Journal of Superhard Materials最新文献

High-entropy ceramics (HECs) have garnered significant attention due to their unique microstructure, desirable properties, and vast compositional space. In this study, we utilized homemade TiN_0.3 with anionic vacancies as a sintering aid, equimolarly mixed with VN, CrN, and NbN. Our results demonstrate the following: Firstly, high-entropy nitride ceramics with a single rock salt phase were successfully synthesized within a holding time of 5 min. Secondly, the samples exhibited their maximum hardness, flexural strength, and fracture toughness values at a holding time of 15 min-measuring at 21.51 ± 1.50 GPa, 1271 ± 24 MPa, and 3.63 ± 0.35 MPa m^1/2, respectively.

The present study focused on characterizing Cu₇₀–Sn₂₀–Ti₁₀ solder alloy powder used for brazing diamond grits in a vacuum at 960°C for 20 min. The study covered the macroscopic and microscopic morphology of Cu–Sn–Ti/diamond, the products and thickness of the interfacial reaction layer, the surface morphology of diamond grits, and the phase and morphology of surface attachments after reaction. Additionally, the effects of graphitization and compressive strength of the diamond after the reaction were also studied. The study’s results revealed that the solder alloy could climb up to the diamond grits effectively and exhibited excellent wettability. Microscopically, a TiC reaction layer was observed at the interface between them, and the thickness of the reaction layer was about 1.92 μm, leading to the realization of a chemical metallurgical combination. After brazing, the uncovered surface of diamond grits appeared smooth and did not show graphitization, except for slight graphitization in a few corrosion pits. Moreover, no significant change was observed in the compressive strength of the diamond before and after brazing.

This study presents a theoretical approach for assessing the brittle strength of multiphase polycrystalline materials and demonstrates its application to two-phase cBN–TiN ceramics.

To improve further the designs and ensure the stable operation of vacuum electronic devices that function in the ultra-high frequency (UHF) range at 1–100 GHz, the characteristics of microwave radiation absorption have been enhanced. We addressed the highly complex task of producing bulk absorbers made from AlN–Mo composites with a high attenuation level of 10–12.3 dB, which corresponds to a microwave radiation absorption coefficient of 37–56 dB/cm. They achieved a good low voltage standing wave ratio (VSWR) value of 1.5–1.6 in the frequency range of 9.3–10 GHz. The study found that chemical treatment of the absorber’s surface, which involves removing molybdenum particles using an acid mixture, improves matching by reducing microwave radiation reflection values, consequently decreasing the VSWR peak by 26–30%.

The paper reviews current advancements in diamond processing and dressing techniques, highlighting the specific methods of surface modification for diamond grains to alter their properties intentionally. It discusses the scientific principles underlying the development of plastic grinding processes for brittle materials and emphasizes the relationship among specific energy, diamond tool wear, and surface roughness. Laser rough dressing effectively removes excess abrasive layers rapidly, while precision electroerosion dressing enhances profile accuracy and restores the cutting ability of the grinding wheel. The positive effects of using porous, defective diamond grains are demonstrated. The development of diamond grains with high self-sharpening properties and improved bonding within the binding material is discussed. Furthermore, the paper establishes the effectiveness of adding B₂O₃, TiO₂, and Al₂O₃ oxides to modify the surface of diamond grains, protecting against oxidation. It notes the beneficial impact of multilayer coatings containing cubic boron nitride (cBN). The addition of B₄C and V₂O₅ improves the retention of diamond grains in diamond-containing composites.

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.