.56 - 7.05 MPa • m1/2) in combination with the magnitude and nature of the conductivity. These facts point, that the obtained ceramic matrix composites can be promising in industries such as nuclear physics and the nuclear industry. The obtained composites tested at the enterprise "Ivchenko-PROGRESS", samples of composites of cBN-NbN-Al-Al2O3w and cBN-NbN-Al-SiCw systems received a positive assessment for further implementation in the iron-based alloys processing