Journal of Superhard Materials最新文献

The effect of the composition of a SiC–Al₂O₃ composite on the hardness and fracture toughness calculated by an indirect method from the total length of cracks in the corners of rhombic imprints on a Vickers hardness meter has been studied. The dependences of the hardness and fracture toughness of these composites on the content of composite components have been established.

As a result of studying the regularities inherent in the process of treated material removal and the formation of a polished surface nanoprofile during the polishing of aluminum optical components with a disperse system of copper metaborate micro- and nanopowders, it has been established that the formation and elimination of sludge nanoparticles occurs due to energy transfer from the polishing powder particles to the treated surface by the QD-FRET mechanism of Förster resonance energy transfer mediated by Al₂O₃ quantum dots (QDs) formed on the surface of aluminum. It has been shown that the rate of treated material removal in the process of aluminum polishing with a disperse copper metaborate–kerosene based system depends on the quality factor of the microresonator formed by the surfaces of a treated material and a polishing powder particle and the lifetime of the excited state of quantum dots on the treated surface according to the general regularities of the polishing process. It has been established that the results of theoretical calculation for the treated material removal rate are in good agreement with the experimental data of measuring the aluminum polishing rate at an error of 1–5%. It has been demonstrated that, in terms of polishing rate and polished surface roughness for aluminum optical components, it is advisable to use a disperse system of copper metaborate micro- and nanopowders.

We conducted a thermodynamic analysis of the structural formation of class I and II bi-mesocomposites in cemented carbides composed of mesoelements and a matrix. We derived expressions describing the change in Helmholtz free energy during solid-phase and liquid-phase sintering of these bi-mesocomposites. The results show that forming stable bi-mesostructures in cemented carbides requires solid-phase sintering for class I mesostructures, whereas producing class II bi-mesocomposites by liquid-phase sintering requires effective wetting of the mesoelements. Using this approach, we obtained a WC–20 wt % Co–2 wt % C bi-mesostructure through liquid-phase sintering.

Using MoO₃, Mo, Al and Si powders as raw materials, MoSi₂ and MoSi₂–Al₂O₃ composite were prepared by mechanochemical reduction and hot press sintering techniques. The microstructure and dry sliding wear behavior of the samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and a ball-on-disk reciprocating tribometer. The results showed that MoSi₂–Al₂O₃ composite has a fine microstructure, high hardness (13.4 GPa) and fracture toughness (7.2 MPa m^0.5) compared to the pure MoSi₂ material. The wear test results indicated that MoSi₂ and MoSi₂–Al₂O₃ composite exhibited good tribological properties against sliding GCr15 steel balls under different loads. The friction coefficient and wear rates of the samples decreased as the applied load increased. Compared to pure MoSi₂, MoSi₂–Al₂O₃ composite exhibited better wear resistance due to its high hardness, fracture toughness and good surface lubrication characteristics. The dominant wear mechanisms of the composite were adhesion, tribo-oxidation, plastic deformation and spalling.

The high-pressure studies are less explored on high boron-based transition metals (HBTM) ternary compositions. Despite applications, most of the literature on boron-based compounds is limited to the studies of mono and di boron-based (AB and AB₂) compounds. This review reports the detailed theoretical and experimental studies of HBTM ternary compounds to direct this research area. Most of these compounds are employed as hardness materials, magnetic materials, superconductors, 2D materials, catalysts etc. The discussion is extended to various recent HBTM ternary compounds followed by significant advancements and challenges as a promising domain.

We present an improved theoretical model for the lattice thermal conductivity of binary compounds, grounded in the latest understanding of phonon scattering mechanisms. The model enables quantitative evaluation of the effects of temperature and isotopic composition on thermal transport. It shows excellent agreement with available experimental and computational data for cubic boron nitride (cBN). Using this framework, we analyze for the first time the influence of ¹⁵N isotope concentration on the thermal conductivity of cBN.

A double-layer design has been developed for the cutting insert of drill tools by using the WC–Co hard alloy with different cobalt content and tungsten carbide grain size with a sharp boundary between zones of different granularity to increase the wear resistance and impact strength of tools and the rate of percussive rotary drilling in hard rocks up to 50%. The upper layer of the cutting insert is composed by a coarsely grained structure (6 µm), and the lower layer represents a finely grained structure (2 µm) with an increased fracture toughness. The results of this study can be used in mining, oil and gas, and building industries to improve drilling efficiency.

This study presents results aimed at developing a novel method for electrochemical induction of paramagnetic centers on the surface of carbon materials, which not only enhances adhesion between the filler and the matrix but also promotes long-term durability and preserves the initial level of interfacial contact characteristics under prolonged exposure to temperatures up to 500°C in air. Experimental results confirmed a positive correlation between the concentration of paramagnetic centers on the composite interfacial surface and its mechanical properties, specifically the flexural strength and elastic modulus. The study demonstrates that phthalonitrile oligomers combined with fibrous fillers are suitable as matrices for the fabrication of abrasive composites with high thermomechanical performance. Such composites are designed for use in components and assemblies operating under extreme conditions. The implementation of this novel surface modification method for carbon materials significantly improves the mechanical properties, thermal stability, and heat resistance of composites based on phthalonitrile matrices.

Some methodological aspects of quantitative analysis for the characteristics of the cutting edges of abrasive powders are considered. It is pointed out that the approach based on the use of a grain projection is predominant in the practice of determining the values of these characteristics. The possibility and necessity of transition to the methodological scheme based on the 3D shape of a grain in a similar problem is substantiated. A methodological scheme taking into account the real morphology of grains of such grinding powders is proposed to provide a higher plausibility of initial values for the characteristics of their cutting edges. An analytical interpretation is given to the number and sharpening angles of the cutting edges of high-strength synthetic diamond (SD) grinding powders. Using grinding powders AS400 500/400 and AS200 630/500 as an example, the reasonability and advantages of the methodological scheme with the 3D shape of a grain as a generating object of the actual cutting edges of high-strength SD grinding powders is illustrated. At the same time, the methodological scheme using a grain projection as a generating object of cutting edges is not rejected. The recommendation to apply the known method of estimating the characteristics of cutting edges by the geometric modelling of an abrasive powder grain projection with star-shaped polygons is substantiated for non-high-strength SD and other abrasive powders at a quantitative level. It has been established that both considered methods give a rather satisfactory result in terms of coincidence between the sharpening angles of cutting edges (relative error is less than 1%) and a less satisfactory result, which is acceptable yet for practical applications, in terms of coincidence between the numbers of cutting edges (relative error is 14–17%).

Melting of boron-rich chalcogenides, rhombohedral B₁₂S and B₁₂Se, has been studied at pressures up to 8 GPa using in situ electrical resistivity measurements. It was found that above 2.5 GPa both chalcogenides melt congruently. The melting curve of B₁₂Se has a negative slope of ‒30(3) K/GPa, indicating a higher density of the melt compared to the solid phase, while a very unusual zero slope of –1(2) K/GPa is observed for B₁₂S. The melting points at ambient pressure were estimated to be 2270(7) K for B₁₂S and 2250(16) K for B₁₂Se.