Journal of Superhard Materials最新文献

PcBN (polycrystalline cubic boron nitride) carbide insert were synthesized with cBN/Zr/Al as raw material under high temperature and pressure. The effects of synthesis pressure on the interfacial morphology, wear resistance, microhardness and flatness of PcBN carbide insert were investigated. The test results show that with the increase of synthesis pressure, the composite interfacial bond is more dense and homogeneous, and the bonding strength between the cBN layer and the alloy substrate is higher. Additionally, the density, microhardness and abrasion resistance of the PcBN carbide insert were improved. Meanwhile, under the ultra-high pressure, the thickness deviation of the PcBN carbide insert gradually decreases, the thickness distribution gradually becomes uniform, and the flatness of the samples gradually becomes better.

As a result of studying the mechanism of optical glass polishing by means of disperse systems from ceria powders, it has been established that glass is eliminated via the removal of sludge nanoparticles from the treated surface during its interaction with polishing powder particles, which occurs in an open microresonator formed by the surfaces of the treated material and polishing powder particles due to Förster resonant energy transfer between the energy levels of polishing powder and treated material particles. It has been shown that, in a bimodal system with a discrete spectrum of natural frequencies, the number of sludge nanoparticles generated in the treated surface–disperse system–lap surface grows with an increase in the bulk wear coefficient, the lifetime of the excited state of treated surface clusters, and the microresonator Q factor. A method of calculating the treated material removal rate and the roughness parameters of polished surfaces has been developed to establish that the deviation of the calculated polishing rate from experimental data is less than 2%, and the errors of calculating the arithmetic mean R_a and mean square R_q deviations of the polished surface profile attain 10%, and the calculated maximum profile height R_max is 40–50% underestimated as compared to experimental data.

We investigated the effect of surface coatings on cubic boron nitride (cBN) grains regarding tool wear resistance and processing efficiency. At a low processing rate (50 mm³/min), the wear resistance enhancement factor was 1.66 for the B₂O₃ + CeO₂ coating. Conversely, at a higher processing rate (200 mm³/min), the wear resistance enhancement factor decreased to 1.13 for the B₂O₃ + B₄C coating. The study demonstrated that under these processing conditions, surface coating of cBN grains with a combination of oxide and carbide (B₂O₃ + SiC) is preferable. This preference is based on improved grinding wheel wear resistance and reduced surface roughness (R_a) of the machined surface. Furthermore, at increased grinding efficiency, any coating on cBN grain surfaces decreases the t50 parameter, thereby decreasing the holding capacity of the rough surface generated during grinding with such wheels.

A comparison between synthetic HPHT diamonds and natural diamonds has been conducted, highlighting substantial differences between them. Key distinctive features of synthetic HPHT diamonds have been identified, facilitating their differentiation from natural counterparts. The authenticity of HPHT diamonds found in rocks from the Ukrainian crystalline shield has been examined. Samples from concentrates of crystalline and terrigenous diamond-bearing rocks, exhibiting similarities to synthetic HPHT crystals, serve as pseudoindicators of diamond potential in geological formations and necessitate thorough investigation.

The study investigated the wear rate dependences of diamond-impregnated drill bits consisting of composite diamond-containing materials (CDMs): specifically, 25C_diamond–70.5WC–4.5Co and 25C_diamond–68.62WC–4.38Co‒2ZrO₂. These materials were fabricated via spark plasma sintering at temperatures ranging from 20 to 1350°C under a pressure of 30 MPa for 3 min. Testing was conducted under rotational speeds and axial load conditions typical for granite drilling. It was demonstrated that incorporating 2 wt % of ZrO₂ nanopowder into the composition of 25C_diamond–70.5WC–4.5Co resulted in a threefold reduction in wear rate. The highest wear resistance of these diamond-impregnated drill bits was observed at rotational speeds of 250 rpm and axial loads of 900 kg, as well as at 750 rpm and 1250 kg axial load. Comparatively, the enhanced wear resistance of diamond-impregnated drill bits made from 25C_diamond–68.62WC–4.38Co‒2ZrO₂, in contrast to those made from 25C_diamond–70.5WC–4.5Co, can be attributed to factors such as finer grain size, higher relative density, improved strength under compression and bending, increased fracture toughness, and the formation of strong bonding between diamond grains and the hard-alloy matrix. These findings, combined with the fine-grained structure of the hard-alloy matrix and high diamond retention, indicate that these diamond-impregnated drill bits have potential for application in developing new tools with superior operational properties for drilling hard rock formations.

The review and comparative analysis of known literature approaches and methods for predicting the packing density of binary powder systems are carried out. A theoretical model is proposed for a binary mixture to provide the spline approximation of calculated and research data with an appropriate accuracy. The model parameters are physical values, whose comparison for different binary systems makes it possible to estimate both the effect of a method of their formation on the packing density and the degree of adequacy to real powder materials for the available theoretical models.

We investigated semiconductor composite materials of the AlN–50% SiC–Y₃Al₅O₁₂ system, obtained by free sintering, which exhibit a high level of microwave absorption of 4.6 dB/mm. The activation energy values of electrical conductivity (E_a) for the obtained composites were calculated within the temperature range of 20–800°C. At temperatures close to room temperature (20–150 °C), E_a ranges from 0.120 to 0.075 eV and increases to 0.270–0.275 eV as the temperature rises to 350–800°C. The determined photon energy values of the electromagnetic wave, in the frequency range from 1 to 100 GHz, are from 4.13 × 10^–6 to 4.13 × 10^–4 eV. Using quantum electrodynamics at the atomic level, we described the process of microwave radiation absorption in the AlN–SiC semiconductor composites. Low-energy photons of electromagnetic waves incident on the surface of the AlN–SiC composite transfer their energy to the conduction electrons in the near-surface layers of the SiC phase and are absorbed by them. The conduction electrons emit photons at the same frequency of the electromagnetic wave, predominantly into the same SiC grains, within 10^–8 s. This interaction results in the absorption of electromagnetic radiation, leading to the dissipation of wave energy and subsequent heating of the entire composite: initially, the SiC phase particles and, subsequently, the AlN grains.

A comprehensive study is performed on the effect of vacuum arc conditions on the formation of TiCN coatings, specifically focusing on parameters such as the bias potential applied to the substrate, nitrogen partial pressure, and the composition of the C₂H₂–N₂ gas mixture. Our investigation encompassed analyses of the coatings’ chemical composition, structure (lattice parameter, texture factor, orientation, grain size, level of microstrains), and mechanical properties (microhardness, adhesion strength indicators, and coefficient of friction). The results reveal that the coatings predominantly exhibit a polycrystalline nature and possess a cubic B1-NaCl structure, characterized by visible diffraction peaks in the range of 2θ from 30° to 80°, corresponding to reflections (111), (200), (220), and (222). The lattice parameter of TiN was found to increase from 0.4291 to 0.4301 nm with variations in the concentration of C₂H₂, while the texture coefficient concurrently increased from 5.91 to 5.97. The hardness of the coatings at a bias potential U_bias = –200 V exhibited variation from 31.7 to 33.9 GPa, depending on the C/N ratio. Variations in the elemental composition of the coatings led to changes in adhesion strength, with failure occurring at a load F = 62.1 N. The coefficient of friction was measured at μ = 0.45 under these conditions.

Fully-sintered zirconia ceramic (ZrO₂) is a typical hard-to-machine material, and fabricating small holes in this material with high precision remains a challenging task. In this study, the PCD tools and helical milling process are used to investigate this problem. First, a finite element model is established, and cutting simulations with variable thickness are carried out to identify the effect of axial depth of cut on cutting force and surface quality. The range of milling parameters for single-factor experiments is also preliminarily determined. Second, taking the milling force (F) as the evaluation index, single-factor experiments of small hole helical milling are carried out using a PCD tools to determine the range of milling parameters (spindle speed n, feed per tooth f_z and axial depth of cut a_p) for orthogonal experiments. Then, orthogonal experiments are carried out, with inner hole surface roughness (R_a) and crack width at the hole entrance (Δ_w) taken as the evaluation indexes of machining effectiveness. The rake face wear band width (V_A) and the flank face wear band width (V_B) are taken as the evaluation indexes of the PCD milling cutter wear. Through nonlinear regression analysis and the range analysis are performed to construct nonlinear models and obtain the influence laws of milling parameters for R_a, Δ_w, V_A and V_B evaluation indexes, respectively. Finally, the optimal combination of parameters obtained from the analysis is analyzed for small hole optimization experiments, obtaining better R_a, narrower Δ_w, and longer tool service life. The obtained results provide several technical guidelines for milling small holes in Fully-sintered zirconia ceramics with PCD tools.

A technological process has been developed for forming coatings on the surface of diamond grains using two and three components: soluble boron oxide (B₂O₃) and insoluble aluminum oxide (Al₂O₃) or insoluble carbide (B₄C, SiC, TiC). To achieve guaranteed increases in the wear resistance of diamond wheels when grinding hard alloys, it is necessary to apply a coating of boron oxide and boron carbide (B₂O₃ + B₄C) to the surface of the diamond grains. The positive effect of such a coating on the surface of the diamond grains is more pronounced under increased force and heat loads in the grinding zone. The holding capacity of the processed rough surface in terms of the t50 support surface curve parameter is preferable when the surface of diamond grains in diamond powder wheels AS6 125/100 is coated with a mixture of B₂O₃ + B₄C. Thus, for diamond grains, considering both the wear resistance of diamond wheels and surface roughness parameters, it is recommended to use diamond grains with a surface coating of B₂O₃ + B₄C in wheels for grinding hard alloys.