Journal of Superhard Materials最新文献

The possibility of MgAl₂O₄ synthesis at high pressures and high temperatures (by the HPHT method) has been studied for за Mg₂B₂O₅–Al, MgO–Al₂O₃, and MgO–Al₂O₃–Al systems. It has been established that, for the Mg₂B₂O₅–Al system, the highest quantity of MgAl₂O₄ is observed at a pressure of 2GPa and a temperature of 1600°C. A further increase in temperature and pressure leads to a growth in the content of boron-containing phases. For the MgO–Al₂O₃ and MgO–Al₂O₃–Al systems, as well as for the Mg₂B₂O₅–Al system, the MgAl₂O₄ phase content is observed to decrease with an increase in the compaction pressure. It’s indicate that an increase in pressure suppresses the interaction between the initial components for all the systems. The addition of aluminum as a liquid-phase component makes it possible to extend the pressure range, within which the MgAl₂O₄ phase is observed to form, to evidence that this approach to MgAl₂O₄ synthesis is promising for further application.

In the carbon–cobalt–tungsten phase diagram, polythermal sections were calculated at pressures of 0.1 and 6 GPa for the phase composition of the diamond layer of diamond hard-alloy plates within the models of phenomenological thermodynamics by using the Thermo-Calc software, literature data on interaction parameters, and equations of states for competing phases. The comparison of calculation results with experimental studied on the phase composition of diamond hard-alloy plates demonstrated their agreement.

Nanodiamond particles and graphene oxide (GO) powders were used as raw materials to construct nanodiamond/reduced GO (rGO) composites by utilizing the explosive reaction of GO. The XRD, FTIR, and XPS results indicate that rapid heating can induce explosive reactions in GO. GO was rapidly reduced to graphene by this explosive reaction. The SEM results indicate that GO undergone obvious expansion and peeling, and the nanodiamond particles were fully loaded onto the rGO sheets.

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.