Journal of Superhard Materials最新文献

Unusual inclusions of manganese and manganese-nickel compounds in microdiamonds (0.3–0.5 mm) of unknown origin, picked up from geological samples of various rocks on the Ukrainian Shield, have been studied by transmission electron microscopy. These microdiamonds are planohedral crystals of cubo-octahedral and cubic shape. Most of the inclusions have rounded irregular shapes and their size is in the range of ten to a few hundred nm. They have been identified based on their chemical composition and diffraction patterns as Mn-silicates, Mn-oxides, Mn–Ni and Mn–Ni–Si compounds of varying composition, graphite and KCl. In terms of crystal shape, phase and composition of inclusions, the studied diamonds are completely different from natural ones, but very similar to synthetic diamonds, grown at high pressure—high temperature in the Mn–Ni–C system at the Institute of Superhard Materials of the National Academy of Sciences of Ukraine (Kyiv). Given this, it is concluded that they are synthetic and most likely originate from diamond tools used during the collecting and processing of rock samples.

The structure formation features and mechanical properties of the AlN–С–TiB₂ ceramic composite containing 2 wt % of diamond powder and 13 wt % of TiB₂ for vacuum electronics applications were investigated. Composite samples were sintered by hot pressing at a temperature 1900°C and a pressure of 20 MPa. Using structural and X-ray diffraction studies, the AlN, Al₃(O, N)₄, TiB₂, TiC, Y₃Al₅O₁₂, and C (graphite) phases were revealed in the material. When measuring the mechanical properties, it was found that the Vickers hardness of the studied composite materials is 12.5 ± 0.44 GPa at a load on the indenter of 9.8 N. Increasing the indenter load to 49 N led to the formation of cracks, and the fracture toughness under such conditions was 5.82 ± 0.11 MPa m^0.5.

The etching behavior, mechanism, and efficiency of diamond were systematically compared for the silicon-thermal method and direct etching using pure Fe powder or Fe₂O₃₂O₃ alone. XRD, SEM, and thermodynamic analyses showed that the silicon-thermal reaction system (Fe₂O₃–Si), owing to its strong exothermic effect (ΔH ≈ –1070 kJ mol^–1), generated an active high-temperature etching medium in situ, dominated by Fe and FeO and accompanied by the formation of silicates. Together, they created a dynamic etching environment described as “high-enthalpy-driven multiphase coupling catalysis-dissolution-migration”. The introduction of CaO further led to the formation of Ca₂SiO₄, which significantly enhanced the etching effect by stabilizing the FeO phase and improving mass transport, particularly inducing complex and deep etch morphologies on the diamond (111) planes and grain boundaries. Experiments demonstrated that the etching efficacy of the silicon-thermal method was significantly superior to the mild etching achieved by pure Fe or Fe₂O₃ alone. This research provides a new strategy based on silicon-thermal reduction for the efficient and deep surface processing of diamond.

In this communication two novel orthorhombic allotropes trig-C₁₂ with trigonal C(sp²) and tetr-C₁₂ with tetrahedral C(sp³) are proposed from crystal engineering and unconstrained geometry optimizations to ground state structures using calculations based on the quantum density functional theory DFT. The two allotropes in space group P2₁2₁2₁ were identified with original topologies 3,3,4T2 and cai-4,4-Pnma respectively. Both are metastable with respect to diamond and present super hard properties with a larger density and hardness for tetr-C₁₂. Electronic band structures reveal conductive trig-C₁₂ and semiconducting tetr-C₁₂.

Melting of rhombohedral boron subarsenide, B₁₂As₂, has been studied at pressures up to 8 GPa using quenching. It was found that above 2.5 GPa B₁₂As₂ melts congruently, and the melting curve has a positive slope (30 ± 6 K/GPa), indicating a lower density of the melt as compared to the solid phase. The melting point of B₁₂As₂ at ambient pressure has been estimated to be 2110(40) K.

The chemical interactions between components and high-pressure high-temperature (HPHT) reaction sintering processes (p = 7.7 GPa, T = 2200°C) were studied for superhard composites of groups BH and BL in the cBN–Me and cBN–TiCN–Me systems (where Me = Ni, Co, W with a content of 30 vol %). It was established that, during sintering for 60 s, there is no chemical interaction between the cBN–Me charge components, while the formation of a small amount (1–3 vol %) of additional phases (Ni₃B or Co₃B, W₂B, and W₂C) is observed for the cBN–TiCN–Me composites. For all the systems, the resulting metal ceramic has zero porosity and has a monolithic, homogeneous microstructure, in which the original morphology of cBN grains is preserved. The Young’s modulus ranges from 370 to 427 GPa, and the Vickers hardness is 18–25 GPa.

Based on an investigation of the scattering behavior of sludge nanoparticles and wear nanoparticles originating from the polishing powder during the polishing of copper optical components using a dispersed system of micro- and nanopowders of copper metaborate in kerosene, as well as the formation of a deposit composed of copper oxide nanoparticles on the polished surface, it was established that the dependence of the total scattering cross section of sludge nanoparticles on the radius of the circular zones of the component is characterized by maximum values at radii of 10, 15, 17.5, and 20 mm. These maxima correspond to the highest probability of deposit formation on the processed surface, specifically within these circular zones. Investigation of the influence of the emergent properties of quantum sludge nanoparticles and polishing powder wear nanoparticles on their collective behavior, self-organization, and assembly during motion within an optical resonator of variable length formed by the surfaces of the workpiece and the polishing lap demonstrated that a deposit composed of sludge nanoparticles forms on the processed surface of the copper component. Fragments of this deposit are discretely distributed along concentric circles whose radii coincide with the values calculated using the quantum theory of nanoparticle scattering. It was further shown that, during the polishing of copper optical components using micro- and nanopowders of copper metaborate dispersed in kerosene, the material removal rate reaches 28.6 × 10^–13 m³/s, which is in good agreement with the experimentally determined polishing productivity of 1.5 ± 0.1 mg/min, or 7.3 ± 0.4 μm/h, or (28 ± 1) × 10^–13 m³/s, with a deviation of 5–6%. Experimental observations confirmed that the deposit composed of sludge nanoparticles, whose fragments consisted of copper oxide, was indeed present on the polished copper surface along concentric circles with radii of 10 and 15 mm, as well as within the circular zone having a radius of 17–20 mm.

The current papers on the surface modification of diamond grinding powder grains by applying cubic boron nitride (cBN) coatings to them are reviewed. The results of these studies indicate the efficiency of such modification and the positive impact of cBN films on diamond surfaces. It was found that the best binder for cBN coating is gelatin, while glue BF6 and polyvinyl alcohol (PVA) are approximately the same, though PVA is better at a lower material removal rate, and glue BF6 is more advisable, when the material removal rate is higher. Performed studies show that, from the technological viewpoint, PVA is preferable for coatings, especially when they contain nanosized cubic boron nitride (nano-cBN). It was established that the deposition of a coating containing nano-cBN to the surface of high-strength diamond grains AC15–AC20 significantly increases the wear resistance of diamond wheels, presumably, due to the improved retention of diamond grains in the binding material.

The phase stability, mechanical properties, and electronic structure of (Ti, W)C solid solutions are computationally investigated, specifically, by density functional theory (DFT) and the cluster expansion method, with a focus on composition variations and their effect on the properties. The results reveal that Ti_0.5W_0.5C exhibits higher thermodynamic stability, whereas intermediate compositions, such as Ti_0.67W_0.33C achieve peak hardness (~33 GPa) due to the synergistic effect of Ti–C covalent and W–C metallic bonds. Electronic structure analysis reveals that the bonds have a hybridized nature, which impart the material with mechanical resilience and thermal stability. The introduction of tungsten exerts a pronounced influence on elastic and vibrational properties, enhances the bulk modulus, and enables the tailored tuning of material properties. These findings provide an important scientific foundation for the design of high-performance materials for application in metal cutting, wear-resistant coatings, and structural components.

The surface of a specimen made of WC–5TiC–10Co alloy T5K10 with a gradient WC–13Co surface layer was investigated to demonstrated that additional sintering under a pressure of 50–60 Pa in a nitrogen atmosphere at 1400°C for 20 min in contact with a pre-applied TiN nanopowder slurry results in a dark outer layer (DOL) of 0.2–3.0 mm in size with a dense heterophase structure containing a Co–W–Ti matrix doped with N and C and dispersed ceramic TiNC grains of various morphology. The mechanism of the formation of this gradient structure was identified as the infiltration of some Co–W–C melt solution generated under thermokinetic sintering conditions from the WC–13Co layer (reduced to 7%) into the porous TiN nanopowder layer. This is followed by liquid-phase sintering accompanied by the partial substitution of nitrogen in TiN with carbon, Co and W dissolution, porosity elimination, and the development of a heterophase structure. Microhardness measurements revealed the values of 14.5 GPa for the WC–7Co layer and 16.1 GPa for the newly formed DOL. The resulting gradient structure shows strong potential for applications in cutting tools for the machining of high-alloy steels.