UDC 544.34:539.89
A. A. Kurakevich (Kyiv)
Superhard phases of simple substances and binary compounds of the B—C—N—O system: from diamond to the latest results (review)
The main known and hypothetical single (single-element) and double (two-element) phases of the B—C—N—O system are described, both superhard with diamond and boron structures, and precursors for their synthesis. Attention is paid to their structure, main mechanical properties, as well as a set of methods for recognition and characterization. For some phases recently described in the literature, the conditions for their synthesis at high pressures and temperatures are indicated.
Keywords: B—C—N—O system, diamond, boron, superhard materials, phase transformations, high pressures, high temperatures.
UDC 548.3:666.233
V. Yu. Dolmatov (St. Petersburg)
On the elemental composition and crystallochemical parameters of detonation nanodiamonds
A new method for detonation synthesis of nanodiamonds in the presence of strong reducing agents is described, and a method for determining their elemental composition is improved. New nanodiamonds can have an ideal crystal lattice, abnormally high purity (the amount of non-combustible impurities drops to 0.07 ‰ (by weight)), high carbon content, and their yield increases twofold. New nanodiamonds have one oxidation peak with atmospheric oxygen at ≈ 700 °C.
Keywords: detonation synthesis, carbon, nanodiamonds, crystallochemical parameters, crystal lattice.
UDC 539.4:661.657.5
V. T. Golovchan (Kyiv)
On the Strength of Polycrystals of Dense Modifications of Boron Nitride
An analytical algorithm for calculating stresses in grains of polycrystals of dense modifications of boron nitride is presented. The established relationships between the tensile and compressive strengths are based on the Griffiths fracture hypothesis for a biaxial stress state. The influence of technological residual thermal stresses on the strength of wurtzite boron nitride, which are formed in its grains during sintering at the cooling stage due to the anisotropy of thermal expansion, is taken into account.
Keywords: analytical algorithm, polycrystal, cubic boron nitride, wurtzite boron nitride, tensile strength, compressive strength.
UDC 539.4:620.2
V. I. Kushch, S. B. Polotnyak (Kyiv)
Structural-statistical model of a hard alloy with damage
An approach to constructing a micromechanical theory of hard alloy strength based on a combination of structural modeling and statistical theory of extreme values is proposed. Computational experiments on a structural model were conducted in order to construct a continuum theory of damage accumulation in a hard alloy and to clarify the parameters included in the criteria for the strength and durability of hard-alloy products. A relationship was established between the introduced parameter of microdamage and the Pisarenko-Lebedev static strength criterion. The possibilities of improving the proposed theory and its application in practical calculations of hard-alloy products for strength and durability are discussed.
Keywords: hard alloy, structural modeling, local stresses, damage accumulation, destruction, strength, statistical approach.
UDC 539.266
O. S. Roik, S. O. Lisovenko, V. M. Perevertailo, V. P. Kazimirov, O. B. Loginova (m. Kiev)
Modeling and analysis of the structure of Ni35Mn57C8 melt
An X-ray diffraction study was carried out on the Ni35Mn57C8 melt at 1300, 1400 and 1500 °C. From the extraction of experimental curves of the structure factor using the RMC method, a structural model of the melt at all follow-up temperatures was reconstructed. The local structure of the identified models was followed using the statistical-geometric Voronoi-Delaunay method. A new analysis of the structure of Ni92C8, Ni38Mn62 and Ni35Mn57C8 melts has been carried out. It is shown that when melted from Ni92C8 melt in Ni35Mn57C8 melt, carbon atoms may exhibit increased friability.
Key words: Ni–Mn melt, X-ray diffraction tracing, local order, pairwise division function.
UDC 621.623
Yu. D. Filatov, V. I. Sidorko, A. Yu. Filatov, S. V. Kovalev (Kiev), U. Heisel, M. Storchak (Stuttgart, Germany)
Surface roughness in finishing diamond abrasive machining
It is shown that the roughness of a polished surface depends on the ratio of the frequencies of natural oscillations of molecular fragments on the surfaces of the tool and the workpiece. The roughness of the machined surface is most influenced by the number of molecular fragments that make up the sludge particles, their most probable size, the frequencies of natural oscillations of the fragments of the workpiece and the workpiece, the thermal conductivity of the workpiece and the machining modes.
Keywords: surface roughness, polishing, sludge particles.
UDC 621.941
N. E. Stakhniv, L. N. Devin, I. A. Petrusha, A. S. Osipov (Kyiv)
Dynamic phenomena in finishing turning of hardened steels with a tool made of a composite based on CBN
The results of the study of the process of finishing turning of hardened steel KhVG are presented hardness of HRC 60-62 with a tool equipped with a round cutting insert made of a composite based on cubic boron nitride (cBN-Si3N4 system). The influence of technological processing modes on the components of the cutting force, the magnitude of vibrations, and the roughness of the machined surface is established. Practical recommendations for choosing the modes and conditions of processing are given.
Keywords: finishing turning, composite, cubic boron nitride, processing mode, cutting forces, roughness, vibration.
UDC 004.942:621.785:621.9.025.7
V. A. Dutka (m. Kiev)
Routine analysis of the results of hardening of a carbide cutter holder in various raw materials after induction brazing
The results of predicting the hardness and hardness of a hardened near-surface ball of a steel (steel 35KhGSA) carbide cutting tool holder when hardened in aqueous salts and bases, water and lubricants at different temperatures are presented. The importance of thermokinetic trajectories of cooling points on the surface of the holder in the first two mixtures and oils at room temperature has been shown very clearly. As a result of a numerical investigation of the hardening process in water at a temperature of 100 °C, the effect of a sharp increase in the fluidity of the cooling surface of the holder – 2-3 times – was revealed at the moment the cooling trajectory enters the region of phase transformation of austenite into bainite. For the final hardening of salts and bases in water, the functional importance of the material hardened to the maximum hardness of the near-surface ball of the holder at the freezing temperature is removed.
Key words: computer modeling, induction soldering, hardening, hardness, hardness of the hardened ball.