Journal of Superhard Materials最新文献

Sintering processes were studied for TaB₂ and its mixtures with 20 and 30 wt % of SiC, ZrSi₂, and MoSi₂ under hot pressing (HotP) and high pressure–high temperature (HPHT) conditions and TaB₂ and its mixtures with 20 and 30 wt % of SiC under spark plasma sintering (SPS) conditions. The introduction of additives led to the formation of solid solutions on the basis of TaB₂ and SiC and new phases. For TaB₂, the Vickers hardness was Н_V(9.8 N) = 32.4 GPa after HotP and Н_V(49 N) = 20.8 GPa after SPS (1950°C, 0.05 h), and the fracture toughness was K_Ic (49 N) = 7.6 MPa m^0.5. The Young modulus was essentially improved from 532 to 853 GPa by adding 20 wt % of SiC after HotP. Sintering TaB₂ mixtures with 30 wt % of SiC resulted in the materials with Н_V(9.8 N) = 39.4 GPa, K_Ic(9.8 N) = 6.75 MPa m^0.5(HPHT) and Н_V(49 N) = 25.4 GPa, K_Ic(49 N) = 10.8 MPa m^0.5(SPS).

This study compares the material removal mechanisms and thermal effects of femtosecond and nanosecond lasers on polycrystalline cubic boron nitride (PcBN). Using 800 kHz femtosecond and 35 kHz nanosecond lasers, the surface morphology and phase evolution were analyzed via SEM, EDS, and XRD. Results show: femtosecond lasers preferentially remove the AlN binder via ultrashort pulses—evaporation dominates at 0.5 W, while cBN fracture occurs at 1.3 W. Nanosecond lasers induce cBN-to-hBN phase transition and rough surfaces due to thermal accumulation. At 10 W, femtosecond-processed grooves exhibit smooth walls, whereas nanosecond lasers generate cracks and recast layers. XRD confirmed no hBN phase in femtosecond-processed regions, but minor hBN peaks in nanosecond-processed samples. High-repetition-rate femtosecond lasers demonstrate superior performance in minimizing thermal damage and enhancing machining quality.

This study demonstrates that using AC20 grinding powder selected for uniformity in grain strength and size through adhesive–magnetic sorting in liquid significantly enhances the wear resistance of diamond wheels by up to sixfold. Wheels fabricated with AC32 grains selected from AC20 powder show a threefold increase in wear resistance, while those with AC50 grains achieve a 1.5-fold improvement. In all cases, wheels produced from selected diamond grains exhibit higher wear resistance than those made from the initial, unsorted AC20 powder. The surface roughness parameter (R_a) of workpieces ground with wheels prepared using different adhesive–magnetic sorting options remains essentially unchanged. However, experiments revealed that wheels containing selected AC32 125/100 grains produce polished surfaces with the lowest holding capacity, a factor that must be considered when using such wheels in grinding applications.

The structure and properties of functionally gradient ceramic synthesized from an exothermic 70ZrO₂–24Al–6С (wt %) mixture under hot pressing in contact with colloid graphite are described. It has been established that two layers with a gradient structure are formed on the surface of the specimen with a structure that includes two complexly alloyed carbide ZrC and oxide Al₂O₃ based phases with a volumetric ratio of 55 : 45 and a size of 2–15 µm % and disperse (1–3-µm) 10Zr₂Al and 5ZrO_2(М) (wt %) inclusions. The layer with a gradient microstructure formed at the interface with the basic microstructure (BMS) with a thickness of 1.0–1.2 mm contains both the complex ZrС–Al₂O₃ based phases and finer (0.5–2-µm) spherical inclusions with a volumetric ratio of 45 : 55 without disperse Zr₂Al and ZrO_2(М) inclusions. The microhardness HV15 of the specimen with gradient and basic microstructures is 19.6 and 16.6 GPa, and the fracture toughness is K_Ic = 5.5 and 6.2 MPa m^0.5, respectively. The outer dark layer, which has a thickness up to 0.5 mm and contains up to 50 wt % of carbon and disperse (1–2-µm) inclusions on the basis of carbide ZrC and oxide Al₂O₃, has microhardness up to 4 GPa. Cutting inserts with a gradient microstructure have an advantage over inserts with the basic microstructure in the dry finish turning of steel KhVG (58 HRC) that grows with an increase in the cutting speed from 120 to 220 m/min. The reason for the formation of the functionally gradient fine-grained two-layer structure with a change in chemical composition with improved cutting properties is a temperature gradient on the specimen surface, a high activity of alumocarbothermal chemical interaction in the initial mixture, and partial migration under pressure during the hot pressing of an Al–Zr₂Al melt from the basic structure into the contacting layer from the colloid graphite and their chemical interaction in the oxygen atmosphere.

Two novel monoclinic (space group C2/c) carbon allotropes, m-C₈, with ths and dia topologies, were proposed through crystal structure engineering. The ths allotrope is built by three-dimensional tiling of trigonal carbon units, which is different from tiling of C4 tetrahedra in the case of dia m‑C₈. Structural studies were supported by density functional theory (DFT)-based calculations of ground state structures and energy-derived properties. Extensive investigations of cohesive energies, energy-volume equations of state, mechanical (elastic constants and moduli, hardness) and dynamical (e.g., phonons) properties revealed the new allotropes to be cohesive and stable both mechanically and dynamically. Although they are metastable compared to diamond, their formation is possible under non-equilibrium conditions as a result of alternative metastable behavior.

The effect of the microstructure of tungsten carbide–cobalt (WC–Co) composites on their mechanical properties, such as hardness and wear resistance critical for cutting tools and drilling equipment was considered. An innovative method of microstructural analysis based on image processing was proposed as a faster and more efficient alternative to traditional methods like scanning electron microscopy (SEM) and X-ray diffraction. The porosity and tungsten carbide particle and cobalt binder phase distribution were investigated by image preprocessing, phase segmentation, and quantitative SEM analysis. The results demonstrate a high precision of the method in estimating the key characteristics at an essential decrease in time and expenditures and make it possible to improve the quality and durability of WC–Co materials in industrial applications.

This study explores experimental approaches to cooling heat-removal liquids based on distilled water for six-punch press systems operating under a total loading force of 6 × 48.5 MN during the growth of structurally perfect diamond single crystals by the temperature gradient method. A cooling system for hard-alloy punches was designed and fabricated with programmable control of flow rate in each of the six independent circuits, based on punch temperature feedback. Experiments showed that varying the coolant flow rate between 4 and 10 L min^–1 at temperatures of 18 and 24°C enables adjustment of the growth-cell control-point temperatures within 18–35°C, respectively. Regulating the punch cooling conditions according to a predefined algorithm during the diamond growth process maintains the optimal temperature distribution within the growth cell, enabling the formation of structurally perfect, flat-faced diamond single crystals weighing up to 20 carats or more.

This study examines selected aspects of the formation of nonporous ceramic-matrix composites of the BL group in the cBN–HfC system, where hafnium micropowder serves as a sintering activator. The results demonstrate that, during HPHT experiments at 2300°C, the system undergoes reactive sintering characterized by the disappearance of the metallic phase and the formation of fine-grained HfB₂ through two mechanisms, with a volume fraction of up to 8%.

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.