Journal of Superhard Materials最新文献

Based on the analysis of the established empirical relationship between elastic constants and melting temperatures for cubic pnictides of Group IIIa elements, the melting temperatures of hypothetical cubic BSb and BBi have been predicted. A critical review of the melting data for (super)hard cubic boron pnictides BX (X = N, P, As, Sb, Bi) has been performed, showing that their melting temperatures at ambient pressure, as well as their Vickers hardness, are linear functions of the pnictogen Mendeleev number.

The study is devoted to the electrodynamic properties of composite materials based on AlN–5 wt % C (carbon black) or AlN–5 wt % C (diamond powder) and 5% molybdenum in the frequency range of 1–10 GHz. The materials were obtained by free sintering at a temperature of 1850°C. The results demonstrate that the real and imaginary parts of the relative permittivity of the composites containing carbon black and diamond powder with molybdenum at a frequency of 10 GHz are ɛ' ≈ 16.1, ɛ'' ≈ 4.3 and ɛ' ≈ 9.3, ɛ'' ≈ 0.7.

The densification of boron carbide based powder mixtures under flash pressure sintering was modeled. The computer model developed for this purpose was based on the Skorokhod–Olevsky–Shtern porous material densification theory and takes into account the grain growth kinetics under sintering. The model parameters were determined from the results of laboratory and computational experiments. Model adequacy was confirmed by comparison with available experimental data.

Original carbon allotropes, orthorhombic C₈, C₁₀, C₁₂ and C₁₄ presenting mixed sp²/sp³ carbon hybridizations with C=C ethene-like and C=C=C propadiene-like embedded units are proposed from crystal engineering and calculations within the framework of the quantum density functional theory DFT. The carbon allotropes with topologies related with jeb, mog, as well as new topologies, show alternating tetrahedral and trigonal carbon stackings along the a-orthorhombic direction (vertical) close to but different from “isoglitter”. The carbon allotropes (C₈, C₁₀, C₁₂, C₁₄) were shown to be cohesive and stable both mechanically (elastic properties) and dynamically (phonons), with calculated Vickers hardness (H_V) magnitudes ranging between 25 and 52 GPa, the latter magnitude assigned to C₁₂ possessing the largest number of tetrahedral versus trigonal stackings. High phonon frequencies ω ∼ 50 THz were attributed to stretching mode of C=C (in C₈ and C₁₂) and C=C=C (in C₁₀ and C₁₄) units with good agreement with experiment for Raman molecular identifications. Observed magnitudes of ω ∼ 40 THz were proposed as signatures of C–C simple bonds in the tetrahedra as in diamond. The electronic band structure and electronic density of states DOS shown exemplarily for C₈ point to metallic-like behavior assigned mainly to the itinerant role of trigonal carbon π-electrons.

Some physical and technological features of the electroconsolidation process were considered to determine its place among numerous electrodischarge sintering methods. Principal advantages over the other nanopowder compaction methods were noted. The effect of sintering regimes on the formation of a microstructure, the specific features of inhibition under heating in the growth of grains, and the temperature of the graphite press mold and the rate of its heating on the physicomechanical properties of ceramic composites was studied. Some original data on the electroconsolidation process were reposted alongside with the physicochemical properties of nanocomposites synthesized by this method. The probable scheme of electrodischarge processes under high-ampere currents through the graphite press mold is presented.

The effects of sintering parameters and liquid phase content on the properties of Fe-rich based pre-alloyed impregnated diamond bit (IDB) matrix were investigated using orthogonal experimental design. Based on the analysis of the results, it was found that sintering temperature and liquid phase content have significant effects on the bending strength, hardness, relative density, and wear rate of the matrix. For metal matrix composite (MMC), as the sintering temperature increased from 900 to 1050°C, the bending strength, hardness (HRB), and relative density of the MMC decreased first, then increased, and finally decreased again, while the wear rate increased with temperature. With increasing liquid phase content, the four properties of the MMC showed a similar trend of increasing first and then decreasing. Comparatively, the effects of holding time and sintering pressure on the properties of the matrices were smaller than those of sintering temperature and liquid phase content, but they also had significant effects on some properties of the matrices. Holding time had a more significant effect on hardness and wear resistance, while sintering pressure only had a significant effect on hardness. After adding diamonds, the bending strength of diamond matrix composite increased first and then decreased with increasing temperature, while the bending strength continued to decrease with the increase of liquid phase content. This study provides a feasible method for studying the effects of various sintering parameters and liquid phase content on the properties of Fe-rich pre-alloyed IDB matrix, which is helpful for optimizing the preparation process of drill bits.

The effect of boron oxide on the surface of grains from superhard materials on the performance characteristics of grinding tools is studied. The possibility of increasing the strength of cubic boron nitride (cBN) grains by their thermal treatment in air at a low temperature due to the filling of their defective space with a B₂O₃ film is shown. The results of tests show that the wheel containing cBN powder have higher wear resistance and lower specific grinding energy. It is demonstrated that just boron oxide on the surface of grains from superhard materials is an important factor of increasing their performance characteristics in grinding tools.

The article presents the results of a study on the thermal conductivity of ceramic cutting materials produced from exothermic mixtures of Cr₂O₃ with AlN and ZrO_2(M)–Al–C via hot pressing. The characteristics of the resulting materials were compared with those of commercial cutting ceramics Al₂O₃–TiC grade CC650 (Sandvik Coromant, Sweden).

Abstract—As a result of studying the mechanism of polishing with a disperse system from micro- and nanopowders for polystyrene scintillators, sludge nanoparticles (SP) and polishing powder wear particles (PP) were established to form due to Förster resonance energy transfer (FRET) occurring in a four-mode regime in the open microresonator formed by the surfaces of a treated material and a polishing powder particle. The disperse phase particles in the polishing disperse system were demonstrated to wear twice faster as compared to treated material removal. The total cross section of SPs scattering on PPs (31.1 Mb) during the scattering of quantum nanoparticles in the open resonator formed by the treated material and lap surfaces was shown to be much larger than the total cross section of PPs scattering on SPs to result in the absence of a deposit from polishing powder wear nanoparticles on the treated surface and the presence of a deposit from sludge nanoparticles on the lap surface. The results of calculating the material removal rate were established to agree with the data of experimental polystyrene polishing rate measurements at a deviation up to 4%, and SP deposit fragments on the lap surface were from 0.2 to 1.0 mm in size and discretely arranged within an annular zone with a radius of 24.5 mm. The polishing of polystyrene based scintillation elements with a disperse system from micro- and nanoparticles was shown to improve the pulse shape discrimination of fast neutrons and gamma quanta by high aspect ratio detectors by 14%.

We investigated the effect of steel milling on the structure of SiC–Al₂O₃ composite materials, synthesized in steel drums using steel milling bodies. The study focused on examining the physical and mechanical properties, specifically the flexural strength and hardness, of the synthesized samples. Optimal values of these characteristics were determined based on the composition of the composite and the specific processing conditions employed.