Institute of Superhard Materials

1. It has been established that amorphous boron nitride (a-BN), obtained by a modified urea process in combination with thermomechanical treatment of the charge, is characterized by increased chemical activity – during the absorption of moisture from the open atmosphere, partial hydrolysis of the compound occurs, orthoboric acid H3 BO 3 , ammonium pentaborate NH 4 B5 O8 × 4H 2 O and ammonium nitrate NH 4 NO 3 are formed, which play a key role in the recrystallization of a-BN into cubic boron nitride (cBN). Therefore, the complete transformation with the formation of spatial segregations of cBN nanoparticles (crystals) at a pressure of 6.5 GPa and a temperature of 1400 °C occurs within 45 s, which is the basis for the development of a technology for the synthesis of nanodispersed cBN powders with their subsequent use for sintering superhard materials I.A. Petrusha; D.Yardeni, O.Prilutsky, R.Shneck (Dan Yardeni associates Ltd., Ben-Gurion University, Israel;, N.M. Bilyavina (Taras Shevchenko National University of Kyiv), O.S. Osipov, T.I. Smirnova.
2. The solubility of gallium nitride in the melt of the Fe-N system under conditions of high pressures (up to 8.3 GPa) and temperatures (up to 2100 ° C) was determined by the methods of measuring the mass of samples and local X-ray spectral analysis. It is shown that at a pressure of 6.8 GPa the limiting solubility of GaN increases from 8% (wt.) at 1750 ° C to 27% (wt.) at 2100 ° C, and at a pressure of 8.3 GPa – from 1% (wt.) at 1150 ° C to 29% (wt.) at 2000 ° C. Temperature dependence of the limiting solubility GaN is the scientific basis for the development of the process of crystallization of gallium nitride single crystals from melts of the Fe-Ga-N system. Ak. NAS of Ukraine V.Z. Turkevich, I.A. Petrusha, O.S. Osipov.
3. The kinetic features of the growth of diamond single crystals obtained by solution-melt crystallization in the region of thermodynamic stability were studied, using a six-punch high-pressure apparatus with a force of 28.5 and 48.5 MN and growth cells with a volume of 11.3 and 24 cm 3 , respectively, to obtain crystals weighing from 5 to 15 carats; the compositions of solvents based on Fe-Co with additives of Mg and Ti(Zr) were optimized to obtain structurally perfect single crystals of diamond type. It is shown for the first time that an increase in the growth rate by 2.5–3 times while maintaining the level of structural perfection of single crystals of type Ib, as well as mixed types Ib+IIa and Ib+IIb, is achieved by using a Fe-Co-Mg solvent with a magnesium content from 1.8 to 5.7 at. % by varying the growth conditions. Corresponding Member of the NAS of Ukraine S.O. Ivakhnenko, V.V. Lysakovsky, T.V. Kovalenko, A.V. Burchenya, O.O. Zanevsky.
4. The process of densification under the action of high pressure and high temperature of diamond powders synthesized in the Mg–Zn–C system, and the physical and mechanical properties of the obtained polycrystals have been studied. It is shown that sintering without additives of a mixture of synthesized diamond powders – with a grain size of 100/80 (40%) and finely dispersed with a diamond particle size of less than 40 microns at a temperature of 1800 ° C and a pressure of 8 GPa allows to achieve a densification degree of 98.7%, while the highest level of densification, which is achieved at a pressure of 8 GPa and high temperatures during sintering of diamond powders synthesized in systems based on iron group metals, is 96.8%. The hardness of the resulting polycrystal, determined at a load on the Knup indenter of 9.8 N, is 50.7 GPa, which is 67% of the hardness of a single crystal of natural diamond of type Ia (face (100)). O.O. Bochechka, O.I. Cherniyenko, O.V. Kushch, V.S. Gavrylova.
5. For the first time, thermobaric parameters of sintering in a high-pressure apparatus (HPA) of ceramic materials based on refractory compounds B4C, SiC, Si3N4, Al2O3 and ZrO2 have been determined, under which grain growth does not occur. This increases the hardness and wear resistance of the resulting materials, which can operate in extreme friction conditions. Tribological tests of sintered ceramic materials in highly loaded hybrid sliding and rolling friction pairs, carried out jointly with the Nanotribology Laboratory (NAU MES of Ukraine), showed the prospects of using two types of ceramics, namely boron carbide and silicon nitride. Experimental batches of ceramic balls made of B4C, SiC and Si3N4, produced by sintering in the AVT, were transferred to the Ivchenko-Progress Design Bureau for resource testing, and the manufactured ceramic rings made of reaction-sintered SiC will be tested at the Southern Plant of End Seals LLC for the assembly of NPP pumps. Corresponding Members of the NAS of Ukraine A.L. Maistrenko, V.G. Kulych, O.I. Borymsky, S.V. Sokhan, V.A. Dutka, O.U. Stelmakh.
6. A material based on the MAX phase Ti3AlC2 has been developed, during the synthesis of which, by reducing the pressing pressure and holding time, crystallization of solid inclusions of aluminum oxide is not allowed, which ensures a low coefficient of friction in a pair with copper. This made it possible to develop electrical contact inserts for tram and trolleybus pantographs, the wear of which, after undergoing experimental and industrial testing on the routes of the depot of LKP “Lvivelectotrans” under dry friction conditions, was 0.43 mm/1000 km with a total mileage of 7000 km, and which turned out to be 2.7 times less than the wear of traditional inserts made of aluminum alloy AK12 with lubrication, while the wear of the contact wire decreased by 9 times. Corresponding Member of NASU T. O. Prikhna (INM NASU), O.P. Ostash (FMI NASU V.B. Sverdun (INM NASU), V.Ya. Podgurska (FMI NASU), T.B. Serbeniuk (INM NASU).
7. The method of programmed thermal desorption was used to study the physicochemical characteristics of diamond grinding powders of the AC20 brand of magnetic and non-magnetic non-conductive fractions of grain size 100/90, obtained by distribution in magnetic and electric fields. It was shown that the surface of all samples is covered with a large number of OH groups, which form water molecules in the process of desorption from the surface of diamond powders. The thermal desorption peaks of water have a symmetrical shape and are observed in the entire studied temperature range. At the same time, a lower water content was recorded on the surface of diamonds of the non-magnetic non-conductive fraction with a smaller specific surface area. O.B. Loginova, G.D. Ilnytska, I.M. Zaitseva, V.V. Timoshenko.
8. It was established that that the use of high pressures (4 GPa) for sintering ZrB 2 -SiC powders allows obtaining a composite heat-resistant material (melting point higher than 2200 ° C, specific gravity 5.09 g/cm 3 ) with increased, in comparison with the best world analogues, hardness (Hv (9.8H) = 25.4 ± 0.7 GPa compared to 17.6 ± 0.5 GPa) and crack resistance (K 1C (49 H) = 7.8 MP m 0.5 compared to 7.5 MP m 0.5 ). Corresponding Members of the NAS of Ukraine T. O. Prikhna, A. S. Lokatkina, O. I. Borymsky, V. Ye. Moshchil.