UDC 621.921.34:548.736.15
T. V. Kovalenko, S. A. Ivakhnenko (Kyiv)
Properties of diamonds grown on a seed in the magnesium–carbon system
The features of diamond growth on a seed in the Mg–C growth system at p ≤ 8.2 GPa and T = 1800–2000 °C were studied. The grown diamonds were studied by Raman, photoluminescence and IR spectroscopy. It was shown that the single crystals obtained in this system are conditionally nitrogen-free of type IIa + IIb. The reasons for the capture of the main impurities – boron and silicon – were considered.
Keywords: diamond single crystals, magnesium-based systems, seed, silicon, boron.
UDC 661.689
A. A. Sivkov, D. S. Nikitin, A. Ya. Pak, I. A. Rakhmatullin (Tomsk, Russia)
Production of ultradispersed crystalline silicon carbide by plasmadynamic synthesis
Direct plasmadynamic synthesis of ultradispersed cubic silicon carbide β-SiC was implemented under the action of a supersonic pulsed jet of carbon-silicon electric discharge plasma on a copper barrier in an argon environment. A powder product with a high content of β-SiC was obtained, the single crystals of which with an average size of ~ 100 nm have a regular natural faceting.
Keywords: plasmadynamic synthesis, ultradispersed silicon carbide, X-ray diffractometry, transmission electron microscopy.
UDC 666.233
V. Yu. Dolmatov (St. Petersburg, Russia)
V. Myllymäki (Helsinki, Finland)
A. Vehanen (Vantaa, Finland)
A Possible Mechanism for the Formation of Nanodiamonds during Detonation Synthesis
A new mechanism for the formation of nanodiamond particles during detonation synthesis is proposed according to the following scheme: the decomposition of trinitrotoluene molecules into basic radicals – a radical-like dimer of C2 and CH3•, hexogen molecules – into C2, benzotrifuroxane molecules – into C2; the formation of cyclohexane from C2 or directly from adamantane molecules in a radical form; the interaction of the diamond-like core (adamantane radical) with the dimer of C2 and with methyl and other monocarbon radicals; the growth of detonation nanodiamond particles is similar to the CVD process. It is shown that the nucleation of radical-like adamantane molecules occurs in the range from the middle of the chemical spike zone to the Chapman-Jouguet plane, while diamond particles grow simultaneously, their growth is completed at the initial stage of isentropic (Taylor) expansion of gaseous detonation products capturing solid carbon particles.
Keywords: formation mechanism, shock wave, chemical spike zone, detonation nanodiamonds, radicals, cyclohexane, adamantane.
UDC 548.74:681.723
A. P. Chepugov (Kyiv)
A. N. Chaika (Chernogolovka, Moscow region, Russian Federation)
V. I. Grushko, E. I. Mitskevich, O. G. Lysenko (Kiev)
Boron-doped diamond single crystals for high-vacuum tunneling microscopy probes
The article presents the results of studies of the structure of diamond single crystals grown by the temperature gradient method in order to obtain samples with the most uniform characteristics for the manufacture of probes for scanning probe microscopes of a given axial orientation and with a controlled distribution of the dopant. The use of such probes in scanning tunneling microscopy reduces the probability of occurrence of random tunneling channels involving surface states associated with the presence of boron atoms in the diamond structure and increases the reliability of experimental data. The results of the study of the graphite surface (0001) by scanning tunneling microscopy demonstrate the high stability of single-crystal diamond probes and the possibility of achieving atomic resolution with their help.
Keywords: scanning probe microscope, SPM probe, semiconductor diamond, high-vacuum tunneling microscopy.
UDC 621.726:669.018.45:533.92
S. N. Dub, G. P. Kislaya, P. I. Loboda (Kyiv)
Study of mechanical properties of a LaB6 single crystal by nanoindentation
The nanoindentation method was used to study the specifics of the elastic-plastic transition in a lanthanum hexaboride single crystal with deformation localization in the submicron region both at low (cleavage) and high (mechanical polishing) dislocation density in the sample. During tests on a single crystal cleavage along the cleavage plane (001), a sharp elastic-plastic transition (pop-in) was observed as a result of homogeneous nucleation of dislocations in the contact area at shear stresses close to the theoretical shear strength of LaB6. After mechanical polishing, the elastic-plastic transition upon indentation occurred smoothly as a result of the movement and multiplication of dislocations already existing in the contact area. Strain hardening of the sample surface caused an increase in hardness by 5 GPa at an indentation depth of 120 nm.
Keywords: LaB6, sapphire, nanoindentation, elastic-plastic transition, theoretical shear strength.
UDC 621.941
N. E. Stakhniv (Kyiv)
Study of the effect of cutting modes on the roughness of the machined surface during finish turning of hardened steels with cutters made of a CBN-based composite
The results and research of the process of finishing turning of hardened steel KhVG with a tool equipped with a round cutting plate made of a composite based on cubic boron nitride (system cBN–Si3N4). Based on the analysis of the roughness of the machined surface, cutting modes were established that ensure stable conditions for the interaction of the cutting tool with the workpiece.
Keywords: turning of hardened steels, round cutting plate, composite based on CBN, roughness of the machined surface.
UDC 621.922.34:615.477.2
E. A. Pashchenko, S. E. Sheikin, D. V. Efrosinin, A. N. Chernenko, R. V. Milotsky (Kyiv)
Tool for precision diamond processing of spherical heads of endoprostheses made of pure titanium
Abrasive composites based on modified epoxy resins and synthetic diamonds have been developed. They are three-level adaptive systems that allow processing of commercially pure titanium without setting. The tool containing these composites made it possible to create an effective technology for manufacturing hip joint endoprosthesis heads from commercially pure titanium.
Keywords: hip joint endoprosthesis head, abrasive composites, commercially pure titanium.
UDC 621.9.014
A. A. Vinogradov (Kyiv)
On the calculation of cutting forces and characteristics of contact interaction of chips with the tool when cutting ductile metals
Based on a comparative analysis of experimental and calculated by two different dependences of cutting forces, it is shown that the tangential stresses in the conditional shear plane during chip formation are equal to the actual tensile strength of the metal being processed during its mechanical testing. Methods are proposed for estimating forces and stresses separately on the areas of plastic and elastic contact of chips with the tool, as well as a number of other characteristics of chip formation, based on the measured shrinkage of chips Kl. It is proposed to determine the angle of action of the cutting force as the sum of the angles ω = (p /4 – Ф) + Δω, where Δω decreases with an increase in the rake angle of the tool at γ ≥ 0, but has virtually no effect on the accuracy of estimating the main component of the cutting force Pz. Examples of determining the cutting force when machining grades 10 and 08Kh18N10T steels with a tool with γ = 0 and 20° are given.
Keywords: metal cutting, tool, positive rake angle, cutting forces, chip formation, calculation of forces and stresses.
UDC 558.21
N. V. Novikov, Yu. N. Krivosheya, L. K. Shvedov (Kiev)
Accuracy of diffraction patterns obtained on an X-ray diffractometer using the Dobrovolsky-Shvedov method in a cell with diamond anvils
An analysis of the accuracy of diffraction patterns obtained on a DRON-3 X-ray diffractometer using the Dobrovolsky-Shvedov method in a cell with diamond anvils was carried out. The samples were conventional reference materials – polycrystalline silicon and NaCl, and long-term stability was tested on a steel sample.
Keywords: X-ray diffraction analysis, diffractometer, diffractogram, diamond anvil cell.