Journal of Superhard Materials最新文献

As a result of studying the regularities of interaction between polishing powder wear and sludge nanoparticles during the polishing of polymer optical materials by disperse systems of micro- and nanopowders on the basis of ab initio calculations according to the quantum scattering theory, it has been established that polishing powder wear nanoparticles are elastically scattered on sludge nanoparticles exclusively at angles of 0° and 180° over the differential scattering cross section 10⁴–10⁵ times larger than for other angles. It has been shown that the total cross section for the scattering of wear nanoparticles on sludge nanoparticles exponentially decreases with an increase in their average size and grows with increasing concentration. When the polymer materials are polished with disperse system DS1, the total cross section for the scattering of wear nanoparticles on sludge nanoparticles exponentially decreases with an increase in the quality factor of a resonator. When disperse system DS2 is used, the total cross section for the scattering of wear nanoparticles of sludge nanoparticles is independent of the quality factor of a resonator. It has been shown that the formation of a deposit from polishing powder wear particles on the surface of a part is most probable at maximum total scattering cross sections. It has been experimentally established that a deposit in the form of a film with a thickness of 1.5 and 0.3 µm completely or partially coats the surface of a part when polystyrene or polyallyl diglycol carbonate is polished with disperse system DS2.

Abstract—We review the state-of-art and optimization of powder synthesis methods and manufacturing technologies for high-entropy diborides. The process of producing dense materials has been assessed, and a forecast of the direction of their development has been proposed.

In the process of face grinding under multipass and plunge-feed treatment conditions, the cutting surface of a wheel sustains radial transformation. If the critical grinding rate is attained when the cutting surface of a wheel has no reserves for growth, a further increase in the grinding rate leads to the abrupt wear of wheels. Since the cutting surface area of a wheel is further stable, there may be the phenomenon of lagging in the values of grinding wheel performance characteristics, if the grinding rate is decreased at such a stable surface area. Such a lag is observed for the wheel wear, specific energy consumption, and effective grinding power, but not for the roughness parameters. It has been shown that the cutting surface of a wheel can be adjusted to the critical grinding rate when the cutting surface area attains a maximum for further operation with lower critical losses in the grinding rate to reliably ensure a decrease in the wheel wear and grinding energy consumption.

The results of thermodynamic modeling of superhard materials based on cubic boron nitride (cBN) with a tantalum nitride (TaN) binder and additions of aluminum, as well as microfibers of various physicochemical nature (oxide (Al₂O₃, Mg₂B₂O₅) and non-oxide (SiC, Si₃N₄)), are presented. The theoretically calculated chemical interactions between the components of superhard composite materials are experimentally verified. The chemical nature of the microfibers significantly affects the reaction interaction between the cBN matrix material and TaN binder in the presence of liquid aluminum, resulting in the formation of tantalum boride.

Nano- to micrometre-sized overgrowths on the (0001) surface of impact apographitic diamond were characterized. The structures are documented as octahedra, occasionally cubes, their contact and penetration twins, and irregular intergrowths. The internal of these overgrowths structures and their chemical composition were studied. Their postulated globular structure and block growth mechanism published earlier were disproved. A mechanism for the formation of these overgrowth structures is presented.

The study reveals that the structure of Cr₂O₃–22 wt % Cr cermet, obtained from a mixture of chromium oxide and chromium by spark plasma sintering at a temperature of 1520°C and a pressure range of 40–300 MPa, consists of a chromium oxide matrix with globular 0.5- to 20-μm Cr inclusions, comparable in size to the particles of the initial mixture. At pressures ranging from 300 to 800 MPa, elongated inclusions appear in the structure, the concentration of which increases with the rise in pressure during spark plasma sintering, leading to a decrease in globular grain size. The cermet exhibits maximum Vickers hardness and crack resistance values, determined by the Palmqvist method at 20.2 GPa and 7.6 MPa m^1/2, respectively. Its stability under intermittent dry cutting with 9Kh12F steel (HRC 58–60) is comparable to ceramics based on Al₂O₃–TiC from Sandvik Coromant (Sweden).

The synthesis of diamond was performed at a pressure of 8 GPa and a temperature of 1700°C in the Mg–Zn–C system and, after the product was chemically purified, the resulting diamond powder was classified by grain sizes. The effect produced by the ratio between coarse and fine diamond powder fractions and the sintering parameters on the structure and physicomechanical properties of sintered diamond polycrystals was studied. The wear resistance of synthesized samples was investigated when turning a cylindrical X drillability granite core sample from the Korostyshiv deposit. The high-pressure sintering of a mixture of synthesized coarsely and finely dispersed diamond powders was shown to provide a 2.46-fold decrease in the residual porosity as compared to sintering under the same pressure for the diamond powders synthesized in the systems based on iron group metals. Among the resulting polycrystalline samples, the highest hardness determined at a Knoop indenter load of 9.8 N was 66 GPa to attain 87% from the hardness of natural type Ia diamond single crystal (face (100)). Polycrystalline diamond elements sintered in a Toroid 30 high-pressure autoclave at a pressure of 8 GPa and a temperature of 1780°C from the purified product of synthesis in the Mg–Zn–C system with a diameter of 15 mm and a height of 3 mm demonstrated the highest wear resistance, which was 5.6–10.9 times higher than for the reference specimen sintered from the powder synthesized in the Ni–Mn–C system.

The structure, mechanical characteristics, and high-temperature stability in vacuum and air of ZrB₂ and HfB₂-based materials sintered at a high quasi-hydrostatic pressure (4.1 GPa) under hot pressing (at a pressure of 30 MPa) with and without SiC and Si₃N₄ additives have been studied. It has been shown that short-term sintering (4 min) under high pressure conditions and at a comparatively low temperature (1800°C) essentially improves the mechanical properties of these materials as compared to the similar materials synthesized by the other method (hot pressing and spark-plasma sintering). In the case of sintering at a high pressure (4.1 GPa), the addition of 20 wt % SiC to ZrB₂ and 30 wt % SiC to HfB₂ leads to a decrease in the specific gravity of ZrB₂ and HfB₂ and increases their hardness by 17 and 46% and fracture toughness by 40 and 21%, respectively. When SiC is added, there occurs the formation of solid solutions through the mutual diffusion of C and Si into the ZrB₂ or HfB₂ matrix phases and the slight diffusion of Zr and Hf into SiC-enriched areas. The improvement of the mechanical properties of ZrB₂ and HfB₂ sintered at a high pressure without additives is explained by the formation of stronger bonds between the sintered material grains. The addition of SiC to ZrB₂ slightly decreases the Young modulus, but increases the damping ability of the synthesized materials. The simultaneous addition of SiC and Si₃N₄ to ZrB₂ leads to an increase in the hardness to a smaller extent, but results in a further increase in fracture toughness. The melting temperature in vacuum of sintered ZrB₂ and HfB₂ has proven to be much higher as compared to the materials with SiC additives. The composite material synthesized from a HfB₂–30 wt % SiC mixture has a density ρ = 6.21 g/cm³, a microhardness H_V(9.8 N) = 38.1 ± 1.4 GPa, H_V(49 N) = 27.7 ± 0.24 GPa, H_V(98 N) = 26.3 ± 2.03 GPa, and a fracture toughness K_Іс(9.8 N) = 8.2 ± 0.2 MPa m^0.5, K_Іс(49 N) = 6.8 ± 0.6 MPa m^0.5, K_Іс(98 N) = 6.4 ± 0.11 MPa m^0.5, which are much higher than the similar characteristics of HfB₂ sintered under the same conditions, but without the additives.

As a result of studying the regularities of interaction between sludge nanoparticles with polishing powder wear and lap nanoparticles during the polishing of polystyrene, polymethylmethacrylate, and polyallyl diglycol carbonate by the dispersed systems of micro- and nanopowders on the basis of ab initio calculations in compliance with the quantum scattering theory, it has been established that sludge nanoparticles are elastically scattered on wear nanoparticles. The differential scattering cross section has a maximum at scattering angles of 0° and 180° to exceed the maximum value for the other angles by 2 × 10⁴–5 × 10⁴ times. It has been shown that sludge nanoparticles move in the process of polishing along the optical resonator axis between the treated surface and the lap surface to be scattered only forward and backward. It has been established that the total scattering cross section of sludge nanoparticles exponentially grows with an increase in their concentration and essentially decreases with an increase in the size and kinetic energy of nanoparticles. When the resonator Q factor is increased from 7.9 to 105.5, the total scattering cross section of sludge nanoparticles exponentially decreases from 120.8 to 0.6 Mb. It has been demonstrated that the calculated total scattering cross sections of sludge nanoparticles correlate with a high degree of accuracy with the experimentally determined rate of material removal under polishing.