Journal of Superhard Materials最新文献

This study proposes a thin protective polycrystalline diamond CVD coating for cutting tools equipped with a polycrystalline synthetic diamond material produced via the HP–HT method. The deposition parameters were optimized in a magnetically stabilized glow discharge plasma. The coating was synthesized in a hydrogen–methane mixture at a partial pressure of CH₄ ranging from (2.2–2.7) × 10² Pa. The effect of the temperature of the polycrystalline diamond substrate during deposition on the structure of the synthesized coating was investigated. Results indicate that at temperatures between 1060 and 1150°C, diamond crystals in the coatings exhibit well-defined faceting with rectangular or triangular faces of micrometer-scale dimensions. A further increase in synthesis temperature leads to the formation of less-ordered fine-grained components on the surface of the larger, well-formed diamond crystals. At a deposition temperature of 1110–1150°C, a pilot batch of cutting inserts was fabricated using a polycrystalline synthetic diamond material with a 30-µm-thick polycrystalline diamond CVD coating. The impact of the coating on the performance characteristics of tools equipped with these inserts was evaluated during the machining of AK12M2MGN aluminum alloy and MK90 technical ceramics. Results indicate that the coated tool produced machined surfaces with lower roughness when processing the aluminum alloy, while exhibiting a 1.52–1.75-fold increase in wear resistance when machining technical ceramics. This improvement expands the application range and enhances the efficiency of diamond-polycrystal-equipped tools. The study established a synthesis temperature limit of 1175°C, beyond which the coating develops inferior performance characteristics.

The surface state of low-strength diamond grinding powders synthesized in the Ni–Mn–C system has been studied, and the content and composition of their intracrystalline inclusions and impurities before and after thermochemical treatment in an alkaline melt have been determined. It has been established that, in the incombustible residue of diamond powders, carbon solvent alloy elements are predominant to attain from 93.3 to 58.5% from the total quantity. In the initial fractions in the inclusions and impurities of diamond powders, the ratio between Ni and Mn remains at the level typical for the growth medium composition, but the incombustible residue in magnetic fractions after thermochemical treatment contains more Mn. The content of carbon solvent alloy elements (Mn + Ni) decreases almost by two times in the initial fraction, by 2% in the magnetic fraction, and approximately by 17% in the nonmagnetic fraction. According to X-ray spectral microanalysis data, after treatment at a temperature of 800°С, the first appearing on the surface of diamond crystals are inclusions containing Ni and a small quantity of Mn to be followed by Mn enriched solvent alloy inclusions. The appearance of such inclusions and the sequence of their exposure on the surface is explained by the specifics in the distribution of components in the phases of Ni–Mn–C alloys and the capillary extrusion phenomenon, which is also observed on the surface of diamond crystals synthesized in other growth media after annealing. It has been shown that, after thermochemical treatment in an alkaline melt, the incombustible residue decreases approximately by two times, the incombustible residue content decreases approximately by two times, and the magnetic properties of diamond powders weaken by 1.4 times due to the dissolution of separated inclusions. The diamond crystals containing a lower quantity of intracrystalline impurities and inclusions have a higher strength. The total content of inclusions and impurities in the incombustible residues of diamond grinding powders before and after thermochemical treatment decreases by 2.4 times, and the content of carbon solvent alloy elements in them becomes 1.6 times lower. The content and composition of intracrystalline inclusions in diamond powder samples can be more precisely determined after thermochemical treatment.

The study developed an experimental-computational procedure for investigating the rheological properties of thermoplastic slip. This approach integrates laboratory and computational experiments conducted in parallel to determine viscosity parameters by ensuring agreement between calculated and experimental data. The experimental component employs penetrometry, a method that is simple to implement and does not require specialized equipment. The computational component involves analyzing a model boundary-value problem for the Navier–Stokes equations using the finite element method or applying the analytical model developed in this work. The viscosity characteristics of slip based on paraffin and polydisperse SiC powder enable the prediction of the slip-casting process for large-scale, thin-walled silicon carbide ceramic components.

The data on the goniometric study of the most common sculptures on the surface of natural diamond crystals are summarized. These sculptures consist of flat microplanes, which appear during the growth or dissolution of diamond crystals. They are a component of their surface and take an immediate part in the creation or destruction of diamond crystal faces. The results of goniometry for trigonal and ditrigonal hatchings on octahedron edges, straight- and inverse-parallel triangular and hexagonal pits on octahedron faces, quadrangular pits on cube faces, and drop-shaped hillocks and caverns on rounded dodecahedron faces are considered. It is shown that the most common microplanes of sculptures crystallographically correspond to the simple crystal forms, which often have large symbols and form clusters generally around the most important diamond structure forms.

Single crystal diamond is a material of tremendous interest for a wide range of advanced applications due to its unmatched properties. Despite the potential of diamond-based devices, commercialization has been hindered by significant technological challenges, particularly the need for high-quality, technological-grade materials to fully realize their advantages. It is widely accepted that high-quality single crystal diamonds grown by MPCVD are classified as type IIa, meaning their nitrogen concentration is less than 1 ppm. In this study, an attempt was made to grow high-quality single crystal diamonds with nitrogen impurities below 1 ppm, using welding material to maintain the substrate temperature at the optimum growth temperature. The quality and nitrogen-related defects were evaluated by examining optical properties through Raman, UV–Vis, and FT-IR spectroscopy. Raman spectroscopy confirmed the presence of the pure diamond phase in the spectra of sample, peak was observed at 1332.5 cm^–1 with FWHM 1.5 cm^–1, while FT-IR spectroscopy confirms a nitrogen concentration of less than 1 ppm. UV–Vis spectroscopy at 502 nm revealed the presence of an H3 defect, quantified at 206 parts per billion (ppb). Our findings indicate strong dependency of controlled growth parameters over nitrogen concentrations during the synthesis process of single crystal diamonds.

Melting of new boron-rich chalcogenides, orthorhombic B₆S and B₆Se, 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, and the melting curves have a negative slope (‒61(5) K/GPa for B₆S and –80(2) K/GPa for B₆Se), indicating a higher density of the melts compared to the solid phases. The melting points at ambient pressure were estimated to be 2190(30) K for B₆S and 2347(12) K for B₆Se.

The presence of adsorbed water and hydroxyl groups on the actual surface of modern diamond grinding powders with low strength (grades AC6–AC32) was investigated. By preliminarily separating diamond grinding powders into magnetic, nonmagnetic, and initial fractions, a fraction with the highest amount of water on the surface of the diamond grains can be identified—the magnetic fraction. The Ni–Al composite coating on the diamond surface, as well as the coating with carbon nanotube additives, contribute to the formation of a more developed surface compared to the initial uncoated samples, as evidenced by the greater presence of water.

Now there is still no unified standard for the evaluation of mixing uniformity in the abrasives industry. Taking the powders commonly used in resin bonded grinding wheels as the research objects, a simple sampling specification and uniformity statistical method were designed in this paper. By means of various detection methods, the homogeneity of the mixture was evaluated from macroscopic and microscopic perspectives. The results showed that organic solvent method was suitable for macroscopic analysis of resin bond. X-ray fluorescence spectrometry (XRF) was suitable for macroscopic analysis of fillers. Calcination method was suitable for macroscopic analysis of substances which can be oxidized in the air. The optical microscopy method was suitable for on-line real-time control of the raw material powders. Scanning electron microscope (SEM) observation was suitable for micro-uniformity analysis.

This study examines the electrical resistance of pressureless sintered ceramic composites of AlN–50 wt % SiC, which are suitable for use as bulk microwave radiation absorbers. For four groups of samples with quality factors Q = 30, 33, 37, and 44, the average surface resistances are 42, 64, 92, and 136 kΩ, respectively, while the average bulk resistances are 2.8, 4.1, 5.2, and 7.0 kΩ, respectively. An analysis of the experimental data revealed a correlation between surface and bulk electrical resistance. In general, higher bulk resistance corresponds to higher surface resistance. Moreover, as the quality factor increases from 30 to 44, the surface resistance exceeds the bulk resistance by factors ranging from 14.7 to 19.5.

For the diamond grinding of ceramic silicon nitride balls based on a plane with circular feed under oscillation, some results of experimental study on the effect of their positioning scheme and processing regime on the precision of their shape and the shape of the worn surface of a diamond wheel were reported. The shape accuracy criteria of ground balls were their diameter variation and the shape factor of their out-of-roundness profile and the radial slope angle of the working surface of a wheel and the curvature coefficient of its worn surface. This effect was described by adequate linear functions for the ball diameter variation from the wheel feed depth and rotation speed and the wheel profile inclination angle and curvature coefficient from the wheel feed depth and the rotation speed of the table with the balls. The processing regime parameters, at which the studied scheme of positioning the balls is reasonable, were predicted.