UDC 661.65:661.55
S. N. Dub, R. S. Shmegera, I. K. Zasimchuk (Kyiv)
Yield strength in submicrovolumes of single crystals
The nanoindentation method was used to study the specifics of the transition from elastic to elastic-plastic deformation in defect-free single crystals with deformation localization in the submicron region. For the tested single crystals, an abrupt transition from elastic to elastic-plastic deformation was observed at depths of about 20-50 nm. To find the yield strength from nanoindentation data, an analysis of the stress-strain state in the contact area was used. It was shown that the yield strength in submicrovolumes of single crystals is tens to hundreds of times greater than their yield strength at the macroscopic level and approaches the theoretical elastic shear limit. Within the framework of the phenomenological model of dislocation nucleation, the mechanism of transition from elastic to elastic-plastic deformation is discussed. It is shown that the transition is caused by homogeneous nucleation of dislocations in the contact.
Keywords: nanoindentation, yield strength, theoretical strength.
UDC 621.921.34; 666.233.004.14
V. A. Mukhanov, A. A. Kurakevich, V. L. Solozhenko (Paris)
Interrelation of hardness and compressibility of substances with their structure and thermodynamic properties
A strong correlation dependence is established between the structure and specific Gibbs free energy of atomization of a substance, on the one hand, and its hardness and volume compressibility, on the other hand. Within the framework of the proposed model, hardness is directly proportional to the specific free energy per bond in isodesmic crystals. The introduction of a correction factor for the ionic component of chemical bonds allows us to estimate the hardness of compounds with both covalent (polar and non-polar) and ionic bonds. Within the framework of the proposed approach, it was possible for the first time to correctly calculate the dependence of hardness on temperature using diamond and cubic boron nitride as an example.
Keywords: hardness, compressibility, structure, thermodynamic properties, Gibbs free energy, diamond, cubic boron nitride.
UDC 544.31:621.762
A. F. Lisovsky (Kyiv)
Thermodynamics of the interaction of an ensemble of nanoparticles with a macrophase
An expression is obtained that describes the change in the Gibbs potential for a system consisting of an ensemble of nanoparticles and a macrophase. It is shown that in such a system, diffusion flows of matter from nanoparticles to the macrophase take place. The conditions under which a nanoparticle or an ensemble of nanoparticles can be in an equilibrium state and retain their size and shape for an indefinite period of time are determined.
Keywords: thermodynamics, nanoparticle, macrophase.
UDC 666.3:539.5
T. B. Serbenyuk, L. I. Aleksandrova, M. I. Zaika, V. V. Ivzhenko, E. F. Kuzmenko, M. G. Loshak, A. A. Marchenko, T. O. Prikhna, V. B. Sverdun, S. V. Tkach, O. I. Borimsky, I. P. Fesenko, V. I. Chasnik (m. Kiev)
M. Wendt (m. Jena, FRN)
Structure, mechanical and functional properties of aluminum nitride-silicon carbide ceramic material
By the method of high sintering, two-phase ceramic composites of the dielectric-conductor type with different types of conductor phases were produced – ceramics based on aluminum nitride in one phase divisions of silicon carbide inclusions of fine size. Such composites are characterized by Vickers hardness HV (150 N) 9.5–15.8 GPa, Palmquist fracture toughness 3.0–4.2 MPa∙m0.5, bending strength 132–209 MPa, thermal conductivity 37-82 W/(m∙K), attenuation coefficient of micro-electromagnetic energy up to 36.3 dB/cm. It has been established that due to the larger grain size of the silicon carbide phase in ceramics based on aluminum nitride, thermal conductivity increases and the attenuation of microconductor energy changes, It is important to note the vital role of grain boundaries when scattering both phonons and microviolet vibration on them.
Key words: composites, AlN, SiC, microstructure, hardness, crack resistance, thermal conductivity, attenuation of electromagnetic energy.
UDC 621.9.047.666.792
B. Staniewicz-Brudnik (Kraków, Poland)
S. Szarska (Wroclaw, Poland)
K. Gamrat (Kraków, Poland)
The influence of mechanochemical treatment of sintered submicrocrystalline corundum substrates on the structure of bioglass composites
The influence of mechanochemical treatment of submicrocrystalline sintered corundum on the structure of bioglass composites containing a-Al2O3 and CaO–SiO2–P2O5 glasses was examined in the context of the possibility to form hydroxyapatite after being immersed in the simulated body fluid solution. Measurements of specific surface area and size and X-ray analysis of submicrocrystalline sintered corundum were conducted. Bioglass composites were obtained by placing submicrocrystalline sintered corundum grains in the CaO—SiO2—P2O5 sol system, gelling and sintering at 800 °C. The specimens were examined under a scanning electron microscope before and after immersion in the simulated body fluid solution for 24 and 120 h. Using the VCS algorithm, calculations of thermodynamic stability of compounds occurring in these bioglass composites were carried out, verifying the X-ray analysis.
Key words: mechanochemical treatment, submicrocrystalline sintered corundum, bioglass composite, hydroxyapatite, SBF, SEM, VCS algorithm.
UDC 661.666.2:620.197
Yu. O. Nikitin, I. G. Chernish, V. V. Zaporozhets (m. Kiev)
Features of the structure of modified thermally expanded graphite
Experimental data on the microrelief, elemental storage and distribution of the modifier along the surface of thermally expanded graphite were provided. The morphological changes of thermo-expanded graphite particles under the influence of temperature and changes in the distribution of the cluster structure of the modifier on the surface of the thermo-expanded graphite particles depending on the concentration of the output modifying agent are shown.
Key words: thermal expansion graphite, microrelief, elemental storage, structure, modifier.
UDC 539.2
V. I. Kovtun, Ya. V. Zaulichny, A. Yu. Garmash,
O. N. Grigoriev, V. M. Volkogon (Kiev)
X-ray emission СKα spectra of tungsten carbides before and after shock-wave treatment
The method of X-ray ultra-soft emission spectroscopy was used to study the СKa spectra of hexagonal tungsten carbide subjected to shock-wave treatment in a three-loop device at a pressure in the detonation wave front of ~ 20 GPa (with an increase in each subsequent circuit) and a detonation velocity of 7300 m/s. It was found that changes in the WC spectra after shock-wave treatment in the first circuit indicate the formation of vacancies with the release of free carbon on the surface and its amorphization, in the second – partial formation of a diamond-like film on the surface, in the third (at maximum pressure) – the emergence of a metastable state. Comparison of the CKa spectra with theoretical calculations allows us to explain the mechanisms of tungsten carbide stabilization by changing its electronic structure under the action of shock-wave treatment.
Keywords: tungsten carbide, shock waves, CKα spectra, X-ray emission, Cp states, energy distribution.
UDC 679.8
V. I. Sidorko, V. V. Peglovskiy, V. N. Lyakhov (Kyiv)
The influence of silicon oxide content in natural stones on their strength properties, diamond grinding productivity and power consumption
The influence of silicon oxide content in natural stones on their Mohs hardness, uniaxial compressive strength, microhardness, diamond grinding productivity and power consumption during grinding was studied. It was shown that an increase in the content of this component in the composition of natural stones affects the strength properties and the power consumed during processing, and also significantly affects the productivity of diamond grinding.
Keywords: silicon oxide, natural stones, diamond grinding, strength properties, hardness, compressive strength, productivity, power consumption.
UDC 621.9:621.923
V. I. Lavrinenko, M. N. Sheiko, E. V. Dabizha, I. V. Bondar, P. I. Bologov, A. G. Lubnin (Kyiv)
The influence of ion-plasma coatings on the performance properties of diamond dressing tools
The influence of ion-plasma coatings on the performance properties of diamond dressing tools under diamond-abrasive machining conditions is studied. It is shown that a promising way to improve the efficiency of dressing tools manufactured by electroplating and electroforming methods is the use of thick wear-resistant coatings of titanium nitride and carbide with compensating layers of plastic metal (cobalt).
Keywords: ion-plasma coatings, diamond layer, dressing tool, titanium carbide, titanium nitride, cobalt.
UDC 541.1:546.46
V. Z. Turkevich, A. V. Kozyrev, P. A. Nagorny (Kiev)
Phase diagram of the Mg-O system at a pressure of 2 GPa
Thermodynamic calculation and experimental studies of phase equilibria in the Mg-O system were performed, and a phase diagram of this system at a pressure of 2 GPa was constructed. The system is characterized by the presence of only one eutectic equilibrium at 1100 K, which involves magnesium, magnesium oxide MgO and a liquid phase.
Keywords: phase diagram, thermodynamic calculation, phase equilibrium, eutectic equilibrium, liquid phase, Gibbs energy.
UDC 546.27:539.533
V. L. Solozhenko, A. A. Kurakevich (Paris)
A. R. Oganov (Zurich)
On the hardness of a new boron phase — orthorhombic g-B28
The hardness of a new high-pressure boron phase — orthorhombic g-B28 — was studied. According to the obtained data, g-B28 has the maximum (~ 50 GPa) hardness among the known crystalline modifications of boron.
Keywords: orthorhombic boron, hardness.