UDC 546.25-162:536.42
V. V. Danilenko (Kiev)
Energy of detonation nanodiamond particles
Based on the study of the balance of internal and surface energies of detonation nanodiamond particles, the boundaries between micro- and nanoparticles and the boundaries by particle sizes between the regions of existence of detonation nanodiamond particles with an amorphous shell and without a shell were determined, the dependences of the onset temperature of volume and surface graphitization of detonation nanodiamonds on the size of their particles were calculated. Based on these estimates, the oxidation process of detonation nanodiamonds in air was analyzed. The issue of the minimum stable size of detonation nanodiamond particles is discussed.
UDC 548.74+681.723
O. G. Lysenko, N. V. Novikov, A. G. Gontar, V. I. Grushko, S. N. Ivanov, A. A. Shcherbakov (Kyiv)
Semiconductor diamond tip for combined scanning probe microscopy
The article presents methods for selecting synthetic semiconductor diamond single crystals for the tip of scanning probe microscopy, the technology for manufacturing nanoprobes, and the results of their combined use in scanning and indenting surfaces. It is shown that ensuring the stability of the shape of the conductive tip of scanning probe microscopy is possible due to the use of a nanoprobe made of semiconductor diamond. Taking into account the technological conditions of diamond processing and nanoprobe manufacturing, the selection of initial semiconductor diamonds of octahedral habit is performed. A technology for manufacturing semiconductor diamond nanoprobes with a tip in the form of a Berkovich pyramid has been developed. Based on the analysis of the general dependence of the tunneling current as a function of the scanning parameters, as well as the tip and sample materials, the optimal modes of the surface scanning parameters by a semiconductor nanoprobe have been determined. The results of experimental studies of test gold samples for indentation and surface scanning at the nanoscale level are presented.
UDC 669.018.25:620.22
V. P. Bondarenko, M. G. Loshak, L. I. Aleksandrova, V. N. Tkach, S. V. Tkach, V.P. Botvinko, E.V. Vertsanova (Kyiv)
On the nature of distribution of chromium and tantalum in tungsten hard alloys with microadditives of their carbides
A decrease in the average grain size of tungsten carbide in tungsten hard alloys during sintering was confirmed when alloyed with microadditives of chromium and tantalum carbides. Tantalum was not detected in the cobalt binder phase, but was concentrated along the intergranular and interphase boundaries, while the main amount of chromium introduced as carbide is in the binder phase.
UDC 548.39:539.2
N. A. Bondarenko, O. G. Kulik, V. A. Mechnik (Kyiv)
Study of the interaction of CrB2 and W2B5 borides with components of the hard alloy WC—6Co
The interaction of CrB2 and W2B5 borides with components of the hard alloy WC—6Co under heating conditions up to 1300—1600 °C was studied. It was shown that when heating pressed mixtures of WC—6Co with these substances, their interaction occurs, leading to the formation of new phases, both equilibrium and nonequilibrium for a given composition.
UDC 621.762.4.045-669.018.95
A. I. Tolochin, A. V. Laptev (Kiev)
Structure and properties of WC—36 Co composite obtained from ultrafine mixtures of WC+Co and WC+Co3O4 powders
The processes of compaction, structure formation and mechanical properties of WC—36 ‰ (by weight) Co alloy obtained from ultrafine mixtures of powders, in which metallic cobalt was used as the initial component in one case and cobalt oxide in the other, were studied. Compaction was carried out by high-energy hot pressing in a wide range of temperatures mainly in the solid phase. The processes of oxygen removal or metal reduction from the oxide and compaction under high pressure were combined in one stage. The possibility of obtaining dense and strong composite samples at low (1150—1250 °C) temperatures was shown. The main fundamental difference in obtaining a tungsten-cobalt alloy from two mixtures is the slowing down of the compaction and structure formation processes in the solid-phase sintering region in the case of using a carbide-oxide mixture. Higher mechanical properties are achieved on samples from a carbide-metal mixture during compaction in the solid phase, while a finer-grained and more homogeneous structure is realized on samples from a carbide-oxide mixture. UDC 621.762.5:669.018.25
N. M. Prokopiv, V. P. Bondarenko, O. V. Kharchenko, I. A. Gnatenko (Kyiv)
The effect of thermocompression treatment on the structure and properties of the WC-8Co alloy with Cr3C2 additives
The results of a study of the effect of thermocompression treatment under a gas pressure of 3 MPa on the structure and properties of an alloy with a composition in ‰ (by weight) WC-8Co containing up to 1 ‰ Cr3C2 are presented. It is shown that thermocompression treatment increases the ultimate strength of the alloy in bending due to a decrease in porosity.
UDC 537.362:553.65
I. Kh. Abdukadyrova (Tashkent)
On the patterns of the radiation effect of modifying the electrical properties of corundum
The laws of uniformity of the change in the radiation effect of modification of the electrical properties of corundum crystals as a function of temperature (within 25-400 °C) and the absorbed dose of ionizing radiation (105-108 rad). In particular, a nonlinear dependence of the radiation effect was established for the electrical conductivity and the dielectric loss tangent of the crystals, which has some features in the form of extremes and kinks in the curves. Anomalies in the form of a minimum in the region of 100-200 °C and about 400 °C were revealed for the electrical conductivity. An extreme change in the radiation effect and the appearance of a maximum (200 °C) located near the induced peak of losses were found for the dielectric loss tangent. An increase in its amplitude with increasing field frequency and the absence of a shift in location towards high temperatures were shown. The discovered maximum may be a consequence of the superposition of two mechanisms that determine the features of the temperature dependence of dielectric losses and may be due to relaxation polarization. UDC 621.921.34-492.2
N. V. Novikov, G. F. Nevstruev, G. D. Ilnitskaya, V. I. Kushch, V. N. Kolodnitsky (Kyiv)
Quality Assessment of Superhard Material Powders. Part 2. Practical Application of a New Method for Assessing Quality Characteristics
The practical application of the developed universal method for assessing the quality of superhard material powders for analyzing the main characteristic — static strength — is considered. Using the example of synthetic diamond powder grade AC80 with a grain size of 315/250, the weighted average strength indicator, its homogeneity, and powder composition by strength are determined, and the sorting process is simulated and the production of powders with higher homogeneity in strength is predicted. Based on the developed principles, a computer program for assessing the strength characteristics of superhard material powders is created. An experimental verification of the developed program for calculating the strength characteristics of diamond powders of grades AC125 with a grain size of 400/315 and AC6 with a grain size of 160/125 was carried out.
UDC 621.73.011
O. A. Rosenberg, E. A. Pashchenko (Kiev)
Study of the structural features of powder media subjected to cold stepwise plastic deformation
The article presents the results of a study of the evolution of the structure of porous media (compacts based on iron powders) in the process of cold stepwise plastic deformation. The qualitative differences of the stepwise compaction process, in which only a certain part of the compaction volume is loaded at any one time, from conventional axial pressing based on simultaneous loading of the entire volume are analyzed. Experimental data on the formation of unusual substructures in porous media with increased permeability in the process of cold stepwise plastic deformation are presented. The differences in the structure of interparticle contacts in compacts obtained using different compaction schemes are analyzed.