Based on crystal chemistry search and density functional theory (DFT), original tetragonal and orthorhombic C10 allotropes are proposed with super dense and ultra hard behaviors. Such properties pertain to the exceptional arrangement of distorted corner sharing as well as short C–C connections. The resulting structures are characterized by original topologies. Phonon band structures show stable low frequency acoustic modes as well as higher optic modes with 40 THz band close to experimental diamond Raman line for the orthorhombic allotrope. The calculated specific heat CV curve shows shape agreement with experimental diamond values particularly for orthorhombic C10. The electronic band structure exhibits semi-conducting and insulating behaviors for tetragonal and orthorhombic allotropes respectively.
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
This study investigated the carbothermal reduction etching behavior of the Fe2O3–C system on diamond (100) and (111) crystal planes at 1000°C. The results indicate that Fe and FeO, generated from the reduction of Fe2O3 by carbon, serve as the primary active agents for etching. However, significant differences in the etching mechanisms were observed between the two crystal planes. On the (111) plane, step-preferred etching led to the formation of triangular pyramidal pits, with the extent of etching diminishing as the carbon content increased. In contrast, the (100) plane exhibited square-shaped etch pits, and higher carbon content promoted deeper etching. This research elucidates the regulatory mechanism of anisotropic etching and raw material composition on etch morphology, providing a theoretical foundation for controlled etching processing of diamond.
At a pressure of 8 GPa and a temperature of 1700°C, diamond crystals were synthesized in the Mg–Zn–B–C system, the synthesis product was chemically purified, and the resulting diamond powder was classified by grain size. The grain size distribution of mixtures of coarse- and fine-dispersed diamond powders synthesized in the Mg–Zn–B–C system was examined before and after exposure to high pressure, the influence of the initial mixture composition on the degree of comminution under high pressure was evaluated, and its relationship with the kinetics and densification level of polycrystals formed from these mixtures during subsequent high-temperature treatment was established. Raising the average particle size of the initial powder from 5 to 30 μm increases the degree of comminution by a factor of 6, which leads to powder densification during the high-temperature sintering stage at a pressure of 8 GPa and a temperature of 1800°C to a level of 99
In this study, B4C–TiB2 composite materials were successfully fabricated via in situ reaction using a high-pressure and high-temperature sintering with 90 wt
Under conditions of high pressures and temperatures, the interaction between cBN micropowder and a high-entropy alloy (HEA), specifically 37Ni19Fe19Cr17Co4Ti4Al (vol
As a result of studying the regularities in the scattering of sludge and polishing powder wear nanoparticles during the polishing of copper and aluminum with dispersion systems of copper metaborate micro- and nanopowders in a dispersion medium of kerosene or water, as well as the formation of a deposit from these nanoparticles on the working surface of the lapping tool, it was found that the lapping tool surface can be reached only by the sludge particles scattered forward and by the polishing powder wear particles scattered backward, for which the differential cross sections varying within the limits of 2.3–102.0 Gb sr–1 and 0.7–4.8 Mb sr–1 significantly decrease with increasing separation between sludge nanoparticles, polishing powder wear nanoparticles, and a dispersion medium by dielectric permittivity. It was shown that the total scattering cross sections of nanoparticles σm and σp, varying within the limits of 0.05–1.78 Mb and 0.37–0.53 Mb, also decrease with increasing separation between sludge nanoparticles, polishing powder wear nanoparticles, and a dispersion medium by dielectric permittivity, and maximum σm/σp = 3.3 and minimum σm/σp = 0.1, which are characteristic of interaction between nanoparticles in the copper–kerosene and aluminum–water systems, indicate that the deposit on the working surface of the lapping tool will be more probably formed from sludge nanoparticles in the first case and from polishing powder wear nanoparticles in the second case. It was experimentally confirmed that a deposit of copper particles is observed on the surface of the lapping tool, when copper is polished with copper metaborate micro- and nanopowders in the dispersion medium of kerosene, and a deposit of copper metaborate particles is observed, when aluminum is polished in the dispersion medium of water.
This paper reports experimentally determined values for the dielectric permittivity ε' and dielectric loss tangent tanδ of pressureless sintered AlN based composites with conductor (Mo) particles in a wide range from zero to the critical concentration of molybdenum particles, i.e., near the percolation threshold. It is shown that, in the studied composites, both the real ε' and imaginary ε” parts of the dielectric permittivity monotonically grow with increasing content of conductor particles, reach maximum values near the percolation threshold, and equal to ε' = 25–32–48. The microwave energy absorption of AlN–Mo composites with different content and size distribution of conductor particles was measured. The relationship between the dielectric losses ε” and the level of microwave absorption L depending on the content of conductor particles near the percolation threshold was established.
A review of papers evidencing the positive significance of the specific surface area of abrasive synthetic diamond powders and the methods of influencing the change in its value was carried out. The trends in the modern development of methods for the indirect analytical estimation of the external specific surface area as a technological property of such abrasive powders were analyzed. The methodological features of the application of extrapolation-analytical and fractional-averaging methods in determining the external specific surface area of abrasive synthetic diamond powders were studied. The comparative study of the application of these two methods to high- and increased-strength abrasive synthetic diamond powders was performed. It was established that the application of the fractional-averaging method to high-strength abrasive synthetic diamond powders makes it possible to obtain more reliable indicators of external specific surface area as compared to the extrapolation-analytical method. The degree of increase for the studied high-strength abrasive powders was changed from 1.5 to 2.35 times. The factors influencing the increase in the specific surface area were identified. Some practical recommendations concerning the validity and feasibility of the fractional-averaging method for determining the external specific surface area of synthetic diamond abrasive powders of this class were formulated.
The specific features of the diamond treatment of products from silicon nitride based ceramic have been studied. It has been shown that such ceramic is intermediate between oxide and oxide–carbide ceramic by the degree of oxidation, the temperature in the zone of treatment in the process of grinding, and the force indicators of the diamond grinding of ceramic materials. It has been established that, in terms of specific energy intensity, oxide ceramics are characterized by the lowest energy intensity in the process of their treatment. As compared to these ceramics, the energy intensity of the grinding of oxide–carbide ceramic is 2–3 times higher, and nitride ceramic is characterized by the highest specific energy intensity under both deep and elastic grinding conditions, so this fact should be taken into account when determining the conditions for the treatment of products from nitride ceramic.
The article presents a theoretical analysis of the possibility of the formation and behavior of short-lived transformation structures in polymeric materials under conditions of high input energy densities, typical of the dynamic contact zone of the tool composite with the processed material. The role of spin relaxation processes in the formation of characteristic response times of polymeric materials to intensive energy input is shown. The features of the dynamic behavior of polymeric structures under the mentioned conditions are considered. The possibility of determining the characteristic time that determines the rate of energy exchange between the electronic and vibrational subsystems of the polymer bond using the NMR method is shown.
The study investigates the structure of composite materials fabricated based on WC–Co alloys with varying contents of zirconium dioxide and chromium diboride using spark plasma sintering. The work examines the combined effect of ZrO2 and CrB2 additions on the performance characteristics of WC–Co composites, including the friction coefficient and wear rate during reciprocating dry sliding tests against an Al2O3 counterbody (ball) at room temperature under a load of 100 N. The sintered composites 94WC–6Co (sample 1), 89.3WC–5.76Co–4ZrO2–1CrB2 (sample 2), 86.48WC–5.52Co–6ZrO2–2CrB2 (sample 3), 82.72WC–5.28Co–8ZrO2–4CrB2 (sample 4), and 78.96WC–5.04Co–10ZrO2–6CrB2 (sample 5) exhibit well-formed isomorphic WC crystals with distinct faceting and sharp edges. The microstructure is polydisperse and combines large prismatic WC grains up to 10–15 µm with a finer fraction that fills the intergranular space. After tribological testing, the friction coefficient μ in the sample–counterbody contact for sample 1 ranged from 0.75 to 0.85. For samples 2, 3, 4, and 5, μ ranged from 0.3–0.41, 0.5–0.6, 0.7–0.8, and 0.82–0.95, respectively. The wear rate for samples 2, 3, and 4 are (2.143 ± 0.532) × 10–7, (3.216 ± 0.758) × 10–7, and (6.784 ± 0.852) × 10–7 mm3/(N m), respectively, which is 3.7, 2.5, and 1.2 times lower than that of sample 1, placing them among highly wear-resistant materials. Composites containing ZrO2 and CrB2 additions (samples 2, 3, and 4) demonstrate superior tribological performance compared with sample 1 because they exhibit greater resistance to abrasive and adhesive wear. The additions promote the formation of a finer-grained structure with a uniform distribution of WC grains and dispersion strengthening at the interfaces between WC grains and the cobalt binder phase Co. However, increasing the content of ZrO2 and CrB2 to 10 and 6
The theoretical analysis of a single intermittent cutting cycle was carried out to demonstrate that the units of a “lathe–fixture–tool–part” set as an oscillatory system sustain dynamic loads with a corresponding dynamic coefficient. However, the oscillation of the forces measured by a dynamometer does not characterize the change of part–cutter contact (cutting) forces as such. In the case of intermittent cutting, there occur additional loads (additives) to the established cutting force. To determine the perturbing cutting force by the known system oscillation dependence (inverse problem), the Green’s function method and the Volterra first-order integral equation are applied. The kernel of the equation is formed by the dynamic calibration of a dynamometer, and all the information about the oscillatory system is “wired” in it. The efficiency of the method is demonstrated on some examples, and the mentioned additive and dynamic coefficient of cutting forces as such were calculated as a solution for the integral equation.
As a result of studying the regularities of energy transfer between the surface of a treated part and a polishing disperse system of copper metaborate micro- and nanopowders in a disperse medium in the form of kerosene or water, it has been established that the treated material removal rate, polishing powder wear rate, and polished surface roughness parameters grow with a decrease in transfer energy to evidence that the regularities of polishing the optical surfaces of parts from metal and non-metal materials are similar. It has been shown that the transfer energy depends on the spectral separation between a treated material and copper metaborate and the separation by dielectric permittivity between a treated material, a polishing powder, and a disperse medium and is determined by their ratio. The effect of the dielectric permittivity of a disperse medium on the polishing characteristics of optical components from copper and aluminum has been studied to demonstrate that this ratio may be a criterion for the efficiency of energy transfer from polishing powder particles to a treated surface, as it provides the possibility to determine the ratio of the treated material removal rate to the polishing powder wear rate, which is higher than unity when kerosene is used as a disperse medium, and lower than unity when the disperse medium is water. In addition, it has been shown that the theoretically calculated values of the treated material removal rate for the polishing of copper and aluminum by disperse systems of copper micro- and nanopowders with a disperse medium of kerosene or water are in good agreement with experimental polishing performance data with a deviation of 2–7
The structure and mechanical properties of AlN–C–ZrB2 composite ceramics for electrical applications, based on AlN with 2 wt
Based on the formulas derived for the electromagnetic wave reflection coefficient Г at a dielectric loss tangent tanδ from 0 to 100, the dependences of Г are calculated for the dielectric permittivity ε' in the interval 1 ≤ ε' ≤ 100 and tan δ in the interval 0.01 < tan δ <100. The analysis of calculated Г–ε' and Г–tanδ dependences shows that a radical solution to reduce Г is the application of composites with ε' ≤ 10–15. The dielectric characteristics ε', ε”, tan δ, and reflection coefficient Г of existing AlN based composites are analyzed in a frequency band of 12–40 GHz at 16.6–17.9 vol
The formation of superhard ceramic-matrix composites of the BL group in the cBN–TiC–ZrN–Me (Me = Co, Hf, W) systems was investigated. The materials were synthesized by HPHT sintering (p = 7.7 GPa, T = 1800 and 2300°C) of mixtures with a composition of (vol
The synthesis of a carbon solid solution in silicon carbide (SiC–C) under “smoldering” self-propagating high-temperature synthesis (SHS) conditions in the presence of titanium dioxide was investigated, and the structure and properties of ceramics obtained by high-pressure sintering were studied. It was established that SiC–TiC composite powder is synthesized from a mixture of thermally expanded graphite (TEG) and silicon with a mass ratio of 1 : 2.7 to 1 : 4 and a titanium dioxide content of 35 wt
The application of metal coating on cubic boron nitride (cBN) particles surfaces has emerged as an effective strategy for enhancing abrasive bonding performance, with thermal stability of these coatings recognized as a critical parameter in practical applications. This study investigates titanium–copper (Ti–Cu) coatings deposited onto cBN particle surfaces through vacuum vapor deposition techniques. Experimental findings demonstrate that Ti–Cu coatings exhibit significantly enhanced thermal stability at elevated temperatures (750°C) compared to conventional titanium coatings. This advancement stems from the synergistic integration of precise vacuum deposition process control with the inherent advantages of Ti–Cu composite materials, offering promising solutions for next-generation abrasive tools such as grinding wheels and cutting instruments.
This study reports the preparation of AlN–TiN ceramic composites with high TiN content, near the percolation threshold, by pressureless sintering and examines their properties. The analysis addresses microstructural characteristics, measured thermal conductivity at room temperature, and electrical resistivity in the 300–700 K temperature range. The study also proposes a mechanism responsible for the drastic change in electrical conductivity in the as-obtained composites.
